In CEMA#5 table7-4 there is information and suggestion about top cover thickness.There, according to class of material(fine,heavy...) a range of cover thickness has been suggested. ■

Belting is the most expensive item in conveying and the amount of rubber in the covers should be minimised to match the life expectancy of the belt. Breaker layers and compound mix are irrelevant/excluded. Rubber wears down and when it has reached the limit it gets thrown out. Ideally, the belt life should be an equal dividend of the designed plant life. If the plant life extends beyond its design it doesn't matter: the operator is saving CAPEX somewhere. As a first step you can adopt CEMA recommendations for your perceived duty. Centre distance and loading frequency/severity play an important part. Top and bottom covers need to have the same life.

There are many discussions on these forums for reference and also reading manufacturers' handbooks will give further insights. ■

There is (was?) guidance in DIN 22101.

Regards,

Lyle ■

Originally Posted by johngateley

.....Rubber wears down and when it has reached the limit it gets thrown out. ......Top and bottom covers need to have the same life. .......

Dear Mr.John and all ,

Many times, I get the recommendations from my maintenance subordinates and compulsions from operation engineers as soon as the belt becomes thin.

But I take replacement of conveyor belts only after the top cover is worn out and first ply becomes visible. I love taking "calculated risks". :-)

Interested to know the replacement strategy in your plants.



As far as I know, usually top cover worn out faster than bottom cover, as it is subjected to impact. Same life of both covers is not seen, though

top cover thickness is greater than that of bottom cover.

For the discussion purpose, kindly assume that we are talking about wear resistant belts.



Thanks & Many regards to all,

S.Ganesh ■

What I should have said was 'both covers should ideally have the same life.' Thickness increments are usually one millimeter which gives at least half a millimeter leeway. I've only just realised that by the way: but its true. Suppose you have 3mm bottom cover and the higher wearing top cover has 12mm. If the 3mm wears out faster then 3.5mm might have been better to give more life before the top cover gets thrown out with the rest of it. So with 1mm increments we are always throwing out 0.5 mm on either cover. Is it worth worrying about when a detached liner can sling 2 slitted nearly new belts into touch without blinking an eye? ■

There are many factors that influence top and bottom belt cover thickness:

1. Top cover selected for wear life (abrasion, gouging; temperature environment) based on rock properties, chute design that defines impact and shear, and product temperature.

2. Bottom cover selection has many properties to consider based on belt construction ( steel cord vs. fabric carcass). For steel cord belts, the minimum cover gauge often sited must be > 70% of cord diameter to resist shear stress of cord pulling through bottom cover. This is somewhat a urban myth. Studies have been performed with pulleys of varying diameters and belt tensions to find the bottom cover threshold. Not so easy as 70%. Belt rubber fatigue under cord is dependent on many parameters including pulley diameter, cord diameter, belt tension, belt safety factor, ambient temperature, type of belt construction ( trough or pipe) and internal reinforcements, type of idler shape, spacing, and roll diameter, clean or dirty side belt contact, snub, bend or drive pulley and idler transition arrangement, ......

The above are a few of the design parameters that governs belt cover selection. How this is done is beyond a few words. ■