TWO-STAGE EXTRUSION

FIGURE 2.19 Single-flight, two-stage extrusion screw with mixing section. 

For the tests of preparing dynamic vulcanizates in the continuous process of reactive extrusion a twin-screw mixer-extruder DSK 42/6D manufactured by Brabender was used. The vulcanizates were produced dynamically in the process of one-stage or two-stage extrusion process, setting the favorable operating parameters for the device, which had been determined based on multiple tests distribution of temperatures in each heating area... 

Silane crosslinking works by first grafting reactive groups onto the PE molecule by addition of silanes and very small amounts of peroxide, in a one- or two-stage extrusion process. The crosslinking is effected by moisture or water and is accelerated by a tin catalyst [36]. 

Except in special Bekum two-stage extrusion blow molder, all extrusion parisons are blown at too high a temperature to orient the plastic. Injection blow inherently gets some orientation from the injection stage during cavity filling. Also, since plastic temperature drops about 150 °C styrene orients into a strong container. No effect on RE. 

For example, if a two-stage vented extruder has a screw that was designed for resins with an Mi range of 2 to 20 dg/min, and plant personnel are asked to manufacture a resin with an MI of 100 dg/min, the extruder may not process the resin acceptably. For this case and flood feeding, the extruder is likely to have resin flowing into the vent because the first stage can deliver more resin than the second stage can pump. One practical solution to this problem is to operate the slide valve in a partially open manner such that it controls the rate of the extrusion process. This will allow the extruder to operate at a lower specific rate and allow operation without the flow of resin into the vent. 

Kiihn, R., Burkhardt, U., Heidemeyer, P, Optimization of quality and throughput at low revolution speeds in an advanced two stage compounding system, SPE/ANTEC Proceedings (2007), Extrusion Division, Paper No. 0392... 

Two-stage EBM treats the parison as a true preform by separating the functions of parison preparation and BM. Parisons are produced by conventional tube extrusion methods (Chapter 5). The tube is cooled and cut into parison lengths that are stored before being reheated and BM in the normal way. 

Intermittent accumulator EBM machines use a normal conventional axially fixed continuously operating extruder to prepare the melt. The accumulator is a heated reservoir where the melt is temporarily stored in the intervals between parison extrusion (similar action of a two-stage injection molding machine (IMM) as reviewed in Chapter 4. Also used is a conventional reciprocating IMM that delivers melt through a die into a blow mold. 

Extrusion stretch blow molding (ESBM) is a one-stage or two-stage process using two mold/mandrel sets where one is for preblow and the other for final blow. An extruded parison is first pinched off and blown... 

The possible development of LA into a cross-over chemical between carbohydrates and petrochemicals has recently spurred the development of more efficient procedures for its production. Most start from cheap starting materials such as lignocellulose residues and waste paper in acidic medium at approx. 200 °C the theoretical yield of such a procedure is 0.71 kg kg-1 (see Fig. 8.36). In a patent application for a two-stage procedure the claimed yields were 62-87% of the theory, depending on the raw material [195]. A much simpler, extrusion-based procedure has been described but even when fitted with a second stage the yield was not better than 66% of the theory [196]. Efficient DSP is not trivial and the chromatographic separation that has been described [197] is obviously not compatible with the aimed-for commodity status of LA. Alternatively, the LA can be esterified in situ [197]. 

The two-stage model is conceptually very useful because it separates the thermodynamics of insertion from helix assembly. When examining the stability of membrane proteins in the bilayer, the second stage is presumably the most relevant since the extrusion of the protein back into the aqueous environment should be extremely unfavorable. This idea is supported by the experiments discussed below. The two-stage model may not contain sufficient detail to describe the folding process in all cases, however. For example, the F and G helices of bacteriorhodopsin do not spontaneously form helices in vesicles, indicating that these peptides require assistance from the remainder of the protein to fold properly (Hunt et al., 1997). 

The OPS extrusion process typically uses a two-stage vented extruder. The most common size OPS lines use either a 200 or 220 mm diameter extruder. The length-to-diameter (L/D) ratios range from about 24 to 32, the higher ratio extruder... 

Most thermoplastic processes utilized for HIPS applications use a single screw to melt and pressurize the polymer. Screw extruders in industry used with HIPS can have screw diameters from 20 to 200 mm and can melt process over 2000 kg/h. Two-stage, vented screw designs are predominantly used for extrusion of HIPS, whereas single-stage reciprocating screws, with a nonreturn valve, are common in the HIPS injection molding process. 

However, at shorter wavelengths (but still below the ionization threshold) molecular extrusion of hydrogen occurs, as evidenced by the fact that some of the hydrogen which is produced cannot be quenched by added free radical inhibitors. The main source of this molecular hydrogen seems to be two-stage breakdown via a carbene, as suggested for the reaction of 3,3,3-trideuteriopropyne (equation 6). 

Figure I (a) Blown film extrusion, (b) Linear, two-stage production of biaxially-oritented PP...

For extrusion of Centrex ASA/AES ter-polymer rubber modified blends and SMA/ABS blends (Cadon ), standard practices recommended for other styrenics systems should be used. Thus, when a single screw machine is selected, a two-stage screw is preferred, but a single-stage screw may also be used. When using two-stage screws, the recommended compression ratios are... 

Eor PA/ABS blends, e.g., Alphaloy MPA, Elemid , Diaaloy N, Kane ace MUH, Malecca S, Maxloy A, Monkalloy N, N5, Novaloy -A, Stapron N, SX, Techniace TA, Toyolac Adloy, Triax 1000, Ultramid ), single or twin screw extruders are suitable. However, the latter are preferred. Typical ABS extrusion procedure should be followed. Eor two-stage screws, a first stage compression ratio of 25-2.1 and pump ratio 1.5-2 are recommended. 

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