Belt and hose maintenance

A well-designed industrial belt drive can operate for many years when periodically maintained and used under normal conditions. Problems can arise, however, due to   environmental factors, storage and improper drive maintenance.

Anticipating problems and understanding the troubleshooting process can help protect belt drives from future service problems. Here are some good user guidelines:

Heat problems
Heat is a major cause of belt failure. The three primary sources of heat buildup in belts are ambient conditions, improper maintenance resulting in belt slippage and severe operating conditions.

To avoid high ambient heat, increase ventilation around the drive. This can be done by using fans and air blowers, or sheaves that have spokes and fins that create air flows to cool the belts. Also provide better ventilation in the drive guard. Simply letting the heat out can sometimes dramatically lower the temperature.

If ambient conditions have been eliminated as the cause of overheating, belt slippage or severe operating conditions are prime suspects.

Improper belt tension causes slip that generates unwanted heat. The correct tension is the lowest tension at which belts will run and not slip when the drive is under a full load. Less obvious causes are poor drive guard design, inadequate ventilation, misalignment, worn pulleys, or foreign objects such as dirt, oil and water in the drive.

Unusually severe operating conditions or improperly designed drives can cause high internal belt temperatures. Some of these are:
• Use of larger motors or engines than originally specified.
• Higher loads than expected.
• Use of high speed motors with a corresponding reduction in pulley size.

Internal heat problems can be corrected by decreasing the belt load, by designing the drive with more belts or wider belts, or by decreasing belt bending stress, which is a major factor in internal belt temperature. These stresses can be reduced by using a larger pulley, changing to a different belt cross section, or using a molded notch belt.

Proper alignment and tension
Faulty drive alignment and tension are also significant causes of failure of industrial belt drives. Misalignment, improper tension or foreign objects in the drive usually are indicated by unusual belt or pulley wear patterns.

The friction created by a loose V-belt slipping in the pulley causes belt sidewalls to become glazed, or shiny, and lose their gripping strength. Grease and oil on the pulley also can cause this.

Deep bottom cracks that appear at regular intervals are caused by the V-belt turning around too-small of a pulley. Oil weakens the compound bonds of a V-belt, making it soft, spongy, and finally fall apart in layers. Pitted or streaked sidewalls, or a tensile break, can indicate a foreign object in the pulley.

Synchronous belts replace roller chains on conveyor, HVAC and food handling drives because they are clean running and require no maintenance. However, they will begin to wear out at the end of their normal service life at the base of the tooth where it joins the belt. Cracking generally will begin on the forward side of the tooth (in the direction of belt travel).

Hardware issues
Unusually loud belt drives can result from three causes: incorrect belts, worn pulleys, or debris in the pulleys. Pulleys must be examined for the correct belt size prior to installation, and, in synchronous drive systems, must be checked for the correct tooth profile.

A common misperception is that metal sheaves and sprockets never wear out. Many belt drive problems can be traced to something wrong with a metal component. Replacing worn pulleys is the only solution for unusual belt noise and wear caused by this situation.

Oil contamination and dirt/dust buildup are the easiest belt failure problems to identify. When pulleys are contaminated by debris, they must be cleaned, their shielding improved, and any rust, paint or dirt must be removed from the grooves.

Handling
Mishandling can also contribute to premature belt failure:

1)  When installing new belts, never pry them on sheaves or pulleys. This could break the internal cord reinforcement or cut the bottom of the belt. Rather, take up the center 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 are in place, rotate the drive by hand for a few revolutions, re-check the tension and secure the motor mounting bolts to the correct torque or reposition the idler.

2)  Never crimp or twist belts. This can damage the internal cord reinforcement.

3)  With proper storage, rubber belts have a shelf life of five to seven years; polyurethane synchronous belts will last 10 to 12 years in storage. Store belts in a cool, dark area, at temperatures between 50 to 75 degrees F, preferably in original cartons. Or, hang them on properly designed belt racks or hooks. Belts can be damaged by coiling them too tightly or by bending them sharply.

Keep belts away from oil, grease, chemicals and ozone sources such as arc welders and other electrical equipment or motors.

Although any belt will wear out eventually, maintenance personnel can help to ensure a full life by:

• Installing belts properly, aligning the drive and setting the proper tension. Both V-belts and synchronous belts do best with a tension for the load transmitted.

• Doing a run-in procedure for new belts. For V-belts, this consists of starting the drive, letting it run under full load and then stopping, checking and retensioning to the specified values. Running belts under full load lets them seat themselves in the grooves. Once properly installed, synchronous belts rarely need retensioning.

• Maintaining a clean environment and protecting the drive from objects that may be caught between the belt and pulley.

• Setting a replacement schedule. Depending on its environment, a belt drive’s service life might be weeks, months or years. Replacing belts near their ultimate service life helps prevent unscheduled downtime.

• Maintaining good records. Maintenance personnel will sometimes replace a motor with one with higher horsepower. This can lead to premature failure for both belt and metal drive components designed for the smaller motor.

Industrial hose maintenance
Hose is a versatile conduit, but it is also vulnerable to damage. Failure can be expensive in terms of downtime, lost material, damaged equipment and personal injury. To obtain maximum service for any type of industrial hose, the user must consider the application, take reasonable care of the hose assembly and observe safety regulations and procedures.

Selection of industrial hose
Proper hose selection is the first step in preventive maintenance. Selecting the best product for the application will produce the maximum life expectancy from the product for the best value.

When selecting hose, use the acronym STAMPED:

Size: Inside diameter, outside diameter and length.

Temperature: Minimums and maximums of the system.

Application: How and where: suction or discharge application; continuous, intermittent or occasional service; minimum bend radius; special construction (crush-resistant, static conductivity); special needs, UL, government, FDA, etc.

Material Conveyed: Air, water, chemicals (concentration and temperature), petroleum, steam, etc. Are the hose tube, cover, couplings and O-rings compatible with the fluid being conveyed?

Pressure: Maximum rated working pressure, suction and burst pressure.

Ends: Straight, male, etc.

Delivery: When, where and quantity.

Maintenance procedures
Hose has service limitations and will fail prematurely if they are exceeded. General procedures are elementary, but are easily overlooked. They are especially important because of the limited amount of maintenance or repair that can be made to extend the life of an industrial hose.

Here are some basics:

1. Storage: New hose, stored carefully, has a shelf life of about five years before deterioration will reduce service life.

2. Hose should be stored in its original packing container or crate, out of direct sunlight.

3. Avoid extremes of temperatures, exposure, ozone or direct heat.

4. If hose is shipped coiled, lay coils flat on the shelf. Hose shipped straight should be stored straight.

Environment
In general, avoid conditions that will accelerate hose aging. If conditions are unusually severe, use hose designed for them. Avoid extreme heat or cold unless the hose has been designed and built to withstand such extremes. Typical industrial hose will perform well in temperatures from 0 to 150 degrees F. At -20 degrees, the hose will lose some flexibility. At -30 to -40 degrees, normal hose may crack if flexed sharply. Special hoses are available that are serviceable down to -60 degrees F.

The limitations above 150 degrees F vary with the type of elastomer and service. Follow the manufacturer’s guidelines for hose to be used in high ambient temperatures.

Exposure to high ozone levels will cause a hose cover to crack. This can be severe in high smog areas or near electrical generating machinery.

Consider weathering. Hoses in continuous service outdoors should have weather resistant covers. Always avoid exposure to oil or corrosive chemicals.

External abuse
Do not over-bend the hose to the point of kinking. Always observe minimum bend radius recommendations. Wire-reinforced hoses may have greater rigidity, but they can be crushed or deformed by external weight or forces.

Couplings and hoses can be damaged by too much end pull. A hard pull at any angle may kink the hose next to the coupling, especially in subzero temperatures.

Large diameter hoses (4 inches inner diameter and larger) have special considerations for moving and handling materials. One problem may be overstressing the hose carcass. Handle heavy hoses with slings, every 6 to 10 feet, and do not lift long sections by the middle with ends hanging down.

Another consideration: sometimes the hose cover is exposed to wear in one certain spot. In this case, add a protective outside cover to avoid wearing through the hose cover and exposing the reinforcing material.

Safety considerations
Safety and inspection are critical to assuring long service for hoses. If proper inspection procedures are followed on a routine basis, more than 75 percent of all maintenance problems can be eliminated.

A defective component is rarely the cause of a problem with a belt drive or a hose transfer application. If you have eliminated other possible causes and feel that you do have a defective part, contact your belt or pulley distributor or hose supplier to verify your concern and correct the problem.

This article appeared in the October/November 2005 issue of MRO Today magazine. Copyright 2005.

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