Have you ever wondered the difference between Rexline EP (PN) vs Standard Imported Conveyor Belt EE (PP) Fabric ? Finally, Rexline engineering makes the cut. Rexline EP Fabric is a Polyester/Polyamide (Nylon) fabric where the Polyester is in the longitudinal (wrap) direction and the Polyamide (Nylon) in the across (weft) direction.
Standard Imported Conveyor Belt EE Fabric is a fabric which is in both directions Polyester used in the fabric. Longitudinal and across (wrap and weft) direction.
Both fabrics are widely used as a filament for a conveyor belt carcass. A carcass is the tensile member in the conveyor and takes the tension which is required to set the conveyor through the pulleys in motion. Also, the carcass absorbs the impact at the loading point. In other words, a conveyor belt without carcass would stretch endless and would be punched from the goods immediately.
Fact: Polyester has less permanent and elastic elongation compared to Polyamide (Nylon). From a tensile strength point of view, both fibres are roughly equal.
The first loading and the cycle loading elongation differs on Polyester a lot more compared to Polyamide (Nylon), which stretches and relaxes at a higher rate.
Definition: When wrap and weft yarn interlace in fabric, they follow a wavy path. This waviness of yarn is called crimp and ultimately forms part of an elastic stretch pattern.
The crimp has a very important role on multiply conveyor belts. When a conveyor belt turns around a pulley, the outer plies describe a longer way due to the larger radius. It is mostly the crimp which swallows these different stretches of the plies. Higher elongation of Polyamide allows a PP (or NN) carcass for a smaller Pulley diameter compared to a Polyester carcass.
The green yarn represents the longitudinal or wrap yarn. The red yard represents the across or weft yarn.
As a rough guideline, 1/3 of crimp is stretched through the counterweight. The other 2/3 are required for pulley turn around and to absorb impact.
Crimp in wrap or longitudinal direction
Crimp in waft or across direction
The impact at the loading point is to almost 100% absorbed by the carcass member. The rubber cover must be seen as a wear carrier only. The impact resistance is determined by the tensile strength and elasticity of the fibres and by the weave type and direction (fabric belts only). The fact that there is no (or very less) crimp wave in the across direction means that the impact must be absorbed by the strength and elongation of the fibre in weft direction only and not being supported by stretch elongation of the crimp. Especially a high elastic elongation feature in the fibre can absorb impact over a long period of time with less fatigue. An overloaded impact onto the carcass will on a Polyester/Polyester carcass always result in a weft fabric break first due to the same stretch but less crimp within both fibres. The Polyamide fibre with the higher elongation and elastic stretch within the fibre itself will counteract the stretch loss of the non (or very little) existence of the crimp in the weft direction and will be able to resist higher impact without a break, swallowed due to the higher elongation within the fibre.
Belt capacity is determined by belt width, belt speed and belt trough. A larger trough angle (up to 45 degree) provides maximum belt loading capacity and improves the efficiency of a conveyor system. When a conveyor is forced into a trough at the carrying side, the plies near the bottom covers are stretched at the flat to trough transition (tail pulley) and stay stretched until the trough to flat transition relaxes the belt again (head Pulley). The thicker the carcass, the more stretch the outermost ply must absorb to resist the bend. Polyamide with the ability to stretch further than Polyester has a clear benefit by this means and again no (or very little) crimp to support this constant motion. Improved troughability distinguishes a feature from Rexline EP vs Standard Imported Conveyor Belt EE fabric belts.
In my mind Rexline EP belts have from a technical perspective clear advantages compared to Standard Imported Conveyor Belt EE fabric belts. The thicker the carcass and the heavier the impact the bigger the difference between a Standard Imported Conveyor Belt EE Fabric and Rexline EP belt. In other words, the difference between a Rexline EP320/2 and a Standard Imported Conveyor Belt Fabric EE320/2 is rather marginal, while the difference on a Rexline EP1250/5 to a Standard Imported Conveyor Belt Fabric EE1250/5 is quite significant in the longevity of the conveyor.
Rexline EP belts also have advantages on heat resistance conveyors due to an improved bonding, but this issue is not elucidated in this writ.