Setup, Burnout, Casting & Cleanup
Shor platinum investment is especially compounded for the casting of platinum, palladium and other high-temperature metals. When used in accordance with instruction, it will consistently give sound, smooth castings.
Before opening the drum, roll and tumble it end over end for at least five minutes to assure uniformity of the powder.
Platinum investment powder tends to separate into its ingredients during transport and storage. To minimize this, Shor Platinum Investment is packaged only in 25 pound drums, which are easy to roll and tumble to insure uniformity of the powder. Packaging in larger drums would increase the rate of ingredient separation, and the drums would be too large to allow for convenient mixing of the powder.
- In place of the rubber sprue base that is customarily used in casting, use a piece of asbestos paper or non-asbestos paper about 4" x 4" x 1/8" thick. Then fasten a cone-shaped wax button, about 1" high and 1" diameter, to the center of the asbestos and mount your wax patterns on the wax button.
- Line an appropriately sized flask with 1/16" thick asbestos (or non-asbestos) paper to within 1/4" of each end. Asbestos or non-asbestos paper, 1/2" shorter than the flask length, should be used for this purpose.
- Wrap a piece of 2" gummed tape around the top end of the flask (the end opposite the button). Alternatively, you can use a rubber flask extender. The paper or rubber flask extender should continue approximately 1" beyond the end of the flask.
- After mounting the wax patterns, place the lined flask over the wax pattern assembly. Secure the flask to the asbestos paper base by spreading hot wax around the junction of the flask and asbestos paper. This entire assembly would then be placed on a piece of wood or metal so that it can be moved easily to and from the vacuum investing machine without disturbing the investment or wax patterns.
- The importance of accurate weighing and adequate mixing cannot be over emphasized. Guessing at proportions, or proportioning by eye is the surest way to casting failures. Follow label directions carefully.
- Prepare binder working solution by pouring 8 fluid ounces (one bottle) of binder concentrate into a clean one-gallon bottle. Add 12 fluid ounces of distilled water. This makes one gallon of binder working solution.
- Mix 100 parts investment powder, by weight, not by fluid ounces, with 30 parts of binder working solution, by weight, not by fluid ounces. For example, 10 ounces of powder are mixed with 30 ounces of binder. There is a weight to the cups or buckets in which the investment powder and in which the binder working solution are held. You must subtract the weight of these containers from the weight of your investment and binder to get the true weight of these materials.
- Alternatively, if using a metric (gram) scale, the binder can be measured instead of weighed. One cc of binder weighs one gram. Therefore, 39 ml of binder (measured in a glass graduated cylinder), will weigh 30 grams, and should be mixed with 100 grams of powder. These ratios of 39 ml binder to 100 grams investment do not vary, no matter how much powder is used.
A heavy duty mixer, such as the Hobart K-45, should be used. Lightweight mixers will burn out in a very short period of time.
- Add the binder first.
- The powder should be added gradually to the binder as the mixer runs at a slow speed. Mixing should continue for at least 10 minutes, and preferably 15 to 20 minutes. After thoroughly mixing, vacuuming is carried out in the usual fashion.
- Fill the flasks with investment up to the top of the paper collar, and put aside to set undisturbed for at least one hour.
- At the end of this time, remove the paper collar and cut of the investment extending beyond the flask.
- Remove the paper base.
We recommend that you allow the flasks to stand overnight. They should always be invested and cast in the same day.
- Place the flask in a furnace at room temperature to 200° F during the first hour. Raise to 350° F during the next half hour.
- Over the next 2 hours, raise the furnace to 1600º F.
- Maintain the temperature at 1600º F for one hour.
- The flasks are now ready for casting.
Because of its extremely high melting point, platinum chills very quickly when the torch flame is removed. A casting machine with a very quick start, such as the Shor Platinum Casting Machine, must be used if melting the platinum by torch. Alternatively, high frequency machines, such as the Shor Induction Platinum Casting Machine can be used.
With natural gas, an oxygen pressure of about 40 psi should be used and the flame should be adjusted to have a very short inner cone about 1/2" long.
Caution: When melting wear very dark glasses. Keep moving the flame in a counterclockwise direction, until the metal is molten and is rolling freely. Swing the torch away and release the casting machine in one quick motion in order to avoid chilling of the metal.
- Allow the flask to cool until it can be held in an asbestos glove. Break away as much investment as possible by hand.
- Leave the casting in Safe-D-Vest until completely clean. This will take several hours or overnight.