Induction Shrink Fitting Steel Tube

Induction Shrink Fitting Steel Tube With IGBT Heating Units Objective Heating a steel tube to 500-1000°F for a shrink-fitting application. Determine expansion (growth) of ID at varying temperatures. Material Steel tubes 7” OD x 4.75” ID x 5” heat zone Type ‘K’ thermocouple to measure temperature Thermal blanket Temperature 500, 800, 1000 °F (260, 427, 538° C) Frequency 66 kHz Equipment DW-HF-7.5, 7.5 kW, 150-400 kHz induction power supply, equipped with a remote heat station containing two 1.5 μF capacitors (for a total of 0.75 μF) A multi-turn, special series-parallel induction heating coil designed and developed specifically for this application. Process Initial tests were completed on a sample without a thermal blanket. A thermocouple is slipped between the copper ring and the steel tube to measure temperature. The part measured 4.940” (at room temperature with an ID gauge.) The part reaches 1000°F (538°C) in about 10 minutes. The chart below shows the comparison between theoretical and experimental measured results Results/Benefits The part measures 4.975” at 1000°F yielding an expansion of 0.035” (4.975 minus 4.94). At 500 and 800°F the expansion numbers were 4.950 and 4.964 respectively. When using a thermal blanket the heat time is reduced by about 90 seconds (8.5 minutes as opposed to 10 minutes).                                   https://dw-inductionheater.com/induction-shrink-fitting-steel-tube.html?feed_id=245052&_unique_id=663e2b192793f

Shrink Fittting Part Removal application with Induction Heating

Objective This is a Shrinkfit Part Removal application. The customer’s current process uses a press to push the inserted part out. However, this requires significant force and time. By applying heat, the housing can expand just enough to allow for the easy removal of the inserted part with minimal force. The customer’s time requirement is to complete the Shrinkfit Part Removal within 7 minutes.

Equipment DW-HF-15kw induction heating machine Materials • Aluminum pump housing Part OD 2.885” (73.279mm), wall 0.021” (.533mm) Key Parameters Temperature: Approximately 400°F (204°C) Power: 4 kW Time: 100 seconds

Process:

1. To complete the Shrinkfit Part Removal, place part into coil, so the top of the housing is as close as possible to the top of the coil.
2. Some experimentation was needed to determine the ideal time and power. We found that 100 seconds was ideal for removal of the part, which was significantly lower than the customer’s limit of 7 minutes

Results/Benefits: The tested assembly can be heated to the required temperature in less than 7 minutes using the DW-HF-15kw induction heating system and custom designed coil. Heat time for the Custom Coil was 100 seconds, Temperature needed to be close to 400°F (204°C) in order to expand the part sufficiently for removal. The part was removed with some pulling force applied to it as the pump housing was reaching 400°F (204°C). This Shrink Fit application was further reviewed to determine if a lower power induction heating system could be used. In this case, the customer’s requirement was 7 minutes, and we achieved the part removal in 100 seconds. Could a lower power system remove the part at a lower cost? A lower power system would be acceptable if our goal is part insertion. For Shrink Fit – Part Insertion, a slower heating rate would still result in a successful process. However, with Shrink Fit – Part Removal, it is important to heat rapidly. A slower heat rate would result in the inserted part also heating, and also expanding. The inserted part potentially would remain “stuck”. By heating rapidly, we avoid this issue. The customer in this case has decided to both use a system for part insertion AND part removal. A 4 kW system is fine for the Shrink Fit – Part Insertion; and the 7 kW DW-HF-15kw induction heating system will be used for the Shrink Fit – Part Removal

• Precise control of the time and temperature
• Power on demand with rapid heat cycles
• Repeatable process, not operator dependent
• Safe heating with no open flames
• Energy efficient heating

https://dw-inductionheater.com/shrink-fittting-part-removal-application-with-induction-heating.html?feed_id=239866&_unique_id=660d9bf09ed9c

Induction Shrink Fitting Steel Tube

Induction Shrink Fitting Steel Tube With IGBT Heating Units Objective Heating a steel tube to 500-1000°F for a shrink-fitting application. Determine expansion (growth) of ID at varying temperatures. Material Steel tubes 7” OD x 4.75” ID x 5” heat zone Type ‘K’ thermocouple to measure temperature Thermal blanket Temperature 500, 800, 1000 °F (260, 427, 538° C) Frequency 66 kHz Equipment DW-HF-7.5, 7.5 kW, 150-400 kHz induction power supply, equipped with a remote heat station containing two 1.5 μF capacitors (for a total of 0.75 μF) A multi-turn, special series-parallel induction heating coil designed and developed specifically for this application. Process Initial tests were completed on a sample without a thermal blanket. A thermocouple is slipped between the copper ring and the steel tube to measure temperature. The part measured 4.940” (at room temperature with an ID gauge.) The part reaches 1000°F (538°C) in about 10 minutes. The chart below shows the comparison between theoretical and experimental measured results Results/Benefits The part measures 4.975” at 1000°F yielding an expansion of 0.035” (4.975 minus 4.94). At 500 and 800°F the expansion numbers were 4.950 and 4.964 respectively. When using a thermal blanket the heat time is reduced by about 90 seconds (8.5 minutes as opposed to 10 minutes).                                   https://dw-inductionheater.com/induction-shrink-fitting-steel-tube.html?feed_id=227471&_unique_id=650786de3142b

Shrink Fittting Part Removal application with Induction Heating

Objective This is a Shrinkfit Part Removal application. The customer’s current process uses a press to push the inserted part out. However, this requires significant force and time. By applying heat, the housing can expand just enough to allow for the easy removal of the inserted part with minimal force. The customer’s time requirement is to complete the Shrinkfit Part Removal within 7 minutes.

Equipment DW-HF-15kw induction heating machine Materials • Aluminum pump housing Part OD 2.885” (73.279mm), wall 0.021” (.533mm) Key Parameters Temperature: Approximately 400°F (204°C) Power: 4 kW Time: 100 seconds

Process:

1. To complete the Shrinkfit Part Removal, place part into coil, so the top of the housing is as close as possible to the top of the coil.
2. Some experimentation was needed to determine the ideal time and power. We found that 100 seconds was ideal for removal of the part, which was significantly lower than the customer’s limit of 7 minutes

Results/Benefits: The tested assembly can be heated to the required temperature in less than 7 minutes using the DW-HF-15kw induction heating system and custom designed coil. Heat time for the Custom Coil was 100 seconds, Temperature needed to be close to 400°F (204°C) in order to expand the part sufficiently for removal. The part was removed with some pulling force applied to it as the pump housing was reaching 400°F (204°C). This Shrink Fit application was further reviewed to determine if a lower power induction heating system could be used. In this case, the customer’s requirement was 7 minutes, and we achieved the part removal in 100 seconds. Could a lower power system remove the part at a lower cost? A lower power system would be acceptable if our goal is part insertion. For Shrink Fit – Part Insertion, a slower heating rate would still result in a successful process. However, with Shrink Fit – Part Removal, it is important to heat rapidly. A slower heat rate would result in the inserted part also heating, and also expanding. The inserted part potentially would remain “stuck”. By heating rapidly, we avoid this issue. The customer in this case has decided to both use a system for part insertion AND part removal. A 4 kW system is fine for the Shrink Fit – Part Insertion; and the 7 kW DW-HF-15kw induction heating system will be used for the Shrink Fit – Part Removal

• Precise control of the time and temperature
• Power on demand with rapid heat cycles
• Repeatable process, not operator dependent
• Safe heating with no open flames
• Energy efficient heating

https://dw-inductionheater.com/shrink-fittting-part-removal-application-with-induction-heating.html?feed_id=222811&_unique_id=64d6f0dc94af1

Induction shrink fitting and thermal disassembly

Induction shrink fitting and thermal disassembly process

Induction shrink fitting and thermal disassembly is a method of fitting a metallic ring around a shaft or hub by heating the ring with an induction heating method. The metal ring is made to expand and then cooled with the shaft or hub inside. The two metal parts contract after cooling, and the metal ring is in a shrink-fit position. An induction shrink fitting machine uses induction heating technology to heat a metal ring to high temperatures to cause the metal ring to expand and then contract it to fit tightly over a shaft or hub. How do Induction Shrink fitting machines work? The induction shrink fitting machine heats the metal ring with an electromagnetic field, causing the metal ring to heat up due to eddy currents. The coil of the machine generates electromagnetic waves which induce the currents in the metal ring, and it heats up. The temperature is controlled with different settings of voltage, frequency, and processing time. The process of heating and cooling with the shaft or hub is done until they fit tightly. The Benefits of Induction Shrink fitting machines The benefits of Induction shrink fitting machines are numerous. Here are a few: 1. High speed and efficiency – Induction shrink fitting machines heat metal at a fast rate, making it possible to complete the process in a short time. 2. Precision – Induction heating provides precise heating using controlled energy input, producing consistent and accurate results. 3. Safety – Induction shrink fitting reduces health and safety risks by eliminating the use of oxyacetylene burners, gas flames, or other heating methods. 4. Cost-effective – Induction shrink fitting requires less energy and reduces the cost that would be used to pay for prolonged heating or the use of other heating solutions. The use of induction shrink fitting is common in many industries, including automotive, aerospace, construction, and manufacturing. It is widely used for assembling bearings, gears, couplings, and other components that require a tight and secure fit. The method has proven to be an effective and efficient alternative to traditional assembly methods, providing a strong and durable joint that can withstand high levels of stress and vibration. Conclusion Induction shrink fitting machines have revolutionized the way that industries fit metal parts together. The technology offers quick, accurate, safe, and cost-effective methods of heating metal parts. The metal parts produced through induction shrink fitting are of high quality, durability and strength.induction shrink fitting is a valuable tool for assembling components with precision and accuracy, reducing the risk of part failure and increasing efficiency in manufacturing processes. Induction shrink fitting is ideal for industries that require high precision metal parts, including aerospace engineering, automotive and electronics industries.  

Induction shrink fitting and thermal disassembly

Induction shrink fitting and thermal disassembly process

Induction shrink fitting and thermal disassembly is a method of fitting a metallic ring around a shaft or hub by heating the ring with an induction heating method. The metal ring is made to expand and then cooled with the shaft or hub inside. The two metal parts contract after cooling, and the metal ring is in a shrink-fit position. An induction shrink fitting machine uses induction heating technology to heat a metal ring to high temperatures to cause the metal ring to expand and then contract it to fit tightly over a shaft or hub. How do Induction Shrink fitting machines work? The induction shrink fitting machine heats the metal ring with an electromagnetic field, causing the metal ring to heat up due to eddy currents. The coil of the machine generates electromagnetic waves which induce the currents in the metal ring, and it heats up. The temperature is controlled with different settings of voltage, frequency, and processing time. The process of heating and cooling with the shaft or hub is done until they fit tightly. The Benefits of Induction Shrink fitting machines The benefits of Induction shrink fitting machines are numerous. Here are a few: 1. High speed and efficiency – Induction shrink fitting machines heat metal at a fast rate, making it possible to complete the process in a short time. 2. Precision – Induction heating provides precise heating using controlled energy input, producing consistent and accurate results. 3. Safety – Induction shrink fitting reduces health and safety risks by eliminating the use of oxyacetylene burners, gas flames, or other heating methods. 4. Cost-effective – Induction shrink fitting requires less energy and reduces the cost that would be used to pay for prolonged heating or the use of other heating solutions. The use of induction shrink fitting is common in many industries, including automotive, aerospace, construction, and manufacturing. It is widely used for assembling bearings, gears, couplings, and other components that require a tight and secure fit. The method has proven to be an effective and efficient alternative to traditional assembly methods, providing a strong and durable joint that can withstand high levels of stress and vibration. Conclusion Induction shrink fitting machines have revolutionized the way that industries fit metal parts together. The technology offers quick, accurate, safe, and cost-effective methods of heating metal parts. The metal parts produced through induction shrink fitting are of high quality, durability and strength.induction shrink fitting is a valuable tool for assembling components with precision and accuracy, reducing the risk of part failure and increasing efficiency in manufacturing processes. Induction shrink fitting is ideal for industries that require high precision metal parts, including aerospace engineering, automotive and electronics industries.   https://dw-inductionheater.com/product/induction-shrink-fitting-and-thermal-disassembly?feed_id=195547&_unique_id=6437ac068b246

Shrink Fittting Part Removal application with Induction Heating

Objective This is a Shrinkfit Part Removal application. The customer’s current process uses a press to push the inserted part out. However, this requires significant force and time. By applying heat, the housing can expand just enough to allow for the easy removal of the inserted part with minimal force. The customer’s time requirement is to complete the Shrinkfit Part Removal within 7 minutes.

Equipment DW-HF-15kw induction heating machine Materials • Aluminum pump housing Part OD 2.885” (73.279mm), wall 0.021” (.533mm) Key Parameters Temperature: Approximately 400°F (204°C) Power: 4 kW Time: 100 seconds

Process:

1. To complete the Shrinkfit Part Removal, place part into coil, so the top of the housing is as close as possible to the top of the coil.
2. Some experimentation was needed to determine the ideal time and power. We found that 100 seconds was ideal for removal of the part, which was significantly lower than the customer’s limit of 7 minutes

Results/Benefits: The tested assembly can be heated to the required temperature in less than 7 minutes using the DW-HF-15kw induction heating system and custom designed coil. Heat time for the Custom Coil was 100 seconds, Temperature needed to be close to 400°F (204°C) in order to expand the part sufficiently for removal. The part was removed with some pulling force applied to it as the pump housing was reaching 400°F (204°C). This Shrink Fit application was further reviewed to determine if a lower power induction heating system could be used. In this case, the customer’s requirement was 7 minutes, and we achieved the part removal in 100 seconds. Could a lower power system remove the part at a lower cost? A lower power system would be acceptable if our goal is part insertion. For Shrink Fit – Part Insertion, a slower heating rate would still result in a successful process. However, with Shrink Fit – Part Removal, it is important to heat rapidly. A slower heat rate would result in the inserted part also heating, and also expanding. The inserted part potentially would remain “stuck”. By heating rapidly, we avoid this issue. The customer in this case has decided to both use a system for part insertion AND part removal. A 4 kW system is fine for the Shrink Fit – Part Insertion; and the 7 kW DW-HF-15kw induction heating system will be used for the Shrink Fit – Part Removal

• Precise control of the time and temperature
• Power on demand with rapid heat cycles
• Repeatable process, not operator dependent
• Safe heating with no open flames
• Energy efficient heating

Induction Shrink Fitting Steel Tube

Induction Shrink Fitting Steel Tube With IGBT Heating Units Objective Heating a steel tube to 500-1000°F for a shrink-fitting application. Determine expansion (growth) of ID at varying temperatures. Material Steel tubes 7” OD x 4.75” ID x 5” heat zone Type ‘K’ thermocouple to measure temperature Thermal blanket Temperature 500, 800, 1000 °F (260, 427, 538° C) Frequency 66 kHz Equipment DW-HF-7.5, 7.5 kW, 150-400 kHz induction power supply, equipped with a remote heat station containing two 1.5 μF capacitors (for a total of 0.75 μF) A multi-turn, special series-parallel induction heating coil designed and developed specifically for this application. Process Initial tests were completed on a sample without a thermal blanket. A thermocouple is slipped between the copper ring and the steel tube to measure temperature. The part measured 4.940” (at room temperature with an ID gauge.) The part reaches 1000°F (538°C) in about 10 minutes. The chart below shows the comparison between theoretical and experimental measured results Results/Benefits The part measures 4.975” at 1000°F yielding an expansion of 0.035” (4.975 minus 4.94). At 500 and 800°F the expansion numbers were 4.950 and 4.964 respectively. When using a thermal blanket the heat time is reduced by about 90 seconds (8.5 minutes as opposed to 10 minutes).                                  

Shrink Fittting Part Removal application with Induction Heating

Objective This is a Shrinkfit Part Removal application. The customer’s current process uses a press to push the inserted part out. However, this requires significant force and time. By applying heat, the housing can expand just enough to allow for the easy removal of the inserted part with minimal force. The customer’s time requirement is to complete the Shrinkfit Part Removal within 7 minutes.

Equipment DW-HF-15kw induction heating machine Materials • Aluminum pump housing Part OD 2.885” (73.279mm), wall 0.021” (.533mm) Key Parameters Temperature: Approximately 400°F (204°C) Power: 4 kW Time: 100 seconds

Process:

1. To complete the Shrinkfit Part Removal, place part into coil, so the top of the housing is as close as possible to the top of the coil.
2. Some experimentation was needed to determine the ideal time and power. We found that 100 seconds was ideal for removal of the part, which was significantly lower than the customer’s limit of 7 minutes

Results/Benefits: The tested assembly can be heated to the required temperature in less than 7 minutes using the DW-HF-15kw induction heating system and custom designed coil. Heat time for the Custom Coil was 100 seconds, Temperature needed to be close to 400°F (204°C) in order to expand the part sufficiently for removal. The part was removed with some pulling force applied to it as the pump housing was reaching 400°F (204°C). This Shrink Fit application was further reviewed to determine if a lower power induction heating system could be used. In this case, the customer’s requirement was 7 minutes, and we achieved the part removal in 100 seconds. Could a lower power system remove the part at a lower cost? A lower power system would be acceptable if our goal is part insertion. For Shrink Fit – Part Insertion, a slower heating rate would still result in a successful process. However, with Shrink Fit – Part Removal, it is important to heat rapidly. A slower heat rate would result in the inserted part also heating, and also expanding. The inserted part potentially would remain “stuck”. By heating rapidly, we avoid this issue. The customer in this case has decided to both use a system for part insertion AND part removal. A 4 kW system is fine for the Shrink Fit – Part Insertion; and the 7 kW DW-HF-15kw induction heating system will be used for the Shrink Fit – Part Removal

• Precise control of the time and temperature
• Power on demand with rapid heat cycles
• Repeatable process, not operator dependent
• Safe heating with no open flames
• Energy efficient heating

Induction Shrink Fitting Steel Tube

Induction Shrink Fitting Steel Tube With IGBT Heating Units

Objective Heating a steel tube to 500-1000°F for a shrink-fitting application. Determine expansion (growth) of ID at varying temperatures.
Material Steel tubes 7” OD x 4.75” ID x 5” heat zone
Type ‘K’ thermocouple to measure temperature
Thermal blanket
Temperature 500, 800, 1000 °F (260, 427, 538° C)
Frequency 66 kHz
Equipment DW-HF-7.5, 7.5 kW, 150-400 kHz induction power supply, equipped with a remote heat station containing two 1.5 μF capacitors (for a total of 0.75 μF)
A multi-turn, special series-parallel induction heating coil designed and developed specifically for this application.
Process Initial tests were completed on a sample without a thermal blanket. A thermocouple is slipped between the copper ring and the steel tube to measure temperature. The part measured
4.940” (at room temperature with an ID gauge.) The part reaches 1000°F (538°C) in about 10 minutes.
The chart below shows the comparison between theoretical and experimental measured results



Results/Benefits The part measures 4.975” at 1000°F yielding an expansion of 0.035” (4.975 minus 4.94). At 500 and 800°F the expansion numbers were 4.950 and 4.964 respectively. When using a
thermal blanket the heat time is reduced by about 90 seconds (8.5 minutes as opposed to 10 minutes).

 



 

 

 

 

 

 



 

 

 

 

 

 

 



 

 

 

Shrink Fittting Part Removal application with Induction Heating

Objective This is a Shrinkfit Part Removal application. The customer’s current process uses a press to push the inserted part out. However, this requires significant force and time. By applying heat, the housing can expand just enough to allow for the easy removal of the inserted part with minimal force. The customer’s time requirement is to complete the Shrinkfit Part Removal within 7 minutes.

Equipment DW-HF-15kw induction heating machine Materials • Aluminum pump housing Part OD 2.885” (73.279mm), wall 0.021” (.533mm) Key Parameters Temperature: Approximately 400°F (204°C) Power: 4 kW Time: 100 seconds

Process:

1. To complete the Shrinkfit Part Removal, place part into coil, so the top of the housing is as close as possible to the top of the coil.
2. Some experimentation was needed to determine the ideal time and power. We found that 100 seconds was ideal for removal of the part, which was significantly lower than the customer’s limit of 7 minutes

Results/Benefits: The tested assembly can be heated to the required temperature in less than 7 minutes using the DW-HF-15kw induction heating system and custom designed coil. Heat time for the Custom Coil was 100 seconds, Temperature needed to be close to 400°F (204°C) in order to expand the part sufficiently for removal. The part was removed with some pulling force applied to it as the pump housing was reaching 400°F (204°C). This Shrink Fit application was further reviewed to determine if a lower power induction heating system could be used. In this case, the customer’s requirement was 7 minutes, and we achieved the part removal in 100 seconds. Could a lower power system remove the part at a lower cost? A lower power system would be acceptable if our goal is part insertion. For Shrink Fit – Part Insertion, a slower heating rate would still result in a successful process. However, with Shrink Fit – Part Removal, it is important to heat rapidly. A slower heat rate would result in the inserted part also heating, and also expanding. The inserted part potentially would remain “stuck”. By heating rapidly, we avoid this issue. The customer in this case has decided to both use a system for part insertion AND part removal. A 4 kW system is fine for the Shrink Fit – Part Insertion; and the 7 kW DW-HF-15kw induction heating system will be used for the Shrink Fit – Part Removal

• Precise control of the time and temperature
• Power on demand with rapid heat cycles
• Repeatable process, not operator dependent
• Safe heating with no open flames
• Energy efficient heating

Shrink Fittting Part Removal application with Induction Heating

Objective This is a Shrinkfit Part Removal application. The customer’s current process uses a press to push the inserted part out. However, this requires significant force and time. By applying heat, the housing can expand just enough to allow for the easy removal of the inserted part with minimal force. The customer’s time requirement is to complete the Shrinkfit Part Removal within 7 minutes.

Equipment DW-HF-15kw induction heating machine Materials • Aluminum pump housing Part OD 2.885” (73.279mm), wall 0.021” (.533mm) Key Parameters Temperature: Approximately 400°F (204°C) Power: 4 kW Time: 100 seconds

Process:

1. To complete the Shrinkfit Part Removal, place part into coil, so the top of the housing is as close as possible to the top of the coil.
2. Some experimentation was needed to determine the ideal time and power. We found that 100 seconds was ideal for removal of the part, which was significantly lower than the customer’s limit of 7 minutes

Results/Benefits: The tested assembly can be heated to the required temperature in less than 7 minutes using the DW-HF-15kw induction heating system and custom designed coil. Heat time for the Custom Coil was 100 seconds, Temperature needed to be close to 400°F (204°C) in order to expand the part sufficiently for removal. The part was removed with some pulling force applied to it as the pump housing was reaching 400°F (204°C). This Shrink Fit application was further reviewed to determine if a lower power induction heating system could be used. In this case, the customer’s requirement was 7 minutes, and we achieved the part removal in 100 seconds. Could a lower power system remove the part at a lower cost? A lower power system would be acceptable if our goal is part insertion. For Shrink Fit – Part Insertion, a slower heating rate would still result in a successful process. However, with Shrink Fit – Part Removal, it is important to heat rapidly. A slower heat rate would result in the inserted part also heating, and also expanding. The inserted part potentially would remain “stuck”. By heating rapidly, we avoid this issue. The customer in this case has decided to both use a system for part insertion AND part removal. A 4 kW system is fine for the Shrink Fit – Part Insertion; and the 7 kW DW-HF-15kw induction heating system will be used for the Shrink Fit – Part Removal

• Precise control of the time and temperature
• Power on demand with rapid heat cycles
• Repeatable process, not operator dependent
• Safe heating with no open flames
• Energy efficient heating

Induction Shrink Fitting Steel Tube

Induction Shrink Fitting Steel Tube With IGBT Heating Units Objective Heating a steel tube to 500-1000°F for a shrink-fitting application. Determine expansion (growth) of ID at varying temperatures. Material Steel tubes 7” OD x 4.75” ID x 5” heat zone Type ‘K’ thermocouple to measure temperature Thermal blanket Temperature 500, 800, 1000 °F (260, 427, 538° C) Frequency 66 kHz Equipment DW-HF-7.5, 7.5 kW, 150-400 kHz induction power supply, equipped with a remote heat station containing two 1.5 μF capacitors (for a total of 0.75 μF) A multi-turn, special series-parallel induction heating coil designed and developed specifically for this application. Process Initial tests were completed on a sample without a thermal blanket. A thermocouple is slipped between the copper ring and the steel tube to measure temperature. The part measured 4.940” (at room temperature with an ID gauge.) The part reaches 1000°F (538°C) in about 10 minutes. The chart below shows the comparison between theoretical and experimental measured results Results/Benefits The part measures 4.975” at 1000°F yielding an expansion of 0.035” (4.975 minus 4.94). At 500 and 800°F the expansion numbers were 4.950 and 4.964 respectively. When using a thermal blanket the heat time is reduced by about 90 seconds (8.5 minutes as opposed to 10 minutes).