US2835019A - Method for casting ceramic shapes - Google Patents

Description

May 20, 1958i E. THlEss METHOD FOR CASTING CERAMIC sHAPEs Filed Sept. 12, 1955 f METHD vFOR- CASTING CERAMICSHTE-S Electric Company, a corporation of Newy York *Applica'til September# 12,I 1955, S'i'al 'N0."533,688 z-lclaims. (Cl. zs-1s6) `This invention relates tothemanufacture' of ceramic members, `and .more particularly, yto a method for-casting ceramic' shapes.

In the prior artfitis well known to form 'relatively large porcelain bushingsbyv a-ca'stingprocess `utilizing an upright porous mold havingiaV cavity therein complementary to thetvconfigurationr of. the porcelain bushing. Conventionally, ahose of casting slip istdirected intoV the upper end of the cavi-ty to till same. Inasmuch as the casting `slip enters the cavity'on one side the casting slip r.Hows in two paths from said one side to the opposite side of the cavity. `These `twoflows of the casting slip meet at said opposite side `and form `what is known in the lartras a having been introducedwby thei'da'rk,iine, lignitefpa'rticle containing' ball-claysof alkaline casting slip. nApparently, l this colloidal orga-nic matten-and `"the ycolloidalfcl'ay "fractions, being lighter in weight,V segregate from the liquid slip and are carried to the surface where theslip meets during drying and firing.

It is Very diflicult to avoid the formation of slip meet-- ing marks in casting articles from ceramic casting slips. For instance, it has been observed that if the slip is poured into the mold from two opposite places two slip meeting lines will be formed. Additionally, experiments whereby the mold was iilled from the bottom instead of the top have also not been entirely successful in eliminating slip meeting lines and weak areas.

In filling such molds it is also important that air entrapment in the cast piece be avoided. Such air may be present in the ceramic slip, but more often it is introduced into the cast insulator shapes by splashing of the slip in the mold or by filling the molds faster than the air can be safely displaced from the mold cavity.

Accordingly, itis an object of this invention to provide a method for casting ceramic shapes whereby slip meeting marks and entrapped air are eliminated.

I have discovered that rotary stirring of the slip as it rises in the mold will to a considerable degree eliminate slip meeting marks.

Additionally, the slip must be so poured into the mold cavity as to enable air present in the slip to be able to free itself, and the pouring must be controlled and at a predetermined rate to avoid splashing and to avoid filling the mold cavity faster than air can be safely displaced from the mold cavity.

My invention comprises a method of casting a hollow ceramic shape in a mold having a casting cavity therein for forming said ceramic shape, said method including pouring a stream of ceramic casting slip into said cavity United States Patent 0 organization and method of operation, together .with furf then objects and-:advantages thereof, may best be vunderstood-by Vreferenced-0;fthefollowingV description taken in connection with-the accompanying drawing.

Ratented May 20, 1958 ICC yand simultaneously-movingsaid.stream about said cavity during said pouring.

My invention furthercomprises a method of casting a hollovvelongatedceramictshapein` a mold having agen- `erallyfupright castingtcavity.therein for forming said ceramic-shape, said method including controlled pouring of.;afdownwardly--directed streamw fof. ceramic casting. slip into said cavityalong thel innert surface `of. saidV cavity. at

The featuressof.myinvention which I believe to be novel are setI forthfwithsparticularity.inthe yappended claims. Myinvention itself, `however,1both `as..to its In the drawing, Eig. l isla partly broken away elevation *viewvofvone formeof'myfinvention. Fig.\2 Vis a partly r. broken `away sectional-view of my invention .taken along theline -2-2 yof- Fig. 1. i'Fig 3 is .a partly broken away --elevation'view of-a finishedyinsulatorssimilar totthatillustratedas being-formedin Fig. ll. t Like reference numerals Lwill betiusedfthroughout--the variousfigures to indicate Parisimold, havingta'generallyf annular elongated upright casting cavity 1 therein. :Themold cavity lis-delined by fa-tapered lcentral core section 2`and. two-mating generally conicalmhollow' ,outer`- mold l halves 3 i which. are -banded 'CAD ltogether/:by Ybands i 4 and--concentrically spaced from. cen- 'ftral` core -section 2. YThe porous mold isiused tomanu- -facture by-casting afhighvoltageporcelain-insulator bushwofwpetticoats Stethereon.

The bottom'A off' the moldffis closed=,byaa-basesealing plate-'6,` and-positioned. on:thetoprofsthefmoldis Va pouring and stirring tripod apparatus. The pouring and stir ring apparatus comprises a vertical tubular member 7 aligned with the axis of cavity 1 and rotatably mounted in a stationary hub member 8. The' hub 8 is mounted in spaced relationship with respect to the upper end of the mold by virtue of at least three adjustable legs 9 whose radial spread with respect to the axis of tube 7 can be adjusted by virtue of sleeves 10 and set screws 11. Mounted on the hub 8 is a support bracket 12 which supports an adjustable speed drive motor 13 whose shaft carries a small gear 14. Small gear 14 engages and drives a large gear 15 which is coupled to the tube 7 whereby rotary motion is imparted to tube 7. The upper end of the tube 7 has a funnel 16 attached thereto adapted to receive ceramic casting slip from an inlet pipe 17 having a valve 18 therein. The lower end of the tube 7 has a generally crank-shaped outlet pipe 19 connected thereto and the lower end of pipe 19 is fitted with a nozzle 2t) according to the rate of slip flow desired.

It will be noted that the outer surface of the core section 2 has a conical taper imparted thereto which is narrowest at the upper end thereof and widest at the lower end thereof. The radial distance of the nozzle 20 from the axis of tube 7 is selected so that the downwardly directed stream 21 of the casting slip will approach the tapered surface of core section Z at an acute angle and rundown the tapered surface of core section Z. This gives any air present in the slip an opportunity to free itself and also avoids splashing of the slip.' The nozzle 2t] is selected so as to give a rate of slip flow or rate of slip rise in the mold cavity 1 whereby air in the cavity 1 proper and in the petticoat cavities 5' have suflcient op- Y portunity to escape before lling.

While the stream 21 is being poured the .motor 13 due to gears 14 and 15 causes the stream 21 to continuously move around or about the annular outline of the cavity 1 at a relatively slow lspeed along the tapered surface of core section 2. Suchtrotary stirring of the slip by rotary feeding of the stream 21 I have discovered eliminates slip meeting marks which will result from stationary hose feeding. For an insulator approximately 3 feet high having an inner and outer diameter of about 6 and 12 inches respectively 4 to 6 revolutions per minute of the stream 21'and a rate of ow of about 1 cubic foot per minute have proven satisfactory. It will be obvious that the number of revolutions per minute of the vstream 21 and the rate of ow of the slip will vary according to the size and configuration of the insulator being cast. However, a slow rate of ow is selected so that at least several passes of the stream around the mold are required to fill the same, and the speed of travel of the stream around the mold is slow so as to avoid centrifugal separation of the ingredients of the casting slip. For the same reason the mold is stationary. That is, high speed rotation of the stream or rotation of the mold causes centrifugal segregation of the slip ingredients which will result in a cast piece vwhich is mechanically and electrically unsound.

In actual practice the funnel 16 can be made large enough to prohibit spilling over of the slip from the funnel 16 even though the valve 18 is fully opened. Initial pouring of the slip into the funnel 16 I have found to be useful since air present in the slip has an opportunity to escape therefrom while in the funnel 16.

As will be obvious to those skilled in the art, after the 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. In a method of forming large elongated cylindrical ceramic electrical insulating bushings by casting, the improvement of lling an upright mold having a large elongated cylindrical casting cavity without the formation of slip meeting marks, said improvement comprising pouring a stream of ceramic casting slip into the upper end of said mold and simultaneously rotating said stream about said mold while said mold is stationary, said stream having a rate of travel about said mold which is insufficient to cause centrifugal separation of the ingredients of said casting slip and requiring at least several passes about said mold to ll the same.

v2. In a method of forming large elongated cylindrical ceramic electrical insulating bushings by casting, the improvement of slowly iilling an upright mold having a large elongated cylindrical casting cavity Without the formation of slip meeting marks in the piece to be cast, said improvement comprising directing a downward stream of ceramic casting slip into the upper end of said mold at an acute angle against an interior surface of said mold and simultaneously slowly rotating said stream around said mold while said mold is stationary, said stream having a low rate of ow and requiring several passes around said mold to fill the same, and said stream being rotated around said mold at a slow speed to avoid centrifugal segregation of the ingredients of said casting slip.

References Cited in the le of this patent UNITED STATES PATENTS 1,304,571 Kirk et al May 27, 1919 1,885,774 Showers Nov. 1, 1932 2,026,624 Flower Ian. 7, 1936 FOREIGN PATENTS 745,431 France Feb. 14, 1933 652,418 Great Britain Apr. 2S, 1951

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