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Hiep

Information on making air release molds

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Hi everyone, 

im looking to get into tile production work and there seems to be very little information online about casting air release dies.  For the most part, I’m getting an idea of the materials needed for this project but no idea on the process of when to air purge the die at what temperatures and how much pressure to pass through.  

I eventually hope to get a larger space to acquire a press machine, but for now my knowledge and experience is limited.  Is there anyone that can help with the technical aspects of casting these “ram style “ dies? I am willing to meet with anyone that is open  and able to showing and sharing

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Ram press, and ram press/air release are two different styles of molds. I worked in a tile shop for a year; no air release systems in the shop whatsoever. All molds were made off of silicone/urethane masters, from pottery #1 or #2 plaster. Molds are made thick; if the tile was 1" thick (high relief), then the mold might be 4-5" thick. The molds were filled with clay which was pugged through a tile die, then slab rolled to approx. 1/4"-1/2" thicker than final tile thickness. The slab was cut approx 1/8"-1/4" smaller in dimension than the mold opening, the slab was placed into the mold, used chamois (any durable, porous material) to keep the plywood "press boards" from sticking to the tile, and the whole shebang (mold with clay, chamois, pressboard (could be numerous depending on the mold) was stuck either in an arbor press, or a homemade "ram press" (car jack on a frame), and the tile was pressed.  The excess clay was cut off with a wire tool (think more cheese slicer than potters wire), back of tile was smoothed out, hanging hook and studio stamp were added. The mold was sat in front of a fan for about 10-15 minutes (gets longer as the mold absorbs more water....later in the day....) until the clay began to pull from the edge of the mold, a couple of small blasts of compressed air, and then was flipped over to release the tile. The edges of the back of the tile were cleaned up, and then left to dry in a controlled room to keep warpage to a min.

   A ram press is a hydraulic press, historically introduced by the company Ram, however air release systems can work with any number of styles of presses, all the way from hand pressing, to major hydraulic presses. A perforated tube is set into the mold, approx 1/4" -1/2" from the surface of the pressed object (embedded in plaster 1/4-1/2" from what you are duplicating), and there is a quick release air connection at the end of your mold. Instead of air drying the tile after pressing, the air release allows you to flip your mold over immediately after pressing, activate your compressed air, and force the water which was forced into the mold during the pressing, back out, thus releasing the tile. Any mold, including air release molds, are going to have a limit as to how many castings can be made before the mold is saturated and needs to rest before being used again, however air release do provide a much higher production rate.

   As to what size of tubing, how much perforation, how deep to embed the tubing, how many "loops" of tubing in the mold, and how much air pressure to use is beyond my expertise. I would assume that the more detailed your tile, the more pressure, or more air flow (more loops/tighter loops) in your mold you will need. How deep to embed will depend on the detail of your tile, the type of plaster you are using (#1, #2, hydrocal, ultracal....?), and lastly the amount of air will depend greatly on how porous your molds are. The less porous, the less air, unless you plan on exploding your molds. I would start off using 10-15 psi (maybe less), and work your way up from there. You could wet the mold with plain ol' water, have the mold cavity facing you, and activate your air, when you start to see the water being pushed back out of the mold, and air bubbles is where I would stop with the air pressure. Too much pressure and you will destroy your molds.

    Finally, unless you are getting into serious tile production, and I mean thousands of tiles per day, there is no reason to make your life much harder by making air release molds, especially if your mold making experience is little to none. When I worked in the tile shop I would personally make anywhere from 150-200 tiles per day, depending on the size and intricacy of the tiles, and all of that was done with VERY basic molds (master laid flat on stone counter, coddles sealed with scrap clay, and #1/#2 brushed first onto surface and then poured over, and bubbles worked out), and very basic equipment. The arbor presses are "readily" available for pretty cheap, and come in a variety of sizes. Making your own hydraulic car jack press is cheap too, especially if you can weld. True, air release would bump that production up 2-5 fold, but how many tiles can you finish, fire, glaze, and fire too....

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Thank you for taking the time to share with everyone hitchmss. I will look into the silicone masters and arbor press.  What I find most appealing about the air release molds is the amount of space it can save with all the drying and in between. But you have brought it to my attention that those molds have a limit per day as well.  I saw a harbor freight 12 ton hydraulic press for cheap ($60) as well and might consider that. 

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On 12/14/2018 at 2:47 PM, Hiep said:

Thank you for taking the time to share with everyone hitchmss. I will look into the silicone masters and arbor press.  What I find most appealing about the air release molds is the amount of space it can save with all the drying and in between. But you have brought it to my attention that those molds have a limit per day as well.  I saw a harbor freight 12 ton hydraulic press for cheap ($60) as well and might consider that. 

Happy to help. If you're unfamiliar with masters, mothers, waste........molds/prototypes, I would suggest some basic introductory books into making ceramic molds. The silicone masters were made this way; prototype was created from wax, or wax based clay, urethane rubber was poured over the prototype as it sat flat on stone counter. Once urethane was hardened, the prototype was removed, and then the urehtane mold was flipped over, and filled with a high quality silicone rubber. This "master" was used to make all of the production molds (depending on the tile there could be anywhere from 1-4 molds for each design around the shop). Once the master was done being used to make production molds, it was put back into its urethane mold,  flipped so the urethane was up, and plaster was poured over top. Even though urethanes are stiff, they will "shift" over time, especially if the rubbers are in a hot/sunny area. The silicone really will shift a lot more than the urethane, and the plaster "housing" that was made helped to support the master so its detail wouldnt degrade over time. You can also just pour plaster over the mother, w/o the urethane, and this will work too. Silicones/urethanes are relatively cheap, especially if you buy the higher VOC stuff and just deal with the fumes. We used to use Polytek for all the rubber materials; great products, but not cheap= $300+ for 5 gallons of silicone. 

Yes, in theory you could save a lot of space with an air release system; one mold instead of 3-4, but again, unless your making a lot of tiles per day, and have lots of designs, then its not a big storage issue, unless your studio is tiny. The space we worked out of was maybe 800 sq feet which included three pressing stations, slab roller, mold making area, mold making materials storage, mold drying cabinet, glaze material storage, glazing area, drying area, compressor, pug mill..... and about 500 molds. Rolling wire shelving is great for storing the molds on, or old bookshelves. You can easily fit 100+ "tile sized" on one 18" x 48" x 72" wire shelf. Ive never been into a shop that uses molds which arent packed into every nook and cranny. Its just a part of the process; to make work you have to have molds. If you make "thin" molds, and can find a deeper shelved flat file cabinet, those are great. Its where we'd store all the master copies.

   You dont need to spend a ton on a press; we had a hydraulic press which was built off a shop press like the HF you mention. You'll need to make a "table" on which your molds can rest while in the press; we used layers (maybe 4-5 depending on mold thickness and stroke of piston) of 3/4" plywood glued together on both the top and bottom of the press. Wood is a "little" more forgiving than steel; if you used a steel "bed" and your molds werent perfectly flat, youd crack them very easy, still easily done with the hydraulic presses; i broke at least a few molds back in the day. If you can rework the jack to be on the bottom of the "H" and press UP, instead of down, it will be much easier for you to see the mold/clay as you press your tile. Otherwise you'll have to bend over as you press tiles to watch your mold. You could also mount the press on a platform to raise it off the floor, but then can you reach the jack's handle?

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