Radial clearance is the fitting clearance between the screw and charging barrel. If the clearance is too large, the plastication capacity of the machine shall be reduced and the refluence of refused materials during injection shall increase, should the clearance be too small, the difficulty for the mechanical processing of screw and charging barrel as well as the power consumption of screw shall both be increased. Usually the radial clearance =(0.002-0.005)D o Length-Diameter Ratio and Segmentation The ld radio of screw refers to the ratio between thread length of the screw and the diameter screw, generally taking 16-20. The larger the ratio, the better the quality of plastication is, the temperature shall be more uniform and the effect of mixing and fusing shall be better; meanwhile the rotation speed of screw shall be improved on the premises that the quality of plastication be ensured. If the LD radio is too large, however, it shall be difficult for the mechanical processing of screw and charging barrel. Hence, when the quality is ensured, the ratio should be taken as small as possible, since short screws are not only easy to be manufactured but also can shorten the body of njection molding machine. Furthermore, it is also easy for cleaning The segmentation of screw refers to the proportion in the threaded part of the screw as taken by the feeding section, plastication section and measurement section of the screw for injection, where the feeding section generally takes 50%, and the compression and measurement section each takes 25% Depth of Spiral Flute and Compression Ratio The charging barrel is a container for heating and pressurizing plastics. The feeding of injection molding machine mostly depends on the deadweight of granular materials which freely fall into the charging barrel through the hopper. Therefore, shape of the inlet of the barrel should be suitable for the deadweight falling of granular materials, so that the transmission capacity during automatic feeding can be ensured During injection, the fused materials in the charging barrel, subjecting to the movement of screw, flow rapidly through the nozzle and into the mold cavity, thereby being molded. The nozzle thus plays such part as connecting the charging barrel and the mold as well as endowing the materials with high injection speed. The materials, when flowing through the nozzle, shall undergo large-scale cutting and be further plasticated due to the reduction of the nozzle's inner diameter On the other hand, the moisture in the raw materials of plastics shall directly influence the quality of injected products, especially engineering plastics. It is therefore quite necessary to pre-dry he moisture absorptive plastics, which can not only improve the(products')surface glossiness improve the bending strength and tensile strength and avoid occurrence of silver lines, crackles, air bubbles and spots inside the parts, but also can improve the plastication capacity and shorten molding cycle. The moisture in the raw materials of plastics exists into two types. One is that the materials absorb moisture and enter the inside of the matrix, such as ABS and Perspex etc. The other is that the materials is wet on the surface, the moisture only wraps around the surface of the basal body and seldom infiltrates to the inside, such as polyethylene and 6-3 list the admissible injection molding temperature range for partial plastics and their drying condition. During the drying, different method should be adopted according to the different materials and different forms of moisture absorption. Attention should be made that whichever nethod is used. the dried materials must be sealed for storage or heated and insulated cannot be exposed in the air for too long time(including in the hopper with a lid thereon), whereinRadial clearance is the fitting clearance between the screw and charging barrel. If the clearance is too large, the plastication capacity of the machine shall be reduced and the refluence of refused materials during injection shall increase; should the clearance be too small, the difficulty for the mechanical processing of screw and charging barrel as well as the power consumption of screw shall both be increased. Usually the radial clearance e = (0.002 ~ 0.005)D . z Length-Diameter Ratio and Segmentation The LD radio of screw refers to the ratio between thread length of the screw and the diameter of screw, generally taking 16~20. The larger the ratio, the better the quality of plastication is, the temperature shall be more uniform and the effect of mixing and fusing shall be better; meanwhile, the rotation speed of screw shall be improved on the premises that the quality of plastication be ensured. If the LD radio is too large, however, it shall be difficult for the mechanical processing of screw and charging barrel. Hence, when the quality is ensured, the ratio should be taken as small as possible, since short screws are not only easy to be manufactured but also can shorten the body of injection molding machine. Furthermore, it is also easy for cleaning. The segmentation of screw refers to the proportion in the threaded part of the screw as taken by the feeding section, plastication section and measurement section of the screw for injection, wherein the feeding section generally takes 50%, and the compression and measurement section each takes 25%. z Depth of Spiral Flute and Compression Ratio The charging barrel is a container for heating and pressurizing plastics. The feeding of injection molding machine mostly depends on the deadweight of granular materials which freely fall into the charging barrel through the hopper. Therefore, shape of the inlet of the barrel should be suitable for the deadweight falling of granular materials, so that the transmission capacity during automatic feeding can be ensured. During injection, the fused materials in the charging barrel, subjecting to the movement of screw, flow rapidly through the nozzle and into the mold cavity, thereby being molded. The nozzle thus plays such part as connecting the charging barrel and the mold as well as endowing the materials with high injection speed. The materials, when flowing through the nozzle, shall undergo large-scale cutting and be further plasticated due to the reduction of the nozzle’s inner diameter. On the other hand, the moisture in the raw materials of plastics shall directly influence the quality of injected products, especially engineering plastics. It is therefore quite necessary to pre-dry the moisture absorptive plastics, which can not only improve the (products’) surface glossiness, improve the bending strength and tensile strength and avoid occurrence of silver lines, crackles, air bubbles and spots inside the parts, but also can improve the plastication capacity and shorten molding cycle. The moisture in the raw materials of plastics exists into two types. One is that the materials absorb moisture and enter the inside of the matrix, such as ABS and Perspex etc. The other is that the materials is wet on the surface, the moisture only wraps around the surface of the basal body and seldom infiltrates to the inside, such as polyethylene and polypropylene etc. Table 6-2 and 6-3 list the admissible injection molding temperature range for partial plastics and their drying condition. During the drying, different method should be adopted according to the different materials and different forms of moisture absorption. Attention should be made that whichever method is used, the dried materials must be sealed for storage or heated and insulated, since they cannot be exposed in the air for too long time (including in the hopper with a lid thereon), wherein