PROPER BELT SELECTION – A COMBINATION OF KEY OPERATING FACTORS
Since the belt itself is one of the most costly components of a typical conveyor system, it is obviously important to select the right GRT belt for the job. When recommending a belt, whether on a new system or as a replacement on an existing system, an objective study of the system and all the relevant operating conditions is of utmost importance. Belt selection must take into account six key criteria: system tension, load support, troughability, impact rating, pulley diameters, and covers (compound and thickness).
Tension
The tension members in a belt carcass provide the longitudinal strength to move the load and also withstand torque from the system start up. Belt tension is normally defined as required PIW (pounds per inch of width) and can be calculated using the following quick method:
| PIW = | HP (1 + K) 33,000
S x W |
PIW…….Unit Tension
HP………System Motor Horsepower
K………..Drive Factor
S………..Belt Speed (Foot Per Minute)
W……….Width of Belt
33,000…Constant
SCREW TAKE-UP COUNTERWEIGHT TAKE-UP
| DRIVE PULLEY DEGREE OF WRAP | BARE PULLEY F=0.22 |
LAGGED PULLEY F=0.25 |
BARE PULLEY F=0.30 |
LAGGED PULLEY F=0.35 |
|---|---|---|---|---|
| 180° [a] | 1.00 | .84 | .64 | .50 |
| 200° | .86 | .72 | .54 | .42 |
| 210° [b] | .80 | .67 | .50 | .38 |
| 220° [b] | .74 | .64 | .46 | .35 |
| 240° [b] | .66 | .54 | .40 | .30 |
| 300° [b] | .46 | .37 | .26 | .19 |
| 360° [b] | .33 | .26 | .18 | .13 |
| 420° [b] | .25 | .19 | .12 | .08 |
| 480° [b] | .19 | .14 | .09 | .06 |
Load Support
Proper carcass traverse rigidity must be maintained throughout the belt life to support the load capacity of the belt and bridge the idler junction gaps. Load support values for GRT belts, based on the number of plies and the type of belt, are provided in the proceeding pages and stated as a maximum width in inches.
Troughability
In addition to having adequate load support, the belt must still be flexible enough to make proper contact with all three troughing idler rolls when the belt is empty. If not, proper belt training cannot be accomplished. Troughabiilty values for GRT belts are provided in the preceeding pages and stated as a minimum width in inches.
Impact Rating
The type of fiber, or tension member, weave design, and number of plies determines the impact rating of a belt, and its ability to absorb impact energy. This information in addition to knowledge of the size and type material to be conveyed, how the material is to be loaded, and the conveyor system’s impact arrangement, allows us to choose the proper GRT belt. Impact rating of a belt carcass, as stated in drop to belt in inches, must not be exceeded.
Pulley Diameters
Proper sized pulleys allow the belt to operate at its full tension rating without additional stress and compression on the inner plies. Minimum pulley diameters for conveyor systems are stated in inches for various belt carcasses and differing tension ratings.
Covers
Covers are compounded for a wide variety of applications and are selected to be compatible with the actual materials that are to be conveyed. GRT offers a full line of cover compounds, as explained in the previous pages that will handle almost any conveying applications. Cover thickness for a specified compound is also a function of the application, the type material to be conveyed, and frequency of the loading cycle. A chart has been provide on page 10 for recommended thickness of a GRT belt cover.
While this method is quick, it does not represent the most accurate method for belt tension selection. A more precise and exact calculation can be made by using the Conveyor Belt Data Form supplied on this site (click here). Completely fill in the form and send to the factory for review and recommendation of a proper GRT belt for your use.