IC SHELL FORMULATION WITH FUSED ALUMINA PRIMARY...

FOUNDRY

REFRACTORY FOUNDRYKILN

FURNITURECERAMICS FILLERS BUILDINGS ELECTRONICSAGRICULTURE

PICTOS APPLICATIONS

IC SHELL FORMULATION WITH FUSED

ALUMINA PRIMARY AND MOLOCHITE™ BACK-

UP FOR CASTING OF Ni- AND Co-BASED

SUPERALLOYS INTRODUCTIONThe use of fused alumina as a refractory flour and stucco in

the face-coat of the Investment Casting mould is more and

more frequent, particularly as an alternative to zircon for su-

per alloys casting.

The benefits of fused alumina are mainly related to the high

refractoriness, coupled with high purity and low porosity,

which results in mould face-coat particularly stable whatever

is the casting temperature. As a consequence, the introduc-

SHELL DESCRIPTIONThis report describes a shell moulding system, designed for use nickel-based super-alloys, cobalt-based

super-alloys for equiax casting. The primary layers of the shell are composed of fused alumina filler and

stucco. Imerys Fused Minerals produces the fused alumina described in this report. The back-up layers

use Molochite, a proprietary alumino-ailicate material designed for use in Investment Casting. Provided is

a general description of the shell system. It may need to be adapted slightly by individual foundries to suit

their product range and casting methods.

tion of fused alumina significantly reduces the metal-mould reaction and eliminates all surface defects

which result from the impurities that are always associated with zircon (regardless if calcined or not).

1. Shell Formulation summary

COAT BINDER FILLER STUCCO

Primary Coat28-30% SiO

2 Coll.

silica

Fused Alumina AlodurWRG IC SF or WRG IC -325WRG IC ESM

Fused AluminaAlodur ZWSK F100, F90 or F80

Secondary Coat28-30% SiO

2 Coll.

silica

Fused Alumina AlodurWRG IC SF orWRG IC -200

Molochite 30/80DD or Alodur ZWSK F60 or F54

Back-up Coats24-26% SiO

2

colloidal silica

Molochite 50% -120#50% -200#

Molochite 16/30DD

Seal Coat24-26% SiO

2

colloidal silica

Molochite50% -120#50% -200#

None

2

FOUNDRY



PICTOS APPLICATIONS

www.imerys-irm-foundry.com

2. Fused Alumina Slurry

2.1 Materials : RefractoryImerys Fused Minerals provides fused alumina grades under the trademark Treibacher Alodur WRG IC with

a Particle Size Distribution and Particle Shape specifically designed to optimize the flowing and draining

properties of the slurry. Filler loading typically ranges between 76 to 78%, i.e.

In order to produce long-term stable slurry, we recommend to use a special designed fused alumina flour,

named Treibacher Alodur WRG IC SF. Experience to date has shown that this new grade works well. As

an alternative, we recommend to use a blend of our grades Treibacher Alodur WRG IC 200 and Treibacher

Alodur WRG IC 325 (50/50 w/w), which also provides satisfactory results and allows an increased flexibility

in fine-tuning the slurry according to specific requirements.

2.2 Materials : BindersThere are two classes of binder that can be used for the production of fused alumina slurries. The former is

based on pyrogenic aluminium oxide, but it requires firing temperature exceeding 1300°C, and it is mainly

used for the Single Crystal and Directional Solidification processes.

The latter is based on colloidal silica and gives slurries suitable for Equiax casting of any type of alloys with

good flow properties and long working life, extending to many months or even years. These binders are

generally based on aIuminium-modified colloidal silica and works in neutral or alkaline pH conditions. The

firing temperature of the shell is in the usual range of 1000 -1100°C and these slurries are perfectly suitable

for casting of Ni-based superalloys.

Other additions to primary slurry include a wetting agent (surfactant) to help the slurry adhere to the wax

pattern surface, and a de-airing additive (anti-foam). These are widely available under a variety of trade

names.

2.3 Slurry PreparationThe above slurry recipe may require two-step addition of the flour, depending on the mixing tool used. The

viscosity of the new slurry may become too high for the mixing equipment to work properly. If this occurs,

the slurry should be mixed as follows:

• Day 1 Place the binder in a mixing vessel

Add wetting agent (surfactant) and de-airing additive (anti-foam).

Start the mixer and gradually add the Treibacher Alodur WRG IC SF filler until the slurry

becomes too viscous to continue.

Leave to mix in overnight.

• Day 2 Add de-ionised water to replace what has evaporated overnight (based on experience with

the slurry tank size and location).

Add the rest of the Treibacher Alodur WRG IC SF filler if it will go in, or as much as

possible without damaging the mixer motor.

Leave to mix in overnight.

• Day 3 Add de-ionised water to replace what has evaporated overnight (based on experience

with the slurry tank size and location).

Check binder silica content in the slurry – adjust if required.

Check and correct slurry parameters. If acceptable the slurry can be used.

76% (+/- 2%) Treibacher Alodur WRG IC SF

24% (+/- 2%) Colloidal Silica binder

3

FOUNDRY



PICTOS APPLICATIONS


2.4 Slurry Parameter ControlAll foundries have their own preferred methods for checking and controlling slurries. Most foundries check

viscosity with a flow cup and usually control several other parameters. Because of the range of pos-

sible checks, the type of settings preferred by individual foundries, the stage of the slurry’s life and other

factors, it is not possible to specify one set of parameters to satisfy all. The following is a guide to the ge-

neral working area for the major parameters:

New primary slurries tend to have high viscosity, so plate weight is set low in order to accommodate this.

Try to avoid setting plate weight too low (

4

FOUNDRY



PICTOS APPLICATIONS


5. Back-up SlurryThe back-up slurry consists of Molochite and colloidal silica binder containing ~24-25% silica. Most foun-

dries using robots for dipping and running Molochite slurries, use -200# flour, whereas hand-dip foundries

sometimes favour -120# filler. For robot dipping, a better result can be achieved using a 50/50 blend of the

two. This produces a wider particle size distribution, resulting in better slurry properties and reduced shell

cracking.

Filler loading is approximately 64%. The resulting slurry will have an SG of approximately 1.75-1.80gm/ml,

and viscosity in the range 9-13 seconds using a Zahn cup No 4. To increase the shell build-up, higher visco-

sities might also be used, depending on the geometry and complexity of the wax tree.

The viscosity/SG or viscosity/plate weight relationship in Molochite back-up slurry is fairly stable over time,

particularly as back-up slurry is used up and replenished frequently. The slurry can be controlled by adjus-

ting viscosity or SG to a set point at the start of each shift and only checking the other variable on a weekly

basis to monitor the health of the slurry.

Most modern investment casting binders are ‘polymer modified’ which means that they contain organic

additives. The additives fulfil several functions including: enhancing green strength, speeding up the shel-

ling process and increasing shell permeability. These additions are not strictly speaking essential, but they

do simplify the task of producing consistently good quality moulds.

N.B. It should not be necessary to add wetting agent to the backup slurry. Anti-foaming agent is often helpful to decrease

porosity in the shell and helps filling deep pockets.

6. Back-up StuccoAll of the back-up sanded coats use Molochite 16/30dd stucco. The final coat is a seal coat i.e. left without

stucco. There is no universal rule as to the number of coats to apply, but the table below is a rough guide.

Pour weight No of shell coats(including primary and seal coat)

< 25 kg 7 - 8 coats

25 - 40kg 8 - 10

40 - 80kg 10 - 14

> 80kg 14+

IC SHELL FORMULATION WITH FUSED ALUMINA PRIMARY...

Documents

Transcript of IC SHELL FORMULATION WITH FUSED ALUMINA PRIMARY...