The following pages will describe the various types of problem that we have experienced in the molding of ABS.
Product design, material selection, and molding conditions
The following problems either occur individually or in combination. Click on one of the following items for more details about the corresponding problem.
Gaseous components in the plastic appear at the molding surface and collapse.
The term "short shot" or "short mold" is used to refer to a phenomenon where plastic being injection molded does not reach certain portions of the inside of the die before solidifying.
|Location||On surfaces||Ribs and bosses||Corners and tips|
|Cause||Generation of gas||Material thickness and gas volume||Plastic viscosity|
The term "jetting" is used to describe the phenomenon where plastic passing through a gate does not adhere and where flow patterns are formed on the surface of the molded product.
|Appearance||Plastic at a relatively low temperature is injected from the nozzle during the initial stage of molding, upon coming into contact with the mold wall, this plastic becomes highly viscous and swirling takes place; furthermore,as hotter plastic is continually injected into the die, the original material is pushed deeper into the die and leaves flow marks.|
The term "flow mark" is used to describe the phenomenon where a striped pattern is formed around the gates when plastic has flowed through the die.
The phenomenon of color streaking is characterized by localized changes in the color of a molded component or by streaking.
|Characteristics||Variation from the original color||
A streaking pattern in a molded product
|Cause||This type of problem is principally caused by poor thermal stability of the coloring agent. Furthermore, it occurs more easily in locations such as welds, ribs, and the like which are likely to induce shear flow.||
The term "weld line" is used to describe the narrow V-shaped line that occurs at the point where two different flow fronts meet.
The terms "flash", "fins", and "spew" are used to refer to excess molding material that penetrates into mold gaps (i.e., between parting faces, slide push-out faces, and inserts, etc.) in a molten state.
The term "delamination" is used to refer to a condition where a thin micaceous layer develops on the molded product and then becomes separated.
|Cause(1)||Inclusion of a plastic which has poor compatibility with ABS (i.e., PP or PS, etc.)|
|Countermeasures||Carry out cleaning.
- Inside the cylinder
- Inside the hopper
- Inside the air feed lines
- Inside the dryer
|Cause (2)||When the die and plastic temperatures are extremely low, the difference in temperatures between the outer walls and the fluid layer results in the development of a thin hard coating which then peels.|
Standardize the resin temperatures.
- Raise the temperature of the resin
- Raise the temperature of the die
The term "stringiness" is used to refer to a phenomenon where string-line sections of plastic which are formed upon opening of the die adhere to the inside of the die and are transferred to the product during the next shot, resulting in string-line unevenness on the surface of the molded component.
Thin plastic string formed at the tip of a sprue
|Plastic string after transfer to the molded component|
|Cause||High nozzle temperatures|
Sink marks or shrink marks are hollows or indentations that occur on the outer surfaces of molded components.
Warping or Twisting
"Warping" is a term used to describe the deformation which occurs when there are differences in the degree of shrinkage at different locations within the molded component.
UMG ABS Ltd. accepts no responsibility for the quality or safety of any customer products which use our materials or which have made use of any type of data provided by this company.
Customers are requested to independently determine the suitability of our materials for their products. We also request that sufficient attention also be paid to laws, regulations, and industrial rights.