US2948934A - Apparatus for the manufacture of centrifugally cast tubular metal articles - Google Patents

Description

Aug. 16, 1960 F. H. COUPLAND JR., ETA 2,948,934

. Us FOR THE MANUFACT APPARAT iJRE OF CENT UGALLY CAST TUBULAR METAL ARTICLES Original Filed Feb. 23, 1951 2 Sheets-Sheet 1 AVIIAWIAQIA,

INVENTORS Q Dank co zanm n EduJl'rL H. Phelpm John/M. Crazford Kennefih B. DazueL Aug. 16, 1960 F. H. COUPLAND. JR.. ETAL 2, 4

APPARATUS FOR THE MANUFACTURE OF CENTRIFUGALLY gAST TUBULAR METAL ARTICLES 1 s1 2 SheetsSheet 2 Original Filed Feb I NVENTY )RS Han/c H. cou Edwin, H. P/zeqw' Jolvz M Cram/ 0rd W Wavy). CW2! ATTORNEYS United States Patent APPARATUS FOR THE MANUFACTURE OF CEN- TRIFUGALLY CAST TUBULAR METAL AR- TICLES Original application Feb. 23, 1951, Ser. No. 212,468. Divided and this application Apr. 15, 1953, Ser. No.

6 Claims. 01. 22-1135 This invention relates to the manufacture of centrifugally cast tubular metal articles, and is particularly concerned with an improved apparatus for centrifugally casting iron and steel pipe, tubing and similar hollow bodies of generally cylindrical form by the method disclosed and claimed in application Serial No. 212,468, filed February 23, 1951, now abandoned, of which the present application is a division.

Inasmuch as the invention is especially well adapted to the production of cast iron pipe, the following disclosure will be directed primarily to this particular application of the inventive concept. By so doing, however, it is not intended to limit the scope of the invention to the centrifugal casting of cast iron pipe, because it will be obvious that it has equal utility in the manufacture of other types of hollow metal castings.

Heretofore, there have been in general use in the industry only two different methods of centrifugally casting cast iron pipe; the Sandspun method employing a sand mold formed by ramming green sand around a pattern inside a metal flask, and the de Lavaud process in which a metal mold is used.

In the Sandspun procedure, the sand mold must-be made relatively thick, two inches being a representative thickness, in order to facilitate ramming and also prevent the molten metal from being forced out through the vent holes which are provided in the metal flask to permit ready escape of the water vapor and other gases formed during the casting operation. The use of sand molds requires an extensive amount of mechanical equipment for storing, supplying and reconditioning the sand, ramming the sand into the flasks, maintaining the flask and patterns in properly centered positions, and cutting out the sand before stripping the cast pipes from the molds. Considerable labor is also expended in performing the various manual operations necessary in ramming and stripping the molds. These disadvantages of the sand mold process are offset to a substantial extent by the fact that the resulting castings have the desirable characteristics of a typical sand cast gray iron structure and do not require annealing.

In the de Lavaud method the metal mold is normally water-cooled to reduce the mold temperature produced by the rapid transfer of heat from the molten iron, although in some instances air cooling is adequate, and it is usually attempted to protect the mold during casting by the use of a relatively thin coating or facing of suitable composition, such as dry powdered ferro-silicon or a water suspension of such refractory materials as silica flour and bentonite. In most cases, however, such mold coatings do not retard -the freezing rate sufficiently to prevent chilling of the iron, and a subsequent annealing treatment is necessary to reduce the hardness and brittleness of the as-cast product. In metal mold casting, it .is normally impossible to vent the mold because the liquid iron would flow out through the vent holes, or plug them up, during the casting operation. Consequently, it is one of the limitations of the de Lavaud process that the mold facing used may not contain gas-forming materials, because the only available path for escape of the gases is through the freezing metal with the resultant danger of forming blowholes and leaks in the casting. The difiiculty of providing an adequate protective coating on a non-vented metal mold without causing trouble due to gas formation in the coating also accounts for the excessively high maintenance and replacement costs which are incurred in the use of metal molds. 'Compared with the sand mold process, the principal advantages of the metal mold procedure reside in the relatively higher rate of production per casting machine which results from the rapid rate of solidification of the poured metal, and the fact that it is not necessary to form a new mold for each casting.

The apparatus of the present invention is especially adapted for use in a process which successfully combines the advantages and eliminates the disadvantages of the previously known rotary sand mold and metal mold procedures by providing a novel method of forming and using sand lined, vented metal molds to produce high quality unchilled castings rapidly and efliciently, at low cost and with substantially less capital investment than is required for other centrifugal installations.

The improved mold employed in the new method comprises a noyelly constructed, vented metal mold and a smooth, uniformly hard, bonded refractory lining of selfsustaining character which is rapidly and accurately formed by a carefully controlled centrifugal procedure, and which, while of substantially less thickness than the sand molds ofthe prior art, is effective both to avoid un duly rapid freezing of the casting metal and to protect the metal mold against overheating and wear. The mold lining is composed of a mixture of silica sand or other granular refractory and a dry thermosetting resin which, when heated to a predetermined temperature, forms a homogeneous, strongly bonded refnactory capable of adhering tenaciously to the metal mold. Once the sand resin mixture has fused and set, it constitutes a smooth, dense coating on the interior of the mold which will readily withstand the washing action of the molten metal during casting, but, after the casting has frozen, will disintegrate as a result of burning of the resin under the heat of the solidified metal so as to permit rapid, easy stripping of the casting from the mold. Lined molds of this character may be prepared in quantity with the use of relatively little sand, and, being non-hydroscopic, may be held in storage for indefinite periods of time before being used for casting.

The principal object of this invention is to provide a sand lined metal mold of novel character for making centrifugally cast metal pipe and similar articles by an improved process which produces clean, smooth castings having generally the same properties as those obtainable by the Sandspun method, but does so more quickly, at lower cost and with substantially less equipment and labor than the prior procedure.

Other objects, including the provision of a novel form of vented metal mold, will appear more fully upon consideration of the detailed description of the invention which follows. In this connection, it is to be expressly understood that the specific mold lining and pipe casting procedure hereinafter described and the particular apparatus shown in the accompanying drawing are illustrative only and are not to be construed as representing the full scope of the invention defined in the appended claims.

In the drawings, wherein like reference characters indicate like parts throughout the several views:

Fig. 1 is a side View, partially in section, of one form of mold constructed in accordance with the invention,

3 this view also showing the trough by which the san resin mixture may be introduced into the metal mold in the position occupied thereby just before the mixture is dumped into the rotating mold;

Fig. 2 is an enlarged cross section of the metal mold and trough. taken substantially on line 22 in Fig. 1;

Fig. 3 is a cross section similar to Fig. 2, but showing the trough in inverted position;

Fig. 4 is a partially sectioned side view similar to Fig. 1 showing the sand lined mold as it exists just prior to pouring of the molten metal;

Fig. 5 is an enlarged half axial section of the bell end of the metal mold of Fig. 1 showing the removable metal insert for shaping the outer surface of the bell of the pipe and the means by which said insert is detachably fixed in place;

Fig. 6 is an axial sectional view, on an enlarged scale, of the novel form of vent embodied in the metal mold of Figs. 1 and 4; and

Fig. 7 is a view similar to Fig. 6 showing a modified form of vent.

The method of making a cast iron pipe by use of the apparatus of the present invention comprises a series of coordinated steps performed at successive stations of aproduction line system adapted for continuous, closed cycle operation.

In practice, the beginning of the cycle may be taken to be the centrifugal casting step wherein a charge of molten iron is poured into a rotating mold comprising a vented metal mold having a resin bonded sand lining and rotation of the mold is continued until the cast metal solidifies or freezes into the form provided byv the mold; During the casting, the mold is supported in a substantially horizontal position on, and is rotated by, the motor driven rollers of an ordinary centrifugal casting machine, and the molten iron is delivered into the mold from a tiltable ladle by a relatively short pouring trough of" conventional construction. In making extra long or extra heavy pipe, it may be desirable to use a longer trough extending a substantial distance into the mold andto withdraw the trough as the metal is poured to facilitate longitudinal distribution of the charge. While the metal may be poured from either end of the mold, or even simultaneously from both ends, it is preferable to introduce it from hte spigot end when the pipe is to have a bell or flange so that the colder metal will flow into the heavier sections and the hotter metalwill form the thinner sections of the casting.

If desired or necessitated by the size and weight of the mold, the mold may be rotated at a uniform speed throughout the casting operation, which speed must be sufficient to form the casting on the mold wall centrifugally as the metal is introduced. This is known as high speed casting and involves a relatively high speed of rotation such as to create centrifugal forces at the inner surfiace of the mold on the order of 60.g to 75 g, Where g represents the force of gravity. For example, in-making a 20" pipe by the high speedicastin-g procedure, it is desirable to rotate the mold at from 450 to 500 rpm.

It is preferable, however, to introduce the molten iron into the mold while the latter is rotating at aspeed below that at which the metal is caused to cover the mold wall by centrifugal force, so that the metal may first distribute itself longitudinally in the form of a trough or slab on the bottom of the slowly spinning mold. Then, as soon as all or the major portion of the charge is in the mold, the rotation is accelerated to a speed at which the metal will distribute itself circumferentially and form the pipe under centrifugal action. This procedure is called low speed casting, and is particularly desirable because any loose particles of the mold lining or impurities in the molten metal, together with the slag, will float on top ofthe slab lying along the bottom of the mold and will not be trapped against the mo d in within the wall of the casting.

mately 75% of the molten iron charge is being poured.

In utilizing the low speed casting technique which is particularly adaptable to the molds provided by the present invention because they are substantially lighter than the sand molds used in the Sandspun process for making pipe of the same diameter, the mold is spun at a relatively low speed of from 50 to rpm. while approxiintothe mold, and isthen very rapidly accelerated; within a period of from 5 to 10 seconds, to a relatively high speed on. the order of ten or more times the low speed... For example, in casting a 6" pipe, the mold may be rotated at approximately 50 r.p-.m. for about 12, seconds after pouring. of the metal begins, during which time 75% of the metal in the ladle is delivered into the mold. The speed is then increased in about 6 seconds to ap proximatelySSO r.p.m., equivalent to about 60 g, and'the the high speed rotation iscontinued until the casting sol fies, which takes only about one minute. Due to the fact that the resin bonded sand linings ofthe molds of the present invention are very much thinner than the sand molds of the prior art, the length of time required for the casting step is substantially less than in the Sandspun process, the saving in time being between two and. three minutes per cast with a consequent increase in production rate.

Since the temperature of the molten iron is in the neighborhood of 2400 to 2500" F. when it is poured and comes into contact with the mold lining, the heat.

of the metal quickly burns out the resin in the lining, thus destroying the bond between the. granules of sand and the adhesion of the sand to the metal wall of the mold. The result is that, by the time the mold has been.

transferred from the casting station to the stripping station, the lining is devoid of strength and the pipe is ready to be stripped without any further. operation on. the lining.

At the stripping station, the casting is removed from; the; mold, carryingwith it most of the lining intheform.

mold by the castmetal because, upon completionof the. stripping operation, the empty mold is returned to the. lining. station where it is prepared for the next cast, atwhichtime it is essential that the temperature of the mold wall be within a predetermined range such that the. heat therefrom will-be sufficient to fuse the new lining;

into a strongly bonded-mass, but not so high as tochar any of the resin in the lining. Accordingly, it is preferable .to strip themold within-a minute or two after the. casting hasfrozen, and toso time the .return of the. emptymoldto the lining station that normal atmospheric.

cooling during the return Will reduce the moldtempera ture to withingthe range from300 to 600 F., and-preferably. to between 400 and 500 'F., the-permissible:

limits of said temperature being dependent-upon the kind and amount of resin binder used in the lining; If neces-' sary, artificial cooling may be resorted-to inorderto reduce1themold temperature towithin the desiredrange between the stripping and lining stations.

If, for any reason, the metal mold is cold when ready to be lined, or itstemperature is below the desired minimum, it may be heated in any suitable manner, as by gas torches or ina-heating chamber. In-normal opera tion of th'e method, however, each mold'is lined'while thezmetal Wall stillretains sufficient heat 'from the previous casting step to exert the desired meltingand polymerizing effect on the-resin of thelinin'g mixture.

At the lining-station, the metal mold is" provided If desired, the burned.

with a relatively smooth, hard, self-sustaining coating ad-' herent to the mold wall composed of a mixture of silica sand, or other granular refractory, and a thermosetting resin, the two ingredients being thoroughly mixed together in proportions of from 95.0 to 98.5% by weight of sand and from 1.5 to 5.0% by weight of resin. While various types of resin binders may be used, a two-stage phenol formaldehyde resin containing approximately of hexamethylenetetramine has been found quite satisfactory and is preferred because it melts and polymer-izes when heated to any temperature between 300 and 600 F., a range within which the temperature of the metal mold may be readily maintained during repeated casting cycles.

The term two-stage phenol formaldehyde resin refers to a resin which is produced by first reacting to a controlled degree phenol and a limited amount of formaldehyde, and then incorporating additional formaldehyde in the resin in the form of hexamethylenetetramine which decomposes on heating to formaldehyde and ammonia. The characteristics of such a resin are its dry powder form, insolubility in water, fusibility above 300 F., and capability after melting of polymerizing to an infusible phase with strong bonding properties. Among the commercially available resins of this type suitable for use in the method of the present invention are Thor 278, manufactured by the Borden Chemical Company, and R-136, manufactured by the Barret Company. This particular type of resin has the further advantage that it undergoes a distinctive color change as it polymerizes which provides a visual indication of when the lining has set. A phenol furfural resin containing hexamethylenetetramine has also been used, but is not as satisfactory as the phenol formaldehyde type in that it does not exhibit the color change above mentioned.

The sand used for the lining should be a good quality, washed silica sand which has been thoroughly dried and then screened to eliminate all foreign matterand provide a sand of the grain size and distribution necessary to produce the desired smooth mold finish. Sand having an AFS grain fineness of from 40 to 150 is preferred for the making of cast iron pipe, a typical sand having an AFS grain fineness of 100 with 70% on screens. 70 through 200. When casting steel, coarser sand may be used in order to facilitate escape of the greater amount of gas which is generated with the higher casting temperatures of steel. It has also been found that, within the permissible range of grain sizes, the coarser the sand, the rougher the surface of the lining, but the more uniform its thickness. Relatively fine sand, on the other hand, provides a smoother lining, but is apt to result in a wavy surface with a consequent non-uniform thickness.

In preparing the lining mixture, carefully weighed quantities of the dry, screened sand and the bonding resin in dry powder form are charged into a suitable mixer or muller in the proportions above indicated, 97.0% sand and 3.0% resin being preferred, and throughly mixed together, after which the mixture is transferred to a storage bin from which measured quantities are dispensed as the molds are lined.

The metal molds used in producing pipe in accordance with the present invention are generally similar in construction to the mold flasks heretofore used in the Sand-' to be produced, the outer surface of the mold being provided with spinning bands or tires for rotating the mold on the motor driven rollers of the lining and casting machines. One end of the mold may be equipped with a hell shape for casting pipes complete with bells orflanges,

the other end being adapted to receive a stop-off plate or core to prevent the molten metal from running out during casting. The inside surface of the mold which forms the outside contour of the casting may have any shape which will allow the solidified casting to be withdrawn from one end of the mold, or a split mold may be used for producing other contours. The metal mold is preferably vented in order to permit the escape of the gases generated in the lining during casting, particularly when making steel pipe or relatively long pipe of other metals, although vents may not be essential if the mold is relatively short.

In forming the mold lining, the empty metal mold, still hot from the preceding casting or having been other- Wise heated to the desired temperature, and with either one or two annular lining stop-off plates attached to its ends, is placed on the rollers of a suitable spinning mechanism, similar to the conventional centrifugal casting machine, and is rotated at a relatively slow speed while a measured quantity of the loose, dry sand-resin mixture is introduced into the interior of the mold and distributed uniformly along the axis thereof. If desired, the inside surface of the metal mold may be blacked or coated,

with carbon with an acetylene flame prior to the lining operation. When this is done, there is less tendency for the sand of the lining to adhere to the mold Wall when the cast-ing is stripped from the mold, and whatever sand may remain in the mold after stripping can be readily brushed, blown or poured therefrom.

Although the sand resin mixture maybe delivered into the mold in various ways, as by spraying it with air through a nozzle which is passed through the mold or by means of an auger conveyor similar to that used for the cement lining of pipes, the preferred method is to place the required volume of mixture to produce a given thickness of lining in a trough of substantially the same length as the mold, evenly distributing the mixture over the full length of the trough, insert the trough in the slowly rotating mold, and then quickly invert the trough so as to allow the lining mixture to drop out on the lower portion of the inside surface of the mold wall. Immediately after dumping the mixture, the trough is quickly withdrawn from the mold so as to prevent it from absorbing heat which might adversely affect the next lining charge. It is important that, when the trough is inverted to deliver the lining mixture into the mold, the rotation of the mold be slow enough that the particles of the mitxure are not held to the mold wall by centrifugal force, but are allowed to roll along the bottom of the inner surface of said Wall. This slow rotation of the mold is continued until the grains of sand begin to adhere to the wall as the heat therefrom affects the thermosetting resin binder, i.e., for a period of from 2 to 10 seconds after the trough is dumped.

A-fter continuous adherence is established, rotation of the mold is quickly accelerated to a relatively high speed sufficient to hold the remaining loose granules of the mix ture firmly to the mold wall by centrifugal force and thereby distribute and tightly pack the mixture uniformly over the inner surface of the mold. The high speed rotation is continued until substantially all of the resin has polymerized and bonded the sand particles together to form a relatively smooth, hard refractory lining adherent to the mold wall, which result is attained in from 15 to 30 seconds of high speed rotation, depending upon the thickness of the lining and the flask temperature. When the preferred phenol formaldehyde resin is used, ouring or setting of the lining is clearly indicated. by its change in color from near-white to lemon-yellow or light tan. Should the lining be darker than the desired color, it would indicate that the temperature of the metal mold is above the proper range and that some of the resin in the lining is apt to char and thereby weaken the lining if the mold is permited to stand for any substantial length of time before being used for casting...

It: has been discovered by experimentation that the proper spinning speeds of the mold during the lining operation are best determined by the centrifugal force created at the inner surface of the mold wall and by expressing said force in terms of g, the force of gravity, in accordance with the formula where N is the speed of rotation of the mold in revolutions per minute and D is the inside diameter of the metal mold in inches. In order to obtain the desired results, the initial spinning speed to be maintained While the lining mixture is being poured into the mold, and until the particles thereof begin to adhere to the mold wall, should be such as to create a centrifugal force not greater than 0.5 g, and preferably on the order of .1 g. After the particles begin to adhere to the surface of the mold wall, the speed of rotation should be accelerated so as to produce a force not less than 5.0 g, and preferably 8.0 g. or higher. For example, with a metal mold having an inside diameter of 7", the lining mixture should be introduced while the mold is spinning at about r.p.m., giving a value of 0.12 g according to the above formula, and after partial adherence is established, the spinning speed should be accelerated to about 300 r.p.'m., which is equivalent to 9.0 g. While the required spinning speeds will vary with molds of different diameters, the g factors are maintained substantially constant for all size molds.

The advantages of forming the mold lining while thus controlling the speed-of rotation of the mold are several. For example, if the lining mixture is introduced while the mold is rotating more rapidly than permitted by the above limitations, the lining will tend to be rippled and uneven, while if the rotation is too slow in the second stage when the resin is setting, the coating will lack density and be relatively soft. By proceeding in accordance with the method described, a smooth, hard, dense coating of any desired'thickness, within the limits hereinafter stated, can be produced.

Another advantage of this lining method is that it permits the use of a vented metal mold in spite of the fact that the lining is centrifugally formed. If a vented mold is-spun too rapidly when the lining mixture is first in- -tr'oduced, the particles thereof will tend to be forced out through the vent holes, resulting in an uneven and nonuniform lining, with a very thin or nonexistent coating over each vent hole. By employing the two speed rotational procedure, small quantities of the lining mixture are permitted to enter andharden in the innermost portions of the vent holes during the initial low speed rotation and thereby effectively seal them against expulsion of sand or resin at the subsequently higher spinning speed. The lining so produced is, however, quite permeable to gas, particularly as the resin burns out during the casting operation, so that the vent holes adequately serve their intended purpose. For example, it-has been found that vents having Ma" diameter openings into the interior of the metal mold, spaced from 3" to 8 apart, can be eifectively closed and sealed with a permeable refractory coating by the present method.

-While the thickness of the mold lining may be varied somewhat to produce pipes of different diameters in the same metal mold, it has been found preferable in practice tocarefully control the lining thickness for best repetitive production. The factors governing the thick ness of themold lining have already been indicated in functional terms in the general description of the invention'. Although diameter, metal casting temperature, and other considerations may affect the required lining thicknessto some extent, the principal factor determining the optimum value of saidth ickness is the thickness of the metal casting-to be produced. For example, it has been determined experimentally thatfor castings having a wall thickness from A" to /2 a'- mold lining thiclene'ssof from 0.07 to 0.11" meets the requirements most effectively. For thicker castings, thicker linings are desirable.-

ness of the casting. Typical values obtained from this formula are as follows:

Casting Lining Thickness Thickness Inches Inches 0. 0. 055 O. 25 O, 075; 0. 50 0. 106 1. 00 O. 2. 00 0. 212

After the mold has been lined" in the manner above described and the lining stop-off plates have been re moved, the lining is preferably provided with a wet fac-- ing which closes the spaces between the sand grains and" gives a smoother finish to the casting. When the metal to be cast is cast iron, the facing or blacking consists of a water suspension of ground coke andclay; when'-cas'ting steel, a slurry of silica flour and bentonite is pre ferred. Although the facing may be applied in any suitable manner, as by pouring, spraying or brushing it onto" the inner surface of the mold lining, the preferred procedure involves pouring the facing into the mold througha funnel while the mold is rotated at a relatively slow speed, withdrawing the funnel and then passing a brush through themold while the latter is rotated at a su'bstaii tially higher speed so as to uniformly distributethe fac'-' ing over the lining surface. The facing operation may conveniently be performed at the lining station using the same mold spinning mechanism as that employed for the lining step. The facing'dries relatively quickly'a'fter it has been applied, due to the heat'of'the 'mold wall, andburns out when the molten metal-is poured during'the subsequent casting step.

' prevent chilling of the end of the casting. The m-old'is now ready to repeat the cycle beginning'with the casting step previously described, and may therefore be transferred directly to the casting station. On the other hand, since the facedlining has no afiinity forwater, the lined mold of the present invention can be prepared far in advance of casting and kept for an indefinite period of time before use, if so desired. v

As previously mentioned, the'metal molds employed in practicing the new method embody certain features of novelty in comparison with those previously known. One form of moldembo dying the improvements of the invention has therefore been shown in Figs. 1-6 of theaccompanying drawings, which figures also illustrate the mold lining operation and the characteristics of the mold as it exists when ready for the casting step.

Referring first to Fig. -1, which shows the metal mold" before the resin bonded sand'lining has-been formed, it will be seen that the mold is made up of three main parts, an elongated b'ody or center section 61- ofsub stantially cylindrical "form (the greater portion of'wh ich ha'sibeen'-=broken away'in F-ig; 1), a belhend'sectfon fii 9 which is threaded onto and body 61, and a spigot end section 63 similarly threaded and welded to the opposite end of the body.

The body section 61, which is preferably formed of 64, an enlarged guide flange 66 which cooperates with a' guide rail in known manner to properly position the mold in an axial direction with respect to the rollers of the rotating mechanisms at the lining and casting stations. If desired, one of the spinning bands may be grooved to receive the rollers of the rotating mechanisms and so located as to cooperate with the guide rail, in which event the guide flange 66 may beomitted.

The bell end section 62 of the mold, which is preferably made of cast steel, has an inner cylindrical portion 67 which forms a prolongation of the body section 611 and an outer hopper portion 68 of outwardly flared, substantially frusto-conical form adapted to house a removable insert 69 for shaping the outer surface of the bell or flange end of the pipe to be cast in the mold. The insert 69 of the present invention is of relatively permanent character, being made of metal, either cast iron or steel, and is detachably held in place within the hopper 68 by novel means which insure accurate centering of the insert with respect to the rest of the mold andtight engagement between the inner end thereof and the abutting end of the inner cylindrical portion 67 of the bell end section 62.

As shown best in Fig. 5, the outer peripheral surface of the metal insert 69 conforms to the inner surface of the hopper portion 68 of the metal mold and has formed therein a plurality of radially extending recesses 70 equally spaced circumferentially of the insert, the outer portions of which recesses are cylindrical while the inner or bottom portions thereof are substantially conical, as indicated at 71. Each of recesses 70 is adapted to receive the similarly conical inner end 72 of a radially extending cap screw 73 which is threaded through the wall of the hopper 68. Inasmuch as the cylindrical and conical portions of each recess 70 are of greater diameter and depth, respectively, than the body and conical end of the cooperating screw 73, and the conical portion of the recess and the conical end of the screw are of the same angularity, it will be apparent that, as the screws are threaded inwardly and their conical ends 72 engage end of the insert and the abutting end of cylindrical portion 67 of bell end section 62, as indicated at 74.

The inner circumferential surface of insert 69 mayhave any desired shape, depending upon the form which it is desired to impart to the corresponding end of the cast pipe, but is such that, when the insert is in place, said surface forms a smooth continuation of the inner cylindrical surface of portion 67 of hell end section 62 which in turn constitutes a prolongation of mold body section 61. In practice, each insert 69 is interchangeable with a number of others having diiferent inside contours. Since the mold lining method previously described results in a smooth, dense refractory lining over the entire interior surface of the mold, including the welded to one end of the insert 69, the joint between the-inner end of the latter and the mold body is effectively covered by the lining and leaves no mark on the outside surface of the casting.

The outer end of hopper portion 68 of the mold is provided with a substantially cylindrical rim '75 wherein are formed a plurality of circumferentially spaced, radially extending holes '76 adapted to receive wedge-shaped keys 77 which are driven into said holes from the inside of the rim so that, when the mold is rotated, centrifugal force tends to force the keys even tighter into the holes. The keys 77 engage and hold in place against the outer end of insert 69 either the annular lining stop-off plate 37 shown in Fig. 1 when the latter is used during the lining operation, or the bell socket core 45 shown in Fig. 4 which is used during the casting step.

Although the present invention is particularly concerned with the use of interchangeable, permanent metallic inserts 69 and the obvious advantages resulting therefrom, it will be apparent that ordinary sand insert cores might be used instead, if desired, in which case the cap screws 73 could be eliminated and the sand cores held in place by the wedge keys 77.

' The spigot end section 63 of the metal mold is also preferably made of cast steel and consists of a substantially cylindrical prolongation of center section 61 having at its outer end a radially extending flange 78 forming a convenient means for detachable connection to the mold of the lining stop-01f plate 36 of Fig. 1 and the casting stop-off plate 46 shown in Fig. 4. In each case, the stop-off plate is provided with a plurality of axially extending stud bolts 79 adapted to pass through holes in the flange 78 and receive nuts 80 which secure the plate to said flange. While the inner surface of lining stop-01f plate 36 is smooth so as to form a square edge at the end of the mold lining, the corresponding surface of casting stop-off plate 46 is provided with an annular groove 81 which faces the spigot end of the pipe to be cast in the mold (indicated in broken lines in Fig. 4) and is filled with a quantity of resin bonded sand of the same composition as the mold lining which serves to prevent chill-' ing of the end of the casting. It is also preferable to face the bonded refractory filling of groove 81 with the same blacking as that applied to the mold lining.

Instead of dividing the metal mold into three sections as shown, it is obvious that the cylindrical portions 61, 63 and 67 may be made in one piece with a separately formed hopper portion 68 threaded and welded thereto, or, alternatively, that the entire mold may be machined from a single casting.

The apparatus for preparing and delivering into the rotating mold the sand-resin mixture for forming the mold lining includes a movable lining trough 29 which, as indicated in Figs. 1, 2 and 3, may be substantially U-shaped in cross section and provided with vertical division plates 30 and 31 defining the ends of the portion of thetrough into which a measured quantity of mixture may bedelivered from a hopper (not shown) which is so designed as to hold the desired amount of mixture necessary to produce a lining of given thickness. Any suitable means, such as a strike or a leveling vibrator, may be used for evenly distributing the sand-resin mixture throughout the length of the trough.

The trough 29 is so mounted that it can be moved quickly into and out of the mold 114 as the latter is rotated, on the rollers of the lining station, for which purpose the trough may be slidably supported in suitable fixed guides or mounted on a movable carriage running on rails (not shown). If desired, a trunnion 34 may be provided at the end of the lining machine opposite the carirage for receiving a cylindrical extension 35 on the end of the trough 29 (see Fig. 1) so as to ensure that the trough is properly supported and centered axially with respect to the mold. The mounting of the trough, whether it be in fixed guides or on a carriage, is such that,

. after the trough has been inserted in the spinning mold, it-

meet

11 ma be quickly inverted as indicated in Fig. 3 to the sand-resin mixture onto the bottom portion of the mold wall and then rotated back to its original position and rapidly'withdr'awn from the mold before the latter is accelerated for the high speed portion of the lining operation.

Iirpursuan'ce of the advantages resulting from the use of vented molds, an improved form of vent has been de vised which is particularly efiective with the mold lining procedure described above. As indicated in Figs; l-4; the metal mold is provided with a relatively large number of uniquely constructed vents, indi'cated generally at 82', constituting openings through the mold wall for escape of the gases formed during casting. The vents 82 are distributed moreor less uniformly over" the entirelength of the mold, with the exception of the hopper portion 68 and the spinning band portions 64 and 65. The number and'positioning of the vents should be such as to permit ready escape therethrough of substantially all of the gas generated during the casting operation, and will depend upon a number of factors such as the thickness of the lining, the percentage of resin binder therein; the grain size of the lining sand, the character and thickness or the facing on the lining, and the temperature of the metal being cast. As an example, it has been found that, in a mold for casting a 6 cast iron pipe 20 feet long, four axially extending rows of vents located 90 apart with a spacing of approximately 3.7" between adja'cent vents in the same row, the vents in adjacent rows bein'gstaggered, Will'be adequate under all normal con dition's'of lining thickness, amount of resin binder, etc.

As shown best in the enlarged view of Fig. 6, each vent 82 consists of a radially extending hole drilled through the'mold wall having an outer portion '83 of uni-' form diameter which extends inwardly from the outer surface of the mold almost to the inner surface thereof, and arelatively short inner portion 84 of substantially smaller diameter which opens into the interior of the' mold, the shoulder 85 connecting the outer and inner portions of the hole preferably being inclined as shown, rather thansquare. While the length of the outer portion 83 will-vary with the thickness of the mold'wall, it is desirable tolimit both the length and the diameter of the innenportion 84-to approximately /3", and to make the diameter'of the outer portion 83 approximately three times'th'at of the inner portion.

When a metal mold having vents of this character is lined according to the previously described method, the

inner portions 84 of the vent holes become filled with thesand-r'esin lini-ng mixture during the relatively short p'eriodof'slow rotation of the mold following dumping of thje'lining trough 29'. Since the relatively small amount of sand-resin mixture ineach of said inner vent'portions is'surroun'ded by the heated metal of the mold w'all, thus providing a relatively high ratio of heating surface to volu me-ofthemixture, theresin in each of these quantities melts and polymerizes very quickly and rapidly fuses the sand' grains together in a rigid, gas permeable mass,

and also 'cements'said mass to the surrounding wall of' the inner portion -84 of the vent hole, before rotation of the" mold is a'cceleratedto high speed and the lining indicated at 86 in Fig. 6-isformed. After thisprelim'in'arv closure of the'vent' holes, the-mold lining 861forms in uniform manner over the'entire interior" of the mold and provides an additional coating over the inner ends of the vents of the same thickness and density as the rest of the lining:

In some cases, particularly "when relatively fine sand or be packed witha quantityof -unbon'ded; relatively coarse gra l1 r'r efractory 87, such as sand o ffa' size that will not To this end; as shewn in Fig. 7, the" outerporti'on- 83 of each've'nt ma ingwbmar metar areicieqmprist g hollow; s bs'ta tiall-y cylindrical ni tal n1olrl having a "plurality of vent" 1'2 pass through a /8" niesli screen. In order to hold the packing in place, a cup-shaped metal core box vent 88-, having a plurality of perforations 89 inthe bottom there of, may be fixed in' the outer end of the vent hole, asby peenin'g'. The mold' lining is then formed in the same manner as above" described. With this arrangement, the gases generated in the lining during casting can freely escape through the porous refractory mass 87 and the perforations 89 of the core box vent 88 while the latter effectively prevents the refractory packing from being thrown out of the vent hole under centrifugal force. It will be understood that; in this modification, thepaek ing 87 and core boxvent 88 are relatively permanent parts of the mold, it being unnecessary to renew the'packing for each cast, but only at such times as it is desired to thoroughly clean the vents. e I

There is thus provided by the present invention anew and improved apparatus for centrifugally casting hollow metal articles of cast iron, steel or non-ferrous metals which is particularly well adapted tothe production of pipe, especially pipes having-belled or flanged ends. The apparatus lends itselfwellto rapid and efiicient production of castings with a minimum of equipment and manual labor, and produces high quality, clean castings toclos'e tolerances and of any reasonable shape and size.

While the castings made in accordance with the pres ent procedurehaveall'of the advantageous characteristics of those made in conventional sand molds, including an u'nchilled, close grain structure free from inclusions, the method of centrifugally lining metal molds with a rela tively resinbonded refractory coating avoids such disadvantages of the prior Sandspun procedure as the" necessity for manually ramming a relatively thick green s'an'd' lining around a patternwith the aid of expensive machinery, the use of a large amount of sand andsand handling equipment, and the need for expensive cutting mechanism or other. means for removing the sand lining from between the flask and'the casting before the lattejtl canbe stripped from thernold. The faster freezing of the 'cast me'tal'with the relatively thinner mold lining pro vided by thepresentinvention, as well as the fact that the relatively lighterweight of the molds enables quicker acceleration of their rotation during the casting step, IeL-" suit in an increased production rate in comparison with the sand mold process of the prior art. The procedure herein disclosed likewise embodies most of'the advantages of the old De Iiavaud method employing metal molds, but without such disadvantages thereof as the excessive wear andcracking of the molds due to contact with themolter'f metal, and the necessity for annealing the chilled c'ast ings producedby' said method." 7

The invention also provides an improvedforrn'of' refractory lined, vented met'almold for centrifugal which'is characterized by such novel features as a'rela' tivehfthin, smooth, hard, self-sustaining resin bonded refractory lining, interchangeable metal inserts for shap f ingirregular ends on pipes, and anovelfornrof vent; for permittingescape" of the gases 'whi'ch'are generated during the-castingoperat on: Each of 'these features con; tributestothemoreeconornical production of high grade" castings-which is the ultimate re'sult of' the invention.

Although one specific-embodiment of apparatus embodying thein'ventionha's -been described and illustrated in the accompanying drawings, itwill ibe ob vioustha't the invention is not limited to the particularapparatus shown? but that-various changes, which 'will now suggest them selvesto thoseskilled the art, maybe made the form, details of construction and arrangement of the parts without departing from the inventive concept. Reference is therefore to be had to the appended claims 'foradefinition of the limits of the invention.

What is fcl'aimed is i I p l-. Are'fr'actory lihed' mold for use in 'ce ntrifugallycast holes in the wall thereof and a relatively thin, hard, selfsustaining lining of uniform thickness consisting of a bonded mass of from 95.0 to 98.5% by weight of silica sand and from 1.5 to 5.0% by weight of a fusible phenolic resin, said lining being adherent to the mold wall but adapted to disintegrate as a result of burning of the resin under the heat of the cast metal and having a relatively smooth inner surface against which the metal is to be cast, the thickness of said lining being a minor fraction of the thickness of the casting to be produced but sufficient to prevent rapid freezing of the metal cast against said surface.

2. A refractory lined mold for use in centrifugally casting tubular metal articles comprising a hollow, substantially cylindrical metal mold having a plurality of vent holes in the wall thereof and a relatively thin, continuous resin bonded sand lining of uniform thickness adherent to the mold wall and covering the inner surface thereof, including the inner ends of said vent holes, said lining having a relatively smooth inner surface against which the metal is to be cast and a thickness substantially less than that of the mold wall but sufficient in relation to the thickness of the casting to be produced to prevent rapid freezing of the metal cast against said surface, the character and amount of the resin in said lining being such that substantially all of said resin burns under the heat of the cast metal and thereby destroys the bond between the sand granules of the lining, said vent holes being adapted to permit the escape therethrough of the gases generated in said lining during casting.

3. A refractory lined mold as defined in claim 2 wherein the inner end of each of said vent holes has a gas permeable filling of resin bonded sand.

4. A refractory lined mold for use in centrifugally casting tubular metal articles comprising a hollow, substantially cylindrical metal mold having a plurality of vent holes in the wall thereof, a relatively thin, smooth, continuous, resin bonded granular refractory lining adherent to the mold wall and covering the inner ends of said vent holes, the resin in said lining being of such a character as to burn under the heat of the cast metal and thereby destroy the bond between the refractory granules of the lining, the gases generated in said lining during casting escaping through said vent holes, each of said vent holes having a relatively short inner portion of a diameter not more than about /s" and an outer portion of substantially greater diameter than said inner portion, the inner portion having a gas permeable filling of resin bonded granular refractory.

5. A refractory lined mold for use in centirfugally casting tubular metal articles comprising a hollow, substantially cylindrical metal mold having a plurality of vent holes in the wall thereof, a relatively thin, smooth, continuous, resin bonded granular refractory lining adherent to the mold Wall and covering the inner ends of said vent holes, the resin in said lining being of such a character as to burn under the heat of the cast metal and thereby destroy the bond between the refractory granules of the lining, the gases generated in said lining during casting escaping through said vent holes, each of said vent holes having a relatively short inner portion of less diameter than its outer portion, the outer portion being packed with a relatively coarse, unbonded granular refractory, and means for preventing the escape of said packing through the outer ends of said vent holes.

6. A refractory lined mold for use in centrifugally casting tubular metal articles comprising a hollow, substantially cylindrical metal mold having a plurality of vent holes in the wall thereof, each of said vent holes having a relatively short inner portion of less diameter than its outer portion and having the outer portion packed with a relatively coarse granular refractory of such grain size as to prevent entry thereof into the inner portion, a perforated core box vent fixed in the outer end of each of said vent holes, and a relatively thin, smooth, continuous, resin bonded granular refractory lining adherent to the mold wall and closing the inner ends of said vent holes, the resin in said lining being of such a character as to burn under the heat of the cast metal and thereby destroy the bond between the refractory granules of the lining, the gases generated in said lining during casting escaping through said vent holes.

References Cited in the file of this patent UNITED STATES PATENTS 204,479 Burns June 4, 1878 263,448 Withey Aug. 29, 1882 359,483 Whitley Mar. 15, 1887 428,422 Skinner May 20, 1890 1,559,779 Rice Nov. 3, 1925 1,675,716 Losey July 3, 1928 2,399,606 Schuh et a1 Apr. 30, 1946 2,623,809 Myers Dec. 30, 1952 FOREIGN PATENTS 660,693 Great Britain Nov. 14, 1951 OTHER REFERENCES The Foundry, October 1950, pages 162, 164 and 168. FIAT Final Report 1168, 6 pages.

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