INVESTMENT CASTING FOUNDRY PRACTICE

FOUNDRY JULY/AUGUST, 2010

Investment Casting Foundry PracticeInvestment Casting Foundry PracticeInvestment Casting Foundry PracticeInvestment Casting Foundry PracticeInvestment Casting Foundry PracticeG. M. Rajendra Prasad

A/14, K. H. B. Colony, PuttenahalliYelahanka, Bangalore – 560 106.

Email : [email protected]

Processing Stepsa) Preparing Coating Slurry

1. Take 4.5 liters of Colloidal Silica.

2. To this, add 7.5 kgs of -325# Quartz Flour.

3. Mix it with the stirrer for 30 minutes.

4. Add 4 drops of godrej EZEE soap liquid. (This is awetting agent.)

5. Mix it for 30 minutes. During this process lot of foamwill be generated, and it has to be removed.

6. Add 50 ml of NAV Antifoam solution.

7. Mix it for 30 minutes.

8. Now the coating material is almost ready, but youneed to manually remove few air bubbles still present,along with foreign material, if any. Now your coatingslurry is ready.

b) Preparing Shells

9. Dip the wax pattern tree in slurry.

10. Stucco it immediately with 150# fused quartz.

Now, what is this “stuccoing”?

Whenever you have to paint a wall or a door, youfirst rub (?) the surface with sand paper or emerypaper.

Why do you do that?

Imagine a smooth surface, and a surface withscratches. Surface with scratches will have greatersurface area. This helps in better adherence ofpaint on the surface. But in case of our shell, slurryis as smooth as Talcum Powder, and Wet. So wesprinkle 150# fused Quartz Flour onto the wetslurry coat. This flour adheres to wet slurry surface.

In case of a wall, we had scratches, depression,which increased the total surface area, and in caseof our Shell we have projections of 150# quartzflour on -325# slurry. This also increases totalsurface area.

11. Allow the Shell to dry for 8 hours in normal condition(first coat). Probably one could hasten drying by usinginfra-red heat, but I do not know about it.

12. After 8 hours of drying, dip the shell in -325# slurry,and stucco with 100# fused quartz (2nd coat).

Let me confess at the outset that I am totally ignorant ofthe Science of Investment Casting.

We have been able to develop investment casting, onour own, by trial and error method. We do not even knowif what we have done is conventional or not. I have noteven seen an Investment Casting Foundry.

The process that we have followed has given usresults. Ours is a sand cast foundry, where we make allkinds of steel & alloy steel castings. We developedinvestment castings, on the side lines, for our sisterconcern which manufactures pumps, to reduce great dealof machining at their end.

Excepting a wax injection machine for pattern makingand a stirrer, we did not have any other facility forinvestment casting.

I would like to caution those people, who want to startan exclusive investment casting unit, to ensure thatthey have all the required equipments for an investmentcastings foundry.

Materials : The materials we used were : Colloidal Silica(30%), Godrej EZEE Soap Solution, NAV AntifoamSolution, -325# Fused Quartz, 150# Fused Quartz,100# Fused Quartz, 70# Fused Quartz, 60# Mullite,40# Mullite, 30# Mullite, 16# Mullite, Investment Castingpattern Wax.

Addresses and/or other contact details of companiesfrom whom we procured these materials are given at theend of the article. The other things we used were waxpattern injection machine, a motorized stirrer, an electricalresistant heating furnace and a vessel to treat the shellsin boiling water.

Preparing Wax Patterns & Tree

Prepare your wax pattern and attach it to central sprue.Between the pattern and the central sprue bar anadequately sized cylindrical wax rod (not longer than 10mm) is provided. The wax rod’s diameter depends on thecasting size. It acts as a feeder to the casting. Ensurethat proper venting is provided for air to get out of shellbefore molten metal fills the shell. To this central spruebar several patterns can be attached. Now you have waxtree ready for further processing.


13. Allow it to dry for 8 hours.

Before each time you dip the shell in slurry, stir theslurry once to ensure that dispersal of -325# fusedquartz is uniform in colloidal silica.• Our coating slurry is always of -325# fused quartz.• Our Stucco material size changes.

14. Same steps get repeated with 70# fused quartz ormullite (which is cheaper).

15. Stucco with 50# mullite.



After each coating operation, 8 hours of drying isnecessary. For smaller Castings, about 6 or 7coatings are adequate. For bigger castings, youneed more number of Coats to get a stronger shell.In case of more number of coats, stucco materialwill be 16# mullite.

Now, after all the coatings, shell is ready fordewaxing.

c) Dewaxing the Shells

18. Make a Stand in such a way (with an opening) thatyour shell can be kept upside down. Keep a container,with water in it, under the shell.

19. Start heating the shell with LPG gas flame. Wax meltsand falls into water, so that no wax gets burnt out.

20. After you have ensured that all the wax has meltedand come out, continue to heat the Shell.

Why (Continue to heat the shell)?

Even though all the wax has melted and comeout, a layer of carbonaceous material is stilladhering to the inner surface of the shell. As yougo on heating the shell, air inside the shell expandsand comes out of the shell, and fresh air entersthe shell. Oxygen of the air reacts withcarbonaceous material, and becomes carbondioxide, and comes out of the shell. Keep heatingthe shell till no fumes come out of the shell. Ensurethat you are heating casting portion more than theother portions. Now if you break open one shell,you will see milky white inner surface rather thanblack surface.

Use of Oxygen : In case of castings with largersurface area, the entire carbonaceous layer didnot get burnt out. So, we let a stream of oxygeninto the shell (which is being heated from outside)at a very low pressure. This resulted in burning ofcarbonaceous layer. On breaking of the shell, itsinner surface was found white. As regards to ‘Howlong’ oxygen has to be passed, depends onsurface area of the casting.

21. Wax has ash in it. Fresh wax will have less of ashand used wax will have more. This ash is still adheringto the inner surface of the shell. It has to be removed.

This is done by putting the shells in boiling water.Because of the turbulence, boiling water enters theshell and removes ash adhering to the inner surface.

As regards to the time of keeping the shell in theboiling water, keep it till no foreign matter comingout of the shell is seen.

Take out the shell from water and allow it dry for 8hours. Now your shell is ready for pre-heating beforepouring molten metal into it.

d) Shell Pre-heating and Metal Pouring

22. Put your shells in an electrical resistance furnace,and heat the shells to about 950 °C.

23. Take out the shells about 3 to 5 minutes beforepouring molten metal.

24. Place the shells on a sand bed, cover the shell withdry sand to ensure that shell does not lose heat.During all this, ensure sprue opening is covered, sothat nothing falls into the shell.

25. Just before pouring molten metal, remove the Lid(kept over the sprue opening).

26. Pour the molten metal into the shell.

27. Take out the shell from the dry sand cover, and allowit cool to about 250 °C in natural atmosphere.

28. Break the shell without damaging the castings.

29. Cut the feeder (attachment to central sprue) andvents.

30. Grind the cut portion without damaging the as-castsurface of the casting.

31. Now, get your Investment Casting sand blasted (notshot-blasted, as it leads to dent marks on thecasting).

Now your Investment Casting is ready!

Notesa) How much of Colloidal Silica (binder) is to be used

depends on your casting size. (Refer to step 1)b) How long Oxygen gas has to be passed depends

on surface area of the casting. Larger the surfacearea, longer is the time of passing oxygen. (Referto step 20)

c) How long the Shell should be kept in boiling waterdepends on surface area of the casting. Do notkeep it longer than required. (Refer to step 21)

What is this “required”?

When you do not see any foreign matter comingout of the shell, it (i.e. the shell) can be taken outof boiling water.


Contact Details of the Suppliers

Addresses of the suppliers of materials, from whom weprocured the materials, are given below:

1. Colloidal Silica (30%)

Dr. Khan Industrial Consultants Pvt. Ltd.S-6, Ratnamanjusha, Ravi Industrial CompoundNaupada, Thane - 400 602 (Maharashtra).Cell : 91-932789806Emails : [email protected], [email protected]

2. Fused Quartz

The Universal Fused Quartz & Allied Products Pvt. Ltd.Bangalore.Email : [email protected] Person : Shri Shankar Prasad

3. Pattern WaxM/s. Saffroshine Organics Pvt. Ltd.C-73, MIDC, Chincholi, Solapur - 413 255.Phone : (0217) 235 7272, Cell : 91-98901 97600Contact Person : Shri Rajesh ZadeEmail : [email protected]

4. NAV AntifoamM/s. Navya Refractory Products, Bangalore.Email : [email protected]

Earlier we were using nOctonal liquid from Merck,paying Rs. 2200 per litre; but later changed over toNAV Antifoam, which is priced at Rs. 250 per litre.As regards to performance of removal of foam, Idid not find any difference.

5. Mullite

M/s. Bajaj Associates, Bangalore.Phone : (080) 2228 1141, 2287 0369Email : [email protected]

6. Wetting Agent

Godrej EZEE Soap Solution, which is easily available inthe market.

7. Investment Casting Equipments

Such of those people who want to get into investmentcasting in a big way, you cannot do it the way we did. Wedid it on the side lines. For investment casting equipments,please contact :

Incasst Machines, Hebbal Indl. Area, Mysore - 570 018Contact : Shri Vivek Sangle (Mobile : 91-97411 22101)Email : [email protected] : www.incastt.com

Zircon Vs. Fused Quartz

If you can get 150# zircon and 100# zircon, usethese for 1st & 2nd stucco. From 3rd stuccoonwards it is 70#, 50#, 30# & 16# mullite.

We used fused quartz because of non-availabilityof zircon. This is an option. When your slurry itselfis 325# fused quartz, stuccoing with fused quartzshould not matter.

You can also use -325# zircon flour for basiccoating, 200# zircon for first stucco, 150# zirconfor second stucoo, and 100# zircon for third stucco.

Thereafter go for Mullite Stucco – 70#, 50#, 30#and 16#.

I have explained the process. If you want to start makinginvestment castings, you will have to establish processparameters for your condition.

Remarks : When I started surfing the NET for informationon Investment Casting, I got many other information,but not an IOTA of information on Investment Castingprocess details. Then I decided that I will share thisinformation and our experience by publishing it inFOUNDRY magazine so that my fellow countrymen getbenefitted.

Before I end my paper, as I have already stated in thebeginning, I still do not know the Science of InvestmentCasting. This I am saying just to tell you that if you putyour heart and soul into it, you can improvise the processa great deal. Good Luck!

Acknowledgement : I would like to express my deepsense of gratitude to Shri Babu Sathian, Mg. Dir. ofM/s. Process Pumps (India) Pvt. Ltd. and M/s. AllcastIndustries, Bangalore, for having permitted me to prepare& present this small Paper.

• Foundry is an Old Art, but Young Science.• Investment casting is almost 3000 years old.• The Metallic Sculpture of Dancing Nataraja was made by this Process.

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INVESTMENT CASTING FOUNDRY PRACTICE