Plasticator compression ratio

The injection-molding press was producing a part and runner system that had a mass of 2.15 kg. The mass was plasticated using a 120 mm diameter, 8L/D screw. The screw used for the process had a barrier melting section that extended to the end of the screw, as shown by the specifications in Table 11.9. That is, the screw did not have a metering channel. Instead, the last sections of the barrier section were required to produce the pressure that was needed to flow the resin through the nonreturn valve and into the front of the screw. The specific rotational flow rate for the screw for the IRPS resin was calculated at 9.3 kg/(h-rpm) based on the depth of the channel at the end of the transition section. The screw was built with an extremely low compression ratio and compression rate of 1.5 and 0.0013, respectively. For IRPS resins and other PS resins, screws with low compression ratios and compression rates tend to operate partially filled. The compression ratio and compression rate for the screw are preferred to be around 3.0 and 0.0035, respectively. The flight radii on the screw were extremely small at about 0.2 times the channel depth. For IRPS resin, the ratio of the radii to the channel depth should be about 1. 

The parts produced were in specification and did not have the splay defect. When the press was switched between different colored resins, the purge time was very short and typically required less than 20 parts. The higher compression ratio and compression rate screw combined with channels that had large radii provided a constant plastication rate and no detectable degradation of the resin. 

It is also known [8] that for various kinds of plastics, the ratio between designbending stress and tension stress is 0.5-0.87, that is, ybenJytens 0.5-0.87. The ratio between design compression and tension stresses is ycomprlytens 0.95. 

U.S. Pat. Nos. 6,117,924 [92] and 6,984,676 [93] (both by Crane Plastics Co., TimberTech) describe an extrusion process of making a cellulose-plastic composite material the process includes a significantly higher compression ratio through which the extrusion product must pass. Plastics include polyethylene, polypropylene, PVC, LDPE, and other commercial polymers. 

Styrenic thermoplastic/rubber (Limera ) Conventional free-flow type nozzles with an orifice diameter of 3 mm or larger are commonly used for Limera R. Although screw design is not critical for Limera R, small L/D and compression ratio are preferable. Forcibly plasticizing screws such as the Dahnage screw are not recommended. Melt temperamre should not exceed 280°C. 

ABS/PVC blends (e.g., Triax CBE, Enplex tm) are formulated to provide a broad window of molding conditions. Because of the presence of PVC, shear or thermal degradation must be minimized. Shot size should be about 50% of machine capacity — less than 35% will result in a long residence time, whereas in excess of 65% will increase plasticating time, both of which create conditions for resin degradation. High compression screws should be avoided since they generate excessive shear heat — a linear taper screw with a compression ratio between 1.5 and... 

TS reinforced molding compounds processed in IM require water- or oil-cooled barrels, rather than the electrically heated barrels used for TP. The heat of the TS during screw plastication has to be kept lower than its curing heat. The mold heat is higher than that of the resin, causing the TS finally to react and solidify. If there is excess heat in the barrel, the resin crosslinks and the machine stops operating. A cleanup is required, which can cause machine downtime to be extensive. With a liquid heat control, better control of melt heat is maintained. Also the compression ratio of the screw used to process the TS is one, which helps to keep the heat low and, more important, under control. 

Similar injection-molding equipment design considerations apply to extrusion equipment such as long plasticating screws with 24/1 or higher L/Z) ratios and approximately 3 1 compression ratios. ... 

For example, for one machine equipped with plastic poppet valves (i.e., compressor cylinder valves designed for high capacity but low compression ratios), valve losses as measured by a Beta Scan were reduced from 25% to 10% when the compression ratio was reduced from 1.42 to 1.28. This occurred even though the gas volume moved through the compressor increase by 50%. 

CPU central processing unit CPVC chlorinated polyvinyl chloride CR chloroprene rubber C/R compression ratio CR-39 ally diglycol carbonate CRP carbon reinforced plastics CRT cathode ray tube CS chlorinated solvent CSA Canadian Standard Assoc. 

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