US2974384A - Method and apparatus for balling clay pug - Google Patents

Description

2 Sheets-Sheet 1 E. G. ALCOTT METHOD AND APPARATUS FOR BALLING CLAY PUG Filed June 6, 1957 March 14, 196i March 14, 1961 E. G. ALCOTT METHOD AND APPARATUS FOR BALLING CLAY PUG Filed June 6, 1957 2 Sheets-Sheet 2 S IMULATED UPSET PUG CLAY BLANK SIMULATED STANDARD PUG CLAY BLANK.

DENSITY DENSITY U PSET PUG CLAY BLANK STANDARD P UG' CLAY BLANK.

172 72761; Brass? 6. fF/coff, 5M 70241? METHOD AND APPARATUS FOR BALLING CLAY PUG Ernest G. Alcott, Glen Burnie, Md., assignor to General Electric Company, a corporation of New York Filed June 6, 1957, Ser. No. 663,929

4 Claims. (CI. 25-54) This'invention relates to a method and apparatus for balling clay pug, and more particularly, to a method and apparatus for balling a generally elongated clay blank preparatory to forming of the same into a high voltage suspension insulator shape.

In order to properly form a generally elongated clay blank into a high voltage suspension insulator shape it is necessary to ball the blank so that it will properly fit the forming mold, and by balling is meant preshaping the clay blank so that it will fit its mold to best advantage. Heretofore balling has been done by hand. Bailing is necessary in order to permit entrapped air to escape from the forming mold and facilitate proper flow of the clay during the forming operation.

The hand balling operation has been successful but has many disadvantages. For instance, it is time-consuming and therefore increases manufacturing costs. Also, since it is subject to human judgment a high reject rate may be incurred unless the person doing the hand balling is skilled and uses much care. The insulators are not impulse and load tested until after the manufacturing cycle is finished. This includes forming, drying, glazing, firing and attaching the necessary hardware. If the hand bal1- ing has not been done properly the finished insulator maybe punctured through the head thereof during impulse test or fail during load test which means that the insulator is a total loss.

It is an object of this invention to provide a method and apparatus which will overcome the disadvantages of hand balling. Y My invention comprises a method and apparatus which will overcome the disadvantages of hand balling.

The method comprises simultaneously upsetting the clay structure toward one end of the clay blanks and increasing the density of the clay structure by high pres- 'sure and controlled clay flow. By upsetting the clay "structure is meant causing the laminations of the clay to rub against each other to increase their cohesion.

One form of apparatus for practicing the method comwprises a forming element which has a generally elongated cavity which is closed at one end thereof by a rounded end wall, said end wall having a clay escape aperture of predetermined size and means for forcing the clay blank ,into the cavity against the end wall under high pressure to increase the density of the clay structure and upset the clay structure toward the end wall.

Since my methodyand apparatus upsets the clay structure and increasesthe density of the clay structure, and particularly at one end of the clay blank, my invention jected to the greatest electrical and mechanical stresses,

and by upsetting and increasing the density of this part it is better able to withstand these stresses.

While the specification concludes with claims particu- Patented Mar. 14, 1961 larly pointing out and distinctly claiming the subject matter which I regard as my invention, it is believed the invention will be better understood from the following description taken in connection with the accompanying drawings in which:

Fig. 1 is a partly broken away elevation view of one form of apparatus for practicing my invention;

Fig. 2 is a partly broken away elevation view of a conventional form of finished high voltage suspension insulator;

Fig. 3 is an axial sectional view of a simulated standard pug clay blank. This simulated blank was built up by stacking circular disks of clay one upon the other. The opposite sides of the disks were coated with dye so that disks are separated by layers of dye. This simulated blank was employed to provide visual evidence of the behavior of the clay when balled by my apparatus and method;

Fig. 4 is an axial sectional view of a simulated blank after it has been balled;

Fig. 5 is an elevation view of an actual standard pug clay blank, accompanied by a list of density readings taken along its length;

Fig. 6 is an elevation view of the standard blank of Fig. 5 after it has been balled, accompanied by a list of density readings to indicate the changes in density brought about by my invention.

Referring now particularly to Fig. l of the drawings, shown therein is a machine frame 1 which has a pedestal 2 and a balling die or forming element 3. In the particular apparatus shown the pedestal 2 is stationary and the balling die or forming element 3 is movable up and down. However, this arrangement could be reversed if so desired. The die 3 is moved toward and away from the pedestal 2 since it is connected to and carried by a reciprocatory ram element 4.

The balling cavity of the die 3 is defined by an interior surface 5 which is generally conically shaped. The sides of surface 5 are slightly curved, and the upper end of the balling cavity is closed by a rounded end wall 6 which has a small clay escape aperture 7 formed therein. That is, the apex of the generally conical and slightly curved surface 5 is rounded off and apertured. I

The aperture 7 has a predetermined size dependin upon the size and shape to be formed. It is for the escape of excess clay and air from the balling cavity during pressing. Also, it serves to control the clay flow so that the laminar structure of the clay blank will be ironed together to obtain a tighter cohesive bond between layers of clay and eliminate faults and increase its density. Additionally, aperture 7 permits entrance of atmospheric air pressure into the balling cavity to aid in release of the balled clay blank after pressing. Excess clay expelled out of aperture 7 is automatically removed by an excess clay cut-ofl blade or scraper 8 which is moved across the aperture 7 at the end of pressing by a suitable actuator 9 which is carried by ram 4.

The surface 5 is heated to obtain quick release of the balled blank. Heating can be accomplished by providing the die 3 with a steam jacket It) or the surface 5 can be heated by electrical coils or other appropriate means. The surface 5 is heated for the purpose of converting some of the moisture which is released from the balled blank into a fine layer of steam along the interface between the exterior surface of the balled blank and the balling surface 5. A temperature of about 240-250" F. is satisfactory for this purpose.

In the operation of the apparatus a generally elongated and cylindrical moist blank or pug of clay 11 is placed upright on the stand 2. When a suitable control element is tripped the die 3 will move toward the blank 11 and force it into the shape of surface 5. At the end of the about 20%, is converted into steam at the heated surface 5. This pressed moisture and steam serves as a lubricant for surface 5. Also, the steam pressure aids in overcoming adhesion between the balled blank and surface 5. When the die 3 is raised the balled blank remains on the pedestal 2 and after the cutter 8 returns to the left the machine can be loaded with another blank for another balling cycle.

The bottom of the balled blank may stick to the upper surface of pedestal 2 since it has been pressed thereagainst. Therefore, the top of the pedestal can be made porous and fluid pressure injected through said porous top to aid in easy removal of the balled blank. This can be accomplished by forming an air pressure release chamber 12 in the pedestal and then forming a plurality of apertures 13 in the top of the pedestal and covering said apertured top with a porous cover such as canvas 14.

It may be possible to use the same type of fluid pressure release in the die 3 by making surface porous. However, I prefer to make the surface 5 hard and smooth such as from metal which has been chrome plated. The reason for this is that a surface which is porous will wear and clog as contrasted to a hard smooth surface. Clogging can be overcome by purging the porous surface. However, this will slow the manufacturing process. It may be possible to obtain release of the balled blank from the surface 5 by oiling the surface 5. However, I prefer to use a steam pressure release since plaster of Paris molds are typically used to shape the balled blank into a suspension insulator shape and oil on the balled blank may contaminate the plaster of Paris molds.

A typical finished insulator is shown in Fig. 2. The part 15 has been shaped from the balled blank by a not shown hot rotating plunger and a mold. The mold forms the external surface 16 and the hot rotating die forms the internal surface 17. The mold with the part 15 is set aside to dry and then the part 15 is removed from the mold and glazed, fired and cooled. The metallic clevis cap 18 and eye bolt 19 can be connected to the part 15 by means such as cement 20.

In high voltage installations the head 15 of part 15 is subjected to high voltage stresses. It is also subjected to high mechanical stresses since such insulators are connected in a string to support transmission lines which may be subject to swinging by high winds and heavy loading due to ice accumulations. Therefore, the head must have as high a dielectric and mechanical strength as possible.

My invention meets these requirements in several ways. Fig. 3 illustrates the simulated laminar structure of a blank which has just been formed by a not shown pug mill. The laminations are illustrated as being superposed and extending generally transversely of the blank although it will be understood by those skilled in the art that in an actual blank which has been formed by the extrusion auger of a pug mill the laminations also spiral along the length of the blank due to the extrusion auger of the pug mill. The simulated structure of Fig. 3 was made from a stack of clay disks 21 which were separated by layers of dye 22.

As indicated by the upset clay disks 21' and layers of dye 22' of Fig. 4, in my invention the laminar structure is upset or caused to flow toward the rounded end of the balled blank. This is made possible by the application of high pressure and the controlled flow of clay through aperture 7. Controlled upsetting or flow of the clay laminations under high pressure rubs and presses the laminations together such that they are more cohesive and dense than in the preballed blank so that the head 15' will be less apt to puncture when subjected to high electrical stresses or fail due to mechanical loading. Compacting of the clay was verified by determining the density of clay specimens taken along the length of an actual clay blank before and after balling. The density readings are listed along the right-hand sides of Figs. 5 and 6.

Although the invention has been specifically illustrated with reference to a clay blank which is balled into a generally conical shape having a rounded off end and slightly curved sides it is believed the invention is useful in balling other shapes. Therefore, the term balling is not restricted to forming the particular shape shown in the drawings, but is intended to include other configurations such as trapezoidal, rectangular, hemispherical, or straight sided conical shapes or combinations thereof for the purpose of fitting the pugged blank in the mold to best advantage and for the purpose of increasing the cohesion and density of a pugged blank which has superposed transverse laminations which spiral or coil along the length of the blank. These laminations are formed by the extrusion auger of a pug mill. A piece of clay will open up along these laminations when it is wet and bent and will crack along these laminations when it is dried. In my invention by the use of high internal clay pressures and controlled flow the clay cohesion and density is increased so that it is a more solid homogenous mass after balling than before balling.

The size of aperture 7 and the balling pressures required to obtain the benefits of my invention will depend upon factors such as the size and shape of the piece to be balled, the balling time, the plasticity of the clay and others. However, the following example will illustrate that a small escape aperture relative to the ball die opening and higher internal pressures than are obtained by hand balling are required to obtain the desired clay flow and increased clay density which in turn will give a better finished product.

For a 10 inch suspension insulator ball containing 172 cubic inches of clay is made from a clay plug cylinder having a diameter of 5 inches, a length of 9 inches, and 176 cubic inches of clay. This allows for 4 cubic inches of clay flow. The entrance diameter of the balling surface 5 was 6%; inches and the escape hole 7 had a diameter of /2 inch. This gives a ratio of 1: 172 for escape area to entrnace area. For ball shapes other than the one illustrated in the drawings a different ratio may be necessary.

Three tons of pressure were used to form the ball in 4 seconds which included ram traverse time. The internal clay pressure developed was in the neighborhood of pounds per square inch. The internal pressure will vary depending upon such factors as escape hole size, clay stiifness and moisture content, and percent of ball clay to total clay mix since ball clay is known for its plasticity.

However, considering other factors as being fixed, varying the size of the escape hole of course controls the internal clay pressures attainable. The range of pressure which produces a marketable piece may be considerable. Internal clay pressure and clay flow have a great efiect on the ultimate quality of the clay since they control the density and internal cohesion obtainable. A larger escape hole than /2 inch gives poorer results as the clay is not compacted enough. A smaller escape hole gives relatively better results but requires more power to press the piece in the same time.

While there has been shown and described a particular embodiment of the invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention, and therefore, it is intended by the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An apparatus for balling a generally cylindrical blank of moist clay preparatory to shaping of the same into a high voltage suspension insulator shape, said apparatus comprising a hollow forming element which has an interior surface which is generally conically shaped, the apex end of said conically shaped surface being rounded and having a small clay escape aperture, the other end of said hollow forming element having a large clay entrance opening, a substantially flat pedestal surface having an area approximately coextensive with said large clay entrance opening, means for causing relative closing motion .at high pressure between said pedestal surface and said hollow forming element whereby a generally cylindrical blank of moist clay placed on said pedestal surface is forced into said forming element through said entrance opening against said rounded apex end under high pressure to increase the density of and upset said clay toward said rounded apex end by high internal pressure clay flow through said aperture, the ratio of the size of said escape aperture to the size of said entrance opening being of the order of 1 to 172, and means associated with said hollow forming element for releasing the upset clay therefrom when said pedestal surface and said hollow forming element are moved apart.

2. An apparatus for balling a generally cylindrically blank of moist clay preparatory to shaping of the same into a high voltage suspension insulator shape, said ap paratus comprising a hollow forming element which has an interior surface which is generally conically shaped, the apex end of said conically shaped surface being rounded and having a small clay escape aperture, the other end of said hollow forming element having a large clay entrance opening, the sides of said conically shaped surface being curved slightly, and means for forcing a generally cylindrical blank of moist clay which has generally transversely extending and lengthwise spiralled superposed clay laminations into said forming element through said entrance opening against said rounded apex end and sides under high pressure to increase the density of and upset said clay toward said rounded apex end by high internal pressure clay flow through said aperture, means for severing clay which has escaped through said aperture from the main body of said blank, and means for heating said interior surface to convert moisture released from said blank into steam along the interface between said blank and interior surface, the ratio of the size of said escape aperture to the size of said entrance opening being of the order of 1 to 172.

3. A method of balling clay plug comprising placing a cylindrical pug blank of moist clay on a substantially flat pedestal surface; aligning, over the center of said pug blank, a balling die having a cavity tapering from a relatively large entrance opening to a relatively small escape opening, said openings having a ratio of the order of 172 to 1; heating said balling die; causing relative closing motion at high pressure between said pedestal surface and said balling die until the volume enclosed by said balling die and said pedestal surface is less than that of said pug blank, whereby the outer areas of the upper portions of said pug blank will be compressed downwardly and simultaneously a small part of the upper center portion of said pug blank will be forced through said escape opening; severing the portion of clay forced through said escape opening; and causing relative opening motion between said pedestal and said balling die whereby the upset pug will be left on said pedestal.

4. An apparatus for balling a generally cylindrical blank of moist clay preparatory to shaping of the same into a high voltage suspension insulator shape, said apparatus comprising a hollow forming element which has an interior surface which is generally conically shaped, the apex end of said conically shaped surface being rounded and having a small clay escape aperture, the other end of said hollow forming element having a large clay entrance opening, a substantially fiat pedestal surface having an area approximately co-extensive with said large clay entrance opening on which a generally cylindrical blank of moist clay is placed, means for causing relative closing motion at high pressure between said pedestal surface and said hollow forming element whereby said clay blank is forced into said forming element through said entrance opening against said rounded apex end under high pressure until the volume enclosed by said hollow forming element and said pedestal is less than the volume of said clay blank to increase the density of andupset said clay blank toward said rounded apex end by clay flow through said escape aperture and simultaneous compaction of said moist clay due to said high pressure, the ratio of the size of said escape aperture to the size of said entrance opening being of the order of 1 to 172, and means for heating said interior surface to convert moisture released from said moist clay blank into steam along the interface between said moist clay blank and said interior surface.

References Cited in the file of this patent UNITED STATES PATENTS France Aug. 2, 1907

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