Today's Message Index:
----------------------
1. 10:05 AM - Re: Stratus belt failure (Kelly Meiste)
Message 1
| INDEX | Back to Main INDEX |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Stratus belt failure |
--> Stratus-List message posted by: "Kelly Meiste" <kellymeiste@jcwifi.com>
Below is some interesting reading from "Gates".
Hopefully will shed some additional light on this topic.
Kelly Meiste
601 HD Stratus (120 hours)
++++++++++++++++++++++++++++++++++++++++++++++++++
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) design factors.
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 months).
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 does.
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.
2. Misalignment
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 improper mounting.
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.
3. Handling
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 cord reinforcement.
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 85F
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.
4. Hardware
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 sprocket.
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 factors.
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 the problem.
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 obvious."
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.
Other Matronics Email List Services
These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.
-- Please support this service by making your Contribution today! --
|