The first thing for all of us to remember is that Platinum, just like all other metals, has its own list of characteristics in all phases of manufacturing that must be professionally addressed. The following guide is designed as an easy to use list of Platinum manufacturing related problems, questions, or suggestions that we have come across in the past. The guide is intended to get you looking at ways to improve your operation or reduce your costs to manufacture.  Model and design limitations in this guide will not be addressed.

SECTION I.

1.WHAT CAUSES FINS ON MY CASTINGS?

A.Poor quality investment.
B.Flask put into hot oven.
C.Wrong absorbent paper used.
D.Rough handling of flasks prior to burnout.
E.Too much moisture still in investment when oven temperature reaches 212° F, 100°C (boiling point of water.)
F.Centrifugal speed on your casting machine is too high.
G.Improper powder to liquid ratio.
H.Absorbent paper has absorbed atmospheric moisture and therefore has lost some of the absorbency it is capable of.
I.Wax not eliminated completely before the boiling temperature of the wax is reached. The wax boils and breaks down the adjacent investment surface.

2.WHY DO I GET A ROUGH SHANK SURFACE ON MY CASTING?

A.Improper sprueing.
B.Improper sprue wax used.
C.Poor quality wax used.

3.WHAT ARE THE BASIC CAUSES OF ROUGH SURFACES ON CASTING?

A.Generally from metal temperature too high.
B.Burnout temperature too high.  Overheating of investment will result in deterioration of the investment.
C.Poor original model and/or wax.
D.Poor quality investment.
E.Improper mixing of investment which may leave powder "lumps" in the mix.
F.Cross contamination from gold or silver investing process.
G.Premature breakdown of your crucible which results in particles from the crucible mixing with the Platinum.


4.WHAT CAUSES MY PIECES NOT TO FILL DURING CASTING?

A.Improper sprueing.
B.Centrifugal casting speed too slow.
C.Poor design of piece.
D.Flask temperature too low.
E.Cast temperature too low.

5.WHY DOES MY CAST PIECE GET DISTORTED?

A.Excess centrifugal speed.
B.Rough handling of castings while still hot after removal of investment.
C.Excessive rough handling of wet investment.

6.SINCE I ONLY MIX SMALL AMOUNTS OF PLATINUM INVESTMENT AT A TIME DO I NEED TO WEAR A MASK?

You must definitely use an OSHA approved dust mask/respirator for both investment mixing, cleanup and investment removal.

7.MY PLATINUM MELTING BY TORCH IS TAKING A VERY LONG TIME. WHY IS THIS?

Wrong combination of gas being used.

8.MY PLATINUM METAL CONTAINS DARK "INCLUSIONS" AFTER CASTING?

Generally this is caused by Acetylene gas usage in metal (for torch melting).

9.MY PIECES HAVE A "CRAZED" LOOK TO THEM. WHAT CAUSES THIS PROBLEM?

Generally this is caused by excessive centrifugal speed in your casting machine.

10.I DON'T WANT TO USE DANGEROUS HYDROFLUORIC ACID IN MY FACTORY DUE TO SAFETY CONSIDERATIONS. WHAT ALTERNATIVES ARE THERE?

Remove the Platinum investment with a safer substitute.

11.WHAT CAUSES THE INVESTMENT ON THE TOP OF MY FLASK TO BLOW OFF IN THE BURNOUT CYCLE?

Too much investment on top of the pieces.

12.WHAT IS THE BASIC CAUSE OF POROSITY IN MY CASTING OF PLATINUM?

Improper sprueing of the pieces and overheating of the metal.


13.WHY DOES THE QUALITY OF MY CASTING VARY FROM FLASK TO FLASK?

Casting is an exact science. If you vary the casting conditions so will the quality of the castings.

14.CAN PHOSPHATE BASED MATERIALS SUCH AS "J FORMULA" BE INVESTED IN THE DAY AND BURNED OUT OVERNIGHT?

Your absolute best results will be to invest in the morning, burnout during the day, and cast in the afternoon.

15.WHAT TYPE OF EYE PROTECTION IS NEEDED FOR MELTING OF PLATINUM?

A Minimum Grade 9 eye filter is required for melting of Platinum.

16.I HEAR THAT HOUSE CLEANING IS ESPECIALLY IMPORTANT WHEN DEALING WITH PLATINUM. WHY IS THIS?

Platinum picks up cross contamination very easily.

17.WHY DOES MY BUTTON SOMETIMES FLOW OUT OF MY CAST
FLASK INTO MY CENTRIFUGAL CASTING SYSTEM?

Temperature of the metal is too hot for the centrifugal cycle that you have on your casting machine.

18.CAN I REHEAT A PARTIALLY CURED FLASK?

Unless you are desperate to save the piece the most prudent answer is no.

19.WHAT ARE THE MELTING POINTS, SPECIFIC GRAVITY, AND TROY OUNCES PER CUBIC INCH OF PLATINUM AND PLATINUM RELATED ITEMS?

See chart in original guide.

SECTION II.

Questions Relating to Polishing/Finishing Operations

1.WHAT ARE THE BASIC STEPS FOR FINISHING PLATINUM PIECES BY HAND?

1)Sand sprues flush with a 270 grit paper. Follow cross directional patterns.
2)Use a lightly applied rotary file for the insides of the rings.
3)Sand insides of rings using 280 grit and 320 grit paper.
4)Rubber wheel outside surfaces with coarse and fine grit wheels in succession.  Use cross diagonal, overlapping passes.
5)For any flat surfaces use 250 grit and 320 grit paper in succession. Cross diagonal and overlap passes.
6)Use #400, 500, and 600 grit deburring next. Cross diagonal and overlap passes.
7)Inside rings can be polished with white cutting compounds.
8)White compounds in the 800, 4500, 4000, and 8000 grit range should be used for final finish levels as desired.

2.CAN I BATCH FINISH MY PLATINUM AND GOLD PIECES IN A TUMBLER?

Never mix Platinum with other metals. 

3.CAN I USE TITANIUM TIPPED TWEEZERS FOR PLATINUM?

Tungsten tipped tweezers and picks are the best for handling Platinum.

4.HOW DO I BEST APPLY POLISHING COMPOUNDS FOR PLATINUM?

In general, you can use hard muslin buffs and rock hard split laps.

5.WHAT GRIT ALUMINUM OXIDE EMERY PAPER IS BEST FOR PLATINUM?

Generally, grits from 220 to 300 will work best on Platinum.

6.CAN I USE MY EMERY PAPERS AND/OR POLISHING WHEELS FOR PLATINUM AND GOLD?

Never use Platinum tools, compounds or other supplies with other metals. Contamination will occur.

7.IF MY SURFACE IS CONTAMINATED IS THERE ANYTHING THAT CAN SAVE THE PIECE?

1)Cut out and weld in new, clean alloy.
2)Pickle in a hot 10% Nitric Acid.

8.HOW OFTEN SHOULD I DRESS MY BUFFS DURING THE POLISHING PROCESS?

To be safe you should re-charge your buff after each dressing/use.

SECTION III.

General Questions on Automation of the Casting Process.

1.I DO TORCH MELTING AND WANT TO AUTOMATE. WHERE DO I BEGIN?

If you wish to automate anything, you should look only to the system that is 100% automatic that gives you the best possible product from the best available technology.
 
THE BASIC DIFFERENCES IN CASTING MACHINES ARE AS FOLLOWS:

Casting Machine Type #1
Tabletop units. Basic cost approximately $11,000 -$12,000. Generally little more than motorized spin casters. You will get more infinitely adjustable spin settings and better repeatability than with the basic spin casters.

Casting Machine Type #2
This range of machine is by far the most glutted segment of the market. The stripped models sell in the high teens with the optical pyrometer laden semi-automatic units priced in the mid $30,000 range.

Casting Machine Type #3
This type of machine is the fully automated system that is computer controlled and just about foolproof. These units are offered with or without vacuum and will run from the $50,000 range for a fully automated unit without vacuum to the $60,000-$70,000 range for the units with a vacuum.

2.HOW DO I RESOLVE THE STRAIGHT ARM VERSUS BENT ARM CASTING QUESTION THAT I HEAR PEOPLE ASKING NOW?

The only suggestion is to use the arm that the machine was engineered for; the results are what counts…not people's opinions.

 

V6N2

Platinum Casting Problems and Solutions
Bob Romanoff
Romanoff International

This is an abbreviated version of the original work. For full technical details, please consult the original paper.