a recent development in pattern wax formulation...remet.com your concept to casting partner a recent...

REMET.COM

YOUR CONCEPT TO CASTING PARTNER

A RECENT

DEVELOPMENT IN

PATTERN WAX

FORMULATION

Is there a new paradigm?

By G. Bradley

Paris, April 2016

Presented at 14th WCIC

REMET.COM©Remet UK REMET.COMParis 2016

A NEW PATTERN WAX WITH MULTIPLE ADVANTAGES

A FAST SET-UP……….?

• A need was recognised for a wax with a fast set up.

• Reduced production costs.

• Energy saving and productivity.

• Reduce the cycle time for large components

• Increase throughput and profitability

• The product exhibited other beneficial characteristics.

• Shrinkage was moderated under optimum injection conditions.

• The wax behaved as if it had a higher filler level (sinkage mitigation).

• Cycle time advantages carried through into smaller components.


• The process of wax cooling defines performance during injection.• Conditioning controls crystallisation at paste temperatures.

• Crystals formed behave as a separate solid phase (i.e. like extra filler).

• Higher crystallisation increases viscosity.

• So we have changed the way the crystals are formed as the wax solidifies.

• Lower viscosity in paste wax phase.

• More crystallisation prior to injection but less effect on rheology.

• Operate press at lower injection temperatures.

• Reduces the amount of heat to be removed from the setting wax

• Less exotherm as liquid becomes solid.

• Also reduces heat to be removed.

• The product can behave as a “supercooled” system.

• Instant solidification can occur!!!

TECHNOLOGYUNDERSTANDING WHAT WE’VE DONE


• Waxy materials undergo a transition from liquid to crystalline solid.• Solid is more ordered than liquid.

• Heat of crystallisation released!

• For paraffin heat of crystallisation is ~200J/g. • Specific heat capacity is ~2.5 J/g/K.

• Cooling 10g paraffin by 10oC requires removal of 250J of energy.

• 10g of solidifying paraffin produces 2000J energy emitted to the surroundings.

• This is enough energy to raise the surrounding 100g of paraffin wax by 8oC!

• Thus crystallisation of waxy materials can re-heat the area surrounding the crystals.

• FastForm™ exhibits ~30% lower enthalpy of crystallisation. (DSC measurement.)

TECHNOLOGYWAX CRYSTALLISATION

SOME NUMBERS.


• The injected wax which is in contact with the walls of a mould will rapidly transfer energy to the surrounding thermally conductive mould.

• Wax in contact with the mould solidifies.• The layer of solid wax formed is highly insulating.

• Heat transfer out from the centre of the mould is then slow.

• Wax in the centre of the mould is reheated as the wax crystals are formed.• The reheat energy can remelt the centre of the block.

• Re-heat energy can soften the outer solidified layer.

• Sinkage can result from stresses generated by this melting and recrystallization.

• The outer layer of an injected part can soften as the crystallisation energy is released from the centre of the wax.

• Subsequent re-crystallisation of the re-melted centre distorts the outer softened layer.

TECHNOLOGYWAX CRYSTALLISATION

CONSIDER THE INJECTION OF A CUBE OF WAX. (OBSERVATIONAL DATA.)


• The Rule Of Mixtures is a handy model for predicting the

behaviour of many materials.

• Doesn’t work for some chemical interactions.

• Non-linear behaviour results.

• PIC waxes have been described as engineered “organic alloys”.

• Can exhibit mixed melting point depression (similar to an eutectic

point).

TECHNOLOGYDISOBEYING THE RULE OF MIXTURES

WHEN MATERIALS SCIENCE MEETS CHEMISTRY.

0.0 0.2 0.4 0.6 0.8 1.040

50

60

70

80

Ratio A:B

Meltin

g p

oin

t (

o C)


• Fast Form represents a new approach to pattern waxes by innovative use of materials.

• No reportable chemical classes introduced.

• Formulation guided by increased knowledge of chemistry.

• Product application behaviour is understood.

• Fast Form™ wax is formulated for control of crystallisation.• Crystal formation is main enthalpic and volumetric driver.

• Rate of cooling can have effects on crystal growth. (Conditioning and solidification.)

• Proportion of crystallised material at injection impacts dimensions.

• Crystallisation is a source of mechanical stresses which can crack cores.

• Crystallisation is also responsible for generating heat which must be transferred out of the pattern.

TECHNOLOGYSUMMARY


MEASURING THE CHANGESBY RHEOLOGY

IN COMPARISON WITH SOME OTHER WAXES.



LOOKING FOR A SHARP SET-UP.

55 60 65 70 75 801000

10000

100000

Instrument plate temperature (oC)

Vis

cosity

(C

p)



NOT BUSINESS AS USUAL.

55 60 65 70 75 80100

1000

10000

100000

FastForm

Standard Wax

Instrument plate temperature (oC)

Vis

cosity

(C

p)



SIMILAR RHEOLOGICAL PROFILES WHEN FORMULATION ADJUSTED

TO VARY SHRINKAGE. (FREE LINEAR CONTRACTION IN D.I.N. TEST PART)

55 60 65 70 75 80100

1000

10000

100000

Instrument Plate Temperature (oC)

Vis

cosity

(C

p)

Higher shrinkage Fast Form (1.2%)

Lower shrinkage Fast Form (0.6%)


IN THE REAL WORLDFEATURES AND BENEFITS

• Reduced residual stress and post injection distortion.

• Less bending stress induced by differential cooling across section.

• Improved injection rheology.

• Better surface finish.

• Less filler usage.

IN THE WAX ROOM.

• Better surface.

• Reduced flow lines.

• Reduced air traps.

• Reduced non-fill.

• Less flow variation.

• Better paste phase consistency.

• Shorter equilibration time.

• Stable paste phase.


IN THE REAL WORLDFEATURES AND BENEFITS

AT AUTOCLAVE.

• Wax viscosity drops quickly at melting point.

• Earlier absorption into shell.

• Lower “cerastatic” pressure exerted onto shell.

• Faster, more complete shell evacuation.

• Improved reclaimability.

• There is less stress in the wax to be released as the wax melts.

• Less stress applied to cores.

• Formulation employs less filler for a required shrinkage.

• Smaller amounts of filler residue.


CASE STUDIESCOMMERCIAL PARTS

THROUGHPUT TRIAL (FILLED WAX)


CASE STUDIESROTATING PARTS

DIMENSIONAL TRIAL (FILLED WAX).

• Smaller test piece.

• Wide range of measurable dimensions:• 8mm-136mm.

• FastForm™ Injected @ 52oC.• Normal injection temperature 58oC.

• Injected without chill.• Normal cycle requires chill.

• Injected @ 750 PSI for 25s cycle time.• Die temperature 25oC for both FastForm™ and reference wax.

• Normal injection 700PSI 50s cycle time.

• FastForm™ allowed reduction of cycle time by 50%.


CASE STUDIESROTATING PARTS

DIMENSIONAL RESULTS

Feature Nominal Size mm Tolerance +/- %

(With chill, 100% cycle

time, 58C Injection)

FastForm % from nominal

dimensions

(50% cycle time,

No chill, 52C Injection)

8 3.32 -1.90

24 1.07 0.58

32 0.77 -0.04

40 0.64 -0.50

88 0.68 0.447

120 0.25 -0.01

136 0.45 0.04


CASE STUDIESHEAT EMISSION

SURFACE TEMPERATURE OF 4X5X3CM BLOCK OF WAX POST INJECTION.

ROOM TEMPERATURE: 26-28C. INJECTION TEMPERATURES AS OPTIMISED.

10 20 30 40 50 6035

40

45

50

55

Time (minutes)

Wa

x S

urfa

ce T

em

pe

ratu

re

( o C

)

FastForm

Standard Wax


• Why might FastForm™ offer more stable dimensional performance?

• Consider the interaction of wax and press.• Temperature measurement is via single points.

• Wax has poor thermal conductivity.

• Three-term controllers have limits.

• Wax presses will always show some variation in temperature control just through natural cycling.

• But what if the wax showed limited variation in dimensional performance across the cycle range?

• How far can we go?

WAX DIMENSIONAL VARIATIONSTABLE DIMENSIONAL PERFORMANCE FROM FASTFORM™ CASTING WAX

A PARTICULARLY INTERESTING CASE STUDY….


• FastForm™ wax was injected over a range of temperatures from 52oC- 64oC.

• Four injections were made at each temperature.• At pressures of 20, 40, 60 and 80 Bar respectively.

• The results were analysed using Minitab as if they were all the same injection conditions.

• Part dimension target was set to the mean of the measured parts (111.16mm)

• LSL and USL were set as +/- 0.25mm (VDG)


THE EXPERIMENT.



Normality Test

Results Pass

P-value 0.893

(Anderson-Darling)

111.30

111.15

111.00

Mean

15131197531

0.2

0.1

0.0

Ran

ge

Xbar-R Chart

Confirm that the process is stable.

Normality Plot

The points should be close to the line.

Capability Analysis for UF FF Diagnostic Report


• A series of standard parts (VDG test piece) was injected.

• Expected (24hr) shrinkage of formulation tested = 1.04%

• Parts measured (dimension A) at 2 hrs, 24 hrs and 1 week.

• Temperature controlled to 22oC (+/-0.5oC)

• Data processed for capability and 2-sample T using Minitab

• Target specification limits set as previous to +/-0.25mm

• 24hr process capability compared with standard Litefill wax

• Difference between 24hr and 1 week sample means between -0.04mm and +0.02mm

• 95% confidence


LONG TERM DIMENSIONAL STABILITY.



LONG TERM DIMENSIONAL STABILITY (REFERENCE DATA).



LONG TERM DIMENSIONAL STABILITY.


• Within the expected performance envelope for many new and older wax injection machines, FastForm™ wax formulations will produce parts in a repeatable

reproducible manner.

• The other process advantage of FastForm™ remain extant.

• The parts produced remain dimensionally stable over an extended time period.• In a temperature controlled environment, a stock of parts ready for shelling may be built

up with little risk of dimensional change.



• Controlled shrinkage.• Paste phase contains a consistent population of crystallised material.

• Formulation adaptable to produce unfilled shrinkage broadly of the range 0.5-1.5%.

• Dimensional variation reduced.• Reduced sinkage.

• Re-melting due to enthalpy of crystallisation reduced.• Wax less mobile during part cooling.

• Reduced takt time.• More stable crystallisation process.

• Less heat to be transferred to the surroundings.• Reproducible injection viscosity.

• More stable paste phase.

• Extended temperature range for consistent viscosity.• Reduced injection temperature.

• Once melted FastForm™ stays fluid at lower temperatures than waxes of a similar melting point.

• Energy savings due to lower tank temperatures.

SUMMARYWHAT DO WE EXPECT FROM THIS PRODUCT?


• Improved process.• Resistance to sinkage.

• Shorter cycle times.

• Lower energy demands.

• Stability.• Formulated to an eutectic point.

• Exceptionally stable paste phase.

• Resistant to dimensional variation over a range of injection conditions.

• Flexibility.• Controlled & Managed shrinkage.

• Equally functional as filled or unfilled product.

CONCLUSIONA NEW PARADIGM? OR BUSINESS AS USUAL?

FASTFORM™

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