The Role of Process Parameters in Platinum Casting · were used for casting experiments with variation of atmosphere,casting and flask temperature,tree design and centrifugal machine

By Ulrich E. Klotz* and Tiziana Drago

The Research Institute for Precious Metals andMetals Chemistry (FEM), Katharinenstrasse 17,D-73525 Schwäbisch Gmünd, Germany;

*E-mmail: [email protected]

Platinum is a challenging material for casters because

of its physical properties, which result in possible cru-

cible and flask reactions during melting and casting,

high shrinkage porosity and difficulties in filling of

filigree items. This paper summarises the results of a

collaborative research effort by several industrial part-

ners and FEM on the influence of casting process

parameters. Two common platinum jewellery alloys

(platinum with 5 wt% cobalt and platinum with 5 wt%

ruthenium) and four different investment materials

were used for casting experiments with variation of

atmosphere, casting and flask temperature, tree design

and centrifugal machine parameters. Detailed sample

investigation found shrinkage porosity and surface

defects to be the main problems. Optimised process

parameters for heavy and filigree items were identi-

fied. Future research on platinum casting should focus

on casting simulation in order to reduce experimental

effort and costs.

Introduction In recent years articles on the casting properties of

platinum have been published (1, 2). Different

aspects such as suitable alloys for casting (3–6), tree

design (7–10) and investment reactions (11, 12) have

been discussed, as well as the effect of centrifugal

casting parameters for different alloys and invest-

ments (12–14). Platinum with 5 wt% cobalt (Pt-5Co)

was identified as a very versatile casting alloy,

showing excellent form filling of filigree parts even

for flask temperatures as low as 100ºC (12). Platinum

with 5 wt% ruthenium (Pt-5Ru) on the other hand

showed poor form filling of filigree parts for flask

temperatures below 800ºC (12). Besides casting pro-

perties, functional alloy properties such as colour,

hardness, ductility and magnetic properties have to

be taken into account for jewellery. In this regard

Pt-5Ru is more versatile compared to Pt-5Co or plat-

inum with 5 wt% copper (Pt-5Cu), and can be used

for all jewellery applications.

20 © 2011 Johnson Matthey

•Platinum Metals Rev., 2011, 55, (1), 20–27•

The Role of Process Parameters inPlatinum Casting Investigation of optimised casting parameters for two platinum jewellery alloys

doi:10.1595/147106711X540373 http://www.platinummetalsreview.com/

The present project focused on Pt-5Ru and Pt-5Co

as the most commonly used jewellery alloys.

Investment casting experiments were carried out as

part of a research project commissioned by Platinum

Guild International (PGI), USA, in cooperation with

several industrial partners and FEM. This paper sum-

marises the results given in a presentation at the 24th

Santa Fe Symposium® on Jewelry Manufacturing

Technology in 2010 (15).

ExperimentalCasting experiments were carried out using a TopCast

TCE10 vacuum centrifugal casting machine with

induction heating and a power of 10 kW and a work-

ing capacity of 1500 g. Metal temperature during

heating and melting was monitored using a quotient

pyrometer. Most of the casting trees used a ‘diablo’

type setup. A typical tree containing some standard

items (ball rings and grid) is shown in Figure 1. Four

different investments from different suppliers were

tested. Table I gives an overview of the properties of

the investments and briefly describes the experience

of working with them.

A number of casting experiments were carried out

to analyse the influence of casting parameters (melt

temperature, flask temperature, casting atmosphere,

casting machine type), alloy and investment material

by using standard sample geometries such as ball

rings and grids. The grid represents filigree items and

demonstrates form filling ability. The ball ring repre-

sents heavy section pieces. With the large ball acting

as a hotspot it was expected to provoke investment

reactions and to be prone to shrinkage porosity.

The as-cast samples were evaluated in terms of

surface quality, shrinkage porosity and investment

reactions by optical microscopy, metallography and

scanning electron microscopy (SEM).

Results and DiscussionAlloy PropertiesThe alloys differ in their dendrite morphology,segrega-

tion behaviour and melting temperature. Solidus and

liquidus temperature were calculated using the

Thermo-Calc® software package with the Scientific

Group Thermodata Europe (SGTE) noble metal alloys

database (SNOB1), and are in accordance with

Reference (16). The calculated phase diagrams give

the same melting range for both alloys,but due to seg-

regation the melting range of Pt-5Co is actually about

twice that of Pt-5Ru.This is one possible reason for the

better form filling ability of Pt-5Co. However, segrega-

tion of Co to the melt promotes oxidation of Co and

investment reactions, even for vacuum casting.

Form FillingForm filling is a critical issue for filigree items and was

determined on standard grids (Figure 2). Pt-5Co

clearly has superior form filling ability to that of

Pt-5Ru and shows excellent results for a flask temper-

ature of 850ºC. For Pt-5Ru, form filling considerably

increases with increasing centrifugal speed and flask

temperature. Its optimum flask temperature is 950ºC

for filigree items. Vacuum casting allowed complete

filling of filigree items with two-part investments for

both alloys, as did overheating of the melt for Pt-5Ru.

However, this also promoted investment reactions.


doi:10.1595/147106711X540373 •Platinum Metals Rev., 2011, 55, (1)•

0º180º

270º

90º

Centrifugaldirection

Fig. 1. Example of typical casting tree designwith ‘diablo’ type setup



Tabl

e I

Prop

ertie

s of

Inve

stm

ents

Use

d in

the

Pla

tinum

Allo

y Ca

stin

g Tr

ials

Inve

stm

ent

Man

ufac

ture

r’s

Type

Base

and

M

ixin

gW

orki

ngBu

rnou

t Bu

rnou

tRe

mar

ks

bran

d na

me

liner

time,

min

time,

min

time,

hte

mpe

ratu

re, º

C

No.

1

R&R

Plat

inum

Tw

o-pa

rtPa

per

base

30

10

–12

12.5

87

1 Cu

ring

does

not

sta

rt a

t ro

om

and

liner

tem

pera

ture

, ext

ende

d w

orki

ng

time

poss

ible

No.

2

Lane

PT1

20Tw

o-pa

rtPa

per

base

20–2

5 10

–12

12.0

87

0 Cu

ring

does

not

sta

rt a

t ro

om

and

liner

tem

pera

ture

, ext

ende

d w

orki

ng

time

poss

ible

No.

3

Gol

d St

ar P

latin

One

-par

t/Ru

bber

bas

e 8

5–7

11.5

90

0 Co

ld w

ater

req

uire

d to

rea

ch

Cast

fib

reup

per

wor

king

tim

e lim

it; h

igh

visc

osity

No.

4

SRS

Plat

inò

One

-par

t/

Rubb

er b

ase

8 5–

7 10

.0

900

Cold

wat

er r

equi

red

to r

each

fibre

uppe

r w

orki

ng t

ime

limit;

hig

h

visc

osity

, ris

k of

ben

ding

of

filig

ree

part

s, e

spec

ially

pla

stic

par

ts

Surface of Cast PartsThe surface quality of cast parts is affected by invest-

ment reactions, inclusions of investment particles and

rough or matt appearing surfaces. Table II compares

the behaviour of the two alloys using the different

investments at different flask temperatures.

The best surface quality was observed for Pt-5Ru.

This alloy did not show any investment reactions

despite its high casting temperature. Investment

reactions were observed for Pt-5Co independent of

casting atmosphere and resulted in a blue layer of

cobalt silicate (Figure 3).

Investment inclusions (Figure 4) on the surface

were observed, especially in the case of the one-part

investment No. 4. With increasing flask temperature

the surface became rougher and the inclusions

more frequent. For the two-part investments No. 1 and

No. 2, inclusions were seldom observed, probably

due to their lower porosity and higher stability.

Therefore, the surface quality achieved using these

investments was usually superior to that obtained

with investment No. 4.

The cast parts often showed matt and glossy areas.

The matt areas showed a dendritic-like surface and



Table II

Devesting Performance and Surface Quality for Air Casting of Platinum-CCobalt and Platinum-RRutheniumAlloysaa

Investment Devesting Surface quality of Pt-55Co Surface quality of Pt-55Ruperformance alloy at the flask alloy at the flask

temperature, ºC temperature, ºC

850 950 1050 850 950 1050

No. 1 + ++ ++ n/a +++ +++ n/a

No. 2 +++ ++ ++ + ++(+) ++(+) +

No. 3b ++ +++ +++ n/a + (cracks) + (cracks) n/a

No. 4 ++ + + n/a + + n/a

a+++ (best); ++ (medium); + (worst)bNo. 3 was only used for casting trials with Indutherm MC 15 tilting machine

Flask temperature, ºC

Grid

fill

, %

500 600 700 800 900 1000

100

80

60

40

20

0

Average Pt-5Ru

Average Pt-5Co

Fig. 2. Grid filling asfunction of flask temperaturefor air casting of Pt-5Co andPt-5Ru (except value for550ºC). Averaged valuesof all grids per tree



Co

Pt

Co

CoPtPt

C

O

Co

Si

Co

CoP

C

(b)O

Mg

1

2

(a)

(c)

MgPt

Fig. 3. (a) Investment reactions of Pt-5Co (flask temperature 850ºC); (b) and (c) energy dispersive X-ray (EDX)analysis of reaction products on position 1 (cobalt oxide) and position 2 (cobalt-magnesium silicate)

100 µm

Fig. 4. Inclusions of investmentmaterial (black) on the surface ofPt-5Ru alloy

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

10 µm

were observed on the heavy sections (Figure 5) of the

affected parts. The matt surface was caused by shrink-

age of isolated melt volumes during solidification.

Shrinkage PorosityShrinkage porosity was the main problem for both

heavy bulk and lightweight filigree patterns in the

casting trials performed. The effects of casting para-

meters and the position on the tree were found to be

relatively small.

Table III and Table IV show shrinkage porosity in

the Pt-5Co and Pt-5Ru alloys, respectively. In general,

shrinkage porosity was less pronounced for Pt-5Ru.

There was a significant difference in shrinkage pore

morphology between the two alloys. Pt-5Co showed

few but large pores while Pt-5Ru often showed scat-

tered pores built by intersecting dendrites (Figure 6).

Flask temperature and casting atmosphere had lit-

tle influence. The investment material was found to

influence shrinkage porosity and the lowest levels

were achieved with investment No. 4. This is probably

an effect of the lower thermal conductivity of this

investment, resulting in slower and more homoge-

neous cooling of the melt.

Effect of the Casting MachineA comparison of two types of casting machine, a cen-

trifugal (TopCast TCE10) and a tilting machine

(Indutherm MC 15, capacity 200 g), showed that cen-

trifugal casting produced superior results for form fill-

ing of filigree items. Defect-free castings of the ball ring

were obtained for the Pt-5Co alloy at 950ºC under vac-

uum using the tilting machine, which was not possible

by centrifugal casting under comparable conditions.



100 µm

Fig. 5. Matt surface of a Pt-5Ru castingwith dendritic surface

Table III

Shrinkage Porosity in Metallographic Sections ofPlatinum-RRuthenium Alloyaa

No. 1 No. 2 No. 4

850 Air n/a ++ +++

950 Air ++ ++ +++

850 Vacuum + n/a n/a

950 Vacuum ++ n/a n/a

a+++ (low = best); ++ (high = medium);

+ (very high = worst)

Flask Casting Investmenttemperature, ºC atmosphere

Table IV

Shrinkage Porosity in Metallographic Sections ofPlatinum-CCobalt Alloyaa

No. 1 No. 2 No. 4

850 Air + + +

950 Air + + +



a+++ (low = best); ++ (high = medium);

+ (very high = worst)

Flask Casting Investmenttemperature, ºC atmosphere

Pt-5Ru was difficult to cast in the tilting machine,

because of the low heating rate in the specific model

used, which resulted in hot tearing of the parts.

Machines with higher power and sufficiently short

melting time may enable successful casting of Pt-5Ru.

ConclusionsIn this study shrinkage porosity was found to be the

main problem for both bulk and filigree casting pat-

terns using Pt-5Ru and Pt-5Co alloys. The best results

in terms of shrinkage porosity were obtained with

Pt-5Ru alloy using investment No. 4.

In order to solve the problem of shrinkage porosity,

sprue design and tree setup are most important. Direc-

tional solidification has to be assured. The usefulness

of techniques such as increasing the flask temperature

is limited by the thermal stability of the investment

materials. However, optimisation of casting behaviour

solely by experimental means remains challenging.

Recommendations for Future WorkIn recent years, casting simulation has been demon-

strated to be a valuable tool for gold and silver casting

(17, 18). Sophisticated software packages are avail-

able to determine form filling and shrinkage porosity

depending on alloy, tree setup, melt and flask temper-

ature, allowing optimisation by computer simulation.

This would be especially valuable for optimising the

casting parameters for platinum due to its high price

and extreme casting and flask temperatures.

Detailed knowledge of the thermophysical prop-

erties of the alloys and investments are required.

Such data are currently scarce and they must be

determined. Benchmark experiments with sophis-

ticated thermal recording during the centrifugal

casting process should be performed to calibrate the

casting simulation results.

Investment materials were found to play an impor-

tant role in form filling and shrinkage porosity. It is

assumed that properties such as gas permeability and

thermal conductivity are responsible for this behav-

iour. Therefore, the influence of the water:powder

ratio, burnout cycle, flask temperature and casting

atmosphere requires further investigation to under-

stand how the physical properties of the investments

can be tailored.

Acknowledgements The authors are grateful for the financial support of

PGI, with special thanks to Jurgen Maerz. C. Hafner

GmbH and Co, Germany, provided platinum alloys,

which is kindly acknowledged. The companies

Ransom & Randolph, USA, Lane Industries LLC, USA,

and Specialist Refractory Services Ltd (SRS) UK, are

acknowledged for providing investment materials

and Indutherm GmbH, Germany, is acknowledged for

casting trials. Special thanks to Dieter Ott (FEM,

Germany) for fruitful discussions of the project results

and to the staff members of the metallurgy depart-

ment at FEM, especially to Franz Held and Ulrike

Schindler for casting trials and metallography.

References 1 N. Swan, Jewellery in Britain, 2004, (19), 5

2 N. Swan, Platinum Metals Rev., 2007, 51, (2), 102



(a) (b)

Fig. 6. Different morphologies of shrinkage porosity in the sphere of a ball ring: (a) Pt-5Co; (b) Pt-5Ru

2 mm2 mm

3 G. Ainsley, A. A. Bourne and R. W. E. Rushforth, PlatinumMetals Rev., 1978, 22, (3), 78

4 J. Huckle, ‘The Development of Platinum Alloys toOvercome Production Problems’, in “The Santa FeSymposium on Jewelry Manufacturing Technology 1996”,ed. D. Schneller, Proceedings of the 10th Symposium inAlbuquerque, New Mexico, USA, 19th–22nd May, 1996,Met-Chem Research Inc, Albuquerque, New Mexico, USA,1996, pp. 301–326

5 J. Maerz, ‘Platinum Alloy Applications for Jewelry’, in“The Santa Fe Symposium on Jewelry ManufacturingTechnology 1999”, ed. D. Schneller, Proceedings of the13th Symposium in Albuquerque, New Mexico, USA,16th–19th May, 1999, Met-Chem Research Inc,Albuquerque, New Mexico, USA, 1999, pp. 55–72

6 J. Maerz, ‘Platinum Alloys: Features and Benefits’, in“The Santa Fe Symposium on Jewelry ManufacturingTechnology 2005”, ed. E. Bell, Proceedings of the19th Symposium in Albuquerque, New Mexico, USA,22nd–25th May, 2005, Met-Chem Research Inc,Albuquerque, New Mexico, USA, 2005, pp. 303–312

7 J. Maerz, ‘Casting Tree Design and Investing Technique forPlatinum Induction Casting’, in “The Santa Fe Symposiumon Jewelry Manufacturing Technology 2002”, ed. E. Bell,Proceedings of the 16th Symposium in Albuquerque,New Mexico, USA, 19th–22nd May, 2002, Met-ChemResearch Inc, Albuquerque, New Mexico, USA, 2002,pp. 335–352

8 A. Nooten-Boom II, ‘Controlled Flow = ControlledSolidification’, in “The Santa Fe Symposium on JewelryManufacturing Technology 2004”, ed. E. Bell, Proceedingsof the 18th Symposium in Albuquerque, New Mexico,USA, 23rd–26th May, 2004, Met-Chem Research Inc,Albuquerque, New Mexico, USA, 2004, pp. 315–344

9 A. Nooten-Boom II, ‘Dynamics of the Restricted Feed Tree’,in “The Santa Fe Symposium on Jewelry ManufacturingTechnology 2006”, ed. E. Bell, Proceedings of the 20thSymposium in Nashville, Tennessee, USA, 10th–13thSeptember, 2006, Met-Chem Research Inc, Albuquerque,New Mexico, USA, 2006, pp. 387–419

10 J. Maerz, ‘Platinum Casting Tree Design’, in “The SantaFe Symposium on Jewelry Manufacturing Technology2007”, ed. E. Bell, Proceedings of the 21st Symposiumin Albuquerque, New Mexico, USA, 20th–23rd May,2007, Met-Chem Research Inc, Albuquerque, New Mexico,USA, 2007, pp. 305–322

11 H. Frye, M. Yasrebit and D. H. Sturgis, ‘Basic CeramicConsiderations for the Lost Wax Processing of HighMelting Alloys’, in “The Santa Fe Symposium on JewelryManufacturing Technology 2000”, ed. E, Bell, Proceedingsof the 14th Symposium in Albuquerque, New Mexico,USA, 21st–24th May, 2000, Met-Chem Research Inc,Albuquerque, New Mexico, USA, 2000, pp. 101–116

12 P. Lester, S. Taylor and R. Süss, ‘The Effect of DifferentInvestment Powders and Flask Temperatures on theCasting of Pt Alloys’, in “The Santa Fe Symposium on

Jewelry Manufacturing Technology 2002”, ed. E. Bell,Proceedings of the 16th Symposium in Albuquerque,New Mexico, USA, 19th–22nd May, 2002, Met-ChemResearch Inc, Albuquerque, New Mexico, USA, 2002,pp. 321–334

13 D. Miller, T. Keraan, P. Park-Ross, V. Husemeyer andC. Lang, Platinum Metals Rev., 2005, 49, (3), 110

14 D. Miller, T. Keraan, P. Park-Ross, V. Husemeyer, A. Brey,I. Khan and C. Lang, Platinum Metals Rev., 2005, 49, (4), 174

15 U. E. Klotz and T. Drago, ‘The Role of Process Parametersin Platinum Casting’, in “The Santa Fe Symposium onJewelry Manufacturing Technology 2010”, ed. E. Bell,Proceedings of the 24th Symposium in Albuquerque,New Mexico, USA, 16th–19th May, 2010, Met-ChemResearch Inc, Albuquerque, New Mexico, USA, 2010,pp. 287–326

16 J. C. McCloskey, ‘Microsegregation in Pt-Co and Pt-RuJewelry Alloys’, in “The Santa Fe Symposium on JewelryManufacturing Technology 2006”, ed. E. Bell, Proceedingsof the 20th Symposium in Nashville, Tennessee, USA,10th–13th September, 2006, Met-Chem Research Inc,Albuquerque, New Mexico, USA, 2006, pp. 363–376

17 J. Fischer-Bühner, ‘Computer Simulation of InvestmentCasting’, in “The Santa Fe Symposium on JewelryManufacturing Technology 2006”, ed. E. Bell, Proceedingsof the 20th Symposium in Nashville, Tennessee, USA,10th–13th September, 2006, Met-Chem Research Inc,Albuquerque, New Mexico, USA, 2006, pp. 193–216

18 M. Actis-Grande, L. Porta and D. Tiberto, ‘ComputerSimulation of the Investment Casting Process: Widening ofthe Filling Step’, in “The Santa Fe Symposium on JewelryManufacturing Technology 2007”, ed. E. Bell, Proceedingsof the 21st Symposium in Albuquerque, New Mexico,USA, 20th–23rd May, 2007, Met-Chem Research Inc,Albuquerque, New Mexico, USA, 2007, pp. 1–18

The Authors

Ulrich E. Klotz graduated from theUniversity of Stuttgart, Germany, as aDiploma Engineer in Physical Metallurgyand has a PhD in Materials Science fromETH Zürich, Switzerland. He is Head of theDepartment of Physical Metallurgy at theResearch Institute for Precious Metals andMetals Chemistry (FEM) in SchwäbischGmünd, Germany.

Tiziana Drago has a BSc in MaterialsEngineering with specialisation in surfacetreatments from the Politecnico di Milano,Italy, and an MSc in Materials Sciencefrom the University of Pisa, Italy. She worksin the Department of Physical Metallurgy atthe Research Institute for Precious Metalsand Metals Chemistry (FEM) in SchwäbischGmünd, Germany.



Documents

The Role of Process Parameters in Platinum Casting · were used for casting experiments with variation of atmosphere,casting and flask temperature,tree design and centrifugal machine