Analyze the solution of injection flow marks

Injection molding machine

1. Insufficient injection pressure and pressure holding

The injection pressure and holding pressure are not sufficient to press the condensed skin against the die face, leaving a sink mark of the melt in the flow direction. The injection pressure and pressure are increased, and the condensation layer is pressed against the mold surface until the product is shaped and the flow marks are not generated.

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. The ratio of shot to material is 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 barely filled, the plastic cannot 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.

Increasing the material temperature, injection pressure and holding pressure will 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 by reference to the material manufacturer's recommendations. The material tube is divided into four zones: the rear, the middle, the front and the nozzle. The temperature setting of the material should be gradually increased. For each zone, the increase is 6C.

If necessary, the temperature of the nozzle area and/or the front area is sometimes set to be the same as the middle area.

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, where the melt should reach the desired temperature, but it must be moderately heated to maintain optimum conditions. If the nozzle temperature is not set high enough, the nozzle and the mold are in contact with each other, the heat taken away is too much, the material temperature is lowered, and the injection pressure and holding pressure are insufficient to press the condensed skin against the mold surface, leaving the melt. Shrink marks in the direction of flow.

Increase the nozzle temperature. The nozzle zone temperature is typically set to be 6C above 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.

Increasing the mold temperature, maintaining a high material temperature, and suppressing the 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 mold temperature can be set from the recommended values ​​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. Simulate the filling of different melt transfer systems (including runners, runners, and gates) on a computer with CAE (such as C-MOLD) to find the ideal runner, runner, and gate size ( Including length and section related dimensions such as diameter, etc., is feasible.

3. Excessive exhaust

Insufficient exhaust gas will cause the melt filling to be blocked, 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 begins at the end of each section of the flow path, which allows a large amount of air to be removed before the pouring cavity. The cavity exhaust should not be ignored. On the parting surface opposite the gate, consider adding a vent hole, corresponding to the end of the blind hole of the product, consider adding the ejector pin.

CAE (such as C-MOLD) simulates the filling of the melt, which can help us quickly find all possible final fillings, that is, where the vents are to be added. According to the picture, there is no loss. The addition of a vacuum system for pumping before and during filling is an effective method of venting. For some bite decorative articles, this may be the only exhaust recipe.

plastic

1. Poor liquidity

The cavity with a long flow to wall thickness ratio must be filled with plastic that is easy to flow. If the fluidity of the plastic is not good enough, the melt is slower and slower, and the slower and colder, the injection pressure and the holding pressure are not enough to press the condensed skin against the die surface, leaving the shrinkage of the melt in the flow direction. Material manufacturers can provide professional advice based on specific designs:

The most flowable plastic is selected on the principle that no flash is generated.

2. Improper use of forming lubricant

Generally, the lubricant content is below 1%. When the flow length to wall thickness ratio is large, the lubricant content must be moderately increased to ensure that the condensation is pressed against the die face until the product is shaped and flow marks are not produced. Increasing the amount of lubricant must be done after agreement with the material manufacturer.

operator

Bad habit

The operator switches the door of the forming machine too early or too late, which can result in inconsistent forming results. When the material 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. The injection pressure and pressure holding pressure are not easy to press the skin near the cold spot on the die face, leaving The shrinkage of the melt in the direction of flow. Normally, the operator should be constantly educated to let you know the troubles caused by inconsistent forming cycles and recognize the importance of maintaining good forming practices. Appropriate shift breaks can prevent operators from making mistakes due to lack of physical strength and lack of concentration. Automating with robots and the like is a way to keep the forming cycle consistent.