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This page will summarize solutions to various problems in plastic molding!
Mechanism of gas burning and countermeasures
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Problem 1: Gas burning
Agenda
What is Gas?
What is gas burn?
Countermeasures (1)
Countermeasures (2)
Countermeasure (iii)
glossary
injection molding
mold
nesting
gas
gas vent
gas burn
ガスとは
ガスとは？ What is Gas?
Gas is the vaporization or gassification of volatile components and decomposition products contained in resins at high temperatures. (Since this gas contains volatile components, there is a possibility of ignition depending on the situation.
Gas generation (Gas is generated from the nozzle tip along with molten resin at high temperature)
ガス焼けとは
ガス焼けとは？ What is Gas burn?
When gas generated from resin fills the mold during the injection molding process, the volume of the gas is compressed rapidly as the resin fills the mold because the inside of the mold is basically a sealed space. At this time, the compressed gas becomes hot, causing ignition and explosion. This causes the resin to burn and the surface of the molded product to become discolored. This is called gas burning.
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Gas scorching (resin is scorched by ignition and explosion, discoloring the surface of the molded product)
Countermeasures (1)
対策方法①
If the cylinder temperature at which the molding material is melted is too high, the material will thermally decompose and discolor. If the residence time in the cylinder is too long, the material will also thermally decompose and discolor. At the molding site, high-viscosity plastics tend to be molded at higher cylinder temperatures and speeds to make them flow more easily.
対策方法②
Countermeasures (2)
Gas vents are usually built into a part of the mold and provide a path for the gases in the mold to escape. When the mold is closed or material is injected, the gases are vented out of the mold through the gas vent. The design of the gas vent is optimized for the mold geometry and material properties. Without sufficient gas vents, gases can become trapped inside the mold. trapped in the mold. Conversely, excessive gas venting can lead to material leakage and uneven molding.
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SG-WIND
Countermeasure (iii)
Most gas vents are installed at the final filling point, but gas vents can also be installed in the area of the molded product during the filling process. In molds with slits or holes, weld lines and air traps do not always occur at the final filling point, so gas venting nests can be set at arbitrary locations to make weld lines and air traps less noticeable. Therefore, weld lines and air traps can be made inconspicuous and eliminated. Molding results from setting the gas venting nets in the area where weld lines and air traps occur. The gas venting nets are set in a wide area so that weld lines are not noticeable and air traps do not occur. This time, the product is a palm-sized molded product, but for large molded products such as automobile bumpers, the shape becomes more complex and the amount of resin used increases, so the amount of gas generated will inevitably increase. The larger the molded product, the more important it is to vent the gas.
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Advance①
Gas venting nest: SG-WIND
Gas venting insert designed by a molding shop that also makes molds
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Advance②
CAE: Prediction by flow analysis
Pioneering introduction and accumulation of know-how in the molding industry
Accurately predicts weld lines and air traps
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