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Investment Casting Product Group

At the first meeting of the Investment Casting Product Group there was great interest in developing training programs for front line supervision. A small task group identified and ranked the following as the topics of greatest interest, #1 being of greatest and so on down the list;

  1. Wax Room
  2. Shell Room
  3. Engineering
  4. Melting/Pouring
  5. Tooling
  6. QC
  7. Metallurgy
  8. De-waxing
  9. Investment casting finish
  10. Finishing

We are planning to go ahead and run a course on "Shell Room". To make this course of greater value we will be running the course at a member foundry, Eagle Precision. The course will include a tour of their investment foundry, plus Cannon Muskegon (ingot producer) and Argueso (wax producer) all of these plants are in Muskegon. Eagle Precision have generously offered to host this first training module.

Targeted participants: Operator, shell room supervisor, production manager, engineer/engineering manager, QC, support (purchasing, maintenance).

Participants should bring examples or pictures of examples of issues you would like to discuss. Anything you specifically want to learn?

The schedule is as follows;

5.12.11

8:00 am - Continental breakfast and tour at Eagle Precision, 5142 Evanston, Muskegon, MI 49442.

Tours of Eagle Precision, Argueso (wax producer), and Cannon Muskegon (ingot producer)

12:00 noon - Lunch at Eagle Precision

12:30 pm - Shell training course

Introductions - Malcolm Blair, SFSA

Overview of the course - Instructor: Victor Okhuysen*, Cal Poly, Pomona, CA

7:00 pm Group Dinner (Dutch treat)

5.13.11

8:00 am - Continental Breakfast at Eagle Precision, 5142 Evanston, Muskegon, MI 49442.

12:00 noon - Adjourn.

*The course is detailed as follows and the instructor will be Victor Okhuysen, California Polytechnic University, Pomona, CA. Victor obtained his PhD from Penn State and was in intimately involved in the casting dimensional study. Victor's area of study was investment casting tolerances and he has had extensive experience in this field. Victor continues to work in castings and is responsible for the foundry program at Pomona.

There will be a small fee for this course of $100. This fee will include a copy of the book on shell defects.

shellroom0511.pdf
(106kB)
Registration form and meeting notice.

The course will take place in the meeting room at;

Eagle Precision, 5142 Evanston Ave, Muskegon, MI 49442-4800

There are a number of hotels in Muskegon that you can use, Eagle has a corporate rate at;

Shoreline Inn & Conference Center 750 Terrance Point Blvd. Muskegon, MI 49440 Ph Toll Free 866-727-8483. You need to request the Eagle Alloy corporate rate of $79.00 plus tax.

Hotel reservations should be made as soon as possible.

If you need any additional information please contact Malcolm Blair, 815 455 8240 ext. 202 or blairm@sfsa.org

From participants: Bring examples or pictures of examples of issues you would like to discuss. Anything you specifically want to learn?

Targeted participants: Operator, shell room supervisor, production manager, engineer/engineering manager, QC, support (purchasing, maintenance).

MODULE

LEARNING UNIT

LEARNING OBJECTIVE

 

 

Brief instructor tour to see what the attendees will see to tailor remarks and also to collect relevant samples for show and tell.

Introduction

Pre-seminar survey

 

Tour

(Time TBD throughout the day)

 

 

Introductions

Identify specific goals for each individual in the seminar. Recommended way to take notes.

Introduction

How does the shell building fit into the overall Process?

Part Design/Dimensional

 

 

Wax Assembly (Bridging, structural strength of assembly, orientation of parts, drying)

 

 

Dewax (how it works, bleeders, types of wax)

 

 

Burnout (sintering)

 

 

Pouring (Handling damage, patching)

 

 

Finishing (knockout ease, kolene, blasting, contaminated revert, cutting into ceramic, reclamation)

Materials

Overall shell

Is concrete, with a precipitation cement

 

Slurry

Overall composition and function

 

Stucco

Overall characteristics and function

 

Colloidal silica

What is it? Particle and colloid characteristics

 

Colloidal silica binding mechanism

What happens when CS dries?

 

Colloidal silica maintenance

Concentration control, electrolyte control

 

Carrier (solvent)

Why add deionized water

 

Flours

Characteristics: mineralogy and size

 

Size distribution

What it means, characteristics

 

Properties by materials

Thermal expansion, top temperatures, fused silica, mullite (types), zircon

 

Additives

Minor components: Wetting agents, antifoam, biocides, latex, fibers

 

Wetting agents

Function (wax, ceramics), Matching chemistry to slurry (electrolytes), Primary vs back up

 

Antifoam

Function

 

Biocides

Function

 

Polymer

Function

 

Fibers

Function

Slurry

Function

Analogy to concrete

 

Mixing objectives

Mixing objectives (wetting)

 

Mixing procedures

Sequence: Liquids, solids (sifting), temperature control, done when viscosity does not change 1 second in 1 hour.

 

Mixing Methods

High shear, very high shear, vacuum

 

Composition

Total solids, "good" rheology, strength development

 

Binder

Too concentrated: unstable (or wasted). Too diluted: weak. Carrier (water) to control level.

 

Composition Flour

Flour: Too much, unstable. Too little, very thin coats, perhaps insufficient stucco adhesion.

 

Flour Size Distribution

Wide distribution for improved rheology (thicker with uniform coating)

 

Maintenance

Consistency

 

Maintenance composition

Maintain composition (proper ratios)

 

Maintenance chemical

maintain chemical characteristics (electrolitical)

 

Maintenance turnover

Effects of turnover

Stucco

Function

Analogy to concrete, add bulk

 

Mineralogy and size distribution

As with flour but coarser

 

Reclamation?

Very possible.

Dipping

Dipping cycle into and out of slurry and stucco

Entry angles, forces, submerged time, draining. Slurry and stucco pockets.

 

Manual coating

Weight limitations (size of tree, draining positions slurry and stucco)

 

Robotic coating

Issues: robotic payload (weight and distance combination), accuracy, tank levels, gripping, shaking of tree, safety of robots (cages), programming, broken parts in slurry tank/fluid bed.

 

Stucco coating

Rainfall sanders vs. fluid beds. Clean fluid beds of agglomerates.

Coating sequence

Wash/etch

To remove parting agents from injection and to create changes in the surface of wax.

 

Primary coat

Fine for superior surface finish. Primary coats will have high viscosity slurry (better initial coverage) and finer stucco. Often also more thermally resistant ceramics (zircon). Slow drying (higher humidity/no air) to minimize uneven drying and danger of crazing. Slurry tank free of stucco.

 

Secondary coats

1-3 coats, similar to primary but lower viscosity slurry.

 

Back up coats

Lower viscosity slurry, coarser stuccos to build bulk fast. Lower grade ceramics.

 

Seal coat

Last coat, slurry only, prevents stucco from falling off through handling.

 

Post dewax coat

Only some places to cover cracks post dewaxing. Note dipping difficulty due to buoyancy.

 

Prewets

No significant advantage.

 

Bridging

Between parts. When, why, impact on drying. On ends of holes.

Drying

Wicking

What happens, really.

 

Heat transfer process

Explain that heat has to go in.

 

Humidity

How it works. Boundary layer.

 

Air velocity

Graph of effect: None vs. little vs. much. Note local effects (no wind reaching surface, blind holes). Note impact of boundary layer disruption and heat going in.

 

Air temperature

Effect of heating air: more heat into mold, more moisture carrying capacity.

 

Primary and backup coat drying difference

Temperature differentials vs. speed of heat removal. Temperature drop of shell.

 

Reverse wicking

Moisture is attracted to cool surface of shell. Free surface drying, but limited to exposed pores.

 

Psychometry

Relationship of relative humidity vs. moisture amount in air vs. temperature.

QC Controls

Vendor certification

First line of defense. Compare certs historically.

 

Raw material testing

Once in a while to keep honest

 

Slurry tests

Most important

 

Viscosity

Flow cups/rheometer/plate weight/film thickness (rheology test).

 

Specific gravity of slurry/density

Composition

 

Binder solids

How much "glue" is in slurry

 

Total solids

Flour and colloidal silica particles and latex

 

Gel test

Remaining life of slurry

 

pH

Slurry stability

 

Slurry temperature

Maintenance

 

Finished product tests

Monitor

 

Strength

4 point modified test

 

Permeability

Green is most important, fired is much, much higher.

 

Build thickness

Consistency (with MOR, actual load carrying capacity).

Defects and Troubleshooting

Per questions from the attendees

 

 

 

 

Dewaxing Autoclave

Autoclave, components

Pressure vessel, boiler, accumulator, big valve.

 

Saturated steam pressure/temperature correlation

 

 

Need for speed

Prevent mass wax expansion

 

Initial heat transfer mechanisms

Condensation on surface

 

Wax film into primary coats

Green permeability of shell is key (determined by primary coats).

 

Wax draining, sequential melting points for wax types.

Theoretically, lower melting temperature wax first.

 

Mold placement

Interfere with steam? Form a "cold sink"?

 

Mold repair

All molds are cracked. Are they cracked enough? Probably overrepair and underrepair. Mud is magical.

Post seminar survey

 

 

shellroom0511.pdf
(106kB)
Registration form and meeting notice.

Malcolm Blair
VP Technology, SFSA
Chairman/Secretary ISO TC17/SC11
Steel Founders' Society of America
780 McArdle Drive - Unit G
Crystal Lake
IL 60014
USA

Ph +1 (1)815 455 8240 ext 202
Fax +1 (1)815 455 8241
Cell +1 (1)815 245 4213