Precious Metals 1982. Proceedings of the Sixth International Precious Metals Institute Conference, Held in Newport Beach, California, June 7–11, 1982

619 Pages·1983·14.19 MB·English

by  M.I. El Guindy (Eds.)

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Precious Metals 1982
Edited by:
M.I. El Guindy
Engelhard Industries West, Inc.
Engelhard Corporation
Anaheim, California
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Canadian Cataloguing in Publication Data
International Precious Metals Institute. Conference.
(6th : 1982 : Newport Beach, Ca.).
Precious metals 1982 : proceedings of the 6th
International Precious Metals Institute Conference,
Newport Beach, California, 1982
Includes bibliographical references and indexes.
ISBN 0-08-025396-2
1. Precious metals - Congresses. I. El Guindy, M.I.
(Mahmoud Ismail), 1939- II. Title.
TN759.I57 1982 669'.2 C83-098059-8
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INTERNATIONAL PRECIOUS METALS INSTITUTE
OFFICERS
PRESIDENT DONALD A. CORRIGAN
VICE-PRESIDENT GWYNNE I. EDSON
SECRETARY NELSON B. COLTON
TREASURER SEBASTIAN P. MUSCO
IMMEDIATE PAST PRESIDENT ANDREW COSGAREA JR.
EXECUTIVE DIRECTOR JOHN P. NIELSEN
EXECUTIVE SECREARY ROBERT W. STEINMETZ
LEGAL ADVISOR PETER L COSTAS
ASSISTANT TREASURER MYRON E. BROWNING
BOARD OF DIRECTORS
ARNOLD AARON JOHN W. ESCHENLOHR JOHN P. NIELSEN
ALLEN E. ABRAHAMS RICHARD FERRIS SYLVAIN OSTIER
JAYNE B. BALL HOWARD LANIER DOMINICK J. PASSARO
MYRON E. BROWNING WILLIAM F. LOHMAN CARL E. PETERSON
NELSON B. COLTON DAVID E. LUNDY ROGER J. RUNCK
DONALD A. CORRIGAN W. PETER METZ K.A. STEWART
ANDREW COSGAREA, JR. DAVID R. McLACHLAN ALFRED M. WEISBERG
FRANCIS H. CURREN, JR. RICHARD O. McGACHIE HARRY YARUSS
QUENTIN A. DIETZ SEBASTIAN P. MUSCO EDWARD D. ZYSK
GWYNNE I. EDSON JEFFREY A. NICHOLS
HONORARY BOARD MEMBERS
RICHARD L DAVIES The Silver Institute
GEORGE R. FRANKOVICH Manufacturing Jewelers and Silversmiths
PETER GAINSBURY Worshipful Company of Goldsmiths
IRA E. SHEIN New York Mercantile Exchange
be
6TH INTERNATIONAL PRECIOUS METALS CONFERENCE
GENERAL CONFERENCE CHAIRMAN SEBASTIAN MUSCO
GEMINI INDUSTRIES
TECHNICAL PROGRAM CHAIRMAN AND
EDITOR OF PROCEEDINGS MAHMOUD I. EL GUINDY
ENGELHARD INDUSTRIES WEST, INC.
ASSISTANT TO THE EDITOR AND
COORDINATOR OF ELECTRONICS SESSIONS MYRON E. BROWNING
ROCKWELL INTERNATIONAL
CONFERENCE COORDINATOR DEBBIE L. COLEMAN
DURO REFINING
SESSION CHAIR PERSONS
HEALTH AND ENVIRONMENT JOHN CALDWELL
PIONEER HOSPITAL
CATALYSIS U.V. RAO
GEMINI INDUSTRIES
MINING AND MINERAL RESOURCES (I) ALAN SCHEDLBAUER
ASARCO, INC.
MINING AND MINERAL RESOURCES (II) MAHMOUD I. EL GUINDY
ENGELHARD INDUSTRIES WEST, INC.
ELECTRONICS (I) FRANK FANTINO
FAIRCHILD CORPORATION
ELECTRONICS (II) DAVID MASON
ENGELHARD CORPORATION
ELECTRONICS (III) JOHN DONALDSON
ITT CANNON
FINANCIAL DAVID REESE
MICRO METALLICS CORPORATION
JEWELRY (I) JOSEPH A. GABREY, JR.
BALFOUR COMPANY
JEWELRY (II) FRANCIS T. CORCORAN
STERNDENT CORPORATION
ANALYSIS RICHARD C. KALTENBACH
ENGELHARD CORPORATION
RECOVERY AND REFINING (I) WILLIAM F. PARRY
HANDY AND HARMAN, INC.
RECOVERY AND REFINING (II) RICHARD D. MUSHLITZ
METZ METALLURGICAL CORPORATION
RECOVERY AND REFINING (III) SANAA KHALAFALLA
U.S. BUREAU OF MINES
SECURITY CHARLES S. YOHN
DURO REFINING
xi
PREFACE
The Planning Committee for the Sixth International Precious Metals Conference appropriately
chose the theme to be "Precious Metals Serving Mankind Today and Tomorrow". It was clear to
those in attendance that fundamental changes are taking place not only in the precious metals
community but also in the industry it serves and the Society dependent upon both. The role
these metals play in offering mankind better life has been expanding at a rapid pace over the
past few years. Today, one cannot think of an industry not dependent upon precious metals in
one form or another.
Sessions of this Conference were thus planned to reflect this awareness and to present to the
attendees and readers of this volume papers on a variety of technical innovations in the
application of precious metals. Obviously, we did not neglect the main-stay topics of advances
in recovery and refining and analysis of precious metals. Following the wide swing in precious
metal prices experienced over the past 2 years, hedging and inventory protection became
timely topics. The financial sessions covered these topics well. Heap leaching is the most
recent treatment method for low grade ores. Therefore, a comprehensive discussion on this
technique was included. The aforementioned are only a sample of what the reader will
encounter in this volume.
The Distinguished Achievement Award was presented to Dr. John P. Nielsen, a co-founder and
Executive Director of the IPMI. His lecture representing results of years of investigations is
thus included in this volume of proceedings. The Henry J. Albert Award for excellence in the
field of Physical Metallurgy of Precious Metals was presented to Mr. Joseph Tuccillo for his
work on Gold Alloys. Moreover, the Gemini Industries Research Grant was presented to John
B. Wiley of California State University to carry out research on "Precious Metal Complexes of
Macrocyclic Ligands".
Future IPMI Conferences are scheduled as follows:
7th, 1983 San Francisco, CA
8th, 1984 Toronto, Canada
9th, 1985 New York, New York
10th, 1986 Newport Beach, CA
xiii
John P. Nielsen, Ph.D.
SOLIDIFICATION FUNDAMENTALS OF JEWELRY AND
DENTAL CASTING
John P. Nielsen, Ph.D.
Professor Emeritus of Metal Science, Polytechnic Institute of New York
ABSTRACT
A series of casting hulls were produced of jewelry and dental castings in which
the liquid fraction was centrifuged off the partially solidified casting 1 to 12
seconds after mold filling. Marked differences were found between the coarse and
fine grained type of alloys. Vertices, edges, etc. in the pattern configuration
were sources of solidification nucleation. These nuclei appeared to burst into
existence very rapidly and in turn were the sources of new nucleation, producing
nucleation chains penetrating into the liquid region. These nucleation chains
were in effect fingers of solid enmeshing with other fingers, occasionally
entrapping pockets of liquid metal. Entrapped liquid pockets also occurred when
hot spots were produced in the regions of hot metal impingement on some local
point on the mold wall.
KEYWORDS
Jewelry casting, dental casting, mode of solidification, nucleation of solid,
nucleation chains, hot spots, grain size.
INTRODUCTION
In order that the best sprue design and casting procedure are followed to make a
good jewelry or dental casting it is of considerable help to have a good idea of
the mode of solidification. The ideal mode of solidification that is continually
being sought by the caster is to have the casting begin to solidify at the tip of
the casting, opposite the sprue, with the solid-liquid front progressing steadily
toward the sprue, entrapping no liquid metal pockets en route. The caster uses
certain devices in attempting to achieve this. The sharp tips of a pattern are
usually placed in the mold away from the sprue, these being the points of first
solidification, and his spruing will generally be at the heavy portion of the
pattern, this being the last portion generally to solidify. However, he can hope
for only limited success. Complicated designs sometimes frustrate the
application of these principles, and also, it is rather difficult to get feedback
to check on some sprue design he has in mind. He must work pretty much in the
dark counting considerably on intuition and experience.
This paper describes some fundamental experiments to elicit the mode of
solidification for a very small casting using the investment casting procedure.
3
4 PRECIOUS METALS 1982
The results of this experiment lead to some basic conclusions as to how very
small castings solidify. These conclusions in turn lead to some recommendations
for casting technics, and for future research work.
SOME CASTING CHALLENGES
The casting of precious metals into jewelry has been going on for centuries, and
it is a tribute to the artists and craftsmen involved that some remarkably good
castings have been made. What is interesting is that rather little basic
technology has been applied. Some casting shops today look no different from
what they must have been like hundreds of years ago. Some interesting challenges
confront the jewelry and dental caster. Figure 1 shows some jewelry cast in 22
kt gold, going back to ancient times. Figure 2 is a modern design of a ring
depicting the rather fine detail that can be cast in a gold alloy. Figure 3
shows some wax patterns of two items; a 32-tooth mustache comb (about one inch in
length), and a ring for the tennis buff showing a tennis racquet of 5 strands
crossing each other. At first glance it might seem that these are very difficult
to cast. They are in fact being made every day, and are really not too difficult
to cast. The reason for this is that alloys, when once heated clearly above the
liquidus, have a rather low kinematic viscosity, so that with the aid of
centrifugal force, it is not difficult to get the metal to fill a thread of, say,
1/2 millimeter thick and 1 cm in length before solidification sets in.
Figure 4 shows one end of a dental restoration cast in a gold alloy. The
significance of this design is not so much in the fine detail, there is no
problem with this, but in the dimensional precision; the clasps must fit with a
tolerance less than 0.005". Figure 5 shows some cross sections of gold cast
crowns. The pointed tips of the crowns are called margins and they require
considerable sharpness with precise dimensions. One wedge angle of a margin in
this photo is about 15°, with a tip radius of about 1/10 mm. A wall thickness
at a narrow constriction is about 1/3 mm.
There is one deterrent to the successful filling of extremely fine detail, the
limitation imposed by surface tension of the liquid metal that does not "wet" the
mold material, as is the case for investment casting. (If the metal were to wet
the mold material a tenacious bond would occur between metal and investment, and
castings would be extremely difficult to finish). The surface tension effect is
that of the tendency of a metal to "ball up" when in small droplet form, much
like a mercury droplet resting on glass. If a wax pattern were to be made of a
razor blade, the liquid metal would not penetrate into the sharpest crevice of
the blade root. However, this imposes a minor limitation on most castings, as
such fine detail is not called for by the designer. An interesting challenge for
the caster is to try to produce a mirror finish on a casting. Figure 6 shows a
stamped medallion. The white background is in satin finish while the black is in
mirror finish. When this medallion is converted into a wax pattern and then cast
the mirror finish is lost, and the entire casting comes out with the roughness of
the satin finish. This is partly due to the surface tension effect, the metal
not penetrating the interstices of the mold material, and also to the granular
texture of the mold material imposing its surface roughness.
EXPERIMENTAL PROCEDURE
The customary procedure to determine the mode of solidification for industrial
casting is by "bleeding" the castings, i.e. turning over the mold upside down to
pour off the liquid fraction leaving behind the solidified casting hull. Figure
7 shows a series of 5 bled casting hulls after 5 sec, 1 min., 2 min. 4 min., and
6 min. after mold filling. The casting was presumably of several pounds in
weight, and cast for example in cast iron. In examining the hulls it can be
DISTINGUISHED ACHIEVEMENT AWARD PRESENTATION 5
Fig. 1. 22-kt cast jewelry of ancient design. Fig. 2. S.African gold jewelry, present-day
design.
Fig. 3. Wax patterns of a 32-tooth mustache Fig. 4. Gold alloy dental casting showing
comb, and a tennis racquet ring, both for clasps requiring high dim ensional precision,
gold casting.
Fig. 5. Cross sections of dental crowns Fig. 6. Bronze medallion in satin and mirror
showing sharp margins and thin wall finish which are difficult to reproduce by
r equir e m ents. casting.