Definition of flow marks: A linear trace of the surface of a molded product. This trace shows the direction in which the melt flows.
Injection molding machine
1. Insufficient injection pressure and pressure holding
The injection pressure and holding pressure are not enough to press the condensed skin against the die surface, leaving the shrinkage of the melt in the flow direction. Increasing the injection pressure and holding pressure, the condensation layer is pressed against the die surface until the product is shaped, Flow marks are not produced.
2. Improper stay time
The residence time of the plastic in the material pipe is too short, and the melting temperature is low. Even if the cavity is barely filled, the plastic can not be compacted when the pressure is maintained, leaving the shrinkage of the melt in the flow direction. Ratio should be between 1/1.5 and 1/4.
3. Improper cycle time
When the cycle time is too short, the plastic is not warmed in the material tube, and the melting temperature is low. Even if the cavity is filled up, the plastic can not be compacted when the pressure is maintained, leaving the shrinkage cycle time of the melt in the flow direction. Extend until the plastic is fully melted, and the temperature of the melt is high enough to make the shrinkage of the flow direction unsuitable.
4. The temperature of the tube is too low
When the temperature of the tube is too low, the temperature of the melt is low, and the injection pressure and holding pressure are not enough to press the condensed skin against the die surface, leaving the shrinkage of the melt in the flow direction.
Increase the material temperature, pressure and pressure to press the condensation layer on the mold surface until the product is shaped, and the flow marks are not generated. The material temperature can be set according to the recommendations of the material manufacturer. After the tube is divided, medium, before, In the four zones of the nozzle, the temperature setting of the forward and backward should be gradually increased, and each zone will increase by 6C.
If necessary, sometimes the temperature of the nozzle zone and / or the front zone is set to be the same as the middle zone.
5. The nozzle temperature is too low
The plastic absorbs the heat released by the heating belt in the material tube and the friction heat generated by the relative movement of the plastic molecules caused by the rotation of the screw, and the temperature gradually increases.
The last heating zone in the tube is the nozzle. The melt should reach the desired temperature, but it should be heated moderately to maintain the best condition. If the nozzle temperature is not set high enough, the nozzle and the mold are in contact with each other. Too much heat, the temperature of the material will drop, and the injection pressure and holding pressure will not be enough to press the condensed skin against the die surface, leaving the shrinkage of the melt in the flow direction.
Increase the nozzle temperature. Generally, the nozzle zone temperature is set to be 6C higher than the front zone temperature.
Mold
1. The mold temperature is too low
If the mold temperature is too low, the temperature of the material will drop too fast, and the injection pressure and holding pressure will not be enough to press the condensed skin against the die surface, leaving the shrinkage of the melt in the flow direction.
Increase the mold temperature, maintain a high material temperature, and the pressure and pressure hold the condensation layer on the mold surface until the product is shaped and the flow marks are not produced.
The mold temperature can be set from the recommended value of the material manufacturer. The increment of each adjustment can be 6C, and the glue is applied 10 times. After the forming condition is stable, according to the result, it is decided whether to further adjust.
2. The gate, runner, or / and gate are too small
The gate, runner, or / and gate are too small, and the flow resistance is increased. If the injection pressure is insufficient, the advancement of the melt wave will be slower and slower, the plastic will become colder and colder, and the injection pressure and pressure will not be sufficient. The condensed skin is pressed against the die face, leaving a sink mark in the flow direction of the melt. Different melt transfer systems (including runners, runners and gates) on the computer with CAE (eg C-MOLD) The simulation is carried out to simulate the ideal runner, the size of the runner and gate (including the length and section size, such as diameter), is feasible.
3. Excessive exhaust
Insufficient exhaust gas will make the melt filling block, and the condensed skin will not be pressed against the die surface before the melt wave, leaving the shrinkage of the melt in the flow direction.
Exhaust at the end of each section of the flow channel, so that a large amount of air can be removed before the pouring cavity. The cavity exhaust can not be neglected. On the parting surface opposite the gate, consider adding venting holes, corresponding to product blindness. At the end of the hole, consider adding the exhaust ejector pin.
CAE (such as C-MOLD) simulates melt filling, which can help us quickly find all possible final fillings, that is, where the venting holes are to be added. According to the figure, it is foolproof. Add a vacuum system. Pumping before filling and filling is an effective method of exhausting. For some bite decorative articles, this may be the only exhaust.
plastic
1. Poor liquidity
Flow length greater than the thickness of the cavity, to be filled with the plastic flow easily. If the plastic fluidity is not good enough, slow moving further and further melt glue, more slowly colder, injection pressure and hold pressure is insufficient to condense tight skin the pressing face of the die, in the direction of flow of plastic melt leaving sink marks based on specific design materials manufacturers can provide expert advice:
In the principle of no flash, choose the most flowable plastic.
2. Improper use of forming lubricant
Lubricant level generally below 1%. When the content of the lubricant flow length is larger than the wall thickness, a modest increase in the amount of lubricant required to ensure condensation pressed against the mold surface until the shaped article, no flow marks. Increase generated by It shall be agreed and post materials manufacturers.
operator
Bad habit
If the operator switches the door of the forming machine too early or too late, the forming results will be inconsistent. When the tube heater tries to replenish heat in time due to irregular heat loss, the plastic temperature is not uniform, and there is a cold spot. Pressure and pressure are not easy to press the skin near the cold spot on the mold surface, leaving the shrinkage of the melt in the flow direction. Normally, the operator should be constantly educated to let you know the troubles caused by the inconsistent forming cycle. The importance of maintaining good forming practice habits. Proper shift work can prevent operators from losing their physical strength and lack of concentration, resulting in mistakes. Automation using robots is a way to keep the forming cycle consistent.