US1986985A - Coated metallic centrifugal pipe mold - Google Patents

Description

Jan. 8, H w STUART ET AL COATED METALLIC CENTRIFUGAL PIPE MOLD Filed March 22, 1934 Eeneri Hfiiuarl, q liora/ce 61 Hand far/ml 1;. Haw/old;

A T TOK/VEV -.MQ-UNITED-STATES PATENT oF icE' Patented Jan. 8, i935 r 1,986,985 COATED METALLIC CENTRIFUGAL PIPE 1 MOLD' Herbert W. Stuart, Beverly, Horace S. Hunt, Bur-, lington, and Paul L. Arnold, Edgewater Park,

N.J., assignors to United States Pipe and Foundry Company, Burlington, N. J., a corporation of New Jersey Application March 22. 1934, Serial No. 716,768

5 Claims. (01. 22 1s9 Our invention relates to the coating of metalthe metal surface of the mold and project in lic centrifugal pipe molds with a finely divided large part through the inner surface of the coatl dry coating material of ,such loosely adherent ing formed by the finely divided dry coating ma and loosely coherent structure as results from the terial. The distribution .of the sand grains to 5 application of the flnelydivided dry coating mabring about the actualecontact of a very large 5 terial tothe mold by directinga. jet of a carrier pr p rti n f th rain with the m tallic surgas charged with the. finely divided dry coating face of the mold is'best eilected by charging the material against successive contiguous areas of j of Ca e ga Charged With fi y divided y the mold surface, that is to say, by the method coating material with an additional charge of the I described and claimed and illustrated in one sand. like grains which, owing to their greater 10 mode of application in, the patent granted to mass, will, as the coating is applied to the mold Me'ssraR'ussell and Langenber'g, Number 1,949,433 be projected through the finely divided material of March 6, 1934. In the centrifugal casting of so as to come in large part in contact with the, pipes in molds coated with the finely divided dry metallic mold surface while the size of the grains coating material as described in the said Russell will be such that they will, at the time the molten 15 and Langenberg patent, under certain conditions metal comes in contact with the coating, project with rgard to the fluidity of the molten iron in part beyond the inner surface of the portion poured into the mold, the molten metal will not of the coating formed by the finely divided dry at all times pick up the rotary motion of the mold coating material and come in actualcontact with with sufllcient promptness to insure that after the molten metal.

,. contacting with the coatedmold surface it would By preference we use for the sand like grains of be carried along by the mold with sufficient speed our composite coating silica sand, the .particle to insure that its centrifugal motion will hold size of which, or of any other available sand like it in contact with the mold and, as a result, por-, material, should be such that it will pass a sieve tions of the molten metalwill at times fall away of 20 meshes to the inch, more preferably, a sieve, 5 from the surface of the mold carrying with it of meshes, while approximately 75% of the portions of the coating material and falling upon sand is retained on a sieve of 50, meshes to the the molten metal lying at the time beneath the inch. Any other sand like material having a falling metal and from both causes imperfect hard, compact, crystalline structure and substan- 30 pipes are produced characterized by what are tially nonreactive and nonfusible under condi- 30 known as mold splashes and liable to have undetions existing during the casting of a pipecan sirable areas of chill. The object of our zinvenbe used in place of silica sand, as, for example, tion is to so change or modify the structure of carborundum, but pains should be taken that the the coating applied to the mold that it will at grains of sand like material are of such structure l the same time be less liable to slip on the surface as to retain their form without breaking up under 35 of the metallic mold to which it is applied and the stresses to which they are subjected during more able to take a bettergrip upon the freshly casting and it is also importantthat the sand like poured metal, thereby decreasing the liability ofmaterial should be uncontaminated with clay or the molten metal to slip on'the surface of the other material which might act like a lubricant 0- coating or to cause a slipping of the coating on and prevent the proper adhesion of the sand like 40 the surface of the mold, thus insuring'that the grains to the mold surface or impair their grip rotary motion of the mold shall be more promptly upon the molten metal. transmitted to the molten metal flowing into the i We have found in practice that the necessary mold. These results can, we have discovered, be percentage of the sand like grains to be admixed effected by admixing with the fin ly ivided dry with the finely divided dry coating material will 45 coating material formingthe coating of the vary very largely with variations in the fluidity mold, sand like grains of a hard and. compact, of the molten iron, under certain conditions an crystalline structure and of a. substance or subadmixture of 5% by volume of sand with the finestances substantially non-reactive and substanly divided dry coating material will be effective.

, tially nonfusible under conditionsexisting durwhile under certain other conditions, omen; ind? 50 ing the casting of a pipe, the sand like grains befrequent occurrence,,l..iwerahawe"i fuundzrithatiian ing of materially larger size than the particles admigetlusmofmirdixofithasaiidelikeog ainsewamadffln ly div d dry coating material ,ang QQ1S' vantagfibjlilfi,shill}ffifl lfllbQIfiGlZlEfEkMflTlfiftlOfl3WhiCh tributed through the iingly, d ttidfidiigoil ih am naue ia le toro cilrlin-ipractice weihawe fiouridihat atililqhetf l tl teeblbe d tc rtw ti hleacia mixturovofiao totZfifiijohthmsandhkqgrains? s5 is adequate and satisfactory and presents no objectionablefeatures where conditions as to the fluidity of the molten metal are such that no admixture of the sand like grains with the finely divided dry coating material is necessary.

For practical purposes it has been found desirable that the particle size of the finely'divided -dry coating material should be approximately such that it will passa sieve of approximately 150 meshes to the inch'and it is with material of 'approximately this fineness that we-prefer to use the sand like grains having the characteristics which we have described and a size .which will pass a sieve of 20 meshes to the inch while approximately 75% is retained on a sieve of 50 meshes to the inch.

As pointed out in the Russell and Langenberg patent, it is preferable that the coating applied to the metallic centrifugal mold should not, for

the best results be-materially thicker than is necessary to effect such retardation in the cooling of the molten'metal as will avoid the formation of a chill both because with increased thickness in the coating there is more liability to slips and fractures impairing its continuity and'because the character of the casting is better than where the retardation in the cooling of the metal is greater. Under some conditions, however, it may be desirable to increase the thickness of the coating and'this we have found can be accomplished by the use of our compositecoating which is distinctly less liable to fracture under conditions of use than'is thecoating formed of the finely divided Idry coating material :without the P incorporation'of the sand element.

It is distinctly advantageous that the "finely divided dry coating material should be'used in such quantity that when evenly and compactly distributed over the surface of the mold it will form a coating the depth of which will be less than that of the diameter of a material per centage of the sand-like grains admixed with the finely divided-dry coating material so that such grains even though running in contact with the surface of the-metal mold will,atthe' time molten "metal is charged intothe coatedmol'd,-' project inward beyond the surface of the coating-formedby the finely divided material and'come in actual contact with the surface of the casting.

The admixture of sand like grains with "the finely divided dry coating material facilitates the handling of the coating material in the feeding mechanism in that it materially increases what we may call the fluidity of the composite coating material as comparedwith that of the finely divided dry coating material when usedalone, greatly lessening the liability or the coating material clogging in some part of the feeding mechanism and making the feed-more accurate in any class of feeding apparatus which may beemployed'to deliver the coating material to the carrier gas jet.

Our invention may'perhaps be better understood as described in connection with the drawing which forms part of this specification and in which Figure l is an'elevation of a centrifugal pipe casting machine adapted for use inthe practice of our improved method of coating the mold and Figure 2 is a somewhat diagrammatic'illustration showing one, greatlyexaggerated scale the general structure of our improved'coating asapplied to a centrifugal metallic pipe mold.

The apparatus illustrated in Fig. 1 is essentially the same as that described in the Russell and Langenberg Patent No. 1,949,433. with the exception that in addition to the feeding mechanism indicated at G and operating to feed the finely divided dry coating material through the hopper'F to the gun F, we have indicated at g a supplementary feeding device adapted also to deliver coating material to the hopper F As, in

all other respects, the apparatus indicated is the same as'that described in the Russell and Langenberg patent, it is unnecessary to describe it in detail except perhaps to note that the coating materials fed to the gun F are picked up in'the gun 'by a jet of carrier gas introduced through the nozzle indicated at F and the so chargedsjet of carrier gas transferred through the conduitE'to the nozzle E which directs the jet against the inner surface of the rotating mold D in advance of the contact of the molten metal fed to the mold through the spout C Ordinarily, we have found it to be satisfactory and convenient to charge a single feeding mechanism such as is indicated at G with a thoroughly admixed charge of'the finely divided coating material and sand in the proportion, say of 20 to 25% of sand by volume to that of the finely divid- :ed dry coating materialas a mixture of this character is found to give satisfactory results 'in'the character of the coating applied to the mold under practically all ordinary conditions of the "molten'metal poured intothe mold but where it is desired to more exactly regulate the condition of the coating to the conditionof the-metal, this can be effected by charging onefeeding device,

:such as G, with the 'finely divided dry coating material and another feeding'device, such as g,

withthe sand so thatby regulating the-irate of "feed of the feeding device g. any desired percentage of sand can be fed to'the gun, with the consequent' formation of a coating .in which the sand constituent will more closely approximate that which is found to be best in view of'the charac- 'ter of the molten metal which at any timeis being fed'to the mold. The construction of .the feeding device indicated atG andrgsis preferably that of United States PatentNo. l ,939',703,granted 'December 19, 11933, but :any feeding :device :capable of delivering anicely regulated supply of mold coating materialmay be used and'while we believe that apparatus of the kind indicated in Fig. l and fully described in the patent :to :Rus-

sell and Langenberg is that best adapted for use in coating and casting pipes, it must beun'derstood that our invention is in no wise limited to the use of such an apparatus'but is applicable to any method in which a jet of carrier gas directed-progressively against contiguous areas of 'a' metallic centrifugal mold is charged with .finely divided mold coating material and also with sand grains of the general character which'we haveindicated as usable in connection with our process 1 and adapted in connection with the finelyhdivided material to buildup our new mold'coating as, for example, the apparatus described .and shown in the applications filed by Russell and Langenberg on June 6, 1933, SerialNumbers, 674,502;

of the mold A and to project in large part through the surface of the coating of finely divided dry coating material indicated at B. The drawing, it will be understood, is greatly exaggerated and is to be understood as in the nature of a diagrammatic showing of the general structure of the coating as of the time when the molten metal poured into the mold contacts with it.

As is pointed out in the Russell and Langenberg patent, 1,949,433, the coating of finely divided dry coating material is, at the time of its application to the mold by the jet of carrier gas, permeated by films of the carrier gas, the presence of which naturally increases the thickness of the coating and increases the efficiency of the coating as a retarder of heat transfer. The incorporation of the carrier gas with thefinely divided dry coating material at the time the coating is applied to the mold no doubt facilitates the passage of the sand grains through the finely divided coating material into contact with the surface of the mold but th t at the time of contact of the molten metal ith the coating, a considerable portion of the sand grains project through the finely divided coating material and come in contact with the molten metal is made evident by the fact that a considerable amount of sand grains are found adhering to the casting, though very easily brushed away and not so embedded in the casting as to impair its smoothness.

Having now described our invention, what we claim as new and desire to secure by Letters Patent, is:

1. An internally coated metallic centrifugal pipe mold characterized in that its coating is made up of loosely adherent and loosely coherent finely divided dry particles of mold coating material intermixed with relatively large sand like called for in claim 1, in which the finely divided coating material is of such particle fineness as would pass through a sieve of approximately 150 meshes to the inch and in'which the sand like material is of such particle size that it would pass a sieve of 20 meshes to the inch and preponderantly of such size that it will not pass a sieve of 50 meshes to the inch.

4. A coated metallic centrifugal pipe mold as called for in claim 1, further characterized in that the sand grains of the composite coating are so disposed therein as to contact in large part with the surface of the metallic mold and to project in large part beyond the surface of that portion of the coating formed by the finely divided dry coating material.

5. A coated metallic centrifugal pipe mold as called for in claim 1, further characterized in that the coating is in part made up of a quantity of the finely divided dry mold coating material which, if compactly distributed over the mold surface, would produce a coating of a thickness less than the diametric size of a substantial percentage of the sand grains which are distributed through the finely divided material.

HERBERT W. STUART. HORACE S. HUNT. PAUL L. ARNOLD.

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