Cold vulcanizing can be done on HR Grade belts also. You have to ensure proper vulcanizing adhesives though. ■

First of all air bags are mostly limited by law to 70 N/cm2 (=100 psi) surface pressure in most of the countries because of the danger of explosion. If you forget a little stone on the air bag the result will be like a little bomb! With a fluid (i.e. water) you don't have the same risks. You can operate the water bag with 10 bars (150 psi) for heat resistant belts and 14 bars (200 psi) as required by the belt manufacturers...

Second Air is compressible and water not: it means that water pads will provide not only a good compensation of the bending (=flexion) of the profiles but also will compensate better the tolerance of thickness in the splice area.

Third: the cushion of most of manufacturers of air bag presses can be used for water; it means that it's exactly the same. Consequently there is no real cost differences (the cost for the hydraulic or air pump is also approximately the same).

Fourth the use of mechanical presses with a torque wrench or the use of hydraulic piston presses don't provide any guaranty that the pressure is uniform on all surface. Under the piston the pressure is very high but beside you will not know...And the risks are very high if you have a suddenly leak (it will cut your hand or your leg with 350 bars).

Sixth point: all belt manufacturers are making the belts by hot vulcanizing (not glueing!) with at least 200-400 N/cm2 (285-571 psi) surface pressure. The result is a continously good quality of adhesion of the rubber on the fabric by keeping the needed elasticity all the life time of the belt. This is the best solution today. Consequently the use of glue is only a compromise for normal wear resistant belts. Using 100 psi is also a compromise. Using 200 psi or more is better.

Last point: by using a water bag you can check easily the pressure and the temperature in order to provide the full documentation that the job was done perfectly according to the recommendations of the belt manufacturers: temperature graph of all heating platens; real surface pressure; humidity; time; date; project name; team name etc.

Edgar Jakob

MLT GmbH

www.mlt-deutschland.com ■