Monday, 21 May 2012

Cores and Impression Cores

So, I’ve been reading up on how to make cores for sand casting. A core is a hardened sand part in the mould that is intended to make a void in the casting. You would use this in your mould where you want your casting to be hollow, or have hollow sections.

For example, you are casting a tube, you would make a 2 part wooden cylinder and invest that in the cope and drag, then you would take the wooden cylinder out of the sand and you want to make the casting hollow, so you make a cylindrical core (thinner in diameter than the wooden cylinder). The core should extend past the end of the impression made by the wooden cylinder so that it can “bed” in the greensand. When you pour the molten metal into the flask, the metal will go into the void between the greensand and the core.

For the core to rest in the space, it needs to be hard. It’s going to be spanning at least part of the impression in the greensand without support. This is done by mixing sand with and agent or agents that harden it.

Probably the most straight forward mixtures for this is sand, flour and molasses and water. According to a good recipe for this is sand (80-90%) cornflour (10-20%) and molasses (mixed with water at a ratio of 1 part molasses :9 part water). Other recipes (there are more on the above link) include mixing with sodium silicate, mixes with wallpaper paste, etc.

I need to make a new attachment for my vacuum cleaner to pump air into my furnace, so I’m going to be making a 2 part core for this, basically, a cylinder glued to a rectangular prism (box). The metal needs to be fairly thin so that I can force it (deform it) into the vacuum cleaners exhaust filter clip.


At the moment, this is served by a flimsy bit of galvanised tin. It has worked well so far, but it is starting to fall apart. It would be better if it was one integral part rather than a couple of pieces of tin riveted together.

I’ll post more as this project continues.

No comments:

Post a Comment

Paypal Donations

Donations to help me to keep up the lunacy are greatly appreciated, but NOT mandatory.