Introduction to spin casting
Written by Mandy Johnston
I love starting new projects, especially interactive ones because I never know what direction the project will ultimately take. I am always interested to compare any given point in the process back to its genesis; and muse at the meandering or snowballed path that has been laid out in order to reach ‘here’.
This is a page about materials, their obvious as well as extraordinary uses. I am hoping the assemblage forum will create discussion between artists, and become a place where information and advice can be shared as I have come to feel quite isolated in my love for materials. I am hoping that this collection of information will evolve into a resource for and by artists through their contributions to the website. It will provide a much needed reference point for interested ( -ing) people based in South Africa working with materials that are available. I am hoping that this website will not only offer information about various materials, it will also provide recommendations from one artist to another about exciting, cutting edge or established local service providers. These services must be referred by an artist as endorsement (as far as possible) of quality workmanship.
When the interest shown in a specific material is large enough, assemblage will host materials workshops. Experts in each field will be invited to talk and participate.
If you have come across a use for a material that you feel people have to know about please forward your details to : email@example.com
Spin casting is a very affordable way to make original artworks or parts in metal ( see description of process below). It also makes the casting and replication of an artwork more time efficient than traditional bronze casting. Generally white metals are used for spin casting and the most common are pewter and zinc.
There is really too much to say in this short column, so, I hope to say just enough to instil the confidence you need to have something cast. The obvious uses for this technology are to make sculptures or jewellery pieces. The not so obvious would be spun pieces to form parts of sculptural forms where strength might be needed. For example if you would like to make a top heavy sculpture, the support structures could be spun cast and then set into a resin casting. An extraordinary use I have tested is the idea of artworks that require parts being heated and remaining in tact while others become malleable or even melt.
I have tried a crazy amount of materials to test for use as the material to make the original pieces that will eventually be moulded. The basic rule is that your original piece needs to be able to withstand high temperatures as well as a certain amount of pressure during setting of the silicone mould with heat and pressure(vulcanisation).
I have found that a good material to make your model from is Pratley’s putty. Some putty is quicker setting than others so you need to judge how fast you work in order to be able to make your work. Ceramic materials and hard wood can also be used. The other material that works is a resin called f16. You can buy this from AMT composite suppliers. For this you will need to make a silicone mould of your original and then resin(f16) cast your master copy( check topics list: silicone moulds). The finish of the original you make should be what you ultimately want to get out of the mould so you will need to be vigilant at this point.
In terms of design, the only thing you really need to be concerned about your original coming out as intended are undercuts. These can cause friction and wear and tear of the mould. Moulds are generally made in two halves, for example a coin where the two halves of the mould can be separated equally.
In this example you can see that the back is flat and the front does not have any areas where moulding rubber would go underneath( undercut). The rubber can therefore be separated easily each time it is spun and filled with metal.
For more complex models, try to imagine it being removed from rubber around it.
Undercuts are possible but only very good, professional mould makers will be able to make puzzle moulds so you should talk to the factory mould maker about concerns with design/ model before going ahead.
Eg. This man would be possible, but very difficult to cast whole as there are areas where the rubber would get stuck when trying to remove it from the mould.
The most obvious limitation of spin casting is size. The spinning machines typically only take mould up to 40cm in diameter. Remembering you need too work in the areas around the hole in the centre. This means that larger items need to be make in sections and joined afterwards. If you are making many small pieces you can fit them around the centre in as in the picture below
The common metals that are spun cast are pewter, tin, zinc and lead. Pewter is a soft metal that cannot be used for heavy duty functional object. Zinc is hard but brittle rigid but will snap under pressure. Zinc is much cheaper than Pewter but the mould life is less as it must be heated to higher temperatures.
Description of process
Spin casting is a process whereby a cavity in a spinning rubber mould is filled by pouring molten metal into a central hole. Moulds are created with specialised silicone rubber whereby the original artwork is pressed between two discs of rubber and then vulcanised (baked). The original artwork is then removed leaving behind a cavity. Metal is then poured into a central hole and centrifugally forced into the cavity. Once the metal has been poured each item must be hand sanded, burnished and polished. The mould can be reused as desired but mould life differs according to heat of various metals being used.
Brief description of item: pewter spin caster
Brief description of service received: excellent moulding, good finished items
Contact details:0824167500 begin_of_the_skype_highlighting 0824167500 end_of_the_skype_highlighting Terry
Referral: AMT Composites
Brief description of item: f16 resin
Brief description of service received: excellent
Contact details:011 392 4232 begin_of_the_skype_highlighting 011 392 4232 end_of_the_skype_highlighting