Page 23 - ConveyorBeltMaintenanceManual2010

TYPES OF LAGGING
1. Bolted lagging is usually fabric-reinforced, the fabric being necessary to give proper bolt-holding. This type has no inner or
pulley cover; where no grooving is intended, 1/8” top cover is the proper minimum, but if the lagging is to be grooved, a
minimum of 1/4” top cover must be used.
Bolted lagging is usually applied in two or more circumferential strips, applied under tension with the points in the different
strips staggered around the pulley (On flat-faced pulleys, one strip the width of the pulley may be used).
For open-end pulleys 5/16” or 3/8” diameter flat head elevator bolts with nuts may be used. Alternate methods include slotted
bolts with tapped holes or self-tapping screws for use in welded steel pulleys. It is necessary that the bolt heads be sunk below
the level of the surrounding lagging to prevent damage to the belt as it passes over the pulley. This may be accomplished by
counter-sinking the holes in the pulley or, where the lagging cover is greater than about 1/8”, it is possible to sink the heads
merely by tightening the bolts.
Ends of the strips should be bolted in a dovetail joint as shown in Fig. 30. In addition, bolts should be used in rows running
across the face and around the circumference of the pulleys no further than 10” apart in either direction. Edges of all strips
should be bolted down and it is recommended that all exposed fabric edges be cemented to keep out moisture.
2. Vulcanized lagging is a sheet of rubber, usually 1/2” thick and bonded directly to the metal. No fabric is used because
no bolt-holding reinforcement is needed. It is much longer wearing, has better and more uniform adhesion to the pulley,
and eliminates the hazard of serious belt damage due to a loose bolt.
This type of lagging can be applied in two different ways:
Spiral-wrap method – generally used for lower tension applications. A 4” wide strip is recommended for ease of handling
(Fig. 31). The length of the strip may be calculated by the formula:
In application by the sheet-wrap method, a beveled lateral splice is recommended (Fig. 32). The tie gum side should contact
the beveled leading edge for maximum adhesion at the splice.
3. Grooved lagging should be used on drive pulleys if they are likely to be wet. The grooves break the film of moisture between
the belt and lagging, thereby eliminating slippage. Either bolted or vulcanized lagging can be furnished with grooves. Either
type can be grooved in the field with a tire-groover if there is sufficient rubber to prevent cutting into the fabric carcass or metal
pulley. Herringbone grooving 3/16” deep and wide spaced 1” apart is recommended (Fig. 33).
4. A modified type of bolted pulley lagging is also available, featuring replaceable rubber pads that slip into metal guides bolted
or welded to the pulley (Fig. 34).
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INSTALLATION, MAINTENANCE & TROUBLESHOOTING GUIDE
i n s t a l l a t i o n
C x W
L = –––––––––––– + C4