According to engineering standards, V-belts designated with the same cross section should operate interchangeably with sheaves that have grooves designated by the same letter. For multi-belt drives, however, manufacturers don’t recommend mixing belts from different manufacturers on the same drive because of possible differences in the cross-sectional shape, included angle between sidewalls, or length, Figure 1.

Replacing metric belts

The same recommendation applies to interchanging V-belts manufactured to different international standards, even though interchange guides are available. Such standards express belt dimensions in different units of measure: U.S. standards use English units (inches), whereas metric standards use millimeters.

Machinery designed in Europe according to standards of the International Organization for Standardization (ISO) or DIN (Germany) is widely used by many U.S. industries (e.g., textile looms, packaging equipment, and machine tools).

On much of this machinery, it may be tempting to try to save money by replacing imported OEM V-belt drive components with U.S. (RMA) standard components that are available off-the-shelf from industrial distributors as well as Vbelt and sheave manufacturers.

Interchange catalogs, or crossover guides are supposed to help you match Vbelts made to U.S. standards (RMA) with industrial belts made to metric standards (ISO/DIN). These guides use a soft conversion formula (not exact) to identify the manufacturer’s belts and nearly equivalent metric belts covered by ISO and DIN standards.

By using a cross-section interchange chart, you can match the first two numbers of metric classical belts, or the letters on narrow metric belts, to the corresponding U.S. standard designation, see chart.

After determining the belt type and datum width or top width, you can identify the manufacturer’s equivalent (closest matching) U.S. belt on separate charts in the interchange or crossover guide. These charts also contain length information.

Words of caution

Before substituting a U.S. belt for its metric equivalent based on an interchange chart, check for dimensional differences in cross sections, length, and belt ride-out (distance a belt extends beyond the sheave OD). For multi-belt drives with joined belts, check for compatibility between belt centers and sheave groove spacing.

A U.S. belt may have a different cross section or length than a comparable metric belt, even though their specification numbers indicate interchangeability. Further, it’s common to find metric belts in nonstandard cross sections and lengths that can’t be easily interchanged with U.S. belts.

Some interchange catalogs list differences in length between equivalent U.S. and metric belts, with these differences typically ranging up to 1 in. for the longest belts. The difference in length that can be tolerated depends on the application and the amount of take-up. It is usually up to the equipment operator or maintenance engineer to decide if the difference in length is acceptable for a particular application.

Differences in belt ride-out and included angle of the cross section between equivalent U.S. and metric belts can adversely affect the speed ratio of the drive, as well as power capacity.

Because of differences in groove spacing between U.S. and metric sheaves, Figure 2, interchanging joined U.S. belts with joined metric belts causes the belts to seat improperly in the sheaves. This leads to early belt failure and rapid sheave wear.

If you’re unsure about the effect of any dimensional differences on your application, consult the belt manufacturer. Failure to use compatible replacement belts can lead to reduced belt service life and lost production due to equipment downtime, especially on speed-sensitive machinery typically used in the textile, packaging, and machine tool industries.

Case history

Users often waste time and money because they don’t realize that joined U.S. and metric belts are different. Many exasperated maintenance personnel (along with local distributors as observers) have experienced early belt failure without understanding the cause.

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