US2772176A - Stopper heads - Google Patents

Description

United States ST UPPER HEADS Carl F. Leitteu, Hamburg, N. Y., assignor to Electra Refractories & Abrasives Corporation, Bufialo, N. Y.

No Drawing. Application March 4, 1953, Serial No. 340,380

4 Claims. (Cl. 10656) This invention relates to improvements in stoppers or stopper heads such as are used for controlling the flow of metal from steel ladles and the like, and is a continuation in part of my copending application, Serial No. 154,893 filed April 8th, 1950, now abandoned in favor of this application.

ltis the usual practice in the handling of molten steel to control the flow of the metal from a refractory lined ladle by forcing a so-called stopper or stopper head into contact with a perforate refractory nozzle thru which the molten metal flows when the stopper is raised out of con- ,tact with it. The stopper may be alternately raised and lowered many times in the processing of a ladle full of molten metal and it is essential that each time it is reseated on the nozzle, the metal be shut off promptly and fully. The stopper head itself is held in place by a steel stopper pin inserted axially through the stopper and itself attached to a long steel tube or rod which is used to force the stopper down against the nozzle. This steel tube and the pin are protected from the molten metal by a refractory sleeve surrounding them and by the stopper itself. It is thus important that the stopper be no only highly refractory but that it be of low thermal conductivity to retard the flow of heat through it to the pin, lest the pin become so highly heated as to cause it to fail, releasing the stopper and rendering the whole assembly useless. Even if over-heating of the pin does not cause its complete and immediate failure, overheating may still damage it to an extent which prevents its re-use in subsequent stoppers so that it is definitely desirable that the stopper permit a minimum flow of heat through it to the pin.

There is, however, an even more important factor to be considered in stopper heads which is readily apparent when the nature of their service is considered. The ladle with the'relatively cold stopper in place is suddenly filled with molten metal, at temperatures of 2900 F. to 3100 F. or even higher, which metal surrounds the stopper on all sides and subjects it to tremendous thermal shock which is suflicient to crack or break most ceramic bodies. Such cracking may seriously impair the ability of the stopper to perform its intended function and indeed cause immediate failure and disastrous accidents.

It is the purpose of my invention to provide stopper heads which are refractory and extremely resistant to such cracking by thermal shock, and which are chemically inert so that they do not react with the materials with which they come in contact during use. In other words, my invention produces stopper heads which are phenomenally dependable in service by virtue of resisting each of the destructive forces which ordinarily results in premature trouble from the stopper.

An excellent discussion of stoppers and their use in the steel industry appears in the Open Hearth Proceedings of ;the A. I. M. E. for 1945, pages 121 to 153. In that pubcracks open or shells off as a result of contact with the molten steel. Such failures constitute a serious hazard to the safety of the workmen and may result in loss of.

metal, spoilage of accessory equipment or in inferior castmgs. type of stopper head tested showed crackingof greater or less seriousness. when the. stopper was immersed in molten steel. The expensive nature of the trouble resulting from any leakage has led to the practically universal practice of throwing away all stopper heads (and sometimes the pins too) after use in only one ladle of steel. This is expensive but far cheaper than having'the molten metal fail to shut off cleanly at some critical time;

Stopper heads have for many years beenmade out of a mixture of clay materials plus a certain amount of graphite which is reputed to impart to the body a sort of internal yieldability or flexibility under the heavy pressures applied in service. be

A characteristic composition would Such a mixture is wet up with enough water to permit the mass to be formed into desired shapes either by dry pressingor by plastic forming methods familiar in the art. The material is shaped by one of these methods into heads having the sort of perforate ball shape well known to stopper users and these are thereafter dried and fired in the method common to the ceramic industry.

Attempts have been made in the past to utilize as stoppers bodies consisting principally of graphite, carbon, silicon carbide, etc., but these materials have proved entirely unsuited due in part to their chemical reactivity with the molten metal and in part to their high thermal conductivity which has resulted in burning off the supporting pins. Stoppers formed principally of clay materials have been successful but have been characterized by universal spalling trouble as above described.

7 I have discovered that highly successful stoppers can be made by incorporating'in stopper mixes of the usual type a relatively small proportion of a ceramic grog having a low coefiicient of thermal. expansion, i. e., below about 2.7){10- per degree centigrade. Examples of such grogs are:

The coeflic'ients' of expansion shown are those found in applicants experience with materials actually used when calcined as indicated.

While I find that any of these materials can be used in accordance with my invention to produce stopper heads with improved resistance to heat shock, I prefer to use fused silica on account of its high refractoriness which permits it to be kept submerged in the very hot steel without danger of fusion while the ladle is being emptied. 1

It is, of course, desirable, in order to keep cost down, tolimit the proportion of these high priced ingredients so far as practicable and I have found that in-clay-graphite bodies of the type herein described non-spallin'g characteristics begin to be imparted-with as little as 10% of Patented Nov. 27, 1956 The Carnegie Illinois investigatorsstate that every a low expansion grog and are very strongly evident in bodies containing 12% to 15% by weight of fused silica for example. Still higher precentages can be used without inducing spalling but the use of more than 30% is usually not desirable both because of needless cost and because the thermal conductivity of the stopper with higher proportions of the low expansion grog becomes so high as to result in damage to the stopper pins.

The fused silica or other low expansion grog should be relatively free from material finer than 70 mesh size. It should, on the other hand, all pass an 8 mesh screen. The exact sizes within this range are not critical. Grogs of the types enumerated above, when in particle sizes finer than 70 mesh, tend to be so afiected by prolonged heating as to alter their structure and cause them to lose their low coefiicient of expansion-but such finer grog may be used to reduce the amount of clay grog otherwise required.

As for the other ingredients, the bond clay may be any refractory plastic clay. It should be used in sufiicient proportion to render the body easily formable. In general, from 15 to 50% by weight works out well. The clay grog (as distinguished from the low expansion grog) should likewise usually run from 15 to 50% by. weight of the total mix though less may be used where the clay does not shrink excessively on firing. It may vary within any convenient grit size limits, such as 35 mesh and finer or 8 mesh and finer. The sum of the clay materials (clay and grog) may appropriately be from 50 to 70% of the weight of the entire body. I have found it advantageous at times to add to the mix a quantity of fine aluminum oxide or material consisting of over 60% alumina such as kyanite fines, up to perhaps one fourth the weight of the clay and clay grog present so as to raise the alumina content of that portion of the mix and make the stoppers more refractory and inert at high temperatures.

The graphite content should be kept low for reasons of economy but I have found from 12 to 20% of flake graphite to be desirable in my stopper bodies. This flake graphite should be substantially all finer than mesh and at least half of it coarser than 100 mesh. It may comprise a range of grit sizes but need not be of any special size within the stipulated range. I prefer to use graphite, the free carbon content of which is from 75 to 85% and the tap packing density of which is around 0.75 to 0.85 gmsJper cc.

I recite the following representative mixes by way of illustration but do not wish to be limited thereby (all percentages by weight):

Formula 1 r Percent Fused silica, 8 mesh and finer 44 Madagascar flake graphite 17 Klingenberg clay 39 Formula 2 Percent Firebrick grog, 35/60 mesh 17 Raw kyanite, 100/finer mesh 13 M & D ball clay 36 Cordierite (1l00 Calcine), 8/35 mesh 14 Madagascar flake graphite 20 Formula 3 Percent Firebrick grog, 35/finer mesh 20 Fused silica, 16/35 mesh 14 Fused silica, 8/16 mesh 10 Stopper fines graphite 17 Ball clay 14 Karblite clay- 21 A-,2. calcined alumina Y F 4 the material moldable by ordinary ceramic methods and.

Klingenberg clay is a well known reiractory German ball clay.

Firebrick grog means crushed burned firebrick. It is composed of relatively pure aluminum silicates, sometimes plus free silica and alumina and is a term familiar in the ceramic industry.

M & D ball clay is a typical Mississippi ball clay 'as sold by the Kentucky Tennessee Clay. Company of Mayfield, Kentucky. .A typical analysis is:

' Percent;- SiOz 57.0 A1203 27.9 FczOa 2.2 TiOz 1.3 Alkalies 1.3 Ignition 9.8

Stop er fines graphite designates natural flake Mada I gascar graphite too fine in size forthe most demanding crucible trade which is imported 'by ,various concerns and sold to the producers ofstopper heads in the U. S under this name. I

*Karblite clay is a typical Tennessee ball clay produced by the Bell Clay Company 'of Gleason, Tennessee. A typical analysisis: I

. Percent SiOz V 55.0' A1203 30.9 FezOs 0.9 Alkalies. 2.1 Ignition 11.2

A-2 calcined alumina is a veryi fine' powdered calcined alumina sold by the Aluminum Company of America under that designation. A1203 with up to /2% ,NaaO. I

The ingredients of such'formulas as the foregoing should be mixed together with suflicient Water to make then formed in the way. stoppers are usually formed.

Then after careful drying, the molded stopper heads should be buriedin graphite or other granular carbon and,'while so buried, fired to a temperature sutficient to vitrify. the clay binder. I is dangerously weak if it is not fired hot enough to vitrify' it. The necessity for firing adequately high to develop strength is well recognized in the stopper art but until my present invention such firing had been accompanied by a serious increase in the tendency of the vitrified In the case of the examplesstoppers to spall in service. cited, firing to Cone 9 (1250 C.) for four hours followed by a flash fire to Cone ll 1285" C.) has beenfound satisfactory. 'Too long firing at too high a temperature isapt to devitrify fused silica and should be care-' fully avoided in the processing of stopperscontaining this material. Clays should be selected which do not require firing above temperatures at which they will react with the low expansion grog used.

In service, these stoppers show no cracks whatever It contains over 99%;

This is important as the stopper found to be in better condition after use in stoppers containing 30% or less of fused silica than in those made of Formula 1 for example, but even the latter performed adequately.

Having thus explained my invention and given several examples of its application, what I claim is:

1. A raw mix for the manufacture of stopper heads, said mix consisting of from to 50% by weight of a plastic refractory clay, 15 to 50% by weight of refractory clay grog and from 12 to by weight of flake graphite and comprising from 12 to 20% by weight of fused silica.

2. A stopper head composed of from 12 to 20% by weight of flake graphite, from 12 to by weight of fused silica and to by weight of fired refractory clay.

3. A stopper head consisting of from 12 to 20% by Weight of flake graphite, 12 to 30% by Weight of fused silica, from 50 to 70% by weight of fired refractory clay and additional aluminum oxide up to one fourth the weight of said clay.

4. A stopper head composed of from 15 to 20% by weight of flake graphite, from 12 to 15% by weight of fused silica and the remainder fired refractory clay.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Ceramic Industry, January 1954, pp. 69, 94, and 122.

0. C. Smith: Identification and Qualitative Chemical 20 Analysis of Minerals, 1946, p. 265.

Claims (1)

1. A RAW MIX FOR THE MANUFACTURE OF STOPPER HEADS, SAID MIX CONSISTING OF FROM 15 TO 50% BY WEIGHT OF A PLASTIC REFRACTORY CLAY, 15 TO 50% BY WEIGHT OF REFRACTORY CLAY GROG AND FROM 12 TO 20% BY WEIGHT OF FLAKE GRAPHITE AND COMPRISING FROM 12 TO 20% BY WEIGHT OF FUSED SILICA.