Re: Cover/Ply Adhesion Deterioration
Did you check the interface between the cover stocks and internal interply gum? Typically, there are three interfaces:
1. cover to outer gum of top and bottom ply - loss of bond strength between cover and internal gum.
2. interface of fabric to gum on all faces - delamination from fabric
3. internal gum strength between fabric layers - shear failure of gum rubber
It seems that you have point 1 failure which is probably heat related. The cover to gum bond is being destroyed by heat. ■
Cover/Ply Adhesion Deterioration
Matt,
You might consider carcass gauge and modulus as a contributor to the adhesion drop off.
Most imported belts, out of Europe particularly, have quite high modulus and this is often promoted as an advantage.
To a degree this can be true but when taken too far there is certainly a downside.
Additionally the belts can have heavy skims. In fact your spec demands them.
This combination is not necessarily great in a high flex situation when pulley diameters are at or around minimum recommended.
Increased modulus will increase shear forces during flexing and the relative movement of plys will be greatest in the splice area where there is a discontinuity within the plys and perhaps a degree of vertical misalignment.
Ultimately you can get splice failure, delamination, loss of both adhesive strength and carcass tensile.
We have seen this in the underground coal industry and when you add the affects of heat to the mix, which reduces the ability of the rubber components in the belt absorb these forces, the effect on the fabric/rubber interfaces is increased. ■
Splice Failure
Dear matt
It appears you are carrying hot sinter having temperature more than 180 degree on belt conveyor.
Splicing gum compounds are generally not suitable for temperature more than 200 degree centigrade. Kindly checkup from splice gum compound manufacturer about suitablity of their coumpound for material temperature you are using
A R SINGH ■
Re: Cover/Ply Adhesion Deterioration
Matt,
Are these results in the splice area or in the parent belt. If it is in the splice area it suggests that there is an incompatibility factor with the cements being used as far as the cover componds are concerned. If it is in the parent belt then what Graemme Vickery says has some validity as there is some flexing mechanism or worse, aging mechanism causing a deterioration in the belt. The results are unusual given the drop off in both the top and bottom cover to ply adhesions as logically one surface should generally be in compression during the belt cycle while the other should be in compression and this makes it difficult to see how skim coats and high modulus could be a factor. Has your supplier got a theory or explanation for such unusal results?
Col Benjamin ■
Cover/Ply Adhesion Deterioration
Previously on this forum I raised an issue of a repeated splice failure and the influence of carrying overly hot material. I was also toying with the thought that possibly the action of being reverse bent through the GTU (on such a short belt) combined with the heat was fatiguing the splice.
I sent the splice back to the manufacture in order to see how certain test results faired when compared to the original belt certificate.
The tensile strength of the cover rubber dropped very slightly, the carry cover elongation dropped about 8% with the pulley cover unchanged, the cover rubber hardened by about 10%. These results are expected as when subjected to high temperatures, rubber gradually hardens and loses its elasticity.
The suprise came in the adhesion tests. (belt is 5 plies)
-Carry cover/1st ply. Original belt=11.3kN/m, After it had been in service =3.7kN/m and 2.2kN/m (2 samples)
-Pulley cover/5th ply Original belt=5.3kN/m After it had been in service =1.5kN/m
-The ply to ply values of adhesion did not deteriorate.
AS1332 (Australian Standard on Textile Reinforced Conveyor Belt) specifies that minimum values of Cover to ply adhesion shall be at least 4.3kN/m. Our company's supply spec increases this to 5.3kN/m for the carry cover to 1st ply. These figures are for new belt but the deterioration did concern me.
The logic of the deterioration being heat related is flawed as the pulley cover/ply value was affected but not the ply/ply values.
Any comments? ■