What is the flow mark injection molding? How does the flow mark injection molding occur? How to solve the flow mark troubleshooting in injection moulding?
Flow mark injection molding in plastic
1. Poor flow
Flow Length to Thickness Ratio large cavity must be filled with easy-to-flow plastic. If the flow of plastic is not good enough, the solute becomes slower and slower and colder, and the injection pressure and holding pressure are not enough to press the condensed skin tightly on the mold surface, leaving the shrinkage of the solute in the flow direction.
How to solve this flow mark injection molding?
Material manufacturers can provide professional advice based on specific designs: use the most flowable plastic under the principle of no overflow.
2. Use Molding Lubricant (MLC) with improper lubricant content of less than 1%.
When the flow length to wall thickness ratio is large, the lubricant content should be increased moderately to ensure that the condensation layer clings to the mold surface until the product is shaped and the flow marks are not produced.
How to solve this flow mark injection molding?
Increasing the lubricant content should be agreed upon with the material manufacturer.
Flow mark injection molding in the mold produced
1. Mold temperature is too low
If the mold temperature is too low, the material temperature will drop too fast and the injection pressure and holding pressure will not be enough to press the condensed skin on the mold surface, leaving a shrinkage of the molten rubber in the flow direction.
How to solve this flow mark injection molding?
Increase the mold temperature, keep the material temperature high, and keep the injection pressure and holding pressure to press the condensation layer firmly on the mold surface until the product is set and the flow marks are not produced.
The mold temperature can be set from the material manufacturer’s recommended value. Each adjustment can be made in increments of 6°C for 10 shots, and after the molding condition has stabilized, further adjustments will be determined based on the results.
2. Sprue, runner, or/and the gate is too small
Sprue, runner, or/and the gate is too small the flow resistance will be increased, if the injection pressure is not enough, the advance of the melt wavefront will be slower and slower, the plastic will be colder and colder, the injection pressure and holding pressure are not enough to press the condensed skin on the mold surface, leaving the shrinkage of the melt in the flow direction.
3. Venting is not sufficient to ventilate the plastic
This will prevent the melt from filling, and the melt wave will not be able to press the condensed skin on the mold surface, leaving the shrinkage of the melt in the flow direction.
How to solve this flow mark injection molding?
Consider venting at the end of each runner section to avoid gas entering the cavity. The cavity venting should not be neglected. It is better to use a full circumference exhaust.
Injection molding machine-generated flow mark injection molding
1. Insufficient injection pressure and pressure-holding
The injection pressure and pressure-holding are not enough to press the condensed skin tightly on the mold surface, leaving a shrinkage of the molten glue in the flow direction.
How to solve this flow mark injection molding?
Increase the injection pressure and holding pressure, so that the condensation layer can be pressed firmly on the mold surface until the product is set and the flow marks are not produced.
2. Inadequate Residence Time
The residence time of plastic in the tube is too short and the temperature of melt glue is low, even if the cavity is barely filled, the holding pressure is still unable to compact the plastic, leaving the shrinkage of melt glue in the flow direction.
How to solve this flow mark injection molding?
Shot-to-Barrel Ratio (Shot-to-Barrel Ratio) should be between 1/1.5 and 1/4.
3. When the cycle time is too short
The plastic is not heated up enough in the material tube and the temperature of the melt glue is low. Even if the cavity is barely filled, the plastic is still not compacted when the pressure is maintained, leaving the shrinkage of the melt glue in the flow direction.
How to solve this flow mark injection molding?
The cycle time should be extended until the plastic is fully melted and the melt temperature is high enough to make the shrinkage marks in the flow direction.
4. The tube temperature is too low
If the tube temperature is too low, the melt temperature is low, and the injection pressure and holding pressure are not enough to press the condensed skin on the mold surface, leaving shrinkage marks in the flow direction of the melt.
How to solve this flow mark injection molding?
Increase the material temperature, injection pressure and holding pressure to press the condensation layer tightly on the mold surface until the product is set and no flow marks are produced. The material temperature can be set according to the material manufacturer‘s recommendation.
The material tube is divided into four zones: Rear, Center, Front and Nozzle. The material temperature setting should be increased gradually from rear to front, by 6°C for each front zone.
If necessary, sometimes the nozzle area and / or the front area of the material temperature setting and the same as the middle area.
5. The nozzle temperature is too low to produce flow mark injection molding
How to solve this flow mark injection molding?
The plastic absorbs the heat from the heating bands and the frictional heat from the relative motion 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 molten plastic should reach the ideal material temperature, but must be heated moderately to maintain the best condition.
If the nozzle temperature is not set high enough, the material temperature will drop because the nozzle and the mold are in contact and take away too much heat, and the injection and holding pressure will not be sufficient to press the condensed skin against the mold surface, leaving a shrinkage of the melt in the flow direction.
Increase the nozzle temperature. Generally, the temperature of the nozzle area is set 6 ℃ higher than the temperature of the Front Region.
Besides The What is Flow Mark Injection Molding article, you may also be interested in the below articles.
Summary Of 50 Injection Mold Structure Operation Dynamic Diagrams
Auto Parts Stamping Die Design Concept
18 FAQ Of Injection Molding Machine Mold Clamping