Dear Shane,

Traditionnally belt manufacturers use very heavy high presure press with up to 50 bar/cm2 for producing the rubber belts because it is more economical (the vulcanising time is shorter) and it provide a constant quality (i.e. no bending of the traverses).

If you use the same pressures and temperatures for the splice is it possible to reach a better adhesion and penetration of the rubber in the fabrics. So it will be possible to improve the fatique characteristic of the splice, even with steel cord belts.

The difficulty is that conventionnal field vulcanizing presses must be as light as possible in order to transport them easily: for more than 15 bar and 180 °C the press will be to heavy !

Edgar Jakob

MLT GmbH ■

I have done numerous tests with various textile belts using specified techniques and splice materials in the last ten years.The results have been what should have been expected and at one occasion startling to say the least. One Manufacturer who recommended 90-100 psi showed the best results at 75 psi and tested samples at 100 psi suffered by as much as 15% in strength loss. It would be very advisable to do some controlled testing before hand with various pressures (if you have the capability to work up to the 185 - 200 psi range) other important factors like belt tension. Pulley sizes, impact and so on and so forth should be considered as well. If 25 pounds of adhesion in the splice will give you full life of a splice related to belt life is it cost effective to buy equipment to allow you to cure at higher pressures? I would also add that cure temperatures and times are of utmost importance and go hand in hand with pressure requirements. Some splicing materials will do a much better job (pressure remaining the same of course) when cured at a lower temperature for a longer period of time.

We must also take into account what heat does to synthetic fabrics and to what degree they are hardened during the curing process (reduction in flexibility, shrinkage and reduced adhesion values.) One must also remember that each time a dip treatment is re heated (after factory curing of the belt) the adhesion is reduced to some extent. I have found when it is possible to cure at a lower temperature for a longer time the above factors are somewhat less paramount. As with most things application is important. Honestly there is no right or wrong answer (testing is very important in my mind) If the workmanship in the splice is crap the splice is crap that is the long and short of it. In splicing you do get what you pay for. Ultimately you are paying for Service professionalism and experience. High pressure will not compensate for poor materials or shoddy workmanship

Best Regards

D W Davis ■

Hi Shane

Are you talking about Steel or Fabric splicing or both. ■

Hi Shane

I haven’t had much to do with Imas belting so I’m unsure of the specs, generally there will be a variation of about 50 psi on Steel cord, this is just the minimum – maximum.

Steel – 150 psi to 200 psi [ Dependent on Vulcaniser Rating and ST Rating ]

Most manufacturers like to see around 180 psi where possible.

As you know, Fabric is generally 100 psi, which most Fabric vulcanisers are designed to do.

However if the vulcaniser is rated higher and the belt has a high rating, used on heavy duty system or if there’s a problem with splices, I would recommend increasing the pressure to 125 – 150 psi for reasons outlined in previous posts.

Please note: At that rating a Steelcord press/ bars would be required.

In regard to “the splice to push apart slightly creating gaps on the step lines” .

I believe in most cases the gaps will be due to fabric shrinkage more than being pushed apart, the amount of gap will vary from manufacturer, fabric rating, type, age etc.

Generally a 10 mm strip of 1 - 1.5 mm tie gum on the step line will take up the void.

If the splice is spreading, check that there is suitable vulcaniser overhang past the splice area, this should hold the belt ends in place during the cure.

I believe the standard for fabric is around 200 mm, 100 mm each end, again increasing this to 300 mm won’t do any harm.

Incremental build up of pressure versus temperature during the heating cycle is also good practice.

By the way, what are the Imas specs. ? ■

vulcanizer ■