US2914834A

US2914834A - Method of making ceramic cylinders

Info

Publication number: US2914834A
Application number: US652893A
Authority: US
Inventors: William A Daniel
Original assignee: Bendix Aviation Corp
Current assignee: Bendix Aviation Corp
Priority date: 1957-04-15
Filing date: 1957-04-15
Publication date: 1959-12-01
Anticipated expiration: 1976-12-01
Also published as: GB855561A

Description

L z l I I W. A. DANIEL METHOD OF MAKING CERAMIC CYLINDERS Filed April 15, 1957 L HHHHH. w \%av Llllllllllllllllll llllll R E m M ML V4 0 m W n 1 A A d W Y A B f a 2,914,834 r F MAKINGCERAMIC CYLINDERS William A'. Daniel, Van Nuys, Califi, assignor to Bendix 1 Aviation Corporation, North Hollywood, Calif., a corwporation of Delaware Application April 15,1957, Serial No. 652,893

' Claims. c1. 25-151 This 'invention relates to the manufacture of tubular ceramic objectsandhas particular application to thinwalled hollow "cylinders of-ceramic material that shrink appreciably duringfiring;

.A' general object of the; invention is to reduce distortion of tubular ceramic object's during firing. 1

It is well known that many ceramic materials become quite soft du ring firing and distort in response to relatively slight fofce's. T oredu'ce the distorting force of gravity on hollow cylinders, they are fired in vertical position while resting on a flat surface. However, if the cylinder shrinks, inward movement of the base is resisted by friction ibetween it and the supporting surface so that the lower endisj often belled or oval, and a substantial portion must be cut off and discarded. This belling has been reduced by supporting the cylinder upon a shrinkage ring of the same ceramic and of substantial radial thickness during firing, but shrinkage rings are expensive and are not always successful.

In accordance with the present invention, an end wall of the same ceramic material is formed on the base end of the cylinder. This end wall tends to shrink during firing at the same rate as the cylinder, and has sufficient strength, by virtue of its large radial dimensions, to overvcome the frictional resistance of the supporting surface.

This substantially eliminates any distortion of the cylinder from a true cylindrical shape during firing, after which the lower end is cut off close to the end wall.

. tion is a method of forming a suitable end wall on a centrifugally cast cylinder.

Other objects and features of the invention will be apparent from the following detailed description taken in connection with the drawing, in which:

Fig. l is a longitudinal sectional view illustrating the centrifugal slip-casting of a hollow ceramic cylinder.

Fig. 2 is a schematic diagram showing a mold containing a centrifugally cast cylinder positioned on a porous slab, ready for the casting of an end wall thereon.

Fig. 3 is a diagram like Fig. 2, with the end wall poured.

Fig. 4 is a schematic diagram showing a cylinder with an end wall positioned in a mufiie for firing.

Fig. 5 shows a finished cylinder with the end wall removed.

Fig. 1 shows a portion of a centrifugal casting machine that may be used to produce open-ended, hollow ceramic cylinders. It comprises a porous cylindrical mold 10, which may be of plaster of Paris, and is supported between two end walls 11 and 12.. The end walls have annular grooves 11a and 12a, respectively, for receiving the ends of the mold 10. Gaskets 11b and 12b may be positioned in the annular grooves 11a and 12a, respectively, to effect a fluid seal. The end walls 11 and 12 are supported on an arbor 13 having

nuts

14 and 15 bearing against the outer surfaces of the end walls 11 and 2,914,834 Patented Dec. 1, 1959 2 12, respectively, for securing them tightly against cylindrical mold 10. The arbor 13 has a central passage 13a extending from the end wall 11 past the end wall 12, and has radially extending slots 13b extending therefrom; between the end walls 11 and 12 for the discharge of slipvinto the mold. Slip is supplied to the passage 13a through a hollow bushing 18 encircling the shaft beyond the mold end wall 12 and communicating with the passage 1341 through radial holes 130 therein. The bushing 18 remains stationary while the arbor 13 rotates, and is sealed with respect to the arbor by washers 17 of resilient ma; terial which are compressed between the opposite ends of the bushing 18 and a pair of ball thrust bearings, 16, 16. i In operation, the bushing 18 is connected to a source of slip through a suitable line connected to a nipple 18a on the bushing 18, and, While the arbor 13 is rotated by any suitable mechanism, a desired quantity of slip is forced through the nipple 18a, the hollow bushing 18, the passage 13a in the arbor, and out through the slots 13b into the rotating mold. The slip is quickly forced.

by the centrifugal force into a layer 20 which is hereinafter referred toas the casting or the cylindrical casting. The spinning of the mold is continued until the casting 20 has been sulficiently driedby transfer of water from the slip] into the porous mold 10 to. make the casting self-support the casting 20 adhering thereto is removed from the cast ing apparatus and is set in verticalposition on a porous slab, of material such as plaster of Paris, as indicated at 21 in Fig. 2.

It will be observed that by virtue of the annular grooves 11a and 12a in the mold end walls 11 and 12 of Fig. l,

the cylindrical mold 10 extends beyond the end of the casting 20.

An end wall 22 is then formed on the lower end of the casting 20, while the latter is in semi-wet condition, by pouring a quantity of slip into the cylinder while positioned as shown in Fig. 2. The slip flattens out by its own weight, as shown in Fig. 3, and dries by absorption of moisture therefrom intothe porous slab 21 to form an end wall 22. The assembly of the casting 20 and the end wall casting 22 is permitted to dry in the cylindrical mold 10 and on the porous slab 21 until they detach themof the casting 20 and the end Wall 22 may be then lifted off the slab 21.

The assembly of the

casting

20 and 22, after further drying if necessary, is then placed, as shown in Fig. 4, on a refractory slab 25 which is covered with a layer of leveled refractory sand 26. The casting is enclosed with a refractory tube or muffle 27 and a top plate 28 of refractory material. The entire assembly is then placed in a suitable kiln and fired.

As previously indicated, some ceramic materials become quite soft during the firing operation, and also contract substantially. This contraction normally results in uniform radial contraction of the casting 20, provided such contraction is not impeded by any resistant forces. When a casting 20 without an end wall 22 is supported directly on a refractory slab, the radial contraction at the lower end of the casting is restrained, and belling or distortion from true concentric shape often results. However, the end wall casting 22 prevents such distortion, because it has sufficient body to overcome its frictional resistance to movement along the refractory slab 25, and carries the lower end of the casting 20 with it.

It is important that the end wall 22 extends below the end of the casting 20, and not merely be joined to the inner surface of the casting 20, because the bond between the base 22 and the casting 20 may then be thev lower end of the cylinder 20, it has no tendencyto pull.

radially inwardly away from the cylinder 20 during the firing operation.

1 After the firing has been completed and the assembly has cooled, the end wall 22 and a small portion of the casting 20 may be sawed off, as shown in Fig. 5, to leave the desired open-ended cylindrical ceramic shape. The small portion of the casting 20 that is removed with the end wall 22 is negligible compared with the portion that must often be discarded when the cylinders 20 are fired without the end wall 22 to reduce belling and other distortion.

Although for the purpose of explaining the invention a particular embodiment thereof has been shown and described, obvious modifications will occur to a person skilled in the art, and I do not desire to be limited to the exact details shown and described.

I claim:

1. The method of reducing distortion in a hollow ceramic cylinder during firing thereof comprising: forming at one end of the cylinder while it is in semi-wet condition a ceramic end wall extending across the end and inbonding contact with the end surface of the cylinder; drying the assembly of cylinder and end wall; firing said assembly with said end wall resting on a horizontal supporting surface and the cylinder supported in vertical position entirely on said end wall; and removing said end wall.

2. The method of claim 1 in which said end wall is formed on the end of the cylinder by pour casting.

3. The method of claim 1 in which said end wall extends into said cylinder in contact with a zone of the inner surface thereof next adjacent the end thereof.

4. The method of producing a hollow ceramic cylinder comprising: centrifugal slip-casting a ceramic cylinder in a hollow absorbent cylindrical mold having a removable end closure ext'endinginto the mold whereby one end of the cylinder is-spaced from the adjacent end of the mold; removing said end closure;'supporting said mold with the cylinder therein in vertical position on a flat absorbent surface with said adjacent end'of the mold resting on said surface; casting a-ceramic end wall on said cylinder by pouring slip-into. said. cylinder to a depth suflicient to fill said mold at least to said one end of said cylinder; drying the assembly of cylinder and end wall; firing said assembly with said end wall resting on a horizontal supporting surface and the cylinder supported in vertical position entirely on said end wall; and removing said end wall. I

5. The method of claim 4 in which said slip is poured to a level above said one end of said cylinder, whereby the end wall joins the cylinderboth over the surface of said one end and over a zone of the inner surface adjacent said end.

References Cited in the file of this patent UNITED STATES PATENTS 1,612,916 Gorton Jan. 4, 1927 1,786,385 Andrews Dec. 23, 1930 1,920,589 Payne Aug. 1, 1933 2,173,107 Gould Sept. 19, 1939