In a foundry, a strike off bar is a simple, yet essential tool used to remove excess molding sand from the top of a flask or molding box after it has been rammed.
Understanding the Strike Off Bar
Based on foundry practices and the provided reference, a strike off bar is defined by its material and shape, specifically designed for its function:
- Material: It is typically made from either wood or iron.
- Shape: It is described as a flat bar.
- Edge: One edge of the bar is beveled.
- Surface: The surface intended for striking off is described as perfectly smooth and plane.
Figure 8.6, as mentioned in the reference, illustrates this tool, highlighting its straightforward design.
Purpose and Use
The primary function of a strike off bar in the sand casting process is crucial for creating a level surface:
- Excess Sand Removal: Its main use is to remove the excess sand from the top of a box after ramming.
- Leveling: After the molding sand is packed tightly (rammed) into the flask around the pattern, there is often sand piled above the level of the box's edge. The strike off bar is drawn across the top of the box, using its smooth, plane, and often beveled edge to scrape away this extra sand, leaving a flat, level surface.
- Preparation for Cope/Drag: This precise leveling ensures that the mating surfaces of the cope (top half) and drag (bottom half) of the mold will fit together properly, preventing leaks or shifts during casting.
Think of it like using a ruler to scrape excess flour off a measuring cup to get an exact amount.
Why is a Level Surface Important?
A perfectly level mold surface created by using a strike off bar is critical for several reasons:
- Ensures proper alignment between mold halves.
- Prevents metal from escaping through gaps.
- Contributes to dimensional accuracy of the final casting.
- Reduces the need for post-casting cleanup (fettling).
This simple tool is a fundamental part of manual sand molding, ensuring consistency and quality before the mold is closed and prepared for pouring molten metal.
