Principles of Centrifugal Rubber Mold Casting: Intro

Introduction

1. Intro 1: Who can use this book?
2. Intro 2: What is Centrifugal Rubber Mold Casting (CRMC)
3. Intro 3: The costume jewelry industry and the CRMC process
4. Intro 4: A word about the alloyer
5. Intro 5: Some thoughts on the future

Intro 1: Who can use this book?

This book is written for everyone who has anything at all to do with metal casting: designers, modelmakers, moldmakers, casters, managers, purchasing agents, and students and teachers in trade and fine arts schools. Its purpose is to serve as a reference guide and textbook for a casting process that has unlimited potential: the Centrifugal Rubber Mold Casting process. (Hereafter referred to simply as the CRMC process.) This book provides the first detailed and systematic description of the process. It is based on technical fact and accurate practical observation as well as the personal experiences of the authors. It is as complete and exhaustive as present knowledge of the CRMC process can make it.

For those who are first attempting CRMC, this book provides a self-taught course in the process. The numerous illustrations and detailed explanations will enable the beginning moldmaker to create good quality molds and cast on his own after a little practice, even if he has had no previous experience with the process. The chapters on gating and venting, and the photographs and diagrams of molds are self-explanatory. For the manager concerned with supervising the casting operations of a jewelry shop, this book provides a complete guide to what takes place without his having to become a moldmaker and caster himself. For the experienced moldmaker or caster, this book can point out variables, techniques, and possibilities that have escaped his notice and help him to practice his craft with greater proficiency and creativity at the level of technical precision that it deserves. For people in industry who are looking for new, more efficient ways of manufacturing, this book will suggest a whole range of new possibilities offered by this previously little known manufacturing method. For everyone who is involved in casting, this book will help to standardize the components, technology, and terminology of the process, and provide a reliable reference book where none was available before.

The approach to the subject, how to keep it interesting as well as informative, how to organize the components of the process logically and arrange them so that they are easily accessible, is the result of the author’s background and their long practical experience in the fields of metal and casting. What is offered are proven methods that have worked in the field. As a rule, they should work for almost any mold or casting that anyone will ever attempt. Along with these proven techniques, the many variables that require judgment and experience to master such as alloy selection, temperature mold durometer, gates and vents are discussed. How each affects the outcome of a particular job is clearly explained, and ways to make rational choices are suggested. This book, then, is the first map ever made of a previously uncharted wilderness. It offers a clear path of approach and definite standards where only a vague direction existed previously. The authors hope that in the future this book will serve as a stimulus to further research and provide a point of departure for others interested in expanding the possibilities and refining the techniques of the CRMC process. As an aid to this process and to the continuing exchange of new information about CRMC, the authors offer a consulting service to those casters who encounter problems for which this book offers no ready solutions.

Intro. 2: What is Centrifugal Rubber Mold Casting (CRMC)?

CRMC is a method of producing castings using a rubber mold that has one or more cavities and that revolves around its central axis. Molten metal is poured into the mold’s center and distributed to the cavities through a series of gates and runners by centrifugal force. Centrifugal force results from a machine that spins the mold at a preselected speed while the metal is being poured. The rubber molds used are semi-permanent, low in cost, and quickly and easily made. The metals used are alloys formulated to melt at a low temperature and to have other definite characteristics such as strength, weight, or ductility necessary for the design of the piece being produced.

The term “casting” as used in this book describes both the process and the part that results when the molten metal is delivered into the mold and allowed to solidify. The material used for the mold and the method of making the mold are referred to as the “molding process”. The “casting process” is the molding process along with the method of delivering the molten metal into the mold cavities. “Centrifugal Rubber Mold Casting” includes the entire process of making the molds and casting the molten metal to produce the finished castings.

Intro. 3: The costume jewelry industry and the CRMC process

The costume jewelry industry in the United States employs over 22,000 persons and had a sales volume in excess of 985 million dollars in 1977. (Source: Manufacturing Jewelers and Silversmiths Association) The largest portion of this jewelry was made with castings produced by the CRMC process. CRMC has become so important because it is a simple technique, it is extremely flexible yet economical, and it produces pieces of high quality. It is the one production method that can produce both simple and intricate castings in one piece without expensive equipment and complex processes.

In view of its importance to the jewelry industry, it is strange that CRMC has always been treated as a craft rather than as an art and a science. The method has never received the attention afforded other casting methods. Foundry and die casters have long enjoyed the direct benefits of research and development conducted by the industries that supply them with their raw materials, such as steel, aluminum, and zinc. Major universities regularly include courses in foundry practice. metallurgy, and other related subjects in their engineering programs. Consequently, formulas and equations have been developed and tested that describe precisely such important phenomena as metal fluidity, solidification, crystal structure, ductility, and strengths of materials. These have been published in convenient standard reference works that enable foundry casters to decide quickly and confidently such questions as sprue design, gating, pouring temperature, metal and sand selection. Consultants are easily available to companies that need additional help.

By comparison, the jewelry industry is in a primitive state. The CRMC process is regarded as, at best, a craft to be learned by trial and error and practiced haphazardly by feel, guesswork, and intuition. Companies traditionally acquire their moldmakers and casters by training them on the job or by hiring them away from other companies.

As a rule, CRMC casters do not test their castings for structural integrity, nor do they apply any of the other standards to which even the most ordinary foundry castings must routinely conform. The industry devotes almost nothing to research and development, but relies instead on its own production personnel to stumble on newer and better methods in the course of their daily work. The result is that the CRMC process has remained an imprecise and undeveloped craft, while its full potentialities have not yet begun even to be guessed at.

However, with the establishment of the educational arm of the Manufacturing Jewelers and Silversmiths of America, the Jewelry Institute, of which the Oster Company is one of the founders and strong supporters, the jewelry industry’s attitude toward its manufacturing techniques and processes has begun to change.

The importance of CRMC is finally being acknowledged and the long overdue attention that the process deserves is being given it. At the Institute, the fledgling moldmaker or caster is able to learn his craft under the guidance of highly qualified instructors in modern trade school classrooms on the most recent equipment, utilizing the most modern techniques, and adhering to the most precise technical standards.

To reinforce this educational effort, the A. J. Oster Co. is continuing to invest tens of thousands of dollars annually in research and development of new and better casting alloy and new and better casting techniques. As a result, rubber mold casting is rapidly ceasing to be a craft and becoming, instead, an art the practitioners of whom must meet increasingly exacting technical standards based on carefully researched and clearly formulated scientific knowledge.

Intro. 4: A word about the alloyer

The metals used to cast CRMC rubber molds are alloys of lead, tin, and other metals. These alloys have been specially formulated by the alloyer to have definite characteristics. Today’s alloyer is far more than an “alchemist” who simply melts metals together in a pot in approximately correct proportions, relying on luck and rule of thumb to get things to come out right. Casting alloys that will perform predictably and acceptably and meet the increasingly high standards of the modern jewelry industry - not to mention those of today’s far more sophisticated consumer - cannot be formulated by chance. Continuous research, rigorous quality control, constant laboratory supervision, and adherence to precise standards are necessary from the beginning of a mold to the pouring of the ingot that the caster will eventually receive. Even virgin metals must be handled with meticulous attention and care. Each operation necessary to promote their alloying and alter their properties so that they can be cast successfully must be performed with precision. However, meticulous attention to complex and even subtle details pays off, for it was just such painstaking that enabled the Oster Co. to develop and produce an entirely new series of alloys, Special K and Excelsior. The Oster Co. knows that if they are to meet the challenges of the future, they must pursue a carefully planned program of research that aims at continuous improvement of their products and of modern metallurgical technology. The one clear and reliable sign that a caster can look for to tell him whether or not his alloyer is serious about meeting his customers’ needs is just this: the alloyer’s commitment - in cold, hard cash - to research and development. At the Oster Co., this commitment is part of our creed.

Intro 5: Some thoughts on the future

The marketplace is changing as is the entire costume jewelry industry. From the many small “mom and pop” operations of less than a decade ago, giants are emerging. New marketing methods are being developed. A more sophisticated consumer dictates a new and larger consumer base. The casting industry also must grow and respond positively to more complex and demanding reproduction requirements.

The promotion of newer and better casting methods by the Manufacturing Jewelers and Silversmiths Association and the Association’s establishment of a trade school are giant steps in the right direction. Likewise, the Oster Group’s continuing maintenance of a research laboratory for metals and casting methods and their contribution to the Jewelry Institute are industry services that have more in view than simply marketing alloys. They are a positive statement of a commitment to helping foster industry growth and development.

As casting continues in the near future, newer and better methods of casting will be discovered, developed and publicized. Already, The Oster Group’s research into alloys and alloying has brought many new and better alloys into existence. Continuing research will lead to better molding procedures. Centrifugal Rubber Mold Casting for industrial applications has been developed by the Arconium Corporation Of America Division of the Oster Group and has already proved very beneficial to the malleable iron and industrial safety device industries. CRMC is an industrial process whose time has come. It is no longer a craft. The Oster Group is in the vanguard of those who are working to make it a science.

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Chapter 1: Introduction to the Moldmaker’s Job and Basic Moldmaking