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Green Sand Metalcasting Foundry News

Green Sand Casting Process in Fine Art Education

Posted by Hill and Griffith Company on Jul 17, 2018 7:47:21 AM

Introduction for Sand Casting Process in the Foundry at Camberwell College of Art London.

Introduction for Sand Casting Process with Philip White and Jenny Dunseath in the foundry at Camberwell College of Art London. Video by Chris Follows part of the Process Arts Project.

Green Sand Foundry Process for Fine Art

Pattern Making:

The Pattern is a full size model of the part that makes an impression in the sand mold, with dimensional allocation for shrinkage and finishing. If the casting is hollow, additional patterns called cores are used to create these cavities in the finished product. Patterns are usually made of wood, plastic, metal, or plaster; however, other materials or combinations of materials are used if there are additional specific properties required of the pattern. Every Pattern must have a draft angle of approximately 2° - 3° to all walls parallel to the parting direction to facilitate removing the part from the mold. Paint the surface of the Pattern with Varnish or Shellac to make it water tight and to ensure that the sand does not stick. For a Flat back pattern- put screw holes in the back to aid its removal from the sand.

Molding:

Molding is the multi-step process in which molds are created. In horizontal casting, the mold is contained in a two piece frame, called a Flask. The upper portion of the flask is called a Cope and the lower portion is a Drag. First, molding sand is packed into a Flask around the pattern. After the pattern is removed, Gating and Runner arrangements are positioned in the drag half of the mold cavity and the Sprue is placed in the cope portion. Gating systems are necessary for the molten metal to flow into the mold cavity. Cores are also placed in the drag portion of the mold if they are needed. To finish the mold, the Cope (top) section is placed on the Drag (bottom) section, and the mold is closed and clamped together.

Sand:

Two main routes are used for bonding the sand moulds: The "green sand" consists of mixtures of sand, clay (Bentonite) and moisture. If the sand can be squeezed together and hold its shape, it is suitable for use. The "dry sand" consists of sand and synthetic binders cured thermally or chemically. The sand cores used for forming the inside shape of hollow parts of the casting are made using dry sand components. Between uses, the sand is rejuvenated by adding water and mulling (mixing and smashing). If you do not let the sand dry out all the way, you do not have to mull, just add water. Sand grit is determined just like sandpaper. 150 is very fine and 50 grit is coarse. Fine sand will give good detail, coarse sand will give a pebbly or rough texture.

Materials Melting temperature

Aluminum alloys1220 °F (660 °C)
Brass alloys1980 °F (1082 °C)
Cast iron1990-2300 °F (1088-1260 °C)
Cast steel2500 °F (1371 °C)

Websites:

www.metal-technologies.com/SandCasting.aspx
www.airnyc.org/list/78478/1/sand-casting-step-by-step.html
www.foundry101.com
www.custompartnet.com/wu/SandCasting

Books:

The Complete Handbook of Sand Casting - by CW Ammen
Metal Casting: A Sand Casting Manual for the ... - by Steve Chastain

Credits:

NOTE: Because the sand is used in a damp condition there is minimal sand dust, and this occurs at the mould face immediately around the hot metal casting, clearly visible when the casting is knocked out. At this stage a small watering can or spray will help to stabilize this dry material. A standard dust mask could be worn. It is always worth taking sensible precautions with all processes. With sand casting on the scale imagined here keep a water spray handy and use it when cleaning away any dry material.

Text Information supplied by Jenny Dunseath:

Process Arts
Published on Feb 3, 2009
Category
Education
License
Creative Commons Attribution license (reuse allowed)

(Thanks to Philip White & Jenny Dunseath, we've always enjoyed this video.)

 Transcription,

"Philip White: For instance, this setup, this sand casting process that we're trying to develop is really a completely homemade idea in a sense that all the equipment that we've got here, apart from one or two specialist tools, which are made specifically for sand molding. The tools that we have supplemented our kind of project with are all homemade. Made on the lathe, on the ban saw, and generally speaking, simply made to do the job using patterns that are familiar to the sand casting process.
I set this up at minimum costs. Otherwise, I don't think I would have gotten any funding for it. What we've been able to do is get a little bit of money to buy extra material, for instance, more sand, sieves, and one or two more tools. Because a tool like that, which is a specialist tool, is gonna cost about 30 pounds. Whereas, you built this trowel, it'll cost you four or five pounds.
Speaker 2: Yeah, yeah.
Philip White: So, it's mixing and matching some of the things, which are readily available in hardware shops with one or two, as I say, specialist pieces of equipment.
Speaker 2: So, are you still making equipment, as you think you need it? Are you sort of, "Oh, it'd be useful to have this sort of tool that does this."
Philip White: Yes, I mean, I know that knives have been disappearing from the university canteens.
Speaker 2: Oh, really?
Philip White: Those make very good tools.
Speaker 2: Oh, great. Yeah. That's cheap.
Philip White: So, they've been put to good use. Tools like that are invaluable. This is a brick layer's tool, which his really used for pointing, but it's in fact, very good for cutting channels in molds, with a slight adaption. Sharpening edges, and polishing a little bit to help them to run through the sand.
Relatively inexpensive. Cost about 10 pounds a bag. I went up to the Midlands to get the first lot myself. And, it actually comes from very close to where I got it from. A place called Mansfield. Called Mansfield Red Sand. The important characteristics about it are that it's got an element of clay in it. It's been controlled in the process, and most of the lumps of stone got out. But, it is dug from the ground. It's not over processed. That clay element gives it the ability to be molded, to hold together, and if you want to, make a fairly sound mold from an object.
Speaker 2: So, you actually went up there to get it?
Philip White: Yeah, I didn't dig it from the ground. I did ... I have actually used some building sand myself, and mixed it up with bentonite, which is a very fine clay that is used quite well in ceramics. So, you can actually manufacture your own. In fact it worked very well, worked very well.
We're going to make a casting from a flat back pattern. The reason it's called a flat back pattern, means that it's a single pattern with no extra bits to it. Sand molds can be made from patterns which are really, quite complicated. They're made from several parts, and they come apart, and they go back together again in order for the mold to be constructed in the box. But, this example here is a fairly straight forward flat back pattern, which is similar to these castings here.
There's the pattern. It's got a flat back to it. What's going to happen is, that that object there, is going to be molded in the sand. This plane here is represented by the division between the bottom box and the top box, okay?
So, that will end up sitting there. In a sense, we've got exactly the same thing here. This object, which Jenny has made, is, in fact, a flat back pattern. The screw there is to enable this object to be lifted out of the sand leaving the molded shape of it there.
Speaker 2: So, the slot's on there for?
Jenny Dunseath: That helps because the MDF, when you work MDF, you get slight furry surface. If you put that in sand, it won't lift out nicely. So you need a nice smooth finish so that it will lift out of the sand better.
Philip White: The important thing about this surface is that it must not absorb any moisture, must be dead smooth, the pattern needs to be designed so that it has sufficient draft, and inclined angle, that is, so that it can be lifted out, no under-cast. Unlike the lost wax process, where you can make an object out of wax and it really doesn't matter what shape or form it is, the process enables you to make a mold, and a casting from that material, or from that fold.
Sand casting, has certain limitations, and in order to get the best out of your mold making, without any kind of impossible task of actually mending the mold, the pattern has to be made so that it will withdraw from the sand as easily as possible.
This is a casting from which a mold was made from a pattern. This had already been manufactured. What's nice about it is it shows that they actual thinness of the section, in this process, here, which is not much more than an eighth of an inch thick, and in some places slightly less. It shows how fine a casting, and how reasonable, the kind of detail can be. That ... It's got a lot of work to be done to it, but never-the-less, it's come out pretty good. We're quite happy with the way that has actually been cast.
These are the boxes. The top box and a bottom box. The drag, and the cope. Industrially, these would be made of metal, but that would cost about 180 pounds, if that was made from metal. Of course, industrially speaking, they can be thrown around, treated fairly roughly, and last a lifetime. Whereas these boxes, over a period of time will deteriorate, but, never-the-less, they function absolutely perfectly well for what we're doing.
The good thing about baking is that if you want to make something of a more specific size, e.g. this box here, which is a bit of a mega brute, which we're going to use fairly soon, it's been specially made by Jenny and Bill for a little project that I'm sure you've got ... You're working on.
Of course, you've got lots of boxes up here which show that depending on the size of the object, you can manufacture them to whatever specifications you need."


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