Extrusion line speeds

For the axisynunetric flow model, the stress tensor had foin components in total. These were the elongation stress T22, the hoop stress T33, the shear stress T12 and the radial stress Til. The meanings of these stresses are illustrated in Figure 3 with the main flow in the direction of axis 2 (the extrusion line speed direetion). The foin stress components were plotted for the itmer surface of the jacket tube along the extrusion line direetion. All plots started from the die exit and ended some distance downstream. Figure 4 shows the elongation stress plot as an illustration. The elongation stress has a local peak at the contact point where the extrudate meets the cable central core. 

Wire and Cable. PVC has been used in wire and cable applications since Wodd War II, when the U.S. Navy demanded lower combustibility materials in construction. These products are manufactured by cross-head extrusion, usually from pellet compounds on single-screw extruders. Some line speeds are 1524 m (5000 ft) per minute (60 mph). The compounds are optimized for the requirements, including low temperature flexibility, high use temperature, especially low combustibility, weatherability, and high resistance to cutthrough. 

In this process the plastic is directed against the surface of the substrate immediately before its entry into the nip between a pressure roll and a chill roll. The extrusion rate and the line speed of the substrate determine the coating thickness. The chill roll controls the surface finish of the coating. Extrusion coatings are typically applied in thin layers, ranging down to 0.005 mm. 

Different methods are used. An online ordinary common blown or cast film line uses a machine direction orienter (MDO) on the front end of biaxially oriented film heated chamber extrusion line. If only the machine direction is to be stretched, a series of precision controlled heated rolls can be used. Film is fed through a series of rolls where it is sequentially heated, drawn around rolls that increase in rotational speed providing the stretching action, annealed around larger diameter roll(s), and cooled on a final roll(s). 

This monomer (diol) is used to broaden the processing window, increase line speeds, slow the crystallisation rate and reduce stress in biaxially orientated structures. It is used in concentrations ranging from 1% up to about 18%. The higher concentration PET is usually referred to as PETG and is mainly used for extrusion blow moulding and sheet extrusion. Polymers from PTA and CHDM are approved in the US by 21 CFR 177.1315 recently the use of CHDM as comonomer in PTA-EG polymers has been listed in the US FDA regulation for PET (21CFR 177.1630). Moreover, the use of CHDM has been approved in Europe for plastics intended for food contact applications since the first directive 90/128/EC. 

Tube extrusion is quite similar to the wire insulation process. Processing details depend on the size and type of the tube. Tube can be manufactured by both in-line and crosshead dies. FEP tubing can be produced with outside diameters as low as 1 mm to over 20 mm. This range is broken into three processing zones based on the size of the outside diameter small, medium, and large. The sizing die determines the outside diameter of the extrusion output and the line speed determines the inside diameter. Take-up speed and the die gap, and the difference between the inside diameter of the die and the outside diameter of the tip, set the wall thickness. 

Extrusion coating Poor adhesion a variety of apparently contrary causes related to polymer viscosity, degradation, oxidation, tackiness, temperature melt temperature too low or high/air gap too small/chill roll temperature too cold or hot/line speed too fast/poor match between coating and substrate. 

The principal controls for a blown film line are barrel (cylinder) and die temperatures, die gap, extrusion rate, internal air pressure, bubble diameter, cooling air flow or cooling rate, and line speed (take-off speed). These controls influence the film dimensions and properties. The frost (freeze) line height, which is a ring-shaped zone where the bubble frequently begins to appear frost because the film temperature falls below the softening range of the resin and crystallization occurs, is an indicator for many of these variables. The frost line may not be visible at times. When it is not, the zone where the bubble reaches its final diameter is considered to be the frost line. 

Crompton has introduced Mark 2000 organotin stabilisers for PVC window frames, to overcome processing problems in high-speed extrusion lines. The company also markets a sulfur-free tin stabiliser called Mark 2289, specifically for PVC window profiles that are subject to intense simshine, as in desert areas of the United States. It is said to protect against heat and UV to some extent as well. 

A tape measure can be used to measure distances from about 20 cm up to several meters. Dial calipers are useful for closely measuring extruded products, dimensions of the extruder screws, extrusion tooling, etc. A stopwatch is an indispensable tool for measuring screw speed, line speed, blender calibration, etc. A scale can be used to measure the output of an extruder. A small voltmeter is very useful in making sure that voltage and resistance levels of various components are at their required values. A millivolt source can be used for verifying thermocouple inputs and to check controller response and line continuity. 

The extruder drive should be able to hold the screw speed constant to about 0.1% or better the same holds true for the take-up device. However, this is not always the case on actual extrusion lines. The extruder should be equipped with some type of proportioning temperature control, preferably a PID-type control or better. On-off temperature control is inappropriate for most extrusion operations. 

The residence time of the cable in the high-pressure CV tube determines the extent of the reaction and so dictates the speed of the extrusion line. The temperature in the extruder is also critical, as too high a level will initiate the decomposition of the peroxide and the reaction will start to occur in the extruder. 

Manufacturing speeds Limited by residence time in CV tube, which determines line speed Normal extrusion limits i.e. head pressure and rpm Limited by exposure time to radiation source, which dictates line speed... 

The dope solids for air-gap spinning are higher than for wet spinning, the intent being to achieve quick gelation on extrusion. The spinnerette is positioned a short distance above the bath, which is a solvent/nonsolvent mixture, typically at low temperature. The fiber is spim vertically into the bath, and then rerouted out via a tube or pulley as shown in Figure 12. Spinnerettes may be less then 1000 holes for a textile product or as many as 4000 for a carbon fiber precursor. The remainder of the process resembles the wet-spinning process, except that there are many small bundles that must be kept separate and the final product is taken up on bobbins. Final line speeds may be up to 500 m/min, but because of the small bundle size, machine productivity may be only 5 ton/day. 

For uniform and stable extrusion it is important to check periodically the drive system, the take-up device, and other equipment, and compare it to its original performance. If variations are excessive, all kinds of problems will develop in the extruded product. An elaborate process-control system can help, but it is best to improve stability in all facets of the extrusion line. Some examples of instabilities and problem areas include 1) non-uniform plastics flow in the hopper 2) troublesome bridging, with excessive barrel heat that melts the solidified plastic in the hopper and feed section and stops the plastic flow 3) variations in barrel heat, screw heat, screw speed, the screw power drive, die heat, die head pressure, and the take-up device 4) insufficient melting or mixing capacity 5) insufficient pressure-generating capacity 6) wear or damage of the screw or barrel 7) melt fracture/sharkskin (see Chapter 2), and so on. 

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