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
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
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
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
Q28 How much should right angle diverter belts be stretched?
Q29 How to easily install poly-v HE and HEHT belts without a tool.
Q30 How to choose the length of ConveyXonic Poly-V belts.
Q31 What is the shortest Hytrel belt that can be used on 1.9" (48.3mm) conveyor rollers?.
Q32 Can we weld, splice or join Dura-Belt's thermoplastic belts ourselves (Do it yourself)?
Q33 Can Dura-Belt's stretchy, elastic urethane or Hytrel belts be used on slider beds?
Q34 How long do Twisted belts (Zero-downtime quick-connect belts) last?
Q35 Thermoplastic urethane belts are NOT precision belts. How are they made? Design tips.
Q1: What is the proper way to install elastic belts?
A: Here are rules about installing elastic belts:
- 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.
- Do not stand in the line of a stretched belt, so that if it breaks and flies free, it will likely
not hit you.
- Do not lean backward when stretching belts. If the belt should break or slip, you could fall
backward and injure yourself.
- 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.
- 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.
- 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.
- If you have two static pulleys, then put the belt on one pulley and roll it on the other.
- 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.
- 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
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
type, conveyor design, conveyor width, and level of maintenance.
If your belts are wearing out too soon, ask our Belt
Doctor for assistance.
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Q3: Why do Cyclothane belts last
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: What are Dura-Belt's Terms and Conditions of Sales?
A: To see them click here
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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
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
A: Urethane becomes more brittle as temperature decreases. Belts
that are allowed to sit overnight in low temperature environments
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
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: 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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Q9: Which size of urethane belt should I use?
A: 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?
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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Q12: 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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Q13: 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
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?
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 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
(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 tracking sleeves are located 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). 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). Then remove the belt and reverse it 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.
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
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Q15: 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. 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 tracking sleeve installed with screw driver
Tracking Sleeve Installer Tools. If you have to install a large number of 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
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
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Q16: How do I prevent tracking sleeves and flat belts from
slipping and moving sideways?
A: Do the following:
- 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.
- 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.
- Some installers use two hooks to stretch sleeves over rollers.
If sleeves are stretched more than 40%, they may deform because
urethane has been stretched beyond its elastic limit. This will
reduce sleeves' holding tension. Therefore, do not overstretch
sleeves during installation.
- 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
the roller when it dries.
See previous question above.
- 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
the surfaces together. However, let the cement dry for an hour
before restarting the conveyor.
- 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
- If none of this works, then try a tighter sleeve.
- 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?
A: We cannot weld tracking sleeves for rollers less than 1.5" (38mm) in diameter. If the order is
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
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
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Q21: 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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Q22: 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
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
steam (150°F, 70°C or less) may not significantly harm Hytrel or
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 beltâ€™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?
A: Most applications are designed so that belts wrap
between 120 and 240 degrees around their pulleys. If the force
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
that everything continues to work, even after
the belt becomes limp.
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Q24: 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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Q25: 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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Q26: It is rare, but sometimes round belts squeak. What causes it?
A: The squeak sound usually occurs when:
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.
- The speed of the conveyor is very fast, and
- The slave rollers are relatively long (i.e., heavy) so they have a large moment of inertia, and
- 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
- 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.
You can eliminate the squeak by:
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- 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.
- Reducing the speed of your conveyor.
- Using lighter rollers that have a lower moment of inertia.
- 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.
- 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.
- 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.
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.
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
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
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Q29: How to easily install poly-v, HT and HEHT belts without tools.
Most of our customers do not use a tool to install poly-v, HT and HEHT belts, but rather follow this procedure:
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- 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
- Use a loose roller as a lever by inserting it through the belt that is already located around the adjacent
- Make sure the belt's poly-v ribs fit into the appropriate grooves on both poly-v roller endcaps. HT and HEHT round belts must also fit in the roller grooves.
- 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.
- 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.
- Never stretch a belt with a hook. Hooks will force the belt to bend sharply around a small diameter. This
will damage the belt.
Q30: How to choose the length of ConveyXonic Poly-V 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 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:
and 50mm rollers with 43mm pulley
and 63.5mm rollers with 60mm pulley
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:
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.
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Q31: 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" (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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Q32: Can we weld, join or splice Dura-Belt's thermoplastic belts ourselves (Do it yourself)?
Answer: 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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Q33: Can Dura-Belt's stretchy, elastic urethane or Hytrel be used on slider beds?
Answer: 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.
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Q34: How long do Twisted belts (Zero-downtime quick-connect belts) last?
Answer: 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
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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Q35: Thermoplastic urethane belts are NOT precision belts. How are they made? Design tips.
Answer: 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:
Moreover, when urethane is extruded:
- Shore A Durometer (hardness) can vary by +/-5
- Viscosity (Melt Flow Index) can vary, e.g., by 2 to 10 gr/10 minutes
- 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".
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.
- Thickness can vary by +/-0.005" (+/-0.13mm) or +/-3% whichever is larger.
- Ovality (roundness) can vary, e.g., by 3% for .125" cord
- 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%
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