WAX selection.pdf

8/10/2019 WAX selection.pdf

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Composition, Control and Use of

Investment Casting Wax

Richard Hirst FIMMM

Blayson Olefines Ltd


2/23

Agenda Composition and Structure

Properties Categories

Recycling

Selection

Control and Testing of Wax

Relationship between Wax and InjectionCharacteristics


3/23

Investment Casting Wax

Wax is the oldest thermoplastic material known toman

Beeswax was utilized in the lost wax process bycraftsmen in the ancient civilizations of China & Egypt

Today the name wax applies to any substance

having wax-like properties better described as industrial moulding compounds

If the pattern is wrong, the casting will be wrong

It follows that the choice of wax is critical


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Composition of Investment Casting Wax

Investment casting waxes are complexformulations containing many components : Paraffin wax

Microcrystalline wax

Resins - strong, viscous, brittle

Polymers - ductile Fillers - reduce contraction, improve mechanical

strength

The % addition and control of these additives iscritical in determining the properties of the wax,they make each wax unique


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Structure of Investment Casting Wax

Many variations are formulated to suit differingrequirements

Key properties such as melting point, hardness,viscosity, expansion and contraction, setting rate, etcare all influenced by the structure and composition ofthe wax compound

Understanding the properties of the individualcomponents and how they interact is essential inmeeting foundries individual requirements

The complex composition manifests itself in aphysical behaviour different to that of othersubstances


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Phase Changes of a Typical Wax

Unlike other homogeneous chemicalcompounds, wax does not melt immediatelyon heating but passes through severalintermediate states :

solid plastic semi-plastic semi-liquid liquid


7/23

Expansion & Contraction of Wax

The structure and components used in an investmentcasting wax will influence the expansion andcontraction

Like other materials wax expands on heating andcontracts on cooling

In comparison with a metal the expansion is relativelyhigh

Wax expansion and contraction rates are not uniformbut vary with phase and structure changes duringheating/cooling


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Categories of Investment Casting Wax

Pattern wax

straight (unfilled) emulsified filled

Runner wax Water Soluble wax other Special wax

dipping/patching/adhesive Reclaim & Reconstituted wax


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Wax Recycling

Customers used wax from autoclave returned

to wax manufacturer for reprocessing cleaned & filtered additives to adjust properties to specification

Reclaim wax for runner systems Reconstituted wax for pattern production Environmental and economic benefits


10/23

Wax Selection

Wax selection is determined by the particular applicationand the process criteria are : Injection

state/setting rate/rheology/geometry/equipment/surface finish

Removal,handling,assembly strength/hardness/setting rate/stability/ability to make joins

Dimensional control thermal expansion/contraction/cavitation/distortion

Shelling/mould making strength/wetability/resistance to binders and solvents

Dewax and burnout melting point/viscosity/thermal expansion/thermal diffusivity/ash content Other : cost/availability/recycling/toxicity/environmental


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Process Control of Wax Products

Close control is achieved by :

Automatic temperature control of themelting process

Data monitoring of both temperature of themelt and process equipment

Extensive testing

Statistical Process Control of both rawmaterials and finished products


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Statistical Process Control

O b s e r v a t i o n

IndividualValue

342340338336334332330328326324322320318

0.03

0.02

0.01

0.00

-0.01

_X=0 . 00811

U C L= 0 . 0 2 70 9

LC L=-0.01087

O b s e r v a t i o n

Moving

Range

342340338336334332330328326324322320318

0.03

0.02

0.01

0.00

__M R = 0 . 0 0 7 1 4

U C L= 0 . 0 2 33 2

LC L= 0

1

1

Control chart of incoming ash lev els on f i l ler use d.

Both incoming test results and in-house test results on rawmaterials are fed into a control chart, and use based on the resultsdetermined.

The use of SPC also allows tracking of trends in suppliers

processes, and allowing pre-emptive corrective action.

Out of

Control

(Not used)


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Wax Specification Products are tested to

establish whether they meetspecification

The specification isdetermined during thedevelopment stage

it is a reflection of thecapability of the process

a provisional specification isintroduced which is thenreviewed after 12 batches

The data is used to generatea process capability which isbuilt into the formalisedspecification

74737271706968

LB UB

Process Data

Sample N 13

StDev(Within) 0.679669

StDev(Overall) 0.851196

LB 68

Target *

UB 74

Sample Mean 70

Potential (Within) Capability

Overall Capability

Pp *

PPL *

PPU *

Ppk *

Cpm

Cp

*

*

CPL *

CPU *

Cpk *

Observed Performance

PPM < LB 0.00

PPM > UB 0.00

PPM Total 0.00

Exp. Within Performance

PPM < LB *

PPM > UB *

PPM Total *

Exp. Ov erall Performance

PPM < LB *

PPM > UB *

PPM Total *

Within

Overall

Process Capability of DMP (12 batches)

SPECIFICATION WOULDNEED ADJUSTING INLINE WITH RECORDED

DATA.


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Test Methods

Industry recognised physical tests are :

Congealing Point

Drop Melt Point

Viscosity

Penetration

Ash

Filler content

Mechanical strength


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DSC, Oscillation

DSC analysis gives anindication of the melting

phases of different

compounds.

40 45 50 55 60 65 70 75 80 85

T [C]

0 10

1 10

2 10

3 10

4 10

5 10

6 10

7 10

'[Pas]

0

10

20

30

40

50

60

70

80

90

[]

060085A Osc

' = f (T) = f (T)

060107 (XL21) Osc' = f (T)

= f (T)

Oscillation curves give anindication of the shear properties of

wax at dif ferent temperatures.

Gives a good indication of the

setting properties of a wax.


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Volumetric ExpansionComparison of Microcrystalline w axes and Parr afin waxes (Volum teric Expansion.)

-5.000%

0.000%

5.000%

10.000%

15.000%

20.000%

25.000%

25.1541 30.1761 35.036 40.058 45.242 50.102 55.2859 60.1459 65.1679 70.0279 75.0498 80.0718 85.2558 90.4398 95.1377 100.16

LMP from Korea

MMP FROM KOREA

WAX REX 2460

LMP FROM BLAYSON

Parraff in 56 - 58

Parraff in 62 - 64

Parrafin 68 - 70

C0310

Blayson Japan has developed

a volumetric expansion test to

dewax temperatures.

A unique feature is that data

capture is automatic and not

dependent on operator

measurements.


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Relationship between Wax and

Injection Characteristics


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Wax Fluidity Wax fluidity is key to control of

many problems

flow lines surface finish non fill and air entrapment

A relationship exists betweenwax temperature and fluidity.Important when operating nearthe congealing point

Effect of die temperatureshould not be underestimated

60 65 70 75 80 85

T [C]

0

1

2

3

4

5

6

7

8

9

10

11

[Pa

s]

040178B = f (T)

l0049 = f (T)


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Fluidity Measurement

Wax Fluidity can be measuredusing the Fluidity Spiral

Injected at : fixed wax temperature

fixed die temperature

fixed injection pressure fixed flow rate

Can be used with each newbatch to estimate its flow

characteristics and allowadjustments to be made priorto start of production


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Factors Affecting Fluidity

WAXFLUIDITY

INJECTION

TEMPERATURE

DIE

TEMPERATURE

AIRRESISTANCE/

PRESSURE IN

DIE

SURFACE

TENSION OF

DIE

VISCOSITY

TURBULENCE

AIR

TEMPERATURE

CAVITY

GEOMETRY

INJECTION

PRESSURE

CONGEALING

POINT/ RATE OF

CRYSTALLISATIONDIE THERMAL

CONDUCTIVITY


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Relationships with Injection Pressure

Pressure

Flow

lines

1.00.50.0-0.5-1.0

4.0

3.5

3.0

2.5

2.0

1.5

1.0

S 0.290832R-Sq 95.5%

R-Sq(adj) 94.8%

Fitted Line PlotFlow lines = 2.638 + 1.163 Pressure

Pressure

Surfacefinish

1.00.50.0-0.5-1.0

5

4

3

2

1

S 0.890225

R-Sq 50.3%

R-Sq(adj) 42.0%

Fitted Line PlotSurface finish = 3.150 + 0.7750 Pressure

Recent trials suggest a relationship

between flow l ines and pressure,

higher pressures minimise flow l ines.

Evidence exists for a similarrelationship between pressure and

surface finish (orange peel).

Obviously care must be taken when

using cored parts (core breakage)


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Temperature and Cavitation

Meanof

Sinking

1-1

5

4

3

2

1-1

1-1

5

4

3

2

Flow Pressure

Temperature

Main Effects Plot (data means) for Sinking

Temperature

Sinking

1.00.50.0-0.5-1.0

5

4

3

2

1

S 0.677003

R-Sq 84.6%

R-Sq(adj) 82.1%

Fitted Line PlotSinking = 3.375 - 1.375 Temperature Injection trials suggest a strong link between wax

temperature and cavitation.

Indications are that the cause is the time that the

wax is liquid/semi liquid, increasing thetemperature increases the time.

This explains why sprue size and location affectssinking, and also that sinking is probably relatedto the setting rate of the wax.

Filler reduces liquid by around a third andreduces contraction.

40 45 50 55 60 65 70 75 80 85

T [C]

-1 10

0 10

1 10

2 10

3 10

4 10

5 10

6 10

7 10

'

[Pas]

20

40

60

80

100

[]

L0049 OSC' = f (T) = f (T)

040178B OSC' = f (T) = f (T)


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Summary

Investment casting wax compounds are complex consist of many different components

consequently exhibit a range of properties Wax properties influence pattern behaviour in the

foundry and ultimately the quality of castingsproduced

Correct product choice allied with strict process &quality control procedures is essential

More information available atwww.investmentcasting.com
http://www.investmentcasting.com/http://www.investmentcasting.com/

Documents

WAX selection.pdf