Roller die

The lining sheet is prepared by calendering in thin plies up to 1 mm in thickness, followed by combining the individual layers on the calender to form a finished sheet, usually between 3 mm and 6 mm thick. Alternatively, lining sheet can be manufactured by the roller die process in which the sheet is extruded and then passed through rollers to give the finished thickness. Extrusion is also used for the preparation of unvulcanised rubber tubes suitable for lining pipes up to 200 mm in diameter. 

Many manufacturers supply extruders with interchangeable heads, which can act as strainers, roller die devices or pelletisers. 

Roller die systems can combine a dump extruder with a two bowl calender to produce good quality sheet for application in such products as conveyor belting. Roller head extruders are more integrated with the calender bowls mounted at the front of the extruder cylinder. 

Friction between the roller, die, and material as well as interparticle friction in the mass to be pelleted are responsible for the pull of feed into the nip region and for densification. Smooth surfaces may result in slip and low interparticle resistance to flow will result in a more or less pronounced tendency of the mass to avoid the squeeze (back-flow), thus reducing densification and potentially choking the machine (see above and Figure 321). While the first problem can... 

Nevertheless, machines with concave die rings and internal press rollers do have advantages. For example, if the feed material exhibits a certain elastic behavior, because the forces in the relatively long and slender nip increase slowly, a more complete conversion of temporary elastic into permanent plastic deformation takes place. Fig. 8.41b is another presentation of the forces at work. Feed, ideally deposited in a uniform layer on the die, is pulled into the space (nip) between roller and die and compressed. Friction between roller, die, and material as well as interparticle friction in the mass are responsible for the pull of the feed into the nip and for densification. Smooth surfaces of roller and/or die may result in slip. Axial grooves in the roller, which may also favor build-up of a thin layer of material, and the above mentioned residual layer of densified feed on the die effectively reduce slip. Low interparticle resistance to flow or a distinct plasticity result in a more or less pronounced tendency of the mass to avoid the squeeze" (back-flow), thus reducing densification and potentially choking the machine (see above). 

A wide variety of hot-stamping equipment is available. Sizes range from hand-held heated roller dies to continuous 4-ft-wide rolls for hot stamping ABS. Eqvupment is also available to do border stamping such as decorating perimeters of rollers or dials, like instrumentation dials. 

The rubber compounds are sheeted to form the bonding and cover layers, using a Berstorff roller die extrusion plant. This is essentially a two-roll calender fed by a flat-die extruder. 

Primary processing is the term applied to the preparation from raw materials of the rubber sheeting, ready for belt building. It comprises the mixing of the rubber compounds and their processing into sheets through the roller-die extruder. 

The strip from the final mill is taken overhead to the feed hopper of the Berstorff roller die extruder. This machine is essentially a 12 in diameter extruder for rubber processing with a slot die at its end feeding directly... 

The development of the Roller Die (roller head) equipment made possible the production of wide thick sheets in a single operation, free from air inclusions and blisters. The extruder feeds a slab of material 30-60 mm thick directly into the calender nip, across the full width. The calendering operation is thus a gauge reduction no rolling bank forms, and the action may be regarded as an extension of the extrusion. The two parts of the plant are very close, the lips of the extruder die reaching deep into the calender nip. A pressure sensor is located in the die-lip, and this controls the calender speed to keep the stock pressure in the die constant. This ensures the matched running of the two halves of the plant. 

Another typical rubber extrusion piece of hardware is the roller die. A schematic representation is shown in Fig. 2.9. 

The roller die (B.F. Goodrich, 1933) is a combination of a standard sheet die and a calender. It allows high throughput by reducing the diehead pressure it reduces air entrapment and provides good gauge control. 

Two-roll sheeter heads (Fig. 5) and roller die sheeter heads. These designs have the advantage of reducing or, at the worst, not increasing the temperature of the mixed material. 

Roller die head (Fig. 6) with contoured head and precision two-roll calender to make accurate sheet. 

Fig. 6. Precision roller die. Fig. 7. Pelletizer. Parrel Bridge Parrel Bridge Ltd, 1987. Ltd, 1987.

The MVX has been used to make hoses with a cross-head, and sheet material with a roller die head. This method is economical when the whole of the output of the MVX can be used. If, for example, small extruder lines with an output of 50-200 kg/h are to be used, then direct compounding would be difficult to justify. But for 400-3 000 kg/h direct compound and product production has proved to be very profitable. 

The positive and negative electrodes of pocket-plate nickel-cadmium batteries are made using the same basic design to hold the active materials. The pocket plates are buUt up of flat pockets of perforated steel strips holding the active materials. The thin steel strips are perforated by hardened steel needles or by a technique using profiled roller dies. The specific hole area is between 15 and 30%. The strips are nickel-plated to prevent iron poisoning of the positive active material. 

Other than this device, the use of the single-screw extruder, fitted with either a roller die, roller sheeter, split-tube die, or rubber pelletiser, is still widespread for masterbatch materials, and the use of two-roll mills is common for finished compoimd. 

Continnons mixing holds ont the promise of efficient and consistent mbber processing. In this article, a new powder blender and a continuous mixer are described, followed by a presentation of results from a prototype system. A layout of the system, equipped with a roller die output device is shown. Two dissimilar compounds, SBRandEPDM, were selected for initial evaluation of the single rotor continuous mixer (SRM). The purpose of the SBR compoimd was to... 

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