Blistering can be caused from moisture in the carcass boiling during the vulcanizing process.

Ensure that the carcass in the splice area is dry before splicing. ■

Air pockets may start out as blisters that may not be noticeable until after the sytem has run for a while. That air in the blister cannot escape and as it is compressed and moves around over time the blister now forms into a pocket. ■

Originally Posted by sganesh

Thanks a lot Mr.Gary Blenkhorn,

I feel blistering is very small in size. I do not encounter blisters.

It is AIR POCKET. It starts very small. During every turn around various pulleys, the pocket size increases because of compression of air in the air pocket. The bonding between top & bottom ends at the splice area fails.We pull on for some time, by providing mechanical belt fasteners.

I do preheating only during monsoon time or if the ply surface is damp. Do preheating is always necessary ? What are all the prerequisites for the preheating?

Thanks & Regards,

If when you do the repair, the blister/air pocket is at a ply boundary, then it is associated with the splicing operation.

Moisture is the main cause of this. A single drop of water expands many times in volume when it vapourises. Once the plies separate, the bubble will remain and grow.

Pre-heating is good, however you still have to drive off the moisture. The hotter the air, the more water vapour it can hold, and so any trapped air (no matter how small) will cause problems.

Contact your belt supplier and see if they have an additive that can be used during the vulcanising process to absorb any moisture.

Apart from moisture, the other issue is just an incomplete joint. You may need to check the vulcanising platters to make sure that there is not a "cold" spot that is causing an incomplete splice.

I worked with an engineer who used to work for Goodyear. He said that the majority of tread separation issues were caused by sweat dropping from the operator laying up the tread onto the tread. No matter how well they wiped the sweat off, those tyres would eventually fail through tread separation. ■

Dear Mr Ganesh,

-Pls check if the splicing materials used are of good grades.

- pls check the actual temperature using some kind of pyrometer.. may be there is uneven heat transfer on the belt joints.

- If its a steel cord belt,, then the splicing kit should also be inspected.

We from M/s Thejo Engineering are experts in belt splicing, and pulley lagging. please feel free to write to me,, at michael.r@thejo-engg.com and if in case you have your site in India-- then i shall depute my expert , to check the splice. ■

I have come in a bit late but the problem is caused by either of two failures;

> Not controlling the humidity when the splice was being done such that when the cement was partially drying after being applied to the fabric plies there was moisture condensation on the cement surface. When the vulcaniser was turned on this moisture turned to steam hence the bubble. Eventually unless these bubbles are effectively vented they will travel the full length of the belt and destroy the belt not just the splice. The solution is using heat lamps while splicing to keep the humidity using a wet bulb thermometer at less than 40%

> Closing the splice too quickly with patches of cement that is still wet i.e. not enough drying time. This usually occurs where the ply joins are as the splicers should be applying more cement in this area. End result is the same but usually not as bad as above unless the splicers have been very incompetent. In this case the solution is once again to vent the bubble.

More likely it is the first case

Cheers

Colin Benjamin

Gulf Conveyor Systems Pty Ltd

colin.benjamin@gcsm.com.au

www.conveyorsystemstechnology.com ■