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Four aspects to analyze the problem of silver defects in injection molding

Silver grain is mainly caused by incomplete drying of raw materials, caused by moisture or volatile components (mainly caused by moisture, decomposition gas, solvent gas, air interference). When producing silver filaments, the molding experiment should first be carried out with thoroughly dried pellets. If this is not possible, other causes can be checked.

The specific reasons for the production of silver wire are as follows:

1. Injection molding machine:

(1) The barrel, the screw wears or the rubber head and the apron have a dead angle of the material, which is decomposed by heat for a long time.

(2) If the heating system is out of control, causing the temperature to be too high and decomposed, check whether there are any problems with the heating elements such as thermocouples and heating coils. Improper screw design results in improper venting or easy introduction of air.

2, the mold side:

(1) poor exhaust;

(2) The frictional resistance of the runners, gates and cavities in the mold is large, causing local overheating and decomposition;

(3) The distribution of the gate and the cavity is unbalanced, and the unreasonable cooling system will cause the heat to be unbalanced and the local overheating or blocking the air passage;

(4) the cooling passage leaks into the cavity;

(5) There is a part of unplasticized plastic cold material on the injection molded part, which increases the size of the cold material hole; expands the tail end of the flow channel to form an additional plastic cold material hole; uses electric heating nozzle and nozzle sleeve;

(6) The runners and gates are too small or too long, causing the plastic to condense during transport and, if necessary, increasing the diameter of the runner and the depth of the gate.

3. Process:

(1) Set temperature, pressure, speed, back pressure, melt motor speed is too high to cause decomposition, or pressure, speed is too low, injection time, insufficient pressure, low back pressure, due to failure to obtain high pressure and density Insufficient gas cannot be melted and silver streaks appear. Appropriate temperature, pressure, speed and time should be set and multi-stage injection speed should be used.

(2) The back pressure is low and the rotation speed is fast, so that the air enters the barrel, and the molten material enters the mold. When the period is too long, the melt is decomposed in the barrel due to excessive heat, and the plastic stays in the shot tank for too long, reducing Total cycle time; injection volume is too small for injection molding requirements (20% to 80% of machine injection is recommended).

(3) Insufficient material, the feeding cushion is too large, the material temperature is too low or the mold temperature is too low, which affects the flow of the material and the molding pressure, and promotes the formation of bubbles.

(4) The surface temperature of the molten rubber is too high, and the temperature of the shooting cylinder is lowered; the temperature of the melting glue is too low, so that the filling time of the mold is unstable, the temperature of the shooting cylinder is increased; the temperature of the nozzle is increased; and the filling speed of the mold is increased.

(5) Excessive mold release agent on the mold surface, thoroughly clean the mold surface with white sprinkle

4. Plastics:

(1) The plastic has a large humidity, and the proportion of added recycled materials is too large or contains harmful scraps (the scraps are easily decomposed), and the plastic should be sufficiently dried and the scraps should be eliminated.

(2) Moisture absorption from the atmosphere or moisture absorption from the colorant, and the coloring agent should also be dried. It is preferable to install a dryer on the machine.

(3) The amount of lubricant, stabilizer, etc. added to the plastic is excessive or unevenly mixed, or the plastic itself has a volatile solvent. Decomposition occurs when the mixed plastic is difficult to maintain heat.

(4) The plastic is contaminated and mixed with other plastics.

Four aspects to analyze the problem of silver defects in injection molding