Bimetallic barrels

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. 

As it is claimed that the bimetallic barrels mentioned above wear less than the nitrided barrels, the clearance between the barrel and the screw is maintained longer and hence the optimum performance of this type of system is considerably extended. 

Wear and corrosion of the screw should be made from or surface coated with corrosion and abrasion-resistant metals. Coating screws with wear and corrosion-resistant metals should also be considered. The bimetallic barrel liner and the flight tip metal must be compatible. Otherwise, excessive wear may occur between these two metal surfaces during screw recovery and injection. 

Bimetallic barrels are made by centrifugally casting a bimetallic alloy onto the inside of the barrel. The melting point of the bimetallic alloy is considerably lower... 

A large number of materials are available for the screw and barrel. Most extruder barrels in the U. S. have a liner, which is centrifugally cast into the barrel. The barrel liner is made of a wear-resistant material, often boron-stabilized white irons with a Rockwell C hardness of about 65 containing iron chromium boron carbides. Bimetallic barrels provide better wear resistance than nitrided barrels as reported, for... 

The Extruder Barrel. The cylinder is called the extruder barrel. The barrel is a straight cylinder usually equipped with a bimetallic liner this liner is a hard, integral layer with high wear resistance. In most cases, the wear resistance of the barrel should be better than that of the screw. The reason is that the screw is much easier to rebuild and replace than the barrel. Bimetallic barrels usually cannot be rebuilt. 

The components of the barrel assembly which are in direct contact with hot PVC, must be able to resist the corrosive hydrochloric acid (HCL). To protect against such corrosion the screw, barrel and back flow valve are often produced from stainless steels containing a high chromium content. Chrome plating, in conjunction with nitriding, is often used for bimetallic barrels fully hardened screws are produced from... 

Introduction of zeolites into catalytic cracking improved the quality of the product and the efficiency of the process. It was estimated that this modification in catalyst composition in the United States alone saved over 200 million barrels of crude oil in 1977. The use of bimetallic catalysts in reforming of naphthas, a basic process for the production of high-octane gasoline and petrochemicals, resulted in great improvement in the catalytic performance of the process, and in considerable extension of catalyst life. New catalytic approaches to the development of synthetic fuels are being unveiled. 

The majority of barrels and screws are made from special steels (Tables 2-4 and 3-4), which are nitrided to a minimum depth by special techniques. Low alloy steels are sometimes used with wear-resistant liners. Usually the wear on these bimetallic cylinders is almost three times that of the others. In the processing of abrasive materials, feed sections are sometimes finished in hard metal or other special materials, and matched with the screws. If there is wear in the extruder, then the greatest damage is always on the screw. Often only a new screw is used as a replacement, as it is assumed that the barrel is not damaged. However, usually this assumption is a fallacy. If the screw is worn out, the barrel has been affected to some extent. It may well need complete replacement. 

Bimetallic cylinder n. In most modern extruders and injection machines, the barrel is lined, by centrifugal casting from the melt, with any of several white irons containing chromium and boron carbides and having hardnesses near Rockwell C65. Aster finish-grinding and polishing, the liner, about 1 mm thick, provides excellent resistance to wear or corrosion or both, depending on the formation. The best known trade name is XALOY . 

The clearance between the barrel and screw flights is typically 0.08 to 0.13 mm (0.003 to 0.005 in). To reduce barrel wear, barrels are nitrided or bimetallic liners are inserted into the barrel. Nitriding is the surface hardening of the barrel. This process initially produces higher hardness (Rc 70), but loses that advantage as the barrel wears. Nitriding also provides poor abrasion and only moderate corrosion resistance. In contrast, a bimetallic liner is a 1.5-mm (0.060-in)-thick sleeve that fits in the barrel. As shown in Table 5.5, liner materials depend on the polymer and its additives. Iron/boron materials are used as general-purpose liners, whereas nickel/cobalt liners... 

Superbulk, Wire and cable filler yarn, Ensign-Bickford Industries Inc., Film Fibers Div. Supercarb, Injection high abrasion-resistant barrels, New Castle Industries, Inc. Supercarb Barrel, High-carbide, wear-resistant bimetallic liner for injection molding, Bimex Industries, Subs, of New Castle Industries... 

Bimetallic Cylinder n In most modern extruders and injection machines, the barrel is lined, by centrifugal casting from the melt, with any of several white irons containing chromium and boron carbides and having... 

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