An Investment for Casting Platinum
Revised June 2015
Platinite PT is designed for casting Platinum based alloys by the centrifugal technique. The powder is mixed with water and no special liquids are required.
The performance of this investment will depend on it being mixed and allowed to set as described below. Some minor variation in technique may be desirable to optimize the procedure for the specific flask size and mixing equipment being used.
The style of spruing should be appropriate to the patterns being used. In general if the flask only contains a few patterns they should be sprued from a central button. Larger numbers of patterns may be sprued as a tree.
A piece of absorbent paper with sides approximately 2-3" longer than the diameter of the flask to be used should be cut, The size of the flask and arrangement of the patterns should be such that the patterns are at least l/2 inch from the edge of the flask and the uppermost patterns are from 1 inch to ½ inch from the top of the flask. Attach the base of the tree or the button to the center of the piece of paper. (This may be done before or after the patterns have been attached), Using sticky wax attach the flask to the paper by placing a strong layer of wax around the outside of the flask. It is preferable that there is not a layer of sticky wax around the inside of the flask as this can weaken the investment.
A layer of cardboard or wood should be placed below the flask to support it while it is being invested and vacuumed. This support can be metal wood, heavy cardboard, etc., as long as it is rigid.
Place a collar around the top of the flask to extend 2-3" above the top of the flask. A larger extension is necessary for taller flasks and a smaller one for shorter flasks. A gummed tape or rubber collar may be used. The flask should not be lined.
- Use 34 ml water to 100 grams of Platinite PT. 32/100 - 34/100 Ratio
- Pour the measured water into the mixing bowl. Always add water first.
- Add the powder to the bowl and start incorporation.
- Start mixing using a low speed setting (# 1 on a Hobart Mixer). Any powder not added initially should be added as soon as the initial powder is incorporated. If there is any unincorporated powder on the sides of the bowl or on the mixing blade at 2 minutes after the start of the mixing, then the mixer should be stopped and the powder on the sides should be scraped into the mix before continuing. Once incorporated, the slurry will look like paint. At about 2 ½ minutes, it will take on a granular appearance. If there is residual powder on the wall of the mixing bowl or top of the mixing blade, the motor should be stopped at 5 minutes this material should be incorporated by hand. A total mixing time of 12 minutes should be used. As mixing continues the granular appearance will change to a very fluid appearance. At the completion of mixing, the slurry should be more fluid and easily poured into the flask. At this stage it is ready to be vacuumed, but it will remain very thick
If a mixer other than a Hobart or equivalent is used, then it may be necessary to change the recommended mixing time.
Steps for Vacuuming and Pouring
- Place slurry under vacuum. Hold vacuum until slurry begins to bubble. Time the bubbling for 25 seconds. Release the vacuum. The slurry will now be very fluid.
- Pour the slurry down the side of the flask, without inclining the flask. Avoid pouring directly on to any of the patterns. Fill to a level of 1 inch (25 cm) above the patterns.
- Vacuum the flasks. Hold the vacuum until the slurry begins to bubble, then time the bubbling for 45 seconds. Vibrate vigorously during the vacuum procedure.
- Release the vacuum and add sufficient slurry to fill the collar to a height of 1 ½ inches above the top of the flask. Greater or smaller heights may be necessary depending upon the flask height.
- Place the flask in a warm dry room and leave it undisturbed overnight (14-16 hours). The flask should not be placed on an absorbent surface as excessive removal of liquid from the base of the flask will not give optimum results.
- 1. In the morning, pour off (decant) the excess water that formed on the top of the flask. In some cases, it may be desirable to decant a second time if water reappears on the surface.
- 2. Once the top of the flask is dry (normally one hour after decanting), remove the collar. Carefully trim off, in small increments, any material which is above the top of the flask. If the settled material is at or just below the top of the flask, it is not necessary to trim it. If the top of the settled material is too near the patterns in the flask, then the quantity of slurry added to the collar should be adjusted.
- 3. Before placing the flask in the oven, the paper should be carefully removed form the base of the flask without disturbing the sprue base. A minimum time of 1 hour should pass between decanting and placing the flask in the oven.
- Place the flasks in an oven at 250° F. Hold at this temperature for 2 hours.
- If using a controller, set the ramp to increase to 750° F over the next 2 hours. When the water has finished evaporating, the top surface takes on a cracked glaze finish.
- If changing the temperature by hand, increase the temperature to 500° F and hold this temperature for 2 hours. When the water has finished evaporating, the top surface takes on a cracked glaze finish. At the end of the 2 hours, increase the temperature to 750° F.
- Hold at that temperature of 750° F for 1 hour. It is important not to exceed 800° F for the first 5 hours so that the evaporating water does not crack the investment.
- If using a controller, set the ramp to increase to 1600° F over the next 2 hours.
- If changing the temperature by hand, increase the temperature to 1600° F over the next 2 hours.
- Soak at 1600° F for at least 1 hour and then drop the oven down to casting temperature and soak (hold at that temperature) for a minimum of 1 hour.
The flask should be cooled to room temperature. The may be accomplished by water quenching once the metal has cooled below red heat, provided that the metal can tolerate quenching. The casting can then be pushed out be hand and the remaining investment removed from the casting using a castblaster or water gun. The casting should be further cleaned by the techniques normally used.
Small amounts of gypsum or phosphate investment will contaminate Platinite and cause improper mixing and setting. Do not mix Platinite PT with any other investment!
This material contains crystalline silica and shows limited evidence of causing cancer in humans. IARC Class 2A. Prolonged exposure way cause lung injury (Silicosis). Users must comply with all applicable health and safety regulations relating to the safe handling of crystalline silica. See MSDS for detailed information.
California Prop 65 Warning
This product contains crystalline silica, a chemical known to the State of California to cause cancer.
Except as expressly provided above, there are no warranties by Kerr or Shor, express or implied, including warranties with respect to description, quality, or fitness for a particular purpose.
Limitation of Kerr's and Shor's Liability
In the event of a defect in material or workmanship, Kerr's and Shor's liability is limited, at Kerrs and Shor's option, to replacement of the defective product or part thereof, or reimbursement of the actual cost of the defective product. In order to take advantage of this limited warranty, the defective product must be returned to Kerr. In no event shall Shor or Kerr be liable for any indirect, incidental, or consequential damages whatsoever.