Page 336 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

316 Major Process Equipment Maintenance and Repair

Selectlng the Correct Belts
All the work and experience that goes into designing a V-belt drive is
wasted if the specified belts are not used or the number of belts is
changed. Over-belting is wasteful. Under-belting is even more expensive
in the long run, because overloaded belts wear out faster.
V-belts are identified for size according to industry standards. A com-
bination of letters and numbers as shown in Figure 7-5 indicates the
width across the top of the belt (often referred to as “cross-section”) and
the belt length. Conventional belts come in five widths: A, B, C, D, and
E; while narrow V-belts are made in three widths: 3V, 5V, and 8V. In
addition, there are the light-duty 2L, 3L, 4L, and 5L belts. If you are not
sure which to use, measure the top width of the old belts carefully, or use
the gauges described previously.
Be careful in measuring V-belts. The top widths of the B and 5V belts
are very close; however, the 5V is considerably thicker, and the groove
angles of the sheaves are different. Do not attempt to use these belts in-
terchangeably. The 4L and 5L Light-duty belts are also very close in size
to the A and B belts. But again, groove angles may be different. Light-
duty belts should not be used on heavy-duty drives.

Explosive Atmospheres
Belts on drives in hazardous atmospheres should be kept reasonably free
of encrusted accumulations of nonconducting materials. In addition, all ele-
ments of the drive must be interconnected and grounded as illustrated in Fig-
ure 7-6.

Store Belts Properly
V-belts should be stored in a cool, dry place out of direct sunlight.
They should be kept away from ozone-producing equipment such as arc
welders and high voltage apparatus. Temperature should be below 85”F,
relative humidity below 70 percent. If belts are stored in piles, the piles
should be kept small to avoid excessive weight which could distort the
bottom belts. When belts are stored in boxes, the box size should be lim-
ited. Ideally, belts should be hung on saddle type pegs. With proper stor-
age, belt quality will not change significantly within six years.
Assuming good storage practices, a decrease in service life of approxi-
mately 10 percent per year of storage beyond six years can be expected.
From a norm of six years storage life at 85 OF, it is estimated that the stor-
age limit should be reduced by half for each 15°F increase in tempera-
ture. A significant increase in humidity may cause a fungus to form on
belts, but any effect on the performance of the belt would be very slight.