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Solutions to Belting Problems - Belt Life-span
Dura-Belt   800-770-2358
 
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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: How can we verify that DuraBelt's belts last longer?
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: Which size of urethane belt should I use?
Q9: What's the difference between overlap welds and butt welds?
Q10: Why do overlap welds eventually pull apart under high tension?
Q11: Will our high tension belts damage bearings?
Q12: Do crowns prevent flat belts from moving sideways (walking), i.e. keep belts centered?
Q13: What is the RAVE technique for tracking sleeve installation?
Q14: How do I prevent tracking sleeves and flat belts from slipping and moving (walking) sideways?
Q15: Where can I get tracking sleeves for small diameter rollers?
Q16: Where do I find Dura-Belt's part numbers?
Q17: How do I clean, sterilize, disinfect, sanitize and/or washdown urethane or Hytrel belts?
Q18: How much should belts wrap around each pulley?
Q19: What is the difference between Belt Loading Tension and Belt Tension?
Q20: What is the difference between urethane and polyurethane?
Q21: Do injection molded O-rings make good belts??
Q22: It is rare, but sometimes round belts squeak. What causes it??
Q23: Why do weld joints often protrude slightly in a small bump above the belt's surface?
Q24: Will Dura-Belt's wide-short flat belts track -- belts much wider than long?
Q25: How much should right angle diverter belts be stretched?
Q26: How much should bets be stretched -- stretch factor, stretch percent, stretch amount, pretension belt?

Q1: What is the proper way to install elastic belts?
A: 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 belts on a conveyor is to touch the rollers together, slide the belt into the grooves, then pull the rollers into place. If the roller centers are too close to do this, do not use a narrow tool or hook to pry or pull the belts over rollers. It will over stress a small section of the cord and cause premature belt failure. Instead, use our shoe-horn-like 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 static pulleys, then put the belt on one pulley and roll it on the other.

  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: 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?
A: 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: How can we verify that DuraBelt's belts last longer?
A: We are certain that our belts are the most resilient -- so certain that we will send you twenty free belts to test. Put them and our competitors' belts of identical size and durometer on the same conveyor span. After 3 months cut off all the belts and measure their length. Ours should demonstrate their resiliency by being about 1/8" to 1/4" shorter. Conveyor manufacturers often use this test. Now you can too. Greater resilience means more drive, longer life, and less downtime.
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Q5: What effect does high temperature have on urethane belting?
A: 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?
A: 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?
A: See instructions under the BELT SIZER pull down menu.
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Q8: Which size of urethane belt should I use?
A: See instructions under the BELT SIZER pull down menu.
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Q9: What's the difference between overlap welds and butt welds on reinforced urethane belts?
A: 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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Q10: Why do overlap welds eventually pull apart in high tension applications?
A: 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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Q11: Will our high tension belts damage bearings?
A: 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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Q12: Do crowns prevent flat belts from moving sideways (walking), i.e. keep belts centered?
A: 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, less than 2" (50mm) wide, use 1/31" (0.8mm) thick sleeves. For wider belts use 1/16" (1.6mm) thick sleeves. 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. Our 1/16" x 2" tracking sleeves should be stretched only 2%; otherwise they will be too difficult to install. (Note: Some conveyor manufacturers prefer 1" wide sleeves, others prefer 2" wide sleeves. Both work well, so choose the one that is easier to install for you.)

In our tests we are able to track flat belts with tracking sleeves on only the head (downstream) roller, but many conveyor manufactures prefer to put them on both the head and tail rollers as in the pictures below. They do this because they cannot be sure that their frames are always square (sometimes due to a forklift bump a conveyor) and/or because there may be side forces on the belts as when boxes are pushed on from the sides.

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) tracking sleeve, located in the middle of the belt on the drive roller.
  • Medium wide flat belts up to 9" (230mm) wide -- use a 1/16" thick x 1" wide (1.6mm x 25mm) 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" or 2" wide (1.6mm x 12mm or 25mm) tracking sleeves on both the lead and tail rollers. Locate the outside of the tracking sleeves 2" (50mm) from the edges of the flat belt.

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.)

Orange tracking sleeves on wide flat belt conveyor
Orange tracking sleeves on wide flat belt conveyor
(Available only for 1.9" (48.6mm) rollers. Easier to install, but must use sleeve installer air gun.)

If a flat belt walks (does not track) on rollers with our tracking sleeves, make sure the conveyor frames are not warped. 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 as best you can. Next verify that the tracking sleeves are located and aligned properly. If the belt still walks, put a piece of masking tape near the right edge, remove the belt and measure the length of both edges with a fabric tape measure. If the lengths are significantly different, the belt may not be true enough. Test it by reversing it on the conveyor so the masking tape is on left edge. If it walks in the opposite direction, then it is warped, and you should contact us for a Return Authorization. If the belt is true but still walks, first read Q14 below, then call the Belt Doctor for technical help.

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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Q13: What is the RAVE technique for tracking sleeve installation?
A: 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. Sleeves larger than 1" wide are easily installed by using our sleeve installation air gun to float them down the roller.

Screw Driver Technique:  Here is a new way to install narrow sleeves (1" wide or less) that we recently discovered.  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 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

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) and 1/8" (3.2mm) thick sleeves can easily be installed with our sleeve installation air gun tool. With ticker sleeves, e.g., 1/4" (6,3mm), 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.
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Q14: How do I prevent tracking sleeves and flat belts from slipping and moving sideways?
A: 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. Most of our flat belts and tracking sleeves come with two different surfaces -- a matte side and a shiny side. The matte side has less surface area contact, so it will slip easier. The shiny side has more surface area contact, so it tends to stick to shiny surfaces like galvanized rollers. Therefore, to prevent tracking sleeves from walking, we recommend placing the shiny side against the rollers.

    Also 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 press them to walk sideways. Therefore, we recommend placing the shiny side against the rollers, so the belts will resist walking. Moreover, when tires rub against the belts' matte side, they tend to slide easier over the belts' surface and thus put less side force on the belts. This helps them resist walking.

    If this does not work, then put sleeves on the rollers that are thicker than the flat belts plus tracking sleeves. This will prevent the tires from touching the flat belts, so no side forces will 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 over stretch sleeves during installation.

  4. With sleeves less than 2" (50mm) wide, 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 contact cement (e.g. DAP Weldwood) at 0, 90, 180, and 270 degrees around its circumference under both edges. 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 do have not been know to walk.
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Q15: Where can I get tracking sleeves for small diameter rollers?
A: 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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Q16: Where do I find Dura-Belt's part numbers?
A: 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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Q17: How do I clean, sterilize, disinfect, sanitize and/or washdown urethane or Hytrel belts?
A: 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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Q18: How much should belts wrap around each pulley?
A: 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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Q19: What is the difference between Belt Loading Tension and Belt Tension?
A: 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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Q20: What is the difference between urethane and polyurethane?
A: 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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Q21: Do injected molded O-rings make good belts?
A: 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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Q22: It is rare, but sometimes round belts squeak. What causes it?
A: 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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Q23: 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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Q24: 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
Wide-short flat belt tracks well

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Q25: 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 frequetly.

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
Fenders on Right Angle Diverter Pulleys

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Q26: 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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