Calendering or extrusion

Used in the sense of warming up rubber compound prior to calendering or extrusion. 

Processibility is dependent on the viscosity or plastic flow of the rubber compound,i.e., resistance to flow. Plasticity or viscosity determines the energy requirement of the rubber during milling, calendering or extrusion while the time to the onset of curing, i.e., scorch time, indicates the amount of heat history which can be tolerated before the rubber is converted from the plastic to the elastic state at which time processing becomes virtually impossible. 

Methods for preparation include melt calendering, or extrusion which are detailed subsequently. 

Let-off A device used in coating by calendering or extrusion to suspend a coil or reel from which the material to be coated is fed to the coating machine. 

Ebonite stocks may be prepared for vulcanization by calendering or extrusion. Vulcanization, as with soft rubber, is affected by heat and pressure. In some cases the rubber may be given a soft cure, formed into a desired shape, and then cured to the final hard rubber state. 

Sheeting can be made by calendering or extrusion processes from the compound prepared as in Table 3.3. The viscosity of the rubber compound is required to be checked before further processing. 

Processing behavior They are generally less elastic (reduced nerve ) than M-grades and are, therefore, more easily processed by calendering or extrusion. Additionally, the ram pressure during mixing can be reduced and as a result the compounds have greater scorch resistance. 

Calendering and Extrusion. Priction compounds are used to build up composite stmctures of fabric and mbber. The surface of the calendered fabric must have good green tack, and for that reason compounds to be calendered are best made from a slow crysta11i2ing pepti2able polymer such as Du Pont GRT or Baypren 610. The relative temperatures of the fabric and various roUs must be carefully controUed so that the polymer does not stick to the roUs yet penetrates the fabric (137). 

Film and sheet can, in principal, be made by calendering or by extrusion. Factors that govern the advantages and disadvantages (limitations) of each process can interact in a complex way. Factors to be considered include (1) type of material to be processed, (2) quantity of product to be produced, (3) thickness... 

It can be said that basically the up-stream and down-stream procedures are similar in production lines whether calenders or extruders are used. For a given quantity of output, it is usually necessary to have more extruders than calenders. ITiis situation makes the extrusion fines more flexible and more able to handle relatively short production runs. The extrusion flexibility, when compared to calendering, includes ease of changing product thicknesses, widths, and materials. 

After the reaction is completed, the suspension is transferred to a degassing tank, where steam is used to strip out the unreacted VCM. The PVC, now in a slurry with PVA, is separated by centrifuging and drying. The PVC powder or granules are then ready for additives and plasticizers for fabrication into one of the three mediums in which its used calendered products, extrusion, and molded products. 

Of the various processing techniques used, injection molding and extrusion involve little or no exposure of hot product to the surrounding air, hence they give rise to no significant emission of plasticizer to the atmosphere. This is not the case in the production of sheet and film by calendering or spread coating. 

Plastics film and sheet can be made in a number of different ways (including casting film from solvent or plastisols, pressing, and skiving from material in block form) but in commerce the most important processes for making these intermediates from thermoplastics are calendering and extrusion. 

Calendering and extrusion lines (Chapter 5) produce film, sheet, and for applying plastic coatings to textiles, paper, or other supporting material. Table 9.1 provides comparison in fabricating PVC film. The extrusion process provides flexibility, when compared to calendering, that includes ease of changing product thicknesses, widths, materials, and provides for short production runs. 

Calendering is much more capital intensive than the extrusion process, but higher production rates and more accurate product thickness are obtained. Mini calenders or Calandrette lines (from Battenfeld) are available for the production of rigid and semi-rigid PVC films with lower investment costs. 

A branched macromolecule forms a more compact coil than a linear polymer with the same molecular weight, and the flow properties of the two types can differ significantly in the melt as well as in solution. Controlled introduction of relatively long branches into diene rubbers increases the resistance of such materials to flow under low loads without impairing processability at commercial rates in calenders or extruders. The high-speed extrusion of linear polyethylene is similarly improved by the presence of a few long branches per average molecule. 

VC-. [Borden] PVC or PVOPVAc copolymer resins for blendit, calender-mg, extrusion, p conduit film, tubing, siding, prt les, wire and cable coating, phoitQgnqdi records, floor tile, sol n. coatings, casting, foam applies. 

Vistalon . [Exxon Exxon Chem. Mediterranea SpA] Ethylene/fuopyl-ene or EPDM rubbers for molded goods, calendering, sponge, extrusion, hose, tubing, elec, insulation and jack-... 

The steps beyond filament extrusion are diverse and are usually proprietary. The yarns are pulled from the spinneret, perhaps by air jets, given an electric charge, and are then laid down on a moving screen. Alternatively, the yarns may be pulled away by rolls and drawn between a set of rolls before they are fed to the air jets. In the former case, the yarns are usually only partially oriented, even though they are stretched at very high speeds. After they are formed, the fabrics are thermally bonded by calendering, or needle-punched, or chemically bonded. For information in the patent literature, the reader should see Gillies [181]. 

Dry blending may be used to produce pellets by melt compounding. Machines of single- or twin-screw extruders are normally used. The pellets produced from compounding are processed by conventional routes such as extrusion, calendering or injection moulding. 

Chlorinated PVC can be extruded, calendered, or injection molded. Extrusion screws should be chrome plated or stainless steel. Dies should be streamlined. Injection molds should be chrome or nickel plated or stainless steel. CPVC is used for water distribution piping, industrial chemical liquid piping, outdoor skylight frames, automotive interior parts, and a variety of other applications. 

Rubber. Rubber is commonly plasticized by hydrocarbon oils from the petrochemical industry, particularly to improve melt flow in calendering and extrusion. This practice rarely finds its way into the technical literature or market analyses. 

Impact-resistant properties, especially at low temperatures, low-temperature toughness, melt-processing properties, and dimensional stability of thermoplastic polyurethane elastomers are improved by the addition of a carbonyl-modified polyolefin [54,55]. These improvements are particularly useful for reinforced polyurethanes. Small amounts of polyolefin homopolymer or copolymer with TPU blends are useful for molding plastic articles by injection molding, extrusion, calendering, or similar process for molding thermoplastic articles [56]. 

Calendering and Extrusion. Friction compounds are used to build up composite structures of fabric and rubber. The surface of the calendered fabric mnst have good green strength or building tack. Thus calendered stocks are nsnally made from slow-crystallizing polychloroprene types. Polychloroprene... 

Coarse calcium carbonate with a broad particle size distribution, based on chalk, limestone or marble, or dolomite with an average particle size of approximately 15 pm, is the main filler used in PVC floor tiles. Price is the main specification but control of colour and of levels of coarse particles is needed. It is used as an extender at 200-450 phr. To give extra dimensional stability, reduced water pick-up, and green or hot strength during calendering and extrusion of the carpet high aspect ratio platy particles are used with the calcium carbonate. Stabilisation systems have to be modified to allow for the extra reactivity of the silicate surface. 

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