As a basic formula you can consider a tension of 5-10N/mm² for insulation mode.
That means for 25mm² product the tension will be max. 250N/mm² which is approx. 25kg.
According attached test they have applied on 25mm² product up to 80kg which is ~800N/mmm². Basically the belt caterpillar is not design for this. There is always a relation between clamping pressure, pulling force and the area of the belt which is in contact with the product. For small products like 25mm² the area of the product which is in contact with the belt is much smaller as for e.g. bigger product 185mm². Therefore with 25mm² the max. pulling tension is limited and the product starts to slip or will break.
For 185mm² the area of the product which is in contact with the belts is bigger and allows more friction than with 25mm².
Therefore we recommend to make this test again with 185mm² or 240mm² product.
If TYE says “unable to pull big size” what is happening? Is the product slipping in the belts?
Are they using class1, class2 or class 5 products?
Please provide us a picture of the used belts? Are they still in good condition?
Are they elongated or spanning still works properly?
The air pressure supply to the machine is with 6 bar for clamping pressure?
Can we get a picture of the product as well?