screw diameter and stroke
the plastic molding machine maximum quantity of injection is determined by the diameter and maximum stroke of the screw. The diameter proportionates to the stroke, with a ratia of 3-5. If the ratio is too large and the stroke too long, the working length of screw shall be shortened, thereby influencing the plastication quality of materials. Should the ratio be too small and the stroke too short, to ensure the quantity of injection the diameter of screw must be increased and the diameter of injection oil tank shall also be increased accordingly to increase power consumpation.
2. Plastic molding machine screw lift angle, Rib width and Radial clearance.
Generally screw lift angle =17°40′.
Screw rib width e= (0.08-0.12)D (D is screw diameter). For materials with poor viscosity, the rib width should be taken as large as possible since if it is too small, overflow shall easily occur, yet when the width is too large, power consumption shall be increased, which may cause over-heating.
Radial clearance is the fitting clearnace between the screw and charging barrel. If the clearance is too large, the plastication capacity of the machine shall be reduced and the refulence of 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.
3. Plastic molding machine screw 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 imporved on the premised that the quality of the 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 plastication and measurement section each takes 25%.
4. Plastic molding machine screw 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 deaweight 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 cuttting and be further plasticated due to the reduction of the nozzle’s inner diameter.
