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All fuel gases are dangerous, and you should have a professional install your torch systems and fuel tanks. In addition, the regulator on the fuel tank should have a directional flow restrictor, which allows gases to leave the tank but not re-enter. For safety, use only regulators designed for the fuel you’re using.
~ Jurgen
Platinum in its pure form is very soft and needs to be alloyed. These Platinum alloys have different advantages and are used for specific purposes. The flow properties of the 950/50 Platinum /Cobalt mixtures are best suited for casting. With this alloy, very fine pieces of excellent quality can be cast, and considerable detail can be achieved. Pt/Co has an annealed hardness (HV) of 130 and when cold-worked achieves a hardness (HV) of 270. It polishes well and holds its luster for a long time. When welded with a torch Pt/Co may oxidize slightly. This can be removed by firecoating the object after the initial welding and re-heating it to about 1000° F. Pickle in a 10% solution of nitric acid. The oxidation will not reappear during wear. It is not possible to torch-weld different Pt alloys together as they have different melting points. It is always safe to solder them together using 1500 or 1700 solder. As a point of interest, Pt/Co is slightly magnetic.
Be sure to wear #5 or #6 welding goggles to protect your eyes.
Platinum /Cobalt alloy is slightly ferro-magnetic. This Pt950 alloy has very good flow characteristics and is a superior platinum casting alloy. With its good hardness, it takes on a great polish. The best way to size a Platinum /Cobalt alloy ring is soldering with 1700 solder. Roll the solder paper-thin, wedge it into a very well fitting seam and heat. The seam should be very, very thin. Now use a file to remove excess solder, and BURNISH the seam with a Tungsten burnisher. This should remove all traces of the seam. Now polish and clean the ring.
Jurgen
Today, platinum casting for the small shop is easier than ever - as long as you are sufficiently prepared. Platinum casting is different from gold or silver casting, and insufficient preparation and understanding of the process can still lead to many hours of frustration. Success depends on having good, functional equipment and learning all you can about the process. This seminar will emphasize ways to improve your casting process by discussing how to recognize and eliminate common mistakes and improve efficiency in time and materials.
This seminar sponsored by Platinum Guild International, is part of the program at the Bench Jewelers Conference & Expo, April 24 – 27, 2008 in Los Angeles. For details on all the seminars offered, more conference & expo information, and to register go to: www.BenchConference.com.
One of the most important steps in finishing a platinum casting is burnishing. Burnishing will work-harden the surface, compress it, close small cavities and make polishing easier. This step, when done properly, will reduce rejects from the final polish and save time.
When cast and no other step has been performed, the platinum casting has the hardness of the alloy in an annealed state. Burnishing will add extra hardness to the casting, preventing a score of problems that may show up later if this step is not taken. Castings may bend and take on the shape of the finger and the rings will scratch more easily when not burnished.
Therefore, as a general rule, all platinum castings should be burnished. The best way to burnish a platinum casting is using a tungsten burnisher. The highly polished tungsten burnisher is rubbed across the surface of the piece. This is done with considerable pressure. This action will move the surface, compress it and close small porosity holes in the process.
When platinum is being cast it is almost impossible to avoid some minor porosity from affecting the casting. This may be caused by the structure of the metal, the alloy combination, the temperature, the atmosphere; in short, there may be many reasons for it. As you know, porosity is defined as small cavities in the surface or the interior of the metal. When polished, micro porosity may appear as a haze, larger porosity may appear as small holes. A good caster can use several techniques to reduce this problem to a minimum and produce fine castings.
Since the burnisher is highly polished, it will also create a high gloss polish on the surface treated. The rubbing action hardens the surface and thus, final polishing becomes a much simpler task. It is important to remember that any scratch on the burnisher will be transferred to the piece. So the better the polish of the burnisher, the better the surface of the piece being burnished. It is advisable to use a small amount of oil to lubricate the burnisher. This prevents scratching and makes a smoother better surface possible.
Besides the manual method of burnishing, burnishing can also be done with a rotary burnisher, using a motor tool. Rotary burnishers are available commercially, but can also be easily fabricated by grinding an off center surface on the end of a tungsten rod and polishing it. The rotary motion will create the burnishing action. Another way is to bend the end of a burr to an L-shape configuration and again giving it a high polish. When placed into a rotary hand piece, the shape of this tool will be a very effective burnisher.
In large production, some burnishing can be accomplished by placing the castings in a rotary or magnetic tumbler, where the steel beads and/or steel needles create the burnishing action. It may, however, still be necessary to burnish the pieces by hand.
As burnishing prepares the surface for the final polish and eliminates many minor flaws, it is an indispensable tool for every manufacturer to consider.
Jurgen
