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Synchronous Belt Installation and Tensioning

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1 Synchronous Belt Installation and Tensioning

2 Synchronous belt drives provide many maintenance advantages that help in your daily struggle to reduce equipment repairs and hold downtime to the lowest possible level. Applying the practices provided here will help to ensure that your synchronous drives consistently give reliable service and long life with minimal attention.

3 Installation Check List
1) Disconnect and lock out power source. Observe all safety procedures. 2) Remove belt guard 3) Loosen motor mounts 4) Shorten center distance 5) Remove old belt 6) Inspect belt wear patterns for possible troubleshooting 7) Inspect and clean drive elements-bearings, shafts, etc. 8) Inspect sprockets for wear - replace if necessary 9) Preliminary sprocket alignment 10) Identify proper replacement belt 11) Install new belt 12) Tension belt 13) Final sprocket alignment 14) Replace guard 15) Start drive (look & listen) 16) Re-tension after 24 hours

4 Safety First Be sure to review and comply with all building and safety codes. Disconnect and lockout the power supply. Follow your plant’s safety rules!

5 Relieve Belt Tension After removing the drive guard, loosen the drive take-up and move the sprockets closer together to facilitate the removal of the old belt and to ensure installation of the new belt without damage.

6 Inspect Drive Elements
Inspect and replace faulty or damaged machine elements such as worn bearings or bent shafts This not only reduces the likelihood of future mechanical trouble, but ensures maximum service from the new belt

7 Clean Drive Elements Sprockets should be carefully cleaned of any rust and foreign material. A wire brush followed up with a shop cloth will usually do the job. This is a good time to service the take-up rails by removing any rust or dirt, and lubricating as necessary so tensioning of the new belt will go smoothly and easily.

8 Inspect Sprockets Sprocket condition and alignment are vital to belt life and performance. Never install new belts without a thorough inspection of the sprockets. Look for signs of wear such as bent or missing flanges, worn or damaged sprocket grooves, wobbling sprockets, cracked bushings, etc.

9 Inspect Sprockets The easiest way to check sprocket wear is with a Pi tape. The Pi Tape is graduated to the nearest 0.001" and the sprocket can be measured by placing the tape around the OC of the sprocket. The Carlisle catalog provides the nominal sprocket OD. They are the same for RPP and HTD. OD tolerances for sprockets: up to 50mm (1.969"): +0.08/-0.00 mm (+0.003/-0.000") >50 to 100 mm (>1.969 to 3.937"): /-0.00 (+0.004/-0.000") >100 to 175 mm (>3.937 to 6.889"): /-0.00 (+0.005/-0.000") >175 mm (>6.889"): +0.15/-0.00 mm (+0.006/-0.000")

10 Sprocket and Bushing Installation
Improper sprocket and bushing installation can result in wobble as well as causing bushings or sprocket hubs to crack and possible shaft damage. When installing bushings such as QD® or Taper-Lock types, always follow manufacturer’s instructions. It is important to never lubricate the tapered surfaces before installation. Friction is required to achieve the proper clamping force at recommended bolt torque. Lubrication causes excessive clamping force which usually results in cracking of the bushings at the bolt hole or keyway. Rust, grease and other debris on the shaft and mating surfaces can make installation difficult and affect torque carrying capacity. Clean these elements using a fine grit emery cloth and a clean rag. On flanged bushing types, the flange should never be brought up flush with the hub face. A small gap between the two surfaces is normal. When removing bushings, start at the jack-screw hole opposite the split to avoid cracking the bushing.

11 Sprocket Installation Procedure
1. Thoroughly inspect the bore of the sprocket and the tapered surface of the bushing. Any paint, dirt, oil or grease must be removed. 2. Assemble the bushing into the sprocket. Loosely insert the capscrews into the assembly, but do not lubricate capscrew threads. (Note: install M thru S bushings so the two extra holes in the hub are located as far as possible from the bushing’s sawcut). 3. With key in keyseat of shaft, slide sprocket to its desired position with capscrew heads to the outside. (A few small sprockets may have to be installed with the capscrews on the inside). If it is hard to slide the bushing onto the shaft, wedge a screwdriver blade into the sawcut to overcome the tightness. 4. Line up the assembly so as not to misalign the belts, and tighten capscrews evenly and progressively. Apply the recommended torque to the capscrews. There should be 1/8” to ¼”gap between the sprocket hub and the bushing flange. If the gap is closed the shaft is seriously undersize.

12 Sprocket Safety Maximum Surface Speed
Synchronous belt drives are designed to operate at sprocket surface speeds up to 6500 feet per minute (33 meters per second). Special sprockets are required for operation in excess of 6500 feet per minute. Where vibration is a critical factor, dynamic balancing of sprockets is recommended regardless of the operating speed. WARNING: Cast iron products can safely operate up to a maximum speed of 6500 feet per minute. For speeds greater than 6500 feet per minute ductile iron must be used. Ductile iron has a safe operating speed up to 10,000 feet per minute.

13 Preliminary Sprocket Alignment
Use a straightedge or laser tool to make sure sprockets are aligned correctly A string can be used if a straightedge or laser tool is not available. Be sure the shafts of the driver and driven sprockets are parallel, horizontally and vertically. Be sure the driver and driven sprockets are in a straight line Be sure both sprockets are properly mounted and as near to the bearings as practical (to reduce overhung load on the bearings and shafts).

14 Sprocket Alignment Proper Sprocket Alignment
Synchronous belts are much more sensitive to misalignment than v-belts. Misalignment leads to uneven belt and pulley wear and premature tensile cord failure. Tracking problems can also result from drive misalignment. There are two types of misalignment, parallel and angular. In parallel misalignment, the driver and driven shafts are parallel, but the two pulleys lie in different planes. When the two shafts are not parallel, the drive is angularly misaligned. Any degree of pulley misalignment will result in some reduction of belt life. Total misalignment should be less than 1/16” misalignment per foot of drive center distance.

15 Sprocket Alignment The straight-edge should make contact at four distinct points along the outside perimeter of both sprockets. 1 2 There should be no gaps between the sprocket and straightedge at 3 4 Proper Parallel Horizontal Vertical (Off-Set) Angular Angular (Pigeon-Toed)

16 Identify Replacement Belts
High torque synchronous belts (RPP™ Plus™) are similar in appearance to Super High Torque (RPP™ Panther®) belts. It is important to identify the correct type of synchronous belt. To insure the best performance and maximum belt life, replace with the recommended belt.

17 Installing New Belts Place the new belt on the sprockets. Loosening the drive take-up in advance makes this easy. DO NOT FORCE the belts on the sprockets by using a pry bar or rolling the sprockets.* Do not crimp the belt.* Move the sprockets apart until the belt is seated in the sprocket grooves, and start to tighten the drive just until the slack is taken up. * Prying or forcing synchronous belts onto the sprockets can, and usually does, break some of the load-carrying tensile cords. Crimping will also damage the tensile cords.

18 Increase the center distance to apply tension
The most important factor in the successful operation of a synchronous belt drive is proper tensioning. To achieve long trouble-free service, belt tension must be sufficient to overcome tooth jump and to insure proper meshing with the sprocket. Improper tension is the most common cause of premature belt failure. center distance installation take-up Increase the center distance to apply tension NOTE: RPP Panther belts are constructed to attain proper pitch dimension when subjected to tension. For this reason, the belt may not fully engage in large diameter sprockets without applying tension to the belt.

19 Tensioning Procedure Method 1: Deflection Force Method
A. Determine the required deflection force range B. Calculate or measure the free span length C. Determine the deflection distance D. Measure the actual deflection force E. Increase or decrease the actual deflection force until it is within the required deflection force range

20 Recommended Tension Tables
8M Panther Ultracord

21 Recommended Tension Tables
8M Panther Ultracord

22 Recommended Tension Tables
14M Panther Ultracord

23 Recommended Tension Tables
14M Panther Ultracord

24 Spring Loaded Tensiometer Instructions
1) Measure the span length of the drive. Set the large O-ring at 1/64” for each inch of belt span. For example, set the large o-ring 1/4” for a span length of 16”, at ½” for a span length of 32”, at 1” for a span length of 64” etc. 2) Set the small O-ring at zero and press down the tensiometer at the center of the belt span. Depress the tensiometer until the large O-ring is even with the bottom of a straight edge placed on the outside rims of two sprockets. 3) Remove the tensiometer and observe that the small O-ring has moved from its original setting at zero to the number of pounds required to deflect the belt to the extent noted above. Note: For belts wider than 2 inches, it is suggested that a rigid strip of keystock or something similar be placed across the belt between the point of force and the belt to prevent belt distortion.

25 Electronic Tensioning
Method 2 - Frequency Method Another method to assure precise tensioning works on the principle of forced vibration The Frequency-Finder from Carlisle measures the frequency of vibration which is related to the tension of the belt

26 Calculation of Belt Natural Frequency
T = x K x L2 x F2 Where: T = belt tension in pounds (Lbs) K = mass of the belt span per inch (lbs/in) L = length of vibrating span (in) f = frequency of the belt vibration (Hz)

27 Drive Engineer Tensioning information is also included in our drive design software for the deflection force and frequency methods Drive Engineer may be downloaded from or contact customer service (866) to order CD

28 Tensioning Notes Should jumping teeth occur, increase the belt tension until it ceases The supporting structure should be checked for rigidity to make sure the shafts are not deflecting during periods of peak loading and causing tooth jump Long center distance drives using relatively small diameter sprockets must provide sufficient tension to avoid the tension and slack sides of the belt from intermeshing

29 Final Sprocket Alignment
Synchronous drives are highly sensitive to misalignment. The closer you can come to perfect alignment, the better. Proper alignment helps to equalize the load across the entire belt width, thereby reducing wear and extending belt life. Laser alignment is the most precise method of alignment and will aid in eliminating tracking problems and belt and sprocket wear resulting from drive misalignment.

30 Start Drive While the drive is running - look and listen for any indications of potential problems such as excessive drive noise, misalignment, sprocket wobble, etc.

31 Replace Guard Ensure that the belt will not come into contact with the guard. Often just replacing missing bolts in the guard brackets will remedy this situation. NOTE: Effective noise reduction for power transmission drives can be accomplished by incorporating a flexible noise absorbing material with the protective guard. The guard design must allow a cooling air passage on the top and bottom to prevent overheating the drive.

32 Re-Tension after 24 hours
When retensioning, it is necessary to use Ts min.

33 Troubleshooting Synchronous Drives
Normal Failure Mode The end of the useful life of a synchronous belt is most often characterized by even tooth fabric wear and eventually, tooth separation. Any other type of belt failure could be an indication that there are other problems present within the drive.

34 Troubleshooting Synchronous Drives
Noise Noise can be an issue with synchronous belt drives. The noise created by a drive increases with the belt speed. To minimize noise make sure the drive is aligned and tensioned properly.

35 Troubleshooting Synchronous Drives
Sprocket Wear Sprocket wear can have a great impact on belt wear. When unusual belt wear occurs, the first step is to inspect the sprockets. Excessive tooth wear is obvious with visual inspection. Use a pi tape to evaluate sprocket wear. The best sprocket material for minimizing wear is gray cast or ductile iron. A softer material may wear more quickly. Abrasive environments, drive misalignment, and improper tensioning can lead to rapid belt and sprocket wear.

36 Troubleshooting Synchronous Drives
Sprocket Misalignment The leading symptoms of belt misalignment are excessive edge wear (exposing or fraying the tensile cord), running off the flange, snub breaking (in a stair step pattern) and excessive drive noise. If sprockets are verified to be in alignment and problems persist, frame and bearing supports should be checked for rigidity. The frame may be flexing during operation, causing drive misalignment. Proper Parallel Horizontal Vertical (Off-Set) Angular Angular (Pigeon-Toed)

37 Troubleshooting Synchronous Drives
Excessive Tension Excessive tension of a synchronous drive will cause premature belt failure due to wear and high tooth stress. The noise level of a synchronous belt drive will increase considerably if the belt is over-tensioned. Excessive tension produces fabric wear between the belt teeth exposing the tensile cord and wearing of the sprocket teeth. If tooth shear, snub break, or tooth jump occurs under correct tension, the drive may be under-designed.

38 Troubleshooting Synchronous Drives
Under-Tensioning Under-tensioning is the most common cause of belt failure. It can cause premature belt wear, tooth jump and belt failure. Belt wear is characterized by fabric wear on the tooth flank which can accumulate material between the teeth. Jumping can cause tooth shear and tensile cord breakage. Tooth jump or ratcheting occurs when the belt teeth climb up and out of the sprocket grooves. The most obvious indication of tooth jump is a machine gun like sound. Although there may be no visible evidence of damage, the capabilities of the belt are likely destroyed after tooth jump.

39 Troubleshooting Synchronous Drives
Non-Rigid Frame A less common cause of belt failure is a non-rigid frame which allows the center distance to vary when a load is applied. The supporting structure should be checked for rigidity to make sure the shafts are not deflecting during periods of peak loading and causing tooth jump.

40 Troubleshooting Synchronous Drives
Overloaded Drive Severe overload conditions can cause fabric and sprocket wear on the pressure surfaces, belt tooth shear, snub break, tooth jump and a resulting increase in noise level. These conditions generally force a drive re-design to provide additional capacity. A wider belt will sometimes accomplish this.

41 Troubleshooting Synchronous Drives
Excessive Shock Loads / Start-Up Loads Some applications are not conducive to synchronous belt drives Use special consideration on drives with excessive or extreme shock loads or start-up loads - Some drives may require soft start Positive drive engagement and the high modulus cord (low-stretch) make synchronous belts less tolerant of severe shock loads than v-belts which allow slippage If you require the characteristics of synchronous belts in a shock load application, an RPP Panther synchronous belt is your best choice in these situations

42 Troubleshooting Environmental Problems
Belt Deterioration The synchronous belt can deteriorate when operated in caustic or acidic atmospheres, environments saturated with vapors from hydrocarbon solvents, and ambient temperatures above 185°F or less than -30°F. Specially constructed belts may provide satisfactory service in a number of applications not suitable for stock belts.

43 Troubleshooting Environmental Problems
Excessive Heat Carlisle standard rubber construction synchronous belts are compounded for moderate resistance to heat and should give adequate service life under normal conditions. The operating limits of a standard construction synchronous belt range from a minimum of -32°F to 200°F ambient temperature (230°F intermittently). Polyurethane synchronous belts are only capable of +185°F.

44 Troubleshooting Environmental Problems
Environments with Excessive Debris Synchronous belts should not be used in environments where excessive debris is present Debris can be more damaging to a synchronous belt drive than to a v-belt drive, which has a tendency to eject debris from the sheave grooves as the drive operates Large debris trapped between a synchronous belt and pulley will destroy belt tensile cords or drive hardware Small debris will become compacted in the pulley groove, forcing the belt to ride out away from the pulley and lead to belt failure by destroying the tensile member

45 Troubleshooting Environmental Problems
Environments with Excessive Debris (cont.) Exposure of synchronous belts to oil and other lubricants should be minimized Oil and petroleum distillates may alter the belt polymers and adhesion systems Care must be taken to provide adequate shielding on drives where debris or contaminants are likely Completely enclosing a synchronous belt drive may be acceptable. Synchronous belts generate less heat than v-belts. Air circulation around the drive is not a critical consideration except in extremely high temperature environments.

46 Synchronous Belt Storage
The quality of a Carlisle Belt is not considered to change significantly within eight years, when stored properly under normal conditions. Normal conditions can be defined as temperature below 85°F and relative humidity of 70% or less with no exposure to direct sunlight. Beyond eight years, assuming normal storage, a decrease in service life of approximately 10% per year can be expected. For belts not stored under “normal” conditions, the actual reduction in shelf life is difficult to measure due to lack of precise data and an infinite number of variables involved. When belts are stored under abnormal conditions, conservatism is recommended in estimating shelf life. Improper or prolonged storage can reduce service life considerably.

47 Synchronous Belt Storage
Like V-belts, synchronous belts may be stored on pins or saddles with precautions taken to avoid distortion. However, belts of this type up to approximately 120 inches are normally shipped in a “nested” configuration and it is recommended that the belts be stored in this manner as well. Nests are formed by laying a belt on its side on a flat surface and placing as many belts inside the first belt as possible without undue force. When the nests are tight and are stacked with each rotated 180° from the one below, they may be stacked without damage. Belts of this type over approximately 120 inches may be “rolled up” and tied for shipment. These rolls may be stacked for easy storage. Care should be taken to avoid small bend radii which could damage the belts.

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