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Job Sheet 3 – Variable-Speed Belt Drives

© Festo Didactic 54977-3C

39

Variable-speed belt drives designs

There are two common variable-speed belt drives designs:

•

Variable-speed belt drives with an adjustable center-to-center distance

•

Variable-speed belt drives with a fixed center-to-center distance

Variable-speed belt drives with an adjustable center-to-center distance

Variable-speed belt drives with adjustable center-to-center distance combine one

variable-pitch pulley with one fixed pulley, as Figure 32 shows. The variable-pitch

pulley is often mounted on a motor shaft but can also be mounted on the driven

shaft. An adjustable motor base permits varying the center-to-center distance

between the shafts.

Figure 32. Variable-speed belt drive with adjustable center-to-center distance.

Open position of the variable-pitch pulley

Closed position of the variable-pitch pulley

Adjustable motor

base

Variable-pitch

pulley

Fixed-pitch pulley

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Summary of Contents for Belt Drives 2

Page 1: ...Industrial Maintenance Belt Drives 2 Course Sample 54977 3C ...

Page 2: ...ege students and trainees at the purchaser s site location for teaching purposes The right of use shall in all cases exclude the right to publish the copyright material or to make this available for use on intranet Internet and LMS platforms and databases such as Moodle which allow access by a wide variety of users including those outside of the purchaser s site location Entitlement to other right...

Page 3: ... low level of risk which if not avoided could result in minor or moderate injury CAUTION used without the Caution risk of danger sign indicates a hazard with a potentially hazardous situation which if not avoided may result in property damage Caution risk of electric shock Caution hot surface Caution risk of danger Consult the relevant user documentation Caution lifting hazard Caution belt drive e...

Page 4: ...t Three phase alternating current Earth ground terminal Protective conductor terminal Frame or chassis terminal Equipotentiality On supply Off supply Equipment protected throughout by double insulation or reinforced insulation In position of a bi stable push control Out position of a bi stable push control ...

Page 5: ...Job Sheet 2 Idler Pulleys 23 Job Sheet 3 Variable Speed Belt Drives 37 Job Sheet 4 Multiple Speed Belt Drives 55 Job Sheet 5 Multiple Belt Drives 71 Job Sheet 6 Synchronous Belt Drives 87 Job Sheet 7 High Torque Synchronous Belt Drives 103 Appendix A Equipment Utilization Chart 117 Appendix B Lockout Tagout Procedure 119 Appendix C Post Test 121 ...

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Page 7: ...vided into levels and covers the following topics Introduction to mechanical drive systems Belt drives Chain drives Gear drives Shaft alignment and couplings Bearings and seals Ball screws and linear bearings Clutches and brakes Vibration metering and analysis Notions of lubrication The figure below shows the available course material for the Mechanical Drives Training System ...

Page 8: ...ical Drives Training System course material We invite readers of this manual to send us their tips feedback and suggestions for improving the book Please send these to did de festo com The authors and Festo Didactic look forward to your comments ...

Page 9: ...ious one Manual objectives When you have completed this manual you will be familiar with more types of belt drives You will know how to properly install them and the importance of following specific protocols You will be able to identify the main components of such belt drive systems in industrial installations Safety considerations Safety symbols that may be used in this manual and on the equipme...

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Page 11: ... differ from one student to another For this reason the results and answers given in this manual should be considered as a guide Students who correctly performed the exercises should expect to demonstrate the principles involved and make observations and measurements similar to those given as answers Before a student begins a job sheet ensure that the equipment is in good condition and does not re...

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Page 13: ...Sample Extracted from Job Sheets Instructor ...

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Page 15: ...n also be installed on the driven shaft depending on the application Figure 30 Variable pitch pulley A typical variable pitch pulley has two flanges and a threaded hub that allows the adjustment of the groove width Adjusting the groove width raises or lowers the belt in the groove to position the belt pitch line at a point that yields the desired speed ratio A variable pitch pulley has two setscre...

Page 16: ...mined using the following formula 𝑛𝑛2 𝑛𝑛1 𝐷𝐷 𝑑𝑑 3 1 where 𝑛𝑛1 is the speed of the driving shaft in rpm 𝑛𝑛2 is the speed of the driven shaft in rpm 𝑑𝑑 is the pitch diameter of the driving pulley 𝐷𝐷 is the pitch diameter of the driven pulley Since the speed of the driving shaft is fixed the speed of the driven shaft depends on the pitch diameters of the pulleys A basic variable speed belt drive has ...

Page 17: ... Variable speed belt drives with adjustable center to center distance combine one variable pitch pulley with one fixed pulley as Figure 32 shows The variable pitch pulley is often mounted on a motor shaft but can also be mounted on the driven shaft An adjustable motor base permits varying the center to center distance between the shafts Figure 32 Variable speed belt drive with adjustable center to...

Page 18: ...e between the shafts to be slightly decreased using the motor base to compensate for the belt tension The pitch diameter of the variable pitch pulley is at its maximum which increases the speed ratio of the drive There are different variations for variable speed belt drives with an adjustable center to center distance In some cases both the variable pitch and the fixed pulleys can have grooves whi...

Page 19: ...of the adjustable pulley is at its minimum the pitch diameter of the automatic pulley is at its maximum and the speed ratio of the drive is reduced The opposite change in the pitch of both pulleys keeps the center to center distance between the shafts the same Conversely setting the adjustable pulley to its closed position opens the automatic pulley to compensate the change in the belt tension Whe...

Page 20: ...ed ratio and moving it away from the driving shaft results in a higher speed ratio Figure 34 Variable speed belt drive with an intermediate variable pitch pulley Variable pitch pulley alignment Aligning variable pitch pulleys is slightly different from aligning fixed pitch pulleys The alignment depends on the width of the pulleys present in the system If the pulleys have the same width the alignme...

Page 21: ...between the flanges and the threaded hub Excessive lubrication must be avoided since it can result in premature wear and component failure Operating the pulley in one position for an extended period of time may also cause premature wear of the components This makes the shifting of position more difficult When the variable pitch pulley has one fixed flange the alignment of the belts may be influenc...

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Page 23: ...following checklist You are wearing safety glasses You are wearing safety shoes You are not wearing anything that might get caught such as a tie jewelry or loose clothes If your hair is long tie it out of the way The working area is clean and free of oil The floor is not wet Your sleeves are rolled up Setup 1 Perform the Lockout Tagout procedure a Refer to Appendix B if necessary 2 Fix three extru...

Page 24: ...or motor soft foot before proceeding further Apply the corrections if necessary Pulleys installation You will install the pulleys and set the variable pitch pulley to the closed position 6 Install a key in the keyseat of the motor shaft Align the key with the end of the motor shaft 7 Take the 80 mm nominal diameter pulley and slide it on the motor shaft The pulley hub should be on the motor side M...

Page 25: ...all a shaft 11 Slide the short shaft through the pillow block bearing located on the same extrusion bar as the motor 12 Install a key in the keyseat of the shaft supported by the pillow block bearings 13 Take the 120 mm nominal diameter variable pitch pulley and slide it on the shaft supported by the pillow block bearings The shaft locking setscrew should be on the motor side a From now on the pul...

Page 26: ...This will ease the tensioning of the belt that will be performed later in this job 21 Verify the vertical angular alignment by laying a combination square against the face of the driving pulley Note the position of the bubble 22 Lay the combination square against the face of the driven pulley and note the position of the bubble 23 Adjust the vertical angular alignment so that the position of the b...

Page 27: ... 7 what is the recommended deflection force for the A48 V belt Table 7 Recommended deflection force for classical V belts Belt profile Small pulley pitch diameter range mm Deflection force kg Run in Normal Z 40 60 0 5 0 7 61 and over 0 8 1 1 A 75 90 1 4 2 1 91 120 1 7 2 6 121 and over 2 0 3 1 B 106 140 2 0 3 1 141 and over 2 5 3 7 C 175 230 4 4 6 5 231 and over 5 4 8 1 Deflection force Deflection ...

Page 28: ...ing the main switch to the I on position Make sure the power light on the control panel is turned on 36 Press the safety reset button Testing the system You will start the motor to make sure the system works properly 37 Start the motor by pressing the start button on the variable frequency drive Then set the frequency of the drive to 15 Hz Make sure that the system works properly 38 Increase the m...

Page 29: ...____ Speed ratio approximately 0 7 Modification of the speed ratio You will set the variable pitch pulley to the open position to modify the speed ratio 46 Make sure there is no tension on the belt 47 Loosen the pillow block bearings screws and move the pillow block bearings closer to the motor mounting base 48 Perform the following steps to adjust the variable pitch pulley to the opened position ...

Page 30: ...e 52 Lay the combination square against the face of the driven pulley and note the position of the bubble 53 Adjust the vertical angular alignment so that the position of the bubble on the driven pulley coincides with its position on the driving pulley Insert shims under the pillow block bearings as required a The bubble does not need to be perfectly centered but it must be at the same position fo...

Page 31: ...t 390 rpm 61 Stop the motor and turn off the system 62 Remove the lockout device from the padlock eyes and open the safety guard Wait for the motor to completely stop before removing the lockout device and opening the safety guard 63 Perform the Lockout Tagout procedure a Refer to Appendix B if necessary 64 Using your measured speed values calculate the speed ratio 𝑛𝑛1 𝑛𝑛2 Speed ratio ____________...

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