US1960571A - Method or process for the expansive burning of clays - Google Patents

Description

May .29, 1934. F. w. B UTTERWORTH ET AL 1,960,571

METHOD on PROCESS FOR THE EXPANSIVE BURNING OF CLAYS Filed April 11', 1932 w y E Patented May 29, 1934 UNITED STATES PATENT OFFICE METHOD OR PROCESS FOR THE EXPANSIVE BURNING OF CLAYS Illinois Application April 11, 1932, Serial No. 604,538 17 Claims. (Cl. 25156) This invention relates to a new and improved method or process for the expansive burning of clays and to articles produced by such process. More particularly our invention relates to a method by which cellular articles may be formed of a predetermined size and shape.

We are aware that the expansive burning of clay has been practiced heretofore for the purpose of forming a light aggregate for the manufacture of molded articles. In all such prior processes of which we have knowledge, however, the aggregate formed is irregular in size and shape. The

clay during the burning expands and even ii formed before burning, the form and size are both materially altered by the expansion which is irregular in character and amount.

It is an object of the present invention to provide a new and improved method for forming articles of a predetermined size and shape by the 2 expansive burning of clays.

It is a further object to provide a method whereby the expansion of the clay during the buming may be adequately controlled as to direction and amount.

It is also an object to provide articles of expansively burned clay which are of a desired size, shape and density. a

"It is an additional object to provide a building block or the like which is light, strong, impervious to water. and which has high insulating'propfities and good sound absorption. 7

It is a further object to provide a method of making and burning such blocks or the like whereby the time and fuel required for burning are very materially reduced below that required for usual types of ceramic blocks or tile.

Other and further objects will appear as the description proceeds.

We have shown certain preferred embodiments of our invention in the accompanying drawing, in which- Figure 1 is a perspective view of one form of' blank prior to burning;

Figure 2 is a similar view of the same blank after burning;

Figure 3 is a perspective view showing one form of mold or container used for restraining or limiting the expansion of the blank during the burning process; D

Figure 4 is a transverse section on a reduced scale showing the blank within the container before burning Figure 5 is a view similar to Figure 4 but showing the blank after burning and Figure 6 is a view similar to Figure 4 but showing a different type of container.

The form of blank shown in Figure 1 consists of a rectangular blank 11 of approximately the size and general 'shape which it is desired the finished brick or block should take. This blank 11 is provided with a plurality of rectangular openings 12 which extend all the waythrough the blank. Under the expansion caused by the heat, the blank tends to swell in all directions and by the use of a container or restraining housing this swelling is limited in direction, and further the external swelling is definitely limited in amount. It will be seen that the walls about and between the openings 12 are substantially the same thickness so that t e heat will be transmitted substantially uniformly to the material throughout the blank. This causes the swelling to be substantially uniform and also substantiallysimultaneous. When restrained by the container or housing, the blank will swell to completely fill the containerand any further expansion must be eifected by filling up the openings 12.

As shown in Figure 2, the block 13 is of cellular construction and the openings 12 are completely closed. Also the size of the block has slightly increased in each direction.

lg One form of container or housing suitable for carrying out the method is shown in Figure 3. This container consists of a bottom 14, lateral walls 15, and a removable cover plate 16. The plate 16 is formed with'openings 17 which approximate in form and location the openings 12 which extend through the blanks 11. The cover 16 is shown held in-place by lugs 18 and wing nuts 19. The bottom 14 is provided with openings similar to the openings 17 of the cover 16 and located in approximate alignment with the openings 1'7. The container is provided with the supports 20 whichserve to elevate the bottom of the container above the floor 21 of the kiln or heating chamber in' which the container may be placed.

In Figure 4 the blank 11 is shown in place in the container, the cover 16being fixed in place. The openings 12 are indicated by broken lines. In Figure 5 the section shows the block 13 after burning, this completely filling the container instead of having a clearance on all sides as shown in Figure 4.

Figure 6 indicates a refractory container 22 having a refractory lid or closure 23. This is shown as containing the blank 11 having the openings 12 therethrough'. v

In forming blocks according to our method by the use of a container of the character shown in Figures 3, 4 and 5, the blank is affected by the heat both through conduction through the walls of the container and by gases passing through the openings 1'7 in the top and through the bottom, and through the openings 12 in the blanks until these openings have been filled by the expansion of the material. In the form of construction shown in Figure 6, the blank will be affected solely by heat conducted through the walls of the refractory container. It will be understood that the refractory container may be made of any material adapted to withstand the heat required for burning the block without material injury or deformation. The container may beperforated or not, as desired. There is no great amount of strain imparted to the container by the expansion of the block and consequently no great tensile strength is required.

It will be understood that the forms of container shown, are merely illustrative, as in commercial operation it is probable that containers would be used having a plurality of compartments each of which would contain an individual block. Our process will be describedin connection with the making of bricks or building blocks although it will be understood that it may be equally well applied to articles of other forms, shapes and sizes.

The bricks are made in the regular way by any of the regular processes of molding and are dried in the usual way, the only difference being that instead of being solid, they are made with voids, 30 to of the volume of the brick. The amount of voids will vary with different clays and according to the kind of ware to be produced.

After these bricks or blanks which might be called hollow bricks, come from the dryhouse with a large percentage of the physically combined water evaporated, they are then placed in the fire clay molds or metal molds just a trifle larger than the dried brick.

The process from that point on radically differs from the ordinary burning process by which the ware is contracted.

First, although the ware is theoretically dry, there is always some little moisture present and it is necessary to' expose it to a temperature slightly in excess of the boiling point in order to be sure that all of the physically combined water has left it. a

Second, the temperature is thenincreased to a point well below the dehydrating and oxidation points.

Third, immediately that the ware has attained the above temperature,- it is put into a temperature appreciably higher than that at which it vitrifies or at which the fluxes melt. The effect of this is to melt the fluxes and at the same time, expand the gases contained in the clay, resulting in a rapid and more or less thorough expansion of the ware. The ware being enclosed in and nearly filling a mold of the ultimate size and shape of the desired ware, and the clay body being full of voids, the expansion goes mainly in one direction; that is, toward the voids which are either entirely or partially filled up.

Fourth, the ware is kept at this temperature for a very short time, suificiently long to insure a vitrification of all of the partitions forming the cells in which the gases are trapped, and although the major part of the expansion comes quickly, the expansion will continue for an indefinite period if this high temperature is maintained.

Fifth, the ware is then cooled in the regular way, although our experience is that due to its cellular properties, etc., it can be cooled much quicker without danger than where it is contracted during the burning process.

It has been found that the time required for this method of burning after the physically combined water has been expelled and up to the time of cooling is often as little as fifteen minutes, dependent upon the character of the clay, the maximum temperature of the hot zone and the number and volume of the voids in the unit.

As a specific example, the blank may be placed in a temperature of approximately 1000 F. and the temperature gradually raised until in twentyfive minutes it reaches 2000 F. The rise in temperature may continue until at the end of forty minutes it reaches a maximum of 2240 R, which is maintained for three minutes after which the block is'slowly cooled.

By our method, the amount of expansion can be exactly controlled by the temperature of the hot zone and the length of time in which the ware is allowed to remain at the high temperature point. Thus, from the same material, ware of very great strength and considerable density can be made; or, ware of little structural strength and extremely cellular can be manufactured.

' If it is desired to retain somewhat the same outside appearance of the ware as though it were burned by the ordinary process, the dry hollow ware is made so that there will be very little clearance between it and the refractory mold; and this side of the mold is not perforated, and by maintaining this close juxtaposition, the original texture and condition of the ware is maintaned, even though the expansion is 200%.

Although it seems desirable to form the ware in the usual way as described above, we have found that the following method also produces the same kind of ware. In the place of the regular molding machinery, the raw shale after being ground to fairly uniform particles, say that will pass through a ring and be retained on a. screen with the holes in diameter are coated in a drum or any other apparatus with a coating of a rather weak solution of sodium silicate and while wet, these particles of day are lightly pressed together in the desired form with voids and the sodium silicate allowed to set, after which the ware is treated in the same way as formerly described. The sodium silicate will make a bond between the particles, holding them together in the desired form and this bond will not" be destroyed by heat until a temperature is reached at which another bond. is substituted. By either process the resulting. ware is highly cellular and therefore is very light in weight, it being quite possible in the same clays and shales to secure 200% expansion; that is, the clay or shale will have been converted into a cellular mass three times its original volume.

This ware, burned in this way, as stated above, can be made sufficiently dense to have high crushing strength and still be cellular or can be expanded to almost the entire limit into a very lightweight ware with but little structural strength.

The containers or molds may be knock-down in character or may be slightly tapered to facilitate the removal of the formed blocks. Various means may be used for preventing or limiting adhesion of the formed block to the container. For example, the interior of the container may be coated with graphite or a lime wash, or may the heat of the burning, but the non-fusible ashv will serve to prevent adhesion. Sand used in the mold to prevent adhesion might also aid in,

giving a desired finish to the block, as is customary in various types of face brick at the present time. As a further method of preventing adhesion and giving a desired surface, a paper or membrane having sand caused to adhere thereto by an adhesive such as sodium silicate, may be used for lining the container, the paper or membrane being destroyed by the heat and the sand adhering to the finished block.

blank shown in Figure 1 is also merely illustrative, as a large variety of forms of blank may be used to meet varying conditions and requirements. The openings extending through the block may vary in size and location, and when the block is burned they may be fully or partially closed up as desired. For many purposes for which these blocks are adapted it is immaterial, or in some cases desirable, to have openings extending through the blocks. In such cases the perforations or openings through the blank may only partially be filled by the expansion. In cases where it is desired to have openings through the finished block which openings are of a definite size and character, collapsible or removable mold members or cores may be placed in the container extending through the blank and remaining in place until the heat treatment is completed.

The amount of expansion permitted upon the outside of the blank will vary as desired. In some cases it may be desirable to limit this expansion very closely and force all of the expansion to the interior of the block. Such a method of manufacture will tend to give a smoother and denser surface than where greater exterior surface expansionis permitted. The surface may be treated in various ways as is now known in the ceramic art by having layers of different types of clay or other material placed on the blanks before burning, in order to give any desired finish to the surface of the product. The surface color and texture may be varied by permitting more or less surface oxidation before the burning temperature reaches that necessary for causing the cellular expansion. 1 v

The amount of expansion may be controlled by the nature of the material forming the blank, by its moisture content, by the speed with which the blank is moved through the various heat zones, and by the modification of the temperatures of these zones. By variation of any or all of these elements a block of desired lightness and cell size and content may be obtained.

The kiln or furnace in which this burning takes place can be of any type but in our practice we prefer a tunnel furnace, with the ware moving through a hot zone either on cars according to usual tunnel kiln practice, or on a refractory conveying system. Due to the short time in which the ware is in the hot zone (from three to ten minutes), the ware is produced very rapidly and the burning cost greatly reduced over any other known process.

While we have described and shown various methods of carrying out our invention, these are to be understood as illustrative only, as both method and product are capable of wide variation-to meet differing requirements and we contemplate such changes and modifications as come within the spirit and scope of the appended claims.

We claim:

l. The method of making an expanded ceramic product which comprises forming a ceramic blank, heating the blank to a temperature at which the blank expands to a material extent,

and restraining said expansion.

' 2. The method of making an expanded ceramic product which comprises placing a, blank of ceramic material in a container, said blank being slightly spaced from the container walls and hav ing voids internally thereof, and heating the ceramic material in the container to a temperature at which the material expands to contact It will be further understood that the form of with the walls of the container.

3. The method of making an expanded ceramic product which comprises forming a ceramic blank of approximately the size and of the shape of the desired product, heating the blank to a temperature and with such rapidity that the blank expands to a material extent, and restraining said expansion to hold the desired size and shape for the finished product.

4. The method of making an expanded ceramic product which comprises forming a ceramic blank having voids therein, heating the blank to a temperature at which the material forming the blank expands, restraining external expansion, and permitting internal expansion.

5. The method of making an expanded ceramic product which comprises partially filling with ceramic material a container closable on all faces, closing said container and heating the material in the container to a temperature and with such rapidity that it expands and engages all faces of the container.

6. The method of making an expanded ceramic product which comprises forming a ceramic blank having voids therein, heating the blank to a temperature at which the material forming the blank expands, restraining external expansion to an amount such as to bring the blank to the size and shape desired for the finished product, and permitting internal expansion.

'7. The method of making an expanded ceramic product which comprises forming a ceramic blank having openings extending through the blank, heating the blank to a temperature at which the material forming the blank expands, restraining external expansion and permitting internal expansion into said openings.

8. The method of making an expanded ceramic 0 product which comprises forming a ceramic blank having openings extending through the blank, heating the blank to a temperature and with such rapidity that the material forming the blank expands, restraining external expansion and permitting internal expansion into said openings to completely fill said openings.

9. The method of making an expanded ceramic product which comprises forming a ceramic blank, placing the blank in a container with material between the blank and container walls to prevent adhesion of said walls during the burriing of the blank, raising the temperature of the blank while in the container to such a degree as to cause expansion of the blank forcing it in intimate contact with the container walls, and therecontainer.

10. The method of' making an expanded ceramic product which comprises forming a ceramic blank, placing the blank in a substantially closed container having a cubic capacity greater than the cubic solid content of the blank, and heating the blank in the container to such a temperature as to cause it to expand and fill the container.

11. The method of making an expanded ceramic product which comprises forming a blank having approximately the size and outer contour of the desired product, placing it in a substantially closed container of the size and contour of' the desired product, and heating the blank and container to such a temperature that the blank expands to contact with all walls of the container.

12. The method of making an expanded ceramic product which comprises placing ceramic material in a container of the size and shape of the desired finished product, heating the material in the container to a temperature to drive off physically combined water, slowly raising the temperature to a point somewhat below the dehydration and oxidation points, and quickly raising the temperature to a point at which the fluxes in the material melt and the material expands and vitrifies, the expansion causing it to engage all walls of the container.

13. The method of making an expanded ceramic product which comprises placing ceramic material in a container of the size and shape of the desired finished product, heating the material in the container to a temperature to drive off physically combined water, slowly raising the temperature to a point somewhat below the dehydration and oxidation points, and quickly raising the temperature to a temperature of approximately. 2000 F. or above at which point the fluxes in the material melt and the material expands and vitrifies, the expansion causing it to engage all walls of the container.

14. The method of making an expanded ceramic product which comprises forming a blank having voids therein and being of approximately the size and shape of the desired finished product, enclosing said blank in a container having an interior of the size and shape of the finished product, slowly raising the temperature of the blank to a point below the melting point of the fluxes in the blank and then quickly raising the temperature to the point at which the blank expands and vitrifies to fill the container.

15. The method of making an expanded ceramic product which comprises forming a blank having voids therein and being of approximately the size and shape of the desired finished product, enclosing said blank in a container having an interior of the size and shape of the finished product, slowly raising the temperature of the blank to a point below the melting point of the fluxes in the blank, then quickly raising the temperature to the point at which the blank expands and vitrifies to fill the container, maintaining the blank at this temperature for a short period, and gradually cooling the product.

16. The method of making an expanded ceramic product which comprises forming a blank having voids therein and being of approximately the size and shape of the desired finished product, enclosing said blank in a container having an interior of the size and shape of the finished product, slowly raising the temperature of the blank to a point below 1300 F., raising the temperature quickly to a point above 1950 F., maintaining it at such temperature for a short time, and gradually cooling the product.

1'7. The method of making an expanded ceramic product which comprises forming a blank having voids therein and being of approximately the size and shape of the desired finished product, I.

enclosing said blank in a container having an interior of the size and shape of the finished product, slowly raising the temperature of the blank to a point below 1300 F., raising the temperature quickly to a point above 1950 F., maintaining it at such temperature for approximately five minutes, and gradually cooling the product.

FRANK W. BU'II'ERWORTH. IVAN N. DOUGH'I'Y. IRL R. CLIN'E.

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