Incomplete castings.

[gyruss]

First of all sorry for my bad english.

I have a question concerning casting. Many of my castings are incomplete. It looks like there was some air in the mould that could not escape. I have made a few air vents but it doesnt help.

Does anyone know what could be the problem?
Could the metal be too hot or too cold?

I hope someone can tell me what I'm doing wrong.

Thanks in advance!
Gyruss.

[Prince August]

gyruss said:

First of all sorry for my bad english.

I have a question concerning casting. Many of my castings are incomplete. It looks like there was some air in the mould that could not escape. I have made a few air vents but it doesnt help.

Does anyone know what could be the problem?
Could the metal be too hot or too cold?

I hope someone can tell me what I'm doing wrong.

Thanks in advance!
Gyruss.

Have you read our casting tutorials that we provide on our newsletters. They cover most of the finer points of casting.
There could be many reasons for trapped air:
1) Your metal is not at the right temperature, make sure it is hot enough by testing it with a used match, if the match smokes lightly when dipped into the metal then it is ready.
2) Overclamping the mold. You may be squeezing the mold too much.
3) Pouring the metal too slowly. You must fill the mold at a steady rate so the metal fills the ingate and the weight of the metal is forced into all the parts of the mold. Also this keeps the casting metal roughly the same temp as well.
4) Warm the mold before casting, and apply the CORRECT amount of release powder.
5) Venting as a last resort usually solves the problem. Always vent up to the top of the mold or to a nearby ingate.
Without seing the mold, or what is not filling I cannot be more accurate. Which metal do you use?? Model Metal is the best for details.

[richard]

Hi I brought some used moulds, they had been vented to the bottom of the mould with obvious results, have plugged holes and vented as following. When I have ever had to vent a mould of any type, I have either vented them into the ingate or at least to the top of the mould. This always seems to work and is the method suggested by PA.

[carl]

Your question leaves so much to be answered first. For instance what is the type of Lead or rather if a mixture, what proportions of what? Then are you using metal or the rubbery type moulds? Are you using lots of Talcom type powders on the moulds?
I too have that problem many times but with me it's due to really wierd mixtures of metals for the product. Some melts fast and some do not so I have to really get the metals hot and then I use lots of Talcom powders on the moulds. With my metal moulds, I use powdered charcoal on the moulds and attempt to get the moulds rather hot of very warm.