Dura-Belt   800-770-2358

Frequently Asked Questions

Q1 What is the proper way to install elastic belts?
Q2 How long do urethane belts last (belt lifespan)?
Q3 Why do Cyclothane belts last longer?
Q4 What are Dura-Belt's Terms and Conditions of Sales?
Q5 What effect does high temperature have on urethane belting?
Q6 What effect does low temperature have on urethane belting?
Q7 How can I determine the maximum belt loading tension on a belt?
Q8 What is the difference between Belt Loading Tension and Belt Tension?
Q9 Which size of urethane belt should I use?
Q10 How much should bets be stretched -- stretch factor, stretch percent, stretch amount, pretension belt?
Q11 What's the difference between overlap welds and butt welds?
Q12 Why do overlap welds eventually pull apart under high tension?
Q13 Will our high tension belts damage bearings?
Q14 Do crowns prevent flat belts from moving sideways (walking, wondering), i.e. keep belts centered? Recommended tracking sleeve location, and what to do if a belt does not track, i.e. walks or wanders?
Q15 What is the RAVE technique for tracking sleeve installation?
Q16 How do I prevent tracking sleeves and flat belts from slipping and moving (walking) sideways?
Q17 Where can I get tracking sleeves for small diameter rollers?
Q18 What is our maximum flat belt inclines/declines angle on which boxes can be moved?
Q19 How to easily install stretchy, endless elastic flat belts over rollers?
Q20 Will Dura-Belt's wide-short flat belts track -- belts much wider than long?
Q21 Where do I find Dura-Belt's part numbers?
Q22 How do I clean, sterilize, disinfect, sanitize and/or washdown urethane or Hytrel belts?
Q23 How much should belts wrap around each pulley?
Q24 What is the difference between urethane and polyurethane?
Q25 Do injection molded O-rings make good belts?
Q26 It is rare, but sometimes round belts squeak. What causes it??
Q27 Why do weld joints often protrude slightly in a small bump above the belt's surface?
Q28 How much should right angle diverter belts be stretched?
Q29 How to easily install poly-v HE, HEHT and Hytrel belts without a tool.
Q30 How to choose the length of ConveyXonic Poly-V belts (includes PJ rib and groove dimensions).
Q31 How to make poly-v belts last longer and prevent premature failures.
Q32 What is the shortest Hytrel belt that can be used on 1.9" (48.3mm) conveyor rollers?.
Q33 Can we weld, splice or join Dura-Belt's thermoplastic belts ourselves (Do it yourself)?
Q34 Can Dura-Belt's stretchy, elastic urethane or Hytrel belts be used on slider beds?
Q35 How long do Twisted belts (Zero-downtime quick-connect belts) last?
Q36 Thermoplastic urethane belts are NOT precision belts. How are they made? Design tips.
Q37 Why does RPM decline (roller speed slow down) with each slaved roller? -- Creeping vs. Slipping belts
Q38 How to install poly-v and poly-o endcaps on each end of a conveyor roller

Q1: What is the proper way to install elastic belts?

Here are rules about installing elastic belts:

  1. Always wear eye protection when installing elastic belts. Stretched belts contain a large amount of energy. If belts should break or slip free, they can snap like a whip and put out an eye. This is especially true of hollow belts and twisted belts, which have barbs and hooks on the ends.

  2. Do not stand in the line of a stretched belt, so that if it breaks and flies free, it will likely not hit you.

  3. Do not lean backward when stretching belts. If the belt should break or slip, you could fall backward and injure yourself.

  4. Do not overstretch belts -- not more than 30% beyond the installed length for urethane and 0% for Hytrel polyester. (Hytrel, used primarily in low temperature belts and chemically resistant belts, must never be over stretched even a little because it does not bounce back at all.)  Belts stretched beyond their elastic limit will not bounce back as much and will fail prematurely.

  5. The best way to install endless belts on a conveyor without over stretching them is to touch the rollers together, slide the belt into the grooves, then pull the rollers into place. (For a more detailed description see Q28 below, replacing the word poly-v with round belt.)

    If the roller centers are too close to do this, do not use pliers, a screw driver or a hook to pry or pull the belts over rollers. It can over stress a small section of the cord and cause premature belt failure. Instead, use a metal shoe-horn bent like our shoe-horn tool Round Belt Installer Tool. It greatly facilitates installation and will not over stress the belts.

  6. If more than 70 lbs of force is required to pull the roller in place, you can use a crowbar or winch. Inexpensive winches can be purchased on-line from Lowe's. However, most people angle the roller in order to insert its shaft in the frame hole closest to the belts; then they use the roller as a lever and insert the shaft's other end in the frame.

  7. If you have two fixed pulleys, put the belt on the larger one and roll it on the smaller one.

  8. Never use a screw driver, hook, narrow rod, wire or rope to stretch a belt.  They will over stress the belt, causing it to bend too sharply, violating its minimum pulley diameter and producing a weak point that will neck down and make the belt fail prematurely.

  9. The best way to install twisted quick connect belts, without dropping rollers, is to use our Speedy Belt Installer Tool. If you can easily stretch twisted belts over rollers while keeping them in the frame, then the belts are too long and will stop driving prematurely.
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Q2: How long do urethane belts last (belt life span)?

A properly-designed, urethane belt in an ideal environment should last many years, but not all urethane belts are of equal quality. The difference in performance between a high quality belt and an average belt can be huge. For example, in two large postal distribution centers 40,000 of our competitor's belts became limp after only 10 months on powered roller conveyors. They were replaced with our HT (High Tension) Blue Cyclothane-B belts, and ten years later those belts are still going strong.  In general the average life-span for most high-quality urethane belts appears to be about four to six years with a typical range of 2 to 12 years. Endless round belts usually last considerably longer than twisted connectable belts. Motorized roller belts usually last longer than lineshaft belts.

There are many factors that determine the life-span of a belt, including operating schedule (shifts per week), duty cycle, belt type, belt length, belt thickness, belt durometer, belt stretch, belt speed, pulley or roller size, pulley or roller material, pulley alignment (angle between pulleys), bearing type (sealed vs. shielded), ambient temperature and humidity, amount and type of dust and dirt in the environment, chemical and UV exposure, box weight, box surface, amount of box accumulation (duration and frequency), motor acceleration/deceleration, conveyor type, conveyor design, conveyor width, and level of maintenance. (Also see Longer Lasting Belts.) If your belts are wearing out too soon, ask our Belt Doctor for assistance.
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Q3: Why do Cyclothane belts last longer?

Several factors combine to make Cyclothane belts last longer:

  • 1) We use only 100% virgin polyurethane (no regrind waste). Urethane manufacturers typically recommend using up to 25% regrind waste to improve extrudability and weldability, plus it cut costs by reusing waste. Unfortunately, regrind picks up impurities like dust and has an extra heat cycle that weakens the material and makes belts less resilient, so we don't use it, even though we believe virtually everyone else does. We send our waste to a tube manufacturer. Virgin urethane makes our belts stronger and last longer.

  • 2) Our proprietary process for making Super Strong Welds that are practicably unbreakable -- up to 12 times stronger than conventional joining processes.

  • 3) Our ungouged welds do not neck down much when stretched. Necked belts stretch more at the joint which causes them to get limp prematurely.

  • 4) Our proprietary process for cross-linking long-chain molecules makes our HT belts super resilient at 20% stretch.

  • 5) Our proprietary coloring process lets us color belts after we make them, so that the colorant does not dilute or weaken the urethane.

  • 6) Our superior quality control process -- we inspect 102% of our belts (2% are inspected twice). Compliant with ISO 9000, we constantly strive for improvements.

  • 7) Our World's Longest Belt Warranty induces us to make doubly sure that we ship only high quality belt.

  • 8) Our "Belt Doctor" helps customers find and eliminate problems that cause belts to fail prematurely. Also see next question.
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Q4: What are Dura-Belt's Terms and Conditions of Sales?

To see them click here

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Q5: What effect does high temperature have on urethane belting?

Most urethane that is used in elastic belting is a thermoplastic, so its physical properties decrease as temperature rises. For example, at 120oF (49oC.) its life span as measured by resiliency declines to about 70% of what it is at room temperature; at 150oF (66oC) its resiliency drops to about 10%. Some manufacturers claim that urethane will work continuously up to 180oF (82oC.), but that is only when urethane O-rings are used as seals under compression. Belts under extension will only last a short time at that temperature. In some applications they may seem to last longer because the temperature underneath the rollers is much lower. In such cases, you need to average the temperature on top of the rollers with that underneath the rollers to get the actual operation temperature. It is for these reasons that we are more conservative and recommend a maximum operating temperature of 130oF (55oC.).

If you need elastic, high temperature belts, try our High Temperature Urethane Belts. They will work up to 230oF (110oC), but they are much more expensive and only come in certain sizes. ThermoSET urethane will also work at higher temperatures, but it has to be molded or cast, so only certain sizes are available, and the molds are expensive. Its elastic memory is often poor, so it usually does not make a good elastic belt.
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Q6: What effect does low temperature have on urethane belting?

Urethane becomes more brittle as temperature decreases. Belts that are allowed to sit overnight in low temperature environments can take a set that is difficult to overcome at start up. This can cause even Super Strong welds to shear apart. Although urethane manufacturers often claim that regular urethane will work down to -10°F, we do not recommend using Cyclothane-A below 30°F (0°C). Our low temperature Cyclothane-E will work down to -10°F (-23°C), but for temperatures below zero F (-18°C) we recommend Hytrel ®. It will work down to -40°F (-40°C) and is especially well suited for ice cream plants. Since Hytrel is not as resilient as urethane, it should not be stretched beyond 7%. Care must be taken not to overstretch it during installation.
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Q7: How can I determine the maximum belt loading tension on a belt?

See instructions under the BELT SIZER pull down menu.
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Q8: What is the difference between Belt Loading Tension and Belt Tension?

Some companies define belt loading tension and belt tension differently. Here is how we do it:

Belt Loading Tension is the maximum tangential force that the belt needs to exert in order to turn the driven pulley.

Belt Tension is displayed on our tension calculator. It must be greater than the belt loading tension. Otherwise, the belt will not turn the driven pulley. Ideally belt tension should be 3 times or more than the belt loading tension in order to maximize the belt's lifespan.

Our numbers are conservative, so users sometimes accept a shorter lifespan by using belt tension that is closer to the belt loading tension so they can move heavier loads with a thinner belt.
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Q9: Which size of urethane belt should I use?

See instructions under the BELT SIZER pull down menu.
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Q10: How much should bets be stretched -- stretch factor, stretch percent, stretch amount, , pretension belt?
For a list of typical round and V-belt stretch factors, click here. The stretch on flat belts varies with thickness and width. For the recommended stretch on flat belts, click here.

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Q11: What's the difference between overlap welds and butt welds on reinforced urethane belts?

You can easily see the difference between an overlap weld and a butt weld. An overlap weld usually has a big 2" long bump at the joint where the reinforcing cords are overlapped, whereas a butt weld is just a thin line circling the belt. Overlap splices can last a little longer than butt welds if they are perfectly made, but it is hard to make perfect overlaps. A thick layer of urethane must surround each cord. If the two cords touch each other, or if one cord is too close to the surface, the cord pulls out and the belt stretches prematurely. Trying to make perfect overlap welds often produces quite a few rejects, so the price must be higher than for butt welds. (see next question).
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Q12: Why do overlap welds eventually pull apart in high tension applications?

Since the reinforced cord is not endless or tied, high tension applications will eventually cause the reinforcement to disbond and slide through the urethane.
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Q13: Will our high tension belts damage bearings?

No, because most bearings will take loads considerably larger than our belts can exert. For example, our 3/16" HT Blue belt exerts an initial force of about 25 lbs (12kg), but typical 1.9" (50mm) diameter conveyor rollers will handle a maximum load of 250 lbs (100kg), which is 10 times larger. Moreover, urethane belt tension declines quickly at first. Five minutes after installation, it drops 30%, and after a week the tension levels off at about 14 lbs (30kg). Our idler pulleys use the 6203 bearing, rated at 600 lbs (270 kg) at typical conveyor speeds, so the chances of bearing damage are slim or none. Nevertheless, make sure that your belt tension does not exceed the rating of your application. Our tension calculator lets you calculate the force exerted by our belts.
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Q14: Do crowns prevent flat belts from moving sideways (walking, wondering), i.e. keep belts centered? Recommended tracking sleeve location, and what to do if a flat belt does not track, i.e. walks or wanders?

Yes, a crown on a pulley will prevent "walking or wandering". All flat belts have a tendency to "walk", "wander" or move sideways on flat surfaces. Therefore, uncrowned, flanged pulleys are not recommended because the belt will either rub against the flange and abrade, or stretch and walk up over the flanges. To hold the belt in the center of the pulley, the pulley must be crowned, i.e., larger at the center than on the sides. (See drawing below). All our flat idler pulleys have round crowns of .016" to .020" See crowns on flat idler pulleys. This means that the center diameters are .032" to .040" greater than the diameters at the outside edges of the pulleys.

Flat belt pulley crowns
Flat Belt Pulley Crowns

Flat belts on conveyor rollers. Our tracking sleeves provide a quick way to add a rectangular crown to rollers. For narrow elastic belts, up to 2" (50mm) wide, use 1/32" (0.8mm) thick sleeves 92A durometer. For wider belts use 1/16" (1.6mm) thick sleeves 83A durometer. Our standard 1/32" (0.8mm) thick x 1/2" (12.5mm) wide tracking sleeve is stretched 10%, as is our 1/16" x 1" tracking sleeve.

We do not recommend using 1.9" roller covers as tracking sleeves because they tend to slip and walk sideways since they are only stretched 2%. If you insist on using them, make sure you clean the roller with acetone and then use an adhesive to glue it in place. See Q16 below.

Most conveyor manufactures use tracking sleeves on both the head and tail rollers as in the picture below. They do this because they cannot be sure that their frames are always square (sometimes due to a forklift bumping a conveyor) and/or because there may be side forces on the belts as when boxes are pushed on from the sides. Moreover, no belt is perfectly square so sleeves on both head and tail rollers are highly recommended.

Sleeves on the head roller should be aligned to the sleeves on the tail roller within +/-1/16" so they do not fight each other.

We recommend the following:

  • Narrow flat belts up to 2" (50mm) wide - use a 1/32" thick x 1/2" wide (0.8mm x 12mm) 92A tracking sleeve, located in the middle of the belt on the drive roller. If the center distance between head and tail rollers is small (e.g. 8" or less), this is the only case where only one tracking sleeve is needed. For longer center distances use a tracking sleeve on both rollers.
  • Medium wide flat belts up to 9" (230mm) wide -- use a 1/16" thick x 1" wide (1.6mm x 25.4mm) 83A tracking sleeves, located in the middle of the belt on both the head and tail rollers.
  • Flat belts above 9" (230mm) wide - it is better to simulate wide crowns by using two 1/16" thick x 1" on both the lead and tail rollers. Locate the outside edge of the tracking sleeves 2" (50mm) from the edges of the flat belt.
  • Motorized Drive Rollers (MDRs) do not have thru-shafts so they are not nearly as strong as standard rollers. Wide flat belt focus pressure on the center of MDRs where they are weak. This slightly bends MDRs causing their bearings to ride on their edges. Moreover, wide flat belts wrap 180° around head rollers, reducing heat flow and causing MDRs to overheat. Both of these factors cause premature MDR failure. Therefore, we recommend locating the MDR in the position shown below and driving the head roller with two 88A HEHT round belts or poly-v belts. The ends of MDRs are much stronger and can easily handle the tension of round or poly-v belts.

Tracking sleeves on wide flat belt conveyor
Tracking sleeves on wide flat belt conveyor
(Available on any size roller. Use screw driver technique to install.)

Some conveyor manufacturers assert that the four positions in the picture above are the best tracking sleeve locations to assure flat belts track on slightly out of square frames. Nevertheless, we have seen different conveyor manufactures use different sleeve locations and swear that their locations are the best.

Recently we learned that another manufacturer uses four tracking sleeves, all on the head roller -- where he puts the MDR, contrary to our recommendation. He spaces them equally apart with the outer sleeves located 3" from the belt edge.

Still another manufacturer puts two 1" wide tracking sleeves in the center of the drive roller, where he says they align themselves after running for a while by walking slightly until they find the "sweet spots". (These sleeves are so tight that they should never walk, but he asserts that putting them in the center causes this, and he says they will only walk a few inches before they freeze in place). Then, if the flat belt tracks a half inch too much to the right, he uses the screw driver technique to move the left sleeve a half inch to the left to realign the belt.

We sell tens of thousands of tracking sleeves a year to many different manufactures, so they must work well, but you may want to experiment to find the "sweetest" location for them.

If a flat belt walks or wanders (does not track, i.e. moves sideways) on rollers with our tracking sleeves, make sure the conveyor frames are not warped like a parallogram or the rollers are not misaligned (i.e., not parallel). Use a square to verify that the rollers are angled at precisely 90 degrees with respect to the frames. If they are not, then square the frames and rollers as best you can.

Next verify that the four tracking sleeves are located, as in the above drawing, so they do not fight each other (i.e., so that sleeve edges are aligned precisely on a line from the head to the tail rollers). On very wide belts some conveyor manufacturers add two more tracking sleeves located in the center of both head and tail rollers for a total of six tracking sleeves per zone.

If the belt still walks, put a piece of masking tape on the right edge of the belt; otherwise you will forget which side was on the right (this is CRITICAL). Next remove the belt and verify that all four tracking sleeves are in the correct location and proceed to the next paragraph. If sleeves are not where they should be, take corrective action. If the sleeves have moved, then see FAQ16. After doing this, you can install the belt as it was. Now the belt should not walk.

If all the sleeves are located where they should be, then reverse the belt on the conveyor so the masking tape is on left edge of the belt. If the belt walks in the opposite direction, then the belt is not true (square), and you should contact us for a Return Authorization and replacement. If the belt walks in the same direction, then the frames are not square and/or the rollers are not parallel, and you will need to take more action to square the frames and/or rollers. Alternately, some tracking sleeves are missing, or the sleeves have moved (see FAQ16). This means you will probably have to add the missing tracking sleeves and/or reinstall the tracking sleeves after cleaning the rollers and sleeves with acetone or alcohol.

Note that crowns may not work on belts that frequently reverse direction, because it usually takes about three pulley revolutions before flat belts center themselves on crowns. In such cases you may need to use a flat belt with a V-guide (i.e., a small V-belt welded to the bottom of the flat belt) and flat pulleys with a V-groove in the center. For information on the physics of crowns see flat belt crown. The next two questions provide tips on tracking belt installation and prevention of slipping.
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Q15: What is the RAVE technique for tracking sleeve installation?

Before installing tracking sleeves, clean the rollers with acetone or alcohol to remove any oil or grease that may cause the sleeves to wander.

Installing narrow sleeves (1" wide or less) on rollers is difficult because the sleeve diameter is considerably less than the roller diameter. If you spray RAVE Ultra-Hold hair spray (or the equivalent sticky liquid hair spray, not the powder type) on the end of the roller, the surface remains very slippery while the RAVE is wet, so sleeves will slide on much easier. In about 90 seconds RAVE will dry and act like a glue that prevents the sleeve from moving. Usually the sleeves are so tight, they will not move easily, but hair spray provides added holding power. You can purchase RAVE hair spray at CVS Pharmacy.

If hair spray is not available, you can substitute soapy water. When it dries, it does not form a very strong glue, but it facilitates installation. Heating the sleeves in boiling water will expand the sleeves temporarily. This usually facilitates installation. Do not use a microwave to heat the sleeves because microwaves destroy urethane.

There are several different ways to install the sleeves. Some use two strings looped through the sleeve 180 degrees apart to pull them on. Others build a finger-like stretcher to hold them open while they slide the rollers through. The following screw technique is the most popular.

Screw Driver Technique:  Here is a way to install narrow sleeves (1.18" wide or less). It may appear that the sleeve is too small to fit on the roller, but it can be done fairly easily.  Push the sleeve a tiny way on the roller end. Then insert a small screw driver (e.g. with 1/8" shaft) at an angle between the sleeve and the roller. Now rotate the roller in the direction of the red arrow to screw on the sleeve. The screw driver makes it seem like there are threads on the roller and causes the sleeve to screw on like a nut. It works exceptionally fast when installing on an MDR because you can turn on the MDR and the sleeve will screw its way down the MDR.

One inch wide racking sleeve installed with screw driver
One inch wide tracking sleeve installed with screw driver

Tracking Sleeve Installer Tools. If you have to install a large number of flat belt tracking sleeves, the screw driver technique will likely over-stress your wrists so we have developed inexpensive Tracking Sleeve Installer Tools (pictured below) to make it easier in six easy steps. An arbor press or pneumatic press is required to push the sleeve with the blue tube. The standard kit is for 1.9" (48.3mm) diameter rollers. And extra tool (not shown) is needed for pushing sleeves over roller grooves or poly-v endcaps, so specify that when ordering. There is an extra charge for different diameter rollers that you must also specify when ordering.

Tracking Sleeve Installer Tools
Tracking Sleeve Installer Tools

Never use any type of oil like WD-40 or silicone spray. They will often cause the sleeves to walk.

If more hold is needed, read the next question below. If you need to reposition the sleeve, you can unlock the glue by sliding a small screw driver under it. If you don't have hair spray, soapy water can be substituted. Heating the sleeves in hot water will temporarily expand them so they slide on easier.

Installing wide sleeves (2" or more wide) is easier. Simply clean the rollers with alcohol or acetone to remove any oils. Then our 1/16" (1.6mm) thick sleeves can easily be installed with our sleeve installation air gun tool. This process can be facilitated by heating the sleeves to 130°F (55°C) and/or coating the rollers with soapy water or RAVE hair spray. Do not heat sleeves in a microwave oven because microwaves destroy urethane. To watch a video showing how to install 2" wide tracking sleeves, click here.
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Q16: How do I prevent tracking sleeves and flat belts from slipping and moving sideways?

Do the following:

  1. Rollers are often covered with a thin coat of oil (e.g. cutting fluid) or grease to prevent rust. This can cause sleeves to slip sideways when side pressure is put on the belts. Before installing sleeves, wipe rollers with acetone to remove any oil or grease.

  2. Some conveyed products like tires tend to rotate when they rub against conveyor frames. This rotation puts side forces on flat belts and tracking sleeves that may push them to walk sideways. Therefore, we recommend using narrow flat belts separated by roller sleeves that are thicker than the flat belts plus tracking sleeves. This will prevent the tires from touching the flat belts, and thus eliminate any side forces that might cause them to walk.

  3. Some installers use two hooks to stretch sleeves over rollers. If sleeves are stretched more than 40%, they may deform because the urethane has been stretched beyond its elastic limit. This will reduce sleeves' holding tension. Therefore, do not overstretch sleeves during installation.

  4. With sleeves made from roller covers, we recommend using women's "ultra-hold" hair spray (e.g. RAVE) to facilitate installation. It is slippery when wet and glues the sleeve to the roller when it dries. See previous question above.

  5. If a sleeve has already slipped, clean the roller with acetone and move the sleeve back to its original position. Then use a small screw driver to lift the edge of the sleeve while putting a dab of Loctite 454 super glue or contact cement (e.g. DAP Weldwood) at 0, 90, 180, and 270 degrees around its circumference under both edges. If you use contact cement, you do not have to let each surface dry before bringing the surfaces together. However, let the cement dry for an hour before restarting the conveyor.

  6. If the sleeve still slips, clean the roller with acetone on each side of the sleeve. Then make a barrier on each side of the sleeve by winding 3 or 4 layers of aluminum foil tape around the roller. (We recommend Nashau aluminum foil tape because its adhesive binds so tightly that it is almost impossible to pull apart. If you want to remove it, you have to cut it off with a razor. The adhesive on 3M aluminum tape seems to become gummy and slip after a while, so do not use it.)  If the barrier is about one third as thick as the sleeve, the sleeve will be locked in position.

  7. If none of this works, then try a tighter sleeve.

  8. With flat belts wider than five inches, use 1/16" thick sleeves 20% to 40% as wide as the flat belts. The surface area under such sleeves is so great that they have not been know to walk.
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Q17: Where can I get tracking sleeves for small diameter rollers?

We cannot weld tracking sleeves for rollers less than 1.5" (38mm) in diameter. If the order is large enough, e.g. 500 pieces or more, we can extrude tubing to make them, but for small orders we recommend making them yourself using self-fusing silicone tape. We sell it in rolls 1" wide x 36 yards long. Before installing tape sleeves, the rollers must be cleaned with alcohol or acetone to remove any oil. Otherwise, the silicone may slip. Stretch the tape about double, i.e., 100%, and tightly wind it around the roller a few times to build up thickness. After five minutes, it will fuse into a solid mass, and you will not be able to unwind it. For use with narrow flat belts, e.g. 1" (25mm) wide, you will need to slit the tape to reduce its width to 1/2" (12mm). This is probably best done with a razor after the tape is wound around the roller.

Tape sleeves will not be as uniform in thickness as urethane sleeves, so your flat belt may wobble at bit. We do not have experience with slipping or lifespan, but installers have been substituting them in field emergencies for years, so they must work for an acceptable time.
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Q18: What is our maximum flat belt incline/decline angle on which boxes can be moved?
See Flat Belts on Inclines/Declines.

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Q19: How to easily install stretchy, endless elastic flat belts over rollers?

Because our stretchy, elastic flat belts must be stretched during installation, they may appear difficult to install, but it is much easier than it looks. Simply drop all rollers on one side of the frame. Then slide the flat belt over those rollers while dropping the last roller from both sides of the frame. Install all but the last roller in the frame. The last roller should be hanging inside the belt about an inch from its frame holes. Now grasp the last roller and the belt, insert the roller's shaft at an angle into one frame hole. Then insert a flat screw driver in the opposite frame in the unused adjacent hex hole, i.e., the hole used to skew rollers, usually 1" from the target hole. Now press the screw drive blade against the last roller's edge, using the hole as a fulcrum, and leverage the last roller into the target hole. The hex shaft is perfectly oriented to the hex target hole, so it snaps in quickly with very little effort -- only takes a few seconds. If there are no skew holes, then you would need to drill one. This process greatly facilitates and speeds up assembly.
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Q20: Will Dura-Belt's wide-short flat belts track -- belts much wider than long?

Most flat belt experts will tell you that flat belts need to be longer than they are wide in order to track properly (not walk sideways). Dura-Belt's elastic flat belts are the exception. Our flat belts will track regardless of the length to width ratio. Here is one that is 34.5" wide on 9" centers.

Wide-short flat belt 
		  tracks well
Wide-short flat belt tracks well

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Q21: Where do I find Dura-Belt's part numbers?

Theoretically we have an infinite number of part numbers because we can make belts of any length. To date we have over 10,000 part numbers. That is why it is not practical to show them. Just tell us the description and we'll tell you the part number.

Actually all are part numbers are "smart", meaning they describe the belt. The first two digits are the thickness in inches without the decimal point. letter is a code for the durometer (a = 83A, 85A or 88A, r = 90A, 92A or 95A). The next 5 digits are the cut length in inches. The words describe special attributes, like Rough Green, Orange, HT Blue, Super Red, Static Dissipative, etc. No words means it is standard clear urethane.

For example, our popular 3/16" (.187") x 9.5" HT Blue belt's part number is 18a09.50 HT Blue
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Q22: How do I clean, sterilize, disinfect, sanitize and/or washdown urethane or Hytrel belts?

Food processing plants often disinfect their conveyors by washing down with a 20% bleach solution. Bleach attacks urethane, causing it to crack and lose its elasticity, so bleach should not be used to sanitize urethane belts. Food processors that wash down with bleach should use Hytrel belts. (Make sure Hytrel belts are not overstretched during installation, as Hytrel does not "bounce back" like urethane.)

In our laboratory tests we found that Oxine (Chlorine Dioxide), a biocide disinfectant and sanitizer, has minimal effect on urethane, when used at Bio-Cide's recommended 100 ppm concentration in solution with room temperature water for short exposure times. Moreover, Oxine appears to have virtually no effect on Hytrel belts, even up to 500ppm with prolonged exposure at room temperature.

Urethane belts can also be cleaned by washing them in lukewarm water (120°F, 50°C or less) with dish washing soap like Palmolive or Joy.

Occasional washing of Cyclothane-A urethane will probably not harm the belt, but since it is hygroscopic, frequent washing can slowly damage it, especially if the water is hot. Cyclothane-E belts are not hygroscopic, so frequent washing should not affect them.

Isopropyl alcohol (rubbing alcohol) can be used to clean the surface of urethane, as it evaporates quickly, but prolonged immersion in alcohol will damage urethane.

Steam is not recommended for cleaning any thermoplastic belt because high temperatures reduce belt life. However, steam may cool down substantially by the time it contacts the belts, so flashing them with "cool" steam (150°F, 70°C or less) may not significantly harm Hytrel or Cyclothane-E.

When in doubt, test a few belts before applying any substance to all belts. We recommend immersing a belt in a bottle of the chemical and letting it sit for a week at the belt’s operating temperature. If there is any change in the surface or tensile strength, then the chemical is harming the belt.
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Q23: How much should belts wrap around each pulley?

Most applications are designed so that belts wrap between 120 and 240 degrees around their pulleys. If the force needed to turn a pulley is very small, then you may not need more than 90 degrees of wrap. However, tension in urethane belts declines over time, so what is acceptable today might not work in two years. Therefore, if in doubt, increase the belt wrap as much as possible by moving the pulleys further apart and/or by adding an idler pulley that forces the belts to wrap more about the drive and driven pulleys. The more wrap you have, the less the belt will tend to slip, and the more force will be exerted on the other pulley. If you have enough surface contact (i.e., a lot of wrap), then there may be enough friction between surfaces so that everything continues to work, even after the belt becomes limp.
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Q24: What is the difference between urethane and polyurethane?

There is no difference. In the belting industry they are synonymous. All urethane belts are made from polyurethane, which contains long-chain urethane molecules.
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Q25: Do injected molded O-rings make good belts?

Extruded urethane cord has a much better elastic memory than injection molded O-rings because extrusion orients the long chain molecules in the direction of stretch. Molded O-rings are made with gear pumps that break the long chain molecules and inject them at random, so their molecules are fractured and not oriented in the direction of stretch. Consequently, our extruded belts are stronger and last longer than molded O-rings.

There are other reasons why molded O-rings are inferior. As molten urethane flows along two paths around the circular mold, it picks up contaminates like dust, air pollutants and mold release. It also cools slightly, and when the two paths come together, they form a knit line, the point where the two contaminated surfaces mesh. This point is weaker than the rest of the O-ring because contaminates tend to foil the bond and because the plastic is cooler -- not the optimum fusing temperature. This is the location where most injection molded O-rings break. The other break point is called the gate line, the point were molten plastic enters the mold. Turbulent flow caused by the sudden change in flow direction produces stress that weakens this point.

Moreover, injection molded O-rings require much more energy to bend. A mold by its very nature directs more urethane into the outside half of the belt circumference than to the inside, so molded O-rings always fight to return to their original circular or oblong shape and do not easily conform to straight or serpentine belt paths. This is why back bending molded belts consumes excessive energy. Worse yet, belts on conveyor curves and line-shafts conveyors spiral like a candy cane, constantly turning themselves inside-out. Molded belts need a lot of energy to turn themselves inside-out, and they tend to scuff while doing that, so they often abrade. Extruded belts, on the other hand, have the same amount of urethane on both halves of the belt circumference, so they require much less energy to spiral and confirm more easily to belt paths, even back bending paths.
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Q26: It is rare, but sometimes round belts squeak. What causes it?

The squeak sound usually occurs when:

  1. The speed of the conveyor is very fast, and

  2. The slave rollers are relatively long (i.e., heavy) so they have a large moment of inertia, and

  3. There is no box covering all the rollers on the zone, so there is nothing to force all the rollers to stop at the same rate, and

  4. Without the momentum of a box on the MDR, the MDR stops very quickly, i.e. almost instantly -- like in a few tenths of a second.
The squeak is caused when the MDR forces the belts to stop too quickly, but the angular momentum of the slave rollers is so great that the rollers keep turning. Something has to give, so the belts are forced to slip a little on the slave rollers until the rollers stop turning. When belts with a high coefficient of friction slip, they squeak. The higher the angular momentum of the slave rollers, the more the belts will slip and squeak.

You can eliminate the squeak by:
  1. Ramping down the speed of the MDR so it does not stop so quickly. Itoh Denki's PLC allows you to do this. For example, instead of stopping in 0.2 seconds, set them to stop in 0.5 seconds. If you can program the empty zones to ramp down in speed, like in 1 second , but allow the zones carrying boxes to ramp down faster, then the speed of your conveyors will not be effected.

  2. Reducing the speed of your conveyor.

  3. Using lighter rollers that have a lower moment of inertia.

  4. Switching to belts that have a lower coefficient of friction, like rough green belts that slip without squeaking. However, they may also lower the driving force of the belts.

  5. Switching to thicker, ultra high tension belts that provide greater surface area contact with the rollers, like our .22" (5.6mm) 88A HEHT black belts. However, they are more expensive and more difficult to install because they are stretched 24%. They also require more energy to bend.

  6. Switching to flat belts that have a higher surface contact area, like our 1/32" thick x 1.38" wide (.8mm x 35mm) 83A flat belts. These will not slip on the rollers. However, they are more expensive and require more labor to install.

  7. Theoretically, squeaks can also be caused at start up if the MDR is so powerful that it ramps up to high speed almost instantly, and there are no boxes on all the rollers to force them to all start at the same rate. However, we have not observed this to happen.
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Q27: Why do weld joints often protrude slightly in a small bump above the belt's surface?

When urethane is extruded, it is pulled out of a die and frozen in a water bath. This causes long chain molecules to be aligned in the direction of extrusion, which makes the belt very strong in the longitudinal direction. When belts are welded, the heat changes the morphology of the plastic at the joint, making the molecules are more randomly oriented there. Consequently, stretching the belt causes the joint to neck down more than the rest of the belt. To offset this, we often leave a little bump (e.g., about .010" or .2mm tall) at the joint, so when it necks down, it becomes flush with the rest of the belt. This does not make the joint weaker.

If you prefer to have our weld joints flush with the belt surface, simply specify "grind welds flush".

Incidentally, you may know that steel welds behave differently because a bump at the weld joint makes it weaker. Steel, unlike urethane, is rigid so when tension is applied, the bump does not neck down, but rather focuses tension on the joint, making it prone to fracture. That does not happen with elastic urethane.
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Q28: How much should right angle diverter belts be stretched?

There are two types of right angle pop-up diverters, those that stretch the belts each time they pop up and those that don't. The latter will last longer because they don't have to stretch and relax frequently.

On those that don't stretch, the stretch is usually 10%.

On those that stretch, the stretch is usually 5% before pop-up and approximately 10% after pop-up.

Incidentally, the normal position of pop-up pulleys that stretches belts must be in the down position. If they are normally in the up position, then the belts will take a set and will not bounce back in the down position, so they will soon fall off the pulley.

Sometimes the problem is not the belt stretch, but rather the way the right angle diverter works. Such diverters work best when boxes are braked and come to a complete stop before being diverted 90 degrees. If boxes are not stopped ("diverted on the fly"), then their momentum can cause them to rotate and tip so a box edge dips below belts and lifts them off pulleys. In such cases the solution is to install fenders around the pulleys that force belts back on pulleys after they have been lifted off, as in the picture below.

Fenders on Right 
		  Angle Diverter Pulleys
Fenders on Right Angle Diverter Pulleys

You can purchase these fenders from Dematic.

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Q29: How to easily install poly-v, HT, HEHT and Hytrel belts without tools.

Most of our customers do not use a tool to install poly-v, HT, HEHT and Hytrel belts, but rather follow this procedure:

  1. Always wear eye protection and a safety helmet when installing high tension belts. Even though poly-v belts are only stretched a few percent, they pack a lot of energy. Ditto for HT and HEHT round belts stretched high amounts. If your grip on the loose roller should slip, the roller could become a projectile.

  2. Use a loose roller as a lever by inserting it through the belt that is already located around the adjacent installed roller.

  3. Make sure the belt's poly-v ribs fit into the appropriate grooves on both poly-v roller endcaps. HT, HEHT and Hytrel round belts must also fit in the roller grooves.

  4. Point that loose roller at an angle so its shaft is resting partially in the shaft hole in the frame closest to the belt. That shaft hole will become the fulcrum of the lever.

  5. Grab the other end of that loose roller and push or pull it (like you would a lever) until the shaft near your hands pops into the hole in the opposite frame. Simultaneously, the shaft resting partially in the shaft hole at the fulcrum pops into its frame hole. The belt is now installed. No tools needed.

  6. Never stretch a belt with a hook. Hooks will force the belt to bend sharply around a small diameter. This will damage the belt.
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Q30: How to choose the length of ConveyXonic Poly-V belts (includes PJ rib and groove dimensions).
To determine the ConveyXonic belt's size for different center distances, box weights and number of rollers per zone using your computer or cell phone, download Hutchinson's Belt Size Calculator by clicking here:   Hutchinson's ConveyXonic Wizard.

If you want to understand the numbers on the ConveyXonic belts for all but a few ConveyXonic belt lengths, the numbers after the PJ represent the approximate circumference of the installed belt in millimeters, assuming a belt thickness of approxomately 0.4mm. You can verify this with our Belt Sizer Length Calculator Method 3. First set the V-belt height at 0.4mm, the groove depths and percent stretch to zero. Then enter your pulley diameters and your center distance, and click on Calculate to get the Belt Cut Length, as in the following example. Now choose the closest PJ number to the Cut Length. That PJ number is the ConveyXonic poly-v belt length you should choose.

If the cut length and PJ size numbers are off by a few millimeters, remember that elastic ConveyXonic belts will work over a stretch range from 2% to 7%, so if you substitute values within the min/max center distances in our charts, you should be able to make the two lengths equal. That means you have found the correct size for your application. Here are links to our charts:
1.9" and 50mm rollers with 43mm pulley
2.5" and 63.5mm rollers with 60mm pulley

286.345 so round to PJ286
286.345, so round to PJ286

See Belt Sizer Length Calculator Method 3.

Since the belts can be stretched from approximately 2% to 7%, the circumference can vary by a few mm. This means that you will get the lowest driving force if your center distance is close to the minimum center distance shown in the these charts:
     1.9" and 50mm rollers with 43mm pulley
     2.5" and 63.5mm rollers with 60mm pulley
In that case, you may need to add an extra rib to the belt width if you want to move heavy loads.

For those few PJ numbers that are misnamed, Hutchinson cannot change their part numbers, so you must use the misnamed part number when ordering, but use the blue part number in the foot notes at the bottom of the above charts when calculating the circumference.

Dimensions for ribs on PJ-Section Poly-V Belts and Pulleys

Dimensions for PJ-Section Poly-V Belts and Pulleys

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Q31: How to make poly-v belts last longer and prevent premature failures.

Poly-v belts do not last long in acid, oil or greasy environments. If you are having a high number of failures due to abrasion, cracking or stripping along the belt length, and the problem is not the environment, then the cause may be inconsistent alignment and/or rubbing belts.

The drawing below shows what we mean by "consistent and inconsistent alignment".

Both belts on both roller endcaps need to be exactly parallel to each other, but must not touch. In other words, they must be consistently aligned and not rub against each other. Inconsistently aligned belts and/or rubbing belts will likely fail prematurely.

Misaligned Poly-V Belts may cause Premature Failure

Poly-v belts inconsidtent alighment
Poly-v belts inconsistent alignment

Other possible causes of premature failures include belts rubbing against boxes, pallets or conveyor parts like finger guards or cross-supports. Moreover, belts can slip, overheat and abrade if rollers are forced to keep turning under heavy boxes or pallets that cannot move due to jams or accumulations. In such cases, sensors should be used to detect stoppages and turn off motors before belts begin to slip within 4 seconds after a stoppage has been detected.

Note: The number of starts and stops at very fast acceleration/deceleration combined with high motor torque can influence the durability of poly-v belts. Therefore, Hutchinson recommends no more than 1 million starts and stops per year. Based on 18 hrs/day and 6 days/week usage, this translates to a maximum of 3 starts/stops per minute. You can minimize this problem by accelerating/decelerating at a slower rate, using PLC's that allow you to ramp up/down in speed.

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Q32: What is the shortest Hytrel belt that can be used on 1.9" (48.3mm) conveyor rollers?

Answer: 9.79" (249mm)
.   Hytrel belts are used primarily for very low temperatrure or harsh chemical applications. During installation, they must not be over stretched because polyester, unlike urethane, will not bounce back after being stretched. Unfortunately, when the rollers are closest (touching each other), you cannot put the belt in the groove of the second roller without first stretching it over the 1.9" section of the second roller as in the drawing below. This means that the shortest 3/16" (5mm) belt that can be installed without stretching the belt is 9.79" (249mm) cut length, and the shortest center distance between 1.9" rollers is 2.60" (66mm), assuming a minimum of 8% stretch. When the tolerance range on cut length is included, the minimum belt length should be 9.94" (252mm).

Shortest Hytrel belt = 9.79
Shortest Hytrel belt = 9.79" (249mm) cut length

If you need 2" (50mm) center distance between 1.9" (48.3mm) conveyor rollers at low temperatrues down to -22°F (-30°C), then you need to use poly-v belts.

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Q33: Can we weld, join or splice Dura-Belt's thermoplastic belts ourselves (Do it yourself)?

Dura-Belt provides hot plate splicing kits and tools so that anyone can weld its round, vee, and flat thermoplastic belting. However, our Super Strong Welding process makes welds up to twelve times stronger than you can get with vibrational friction welding tools or hot plat welding tools.

Warning:  Always weld in a well ventilated area because hot urethane fumes (especially smoky fumes) are poisonous. Heated urethane decomposes into small amounts of hydrogen cyanide, the death chamber gas, so do not breathe fumes or let them get in your eyes.

Furthermore, you can join our hollow belting without tools by merely inserting an aluminum barb in the tube ends. However, the maximum stretch is only 7% because greater stretch will pull the barbs out of the belts. Therefore hollow tubing cannot be used in high tension applications, and minimum pulley diameters are greater than those for welded belts.

Warning:  Eye protection must be worn around hollow belts because if a barb pulls out, the belt can strike a person like a bullwip, and the sharp barbs can cut and injure eyes.

Consequently, it is usually more cost effective, time saving and safer to purchase belts already made endless by Dura-Belt -- unless you need to weave belts through a machine in order to join them.

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Q34: Can Dura-Belt's stretchy, elastic urethane or Hytrel be used on slider beds?

Urethane and Hytrel have a high coefficient of friction (COF), so friction generated when they move over metal or UHMW plastic slider beds causes urethane and Hytrel to abrade and/or overheat, stretch and lose their elastic memory. This problem becomes worse if the load is heavy, the speed is high and/or the length on the slider bed is long. With round or v-belts the problem can be minimized by using rough green 88A/90A urethane belts because they have a lower COF due to less surface contact and harder durometer. With flat belts you should use multiply belts with nylon fabric on the bottom. Nylon has a low COF, so it resists abrasion when riding on slider beds.

There is one exception where urethane and Hytrel can be used on slider beds made from aluminum topped with Teflon tape. Teflon's low .05 COF reduces friction heating so low that round belts often work well, especially because aluminum conducts away any heat generated by friction. Teflon tape can also be used on steel slider beds (if you mistakenly built a system that uses slider beds with urethane or Hytrel belts), but the belts probably will not last as long as they would with aluminum beds. In conclusion, urethane and Hytrel belts work great on roller conveyors and pulleys, but not on nearly all slider beds.

Warning never use urethane on slider beds

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Q35: How long do Twisted belts (Zero-downtime quick-connect belts) last?

The picture below shows two "white frosted" belts that were cut after they wore out. Those belts were either slipping on their rollers/pulleys or rubbing against something like the frame's cross-support. When that happens, the belt's surface abrades causing that white frosty look. In addition, the rubbing friction causes the belt to overheat and elongate, which leads to premature belt failure.

Three Worn Twisted Belts with Plastic Hooks and one New One
Three Worn Twisted Belts with Plastic Hooks and one New One

The nice thing about the frosted white color is that you can easily see when a belt is distressed and take action to eliminate the problem before the belt fails.

That yellow colored belt that broke at the loop shows exactly how twisted belts usually fail. It's normal and ultimately unavoidable because the loop is the thinnest part of the belt, and friction between the hook and the loop eventually cuts through the belt loop. That yellow color means the belt was working for a significantly long time before it failed because urethane slowly gets yellower over time.

These are twisted 3/16" thick belts, but the end loops are only 1/8" thick, so the pressure on the loop strand is tremendous -- it's the weakest point on the belt. Friction between the hook and that thin loop ultimately causes the hook to cut through the loop, but crimped steel hooks or pinching/self-lubricating plastic hooks make belts last somewhat longer because they reduce or minimize that friction.

That is why we say: "Twisted belts cost twice as much as endless belts and last half as long, but they virtually eliminate downtime." That's why users buy them.

They were initially designed to act as stopgaps until the plant is shut down for vacation when round belts are replaced, but some users use them in place of round belts because they are so easy to install, especially with our Speedy Belt Installer.

The clear colored belt is new and unused.

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Q36: Thermoplastic urethane belts are NOT precision belts. How are they made? Design tips.

Thermoplastic urethane raw material pellets are manufactured by giant companies like BASF, Dow, Covestro, and Lubrizol. The pellets are melted in an extruder and forced through a die to produce the cord that Dura-Belt splices to make belts with its Super-Strong Weld joints.

Urethane belts are NOT precision belts because thermoplastic urethane is made only in large vats (not a continuous process), so the properties of the product varies with each vat. This means that the output from each vat can be slightly different:

  1. Shore A Durometer (hardness) can vary by +/-5

  2. Viscosity (Melt Flow Index) can vary, e.g., by 2 to 10 gr/10 minutes

  3. Color can vary from smoky white to water clear to yellow to gold colored. Even though belt manufacturers use the term "clear color", the correct color designation used by urethane manufacturers is "natural color".
Moreover, when urethane is extruded:
  1. Thickness can vary by +/-0.005" (+/-0.13mm) or +/-3% whichever is larger.

  2. Ovality (roundness) can vary, e.g., by 3% for .125" cord

  3. Since thickness and ovality varies, each strand of cord stretches by slightly different amounts when pulled straight and cut. This is why the length of long belts can vary by +/-1%
Because of all the possible variations, we recommend that belt designers should factor in a large safety factor -- preferably 2 to 3 times the desired results. Ideally this means that if it takes 1 lb. of force to move your load, you should design belts to provide 2 lbs. or 3 lbs. of force. If you can do that, your belts will last longest, but if that is not possible, belt life may be reduced. Therefore, design your equipment so belts can be easily replaced.

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Q37: Why does RPM decline (roller speed slow down) with each slaved roller? -- Creeping vs. Slipping belts

Elastic belts (including ConveyXonic poly-v belts) don't normally slip. Instead, all elastic belts will creep as they go around the tight side to the limp side of a pulley/roller. This causes a slight reduction in RPM with each slave roller, usually 0.5% to 1.5%. In other words, if the motor is running at 100 RPM, and the creep is 1%, then the first slave roller will rotate at 99 RPM, the second slave at 98.01 RPM, the third slave at 97.03, etc.

Therefore, the more slave rollers on one side of a motor, the greater the reduction in RPM with the last slave, so with 10 slaves the RPM of the last slave is approximately 90.4 RPM. That is why the Motorized Drive Roller (MDR) should be located in the middle of a zone and not on the end. If it is in the middle, there will only be 4 slaves on one side and 5 slaves on the other side of the MDR. This will minimize creep.

Note that 'creep" is the reason that most zones contain a maximum of 10 rollers. Although if you can live with a greater reduction in speed at the end of zones, we have customers that are using our .216" HEHT black belts on zones of 15 rollers moving 100 lb tires. One customer is even using them on 19 roller zones.

Dura-Belt HEHT black belts move 100 lbs on 15 roller zones
HEHT black belts move 100 lbs on 15 roller zones

You can virtually eliminate creep by making pseudo MDRs at the end of zones by using 2 narrow flat belts. You can also make pseudo MDRs by using two long round belts, but all rollers must have 4 grooves.
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Q38: How to install Poly-V and Poly-O endcaps on each end of a conveyor roller.

Some applications require our Poly-V or Poly-O endcaps to be inserted on each end of a conveyor roller. While the installation of the first endcap is easy, the second endcap initially extends out longer than the shaft, so aligning the hex shaped shaft with the endcap's hex inserts may appear to be extremely difficult. This tool solves that problem.

Poly-v and Poly-O endcap assembly tool for endcaps at both ends of conveyor rollers
Poly-v and Poly-O endcap assembly tool
for endcaps at both ends of conveyor rollers

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