Thickness extrusion

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. 

The ophiolite consists of several large massifs. Each of them exposes a more or less complete ophiolitic sequence, comprising a thick mantle section (up to 12 km), a gabbro sequence (0.5-6 km), a sheeted dike complex (1-1.5 km), a thick extrusive sequence (0.5-2 km), and interbedded oceanic sediments (e.g., Lippard et al., 1986). 

Secondary recycling is the recycle of plastic resins into new products with less demanding physical and chemical characteristics than the original application. Mixed plastics are applied most easily in the secondary recycling market because less separation of resin types and less complicated production methods are necessary to achieve a finished product. The most readily recognized secondary plastic product is "plastic lumber" (thick extrusion molded slabs of resin in which some types of resins act as fillers). Plastic lumber is used to make park benches, fence posts, boat docks, playground equipment and the like. The fabrication of mixed plastic lumber is discussed in Part II of the book. 

Solventless Extrusion Process. The solvendess process for making double-base propellants has been used ia the United States primarily for the manufacture of rocket propellant grains having web thickness from ca 1.35 to 15 cm and for thin-sheet mortar (M8) propellant. The process offers such advantages as minimal dimensional changes after extmsion, the elimination of the drying process, and better long-term baUistic uniformity because there is no loss of volatile solvent. The composition and properties of typical double-base solvent extmded rocket and mortar propellant are Hsted ia Table... 

Copper and Copper Alloys Seamless copper, bronze, brass, copper-nickel-aUoy, and copper-silicon-aUoy pipe and tubing are produced by extrusion. Tubing is available in outside-diameter sizes from Vi6 to 16 in and in a range of wall thicknesses varying from 0.005 in for the smallest tubing to 0.75 in for the 16-in size. Tubing is usually specified by outside diameter and wall thickness. 

Fig. 4.19(a) Sheet extrusion (1) thick sheet (2) thin sheet... 

Example 4.4 A blow moulding die has an outside diameter of 30 mm and an inside diameter of 27 mm. The parison is inflated with a pressure of 0.4 MN/m to produce a plastic bottle of diameter 50 mm. If the extrusion rate used causes a thickness swelling ratio of 2, estimate the wall thickness of the bottle. Comment on the suitability of the production conditions if melt fracture occurs at a stress of 6 MN/m. ... 

A plastic film, 0.1 mm thick, is required to have its orientation in the transverse direction twice that in the machine direction. If the film blowing die has an outer diameter of 100 mm and an inner diameter of 98 mm estimate the blow-up ratio which will be required and the lay flat film width. Neglect extrusion induced effects and assume there is no draw-down. 

During extrusion blow moulding of 60 nun diameter bottles the extruder output rate is 46 X 10 m /s. If the die diameter is 30 mm and the die gap is 1.5 mm calculate the wall thickness of the bottles which are produced. The flow curves in Fig. 5.3 should be used. 

Table 5 compares the tensile properties of Vectra A950 in the form of dispersed fibers and droplets in the matrix by injection molding, microfibril by extrusion and drawing [28], injection molded pure thick sample and pure thin sample, and the pure drawn strand [28]. As exhibited, our calculated fiber modulus with its average of 24 GPa is much higher than that of the thick and thin pure TLCP samples injection molded. It can be explained that in cases of pure TLCP samples the material may only be fibrillated in a very thin skin layer owing to the excellent flow behavior in comparison with that in the blends. However, this modulus value is lower than that of the extruded and drawn pure strand. This can be... 

Extrusion coating is ideal for rods, tube and wire. The article is passed through a paint reservoir and then out via a die, which leaves only the correct thickness of paint in place. There are further techniques suitable for flat articles in sheet or web form. Knife coating is ideal for very thin coats, especially on continuous paper or plastic webs. The knife is either a metal doctor blade or a curtain of high velocity air (an air knife) directed onto the surface and it removes surplus material applied previously. 

An extrusion-blown hinge can be compared to a stamping (Fig. 3-21). Hot- and cold-stamped hinges are made by compressing a sheet of material down to the desired thickness [12 to 20 in. (3 to 5 mm)]. Stamped... 

The extrusion line must be capable of running the sheet in a highly controlled and precise environment, to make sure the lenticules are accurately placed (6). Extrusion must also be a clean process in order to prevent image-altering contamination. Sheets are usually extruded in a thickness range of 0.015 to 0.100 in. (0.038 to 0.254 cm). 

The operating pressures and shear rates in the extrusion process are considerably lower than they are in molding. As it exits the die, but not necessarily when it leaves the process, the material is in an essentially stress-free condition. Depending on the wall thickness of the material and the particular material, there is orientation of the plastic to a greater or lesser controllable degree. Thin walls produce higher orientation in materials such as PP, that is a highly crystalline polyolefin, and which orients much more than materials such as PVC. 

The designer should be aware of the fact that this is to be considered in designing with extruded products. The designer can exercise little control over this pull back condition except to be guided by the experience of the extrusion processor to indicate which materials are particularly susceptible to this problem and what the recommended wall thicknesses are to minimize the effect. In general, one of the best ways to improve the condition is to slow down the rate of extrusion. As a result, products have a tendency to pull back. They also will be more costly to produce. 

By extrusion parison control it is possible to minimize the wall thickness variation and the extent of stretching and stretch orientation. These are the province of the processor when the designer is not familiar with BM. Knowledge is required to provide information on what is possible and to select the specific BM process that has the capability to mold the product. The designer should be aware of the possible failure modes and compensate for them in the design. There is little else the designer can do but select the best material and process to make the product. 

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. 

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