US2245747A - Method of treating centrifugal metal molds - Google Patents

Description

- rier or applied directly to ing of refractory material separately applied.

Patented June 17, 1941 UNITED STATES PATENT OFFICE METHOD OF TREATING CENTRIFUGAL METAL MOLDS Clarence Dale Barr, Birmingham, Ala., assignor to American Cast Iron Pipe Company, Birmingham, Ala., a corporation of Georgia No Drawing. Application July 24, Serial No. 286,28

6 Claims.

This invention relates to .a method of treating centrifugal metal molds, as of steel or cast iron, for use in the centrifugal casting of iron or steel pipes, tubes, and the like.

In the'centrifugal casting of iron or-stee l pipes,- tubes, etc., it is customary to provide the mold I with a relatively thin coating to protect the mold against injury from the molten metal'and thereby prolong its life, and also to minimize chilling at the surface of the casting, to facilitate separation of the casting from the mold, etc. A com- (Cl. zit-189) mon procedure is to treat the surface of the mold mold surface just ahead of the stream of molten It has also been proposed to introduce metal. coatingmaterials in the form of pastes or liquids sprayed or blown onto the surface of the rotating mold, usually just ahead of the molten metal, with reliance on centrifugal force in whole or in part to effect the distribution-of the coating material. A wide variety of coating materials have also been proposed, including finely divided.

graphite or lamp black either mixed with a care surface of a coat- Difliculties have been experienced, with the procedures heretofore employed, in securing a uniform distribution of the coating material. Powder and paste, though blown into the mold, are

. not distributed equally over the surface of the mold, even though the distribution is aided by centrifugal force, with the result that variations v duction of a smooth, bright surface at the face of the casting, and if the mold is one for 'producing adesign or special configuration at the surface of the casting, the details of the mold sur-' face are not accurately reproduced in the casting because of variations of thickness at the irreguand materially improved results obtained, by proceeding in' accordance with the method hereinsuspended in the liquid to have an irregular dis-f tribution therein because of the action of gravity thereon or the tendency to agglomerate, so that even a fairly uniform distribution of the vehicle over the face of the mold does not produce a uniform distribution of the solid material after the vehicle has been vaporized. Difficulties have also been experienced in the clogging of the nozzles used with the coating materials heretofore employed.

I have discovered that the difliculties heretofore encountered in the use of the coating materials heretofore proposed as applied in the several sug-. gested ways for coating the surface of metal molds used in the centrifugal casting of iron and steel pipes, tubes and the like, may be overcome,

after described.-

It is therefore an object of this invention to provide an improved method for treating the surfaces of metal molds used in the centrifugal casting of iron or steel pipes, tubes and the like, which will enable the coating material to be distributed over the entire surface of .the mold with substantial uniformity. 4

Another object of this invention is to'provide a method of the type characterizedwhich will produce a coating that lengthens the life of the mold.

Another object of this'invent'ion is to provide a method of the type characterized which will produce a coating having substantially the same heat insulating characteristics throughout .the surface of the mold.

Another object of this invention is to provide a method of the type characterized which will produce a" coating of the mold that is firmly adhesive to the mold surface, and which will not crack,

flake, blister, or be roughened or displaced by contact of the molten metal therewith. I

, Another object of this invention is to providea m'ethod of the type characterized wherein the coatingis stable and inert "and protects the surface of the mold from oxidation or corrosion.

Another object of this invention is to provide a v separation of the casting from the mold.

Another-object of this invention is to provide a method of the type characterized whichemploys a coating material that does not tend to separate into its constituent materials and thereby produce an irregular distribution of the solid material in produce a substantially uniform distribution of mold is provided with a smooth glazed surface and the casting accordingly has a smooth surface with a polished appearance, which is relatively free from blemishes and therefore of materially improved appearance over that heretofore obtained from casting in centrifugal molds.

Another object of this invention is to provide a method of the type characterized wherein the coating is highly resistant to brushing, scraping or other mechanicalaction. v

Another object of this invention to provide a method of the type characterized wherein the coating does not tend to build up materially on the mold surface and therefore avoids caking of the mold surface.

' Another object of this invention is to provide a method of the type characterized which enables the accurate reproduction of finedetail'in the molddesign, even in the production of relatively intricate castings. 7

Another object of this invention is to provide a method of the type characterized which avoids the formation of gases from thecoating material that tend to produce blow holes or gas pockets in the casting during the pouring of the molten metal.

Another object of this invention is to provide a method of the type characterized wherein the coating is relatively inert chemically and therefore does not'react to any great extent with the molten metal.

Another object of this invention is to provide a method of the typecharacterized wherein the coating serves to reduce the chilling of the casting by reason of its heat insulating characteristics, and wherein this insulating effect is sub-1 method of the type characterized which by successive treatments of the mold surface produces a coating thereon which materially increases the life of the mold and improves the surface character of the casting. 1 Another object of this invention is to provide into efl'ect the foregoing objects, by applying to the surface thereof a coating of colloidal graphite in dilute solution or suspension in a volatile .liquid. Any suitable liquid vehiclefor said col- 1 loidal graphite may be employed, but at the present I prefer to use a mineral oil. Before application said mixture is preferably diluted by any suitable liquid miscible therewith, kerosene being at the present preferred, so as to produce a relatively dilute mixture or solution. But while an oil vehicle is preferred, the invention is not limited thereto.

The mold may be coated with the colloidal crease the time consumed before the mold is ready for use. When the,moldris coated while hot-the liquid vehicle should preferably be one of low specific heat so as not toiover chill the mold, and therefore the mineral-oil-colloidalgraphite mixture diluted with kerosene hereinbefore mentioned has been found particularly.

satisfactory: 4 I l r The coating of the present invention is preferably applied immediately after a casting operation so as to take advantageof the heat then present in the mold. Contrary to prior practice,

and thereby eliminate the danger of gas pockets' or blow holes due to volatilization of residual vehicle'upon contact of the molten metal therewith, the coating is preferably applied iztrii medi ately after a. previous use to the mold an while it is still hot.

flhecolloidal-graphite-mineral-oil. mixture may be applied in any suitable way, as by a spray nozzle delivering the liquid throughout three, hundred and. sixty degrees of arc while relative movement is eflectedaxially of the mold between the mold and the spray nozzle, or a nozzle producing a lesser arc of spray may be used if relative rotation is maintained. between the mold and the spray while relative axial movement is maintained therebetween, so that the pray travels in the'form of a helix over the entire surface of the mold. In 'the latter event the spray preferably has a substantial spread in the direction of the axis of the mold, and the rate of rotation between the spray and mold,

whether the spray is rotated or the mold is rotated, and the rate of axial movement between method of the type characterized which is productive of a casting having a materially improved,

appearance; I

Other objects will appear as the description of the invention proceeds.

I have discovered that a metal mew for the productive of, a superior casting, and carrying .the mold and at a uniform speed so that all "portions of the mold receive equal quantities of the colloidal suspension. As the particles ,of

graphite in such colloidal suspension are uniformly distributed through ,the liquid vehicle, the distribution of the graphite is accordingly uni-. form over the surface of the mold, andnot irregular as in the case of liquid mixtures employ ing larger particles which may tend to separate from or agglomerate within the vehicle.

Any suitable pressure may be used'for ejecting the colloidal suspension, suitable pressures having been found to be between forty and sixty pounds per square inch of air pressure. But although particular values as to temperature, pressure, etc., have been suggested it is to be exsure on the spray may be varied with the type 'of nozzle used and also with respect to the speed of relative movement between the spray and the surface of the mold, etc., so as to predetermine the quantity of coating material deposited on each square inch of mold surface, and the rate of relative rotation between the spray and mold and the rate of axial movement between the spray and mold may be correlated with the size of the jet and rate of passage throughthe nozzle, all so as to obtain the desired coverage of the mold surface and thickness of coating desired.

Owing to the fluidity of the coating material and the uniform distribution of the colloidal is not relied upon to obtain the distribution ofv the coating material, but the coating material, which itself has uniform characteristics, is so applied as to produce a uniform deposit of the permanent coating has been formed on the mold surface. Thereafter a single coating of the colloidal-graphite-mineral-oil mixture is applied to the mold surface in advance of each casting operation, as in the manner first above described, and

experience has demonstrated that by so proceeding the amount of colloidal graphite removed during each casting operation approximates that deposited during the latter coating operation, so that on the one hand the coating does not tend to build up, while on the other hand a permanent.

coating effected by the aforesaid preliminary treatment remains on the surface of the mold. Thus the life of the mold is materially increased while the use of the plurality of buffed coats,

results in an improved casting having a surface which'is substantially uniform in the physical and chemical characteristics of its surface and which is also possessed of a smooth shiny surface of greatly improved appearance. When the last described procedure is followed, any suitgraphite in colloidally-small particles all over the surface of the mold. Owing to the fineness of method of the present invention assures a .uni-

form distribution of the coating material there is no'burning. through of the molten metal, or sticking of the casting to the mold, such as is likely to arise if thin or bare spots occur in the coating' The coating so produced is also intimately adherent to the face of the mold and yet it does not cake; it is relatively inert to the cast metal; and it does,not crack, flake, blister,

or become displaced or roughened by contact. of

the molten metal therewith. The uniformity of the coating results in a uniformity in its heat insulating effect, thereby reducing chilling of the casting to a uniform extent throughout the surface of the mold. Furthermore, because of' the'very uniformity of the coating;.the casting will duplicate relatively fine and intricate de signs on the mold surface with precision.

While in its broader aspects the present inmolds for casting iron or steel pipes, tubes, e c., as hereinbefore described, apreferred procedure involves preliminarily treating the mold by applyand bufling the surface-of'each coating after the vehicle has been volatilizedi therefrom, until by able number of coats may be applied in building up the permanent coating on the mold, and

while it isnot essential that every coat be subiected to a buffing operation, the preferred procedure involves subjecting each coating toa rub bing or bumng operation so that the permanent coating so formed on the surface of the'mold' ent invention an improved method for treating iron or steel molds for the centrifugal casting of iron or steel pipes, tubes, etc., has been pro-' vided which realizes'each and all of the foregoing objects and which produces a casting of improved character and appearance. Owing to the uniformity with which ,the coating material is applied to the mold, and the manner in which it is applied, not only are blow holes, blisters and other irregularities avoided on the surface of the" casting, but by reason of the character of oating employed, the uniformity of its ins ating capacity because of the use of graphite of such particle size and so distributed, the uniformity of the action of the graphite on the molten metal, etc., the castinghas uniform physical and chemical characteristics at its surface as well as a smooth polished surface of greatly improved appearance.

. While the preferred procedure of the present invention has been described with considerable particularityit is to be expressly understood that the invention is not restricted thereto, aschanges may be made in the details of procedure, appaw ratus used, etc., and certain features may be I used-without other features, and changes may be made'in the temperatures, pressures, degrees of dilution of the colloidal mixture or solution,

relative speeds of application of the coating material, etc., tomeet the exigencies of particular situations, all as will beapparent to-those skilled in the art. Reference is therefore to be had to the appended claims for a definition of the invention. I r

What is claimedjs':

1. The method of preparing metal molds for vention thus involves the coating of centrifugalt- QLlSe in the centrifugal casting of iron or steel pipes, tubes, or the like, which includes maintaining relative movement between the mold and s v a source of coating material composed of colloidal ing a plurality of coatings as heretofore described such plurality of coatings a relatively'thick and graphite suspended in avehicle of volatile oil, distributing over the inner face of said mold a substantially uniform layer of said coatingmaterial of sufficientr thickness that the suspended graphite therein will provide a continuous layer of graphite over the inner face of the mold, and

effecting deposition of said graphite on and adherence of said graphite to the inner faceof the mold by volatilizing said volatile oil.

2. The method of preparing-metal molds for use in the centrifugal casting of iron or steel pipes, tubes, or the like, which includes maintaining relative rotary and axial movement between a spraying device and the mold, spraying onto the inner face of said mold a substantially uniform layer of coating material composed of colloidal graphite suspended in a vehicle of volatile oil such that the suspended graphite therein will provide a continuouslayer of graphite over the inner face of the mold, and effecting deposition of said graphite on and adherence of said graphite to the inner face of the mold by volatilizing said volatile oil. a

3. The method of preparing metal molds for use in the centrifugal casting of iron or steel pipes, tubes, or the llke,-which includes as a preliminary to each casting operation maintaining relative movement between a hot mold and a source of coatingfmaterial composed of colloidal graphite 'suspended in a vehicle of volatile oil,

distributing over the inner face of saidmold a substantially uniform layer of said coating material such that the suspended graphite therein will provide a continuous layer of graphite over the inner face of the mold, utilizing the heat of the mold to'volatilize said volatile oil and effect a substantially uniform deposit of said graphite on and adherence of said graphite to the inner face of the mold, and permitting'said coating to dry thoroughly before casting thereon.

4. The methodof preparing metal molds for use in the centrifugal casting of iron or steel pipes, tubes, or the like, which includes as a preliminary to each casting operation rotating the mold while still hot from a preceding'cast ing operation, moving a spraying device axially of the mold, spraying on the inner face of the mold a substantially-uniform layer 'of coating material 7 composed of colloidal graphite suspended in a vehicle of volatile oil such that the. suspended graphite. therein will provide'a continuous coating over the inner face of the. mold,

and utilizing the heat of said mold to volatilize said volatile oil and effect'the deposition 'of said colloidal graphite on and adherence of said colloidal graphite to the inner face of the mold.

to theinner face of the mold and drying each coat before applying the next succeeding coat thereto, and then applying to'the surface of said permanent coating a uniformly distributed coat+ ing of colloidal graphite suspended in a vehicle of a volatile oil and evaporating the volatile oil to deposit a temporary coating of colloidal graphite on the surface of saidpermanent coating as a preliminary to each casting operation.

6, Th method according to claim 5 wherein at least one or more of the dried coats are buffed in advance of applying a succeeding coat thereto,

CLARENCE DALE BARR.