Profile roll

Three common methods, which are commonly referred to as roll-crown, roll-crossing, and roll-bending, are employed to compensate for this deformation. Roll-crown indicates that the roll diameter at the center is slightly greater than at the edges. In principle, by applying an appropriate roll diameter and profile, roll deflection can be exactly... 

Sheet extrusion requires a broad die, in which an even distribution of the flowing polymer along its width, and an equal flow resistance at each point, has to be taken care of. Sheets are being extruded up to a width of 3 or 4 m, in thickness up to 3 cm. If desired, sheets can be produced with a wave-shape, by passing the, still plastic, extrudate between two profiled rolls. Film extrusion can be done in a similar way, as a matter of fact with a narrower die gap. After extrusion, sheets and films are cooled in a water bath or on polished cooling rolls. 

A more or less continuous band of compacted material produced in roller presses featuring smooth or shallowly profiled rolls and a gap between those rolls. A method by which a particulate mass is pressed in a stationary die between one moving and one fixed punch. 

Fig. 6.1-6 Di agrams of various arrangements of profiled rolls for roller mills a) peak-to-valley arrangement showing the cracking" of a particle b) parameters determining control of the particle size in a peak-to-valley arrangement c) peak-to-peak arrangement d) example of a peak-to-valley arrangement with modified pitch and gap (courtesy Modern Process Equipment, Inc. (MPE), Chicago, IL, USA)...

Roll Crushers. Traditional roll cmshers effect size reduction by crushing single particles between two counterrotating rolls hence they are cmshed between the two surfaces. The rolls can either be smooth or profiled to aid feeding of coarser materials. Figure 6 shows a particle of diameter x being reduced between two rolls of diameter D. For smooth rolls D/x > 17 is usually selected, whereas for profiled rolls this can be varied to D/x < 10. The feed size-to-gap width ratio is essentially limited to approximately 4. 

Adhesives, automotive, bridge bearing pads, cable jackets, cellular products, coated fabrics, conveyor belts, footwear, hose, power transmission belts, profiles, roll covers, sheeting, and tank lining. 

In the press section the individual rolls are hard or soft covered. The press nip (Fig. 6.7) is created either by two profiled rolls or by a combination of one profiled and one plain roll. Covers with high open surface area, similar to tyre technology, offer the necessary storage capacity for the water squeezed out in the press nip. The various surface designs include grooves, blind drilled holes or suction holes as well as combinations of these. 

Roll mills are employed in a wide variety of applications for medium-coarse down to fine size reduction. By far the most prevalent use is in flour milling where banks of roU mills, beginning with coarse profiles and ending with smooth roUs, are used in series with sifting machines to extract the white flour from the associated bran. 

Calendering can achieve surprising accuracy on the thickness of a sheet. Typically the tolerance is 0.005 mm but to achieve this it is essential to have very close control over roll temperatures, speeds and proximity. In addition, the dimensions of the rolls must be very precise. The production of the rolls is akin to the manufacture of an injection moulding tool in the sense that very high machining skills are required. The particular features of a calender roll are a uniform specified surface finish, minimal eccentricity and a special barrel profile ( crown ) to compensate for roll deflection under the very high presurres developed between the rolls. 

If the clearance between the rolls is small in relation to their radius then at any section x the problem may be analysed as the flow between parallel plates at a distance h apart. The velocity profile at any section is thus made up of a drag flow component and a pressure flow component. 

The roller chain uses a steel roller to engage the sprocket. The rolling action between the roller and the profile of the sprocket teeth causes the roller to rotate on a bushing, creating less friction than the traditional belt drives. There is some axial sliding action between the roller and bushing. 

Flexible polyethylene separators have facilitated a novel cell construction the separator material, supplied in roll form, is wound so that it meanders around electrodes of alternating polarity (Fig. 23), requiring ribs in the cross-machine direction such profiles are available commercially [60],... 

A mixture of powdered poly(vinyl chloride), cyclohexanone as solvent, silica, and water is extruded and rolled in a calender into a profiled separator material. The solvent is extracted by hot water, which is evaporated in an oven, and a semiflexible, microporous sheet of very high porosity ( 70 percent) is formed [19]. Further developments up to the 75 percent porosity have been reported [85,86], but these materials suffer increasingly from brittleness. The high porosity results in excellent values for acid displacement and electrical resistance. For profiles, the usual vertical or diagonal ribs on the positive side, and as an option low ribs on the negative side, are available [86],... 

The calender was developed over a century ago to produce natural rubber products. With the developments of TPs, these multimillion dollar extremely heavy calender lines started using TPs and more recently process principally much more TP materials. The calender consists essentially of a system of large diameter heated precision rolls whose function is to convert high viscosity plastic melt into film, sheet, or coating substrates. The equipment can be arranged in a number of ways with different combinations available to provide different specific advantages to meet different product requirements. Automatic web-thickness profile process control is used via computer, microprocessor control. 

Fig. 2.8.8 (a) Implementation of four-roll mill device, (b) Speed image obtained across a horizontal slice by combining separate x- and y-velocity images, (c) Velocity profile taken across the x-axis of the cell showing the uniform extensional strain rate 8, such that x= ex (adapted from Ref. 15]). 

---