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Factor 1: Melt Fracture
Factor 1: Melt Fracture
Factor 1: Melt Fracture
Factor 1: Melt Fracture
Factor 1: Melt Fracture
Factor 1: Melt Fracture
Factor 1: Melt FractureWhen the melt is injected into a cavity with a large volume under high-speed and high-pressure conditions, it is easy to produce melt fracture.
At this time, the melt surface is laterally fractured, and the fracture area is rough and mixed on the surface of the plastic part to form paste spots
.
When the melt is injected into a cavity with a large volume under high-speed and high-pressure conditions, it is easy to produce melt fracture.
The essence of melt fracture is due to the elastic behavior of the polymer melt.
During this process, the melt will undergo a drastic change in stress and will produce strain.
If the melt encounters sudden shape changes in the runner, such as diameter shrinkage, expansion, and dead ends, the melt stays and circulates at the dead ends.
Pay attention to eliminating the dead angle in the flow channel and make the flow channel as streamlined as possible;
Appropriately increase the temperature of the material, reduce the relaxation time of the molten material, and make it easy to recover and bridge the deformation;
Add low molecular weight to the raw material, because the lower the molecular weight of the melt, the wider the distribution, the more conducive to reducing the elastic effect;
Properly control the injection speed and screw speed;
It is very important to set the gate position reasonably and select the correct gate form.
Practice has shown that the use of enlarged point gates and latent gates (tunnel gates) is ideal
.
Pay attention to eliminating the dead angle in the flow channel and make the flow channel as streamlined as possible;
Pay attention to eliminating the dead angle in the flow channel and make the flow channel as streamlined as possible;
Pay attention to eliminating the dead angle in the flow channel and make the flow channel as streamlined as possible;Appropriately increase the temperature of the material, reduce the relaxation time of the molten material, and make it easy to recover and bridge the deformation;
Appropriately increase the temperature of the material, reduce the relaxation time of the molten material, and make it easy to recover and bridge the deformation;
Appropriately increase the temperature of the material, reduce the relaxation time of the molten material, and make it easy to recover and bridge the deformation;Add low molecular weight to the raw material, because the lower the molecular weight of the melt, the wider the distribution, the more conducive to reducing the elastic effect;
Add low molecular weight to the raw material, because the lower the molecular weight of the melt, the wider the distribution, the more conducive to reducing the elastic effect;
Add low molecular weight to the raw material, because the lower the molecular weight of the melt, the wider the distribution, the more conducive to reducing the elastic effect;Properly control the injection speed and screw speed;
Properly control the injection speed and screw speed;
Properly control the injection speed and screw speed;It is very important to set the gate position reasonably and select the correct gate form.
Practice has shown that the use of enlarged point gates and latent gates (tunnel gates) is ideal
.
It is very important to set the gate position reasonably and select the correct gate form.
Practice has shown that the use of enlarged point gates and latent gates (tunnel gates) is ideal
.
It is very important to set the gate position reasonably and select the correct gate form.
Factor 2: Improper control of molding conditions
Factor 2: Improper control of molding conditions
Factor 2: Improper control of molding conditions
Factor 2: Improper control of molding conditions
Factor 2: Improper control of molding conditions
Factor 2: Improper control of molding conditions
Factor 2: Improper control of molding conditions
Factor 2: Improper control of molding conditions Factor 2: Improper control of molding conditionsThis is also an important reason for scorching and smearing on the surface of plastic parts, especially the injection speed has a great influence on it.
When the flow material is injected into the cavity at a slow speed, the flow state of the melt is laminar flow; when the injection speed When it rises to a certain value, the flow state gradually becomes turbulent
.
This is also an important reason for scorching and smearing on the surface of plastic parts, especially the injection speed has a great influence on it.
Under normal circumstances, the surface of the plastic parts formed by laminar flow is relatively bright and smooth, and the plastic parts formed under turbulent flow conditions are not only prone to smear spots on the surface, but also prone to pores inside the plastic parts
.
Therefore, the injection speed should not be too high, and the flow should be controlled to fill the mold in a laminar flow state
.
If the temperature of the melt is too high, it is easy to cause the melt to decompose and coking, resulting in smearing on the surface of the plastic part
.
Generally, the screw speed of the injection molding machine should be less than 90r/min, and the back pressure should be less than 2mpa, so as to avoid excessive frictional heat generated by the barrel
.
.
Generally, the screw speed of the injection molding machine should be less than 90r/min, and the back pressure should be less than 2mpa, so as to avoid excessive frictional heat generated by the barrel
.
If excessive frictional heat is generated during the molding process due to the long rotation time of the screw when the screw is retracted, the screw speed can be appropriately increased, the molding cycle can be extended, the screw back pressure can be reduced, the temperature of the feeding section of the barrel can be increased, and the raw materials with poor lubricity can be used.
method to overcome
.
method to overcome
.
During the injection process, too much molten material backflow along the screw groove and resin retention at the check ring will cause the molten material to depolymerize and decompose
.
In this regard, resins with higher viscosity should be selected, the injection pressure should be appropriately reduced, and an injection molding machine with a larger length and diameter should be used
.
The non-return rings commonly used in injection molding machines are more likely to cause retention, causing them to decompose and discolor.
When the decomposed and discolored molten material is injected into the cavity, a brown or black focus is formed
.
In this regard, the screw system centered on the nozzle should be cleaned regularly
.
.
In this regard, resins with higher viscosity should be selected, the injection pressure should be appropriately reduced, and an injection molding machine with a larger length and diameter should be used
.
The non-return rings commonly used in injection molding machines are more likely to cause retention, causing them to decompose and discolor.
When the decomposed and discolored molten material is injected into the cavity, a brown or black focus is formed
.
In this regard, the screw system centered on the nozzle should be cleaned regularly
.
If the mold exhaust hole is blocked by the release agent and the solidified material precipitated from the raw material, the mold exhaust setting is not enough or the position is incorrect, and the mold filling speed is too fast, the air in the mold has no time to be discharged adiabatically.
.
In this regard, the blockage should be removed, the clamping force should be reduced, and the poor exhaust of the mold should be improved
.
.
In this regard, the blockage should be removed, the clamping force should be reduced, and the poor exhaust of the mold should be improved
.
The determination of the gate form and position of the mold is also very important, and the flow state of the melt and the exhaust performance of the mold should be fully considered in the design
.
.
In addition, the amount of release agent should not be too much, and the surface of the cavity should maintain a high smoothness
.
.
If the content of moisture and volatile matter in the raw material is too high, the melt index is too large, and the excessive use of lubricant will cause scorching and smearing failure
.
.
In this regard, hopper dryers or other pre-drying methods should be used to treat the raw material, switch to a resin with a lower melt index, and reduce the amount of lubricant
.
.
