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What is the relationship between the compression strength of the sand core and it's breaking strength during casting.I am doing compression testing on silica sand cores made from cold boxes and I'm not sure if the results obtained can be used to determine if the core will not break during casting.The compression results are not always consistent even though the Loss on Ignition test results are consistent, for example a pipe core would a correct total binding content (TBC) but breaks during casting.Anyone out there to help.

RE: Coremaking

Hi taila,

I think this is the wrong forum for this question but, trying to help with the question. The compression strength of cold box cores has little relevance to it's functional bend strength.
It's difficult to help specifically without more information, for example, what material are you casting ? Iron, Aluminium or other ?
How long is the unsupported length of the core between prints ?
Is the feed over the unsupported part of the core ?
Please supply more info' & I'll try to help.

RE: Coremaking

Hi John

Thanks for your response.

I am with an Aluminium Diecasting Foundry and we manufacture cylinder heads and intake manifolds. I have to agree with you when the compression strength has little relevance to it's functional bend strength. I have also been informed that the core does not take the load of metal above it as pressure is constant about a point in all directions.Therefore the metal below the core also supports the cores ability to withstand the so-called "load".

This brings me to a question whether it is necessary to do compression on a particular core to determine the breaking strength and can one use these results to determine whether they will/will not break during casting even if the LOI is within the required specification? (I use the Instron tensile tester for the compression strength of these cores)


RE: Coremaking

Hi Taila,

Ok, this is going to be a bit drawn-out I can tell !
Your colleagues have informed you that:- "the core does not take the load of metal above it as pressure is constant about a point in all directions."
I'm sorry to say that this is not necessarily correct. I also work in an Aluminium Casting Foundry where we also make induction manifolds in both Gravity (permanent mould) Diecasting and Airset (hard-sand) casting. One thing is constant, there is always gravity induced metal pressure whilst filling the mould. I have seen cores break solely because the "ingate" is positioned around the unsupported part of the core. This should always be the first thing to look at.
The next thing is the bonding agent you are using to make the Cold Box cores, is it Co2, Amene or a bonding agent & catalyst mixed in the sand ? This will effect your compressive strength and the ability to withstand "heat-soak".
I look forward to the next instalment !

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