Re: sand blasting sand castings


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Posted by Robert Oblon on March 20, 1999 at 20:00:28:

In Reply to: sand blasting sand castings posted by Rob Frink on March 18, 1999 at 18:51:26:

First I have to respond to the information regarding a car wash...I daught if the pressure system at a self wash car wash has near the pressure required to remove air-set sand and fire scale from your castings and I think there would be lots of people sriving around with the paint removed from theirs cars with 2500 psi or higher water pressure...Plus the pollution problem of all of the sand/fire-scale related material going down the storm drain of the car wash facility. I've never used high pressure water blasting for cleaning castings. I have two inclosed blasting cabinets and use a number of different cleaning mediums. I do almost of my casting using ceramic shell refractory material. I also converted a sand core knock-out machine to take off the initial shell from the casting. Once the casting has most of the shell off, the part are put into the blasting cabinet and in most cases use a fine mesh garnet abrasive, 60-8- grit, or finer to take off any remaining shell material and scale and lightly etch the casting surface. All of my sculpture have finly detailed surface and have found that low pressure with the garnet works very well. Wheather your using sand or investment for your casting mold I feel the the more time spent on your wax or foam or what ever material you are using for your pattern to detail it before it is cast will help provide you with a finer cast surface. Of coarse depending on how you intend to finish the casting will mean how much finishing in metal you will have to do...Easier to do before it's in metal...I have also used glass beads and aluminum oxide mediums for cleaning casting surfaces and they all have different finishing properties. But in the long run I use the garnet for the most cost effect material...It's rare that a casting won't require some sort of chasing before patina or painting, etc. So back to preperation of your pattern before casting and all of the other factors that help provide a cazting with the best interity...New clean metal, ceramic shell that is not stale and/or sand that is dirty and used too many times etc. melting temps. mold temps. You know the drill. Everything from start to finish have a bearing on how your surfaces will turn out and nothing should be over-looked.

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