Re: bas-relief casting short cuts

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Posted by bpfink on July 10, 19100 at 08:57:20:

In Reply to: bas-relief casting short cuts posted by red on July 09, 19100 at 14:25:29:

This could be a most interesting thread. There are many and I will be watching this to see what others post to add to this.

One I worked out about 25 years ago and am still amazed has not been used much more often. It takes each step and reduces it to the most minimal time and material and energy I could get to.

#1 First the relief was done in wax but many other media would work also.

#2 The relief had a rubber mold (negative) pulled off it with a plaster backup mold to hold it's shape for the next step.

#3 Then it had a good parting (silicone mold release) sprayed on and a rubber model was taken off so it is a new flexible urethane rubber positive.

#4 In my case I only took one off, but if this is to be a production item you could repeat this step and take off many more so when pouring the investment you could pour many at a time.

#5 The new flexible positive was mounted on a board and a standard plaster based investment was poured on top it, brushing the first surface so any air bubbles rose and left a perfect surface impression and then a small section pad of 1 x 1 inch chicken wire was set into the top level for later additional handling strength.

#6 When it was set up (about an hour) the sides of the box enclosure were dropped down and the mold removed (hinged on 2 sides so it dropped out easily without forcing... found this better than just a tapered angle system on the sides).

#7 The rubber positive is peeled off the investment. Since it is a flexible unit many undercuts are not a problem.

#8a This is stacked up for later dryout (via a hot sunny day) or burnout when there are as many as needed. In my case an edition of 25. That is also why you might like to have 2 or more rubber positives so a group of investments could be poured at one time. *** The word burnout is misleading since there is NOTHING to burnout in media, but both the mechanical and chemical water of the investment if it is to be cast. This means a simple 550 F (or higher) can do it if the next step is to pour the metal in, but as you will see next all I needed was a dryout phase for the mechanical water so no kiln was even needed.

#9a Then the metal (in my case copper on some, bronze on others) was metalized into the mold. This is a process of spraying molten metal from a torch type unit. An expensive gun that takes the metal from a spool of wire and straightens it, runs it through the gun using either a compressed air turbine or an electric rheostated drive gear and then melts it at the tip with an oxygen acetylene (or mapp gas) flame and sprays it onto the surface of the investment mold with a controlled air push from a 5 HP air compressor. The edition group was smaller 18 inch square wall relief units but....

Back in the 60's and 70's I was doing double relief models that were 7ft high by 6 ft wide and were the two sides of a double door system doing both doors at one time (to be cut apart later and reassembled with steel framing and hinge systems, etc). You may have seen some since there are a number of private homes, businesses, churches, restaurants and Playboy Clubs across the US that may still have them.

#9a The surface sprayed is not done in one pass but many and the build up is first as thin as a tissue paper but with more passes can be as thick as you like. I usually took it to almost 1/8th inch. It is porous since it is composed of fine droplets of the sprayed metal which tend to physically interlock and adhere but not remelt the last pass. This means it is also great on compression, but weaker on tension so any backing or side structure greatly aids it. I used polyester resin and then also added a good fiberglas mat to help lock it to the framing.

#10a The plaster based investment is then removed but since it was not burned out it is still very strong and needs to be cracked, chipped and wire brushed to get it fully off the surface.

Because of this stage, I found adding more sand to the mix made it easier and a proportion of 75 to 80% sand to plaster was sometimes used. Also tried adding old wheat flour but cost was not worth it.

*** One other noted change here is that since these very large door reliefs were done in wax, there was NO rubber mold taken, the wax was steam cleaned out of the mold so it still was a one time lost wax mold but also 100% of the wax was reclaimed.

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Jumping back to

#8b instead of a plaster based mold you can go straight to a fine sand / oil / catalyst investment such as Kenset or other and then no burnout is needed.

#9b and if you cast a back on this mold and include the sprues, cup and vents in the rubber, or grind them in later you can close the mold and pour any liquid bronze, aluminum, pewter, or others in the conventional ways (even cast iron will work in these molds).

So there you have it.

Fill in the missing technical blanks since any description of this type will necessarily omit many fine function details but maybe you will get the gist.

I have whole groups of process photos of many of these relief doors since I used to do art school and college lectures and maybe one day they could be put up on the web somehow, just too busy and uninformed to do it now.

#11 One other addition: in some cases I wanted other elements in these molds (like cast bronze door handles or silver horns on a herd of long horn cattle...for a ranch door or Johnnie's Steak House entry in Omaha, Nebraska) and they can be cast first in convention ways and then worked into the wax or mold and spray cast to lock them in when metalized over. A simple balloon on them where they should be protected, or a fine foil wrapped around will keep them uninvested to the surface so no further cleanup is even needed... and like that.

Enjoy,

Boy, there are so many toys on this physical plane to muck about with.

bpfink

PS. the metalizing equipment is sold in several forms but mine was discarded antique equipment from the METCO CORP. that is still around (last at Perkin-Elmer, Westbury, NY 11590 ... maybe still there). Almost any wire you can buy will spray and this includes steel (which has a core of flux inside it), stainless steel, zinc (they metalize bridges with that) to many different brasses and bronzes with prices per lb that start at about $8 and go up to $25 plus.

Of course I like the straight copper since it is gotten in scrap form at times, is cleaned by dragging up the road with the truck, is sized by pulling through a home made block swedge and is nearly free but for the time. Not a recommended system, but one I use and does work.

bpfink

for more info check out the artmetal search engine with metalizing, and/or see

http://www.kotra.co.kr/product/hs-code/hs81-90/hs84/seiwon-pro.htm

http://www.hsrework.com/Metal.html


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