Re: Investment Casting of LOM Parts

From: Shoichi Terashima (Nissin DTM Co., Ltd.)
Date: Thursday, November 2, 1995

From: Shoichi Terashima (Nissin DTM  Co., Ltd.)
To: RP-ML
Date: Thursday, November 2, 1995
Subject: Re: Investment Casting of LOM Parts
> 2.Do the LOM parts expand in the burnout stage before the shell cracks?
     Though already Al Hastbacka wrote, there is Cercast's 
comparison table (RP Report: v.4, n.11, pp.3-4, Nov. 1994).
Thermal expansion before burnout of LOM part is relatively low among others.
But, ash residue after burnout is said a considerable amount in casting shell.
(It seems the sealant can be absorbed into pattern, causing swelling at heat).

>From experimental casting project held in Japan, the similar result was shown 
     for paper laminated pattern, which in this case patterns from Kira. 
According to this experiment, the paper pattern was easy to burn than polymer.
However, contrary to the above, patterns tend to shrink with heat applying, 
reportedly.  The result was no shell broken for several patterns.  The burnout
ash residue was found as well as so much.  When pattern geometry is simple, 
ash can be carried out with air blow, but may be difficult for thin wall, 
complex cavities ...  Therefore, except ash problem, paper pattern may be 
included in a group that cause less shell cracks.  In this experiment, 
wax, urethane and polycarbonate patterns other than paper were counted in the 
crack-less group.  Face coat selection on paper pattern may be one of key ? 
Regards,
 Shoichi Terashima         _/    .  _/       +            / |  )


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