Ejector Marks

Ejector pin marks are the white or glossy imprints on the casting surface from the ejector pins. This defect also goes by the name of ejector marks as well as pin pushes. It comprises multiple assembly marks resulting from different cavity bumps during the process.

These marks can eventually lead to surface cracks upon using the cast parts. Therefore, knowing the details of ejector pin marks in die casting is necessary. This article briefly looks into its characteristics, sources, effects, and countermeasures.

Characteristics of Die Casting Ejector Mark

Some of the most common identifying features to detect ejector pin marks include –

• Either too prominent or barely noticeable small indentations.
• Glossy, white, or greyish imprints on the die-casting surfaces.
• The overall size can vary in shape and length from 1/8” to 1.0”.
• No continuity to the inner die-cast parts or toward the edges.

Sources of Ejector Pin Marks in Die Casting

The most recognized reasons behind die-casting ejector marks include –

1. Internal Casting Stress

Poor operational actions like excessive injection pressure, unbalanced cooling speed, and superfast dwelling time contribute to internal stress buildup.

2. Erroneous Use of Spray

Applying an insufficient amount or an incorrect agent builds up high ejector resistance, initiating ejector marks from the resulting over-small drafts.

3. Improper Ejector Design

A compromised or imperfect ejector unit during mold design often interferes with ejector speeds, incorporating considerable ejection stress in ejector parts made of plastic.

Deviation from the standard process, machinery, composition, or finishing also triggers some primary issues. Though these problems do not directly influence ejector marks, the defect may eventually appear on the surface.

Effects of Die Cast Ejector Mark

The disadvantages concerning pin pushes are outlined as follows –

• Poor aesthetics due to the compromised surface finishing.
• Eventual worsening of the problem upon commercial use.
• Further triggering other defects like cracks in the long run.

Preventing Ejector Pin Marks in Die Casts

As the issue may develop from the machinery, apparatus, process, or materials, it’s necessary to follow proper standards throughout the production. And it’s possible to avoid ejector pin mark from affecting the die casts by –

1. Avoiding excessively high injection of the molten metal alloy.
2. Reducing the dwell pressure as well as the injection pressure.
3. Optimizing feed systems with a perfect mold-filling
4. Slowing down the cooling speed to extend the cooling time.
5. Increasing the draft to ensure proper retaining of the plastic.
6. Achieving a balanced injection by neatly arranging the pins.
7. Providing maximum smoothness for interior cavity surfaces.
8. Improving the cast/mold structure to ensure uniform cooling.
9. Using the most suitable releasing agent spray on the mold.
10. Keeping the amount of spray satisfactory during the process.

Ejector marks are a somewhat less concerting problem in large-scale die-cast manufacturing. However, total negligence can worsen the problem to a significant extent. And early precautions can effectively save the die-cast parts from any future damage.