Steel Breaker Vs. Fabric Breaker
Synthetic fabric breakers, as is the case of a leno weave with large polyamide weft yarns, are more effective in resisting longitudinal rips and impact damage than are steel wefts. They are more effective for the reasons you expressed, i.e. higher elongation at break, lower modulus and the tendancy to bunch together. Due to the relatively larger diameter of the polyamide wefts and their shape vs. steel, they also do a more effective job of resisting the penetrations which lead to rips. The position of the fabric breaker in the belt cover further enhances its performance. Typically, steel wefts rest directly on the belt cords, while the nylon wefts are separated from the cord plane by a rubber layer. Steel wefts may, therefore, abrade the belt cords or nick them when the belt is impacted. The nylon wefts can do neither and their surrounding rubber allows for energy dispersion/dilution when an object tries to distort the weft. When splicing a belt, it's much simpler and easier on the mechanic's tools to prepare a belt end with a fabric breaker than with a steel breaker. Fabric breakers, of the type described, have less affect on the belt troughability than do steel wefts. In operation, parameters such as transition distancesand convex curve radii are, in general, unaffected. Of course, if high transverse rigidity is required or a high belt weight to resist lifting in a tight radius concave curve, steel wefts may be a solution. Given a choice generally, transverse nylon cord breakers are our preferred protection for steel cord belting. ■
Steek Breaker Vs. Fabric Breaker
Having read the various comments regarding rip and impact resistance we agree with the position that a low stretch bekaert steel cord is not a resilient as a heavy duty nylon cord construction.
We do however not agree with the concept of nylon breakers being preferable to the proprietary SFBT Sempertrans (ex-Michelin) high stretch steel cord breaker.
Unlike the fleximat cords, it has 3.25% stretch at 10% of its tensile (similar to nylon) and a 1.6mm diameter. This makes it very shock absorbant and capable of bunching up when placed at a pitch of 8mm or less.
As mentioned by Peter Alderson the fleximat transverse steelcord lies against the longitudinal cords and can result inboth abrasion and fretting corrosions, whereas the SFBT transverse steelcords are produced in a calendared layer with rubber surrounding them. This is placed on top of the rubberized longitudinal cords in one, two or even three layers to create termendous impact resistance and excellent puncture resistance and rip resistance.
The superior rubber to steel adhesions also offer better resistance to the risk of delamination.
With regards to impact resistnce, a "double-density" two layer Metalcord version has currently been operating over three years accepting lumps of copper ore (160PCF) 24" x 24" x 48" (610mm x 610mm x 1219mm) dropping over 10 feet directly onto the belt.
From the point of view of troughability, we have successfully used two transverse layers of the steel cords in a 30" wide belt troughing 35 degrees in northern Quebec.
The transverse cord construction on its own has no affect on transition distance, pulley diameters, or vertical-horizontal curves.
The longitudinal cords, unlike conventional steelcords are not dependent upon size (especially diameter) for load support and impact resistance because tansverse forces are absorbed by the transverse cords, not the rubber surrounding the longitudinal cords. The result is an ability to use 3mm cords placed closely together to further increase flexibility around pulleys and reduce the chances of punctures.
Mechelin technology also provided SFBT Sempertrans with the ability to provide E-type 7x7 longitudinal cords with similar modulus to conventional cords (0.2% stretch) as well as M-type 4x7 longitudinal cords of very low modulus with 0.6% stretch capable of replacing fabric belts, accept shorter transitions, tighter curves, and accept crowned pulleys.
We have sold this product for thirty years and can attest to its unique abilities.
To see a picture of Metalcord follow this link:
http://www.afmindustries.com/product...alcordjpg.jpg
Best regards,
Bob Butterworth ■
Steel Breaker vs. Fabric Breaker
Use of a suitable breaker fabric, to resist longitudinal rip as well as to absorb operating impact loads, has been mooted for a particular steel cord belt conveyor application.
The options available are -
1. A synthetic fabric breaker with high elongation weft members intertwined in warp cords AND
2. A steel breaker, without any warp - only weft members
I tend to believe that a synthetic fabric breaker should be more effective - one because of its tendency to elongate more and thereby provide increased cutting resistance by "bunching" of weft members and two because of its greater impact absorption ability as a result of a higher elongation at break. I also understand that internationally, a fabric breaker is usally employed.
I would appreciate some advice on this choice, particularly from some one with actual experience of using steel breakers (or synthetic breakers).
I would also like to know any theoretical basis for making a choice between these alternatives. Is there any specific operating parameter - like transition distances, convex curve radii etc. - which I need to consider carefully before opting for one or the other ?
Thanks, in advance, for your responses. ■