Forge & Foundry, Part 4 – Selecting a Shot Blast Machine for Sand Castings

Building upon the information shared in our last Forge and Foundry Series post about sand casting, we now turn to the process of selecting and designing machines to specific sand casting operations.

Selecting the right shot blasting machine for your process and work piece means understanding how the work pieces and machine will interact. Here are common questions Rosler Metal Finishing receives when developing perfectly specified solutions for sand casting.

How do work piece delicacy, size, and weight influence the machine choice?

Before choosing a machine, the following questions must be asked:

  • Are the parts sturdy, allowing for aggressive processing, or must they be handled gently, without any part-on-part contact?
  • Is batch processing possible or must it be continuous?
  • Which work piece handling system is best: rotary drum, troughed belt, wire mesh belt, overhead monorail system, or heavy-duty crane or trolley on rails for extremely heavy work pieces weighing several tons?
  • Can the work pieces be handled by robot or is a custom-engineered shot blast system the best solution?

It is extremely important to find a supplier that can offer a machine that is perfectly matched to the work piece characteristics.

How can coarse contaminants like sand lumps, broken off sprews, gates, risers, rebar, etc. be discharged from the shot blast system?

Shot blast machines for foundry applications are usually equipped with robust vibratory screen conveyors in place of the standard augers. They allow the discharge of sand lumps, rebar, etc., and the safe transfer of the mix of media and loose sand to the elevator. Machines should also be equipped with a rotary screen drum at the elevator exit to remove any larger particles from the media/sand mix, before it passes through the media cleaning system.

Sand-casted parts entering a blast machine

Why is it so critical to remove loose molding and core sand from the blast media, and how can this be done?

Sand is extremely abrasive. Even a small amount of sand (0.5-1 percent) in the media will cause the turbines and blast machine to wear more quickly. There are known cases where, due to a poorly functioning media cleaning system, the throwing blades had to be replaced every eight hours!

Therefore, shot blast machines dealing with more than six percent sand in the blast media must be equipped with a combined dual drum magnetic separator for the safe removal of sand in the blast media and an air-wash separator taking out any remaining sand, broken down media, and dust.

Demolding of a sand casting

How can blast machines for foundry applications be protected against premature wear?

Tiny amounts of sand in the media, scale, and rust from the raw castings as well as the use of granular blast media or large steel shot create a highly abrasive environment for the shot blast machine and turbines. Special precautions must be taken to prevent premature wear.

For example, the blast chamber should be made from 3/8th” (10 mm) thick manganese steel and additionally lined with replaceable wear liners made from manganese steel or chilled iron castings with a thickness of up to 5/8th” (16 mm). The thicker the wear liner package the longer the machine life.

The Rosler Way

The Rosler way means that we work with our clients to learn about their process, develop a better surface finishing technique, and deliver a solution. Sand casting and shot blasting are no exception. Whatever sand castings your process includes, Rosler Metal Finishing can learn about your challenges to develop and deliver a solution. Contact us today to discuss your unique challenges.

Be sure to catch up on our previous posts in the series including:

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