Roll formation

Wear by roll formation is where there is progressive tearing of a layer of rubber which forms a roll. The result is a characteristic abrasion pattern of ridges and grooves at right angles to the direction of movement. The term erosive wear can be applied to the action of particles conveyed in a liquid stream and there can also be corrosive wear due to direct chemical attack of the surface. 

In recent experiments, the application of stress orthogonally to a shearing surface caused a ductile failure of brittle polymer (5, 6). In the first series (5), a variety of plastomers and elastomers were made to slide one on the surface of another, at a constant velocity of 215 cm/sec, under increasing normal loads. The wear characteristics of polymers, including several brittle ones such as PMMA and PS, depend on the applied normal stress. At relatively low pressure, almost no wear was observable, even under magnification the little observed was apparently brittle, ill-defined, microparticulate debris. At intermediate normal loads, 3 to 20 kg/cm2, roll formation was the dominant mode of wear. Such rolls appear on the surfaces of all uncrosslinked polymers whose Tg is below the test temperature and on amorphous and semicrystalline polymers whose Tg is above... 

Case G planar alignment, 6 < 0 o-q < 0. Standard EC (based on the CH mechanism) cannot occur for the material parameter combination e < 0, da < 0 [2] except the a induced" pattern type. Nevertheless, convection associated with roll formation has been observed in ac electric field in the homologous series of N-(p-n-alkoxybenzylidene)-n-alkylanilines, di-n-4-4 -alkyloxyazoxybenzenes and 4-n-alkyloxy-phenyl-4-n alkyloxy-benzoates [52-54]. The characteristics of the patterns the orientation of the rolls, contrast, frequency dependence of the wavevector and the threshold, director variation in space and time etc. - are substantially different from those observed in the standard EC. Since this roll formation process falls outside of the frame of the standard model, it has been called nonstandard electroconvection (ns-EC). 

Fully rotating nips with the winder attached are used for HMW-HDPE film because they result in better roll formation for the very low gauge film. If these are used with upward extrusion, it requires dealing with roll handling on the second story. If extrusion is downward, roll handling is easier, but extrusion is complicated. 

Disperse dyes can also be applied indirectly as a transfer from paper that has been printed with the pattern using an ink jet printer charged with the disperse dye. A heat press, available in various flatbed or roll-to-roll formats, is aptly named, applying both heat and pressure to a substrate. This method fixes or cures the ink as part of the... 

One of the featmes of tnbnlar film process is the roll formation obtained. It is common to rotate the tnhe or collapsing frame. This will distrihnte caliper variations in the film across the woimd np roll. Soft areas and hard hands may he eUminated in the output roll with this process. This process requires low labor content as compared to larger fiat film fines. As all the film is imiformly stretched, the yield of this process may he very high. 

The mechanisms by which wear of rubber occurs when it is in moving contact with another material are complex but the principle factors involved are cutting and fatigue. It is possible to categorise wear mechanisms in various ways and commonly distinction is made between abrasive wear, fatigue wear and adhesive wear. Additionally, wear by roll formation is sometimes considered as a separate mechanism. There can also be corrosive wear due to direct chemical attack on the surface and the term erosive wear is sometimes used for the action of particles in a liquid stream. 

Polymer wear is not well understood and may be divided into abrasion, fatigue and roll formation. The effects of fracture surface energy and tearing energy instead of surface free energy on polymer wear are discussed. Surface free energy appears to influence only the polymer transfer. 

Originally, rol1-formation was proposed by Reznikovskii and Brodskii to be limited to high elastic materials. New evidence shows that sliding friction of polymers with varying degrees of ductivity can also undergo roll formation. Furthermore, polymers usually considered to be brittle at room temperature can be ductile under load (20 to 30 Kg/cm ) about 80° under their Tg s. 

Multi-period problems are usually solved in a rolling format whereby the model is solved at the begiiming of each period. For instance, at the end of the first period, the model is moved forward and the second period becomes the first period and so on. Interaction among the periods is obtained by using an inventory decision variable. For example, a buyer buys Pf units in a period t and let I, and D, be the inventory left at the end of period t and the demand in period t, respectively, then the material balance constraint for period t is... 

Roll Formation. On smooth surfaces, a third mechanism of wear specific to highly elastic and soft materials has been observed to cause the formation of rolled shreds at the sliding interface, and eventual tearing of the rolled fragment. 

---