Wear Resistant Barrel

The increasing use of plastics with abrasive fillers and reinforcements created a demand for an even more abrasion resistant barrel than the standard iron/boron type. The use of glass fiber reinforced compounds for injection molding has been the single most important factor since a fabricator would be lucky if they could reach 6 months of continuous operation. This need has been successfully answered by the development of liner materials containing metallic carbides such as tungsten carbide and titanium carbide extending their life. 

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Figure 16.5 ZSK screw barrel designs monoblock barrel with directly-applied, wear-resistant coating barrel with replaceable insert (Courtesy Coperion Werner Pfleiderer)...

This recently developed barrel-wear protection called Supermet 60 PLUS from Coperion Werner Pfleiderer (in conjunction with HARTEX and Bodycote) has improved the abrasive wear resistance by a factor of 3 compared to the pure matrix material, while retaining its effective corrosion resistance. This technology offers great potential for the manufacture of future special materials [4],... 

Base barrel with oval liner 035 NiCrBSi wear-resistant layer, PM - diffusion bonded 3 58 + 2 XXX XXX On request... 

This process is used to manufacture products with a combination of properties. For example, a ballpoint pen barrel needs to have the rigidity of a stiff material, but it is convenient to have attached a more easily gripped area consisting of an elastomeric material. Another example is the set of keys on a computer keyboard. To improve wear resistance, the characters are co-injected rather than printed onto the key top. Finally, co-injection can be used to encapsulate a low cost material that has poorer properties, such as regrind, inside a shell of prime material. 

Barrel liners Version one part or multiple part, smooth, perforated, with longitudinal strips, with spirals, with keel rails. Fixing with screws, screwless, secured against twisting by strips, secured with bolts. Material rolled sheet metal, welded on strips, cast barrel liners cast steel, wear-resistant chilled casting, hard-faced, stainless steel design, special concrete... 

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. 

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... 

Comparative wear tests [27] indicate that the wear performance of bimetattic barret tiners is better than nitrided barrel surfaces, with a predicted improvement in the barrel life of about four to eight times the life of a nitrided barrel. An additional drawback of the nitrided surface is that the hard compound zone is quite thin. Once the compound zone is worn away, wear will increase more rapidly because the diffusion zone is not as hard and wear-resistant. This becomes more severe as the diffusion zone wears away more deeply. 

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... 

Molybdenum-based hard alloys have also been used on extruder screws. These materials are relatively soft, about 40 Rockwell C, but have good lubricity. In some instances, wear resistance with the molybdenum hardfacing improved about 500% over the more common, but harder, hardfacing compounds. Molybdenum-based hardfacing alloys are used primarily with nitrided barrels, not only in single screw... 

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. 

Extrusion. For processing of TPEEs by extrusion, the single-screw machines are recommended. The screws should have hardened surfaces for good wear resistance. A general purpose extruder barrels may be used with preferable length to diameter (L/D) ratio 24/1 to provide the best melt quality for precision extrusion. The barrel should have at least four independently controlled heating zones. Compression ratios should be between 2.5/1 and 3.5/1, as determined by the depth of the feed zone divided by the depth of the metering zone channel. 

Plastic top plates are made from several different types of thermoplastics. Many are molded from acetal or low-friction acetal. Low-friction acetal is a blend of acetal with another plastic with a very low coefficient of friction. The plastic used must have good corrosion resistance and the plastic must also have good wear resistance in conditions where there is little or no lubrication. The barrels of the top plates must be molded very accurately, for the same reasons that the barrels of steel top plates must be curled very accurately. 

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