Purvis Industries

TAKE-UPS AND ALLOWING FOR BELT STRETCH

Article By: Billy Witherspoon

Business Unit Manager - Heavyweight Belting

All conveyor systems require a type of belt take-up that keeps the belt tight enough to run on a system without slipping and is adjustable to allow for belt stretch.  There are multiple types of belt take-ups.  However, they generally fall into two major categories, belt take-ups that are adjusted manually or belt take-ups that are self-adjusting. The self-adjusting belt take-ups use gravity as a counterweight or some type of stored energy such as like Pneumatic/Hydraulic pressure.  The longer the belt, the more take-up travel will be needed to allow for stretching. A key rule is that for every foot of belt stretch the take-up system will require at least 6 inches of take up travel.

Fenner Dunlop, RockMaster belts, are designed to have 1.5% stretch at max PIW rated Operating Tension. All belts are not rated the same, so we highly recommend our customers to consult the manufacturer’s spec sheets for their specific belt).  A 400 foot Rockmaster belt running at MAX rated operating tension would be expected to elongate or stretch to 406 feet (i.e. 400ft x 1.015% = 406ft) and the extra 6 feet would require at least 3 ft of take-up travel.  On average, most belts are not running at or near the Max Tension rating and will stretch less.  Operating conditions like temperature, moisture, oil or belt overloading can cause the belt to stretch or shrink more than usual. On systems with short take-ups you must make the spliced length as short as possible to allow for lack of adjustment. On longer systems, it is best to run the belt for a period of time to break in and generate the stretching of the belt, then return and shorten or resplice.  Repeat this task if needed, as it could run out of take-up over time.  A 2,000 foot Rockmaster belt running at MAX rated Operating Tension would be expected to elongate or stretch to 2,030ft (i.e. 2,000ft x 1.015% = 2,030ft) and the extra 30 foot would require at least 15 foot of take-up travel.

The MORE Tension you put on a belt the MORE Stretch a belt will experience!

Belt manufacturers recommend that a belt is run with as little tension as possible. There are calculations and programs that will tell you the correct counterweight that a system should have based on the normal operating data. Ideally, the belt should be adjusted just tight enough so that the material/load is conveyed, without the belt slipping on the drive pulley.  This puts less stress on the whole system resulting in increased belt and component life!

For more information on Take-up and Belt Stretch, contact one of your Purvis Industries Sales Representative or connect with our Heavyweight Belting team.