High Frequency Welding

High Frequency Welding Machine Manufacturer/RF PVC welding machine for welding plastic,etc.

High Frequency Welding, known as Radio Frequency (RF) or Dielectric welding, is the process of fusing materials together by applying radio frequency energy to the area to be joined. The resulting weld can be as strong as the original materials. HF Welding relies on certain properties of the material being welded to cause the generation of heat in a rapidly alternating electric field. This means that only certain materials can be welded using this technique. The process involves subjecting the parts to be joined to a high frequency (most often 27.12MHz) electromagnetic field, which is normally applied between two metal bars. These bars also act as pressure applicators during heating and cooling. The dynamic electric field causes the molecules in polar thermoplastics to oscillate. Depending on their geometry and dipole moment, these molecules may translate some of this oscillatory motion into thermal energy and cause heating of the material. A measure of this interaction is the loss factor, which is temperature and frequency dependent.

Polyvinylchloride (PVC) and polyurethanes are the most common thermoplastics to be welded by the RF process. It is possible to RF weld other polymers including nylon, PET, PET-G, A-PET, EVA and some ABS resins, but special conditions are required, for example nylon and PET are weldable if preheated welding bars are used in addition to the RF power.

HF welding is generally not suitable for PTFE, polycarbonate, polystyrene, polyethylene or polypropylene. However, due to the impending restrictions in the use of PVC, a special grade of polyolefin has been developed which does have the capability to be HF welded.

The primary function of HF welding is to form a joint in two or more thicknesses of sheet material. A number of optional features exist. The welding tool can be engraved or profiled to give the entire welded area a decorative appearance or it can incorporate an embossing technique to place lettering, logos or decorative effects on the welded items. By incorporating a cutting edge adjacent to the welding surface, the process can simultaneously weld and cut a material. The cutting edge compresses the hot plastic sufficiently to allow the excess scrap material to be torn off, hence this process is often referred to as tear-seal welding. A typical plastic welder consists of a high frequency generator (which creates the radio frequency current), a pneumatic press, an electrode that transfers the radio frequency current to the material that is being welded and a welding bench that holds the material in place. The machine could also have a grounding bar that is often mounted behind the electrode, which leads the current back to the machine (grounding point). There are different types of plastic welders, the most common being tarpaulin machines, packaging machines and automated machines. By regulating the machine’s tuning, the field strength can be adjusted to the material being welded. When welding, the machine is surrounded by a radio frequency field that, if too strong, can heat up the body somewhat. This is what the operator needs to be protected from. The strength of the radio frequency field also depends on the type of machine being used. Generally, machines with visible open electrodes (unshielded) have stronger fields than machines with enclosed electrodes.

When describing radio frequency electromagnetic fields, the field’s frequency is often mentioned. The permitted frequencies for plastic welders are 13.56, 27.12, or 40.68 megahertz (MHz). The most popular industrial frequency for HF welding is 27.12MHz. The radio frequency fields from a plastic welder spread out around the machine, but most often it is only right next to the machine that the field is so strong that precautions need to be taken. The field’s strength decreases sharply with distance from the source. The strength of the field is given in two different measurements: the electric field strength is measured in volts per metre (V/m), and the magnetic field strength is measured in amperes per metre (A/m). Both of these must be measured to get an idea of how strong the radio frequency field is. The current that goes through you if you touch the equipment (contact current) and the current that that goes through the body when welding (induced current) must also be measured.

Advantages of High Frequency Welding Technology

• HF sealing occurs from the inside out by using the material itself as a heat source. The heat is focused at the weld target so that the surrounding material does not have to be super-heated to arrive at a target temperature at the joint.
• With HF heating is generated only when the field is energized. Once the generator cycles, the heat is turned off. This allows for greater control over the amount of energy that the material sees over the entire cycle. In addition, HF-generated heat does not radiate off the die like on a heated die. This prevents heat-degredation of the material abutting the weld.
• HF tooling is usually run "cold". This means that once the HF is turned off, the material stops being heated, but remains under pressure. In this fashion it is possible to both instantly heat, weld, and cool the material under compression. More control over the weld results in more control over the resulting extrusion, thus increasing the weld strength.
• RF welds are "clean" because the only material needed to produce an HF weld is the material itself. There are no adhesives or by-products involved in HF

https://dw-inductionheater.com/high-frequency-welding.html?feed_id=235572&_unique_id=65e59e5f3fc39

High Speed Heating by Induction Heating System

One of the recent outstanding developments in the heat treating field has been the application of induction heating to localized surface hardening. The advances made contingent with the applica­tion of high frequency current have been nothing short of phenomenal. Starting a comparatively short time ago as a long-sought-after method of hardening bearing surfaces on crankshafts (sev­eral million of these are in use setting all time service records), today finds this very selective surfacing hardening method producing hardened areas on a multiplicity of parts. Yet, in spite of its present day breadth of application, induction hardening is still in its infant stage. Its probable utilization for the heat treating and hardening of metals, heating for forging or brazing, or solder­ing of similar and dissimilar metals, is unpre­dictable. Induction hardening results in the production of locally hardened steel objects with the desired degree of depth and hardness, essential metal­lurgical structure of core, demarcation zone, and hardened case, with a practical lack of distortion and no scale formation. It permits equipment de­sign which warrants mechanization of the whole operation to fulfill production line requirements. Time cycles of only a few seconds are maintained by automatic regulation of power and split second heating and quenching intervals indispensable to the creation of facsimile results of exacting special fixations. Induction hardening equipment permits the user to surface harden only the requisite por­tion of most any steel object and thus maintain the original ductility and strength; to harden articles of intricate design which cannot be feas­ibly treated in any other way; to eliminate usual expensive pretreatment such as copper plating and carburizing, and costly subsequent straight­ening and cleaning operations; to cut down on material cost by having a wide selection of steels from which to choose; and to harden a fully-ma­chined item without the necessity of any finishing operations. To the casual observer it would appear that in­duction hardening is possible as a result of some energy transformation occurring within an induc­tive region of copper. The copper carries an elec­trical current of high frequency and, within an interval of a few seconds, the surface of a piece of steel placed within this energized region is heated to its critical range and quenched to opti­mum hardness. To the manufacturer of equipment for this method of hardening it means the appli­cation of the phenomena of hysteresis, eddy cur­rents, and skin effect to the effective production of localized surface hardening. The heating is accomplished by use of high frequency currents. Specifically chosen frequencies from 2,000 to 10,000 cycles and upwards of 100,­000 cycles are being used extensively at the pres­ent time. Current of this nature in flowing through an inductor produces a high-frequency magnetic field within the region of the inductor. When a magnetic material such as steel is placed within this field, there is a dissipation of energy in the steel which produces heat. The molecules within the steel attempt to align themselves with the polarity of this field, and with this changing thousands of times per second, an enormous amount of internal molecular friction is developed as a result of the natural tendency for the steel to resist changes. In this manner the electrical energy is transformed, through the medium of friction, into heat. However, since another inherent characteristic of high frequency current is to concentrate on the surface of its conductor, only the surface layers become heated. This tendency, called “skin effect”, is a function of the frequency and, other things being equal, higher frequencies are effec­tive at shallower depths. The frictional action producing the heat is called hysteresis and is obviously dependent upon the magnetic qualities of the steel. Thus, when the temperature has passed the critical point at which the steel be­comes non-magnetic, all hysteretic heating ceases. There is an additional source of heat due to eddy currents which flow in the steel as a result of the rapidly changing flux in the field. With resistance of the steel increasing with tempera­ture, the intensity of this action is decreased as the steel becomes heated, and is only a fraction of its “cold” original value when the proper quenching temperature is reached. When the temperature of an inductively heated steel bar arrives at the critical point, heating due to eddy currents continues at a greatly reduced rate. Since the entire action goes on in the sur­face layers, only that portion is affected. The original core properties are maintained, the sur­face hardening being accomplished by quench­ing when complete carbide solution has been at­tained in the surface areas. Continued applica­tion of power causes an increase in depth of hardness, for as each layer of steel is brought to temperature, the current density shifts to the layer beneath which offers a lower resistance. It is obvious that the selection of the proper fre­quency, and control of power and heating time will make fulfillment of any desired specifica­tions of surface hardening possible. Metallurgy of Induction Heating The unusual behavior of steel when heated in­ductively and the results obtained merit a discus­sion of the metallurgy involved. Carbide solution rates of less than a second, higher hardness than that produced by furnace treatment, and a nodu­lar type of martensite are points of consideration that classify the metallurgy of induction harden­ing as “different”. Further, surface decarburiza­tion and grain growth do not occur because of the short heating cycle. Induction heating produces a hardness that is maintained through 80 percent of its depth, and from there on, a gradual decrease through a transition zone to the original hardness of the steel as found in the core which has not been affected. The bond is thus ideal, eliminating any chance of spalling or checking. Complete carbide solution and homogeneity as evidenced by maximum hardness can be accom­plished with a total heating time of 0.6 second. Of this time, only 0.2 to 0.3 second is actually above the lower critical. It is interesting to note that induction hardening equipment is in every day operation on a production basis with complete carbide solution, resulting from a heating and quenching cycle, the total time of which is less than 0.2 second. The fine nodular and more homogeneous mar­tensite which results from the induction harden­ing is more readily apparent with carbon steels than with alloy steel because of the nodular ap­pearance of most alloy martensite. This fine struc­ture must have for its origin an austenite which is the result of a more thorough carbide diffusion than is obtained with thermal heating. Practically instantaneous development of critical tempera­tures throughout the entire microstructure of the alpha iron and iron carbide is particularly con­ducive to rapid carbide solution and a distribution of constituents which has as its inevitable product a thoroughly homogeneous austentite. Further, the conversion of this structure to martensite will produce a martensite which possesses similar characteristics and a corresponding resistance to wear or penetrating instruments.

high speed heating by induction   https://dw-inductionheater.com/high-speed-heating-by-induction-heating-system.html?feed_id=233626&_unique_id=65c3575ae63ce

High Frequency Welding

High Frequency Welding Machine Manufacturer/RF PVC welding machine for welding plastic,etc.

High Frequency Welding, known as Radio Frequency (RF) or Dielectric welding, is the process of fusing materials together by applying radio frequency energy to the area to be joined. The resulting weld can be as strong as the original materials. HF Welding relies on certain properties of the material being welded to cause the generation of heat in a rapidly alternating electric field. This means that only certain materials can be welded using this technique. The process involves subjecting the parts to be joined to a high frequency (most often 27.12MHz) electromagnetic field, which is normally applied between two metal bars. These bars also act as pressure applicators during heating and cooling. The dynamic electric field causes the molecules in polar thermoplastics to oscillate. Depending on their geometry and dipole moment, these molecules may translate some of this oscillatory motion into thermal energy and cause heating of the material. A measure of this interaction is the loss factor, which is temperature and frequency dependent.

Polyvinylchloride (PVC) and polyurethanes are the most common thermoplastics to be welded by the RF process. It is possible to RF weld other polymers including nylon, PET, PET-G, A-PET, EVA and some ABS resins, but special conditions are required, for example nylon and PET are weldable if preheated welding bars are used in addition to the RF power.

HF welding is generally not suitable for PTFE, polycarbonate, polystyrene, polyethylene or polypropylene. However, due to the impending restrictions in the use of PVC, a special grade of polyolefin has been developed which does have the capability to be HF welded.

The primary function of HF welding is to form a joint in two or more thicknesses of sheet material. A number of optional features exist. The welding tool can be engraved or profiled to give the entire welded area a decorative appearance or it can incorporate an embossing technique to place lettering, logos or decorative effects on the welded items. By incorporating a cutting edge adjacent to the welding surface, the process can simultaneously weld and cut a material. The cutting edge compresses the hot plastic sufficiently to allow the excess scrap material to be torn off, hence this process is often referred to as tear-seal welding. A typical plastic welder consists of a high frequency generator (which creates the radio frequency current), a pneumatic press, an electrode that transfers the radio frequency current to the material that is being welded and a welding bench that holds the material in place. The machine could also have a grounding bar that is often mounted behind the electrode, which leads the current back to the machine (grounding point). There are different types of plastic welders, the most common being tarpaulin machines, packaging machines and automated machines. By regulating the machine’s tuning, the field strength can be adjusted to the material being welded. When welding, the machine is surrounded by a radio frequency field that, if too strong, can heat up the body somewhat. This is what the operator needs to be protected from. The strength of the radio frequency field also depends on the type of machine being used. Generally, machines with visible open electrodes (unshielded) have stronger fields than machines with enclosed electrodes.

When describing radio frequency electromagnetic fields, the field’s frequency is often mentioned. The permitted frequencies for plastic welders are 13.56, 27.12, or 40.68 megahertz (MHz). The most popular industrial frequency for HF welding is 27.12MHz. The radio frequency fields from a plastic welder spread out around the machine, but most often it is only right next to the machine that the field is so strong that precautions need to be taken. The field’s strength decreases sharply with distance from the source. The strength of the field is given in two different measurements: the electric field strength is measured in volts per metre (V/m), and the magnetic field strength is measured in amperes per metre (A/m). Both of these must be measured to get an idea of how strong the radio frequency field is. The current that goes through you if you touch the equipment (contact current) and the current that that goes through the body when welding (induced current) must also be measured.

Advantages of High Frequency Welding Technology

• HF sealing occurs from the inside out by using the material itself as a heat source. The heat is focused at the weld target so that the surrounding material does not have to be super-heated to arrive at a target temperature at the joint.
• With HF heating is generated only when the field is energized. Once the generator cycles, the heat is turned off. This allows for greater control over the amount of energy that the material sees over the entire cycle. In addition, HF-generated heat does not radiate off the die like on a heated die. This prevents heat-degredation of the material abutting the weld.
• HF tooling is usually run "cold". This means that once the HF is turned off, the material stops being heated, but remains under pressure. In this fashion it is possible to both instantly heat, weld, and cool the material under compression. More control over the weld results in more control over the resulting extrusion, thus increasing the weld strength.
• RF welds are "clean" because the only material needed to produce an HF weld is the material itself. There are no adhesives or by-products involved in HF

https://dw-inductionheater.com/high-frequency-welding.html?feed_id=218536&_unique_id=64ae28dca2de2

High Speed Heating by Induction Heating System

One of the recent outstanding developments in the heat treating field has been the application of induction heating to localized surface hardening. The advances made contingent with the applica­tion of high frequency current have been nothing short of phenomenal. Starting a comparatively short time ago as a long-sought-after method of hardening bearing surfaces on crankshafts (sev­eral million of these are in use setting all time service records), today finds this very selective surfacing hardening method producing hardened areas on a multiplicity of parts. Yet, in spite of its present day breadth of application, induction hardening is still in its infant stage. Its probable utilization for the heat treating and hardening of metals, heating for forging or brazing, or solder­ing of similar and dissimilar metals, is unpre­dictable. Induction hardening results in the production of locally hardened steel objects with the desired degree of depth and hardness, essential metal­lurgical structure of core, demarcation zone, and hardened case, with a practical lack of distortion and no scale formation. It permits equipment de­sign which warrants mechanization of the whole operation to fulfill production line requirements. Time cycles of only a few seconds are maintained by automatic regulation of power and split second heating and quenching intervals indispensable to the creation of facsimile results of exacting special fixations. Induction hardening equipment permits the user to surface harden only the requisite por­tion of most any steel object and thus maintain the original ductility and strength; to harden articles of intricate design which cannot be feas­ibly treated in any other way; to eliminate usual expensive pretreatment such as copper plating and carburizing, and costly subsequent straight­ening and cleaning operations; to cut down on material cost by having a wide selection of steels from which to choose; and to harden a fully-ma­chined item without the necessity of any finishing operations. To the casual observer it would appear that in­duction hardening is possible as a result of some energy transformation occurring within an induc­tive region of copper. The copper carries an elec­trical current of high frequency and, within an interval of a few seconds, the surface of a piece of steel placed within this energized region is heated to its critical range and quenched to opti­mum hardness. To the manufacturer of equipment for this method of hardening it means the appli­cation of the phenomena of hysteresis, eddy cur­rents, and skin effect to the effective production of localized surface hardening. The heating is accomplished by use of high frequency currents. Specifically chosen frequencies from 2,000 to 10,000 cycles and upwards of 100,­000 cycles are being used extensively at the pres­ent time. Current of this nature in flowing through an inductor produces a high-frequency magnetic field within the region of the inductor. When a magnetic material such as steel is placed within this field, there is a dissipation of energy in the steel which produces heat. The molecules within the steel attempt to align themselves with the polarity of this field, and with this changing thousands of times per second, an enormous amount of internal molecular friction is developed as a result of the natural tendency for the steel to resist changes. In this manner the electrical energy is transformed, through the medium of friction, into heat. However, since another inherent characteristic of high frequency current is to concentrate on the surface of its conductor, only the surface layers become heated. This tendency, called “skin effect”, is a function of the frequency and, other things being equal, higher frequencies are effec­tive at shallower depths. The frictional action producing the heat is called hysteresis and is obviously dependent upon the magnetic qualities of the steel. Thus, when the temperature has passed the critical point at which the steel be­comes non-magnetic, all hysteretic heating ceases. There is an additional source of heat due to eddy currents which flow in the steel as a result of the rapidly changing flux in the field. With resistance of the steel increasing with tempera­ture, the intensity of this action is decreased as the steel becomes heated, and is only a fraction of its “cold” original value when the proper quenching temperature is reached. When the temperature of an inductively heated steel bar arrives at the critical point, heating due to eddy currents continues at a greatly reduced rate. Since the entire action goes on in the sur­face layers, only that portion is affected. The original core properties are maintained, the sur­face hardening being accomplished by quench­ing when complete carbide solution has been at­tained in the surface areas. Continued applica­tion of power causes an increase in depth of hardness, for as each layer of steel is brought to temperature, the current density shifts to the layer beneath which offers a lower resistance. It is obvious that the selection of the proper fre­quency, and control of power and heating time will make fulfillment of any desired specifica­tions of surface hardening possible. Metallurgy of Induction Heating The unusual behavior of steel when heated in­ductively and the results obtained merit a discus­sion of the metallurgy involved. Carbide solution rates of less than a second, higher hardness than that produced by furnace treatment, and a nodu­lar type of martensite are points of consideration that classify the metallurgy of induction harden­ing as “different”. Further, surface decarburiza­tion and grain growth do not occur because of the short heating cycle. Induction heating produces a hardness that is maintained through 80 percent of its depth, and from there on, a gradual decrease through a transition zone to the original hardness of the steel as found in the core which has not been affected. The bond is thus ideal, eliminating any chance of spalling or checking. Complete carbide solution and homogeneity as evidenced by maximum hardness can be accom­plished with a total heating time of 0.6 second. Of this time, only 0.2 to 0.3 second is actually above the lower critical. It is interesting to note that induction hardening equipment is in every day operation on a production basis with complete carbide solution, resulting from a heating and quenching cycle, the total time of which is less than 0.2 second. The fine nodular and more homogeneous mar­tensite which results from the induction harden­ing is more readily apparent with carbon steels than with alloy steel because of the nodular ap­pearance of most alloy martensite. This fine struc­ture must have for its origin an austenite which is the result of a more thorough carbide diffusion than is obtained with thermal heating. Practically instantaneous development of critical tempera­tures throughout the entire microstructure of the alpha iron and iron carbide is particularly con­ducive to rapid carbide solution and a distribution of constituents which has as its inevitable product a thoroughly homogeneous austentite. Further, the conversion of this structure to martensite will produce a martensite which possesses similar characteristics and a corresponding resistance to wear or penetrating instruments.

high speed heating by induction  

High Speed Heating by Induction Heating System

One of the recent outstanding developments in the heat treating field has been the application of induction heating to localized surface hardening. The advances made contingent with the applica­tion of high frequency current have been nothing short of phenomenal. Starting a comparatively short time ago as a long-sought-after method of hardening bearing surfaces on crankshafts (sev­eral million of these are in use setting all time service records), today finds this very selective surfacing hardening method producing hardened areas on a multiplicity of parts. Yet, in spite of its present day breadth of application, induction hardening is still in its infant stage. Its probable utilization for the heat treating and hardening of metals, heating for forging or brazing, or solder­ing of similar and dissimilar metals, is unpre­dictable. Induction hardening results in the production of locally hardened steel objects with the desired degree of depth and hardness, essential metal­lurgical structure of core, demarcation zone, and hardened case, with a practical lack of distortion and no scale formation. It permits equipment de­sign which warrants mechanization of the whole operation to fulfill production line requirements. Time cycles of only a few seconds are maintained by automatic regulation of power and split second heating and quenching intervals indispensable to the creation of facsimile results of exacting special fixations. Induction hardening equipment permits the user to surface harden only the requisite por­tion of most any steel object and thus maintain the original ductility and strength; to harden articles of intricate design which cannot be feas­ibly treated in any other way; to eliminate usual expensive pretreatment such as copper plating and carburizing, and costly subsequent straight­ening and cleaning operations; to cut down on material cost by having a wide selection of steels from which to choose; and to harden a fully-ma­chined item without the necessity of any finishing operations. To the casual observer it would appear that in­duction hardening is possible as a result of some energy transformation occurring within an induc­tive region of copper. The copper carries an elec­trical current of high frequency and, within an interval of a few seconds, the surface of a piece of steel placed within this energized region is heated to its critical range and quenched to opti­mum hardness. To the manufacturer of equipment for this method of hardening it means the appli­cation of the phenomena of hysteresis, eddy cur­rents, and skin effect to the effective production of localized surface hardening. The heating is accomplished by use of high frequency currents. Specifically chosen frequencies from 2,000 to 10,000 cycles and upwards of 100,­000 cycles are being used extensively at the pres­ent time. Current of this nature in flowing through an inductor produces a high-frequency magnetic field within the region of the inductor. When a magnetic material such as steel is placed within this field, there is a dissipation of energy in the steel which produces heat. The molecules within the steel attempt to align themselves with the polarity of this field, and with this changing thousands of times per second, an enormous amount of internal molecular friction is developed as a result of the natural tendency for the steel to resist changes. In this manner the electrical energy is transformed, through the medium of friction, into heat. However, since another inherent characteristic of high frequency current is to concentrate on the surface of its conductor, only the surface layers become heated. This tendency, called “skin effect”, is a function of the frequency and, other things being equal, higher frequencies are effec­tive at shallower depths. The frictional action producing the heat is called hysteresis and is obviously dependent upon the magnetic qualities of the steel. Thus, when the temperature has passed the critical point at which the steel be­comes non-magnetic, all hysteretic heating ceases. There is an additional source of heat due to eddy currents which flow in the steel as a result of the rapidly changing flux in the field. With resistance of the steel increasing with tempera­ture, the intensity of this action is decreased as the steel becomes heated, and is only a fraction of its “cold” original value when the proper quenching temperature is reached. When the temperature of an inductively heated steel bar arrives at the critical point, heating due to eddy currents continues at a greatly reduced rate. Since the entire action goes on in the sur­face layers, only that portion is affected. The original core properties are maintained, the sur­face hardening being accomplished by quench­ing when complete carbide solution has been at­tained in the surface areas. Continued applica­tion of power causes an increase in depth of hardness, for as each layer of steel is brought to temperature, the current density shifts to the layer beneath which offers a lower resistance. It is obvious that the selection of the proper fre­quency, and control of power and heating time will make fulfillment of any desired specifica­tions of surface hardening possible. Metallurgy of Induction Heating The unusual behavior of steel when heated in­ductively and the results obtained merit a discus­sion of the metallurgy involved. Carbide solution rates of less than a second, higher hardness than that produced by furnace treatment, and a nodu­lar type of martensite are points of consideration that classify the metallurgy of induction harden­ing as “different”. Further, surface decarburiza­tion and grain growth do not occur because of the short heating cycle. Induction heating produces a hardness that is maintained through 80 percent of its depth, and from there on, a gradual decrease through a transition zone to the original hardness of the steel as found in the core which has not been affected. The bond is thus ideal, eliminating any chance of spalling or checking. Complete carbide solution and homogeneity as evidenced by maximum hardness can be accom­plished with a total heating time of 0.6 second. Of this time, only 0.2 to 0.3 second is actually above the lower critical. It is interesting to note that induction hardening equipment is in every day operation on a production basis with complete carbide solution, resulting from a heating and quenching cycle, the total time of which is less than 0.2 second. The fine nodular and more homogeneous mar­tensite which results from the induction harden­ing is more readily apparent with carbon steels than with alloy steel because of the nodular ap­pearance of most alloy martensite. This fine struc­ture must have for its origin an austenite which is the result of a more thorough carbide diffusion than is obtained with thermal heating. Practically instantaneous development of critical tempera­tures throughout the entire microstructure of the alpha iron and iron carbide is particularly con­ducive to rapid carbide solution and a distribution of constituents which has as its inevitable product a thoroughly homogeneous austentite. Further, the conversion of this structure to martensite will produce a martensite which possesses similar characteristics and a corresponding resistance to wear or penetrating instruments.

high speed heating by induction   https://dw-inductionheater.com/high-speed-heating-by-induction-heating-system.html?feed_id=213511&_unique_id=648bdbf93766b

High Frequency Welding

High Frequency Welding Machine Manufacturer/RF PVC welding machine for welding plastic,etc.

High Frequency Welding, known as Radio Frequency (RF) or Dielectric welding, is the process of fusing materials together by applying radio frequency energy to the area to be joined. The resulting weld can be as strong as the original materials. HF Welding relies on certain properties of the material being welded to cause the generation of heat in a rapidly alternating electric field. This means that only certain materials can be welded using this technique. The process involves subjecting the parts to be joined to a high frequency (most often 27.12MHz) electromagnetic field, which is normally applied between two metal bars. These bars also act as pressure applicators during heating and cooling. The dynamic electric field causes the molecules in polar thermoplastics to oscillate. Depending on their geometry and dipole moment, these molecules may translate some of this oscillatory motion into thermal energy and cause heating of the material. A measure of this interaction is the loss factor, which is temperature and frequency dependent.

Polyvinylchloride (PVC) and polyurethanes are the most common thermoplastics to be welded by the RF process. It is possible to RF weld other polymers including nylon, PET, PET-G, A-PET, EVA and some ABS resins, but special conditions are required, for example nylon and PET are weldable if preheated welding bars are used in addition to the RF power.

HF welding is generally not suitable for PTFE, polycarbonate, polystyrene, polyethylene or polypropylene. However, due to the impending restrictions in the use of PVC, a special grade of polyolefin has been developed which does have the capability to be HF welded.

The primary function of HF welding is to form a joint in two or more thicknesses of sheet material. A number of optional features exist. The welding tool can be engraved or profiled to give the entire welded area a decorative appearance or it can incorporate an embossing technique to place lettering, logos or decorative effects on the welded items. By incorporating a cutting edge adjacent to the welding surface, the process can simultaneously weld and cut a material. The cutting edge compresses the hot plastic sufficiently to allow the excess scrap material to be torn off, hence this process is often referred to as tear-seal welding. A typical plastic welder consists of a high frequency generator (which creates the radio frequency current), a pneumatic press, an electrode that transfers the radio frequency current to the material that is being welded and a welding bench that holds the material in place. The machine could also have a grounding bar that is often mounted behind the electrode, which leads the current back to the machine (grounding point). There are different types of plastic welders, the most common being tarpaulin machines, packaging machines and automated machines. By regulating the machine’s tuning, the field strength can be adjusted to the material being welded. When welding, the machine is surrounded by a radio frequency field that, if too strong, can heat up the body somewhat. This is what the operator needs to be protected from. The strength of the radio frequency field also depends on the type of machine being used. Generally, machines with visible open electrodes (unshielded) have stronger fields than machines with enclosed electrodes.

When describing radio frequency electromagnetic fields, the field’s frequency is often mentioned. The permitted frequencies for plastic welders are 13.56, 27.12, or 40.68 megahertz (MHz). The most popular industrial frequency for HF welding is 27.12MHz. The radio frequency fields from a plastic welder spread out around the machine, but most often it is only right next to the machine that the field is so strong that precautions need to be taken. The field’s strength decreases sharply with distance from the source. The strength of the field is given in two different measurements: the electric field strength is measured in volts per metre (V/m), and the magnetic field strength is measured in amperes per metre (A/m). Both of these must be measured to get an idea of how strong the radio frequency field is. The current that goes through you if you touch the equipment (contact current) and the current that that goes through the body when welding (induced current) must also be measured.

Advantages of High Frequency Welding Technology

• HF sealing occurs from the inside out by using the material itself as a heat source. The heat is focused at the weld target so that the surrounding material does not have to be super-heated to arrive at a target temperature at the joint.
• With HF heating is generated only when the field is energized. Once the generator cycles, the heat is turned off. This allows for greater control over the amount of energy that the material sees over the entire cycle. In addition, HF-generated heat does not radiate off the die like on a heated die. This prevents heat-degredation of the material abutting the weld.
• HF tooling is usually run "cold". This means that once the HF is turned off, the material stops being heated, but remains under pressure. In this fashion it is possible to both instantly heat, weld, and cool the material under compression. More control over the weld results in more control over the resulting extrusion, thus increasing the weld strength.
• RF welds are "clean" because the only material needed to produce an HF weld is the material itself. There are no adhesives or by-products involved in HF

High Speed Heating by Induction Heating System

One of the recent outstanding developments in the heat treating field has been the application of induction heating to localized surface hardening. The advances made contingent with the applica­tion of high frequency current have been nothing short of phenomenal. Starting a comparatively short time ago as a long-sought-after method of hardening bearing surfaces on crankshafts (sev­eral million of these are in use setting all time service records), today finds this very selective surfacing hardening method producing hardened areas on a multiplicity of parts. Yet, in spite of its present day breadth of application, induction hardening is still in its infant stage. Its probable utilization for the heat treating and hardening of metals, heating for forging or brazing, or solder­ing of similar and dissimilar metals, is unpre­dictable. Induction hardening results in the production of locally hardened steel objects with the desired degree of depth and hardness, essential metal­lurgical structure of core, demarcation zone, and hardened case, with a practical lack of distortion and no scale formation. It permits equipment de­sign which warrants mechanization of the whole operation to fulfill production line requirements. Time cycles of only a few seconds are maintained by automatic regulation of power and split second heating and quenching intervals indispensable to the creation of facsimile results of exacting special fixations. Induction hardening equipment permits the user to surface harden only the requisite por­tion of most any steel object and thus maintain the original ductility and strength; to harden articles of intricate design which cannot be feas­ibly treated in any other way; to eliminate usual expensive pretreatment such as copper plating and carburizing, and costly subsequent straight­ening and cleaning operations; to cut down on material cost by having a wide selection of steels from which to choose; and to harden a fully-ma­chined item without the necessity of any finishing operations. To the casual observer it would appear that in­duction hardening is possible as a result of some energy transformation occurring within an induc­tive region of copper. The copper carries an elec­trical current of high frequency and, within an interval of a few seconds, the surface of a piece of steel placed within this energized region is heated to its critical range and quenched to opti­mum hardness. To the manufacturer of equipment for this method of hardening it means the appli­cation of the phenomena of hysteresis, eddy cur­rents, and skin effect to the effective production of localized surface hardening. The heating is accomplished by use of high frequency currents. Specifically chosen frequencies from 2,000 to 10,000 cycles and upwards of 100,­000 cycles are being used extensively at the pres­ent time. Current of this nature in flowing through an inductor produces a high-frequency magnetic field within the region of the inductor. When a magnetic material such as steel is placed within this field, there is a dissipation of energy in the steel which produces heat. The molecules within the steel attempt to align themselves with the polarity of this field, and with this changing thousands of times per second, an enormous amount of internal molecular friction is developed as a result of the natural tendency for the steel to resist changes. In this manner the electrical energy is transformed, through the medium of friction, into heat. However, since another inherent characteristic of high frequency current is to concentrate on the surface of its conductor, only the surface layers become heated. This tendency, called “skin effect”, is a function of the frequency and, other things being equal, higher frequencies are effec­tive at shallower depths. The frictional action producing the heat is called hysteresis and is obviously dependent upon the magnetic qualities of the steel. Thus, when the temperature has passed the critical point at which the steel be­comes non-magnetic, all hysteretic heating ceases. There is an additional source of heat due to eddy currents which flow in the steel as a result of the rapidly changing flux in the field. With resistance of the steel increasing with tempera­ture, the intensity of this action is decreased as the steel becomes heated, and is only a fraction of its “cold” original value when the proper quenching temperature is reached. When the temperature of an inductively heated steel bar arrives at the critical point, heating due to eddy currents continues at a greatly reduced rate. Since the entire action goes on in the sur­face layers, only that portion is affected. The original core properties are maintained, the sur­face hardening being accomplished by quench­ing when complete carbide solution has been at­tained in the surface areas. Continued applica­tion of power causes an increase in depth of hardness, for as each layer of steel is brought to temperature, the current density shifts to the layer beneath which offers a lower resistance. It is obvious that the selection of the proper fre­quency, and control of power and heating time will make fulfillment of any desired specifica­tions of surface hardening possible. Metallurgy of Induction Heating The unusual behavior of steel when heated in­ductively and the results obtained merit a discus­sion of the metallurgy involved. Carbide solution rates of less than a second, higher hardness than that produced by furnace treatment, and a nodu­lar type of martensite are points of consideration that classify the metallurgy of induction harden­ing as “different”. Further, surface decarburiza­tion and grain growth do not occur because of the short heating cycle. Induction heating produces a hardness that is maintained through 80 percent of its depth, and from there on, a gradual decrease through a transition zone to the original hardness of the steel as found in the core which has not been affected. The bond is thus ideal, eliminating any chance of spalling or checking. Complete carbide solution and homogeneity as evidenced by maximum hardness can be accom­plished with a total heating time of 0.6 second. Of this time, only 0.2 to 0.3 second is actually above the lower critical. It is interesting to note that induction hardening equipment is in every day operation on a production basis with complete carbide solution, resulting from a heating and quenching cycle, the total time of which is less than 0.2 second. The fine nodular and more homogeneous mar­tensite which results from the induction harden­ing is more readily apparent with carbon steels than with alloy steel because of the nodular ap­pearance of most alloy martensite. This fine struc­ture must have for its origin an austenite which is the result of a more thorough carbide diffusion than is obtained with thermal heating. Practically instantaneous development of critical tempera­tures throughout the entire microstructure of the alpha iron and iron carbide is particularly con­ducive to rapid carbide solution and a distribution of constituents which has as its inevitable product a thoroughly homogeneous austentite. Further, the conversion of this structure to martensite will produce a martensite which possesses similar characteristics and a corresponding resistance to wear or penetrating instruments.

high speed heating by induction  

High Frequency Welding

High Frequency Welding Machine Manufacturer/RF PVC welding machine for welding plastic,etc.

High Frequency Welding, known as Radio Frequency (RF) or Dielectric welding, is the process of fusing materials together by applying radio frequency energy to the area to be joined. The resulting weld can be as strong as the original materials. HF Welding relies on certain properties of the material being welded to cause the generation of heat in a rapidly alternating electric field. This means that only certain materials can be welded using this technique. The process involves subjecting the parts to be joined to a high frequency (most often 27.12MHz) electromagnetic field, which is normally applied between two metal bars. These bars also act as pressure applicators during heating and cooling. The dynamic electric field causes the molecules in polar thermoplastics to oscillate. Depending on their geometry and dipole moment, these molecules may translate some of this oscillatory motion into thermal energy and cause heating of the material. A measure of this interaction is the loss factor, which is temperature and frequency dependent.

Polyvinylchloride (PVC) and polyurethanes are the most common thermoplastics to be welded by the RF process. It is possible to RF weld other polymers including nylon, PET, PET-G, A-PET, EVA and some ABS resins, but special conditions are required, for example nylon and PET are weldable if preheated welding bars are used in addition to the RF power.

HF welding is generally not suitable for PTFE, polycarbonate, polystyrene, polyethylene or polypropylene. However, due to the impending restrictions in the use of PVC, a special grade of polyolefin has been developed which does have the capability to be HF welded.

The primary function of HF welding is to form a joint in two or more thicknesses of sheet material. A number of optional features exist. The welding tool can be engraved or profiled to give the entire welded area a decorative appearance or it can incorporate an embossing technique to place lettering, logos or decorative effects on the welded items. By incorporating a cutting edge adjacent to the welding surface, the process can simultaneously weld and cut a material. The cutting edge compresses the hot plastic sufficiently to allow the excess scrap material to be torn off, hence this process is often referred to as tear-seal welding. A typical plastic welder consists of a high frequency generator (which creates the radio frequency current), a pneumatic press, an electrode that transfers the radio frequency current to the material that is being welded and a welding bench that holds the material in place. The machine could also have a grounding bar that is often mounted behind the electrode, which leads the current back to the machine (grounding point). There are different types of plastic welders, the most common being tarpaulin machines, packaging machines and automated machines. By regulating the machine’s tuning, the field strength can be adjusted to the material being welded. When welding, the machine is surrounded by a radio frequency field that, if too strong, can heat up the body somewhat. This is what the operator needs to be protected from. The strength of the radio frequency field also depends on the type of machine being used. Generally, machines with visible open electrodes (unshielded) have stronger fields than machines with enclosed electrodes.

When describing radio frequency electromagnetic fields, the field’s frequency is often mentioned. The permitted frequencies for plastic welders are 13.56, 27.12, or 40.68 megahertz (MHz). The most popular industrial frequency for HF welding is 27.12MHz. The radio frequency fields from a plastic welder spread out around the machine, but most often it is only right next to the machine that the field is so strong that precautions need to be taken. The field’s strength decreases sharply with distance from the source. The strength of the field is given in two different measurements: the electric field strength is measured in volts per metre (V/m), and the magnetic field strength is measured in amperes per metre (A/m). Both of these must be measured to get an idea of how strong the radio frequency field is. The current that goes through you if you touch the equipment (contact current) and the current that that goes through the body when welding (induced current) must also be measured.

Advantages of High Frequency Welding Technology

• HF sealing occurs from the inside out by using the material itself as a heat source. The heat is focused at the weld target so that the surrounding material does not have to be super-heated to arrive at a target temperature at the joint.
• With HF heating is generated only when the field is energized. Once the generator cycles, the heat is turned off. This allows for greater control over the amount of energy that the material sees over the entire cycle. In addition, HF-generated heat does not radiate off the die like on a heated die. This prevents heat-degredation of the material abutting the weld.
• HF tooling is usually run "cold". This means that once the HF is turned off, the material stops being heated, but remains under pressure. In this fashion it is possible to both instantly heat, weld, and cool the material under compression. More control over the weld results in more control over the resulting extrusion, thus increasing the weld strength.
• RF welds are "clean" because the only material needed to produce an HF weld is the material itself. There are no adhesives or by-products involved in HF

High Frequency Welding

High Frequency Welding Machine Manufacturer/RF PVC welding machine for welding plastic,etc.

High Frequency Welding, known as Radio Frequency (RF) or Dielectric welding, is the process of fusing materials together by applying radio frequency energy to the area to be joined. The resulting weld can be as strong as the original materials. HF Welding relies on certain properties of the material being welded to cause the generation of heat in a rapidly alternating electric field. This means that only certain materials can be welded using this technique. The process involves subjecting the parts to be joined to a high frequency (most often 27.12MHz) electromagnetic field, which is normally applied between two metal bars. These bars also act as pressure applicators during heating and cooling. The dynamic electric field causes the molecules in polar thermoplastics to oscillate. Depending on their geometry and dipole moment, these molecules may translate some of this oscillatory motion into thermal energy and cause heating of the material. A measure of this interaction is the loss factor, which is temperature and frequency dependent.

Polyvinylchloride (PVC) and polyurethanes are the most common thermoplastics to be welded by the RF process. It is possible to RF weld other polymers including nylon, PET, PET-G, A-PET, EVA and some ABS resins, but special conditions are required, for example nylon and PET are weldable if preheated welding bars are used in addition to the RF power.

HF welding is generally not suitable for PTFE, polycarbonate, polystyrene, polyethylene or polypropylene. However, due to the impending restrictions in the use of PVC, a special grade of polyolefin has been developed which does have the capability to be HF welded.

The primary function of HF welding is to form a joint in two or more thicknesses of sheet material. A number of optional features exist. The welding tool can be engraved or profiled to give the entire welded area a decorative appearance or it can incorporate an embossing technique to place lettering, logos or decorative effects on the welded items. By incorporating a cutting edge adjacent to the welding surface, the process can simultaneously weld and cut a material. The cutting edge compresses the hot plastic sufficiently to allow the excess scrap material to be torn off, hence this process is often referred to as tear-seal welding.

A typical plastic welder consists of a high frequency generator (which creates the radio frequency current), a pneumatic press, an electrode that transfers the radio frequency current to the material that is being welded and a welding bench that holds the material in place. The machine could also have a grounding bar that is often mounted behind the electrode, which leads the current back to the machine (grounding point). There are different types of plastic welders, the most common being tarpaulin machines, packaging machines and automated machines.

By regulating the machine’s tuning, the field strength can be adjusted to the material being welded. When welding, the machine is surrounded by a radio frequency field that, if too strong, can heat up the body somewhat. This is what the operator needs to be protected from. The strength of the radio frequency field also depends on the type of machine being used. Generally, machines with visible open electrodes (unshielded) have stronger fields than machines with enclosed electrodes.

When describing radio frequency electromagnetic fields, the field’s frequency is often mentioned. The permitted frequencies for plastic welders are 13.56, 27.12, or 40.68 megahertz (MHz). The most popular industrial frequency for HF welding is 27.12MHz.

The radio frequency fields from a plastic welder spread out around the machine, but most often it is only right next to the machine that the field is so strong that precautions need to be taken. The field’s strength decreases sharply with distance from the source. The strength of the field is given in two different measurements: the electric field strength is measured in volts per metre (V/m), and the magnetic field strength is measured in amperes per metre (A/m). Both of these must be measured to get an idea of how strong the radio frequency field is. The current that goes through you if you touch the equipment (contact current) and the current that that goes through the body when welding (induced current) must also be measured.

Advantages of High Frequency Welding Technology

• HF sealing occurs from the inside out by using the material itself as a heat source. The heat is focused at the weld target so that the surrounding material does not have to be super-heated to arrive at a target temperature at the joint.


• With HF heating is generated only when the field is energized. Once the generator cycles, the heat is turned off. This allows for greater control over the amount of energy that the material sees over the entire cycle. In addition, HF-generated heat does not radiate off the die like on a heated die. This prevents heat-degredation of the material abutting the weld.


• HF tooling is usually run "cold". This means that once the HF is turned off, the material stops being heated, but remains under pressure. In this fashion it is possible to both instantly heat, weld, and cool the material under compression. More control over the weld results in more control over the resulting extrusion, thus increasing the weld strength.


• RF welds are "clean" because the only material needed to produce an HF weld is the material itself. There are no adhesives or by-products involved in HF

High Speed Heating by Induction Heating System

One of the recent outstanding developments in the heat treating field has been the application of induction heating to localized surface hardening. The advances made contingent with the applica­tion of high frequency current have been nothing short of phenomenal. Starting a comparatively short time ago as a long-sought-after method of hardening bearing surfaces on crankshafts (sev­eral million of these are in use setting all time service records), today finds this very selective surfacing hardening method producing hardened areas on a multiplicity of parts. Yet, in spite of its present day breadth of application, induction hardening is still in its infant stage. Its probable utilization for the heat treating and hardening of metals, heating for forging or brazing, or solder­ing of similar and dissimilar metals, is unpre­dictable. Induction hardening results in the production of locally hardened steel objects with the desired degree of depth and hardness, essential metal­lurgical structure of core, demarcation zone, and hardened case, with a practical lack of distortion and no scale formation. It permits equipment de­sign which warrants mechanization of the whole operation to fulfill production line requirements. Time cycles of only a few seconds are maintained by automatic regulation of power and split second heating and quenching intervals indispensable to the creation of facsimile results of exacting special fixations. Induction hardening equipment permits the user to surface harden only the requisite por­tion of most any steel object and thus maintain the original ductility and strength; to harden articles of intricate design which cannot be feas­ibly treated in any other way; to eliminate usual expensive pretreatment such as copper plating and carburizing, and costly subsequent straight­ening and cleaning operations; to cut down on material cost by having a wide selection of steels from which to choose; and to harden a fully-ma­chined item without the necessity of any finishing operations. To the casual observer it would appear that in­duction hardening is possible as a result of some energy transformation occurring within an induc­tive region of copper. The copper carries an elec­trical current of high frequency and, within an interval of a few seconds, the surface of a piece of steel placed within this energized region is heated to its critical range and quenched to opti­mum hardness. To the manufacturer of equipment for this method of hardening it means the appli­cation of the phenomena of hysteresis, eddy cur­rents, and skin effect to the effective production of localized surface hardening. The heating is accomplished by use of high frequency currents. Specifically chosen frequencies from 2,000 to 10,000 cycles and upwards of 100,­000 cycles are being used extensively at the pres­ent time. Current of this nature in flowing through an inductor produces a high-frequency magnetic field within the region of the inductor. When a magnetic material such as steel is placed within this field, there is a dissipation of energy in the steel which produces heat. The molecules within the steel attempt to align themselves with the polarity of this field, and with this changing thousands of times per second, an enormous amount of internal molecular friction is developed as a result of the natural tendency for the steel to resist changes. In this manner the electrical energy is transformed, through the medium of friction, into heat. However, since another inherent characteristic of high frequency current is to concentrate on the surface of its conductor, only the surface layers become heated. This tendency, called “skin effect”, is a function of the frequency and, other things being equal, higher frequencies are effec­tive at shallower depths. The frictional action producing the heat is called hysteresis and is obviously dependent upon the magnetic qualities of the steel. Thus, when the temperature has passed the critical point at which the steel be­comes non-magnetic, all hysteretic heating ceases. There is an additional source of heat due to eddy currents which flow in the steel as a result of the rapidly changing flux in the field. With resistance of the steel increasing with tempera­ture, the intensity of this action is decreased as the steel becomes heated, and is only a fraction of its “cold” original value when the proper quenching temperature is reached. When the temperature of an inductively heated steel bar arrives at the critical point, heating due to eddy currents continues at a greatly reduced rate. Since the entire action goes on in the sur­face layers, only that portion is affected. The original core properties are maintained, the sur­face hardening being accomplished by quench­ing when complete carbide solution has been at­tained in the surface areas. Continued applica­tion of power causes an increase in depth of hardness, for as each layer of steel is brought to temperature, the current density shifts to the layer beneath which offers a lower resistance. It is obvious that the selection of the proper fre­quency, and control of power and heating time will make fulfillment of any desired specifica­tions of surface hardening possible. Metallurgy of Induction Heating The unusual behavior of steel when heated in­ductively and the results obtained merit a discus­sion of the metallurgy involved. Carbide solution rates of less than a second, higher hardness than that produced by furnace treatment, and a nodu­lar type of martensite are points of consideration that classify the metallurgy of induction harden­ing as “different”. Further, surface decarburiza­tion and grain growth do not occur because of the short heating cycle. Induction heating produces a hardness that is maintained through 80 percent of its depth, and from there on, a gradual decrease through a transition zone to the original hardness of the steel as found in the core which has not been affected. The bond is thus ideal, eliminating any chance of spalling or checking. Complete carbide solution and homogeneity as evidenced by maximum hardness can be accom­plished with a total heating time of 0.6 second. Of this time, only 0.2 to 0.3 second is actually above the lower critical. It is interesting to note that induction hardening equipment is in every day operation on a production basis with complete carbide solution, resulting from a heating and quenching cycle, the total time of which is less than 0.2 second. The fine nodular and more homogeneous mar­tensite which results from the induction harden­ing is more readily apparent with carbon steels than with alloy steel because of the nodular ap­pearance of most alloy martensite. This fine struc­ture must have for its origin an austenite which is the result of a more thorough carbide diffusion than is obtained with thermal heating. Practically instantaneous development of critical tempera­tures throughout the entire microstructure of the alpha iron and iron carbide is particularly con­ducive to rapid carbide solution and a distribution of constituents which has as its inevitable product a thoroughly homogeneous austentite. Further, the conversion of this structure to martensite will produce a martensite which possesses similar characteristics and a corresponding resistance to wear or penetrating instruments.

high speed heating by induction  

High Frequency Welding

High Frequency Welding Machine Manufacturer/RF PVC welding machine for welding plastic,etc.

High Frequency Welding, known as Radio Frequency (RF) or Dielectric welding, is the process of fusing materials together by applying radio frequency energy to the area to be joined. The resulting weld can be as strong as the original materials. HF Welding relies on certain properties of the material being welded to cause the generation of heat in a rapidly alternating electric field. This means that only certain materials can be welded using this technique. The process involves subjecting the parts to be joined to a high frequency (most often 27.12MHz) electromagnetic field, which is normally applied between two metal bars. These bars also act as pressure applicators during heating and cooling. The dynamic electric field causes the molecules in polar thermoplastics to oscillate. Depending on their geometry and dipole moment, these molecules may translate some of this oscillatory motion into thermal energy and cause heating of the material. A measure of this interaction is the loss factor, which is temperature and frequency dependent.

Polyvinylchloride (PVC) and polyurethanes are the most common thermoplastics to be welded by the RF process. It is possible to RF weld other polymers including nylon, PET, PET-G, A-PET, EVA and some ABS resins, but special conditions are required, for example nylon and PET are weldable if preheated welding bars are used in addition to the RF power.

HF welding is generally not suitable for PTFE, polycarbonate, polystyrene, polyethylene or polypropylene. However, due to the impending restrictions in the use of PVC, a special grade of polyolefin has been developed which does have the capability to be HF welded.

The primary function of HF welding is to form a joint in two or more thicknesses of sheet material. A number of optional features exist. The welding tool can be engraved or profiled to give the entire welded area a decorative appearance or it can incorporate an embossing technique to place lettering, logos or decorative effects on the welded items. By incorporating a cutting edge adjacent to the welding surface, the process can simultaneously weld and cut a material. The cutting edge compresses the hot plastic sufficiently to allow the excess scrap material to be torn off, hence this process is often referred to as tear-seal welding. A typical plastic welder consists of a high frequency generator (which creates the radio frequency current), a pneumatic press, an electrode that transfers the radio frequency current to the material that is being welded and a welding bench that holds the material in place. The machine could also have a grounding bar that is often mounted behind the electrode, which leads the current back to the machine (grounding point). There are different types of plastic welders, the most common being tarpaulin machines, packaging machines and automated machines. By regulating the machine’s tuning, the field strength can be adjusted to the material being welded. When welding, the machine is surrounded by a radio frequency field that, if too strong, can heat up the body somewhat. This is what the operator needs to be protected from. The strength of the radio frequency field also depends on the type of machine being used. Generally, machines with visible open electrodes (unshielded) have stronger fields than machines with enclosed electrodes.

When describing radio frequency electromagnetic fields, the field’s frequency is often mentioned. The permitted frequencies for plastic welders are 13.56, 27.12, or 40.68 megahertz (MHz). The most popular industrial frequency for HF welding is 27.12MHz. The radio frequency fields from a plastic welder spread out around the machine, but most often it is only right next to the machine that the field is so strong that precautions need to be taken. The field’s strength decreases sharply with distance from the source. The strength of the field is given in two different measurements: the electric field strength is measured in volts per metre (V/m), and the magnetic field strength is measured in amperes per metre (A/m). Both of these must be measured to get an idea of how strong the radio frequency field is. The current that goes through you if you touch the equipment (contact current) and the current that that goes through the body when welding (induced current) must also be measured.

Advantages of High Frequency Welding Technology

• HF sealing occurs from the inside out by using the material itself as a heat source. The heat is focused at the weld target so that the surrounding material does not have to be super-heated to arrive at a target temperature at the joint.
• With HF heating is generated only when the field is energized. Once the generator cycles, the heat is turned off. This allows for greater control over the amount of energy that the material sees over the entire cycle. In addition, HF-generated heat does not radiate off the die like on a heated die. This prevents heat-degredation of the material abutting the weld.
• HF tooling is usually run "cold". This means that once the HF is turned off, the material stops being heated, but remains under pressure. In this fashion it is possible to both instantly heat, weld, and cool the material under compression. More control over the weld results in more control over the resulting extrusion, thus increasing the weld strength.
• RF welds are "clean" because the only material needed to produce an HF weld is the material itself. There are no adhesives or by-products involved in HF

High Frequency Welding

High Frequency Welding Machine Manufacturer/RF PVC welding machine for welding plastic,etc.

High Frequency Welding, known as Radio Frequency (RF) or Dielectric welding, is the process of fusing materials together by applying radio frequency energy to the area to be joined. The resulting weld can be as strong as the original materials. HF Welding relies on certain properties of the material being welded to cause the generation of heat in a rapidly alternating electric field. This means that only certain materials can be welded using this technique. The process involves subjecting the parts to be joined to a high frequency (most often 27.12MHz) electromagnetic field, which is normally applied between two metal bars. These bars also act as pressure applicators during heating and cooling. The dynamic electric field causes the molecules in polar thermoplastics to oscillate. Depending on their geometry and dipole moment, these molecules may translate some of this oscillatory motion into thermal energy and cause heating of the material. A measure of this interaction is the loss factor, which is temperature and frequency dependent.

Polyvinylchloride (PVC) and polyurethanes are the most common thermoplastics to be welded by the RF process. It is possible to RF weld other polymers including nylon, PET, PET-G, A-PET, EVA and some ABS resins, but special conditions are required, for example nylon and PET are weldable if preheated welding bars are used in addition to the RF power.

HF welding is generally not suitable for PTFE, polycarbonate, polystyrene, polyethylene or polypropylene. However, due to the impending restrictions in the use of PVC, a special grade of polyolefin has been developed which does have the capability to be HF welded.

The primary function of HF welding is to form a joint in two or more thicknesses of sheet material. A number of optional features exist. The welding tool can be engraved or profiled to give the entire welded area a decorative appearance or it can incorporate an embossing technique to place lettering, logos or decorative effects on the welded items. By incorporating a cutting edge adjacent to the welding surface, the process can simultaneously weld and cut a material. The cutting edge compresses the hot plastic sufficiently to allow the excess scrap material to be torn off, hence this process is often referred to as tear-seal welding. A typical plastic welder consists of a high frequency generator (which creates the radio frequency current), a pneumatic press, an electrode that transfers the radio frequency current to the material that is being welded and a welding bench that holds the material in place. The machine could also have a grounding bar that is often mounted behind the electrode, which leads the current back to the machine (grounding point). There are different types of plastic welders, the most common being tarpaulin machines, packaging machines and automated machines. By regulating the machine’s tuning, the field strength can be adjusted to the material being welded. When welding, the machine is surrounded by a radio frequency field that, if too strong, can heat up the body somewhat. This is what the operator needs to be protected from. The strength of the radio frequency field also depends on the type of machine being used. Generally, machines with visible open electrodes (unshielded) have stronger fields than machines with enclosed electrodes.

When describing radio frequency electromagnetic fields, the field’s frequency is often mentioned. The permitted frequencies for plastic welders are 13.56, 27.12, or 40.68 megahertz (MHz). The most popular industrial frequency for HF welding is 27.12MHz. The radio frequency fields from a plastic welder spread out around the machine, but most often it is only right next to the machine that the field is so strong that precautions need to be taken. The field’s strength decreases sharply with distance from the source. The strength of the field is given in two different measurements: the electric field strength is measured in volts per metre (V/m), and the magnetic field strength is measured in amperes per metre (A/m). Both of these must be measured to get an idea of how strong the radio frequency field is. The current that goes through you if you touch the equipment (contact current) and the current that that goes through the body when welding (induced current) must also be measured.

Advantages of High Frequency Welding Technology

• HF sealing occurs from the inside out by using the material itself as a heat source. The heat is focused at the weld target so that the surrounding material does not have to be super-heated to arrive at a target temperature at the joint.
• With HF heating is generated only when the field is energized. Once the generator cycles, the heat is turned off. This allows for greater control over the amount of energy that the material sees over the entire cycle. In addition, HF-generated heat does not radiate off the die like on a heated die. This prevents heat-degredation of the material abutting the weld.
• HF tooling is usually run "cold". This means that once the HF is turned off, the material stops being heated, but remains under pressure. In this fashion it is possible to both instantly heat, weld, and cool the material under compression. More control over the weld results in more control over the resulting extrusion, thus increasing the weld strength.
• RF welds are "clean" because the only material needed to produce an HF weld is the material itself. There are no adhesives or by-products involved in HF