Extrusion trial

An extrusion trial was performed at the processor s plant using a 38.1 mm diameter production extruder, a proprietary screw design, and resin that had previously exhibited flow surging and reduced rate. The extruder was equipped with three barrel zone heaters with control thermocouples (labeled Tl, T2, and T3) and two pressure sensors. One pressure sensor was located in the midsection (zone 2) of the barrel (P2) and the other at the end of the barrel near the tip of the screw (P3). Both transducers were positioned over the top of the screw such that a pressure variation due to screw rotation would be observed. 

Oparex 15 calcined calcium sulphate (Yesos Ibericos) was evaluated as a filler in plasticised PVC cable insulation compounds in comparison with two grades of calcium carbonate. Improvements were observed in tensile, electrical and low temperature properties, flammability and heat ageing characteristics and chemical resistance for calcium sulphate filled compounds, while no significant differences in water absorption and hydrolysis were noted. Studies of rheological properties showed improved processability in mixing and extrusion trials. URALITA... 

The extrusion trials have been carried out in collaboration with the Unite de Catalyse et de Chimie des Materiaux Divises at the Universite Catholique de Louvain-la-Neuve. 300 g of colloidal silica suspension LUDOX-AS30 was progressively mixed with 97 g of dried Pd-Ag/Si02 catalyst to obtain a thick paste after 20 min of mixing. The paste was introduced in the extruder and extruded at the screw rotation rate of 10 rpm. The extrudates were dried 5 days in the open air at ambient temperature and calcined at 450°C for 12 h. 

In this particular application, the molecular weight of the extruded product had to be above a certain minimum level. This turned out to be a significant challenge because the early extrusion trials did not achieve the minimum MW level in the TPE. As a result, a special screw was designed for this application to minimize the stresses that the polymer melt is exposed to in the extrusion process—this is the CRD mixing screw. 

From this analysis the stability of Cytop in oxygen is estimated to be about 20 days at 250 °C and 417 days at 220 °C. In addition, the thermal stability of Cytop in nitrogen was determined in a similar manner and the time to the onset of decomposition at 250 °C was shifted by more than an order of magnitude beyond the value found for degradation in oxygen. Actual extrusion trials of this material in the melt indicate these predicted lifetimes are reasonable estimates of Cytop s stability. 

Using only the smooth feed, the barrier screw increased specific output rate for SAN and PA by 10-15%. Only PP was used in both smooth and grooved feed zone extrusion trials [36]. 

Table 13.1 Summary of screw details used in starved feed zone extrusion trials by Thompson, Donoian and Christiano [10] and by Elemans and Van Wunnik [11] ...

TABLE 7.15 Compounds for Laboratory Extrusion Trial Compound 1 2 3 4 5... 

Next is to make sample prototype tooling and sample prototype products for the test. Samples made by machining or other simplified model making techniques do not have the same properties as the product made by molding or extrusion or whatever process is to be used (Chapter 3, PROTOTYPES). A product made this way is a sample rather than a testable prototype. Simplified prototypes may reduce trial mold cost and produce adequate test data in some cases. Its main value is appearance and feel to determine whether the aesthetics are correct. Any testing has to be done with considerable reservation and caution. 

Most tests will be made on standard test pieces which may be pieces cut from a component or a sheet, or they may have been moulded separately from the same material. Where test pieces or sheet are produced for the trials it is important that they are produced in as near as possible the same way as the product and that the processing conditions are recorded. Different results can be expected from compression and injection moulding or from extrusion (where a choice is possible). Directional properties can result from the conditions of flowing and cooling in a mould. For example, in a study at ERA, the creep strain of unfilled HDPE, either individually moulded or cut from square plaques, varies by up to a factor of two depending on the orientation of flow [40]. This difference becomes even more marked with short fibre reinforcement. 

The performance of Double Wave screws was provided earlier by Kruder and others [20-22]. For these trials, the extrusion process was capable of higher rates and lower discharge temperatures than well designed conventional single-flighted screws. Three-dimensional flow simulations for a Double Wave and a Triple Wave section were performed by Fan [23] and Perdikoulias [24], These simulations showed the complex nature of the flows, including the acceleration of the flow as it... 

Recycled PVC supermarket trays have been used successfully in production-scale trials to make the foamed layer in coextruded cladding. The extruded product had satisfactory foam density, foam structure and colour. Impact properties were better than those of the control made from virgin PVC this is attributed to the high levels of impact modifier used in tray formulations. These trials demonstrated that PVC straight-on trays can be recycled into foamed extrusions for wood replacement products. 8 refs. 

Preliminary field trials with canola were promising (106, 107). Subsequent work with canola and other oilseeds showed that this new machine, the Hivex expander, can process full-fat safflower (at 42% oil), sunflower (at 42-44% oU), peanut (at 45% oil), and some varieties of full-fat canola and rapeseed as well as cottonseed. Typical preparation prior to extrusion of safflower, sunflower, and peanut is to crack to approximately 1.6 mm (0.0625 in.) particles, or flake heat to approximately 60-71.1°C (140-160°F) and reduce moisture to approximately 8% without denaturing the protein. Canola and rapeseed, being small seeds and low in protein, need to be flaked as thin as possible, 0.15 mm (0.006 in.) if practical. Canola flakes thicker than 0.25-0.3 mm (0.010-0.012 in.) do not extrude very well. If seed protein is denatured too much before extmsion, the canola collets will be loose and crumbly. 

Extrusion of Hypalon tends to be soft when hot. The die correction for the profiles for accommodating shrinkage and swelling of the stock should be done based on a few trials. As soon as the correct profile comes out of the die, it should be thoroughly cooled in a cooling tank with soapy water. 

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