Hello Wahid Hamza,

Lagging choice depends on the application.

The current favorite rubber lagging profile is the diamond pattern (sometimes called double chevron).

The primary reasons for using lagging include:

[1] Increased coefficient of friction to provide a better transfer of drive force to the belt (i.e. lowers the chance of belt slippage on the drive pulley/pulleys). This reason only applies to the drive pulleys.

[2] Exit path for water & fines that get between the belt and pulley. This reason applies to drive, bend, take-up, and tail pulleys.

There are secondary reasons for using rubber lagging, such as cushioning, sacrificial wear media, etc.

Some users prefer to use transverse grooves over the chevron and diamond patterns. And some prefer to use non-grooved lagging to get the maximum coefficient of friction advantage. Using dimpled lagging or ceramic lagging with dimples is done to provide a mechanical lock with the bottom cover of the belt (i.e. the dimples are forced into the bottom cover to provide a positive lock between the pilley and belt - works well unless the pulley spins agains the belt).

As far as wear without lagging is concerned, if you do not have belt slippage against the pulley, you will not have wear. If you have slippage, the pulley can burn through the belt - the purpose of the lagging is to reduce/eliminate the slippage.

grooved lagging will help to prevent belt mistraining that is caused by hydroplaning. Except for the ability of grooved lagging to remove water from the belt/pulley interface, properly applied lagging will not prevent or cause belt mistraining. However, if lagging is allowed to wear unevenly or to accumulate material, it can make belt tracking worse - the same as an unlagged pulley.

Regards, ■

A couple of added points on lagging:

1. All pulleys suffer shell (rim) wear:

a) without lagging the steel shell wears at a rate depending on belt tension and by degree dependent on whether in contact with carry side and degree of abrasive material;

b) with rubber lagging the lagging becomes the sacrificial wear material and also does wear proportional, in degrees, for the reasons given above.

c) all pulleys suffer abrasive wear due to differential speed of belt wrt pulley surface. There are numerous publications and field notes of lagging and steel shell wear on non-driven pulleys. See publications of Zeddes and Hohman from their Dr. dissertations.

In essence, non driven lagging/shell have zero shear stress in contact between pulley and shell at 90 degrees from entry or exit of belt contact, say 3 o'clock, assuming 180 degree horizontal wrap angle. As the belt is observed leaving the zero shear stress state, at 3 o'clock, shear stress increases as the belt tension member deflects its cover, in contact with pulley and the pulleys lagging, in the direction of tension member vector. The deflection reaches a maximum just before losing contact between belt and pulley ( 12 and 6 o'clock). The belt must slip as shear stress is released and laging is worn. Lagging wear is exacerbated around idler transitions. This condition is one reason modern mines use ceramic lagging on non-driven pulleys.

2. Beware on type of ceramic. Some ceramics tear off belt covers. If you begin to lose belt cover, you can say good-bye to the belt within a few years. The wedge effect generated will destroy both lagging and belt covers no matter how they are configured.

3. Beware of grooving patterns and wear. As wear increases, and groove depth is not maintained, the shear and compression defections can negate water channels, and hydroplaning can result.

4. Lorign (sic) patented a special circumferential groove pattern that had a slight lead angle with opposing fleet angles that met in the center. This pattern enhanced belt tracking. Have not seen much of it lately.

Regards,



Lawrence Nordell

Conveyor Dynamic, Inc.

www.conveyor-dynamics.com ■

Dear Wahid Hamza,

Earlier respondents have already given detailed information. I would like to add that :

Rubber lagging is also used when handling material, which tends to stick. The rubber lagging, being flexible surface, changing its shape under pressure, it is resistant to material build-up i.e. it is self-cleaning type.

Rubber lagging is also necessary when handling certain kinds of corrosive materials.

The widely used rubber lagging patterns are (1) Herringbone grooved. It is belt direction specific (2) Diamond grooved. It is not specific to belt direction, i.e. it can suit reversible running of belt (3) Plain type. Number 1 and 2 are mostly used for drive pulley. Number 3 is mostly for non drive pulleys. However, these are generally used lagging patterns but there can be many variants i.e. one can only use grooved lagging for non-drive pulleys.

If the material is non-abrasive or mildly abrasive, one may not use rubber lagging on non-drive pulleys. However, if the material is abrasive or very abrasive, then it is better to use rubber lagging as it will protect the pulley assembly from periphery wear i.e. it will need replacement of only the rubber lagging rather than the whole pulley.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■