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Selection of Molding Machine
For injection molding of SPESIN®, a general-purpose reciprocating screw-type injection machine is used, and 1.2 to 4 times/shot of capacity (ratio between product, sprue and runner volume) may be sufficient. To obtain optimum product properties from SPESIN®, proper control of injection machine temperature, time, and pressure are essential. When injection molding of SPESIN® is completed, residual resin must be cleaned while the cylinder is still warm by using HDPE, PP, or PS resin. Before injection molding work, the injection machine must be heated to the required injection machine temperature of SPESIN®, and a sufficient quantity of resin must be pumped in.
The molding pressure setting varies and is determined, considering the resin grade to be used, the complexity of products, and the dimension of the runner and gate. Normally, minimum pressure is applied at the initial stage of operation, which will be gradually increased until optimum pressure conditions are determined. The proper holding pressure is 50~60% of the primary molding pressure, and back pressure should be determined in consideration of factors such as kneading of resins, gas venting, etc.
Cylinder temperature of the injection machine should be set 20~40 higher than the melting temperature of SPESIN®. Normally, a range of 225 ~270 is appropriate for injection molding, and temperatures over 280 are not advisable. For setting mold temperature, consideration should be given to reduction of internal stress, improvement of surface conditions, and prevention of post-distortion. Generally, 40 of the glass transient temperature (Tg) of PBT resin is ideal for evenly dispersed crystallization and for reducing cycle time. For the glass fiber reinforced grade of SPESIN® (KP212G30), 80 is adequate.
|Injection Machine||FANUC AUTOSHOT 35Ton||115ENGEL ES150P 150Ton g||ENGEL ES75P 75Ton|
Total Cycle Time
Note. : Need to Increase : Need to Decrese : Study for Effecting Factors
In designing injection molded parts, the maximum flow distance for the thickness of each part to be molded is crucial. When the molten resin
temperature is 265℃, the L/t is in the 250~300 range. Flowability of SPESIN® varies according to melting temperature and injecting pressure.
As an example using KP211, with injecting pressure of 1,430kg/cm, L/t is 250 when melting temperature is 250℃, but L/t rises to 300
when melting temperature is 270℃. In designing molds, measures should be taken to minimize flow resistance of molten resin and all
unnecessary scrap should be minimized in designing flow lead. Optimum designing is now feasible by computer.
The proper gas vent should be considered for extrusion molding of SPESIN®, as the gas vent has a major effect on the properties and appearance of molded parts. For general gas vents, small grooves are provided at the parting face opposite the gate. With SPESIN®, it is possible by making grooves of 0.02~0.05 cm depth at 3cm apart. As burr (flash) can be generated, care must be taken not to make the grooves too deep.
In the case of gas venting on a wide surface, and it may be advisable that several diamond-shaped grooves are made by means of scraping. A pricking or pushing pin can be installed to the part where gas is gathered if it is difficult to install a vent line. For the flameproof grade of SPESIN®, it is advisable to install a series of vent lines along the cavity surrounding. In mold designing, the following general factors should be considered for ensuring the highest properties during the molding process of SPESIN®.
a. Material for mould
b. Design of runner and sprue
c. Design of gate
d. Consideration for molding shrinkage