a of papers presented at the 1978,1979, and of the...

A Collection of Papers Presented at the 1978,1979, and 1980 Meetings of the Materials & Equipment and

Whitewares Divisions The American Ceramic Society

Cullen L. Hacider Chairman, Proceeding@ Committee

May 6-11, 1978 April 29- May 2, 1979 September 26-29, 1979 April 27-30, 1980

Cob0 Hall, Detroit, Mich. Convention-Exposition Center, Cincinnati, Ohio Bedford Springs Hotel, Bedford, Pa. Conrad Hilton Hotel, Chicago, Ill.

ISSN 0196-6219

Published by The American Ceramic Society, Inc.

65 Ceramic Drive Columbus, Ohio 43214

'The American Ceramic Society, 1980

The page is intensily left blank

A Collection of Papers Presented at the 1978,1979, and 1980 Meetings of the Materials & Equipment and

Whitewares Divisions The American Ceramic Society

Cullen L. Hacider Chairman, Proceeding@ Committee

May 6-11, 1978 April 29- May 2, 1979 September 26-29, 1979 April 27-30, 1980

Cob0 Hall, Detroit, Mich. Convention-Exposition Center, Cincinnati, Ohio Bedford Springs Hotel, Bedford, Pa. Conrad Hilton Hotel, Chicago, Ill.

ISSN 0196-6219

Published by The American Ceramic Society, Inc.

65 Ceramic Drive Columbus, Ohio 43214

'The American Ceramic Society, 1980

Executive Director & Publisher

Director of Publications

Editor

Arthur L. Friedberg

Donald C. Snyder

William J. Smothers

Associate Editor

Graphic Production

Circulation Manager

Susan Stock Means

Carl M. Turner

Gary W. Panek

Commfttee on Publfcatfonr: J . Lambert Bates, Chairman; Robert J. Beals; H. Kent Bowen; William C. Mohr; Richard M. Spriggs; Louis J. Trostel, Jr., ex ofpcfo; Wiliam J. Smothers, ex ofpcfo; Arthur L. Friedberg, ex oflcio. Edftorfal Aduluory Board: L. J. Trostel, Jr., Chairman; R. L. Berger; W. G. Coulter; R. T. Dkstine; R. A. Eppler; E. J. Friebele; F. A. Hummel; W. J. Lackey; T. D. McGee; G. W. Phelps; D. W. Readey; and W. R. Walle. Edftorlal and Subucrfptfon Ofpceu: 65 Ceramic Drive, Columbus, Ohio 43214. Subscription $60 a year; single copies $12 (postage outside U.S. $2 additional). Published bimonthly. Printed In the United States of America. Allow six weeks for address changes. Missing copies will be replaced only if valid claims are received within six months from date of mailing. Replacements will not be allowed if the subscriber fails to notify the Society of a change of address. CESPDK Vol. 1, NO. 9-10, pp. 745-922, 1980

Preface

This issue was compiled by the Proceedings Committee for the Materials & Equip- ment and Whitewares Divisions, with the cooperation of the program chairman, session chairman, and the various authors. This publication is designed to serve the needs of ceramists and engineers in bringing timely, useful information to them.

The papers in this issue may contain some inadvertent inaccuracies. Readers are encouraged to contact the individual authors in any case of doubt or misun- derstanding.

As the chairman of the Proceedings Committee for the Materials & Equipment and Whitewares Divisions, I wish to thank all who helped in writing and in gathering the papers presented in this volume.

Cullen Hackler Chairman, Proceedings Committee

iii

Table of Contents

Plastic Pressing of. Cordierite Saggers ............................. 745 William C. Mohr and Michael W. Morris

Process Controls in Pressing of Light Refractories . . . . . . . . . . . . . . . . . . 747 William C. Mohr and Gary A. Kos

A Microprocessor Programmer Controller for Kiln Temperature Control ...................................................... 753

R. I . Gruber

Automatic Application of Color on Whiteware by Banding, Spraying, and Other Means ..................................... 761

Three-Color Glass Decoration ................................... 764

R. J. Verba

Gene Collard

Pad Transfer Decorating ........................................ 766 David A. Karlyn

John Geelen The Automation of Hand-Decorating Techniques .................... 767

The Practical Application of Current Automatic Weighing Techniques in the Ceramic Industry .............................. 771

Ceramic Cements: Their Properties and Their Applications for Industry ...................................................... 772

Rheology and the Ceramic Engineer .............................. 775

Solving Production Problems with a Computer ..................... 776

Kenneth A. Kardux

Robert L. Trinklein

J . W. Joudrey

Peter P. Nitchman

Fast Firing of Triaxial Porcelain ................................. 780

788

Nils G . Holmstrdm

New Shuttle Kiln Design for Firing Large Insulators . . . . . . . . . . . . . . . . . L. E. Bauer

Which Is the Yellow for You? ................................... 789 Cullen L. Hackler and Robert E. Carpenter

Evaluation and Comparison of Peaches, Pinks, and Maroons for Corn etitive Color Matching ..................................... 790

Observations on Brown Ceramic Colors ........................... 791

J E. Sturm

William G. Loucka

Basic Principles of Ceramic Decals ............................... 793 Richard G. Norsworthy

V

Color Control in Decal Systems and Its Implications for Decorating Ceramics ........................................... 796

Gary Stevens

Kris T. Brenard Application of Ceramic Decals to Hollowware by Machine . . . . . . . . . . . 801

Isostatic Dry Pressing of Flatware ................................ 804 H. Niffka

Dust-Free Loading and Stockpiling of Dry Bulk Material . . . . . . . . . . . . . 805 Ron Pair

The Refiring of Sanitary Ware ................................... 807 D. K. Hullock

Use of Wad Mills in Materials Handling ........................... 812 M. A. Zanghi

Control Quality Control ........................................ 815

Presentation from the Panel Discussion “Taking the Lead Out” . . . . . . . 818

Presentation from the Panel Discussion “Taking the Lead Out” ....... 819

Presentation from the Panel Discussion “Taking the Lead Out”: Reducing Hazards in the Pottery ................................. 821

Richard F. Jaeger

R. H. Insley

John E. Jozefowski

James R. Platte

Kiln Furniture in a Fuel-Conscious World .......................... 823 D. K. Hewitt

Cordierite Slabs ............................................... 826 William C. Mohr, Bruce E. Dunworth, David B. McCuen, and Michaei W. Morris

§hock-Resistant Extruded and Hand-Molded Kiln Cartop Refractories ................................................... 829

Francis B. Rernrney

The Effect on Thermal Expansion of the Addition of Various Materials to a Cone 01-1 Bright Glaze and Body . . . . . . . . . . . . . . . . . . 838

J. Eleison

What Raw Materials Can Do to Cut Energy Consumption . . . . . . . . . . . . 842 Konrad C. Rieger

The Ceramic Glaze Data Bank ................................... 848 Harold J. McWhinnie

Use of Linear Programming for Reformulation of Triaxial Ceramics ........................................... 852

Salil K. Roy

vi

Inclusion Pigments: New Types of Ceramic Stains and Their Applications .................................................. 860

H. D. de Ahna

Cobalt-Free Black Pigments ..................................... 863

Recent Design Changes in Pebble Mills

Richard A. Eppler

........................... 871

Everything You Want to Know about Semibulk Containers . . . . . . . . . . . 873

John M. Rahter

Herbert Bear Rothman

Plastic Forming in the Tableware Industry ......................... 877 A. Bradshaw and R. Cater

A Whitewares Dream Comes True: Isostatic Pressing, a Tool to Complete Automation .......................................... 882

Alfred Dube

Machinery for Hot Molding Ceramic Parts under Low Pressure . . . . . . . . 886

Combustion Control Saves Fuel, Products, and Money . . . . . . . . . . . . . . . 889

I . Peltsman and M. Peltsman

Roman F. Lempa

Energy Management Strategies Using Microprocessor Instrumentation ............................................... 902

The Thermograph System of Kiln Control ......................... 913

Fast-Firing Sled Kiln for Dinnerware .............................. 917

New Roller Hearth Kiln for Vitrified Tile .......................... 920

John E. O’Neil

D. W. Thomas

Dietrich A. Heimsoth, Rainier Hoffmann, and William C. Ware

Dietrich A. Heimsoth, Herbert Spitzbart, and Eberhard Wolf

vii

Plastic Pressing of Cordierite Saggers

WILLIAM c. MOHR AND MICHAEL w. MORRIS

Electro Div., Fern Corp. Box 151, Crooksville, Ohio 43731

The plastic pressing of saggers made from cordierite-bonded mullite is described in this paper. Cordierite is a lowexpansion magnesium aluminum silicate, which is formed, during firing, from mixturesofballclay, kaolin, and talc. Mullite-type grog is added to control shrinkage and to increase resistance to thermal shock and sag. The saggers being pressed are 30-38 cm wide by 30-61 cm long, with heights of 10-30 cm. The plant described produces saggers by pressing slugs, which are extruded from a vacuum pug mill.

The raw ingredients are batched into a skip hoist. A binder, usually a lignin sulfonate, is added to improve flow during extrusion and pressing and to provide green strength during drying and the early stages of firing. The skip hoist is dumped into a muller-type mixer, and water is added until a very stiff plastic state is achieved. The mixed batch is dumped onto a conveyor belt, which brings the material to a vacuum pug mill. The pug mill operator controls the movement of the conveyor, so that the pug mill receives more batch as required.

The design of the die on the pug mill, the design of the nozzle leading to the die, and the length of the spacer between the end of the auger and the nozzle are all important factors. Unfortunately, since there are no rules governing these items, they must be fixed by trial-andemr experimentation. There are two major difficul- ties that may be encountered in extrusion. The first is an “S” crack, found in the center of the column of clay. This crack is not always noticeable at the pug mill and may not appear until the formed article is fired. The “S ” crack is caused by a lack of healing of the two layers of clay which slide along the auger spiral during extrusion. This ‘ ‘S ” crack can often be eliminated by using a longer spacer between the end of the auger and the die. The second major problem of extrusion is “dog’s teeth,” which occur when the clay column moves irregularly at the comers of the die, causing a series of curved fractures, in which the clay peels outward from the comer of the extrusion. The cause of this defect is excess friction at the comers of the die. It can be remedied by changes in the body composition, by providing lubrication to the die, or by enlarging the back of the die in the comers.

To obtain good pressed ware, it is necessary to have wellevacuated clay that contains no air pockets. Air pockets in the extruded slugs will lead to laminations and blisters in the pressed saggers. The extruded clay column is tested for effective- ness of evacuation by cutting a representative sample of thin slivers. These specimens are laid flat on the tray of a vacuum desiccator. Water or kerosene is then poured into the desiccator, until the specimens are covered with liquid. Vacuum is applied while the specimens are continually observed. Any swelling of the clay indicates the presence of undesirable air pockets.

The cross-sectional size of the extruded column depends on the size of the article to be made. For smaller saggers, vertical wires across the die opening may split the column into two or three slices. The pug mill operator has an adjustable

745

gage that allows him or her to cut the extruded column to the length required for the item to be pressed. The operator gages the column and cuts it with a wire; the pug mill is stopped while the operator measures and cuts. He or she then gets a more accurate check on the amount of clay in the cut slug by weighing it; if the slug is too light, it is returned to the pug mill. However, the slugs, if not of proper weight, are usually oversize, so that the operator trims off a little clay with a knife to bring the slug to the weight desired. A tolerance of 2 0.4% is usually required. The extruded and weighed slugs are stacked in a metal-lined cart; the filled carts are covered with damp canvas to prevent undesirable water loss prior to pressing.

The pressperson applies die oil to the two opposite large surfaces of the slug; this oil is needed in quantity so that the clay, during forming, can slide easily along the die surfaces and so that the pressed piece releases from the die after pressing. To the same end, it is necessary to keep the die surfaces slightly rough so that oil is entrapped there, facilitating release.

The pressing dies are precision-made to exacting tolerances. A die consists of an outer casing and spacers, which are made from cold-rolled steel. The actual pressing surfaces, a liner and top and bottom pads, are made from A2 or 41/50 heat-treated steel. The clearance between the liner and the core is 0.005 cm. This is large enough to allow air release during pressing but small enough to prevent the body from extruding through the clearance during pressing. Pressing is accomplished on hydraulic presses. During pressing 1.7-3.4 MPa are applied, the pressure being varied to meet the requirements of each shape. It is important that each shape be pressed to an even density throughout. Bad density gradients will lead to warping and cracking during drying.

Although one cannot look into the die during pressing, one can mentally construct reasonable models of the manner in which the clay moves in the die. The slug has the form of an orthorhombic prism. When the top punch contacts the slug, the clay begins to flow outward in four columns from the four vertical faces of the slug. These four columns move across the bottom of the die and then turn at right angles and move up the cavities that form the walls of the sagger. Eventually, the four columns broaden out and join. This joint is a possible area of weakness in the sagger, especially since the clay columns are oily. For this reason, most saggers are made in dies that produce a shape higher than that which is desired. In the case of rectangular saggers, the extra height is usually added only at the comers. After the sagger is pressed, it is trimmed with a knife to the exact height required. This allows the poorly knit sections to be cut off and discarded as scrap. All scrap is returned to the mixing operation, and scrap body usually makes up a limited portion of each batch charged into the mixer.

746

Process Controls in Pressing of Light Refractories

WILLIAM C. MOHR

Electro Div., Ferro Corp. Box 151, Crooksville, Ohio 43731

GARY A. Kos

Fern Corp., Louthan Plant 2000 Harvey Ave., East Liverpool, Ohio 43920

This paper concerns the pressing of small refractory articles that in area are not much larger than 30 cm square and in thickness not much greater than 2.54 cm. The bodies consist of alumina, mullite, or fused silica grog, bonded with cordierite or mullite. Relatively inexpensive products are manufactured, such as items for metal casting and kiln furniture for the firing of ceramics and metals.

The selection of raw materials is based on compromises among cost, quality, and requirements. In general, the quality of raw materials is good, so that a minimum of raw material testing is required. Strenuous attempts are made to agree with each supplier on specifications for each raw material. Most materials are received in bags, and each bag is required to be stamped with a lot number for ready reference in case of problems. The particle size of grogs is checked faithfully, and only properly sized grog is used. No routine tests are run on other raw materials, but “hold samples” are taken from each shipment. For each raw material, the “hold sample” inventory consists of a sample from the oldest available shipment, plus samples from the latest three shipments. This “hold sample” program provides valuable reference material in case trouble does develop in the form of an undesirable variation in the quality of a raw material.

The body compositions are controlled by the plant ceramic engineer, who issues batch cards to the plant superintendent (Fig. 1 ) . The superintendent, in turn, issues the batch cards to the mixing room foreman, who assigns the cards to the claymakers. The superintendent, on the basis of production requirements, decides which mixes are to be made and how many batches of each are to be prepared. The water content and the mixing times are specified by the plant ceramic engineer, in accordance with the requirements of the item to be made.

It will be noted that the batch card contains six columns headed “Tank #. ” A “Tank” is a hopper that holds one mixer batch ofprepared body. As the claymaker prepares each batch, he or she writes the lot number of each raw material on the batch card in the space opposite the given raw material and in the vertical column pertaining to the “Tank” that will be filled with the batch being made. This method provides a record whereby each tank of prepared body can be traced back to a given set of raw materials. Having the claymaker fill in the lot number, as he or she batches, is an aid in directing his or her attention toward batching the proper amount of the proper material. When the claymaker has prepared all the batches to be made on a single batch card, he or she signs the card at the bottom, attesting that the job has been done properly. The mixing room foreman then countersigns the batch card, indicating that proper batching has been done under his or her supervision.

747

The bodies are compounded with sufficient raw clay and water to flow well under pressure, so that fairly intricate pieces can be produced with even densities, at forming pressures of 3.4-6.9 MPa. The mixes are prepared in muller-type mixers, and pressing granules are produced by pulverizing the wet batch.

The standard operating procedure for claymakers allows time for the adjustment of each batch to the proper water content, as specified by the plant ceramic engineer. A scale and a forced-hot-air dryer are used by the claymaker to determine water content. The claymaker makes every effort to have the batch come out with the correct moisture, without the need for adjustments. He or she attempts to keep the tolerance on the dry side, so that if moisture adjustment is necessary the adjustment will usually require more water, which is an easy addition to make. Of course, overly wet batches sometimes result; in such a case the claymaker must then add a small amount of dry batch to bring the moisture content down to specification.

The fired size of refractories pressed in a given die is governed mainly by the moisture content of the pressing granules. The proper control of moisture content is, then, a primary process control function. For process control purposes, batches are divided into three categories, based on the size tolerances required in the finished product: A-tight control, B-standard, and C-loose control. The QC laboratory always checks the moisture content of all category A batches to ensure that there are no slipups. The lab checks the moisture content of some category B batches; if significant errors are found, they expand the moisture checking to more or to all category B batches. The lab checks category C batches only when time is available. In this way, the amount of offsize ware is held to a practical minimum. The QC Lab and the claymakers use the same type of moisture determination equipment.

Pressing is accomplished on hydraulic C-frame presses. The plant described is a specialty shop that has no standard shapes but that manufactures hundreds of different items, according to the varying requirements of individual customers. With so many shapes to be made, it is imperative that an accurate record be kept of all the parameters that affect the manufacturing of each individual item. This record is provided on a 21 39 by 27.94 cm (8% by 11 in.) card that is printed on both sides to enable all the necessary information to be catalogued. This card is illustrated in Fig. 2. The mixing parameters should be self-explanatory, in view of the foregoing discussion. In the forming parameters section, the press to be used is specified, along with the gage pressure (tonnage) required. The term “bumps” refers to the number of times the pressure is to be momentarily released and then immediately reapplied. If a vacuum is to be used to eliminate laminations, the necessary negative pressure is given. The item ‘‘gage dimensions” refers to the thickness of the pressed part, which is governed mainly by the depth of die fill. A “go-no go” gage is made for each pressed shape, and the press operator is required to check pieces at regular intervals, which vary according to the tolerance requirements of the particular application. The press room foreman is required to make counterchecks of thickness at regular but less frequent intervals. A quality control technician makes frequent trips through the press room and alerts the foreman to any deviation from standard practice.

In Fig. 2 the column headed “QC Dimensions, ” refers to those dimensions of the piece which are critical to the customer. The dimension designations “A,” “B,” “C,” etc., are marked on the blueprint showing the piece. The QC operator has a copy of the marked print, or a suitable sketch thereof. The QC operator checks these critical dimensions when the pressing of that item begins. If any of the dimensions are supercritical, the QC operator will make hourly checks to see that

748

tolerances are being held and to give the pressed articles a visual inspection to see that no noticeable defects are present.

The heart of forming process control is the process control sheet, which is shown in Fig. 3. A QC technician makes out a copy of this sheet each time an order is made of a given item. This record keeps track of the factors that are ordinarily thought of as constants but that, in fact, change slowly with time. Examples of such factors are raw material quality, efficiency of mixing and pressing granule prepara- tion, and die dimensions.

In the upper left-hand comer of the form, the term “Clay Space” refers to the approximate depth of die fill required to obtain proper pressed thickness. The terms “Cone” and “Schedule” are firing parameters. In the top center of the form, the term “Die SF” denotes the shrinkage factor to which the die was machined when it was built. In the lower part of the form, a sketch of the item is made in the box provided. The critical dimensions of the piece are labeled “A,” “B,” “C,”etc., and are so indicated on the sketch. These critical dimensions are measured and recorded in the spaces provided. “Green Dimensions” are measured on the piece immediately after pressing. The line labeled “Control” shows the green dimensions that past experience has indicated are required to produce correct fired sizes. The measured pieces are carefully marked and are followed through the shop, with the same pieces being measured after drying and after firing. The correct fired dimensions, as required by the customer, are entered on the line designated “Print. ” The die is carefully measured each time an order is produced on it, and these dimensions are entered in the line entitled “Case. ” As the die wears, because of usage, it is necessary to prepare the mix with a slightly higher water content to cause increased shrinkage, so as to maintain the proper fired dimensions.

In some complicated pieces, there are differential forming pressures, so that the shrinkages differ from one dimension to another. If the customer requires very close tolerances, it is necessary to machine the die to account for the varying shrinkages. The data accumulated on these process control sheets are used to calculate what each critical die dimension must be to produce parts that fire to size within the prescribed tolerances.

This process control procedure, when followed closely, yields pressed ware that meets customerrequirements. It is applicable to a broad range of products, from those which have very open tolerances to those which have extremely tight tolerances. These procedures have been developed through long, hard years of experience and have proved to be useful and very effective.

749

Shift 1 2 3 Body Date

Dry Mix Min Claymaker Wet Mix Min Fig. 1. Batch card used by claymaker during batching.

750

DIE NO M e t h o d 01 Roductlon

CIAY SHOP

CornpOSltlon Shrlnkage Factor at M o l stwe Mlxlng R o c e d u r e

Raw M a t e r l a l r A Ib B I t C It .~

W MLxlng Tlme W e t MLx Tlme Grlnd Flne, M c d l u m , Coarse M o l r t v r e Range General Info

M a c h i n e U s e d TO""a4e Bumps VaCYUm

G u a g e Dlmenrlons M a x Mln

FlNlSHING

Esulpment U s e d Rocedure General Info

n y l n g CYCld hrs

Genera l Inlo

pc Dlmenrlons A B C D E

General Info

Sel UD by

Fig. 2. ters.

Form used to record manufacturing parame-

751

PROCESS CONTROL SHEET Date

Curt ome r Order ll Body Press Clay Space Cone

Die // Die SF L HZO R a n w % H20 Actual Tonnage Bottom Pressure

Vacuum Weight F i r e d Weight Dry Weight Green K l l n Placement K I I n

Schedule

Control

I

2

3 4

5 6

Avg

Comments

Signed by

Fig. 3. Process control sheet used by QC technician.

752

A Microprocessor Programmer Controller for Kiln Temperature Control

R. I. GRUBER Honeywell Inc. 1100 Virginia Dr., Fort Washington, Pa. 19034

The firing of ceramics is one of the oldest manufacturing processes known to man, dating back to the early caveman. Techniques improved with time, but furnace operators in the early days were just plain lucky if the furnace temperature and other furnace variables happened to be right. Even in the eighteenth century, operators had to do a lot of guessing and hope that the ware would come out as intended. In those days, kiln temperatures were determined mainly by color. Late in the eighteenth century, Josiah Wedgwood made use of a device based on the fact that clay contracts when heated and that the amount of contraction can be measured on a simple scale. However, it wasn’t until a century or so later that a German ceramist named Seger invented the pyrometric cones that are still widely used today. Pyrometric cones are a good tool for the ceramist; they indicate what has taken place in a kiln as far as time and temperature are concerned. However, they do not tell the operator what the temperature is at any given moment, or what the heating or cooling rates are at critical points in a firing cycle.

In recent years there has been a growing demand for increased production rates, with shortened firing cycles, fewer quality defects, and more uniform results. Over the past 20 or 30 years, the evolution of instrumentation and controls has been a relatively slow process. Most of the changes made have been the result of improve- ment in the state of the art. We have progressed from vacuum tubes to all-solid-state devices. Some new sensors have appeared that increase the accuracy of mea- surements, but basically the traditional recorders and single-loop controller systems prevail today, just as they did 25 years ago.

In the 1950’s computers made their appearance on the instrumentation and control scene, but these systems were so high-powered and costly that their use was limited to large centralized systems, which were found mostly in the process industries. In the early 1970’s semiconductor device manufacturers took a big step forward (i.e., downward) in size and price and introduced the microprocessor unit-sometimes loosely referred to as a computer on a chip. Although making predictions where computers are involved can be a risky business, the microprocessor promises to revolutionize the area of instrumentation and control. Even though they are relatively new, microprocessors have excited the interest of both manufacturers and users of instrumentation. Hardly an issue of an electronics or instrumentation trade journal is published without at least one article on microprocessors.

What are microprocessors? Unfortunately, you will not find the word in Webster’s dictionary. Even in the industry there is a reluctance to pin a specific definition on “microprocessor”; generalities and comparisons are the best you can find. Generally speaking, microprocessors are small integrated circuits with control

753

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