Rubber extruders

The hot-feed rubber extruder is usually characterised by a relatively large screw depth and a relatively short L/D ratio of the barrel of 3 to 8 1 with the greatest number of machines having a ratio of 4 1. The barrel comprises usually a cast iron outer with either a traditional replaceable nitride liner, or, in the case of one manufacturer, of a single piece construction with an integral cast liner which has a surface hardness of Rockwell C60-62 and a hardness depth of 1.5 mm. The functional life for the bimetallic barrels is longer than for conventional nitride liner systems. 

In the production of fine rubber sheets or coated rubber sheets, the main equipment used is a calendering machine. Though rubber extruding machines which are later developments are used for manufacturing some sheet profiles, the calendering machines are the ones used widely in the rubber industry for the manufacture of rubber and coated rubber sheets. Calenders are conveniently used for the continuous production of rubber sheets from different types of rubbers. 

The extruders used for rubber do not require the length of those used for plastics, because they do not need as long a melting section as plastics do. When the plastics industry adopted the rubber machinery, it imitated the rubber extruder design, but as demands for output and quality mounted, the length-to-diameter ratio of the extruder grew over time, until it leveled off at current values. 

In 2004, Berstorff introduced a combined rubber extruder/gear pump, patent pending, for the production of dynamically cross-linked vulcanized thermoplastic elastomers (TPE-V) (DE 101340701 Al). A short rubber extruder, with a gear pump connected downstream,... 

Figure 4.38 Berstorff s combined rubber extruder/gear pump [231...

ANs are those that contain a majority of nitrile polymers. They provide good gas barrier, chemical resistance, and low taste and odor transfer with good impact properties when modified with rubber. Extruded sheet is used extensively in food packaging and rigid packaging applications. This crystalline TP is most useful in copolymers. Its copolymer with butadiene is nitrile rubber. Acrylonitrile-butadiene copolymers with styrene (SAN) exist that are tougher than PS. It is also used as a synthetic fiber and as a chemical intermediate. 

The above considerations explain why with the short dies of industrial practice, rubber extrudates frequently exhibit swelling variations which are actually compensated for by adjusting the takeaway conveyor speed. This is however not always satisfactory and the results presented here suggest that a suitable design of the entrance geometry could reduce post-extrusion swelling variations. 

The process is usually carried out by heating the rubber, mixed with vulcanizing agents, in a mold under pressure. We note that, for extruded rubber goods, the compounded rubber extrudate can be heated in a salt bath or even in hot air. 

Many of the components of a tire, such as tread, sidewall, and apex, are formed by extrusion of the uncured or green rubber. Extruders in a tire manufacturing operation are conventional screw-type systems that fall into two categories ... 

Screw extruders were first introduced into the rubber industry in the late 19th century by Francis Shaw, John Royle, and Paul Troester and became the basis of the machinery companies they created (Fig. 22). The original rubber extruders were hot-feed screw extruders, for which strips of rubber compound preheated on a two-roll mill were added to the extruder. The screws had deep channels and short length/diameter ratios. 

EPDM rubber sheet can also he made using the hot or cold feed rubber extruder machine of 20-30 cm screw diameter. For a hot feed machine the L/D ratio of the screw should be 5 1 and for the cold feed extruder 20 1. 

The first rubber extruders were built for hot feed extrusion. These machines are fed with warm material from a mill or other mixing device. Around 1950, machines were developed for cold feed extrusion. The advantages of cold feed extruders are thought to be ... 

However, there is no general agreement on this issue. As a result, hot feed rubber extruders are still in use today. 

Cold feed rubber extruders, nowadays, do not differ too much from thermoplastic extruders. Some of the differences are ... 

Rubber extruders used to be heated quite frequently with steam because of the relatively low extrusion temperatures. Today, many rubber extruders are heated like thermoplastic extruders with electrical heater bands clamped around the barrel. Oil heating is also used on rubber extruders and the circulating oil system can be used to cool the rubber. Many rubber extruders use water cooling because it allows effective heat transfer. 

The feed section of the rubber extruders has to be designed specifically to the feed stock characteristics of the material. The extruder may be fed with either strips, chunks, or pellets. If the extruder is fed from an internal mixer (e.g., Banbury, Shaw, etc.), a power-operated ram can be used to force the rubber compound into the extruder. The feed opening can be undercut to improve the intake capability of the extruder. This can be useful, because the rubber feed stock at times comes in relatively large particles of irregular shape. When the material is supplied in the form of... 

When the rubber is slippery, as in dewatering rubber extruders, the feed section of the barrel is grooved to prevent slipping along the barrel surface or the barrel I.D. may be fitted with pins. This significantly improves the conveying action of the extruder. The same technique has been applied to the thermoplastic extrusion, as discussed in Section 1.4 and Section 7.2.2.2. 

Another rubber extruder is the QSM extruder [7, 15-20]. QSM stands for the German words Quer Strom Misch, meaning cross-flow mixing. This extruder has... 

Property test NR , CR , SBR rubber extruded plank" Extruded" Cross-linked" Unmodifled Modifled Sheet" cushioning underlay type, PVC- Liquid Sheetf... 

Extrusion. For automotive and building sealing profiles, extrusion is the common shaping technology. In general, EPM/EPDM compounds can be extruded on all commercial rubber extruders. The extrusion behavior of EPM and EPDM compounds must be seen in relation to the compound quality, as achieved during mixing and influenced by the same molecular structural parameters as quoted above (34,37-40). 

Talc. Talc [Mg3Si40io(OH)2] is a platelet form of magnesium silicate with a high aspect ratio. Platelets can orient in the extrusion process, thus providing rubber extrudates with smooth surfaces that can be extruded at high rates. It is commonly used in compounds, which have critical surface appearance such as exterior automotive components or consumer goods. 

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