Eliminate Belt problems
Machinery and Equipment MRO
Use the proper tools and a good pair of eyes to eliminate
almost all your belt drive problems.
Did you know that premature belt drive failures can be attributed
to just a half-dozen commonly encountered problems? Or that
all it takes to solve these problems is just a few tools and
using your head?
That's what Brent Oman, a manager in Gates' power transmission
product application department and his colleagues have found.
They've identified and ranked the six most common sources of
premature belt failure. Neglecting any of these areas of concern
may result in a drive system that does not function properly,
and in which the belts can fail in days, hours or even minutes.
Product application engineers for the Denver-based Gates Corporation
use a number of tools when dealing with customers' belt drive
problems. Their equipment can be as simple as a piece of string
or as sophisticated as an electronic tension tester. In between,
the engineers may also rely on digital photography to analyze
the causes of belt wear.
By troubleshooting these problems, and making periodic inspections,
Oman says that plant engineers and maintenance managers can
eliminate almost all of their premature belt failures.
Other than normal wear and use, the most common sources of
belt drive failures are 1) improper tension, 2) misalignment,
3) handling, 4) hardware, 5) environmental factors, and 6)
1. Improper tension
Belts require very little maintenance. However, all belt types
must be properly tensioned initially. Additionally, V-belts
should be rechecked periodically (no more than three to six
Synchronous belts require correct tensioning when installed,
but then only need occasional monitoring because they have
a tensile cord that doesn't stretch over time like a V-belt
When troubleshooting for improper V-belt tension, make sure
the drive is turned off and locked down, and then look for
glazed or hardened belt sidewalls that indicate the belt is
slipping in the drive. Improperly tensioned synchronous belts
will have unusually heavy wear on the fabric tooth surface.
The calculated tension range at which belts should be installed
depends on the drive components, and the load and speed of
the drive. The belt manufacturer's recommendations should be
followed to determine the calculated installation tension values.
Due to system inefficiencies, belt drives are often carrying
far less load than they were selected to carry. A calculated
tension that is based on the motor nameplate horsepower may
higher than what is required of the real load being carried.
The ideal tension for a V-belt drive is the lowest tension
at which the belt will not slip at the highest load condition.
For synchronous belts, ideal tension is the lowest tension
that properly seats the belt in the driveN sprocket on the
slack side. Ideal tension for both types of belt will result
in the best belt life and lowest bearing loads for a given
power transmission application.
Several tools can be used for accurate tensioning. These include
a pencil-type spring force tension gauge that measures static
belt tension by indicating force at a specified deflection
of the belt span.
Sophisticated electronic sonic tension meters work on the
theory that a belt vibrates at a particular frequency based
on its mass and span length. To test the tension, simply strum
the belt to set it vibrating, and the meter records the resulting
oscillating sound wave.
For newly installed and tensioned V-belts, a run-in procedure
is recommended. This process consists of starting the drive,
letting it run under full load and then stopping, checking
and retensioning to the recommended values. Running belts under
full load allows them to seat themselves into the grooves.
Once properly installed, synchronous belts rarely need retensioning.
Overall, Oman says, proper belt tensioning will eliminate
90 per cent of belt failure problems.
When installing a belt, always check for sheave or pulley
misalignment. Oman has observed that a misaligned V-belt sheave
will cause excessive belt wear on the sidewalls, instability
and belt turnover. Similarly, misaligned pulleys will wear
synchronous belt teeth unevenly across the belt, as well as
overload the tensile cords at the edge of the belt. Improper
alignment also can create objectionable belt noise.
The alignment of the drive should be checked both before and
after belt tensioning, since belt tensioning can possibly move
some components, he advises.
Place a straightedge such as a straight board, straight piece
of aluminum or steel stock, or string pulled taut, along the
outside face of both pulleys. Misalignment will show up as
a gap between the outside face and the straightedge. Pulleys
and shafts can be checked for tilting with a bubble level.
Pulley misalignment may result from the motor shaft and driveN
machine shafts not being parallel, the pulleys not being properly
located on the shafts, and the pulleys being tilted due to
As a general rule, sheave alignment on V-belt drives should
be less than 1/2° or 1/10-in. per foot of drive centre
distance. Alignment for synchronous belts should be controlled
to within 1/4° or 1/16-in. per foot of drive centre distance.
Power transmission engineers regularly see examples of mishandling
that can contribute to premature belt failure. Here are some
of the problems:
a) When installing new belts, never use force or pry them
on sheaves or pulleys. This could break the internal cord reinforcement
or damage the outside of the belt. Rather, reduce the centre
distance on the drive or release the idler to relieve the tension.
If necessary, remove one of the pulleys to install the belt.
After the new belts have been installed and tensioned, rotate
the drive by hand for a few revolutions, and re-check the tension.
If necessary, adjust the tension and secure the motor mounting
bolts to the recommended torque values.
b) Never crimp (bend the belts below their minimum recommended
diameter) or twist belts. This, too, could damage the internal
c) With proper storage, rubber belts have a shelf life of
eight years. Store belts in a cool area with no direct sunlight,
at temperatures less than 85°F and at a relative humidity
below 70 per cent. If the belts are packaged individually in
their own boxes, they should be stored in their original shipping
cartons. V-belts may be stored by hanging them on properly
designed belt racks or hooks. Synchronous belts should be stored
on their sides on shelves. Belts can be damaged by coiling
them too tightly or by bending them sharply. Don't allow them
to become contaminated by oil, grease or other chemicals. Also,
keep belts away from ozone sources such as arc welders and
other electrical equipment or motors.
A common misperception is that metal sheaves and sprockets
never wear out. Gates application engineers report that a significant
percentage of the belt drive problems they investigate can
be traced to something wrong with a metal component. A sure
sign of sheave wear is abnormal belt wear, and belt service
life that progressively worsens with each belt that is installed.
Most sheave wear is due to abrasion caused by airborne particulate
matter in the vicinity of the drive. The abrasive material
can range from sand to iron ore dust. Oman says he has seen
talcum powder and PVC dust totally destroy drives that were
not protected properly.
It is important that belt drives be protected from abrasive
damage by using adequate drive guards. Keep drive guards clear
for proper ventilation and clean pulley grooves to remove the
build-up of dust, grime, rust or other foreign materials.
5. Environmental factors
Certain environmental factors must be considered when drive-performance
does not meet expectations. These include high or low temperature
extremes, dust and grime, chemical vapours, lubricants and
cutting fluids. Harsh weather, high humidity and sunlight exposure
also can decrease drive performance. Check for foreign material
that has become trapped in the lands and grooves of a synchronous
If rubber dust from a belt drive or lubricants from a roller
chain drive in a food processing operation are causing contamination
problems, Oman recommends installing a polyurethane synchronous
drive system with stainless steel pulleys. This combination
is clean running and is not affected by caustic cleaning solutions.
Polyurethane synchronous belts are much more resilient to potential
damage that could be caused by lubricants or cutting fluids.
6. Design factors
Finally, drives must be properly designed and built to last.
In addition to determining the best size and number of belts
to use, the plant engineer must consider other drive-design
For example, pulleys must be manufactured according to industry-accepted
tolerances. Belt guards must be designed for adequate drive
protection, yet provide ventilation. Structural members of
the drive, including framework, motor mounts, machine pads,
etc., must be heavy-duty components that are properly sized
to carry the load. Drives should be designed for minimal vibration
and also for ease of maintenance and inspection.
A defective drive component is rarely the cause of a drive
problem. If you have eliminated other possible causes and feel
that you do have a defective part, contact your belt or pulley
distributor or supplier to verify your concern and correct
Before sending a defective or worn component to the manufacturer,
Oman offers one last piece of advice. Invest in a digital camera
with a close-up lens, and email the "evidence" to
the manufacturer's product application staff.
Oman relates, "Although we do extensive phone interviews
with customers, when troubleshooting, we often get answers
that the customer wants us to hear. But, if the customer is
looking at the failed drive component, and we are viewing a
digital image, we have two sets of eyes looking at the same
problem, and more often than not the answer will be immediately
Brent Oman, general market group manager in the power transmission
product application department of Gates Corporation, Denver,
Col., helped prepare this article exclusively for the readers
of Machinery & Equipment MRO.