US3506060A - Method for continuous centrifugal casting of tubular metal articles - Google Patents

Description

R. s. L. ANDREWS METHOD FOR CONTINUOUS CENTRIFUGAL CASTING 0F April 14, 1970 TUBULAR METAL ARTICLES Original Filed May 6, 1966 12 Sheets-Sheet 1 Q IIHIIIIH] HI" IIiiHIIIIIHIIl III II I FWIIFTIZ. [Vi/ W1 11,1W, max iw Aprll 14, 1970 R, s, ANDREWS 3,506,060

METHOD .FOR CONTINUOUS CENTRIFUGAL CASTING OF TUBULAR METAL ARTICLES Original Filed May 6, 1966 12 Sheets-Sheet a gym J INVENTOR.

' I 4/6?! 34/1/[17149' 1 7d. YMMfl/Mx (0 A il 14, 1970 R. s. L. ANDREWS 3,506,060

METHOD ".FOR CONTINUOUS CENTRU'UGAL CASTING 0F TUBULAR METAL ARTICLES 12 Sheets-Sheet 5 Original Filed May 6. 1966 [ZZZ A ril 14, 1970 R s. L ANDREWS 0 3,506,060

METHOD ,FOR CONT INUOUE CENTRIFUGAL CASTING 0F TUBULAR METAL ARTICLES Original Filed May 1966 12 Sheets-Sheet 4- I. I" Y l\\\\\\\ III. II

. ---III i I x\\\ Q INVENTOR.

M Fifff' .671. i/VIAIW! \Q 1M we; 10m,

A nl 14, 1970 R. s. L. ANDREWS 3,506,050

METHOD FOR CONTINUOUS CENTRIFUGAL OASTZNG 0F TUBULAR METAL ARTICLES 12 Sheets-Sheet 5 Original Filed May 6, 1966 INVENTOR Idlfif 17/. it finflr f R. s. L. ANDREWS 3, METHOD .FOR CONTINUOUS CENTRIFUGAL CASTING 0F April 14, 1970 TUBULAR METAL ARTICLES 12 Sheets-Sheet 6 Original Filed May 6, 1966 A ril 14, 1970 as. L. ANDREWS 3, 06,

METHOD FOR CONTINUOUS CENTRIFUGAL CASTING OF TUBULAR METAL ARTICLES l2 Sheets- Sheet'7 Original Filed May 1966 \LQQ Q U 3,506,060 METHOD FOR CONTINUOUS CENTRIFUGAL GASTINGOF A ril 14, 1970 R. s. L ANDREWS TUBULAR METAL ARTICLES IZ-Sheet -Sheet 8 7 WM w JJ d X0 0 @Q? uifl fi ME W 1 0 i 5 mm JV aware.)

Original Filed May 6 1966 Army's/5m.

April 14, 1970 R. s. L. ANDREWS 3,506,060

METHOD FOR CONTINUOUS CENTRIFUGAL CASTING OF TUBULAR METAL ARTICLES 12 Sheets-Sheet 11 Original Filed May 1966 my m MMTZ 7 wmv W; H F by 2 V -w 4 Z a F0815??? J'. 1.. ANDREWS 0% 7M Jaw/1M.

AJTOE/VIYS.

A nl 14, 1970 R. s. L. ANDREWS 3, 6

METHOD FOR CONTINUOUS CENTRIFUGAL CASTING OF TUBULAR METAL ARTICLES Original Filed May 6. 1966 12 Sheets-Sheet 12 O ilf United States Patent Int. 'Cl. B22d 13/02 US. Cl. 164-118 4 Claims ABSTRACT OF THE DISCLOSURE A method for the centrifugal casting of tubular articles, such as pipe. The method comprises coating a rotatable mold, measuring out an amount of metal for the cast product, inoculating the metal, pouring the molten metal into the spinning mold, cooling the poured metal rapidly until some of the latent heat of fusion has been given up, then cooling the poured metal at a slower rate, and finally extracting the cast tube. Apparatus to automatically accomplish the method, consisting of a rotatable turret containing mold is disclosed. By indexing the turret, the mold may be brought to successive stations to carry out the various steps of the method.

This application is a division of my copending application Ser. No. 548,323, filed May 6, 1966 for Method and Apparatus for Continuous Centrifugal Casting of Tubular Meial Articles, now Patent No. 3,457,986, issued Aug. 5, 1969, the latter being a continuation-in-part of my prior copending application Ser. No. 313,389, filed Oct. 2, 1963.

The present invention relates generally to the centrifugal casting of tubular articles such as pipe, and more particular to method and apparatus for the automatic high speed casting of such articles.

In the manufacture of cast iron pipe, the use of centrifugally spun molds is a common e'rpedient. In recent years molds have been lined with a refractory lining prior to receiving a charge of molten metal. Thus the steps commonly followed in the manufacture of cast pipes include the lining of a mold, the pouring of metal into the mold, and the extraction of the solidified metal from the mold.

Various machines have been designed and put into use for reducing the amount of labor required to perform the casting process. In some machines molds are rotatably mounted around the periphery of a turret and the turret is indexed so as to bring the molds into alignment with a pouring station and an extracting station. In some machines cooling sprays are directed at the molds to reduce the temperature rise to which they are subjected by the molten metal. Still other machines have included means for semi-automatically carrying out the mold lining step of the casting operation.

Although several of the machines used for centrifugal casting of tubular articles automate certain steps in the casting process, none of them is fully automatic. Further, those machines which incorporate means for cooling either the mold or the cast metal within the mold have no means for preventing chilling of the cast metal as a result of the cooling, thus necessitating the annealing of the cast tubular article after it has been cooled.

It is therefore an object of this invention to provide a method and apparatus for performing all of the steps in the manufacture of centrifugally cast pipe continuously and automatically with a minimum of human intervention.

A related object of this invention is the provision of a method and apparatus for continuously and automatically coating a permanent mold with a refractory lining Patented Apr. 14, 1970 of predetermined thermal characteristics, pouring a predetermined amount of metal into the coated mold while spinning the mold then cooling the mold and the cast metal within it without chilling the metal and finally extracting the solidified and cooled metal pipe from the mold.

Another object of this invention is to prolong the useful life of the mold by maintaining it within a predetermined temperature range during each step of the casting cycle. A related object of the invention is to maintain a uniform temperature along the length of the mold during every step of the casting cycle.

Yet another object of the invention is to increase the speed at which poured metal may be cooled in the mold by cooling said metal at a high rate before the metal has solidified and by cooling the metal at a lower rate thereafter. A more specific and related object of the invention is to adjust the rate of cooling of the metal immediately after it has been poured, to a level which would chill the metal excessively if continued after the metal froze, and to automatically reduce the rate of cooling after the cast metal has given up some but not all of its latent heat of fusion to a level which will not cause excessive chilling of the metal.

It is yet another object of the invention to predetermine the temperature at which the molten metal shall freeze in the molds and give up its latent heat of fusion so as to permit more reliable sensing of this temperature for controlling the cooling of the metal. It is a related and more specific object of this invention automatically to regulate the composition of the metal which is poured into the mold so as to assure that the metal will freeze at a single well-defined temperature. Another important object of the invention is to speed up the production of iron castings by standardizing the carbon equivalent of the cast metal through late inoculation so as to improve nucleation of the metal and so as to predetermine the temperature at which the metal shall freeze. A related and more specific object of the invention is to standardize the carbon equivalent of the iron that is poured into the mold at a level at which the metal is eutectic thereby to impart to the metal a single freezing temperature.

A further object of the invention is to provide a selfcorrecting gripper for removing a finished casting from its mold automatically, the gripper having the ability to automatically re-establish its hold on the casting in the event that the gripper should loose its hold.

It is another object of the invention to provide an improved centrifugal casting apparatus which permits the use of highly conductive permanent metal molds which are mechanically lined with a uniform layer of good quality refractory material prior to casting, with the refractory material being removed and reused after each casting cycle.

A related object of the invention is to provide improved pipe casting apparatus whereby the bell portion of the pipe is cast with the body thereof, thus eliminating a heretofore necessary extra step.

These and other objects and advantages of the invention will become apparent from a further reading of the following detailed description taken in conjunction with the appended drawings wherein:

FIGURE 1 is a side elevation of a machine embodying the structural aspects of the present invention;

FIG. 2 is an elevation of the FIGURE 1 machine viewed from its right end;

FIG. 3 is an elevation of the FIGURE 1 machine viewed from its left end;

FIG. 4 is a section of the FIGURE 1 machine taken along the line 44 of FIG. 1;

1 FIG. 5 is a cross section of an exemplary mold Wall, liner and pipe cast in accordance with the invention;

FIG. 6 is an exemplary device for preparing the refractory lining in the mold, shown in fragmentary section;

FIG. 7 is apparatus for casting the bell on the end of the pipe, shown partially in section;

FIG. 8 is an enlarged section of the bell end of one of the molds;

FIG. 9 is a perspective view of the temperature control systems associated with the apparatus;

FIG. 10 is a partially cut away side view of the turret showing the mold cooling sprays within it and showing components of the metal pouring station including a metal inoculating unit;

FIG. 11 is a temperature chart showing the temperature of a mold during the entire casting cycle;

FIG. 12 is a temperature chart showing the drop with time of the metal temperature as it passes from the holding ladle through the weighing ladle into the pipe forming mold, then into the pipe cooling station, and finally to the pipe extracting station;

FIG. 13 is a block diagram of the electrical control system for regulating the flow of coolant into the mold cooling and metal cooling systems;

FIG. 14 is a circuit diagram of a portion of the control circuit shown in FIG. 13;

FIG. 15 is a section taken through a mold in the cooling station of the apparatus to show the manner in which coolant is passed through it in that station; and

FIGS. 16-161 show in sequence the operation of the inoculant dispensing unit.

While the invention is susceptible of various modifications and alternative constructions, a particular embodiment has been shown in the drawings and will be described below in appreciable detail. It should be understood, however, that there is no intention to limit the invention to the specific form disciosed, but rather the intention is to cover all modifications. alternative constructions and equivalents falling within the spirit and scope of the invention as expressed in the appended claims.

With more particular reference now to the drawings, a machine is illustrated therein which is constructed in accordance with the present invention and which is adapted in the embodiment shown to cast pipe centrifugaly through a series of integrated wholly automatic operations sequentially timed and performed on permanent molds rotatably disposed in a turret which is indexed through various operative stations.

1 The operations required to cast pipe, or articles of a similar nature contemplated by the invention, includes cleaning and lining the molds with a refractory material, pouring and evenly distributing the desired quantity of molten material within the molds, cooling the casting and removing the same. As indicated, the present invention contemplates the complete casting of such pipe from beginning to end by provision of the various operative machine elements spaced about the peripheral area of the mold turret as will now be detailed.

PREFACE -In order to facilitate an understanding of the method disclosed herein, there will first be described the structure of the machine used to implement the method. There will then be described that system of the apparatus which control the composition of the metal which is poured into castings and those systems which control the temperature of the mold and of the cast metal within the apparatus so as to explain most clearly those features of the invention which reside in these systems.

(A) STRUCTURAL ARRANGEMENT AND OPERA- TION OF A MACHINE INCORPORATING FEA- TURES OF THE INVENTION (1) In general An exemplary machine constructed in accordance with the present invention for the centrifugal Casting of pipe is illustrated in FIG. 1 at 15. The machine has four groups of molds mounted around the periphery of a rotatable turret. Also disposed around the turret on either end thereof are four operating stations located around the periphery of the turret so as to register with the mold groups at one time. During a casting cycle, each of the mold groups is successively "brought into registry with different ones of the stations by rotation of the turret.

At the first station, the molds are rapidly spun around their longitudinal axes, cleaned and then sprayed with a refractory lining. At the second station the molds receive a lined mandrel at one of their ends, are again rap= idly spun, and molten metal is then poured into the other end of the spinning, coated molds to form the casting. Next, the turret is indexed to position the molds with the molten metal in them at the third station where a high pressure jet of cooling fluid is forced through the inside of the castings to cool and solidify them. Finally, the turret is indexed to bring the mold group with the solidified castings in them to the fourth station where the castings are extracted from the molds by means of expandable tongs mounted on a retractable carriage.

During the first three steps of lining, pouring, and cooling, the molds are cooled by a cooling system located within the turret which directs a spray of coolant at the molds while they are in the coating, pouring and cooling stations. Through this expedient, the temperature rise to which the molds are subjected is limited, thus extending their useful life.

( 2) In detail (a) The turret.-The machine 15 comprises a cylindrical turret 17 mounted for rotation on a horizontal axis supported by a machine framework identified at 19. Reference will be had to FIGS. 2 and 3 for a more complete picture of this framework.

The turret is positioned within the framework and supported about its circumference for rotation by means of rollers 21, secured to the frame 19 by mounting blocks 22 and spaced about the periphery of the turret 17 to provide optimum rotational freedom therefor. As will be seen in FIG. 1, the rollers engage the periphery of the turret 17 in tracks defined by spaced ribs 23, to inhibit any tendency toward axial displacement of the turret. In order to rotate the turret, a power drive is provided in the form of an electric motor 25 having a toothed pinion 26 attached to the armature thereof. A ring gear 28 is fixed to the turret about its perimeter where it is engaged by the pinion 26 to complete the turret drive.

With reference now to FIGS. 4, 6 and 7, the turret 17 carries a plurality of cylindrical molds 32. The molds 32 extend on a horizontal axis through the turret, and in order to increase productivity of the machine, the molds are conveniently grouped within the turret about its periphery in multiples of two molds per group. The size of the group may be varied, however, without departing from the invention.

The molds are supported within the turret shell by means of front and rear cover plates 34, 35. The cover plates 34-35 are formed with holes 37 (see particularly FIG. 7) which receive roller bearings 38 for supporting the molds front and rear. The bearings 3-8 engage a raised collar portion 40, formed for the purpose, on the molds 32, thus permitting the molds to be spun within the rotating turret in the performance of the various operations required for the casting of pipe or like material.

(b) The lining stati0n.In any casting process where a permanent mold is to be employed, it is desirable in order to preserve the mold to control the cooling of the cast article, and to provide a smooth finish thereon to line the mold with a refractory material of a fine particulate material which presents a smooth surface of determinable heat conductivity to the molten material to be cast. In carrying out the present invention, the molds 32 are provided with a refractory lining 43 of controlled material consistency and thickness, automatically in response to the arrival of a group of unlined molds at a lining station.

The automatic refractory lining function of the machine is illustrated in FIG. 6, supplemented by FIGS. 1 and 3. Upon arriving in the lining station, the mold 32 is spun by motor MTRS through its spinner disk 42. A refractory lining is applied under pressure in particulate form to the inner wall of the mold 32. To this end, a spray nozzle arrangement, indicated generally as 45 in FIG. 6, is provided at the lining station." The nozzle assembly comprises a pair of concentric nozzles, one of which, nozzle 47, applies the refractory material, and the second nozzle 48, applies a resin binder.

The nozzle 47 is connected at one end to a hopper 50 which is filled with the refractory material to be applied. A slide 52 is provided with an aperture 53 therein to provide control over the flow of refractory material into the nozzle body. A converging air horn 55 is located in the rear of the nozzle, behind its throat, and is connected to a pressure source through hose 57. Thus, by applying air pressure through hose 57 the refractory material is drawn into the air flow stream and is ejected from the nozzle under pressure against a guide disc 59 which fits about the body of the nozzle 48 and deflects the refractory material outwardly in a conical path against the inner wall of the mold 32.

The present invention contemplates the individual application of refractory material and binder to permit easier handling of both. The nozzle 48, as previously indicated, projects a liquid resin binder into the conical path of the refractory material as it is sprayed on the wall of the mold 32. In this manner, a mixture of binder and refractory material hits the Wall under pressure to form a refractory lining of controlled thickness. Thus, binder material under pressure and in controlled proportion is forced into the nozzle 48 through a hose 63 and against a conical guide 65 formed on or otherwise secured to a control rod 67 mounted in the nozzle 48 and, in the present instance, passing through the rear wall thereof where a nut 68 is provided for convenient coarse adjustment of binder flow from the nozzle by positioning of the conical guide 65 with respect to the end thereof.

In order that a lining of uniform thickness may be provided over the entire length of the mold, the spray nozzle arrangement is preferably mounted on a carriage 70. Since two molds are provided in a group, a pair of spray nozzles are provided to operate in unison, and as seen in FIG. 1, a pair of carriages 70 are provided, and move on a track 72 having an axis parallel to the axis of the molds at the station and so positioned that the nozzles are concentric with the mold axes as indicated in FIG. 6. Thus, as the lining operation is signalled into activity by arrival of the bare molds, pressure is applied to the refractory lining material while at the same time liquid binder is forced into the path of the refractory material ejected from the nozzle and the carriages 70 begin to move at a controlled rate to the right as seen in FIG. 1 extending the nozzle end into the mold and, by moving at the desired rate, eifecting a uniform application of binder and refractory material against the mold interior. Actual movement of the carriage may be conveniently controlled hydraulically and such an arrangement will be described in more detail hereinafter.

The lining 43 is quickly cured by the heat of the mold which has completed a cycle previously and which is at a temperature of about 350 F. The molds are then ready for pouring.

(c) The pouring stati0n.Having prepared a pair of molds in a group by lining them, the turret is indexed, in this instance in a counterclockwise direction as indicated in FIG. 3, to bring the lined pair of molds to a pouring station where a predetermined quantity of molten material is applied to their interiors. As seen in FIGURE 1, the pouring station is indicated generally at and includes a storage cauldron 82 adapted to pour a quantity of molten material into a measuring and pouring bucket or ladle 84 mounted on a swing frame 85 to permit dumping of the contents of bucket 84 into a pouring horn 87 mounted adjacent the end of the mold 32. The pouring ladle 84 and the pouring horn 87 rest on the platform 88 of a measuring scale 89. Again, two molds are presented at the pouring station and while the description has been keyed to the pouring of one mold, it will be appreciated that simultaneous pouring of both molds is undertaken by identical equipment.

As above indicated, the molds 32 are mounted for ro tation within the turret and, in order to accomplish uniform centrifugal casting of the pipe for which the present machine is adapted, the molds in the pouring station are spun on their axes within the turret to effect uniform distribution of the molten material throughout the mold.

To this end, it will be noted in FIG. 8 that the ends of each mold are provided with a removable spin band 90 which comprises an enlarged flanged head which is screwed onto the end of the mold and secured by a locking bolt 92. The spin bands frictionally engage power drives at the various stations where such drives are provided for spinning the molds. Such a power drive is present at the pouring station and is indicated generally at in FIGURE 1. A main drive motor 97, preferably roviding variable speed control, is supported on a vertically movable platform 98 which is connected to elevating cylinders 100. The motor 97 is connected at either side through couplings 102 to shafts 103, which are supported in pillow blocks 104, and through the shafts 103 to drive wheels 105. The wheels 105 engage drive belts 107 mounted about smaller driven wheels 109 supported on the frame 10. In order to permit optimum control over acceleration and deceleration of the molds, the wheels 105 and belts 107 may be toothed to provide a nonslip driving connection. The wheels 109 are mounted for driving spinners 111 which are engageable with the spin bands 90 of the molds by elevating the platform 98 to provide the desired engagement. Once engaged, the molds are spun at a controlled speed, causing the molten material to be spread out and to be uniformly distributed within the mold to form a pipe of uniform thickness and density.

(d) The cooling stati0n.-Having poured the molds, the turret is again indexed counterclockwise to bring them to the cooling station where heat is extracted from the material in a manner to provide a pipe which does not contain heat stresses and which does not require further annealing after the casting has been completed.

It is in keeping with this aspect of the invention that cooling is controlled to avoid chilling the metal. To the end of providing an efficient controlled cooling system, a pressure spray arrangement is provided at 210, and comprises a pair of nozzles 212 aligned with the axes of the molds 32 at the cooling station. The nozzles are connected by conduit 214 to a source of coolant under pressure, which may be water.

Upon arrival of the molds at the coo ing station, a mold cross section has the appearance of the cross section indicated in FIG. 5 with an inner solidified object 41, such as pipe, against an intermediate layer of refractory material 43 bounded on the wall of the mold 32. The arrival of the molds triggers the application of a spray of coolant against the inner surface of the molded pipe 41. The pressure of the coolant is suflicientlyhigh so that a vapor blanket is not permitted to form between the wall of the hot molded object and the coolant spray, which would have an insulating effect which would interfere with optimum cooling. Instead vapor is forced toward the opposite end of the mold by the high pressure spray where a ventilator hood 116 is provided over the end of the mold opposite the spray nozzle 212. An exhaust fan (not shown) may be provided in the exhaust conduit 117 which carries the vapor formed in the molds away, thus permitting continuous contact of the fine spray of coolant material with the molded object.

A novel control system for regulating the application of coolant through the spray nozzles to the cast pipe in the molds so as to control the rate at which heat is carried away from the pipes by the coolant is described in sections Blb and 32b of the specification.

The refractory material permits a predetermined amount of heat flow between the molded pipe and the mold thereby causing an amount of heat to be dissipated in that direction, and the present invention also provides for controlled dissipation of heat through the permanent mold. A mold cooling system for providing continous and precise thermostatic control over the temperature of molds at the lining, pouring, andcooling stations is described in sections Bla and B2a of the application.

By way of a brief introduction, to acquaint the reader with the physical location of this cooling system in the casting machine, reference is here made to FIG. 4, a cross section of the turret which illustrates the mold cooling system of my invention. Controlled dissipation of heat through the molds 32 is achieved by means of a spray system 120 comprising a number of multi-nozzle spray heads 12211-1 positioned at each of the lining, pouring, and cooling stations. Each spray head 122 is provided with a series of nozzles 128 spaced along the length of the molds 32. Each set of nozzles is connected by conduit 124 to a central source of fluid pressure 125 through a valve 126.

Since it is the objective of the system 120 to provide a. predetermined uniform temperature gradient through the mold, sensory controls are provided to determine the heat dissipation from the mold and control coolant spray. To this end, infrared sensory devices 127a-f are provided :lose to the mold surface at positions along the length of the mold and at the various stations where spray nozzles 122 are provided. The sensors 127 are highly sensitive to temperature and each sensor is connected to the valve 126 for the particular set of nozzles associated with it to vary the flow from that set of nozzles to maintain the :emperature along each mold uniform so as to provide Jptimum cooling of the pipe within the molds.

Since heat transfer in the mold is primarily by coniuction of heat energy through the refractory lining and wall of the metal mold, a measure of control over the temperature gradient may be established by correctly proportioning the thickness of the metal mold wall and liner the pipe wall thickness to be cast. A typical proportions represented by the FIG. cross section.

Because of the close control that is exercised over heat iissipation, the molds may be suitably constructed of Jeryllium copper, and will possess a longevity of useful- 1ess heretofore unknown in an automatic operation.

(e) The pipe extracting and mold cleaning station. The cast pipe having solidified and cooled to a tempera- ;ure at which the pipe can be handled for removal from :he mold, the turret is again indexed and the cast pipe noved to an extractor station indicated generally at 130. [t is in keeping with the objectives of the present inven- 1011 that the pipe is automatically removed from the nolds thereby completing the casting of the pipe from Jeginning to end in a completely automatic fashion.

Referring to FIGS. 1 and 3, removal of the pipe is ac- :ornplished by engaging the interior of the pipe with an :xpansible gripping device indicated at 132. As shown, :he gripper device is hydraulically operated and comprises :xpansible grippers or tongs 134 extending from a hylraulic cylinder 136 which is mounted on a carriage 138. The carriage is driven on a track 140 in a direction tovard and away from the mold and in axial alignment :herewith. Upon arrival of a mold containing a cast pipe, 116 carriage 138 is signalled to operate and travels forvard toward the mold, inserting the grippers 134 into the interior of the mold where they are expanded by the automatic hydraulic cylinder to engage securely the inner wall of the cast pipe. Once engaged with the pipe, the carriage reverses and retreats on the track 140, thus drawing the pipe from the mold. It is an additional feature of the invention that in the event that the grippers 134 should disengage for any reason, the extractor will automatically return the grippers 134 to the interior of the pipe which is partially removed and continue the removal process by engaging the pipe and causing the carriage again to retreat. To accomplish this, a sensing device is provided on the carriage such as, for example, an infrared sensor 142 which is focused on the gripper 134 and is connected with the carriage control so that if the carriage begins to retract without the pipe, the sensor will o indicate to the control and the carriage and grippers will be returned to pick up the pipe and continue the removal thereof. The control circuit for accomplishing automatic operation of the grippers and their carriages in response to the heat sensors is further explained in section C of the specification.

Again, since two molds are presented at the extractor station at a time, two extracting devices are provided although one has been described for the purpose of ex planation.

Once the cast pipe has been removed from the molds, the molds are again ready to receive a refractory lining and repeat the process. Before this can happen, however, the refractory material presently in the finished mold must be removed and the mold cleaned in order that it may satisfactorily receive the new lining. It will be understood that the binder has been consumed by the heat of the molten material and pure refractory material remains, being held against the mold by the carbon bond of the burnt-out binder. It is an attribute of the present invention that the refractory material may be removed and reclaimed to be again used in the lining process. Thus, a very excellent and initially expensive material such as zircon or granulated carbon may be used, and reused, without undue expense.

In accomplishing the cleaning and reclamation of the used refractory material, a pair of powered, extensible rotary wire brushes are provided at the lining station, opposite the nozzle system 45. Thus, brushes are provided on shaft 152 which are aligned with the axes of the molds at the lining station. The brushes are mounted on carriages 155 which ride on a rail 157 to and from the mold. The brushes are rotated in any convenient manner such as by air motors provided on the carriage indicated generally at 159 and are traversed into the mold toward the end at which nozzles 45 are disposed.

Referring particularly to FIG. 6, a recovery trough 162 is provided at the end of the mold and the refractory material which is brushed from the interior of the mold and pushed ahead of the brush as the brush traverses the mold, is dumped into the trough 162 where it is returned by an appropriate conveyor system (not shown) to the hopper for reuse. Generally, one pass of the brushes 150 will be sufiicient and the brushes will retract upon completion of the traverse and will signal the nozzles 45 to begin applying a fresh refractory lining to the mold.

(f) The bell molding apparatus.It is still another feature of the present invention that in the casting of socket pipe or the like, the bell end socket of the pipe may be cast simultaneously with the casting of the pipe by means of refractory coated bell end cores rather than requiring that it be cast by means of refractory head cores produced on separate head core making machines and set in the pipe molds prior to each casting cycle.

Referring to FIGS. 1 and 7, an automatic bell forming arrangement is provided and indicated generally at 180. The bell forming apparatus comprises in the present instance, two groups of bell end cores 182, 184 mounted on an indexible turret plate 186 secured and positioned on a frame 188. The bell forming apparatus is so constructed as to permit one group of cores to be engaged 9 with the ends of the molds 32 at the casting station for casting purposes while at the same time the other group of cores is being prepared with a refractory lining in a liner cabinet 190.

Thus, referring particularly to FIG. 7, the cores 182 and 184 are extended respectively into the end of a mold 32 and the liner cabinet 190. In the former, the refractory coated core 182 closes the end of the mold 32 at the casting station and the molden material being spun into the mold passes into the bell forming end Where that end is cast automatically with the pipe.

At the same time, in the lining cabinet a plurality of heating burners 196, are directed against split metal molds 191 into which the bell end cores are inserted and refractory lining identical to that applied to the mold walls is applied thereto through an extruder 195. The heating burners 196, maintain a resin curing temperature at the bell end cores in order to bond the refractory lining thereto. Once the casting operation is completed, the used bell end cores with the refractory lining burned off are retracted and indexed, so that the prepared set of hell cores are now in position to be inserted into the ends of the new molds which have just arrived from the mold lining station of the turret. The prepared sets are then applied to the prepared molds for casting while the used set is being relined.

It will be appreciated that while a number of operations are involved in the casting of pipe as herein described, these operations are performed concurrently at the several stations, the time required for each operation being programmed to be approximately the same so as to permit the turret to be indexed at uniform intervals. By performing several operations concurrently, the speed and economy with which pipe can be cast is greatly increased.

(B) TEMPERATURE AND COMPOSITION CONTROL SYSTEM (l) The mold cooling system The cooling system for maintaining the temperatures of the molds 32 in the turret 17 within prescribed temperature limits is generally shown in FIG. 9. The turret 17 is shown in phantom outline form and within the turret, distributed around the periphery thereof are shown the eight molds 32. Two molds 32 are shown at each of the coating stations A and B, pouring stations C and D, cooling stations E and F, and extracting stations G and H. For sake of clarity, only three of the eight molds, one at coating station B, one at pouring station D, and one at cooling station F are shown in solid lines, the remaining five molds being shown in phantom outline form only.

Each of the six molds 32 located at the coating, pouring, and cooling stations is cooled by a plurality of multinozzle spray heads 122. Of the six sets of spray heads 122 which are used to cool the six molds 32, only three sets, associated with the molds shown in solid lines appear within FIG. 9. FIG. 13 shows a complete mold cooling system for the cooling stations E and F, and the mold cooling systems at the coating and pouring stations are similarly arranged.

The amount of cooling required to maintain the molds at the different stations at a given temperature varies considerably. As one example it will be realized that this rate will be much higher at the pouring station where the molds receive iron at about 2400 F. than at the coating station which receives molds only slightly in excess of the desired temperature. Accordingly, means are provided for individually cooling each mold in the coating, pouring, and cooling stations.

It will also be realized that the rate at which cooling tends to occur is not the same along the length of the turret. Accordingly, in order to avoid variations in the temperature of the molds along their length, means are also provided to effect cooling of the molds in separate zones with the rate of cooling of each zone being governed by the temperature of the mold in that zone. In keeping with this general feature of the invention, the turret 17 is divided into three zones and within each zone coolant is applied at a mold 32 through a multi-nozzle spray head 122 (FIGS. 9 and 13). Thus zones 1, 2, and 3 of the mold 32 appearing in the coating station B are cooled by spray heads 122b1, 122b2, and 122b3 respectively. Similarly, mold 32 appearing in the pouring station D is cooled by spray heads 122d1, 122d2, and 122d3.

To aiford individual control over the temperature of each mold, and for each of the molds individual control over each of its three zones, a separate sub-system is provided for controlling the flow of coolant through each individual spray head 122. Thus a set of three coating station mold temperature controls 20Gb are provided for controlling the flow of coolant through spray heads 122171, 122b2, and 122b3 (FIG. 9). A second set of controls 200d are provided for controlling the passage of coolant through spray heads associated with the pouring station D and a third set of controls 200 are provided for controlling the spray heads in the cooling station F. Since there is one temperature control 200 for each spray head 122, there are six temperature controls for each of the three stations (FIG. 13); there are in all eighteen temperature controls associated with the eighteen spray heads located in the coating, pouring, and cooling stations of the turret 17. However, since only half of the eighteen spray heads are shown in FIG. 9, similarly only half of the eighteen temperature controls 200 appear in FIG. 9.

Flow of coolant through each of the spray heads 122 is controlled by a solenoid operated valve 126 in response to the output of a temperature sensor 127. Taking as an example the system for cooling zone 1 of the mold 32 in cooling station F (FIG. 13), the surface temperature of the mold 32 in zone 1 is detected by temperature sensor 127 1 which generates a signal whose magnitude is a function of the temperature detected by the sensor 127 1. This signal is fed through line 20211 to the coating station upper mold zone 1 temperature control 200 1. The temperature control is set to generate a voltage whenever the temperature detected by the detector 127121 exceeds a predetermined level. This signal is fed from the temperature control through line 204f1 to the control valve 126f1 causing the valve to open and to admit coolant to the spray head 12211. This condition continues until the temperature of the upper mold in zone 1 drops below the preset level at which point the temperature control 200 1 ceases to send a signal to the valve 126]1 causing it to close and coolant to be cut off from the spray head 122]1.

Flow of coolant to the mold cooling spray heads 122f2 and 122f3 at the cooling station F is similarly regulated by valves 12672 and 126 3 under the control of sections 2 and 3 of the cooling station mold temperature controls 20072 and 200]3 in accordance with the temperatures of zones 2 and 3 of the mold 32 as detected by temperature sensors 127 2 and 127 3. Control over the cooling of each mold in the extracting stations A and B and in the pouring stations C and D is similarly accomplished in control systems such as those just described for the cooling stations E and F.

As a result of thermostatically controlled cooling of molds in each of the coating, pouring, and cooling stations, the exterior temperature of a mold as it is successively cycled through the different stations of the pipe casting apparatus is kept within well-defined limits thereby greatly prolonging the life of the molds.

The relatively slight changes to which a mold 32 is subjected through the four cycles of coating, pouring, cooling, and extracting is well shown in FIG. 11 which illustrates the temperature of a mold during its travel through the four stations, three of which are cooled by a cooling system set to turn on when the temperature of the mold surfaces exceeds 350 F.

The mold arrives in the coating station from the uncooled extracting station at a temperature which is slightly in excess of 350 F. As a result, the coating station spray heads are turned on and the mold exterior temperature is lowered throughout the cycle until the mold is indexed out of the coating station into the pouring station. As molten metal is poured into the mold, its temperature rises sharply, causing the pouring station rnold temperature controls to initiate cooling of the mold. Thus cooled, the exterior temperature of the mold reaches onlyabout 380 F. when the mold is indexed out of the pouring station into the cooling station. 7

Once in the cooling station, the exterior temperature of the mold drops under the combined action of the cooling station mold cooling sprays and the internal spray units 210. The action of the internal spray units 210 which will be described in detail hereinafter, is reflected in the re versal of the mold exterior temperature change at points B and C during the time that the mold is in the cooling station. W 7

The mold is indexed out of the cooling station at a tempcrature slightly below the nominal temperature of 350 into the extracting station. In order to prevent seizing of the mold around the pipe within it, molds are not cooled in the extracting station and as a result the mold exterior temperature rises in this station to a point slightly above the nominal temperature of 350 for which the mold temperature'controls 200 are set. W

(2) The internal cooling system In the use of a multi-station automatic pipe casting machine of the type described, it has been observed that the speed at which the machine isoperable can be greatly improved by ificreasing'the rate at which poured metal is cooled at the cooling stationrln this connection, it is particularly significant that since the mold groups around the periphery of the turret are indexed from station to station at the same time, indexing of the molds cannot occur until the slowest of the four operations 'has been completed. Of the four operations of coating, pouring, cooling, and extracting, quite often the cooling step will take the longest time. 7 i

Merely increasing'the capacity of the cooling apparatus at the cooling station is not sufiicient because uncontr olled high rate cooling will'result in' undesirable chilling of the cast metal at the cooling station, requiring subsequent annealing of the pipe.

After a'rnetal has been poured into a mold, it passes through distinct stages. Initially, the metal is liquid' and cools at a rate determined by the thickness of the mold into which it is poured and by the rate at which the mold and the metal within it are being cooled. the temperature of the poured liquid metal drops, the metal reaches 1 second, very important stage which may occur either at a single temperature or over a range of temperatures. During this second stage, the metal changes from liquid to solid and in the process liberates its latent heat of fusion. Following this stage, after the metal has given up all of its latent heat of fusion, the metal solidifies, assuming a grain structure which is largely determined by the rate of cooling after the metal has become solid.

Limiting the following part'of this explanation to iron forsake of citing a specific example, there exists for iron 1 rate of cooling which, when exceeded, causes hard, 'brit= tle white iron to form. The point at which the rate of cooling becomes critical occurs after the metal has given up its latent heat of fusion and'has begun to solidify. In ac- :ordance with an important feature of the invention, advantage is taken of the realization that the rate at Which :he metal is cooled while itis in the'liquid state and also While it liberates its latent heat of fusion is not critical and does not significantly' affect the quality of the cast netal. Accordingly, in further keeping with ,the invention, neans are provided for cooling the metal at a very high rate while the metal is liquid, including most of the .period during which the metal liberates its latent heat of fusion and then changing the rate of cooling just before the metal has liberated all of its latent heat and has begun to solidify at a slower rate which does not cause the metal temperature to drop at alrate at which the metal would begin to acquire the undesirable characteristics of White More specifically, means are provided for detecting the instant when the cast metal has dropped to the temperature at which it begins to liberate its latent heat of fusion, the time required for the metal to give up all of its latent heat of fusion is predetermined either through calculation or by experiment, and a timing device is set to cause a reduction inihe rate of cooling of the metal to occur just before the calculated time has elapsed;

The temperature at which the metal in question solidifies is obviously an important factor in successfully implementing the subject invention. It is therefore important to note that metals and in particular iron compositions do not always solidify at a single temperature. Speaking of iron in particular, the composition may be selected to make the iron solidify at a single, well-defined temperature. An iron having such composition is called eutectic. For sake of simplicity, and again limiting the discussion to iron, it will be assumed at first that the iron which is poured into the mold is eutectic.

Turning now to the metal cooling system and with reference to FIG. 9 at first for a brief general description, coolant is propelled through the poured metal in the mold 32 in station F by means of a spray head located opposite one end of the mold and generally designated by the numeral 210. Located near the other end of the mold 32 is a spectrally selective temperature sensor 220 for monitoring the temperature ofthe metal in the mold. To control the application of coolant through the spray head 210 in response to the sensor 220 and in particular to reduce the rate of cooling just before the cast metal in the mold has given up all of its latent heat of fusion and has begun to solidify, a cast metal cooling control unit 230 is provided.

The arrangement for propelling coolant through the here of the pipe 41 within the mold 32 is shown in FIG. 15. Located at one end of the mold 32 is the spray discharge 219 and an exhaust system for removing steam from within the pipe is shown at the other end thereof.

The spraying system 216 is designed to send intermittent spurts of atomized coolant such as Water through the bore of the pipe 41. Upon coming into contact with the hot inner wall of the pipe, the water spurts are turned into steam rings and are extracted from the pipe by the exhaust system..;These spurts of water enter the pipe to be cooled through an atomizer nozzle 21 2. Wateris fed to the nozzle 212 from a conduit 214 through a solenoid controlled valve 211. Connected between the valve 211 and the nozzle 212 is fan interrupter assembly 213. The function of this assembly is to break up the flow 'of Water through the valve 211 into short spurts of water followed by a quick puff of air. The interrupter assembly 213 includes a main orifice 215 connected between the valve 211 and the atomizer head 212. The orifice 215 opens up into a generally circular casing 215 which houses an interrupter wheel 217 made of a circular rnolded rubber compound. The wheel 217 has four pockets 218 around its periphery and as the 'wheel is causedto rotate under the pressure of water admittedzthrough the valve 211, each of the pockets 218 is charged with a small quantity of water which it discharges into themain orifice 215 towards the atomizer nozzle 212. Located between the nozzle 212 and the interrupter wheel 2 17 and receiving compressed air at a pressure somewhat lower than that of the water is a second orifice 219. Thus as each spurt of water is discharged by the interrupter wheel 217 towards the atomizer head 212, it is followed by a pufl? of air and 13 is caused to expand into a ring of atomized water as may be seen in FIG. 15.

Upon contacting the hot inner surface of the pipe 41, each atomized spurt of water turns into a ring of steam and is propelled towards the opposite end of the pipe and into the ventilator hood 116. To aid the rapid propagation of steam rings through the interior of the pipe 41, the ventilator hood 116 is connected through an exhaust conduit 117 to an exhaust fan or similar means (not shown) whereby an air current is set up through the bore of the pipe away from the atomizer head 212.

Turning now to the pipe temperature responsive control system for regulating the flow of water through the valve 211, the temperature of the pipe 41 is monitored by a spectrally selective temperature sensor 220 which is directed at the bell end of the pipe and which is shown situated in the ventilator hood 116. Spectrally selective temperature sensors of the type suitable for use as the sensor 220 are widely available commercially. One such instrument is the Spectray 65, made by Leeds Northrup Company, Philadelphia, Pa. The instrument has a sensing element that responds to minute changes in the wave length of the object at which it is directed. In terms of the color response to the human eye, the instrument ranges from light cherry red (1550 F.) through orange, yellow, green, blue, violet, to brilliant bluish white (2950 F.) for molten iron or steel.

For use in automatic control circuits, the instrument produces a signal which is a function of the temperature of the object at which the instrument is directed and this signal is then fed into electronic devices which convert it into a form suitable for actuating various control elements. As seen in FIG. 13, each mold in the cooling stations is individually cooled by a spraying system 210 and is individually monitored for temperature by a spectrally selective temperature sensor 220. In particular temperature sensor 220e and spray system 2104: are located at opposite ends of the mold in the cooling station E and temperature sensor 220 and spray system 2101 are situated at opposite ends of the mold in the cooling station F.

As stated previously, it is an important object of the invention to cool the cast metal in the molds within the cooling station at a high rate until the metal has released almost all of its latent heat of fusion and then to reduce the rate at which the cast metal in cooled so as to prevent it from being chilled. In carrying out this aspect of the invention, means, indicated on FIG. 9 as the cast metal cooling control 230, are provided for shutting off each control valve 211e and 211] associated with the spray systems 210e and 210f some time after the cast metal in its particular cooling station has begun to liberate its latent heat.

Considering first the cooling system associated with cooling station E (FIG. 11), the solenoid of the control valve 211:: is controlled by a control relay CR21e which is turned on so as to open the valve 211e when a pair of molds are indexed into the cooling stations. The remaining portion of the cast metal cooling control system, including a set point temperature controller 231e, a delay 2322 and a reset timer 233e are provided for turning off the control relay CR21e so as to shut the valve 211e some time after the cast metal in the cooling station has begun to release its latent heat.

The electrical output of the temperature sensor 220e is fed to the set point controller 231e through line 2212. As will be explained with reference to FIG. 14, the set point controller 2312 is set to close a relay when the temperature detected by the sensor 220e drops to the temperature at which the cast metal releases its latent heat of fusion. Through a delay 232e, used to prevent premature deenergization of the control relay CR21e the reset timer 233e is actuated and it in turn shuts off the control relay CR21e a predetermined time after the cast metal in cooling station E began to liberate its latent heat. This time is calculated to occur before the cast metal has released all of its latent heat so as to discontinue high rate cooling of the cast metal before the metal has begun to solidify.

To control the cooling of the cast metal in the cooling station F, a similar set of control elements, including a set point controller 231 a delay 232 a reset timer 233 and a control relay CR21 are connected between the temperature sensor 220 and the valve 211].

Reference will now be made to FIG. 14 which shows in detail one of the two metal cooling control systems 230 illustrated in block form in FIG. 13. The structure and operation of a cooling control system 230 will be described principally with reference to FIG. 14, with occasional references to FIG. 13 to indicate the operation of the mold cooling sprays. While the explanation of FIG. 14 is geared to the cooling of a single pipe by a single cooling system, it should be kept in mind that the same sequence of events is taking place, albeit independently, in both of the cast metal cooling control systems of the apparatus, as is apparent from FIG. 13.

With reference to FIG. 14, the set point controller 231, which is well known and is manufactured by the West Instrument Corporation of Chicago, 111., includes a meter pointer 234 and a settable pointer 235. The meter pointer 234 is actuated to travel along a scale 236 of the controller 231 by means of a galvanometer 237 under the influence of the voltage signal generated by the temperature sensor 220 connected to the galvanometer 237. Mounted on the settable pointer 235 are a pair of spaced coils 238 which form part of the tank circuit of an oscillator 239 in the set point controller 231. A metal vane 240 is mounted upon the meter pointer 234 and is so placed that when the meter pointer 234 has traveled up the scale to the point where the settable pointer 235 is positioned, the vane 240 is interposed between the coils 238, decoupling them and shutting off oscillation in the oscillator 239 as a result. The output of oscillator 239 is fed to an amplifier 241 whose output is in turn connected to a relay 242 carrying a set of normally closed contacts 242-1. Both the oscillator 239 and the amplifier 241 are energized from a pair of single phase supply lines X1 and X2.

So long as the pointers 234 and 235 are at different positions along the scale 236, the oscillator 239 is permitted to operate by virtue of the intercoupling of its coils 238 and, through the amplifier 241, it maintains the relay 242 energized and its contacts 242-1 open. When the meter pointer 234 is-brought into alignment with pointer 235 and interposes its vane 240 between the coils 238, the oscillator 239 is shut oh, the relay 242 drops out and closes its contacts 242-1. The settable pointer 235 and its coils 238 may be set anywhere along the scale 236 and thus the relay contacts 2421 may be caused to close at any desired temperature sensed by the sensor 220.

Coolant fiows into the pipe interior cooling system through a solenoid operated valve 211, and to appropriately energize the solenoid of the valve 211, a control relay CR21 is provided. Normally open contacts CR21'3 of the control relay 21 are connected in series with the solenoid of the control valve 211 across the power lines X1, X2, so as to open the valve when the relay is energized. This occurs when the turret 17 indexes a pair of molds from the pouring stations into the cooling stations and triggers a limit switch LS25 which is connected in series with the coil of the control relay CR21 across the power lines X1 and X2. The coil of the control relay CR21 is also connected across the lines X1 and X2 through a second set of contacts CR212 on the relay and through the initially closed contacts 233-1 of the reset timer 233. Through its contacts CR212, the relay CR21 locks in.

With relay CR21 locked in and its contacts CR213 closed, the control valve 211 is opened and cooling of the cast metal in the cooling station through the spray system 210 begins. The presence of the hot molds 32 in the cooling station is also detected by the mold temperature sensors 127 (FIG. 13) causing the valves 126 to open and the mold cooling spray heads 122 to receive and spray coolant on the molds 32. The meter pointer 234, which quickly swept up the scale 236 past the settable pointer 235 (to about 235'0 F.) when the sensor 220 initially detected the hot pipe (about 2350" F. for cast iron, see FIG. 12 at d) indexed into the cooling station, now begins to travel down the scale toward the point to which the settable pointer 235 was set.

To initiate the control sequence which will shut off the control valve 211 after release of latent heat by the cast metal, the settable pointer 235 is positioned at the temperature where release of latent heat is expected to occur for the metal being poured. For eutectic iron, this temperature has been determined to be 2150 F. and therefore in FIG. 14 the pointer 235 is shown as being set at 2150 F.

As the cooling cycle continues the meter pointer 234 indicates the rapidly falling temperature seen by sensor 220 looking at the hot cast metal as heat is rapidly removed by the coolant propelled through the pipe and converted into steam. This rapid extraction of heat energy from the interior surface of the cast metal pipe also reduces the flow of heat from its exterior surface in contact with the mold lining through the mold to its exterior surface. A point is reached where the exterior temperature of the mold drops below the 350 set point of the mold exterior temperature controllers 200, (FIG. 11, point a), causing the mold cooling spray 122 to be shut off. The interior metal cooling units 210 continue to pull the cast pipe temperature down rapidly at a rate which exceeds greatly the cooling rate which the metal can tolerate without chilling after it has solidified. In the temperature diagram of FIG. 12, whch is for cast iron, the metal is shown to be cooled at a rate of about 50 F. per second. This high rate temperature drop continues until the metal reaches 2150 F., the point at which the eutectic iron composition begins to release its latent heat.

Once the metal begins to release its latent heat, its temperature remains substantially unchanged until release of latent heat is completed (FIG. 12 at 1). Beginning of the release of latent heat by the metal is detected by virtue of the temperature plateau at which the metal remains during the release of latent heat. Thus the settable pointer 235 (FIG. 14) having been set to the temperature of latent heat release (2150 F), the vane 240 of the meter pointer 234 comes to rest between the oscillator coils 238 while the cast metal gives up its latent heat.

With the vane 240 thus interposed between the coils 238, the oscillator 239, through the amplifier 241 deenergizes the relay 242 and closes its normally closed contacts 242 1. Closing of contact 242-1 energizes a relay unit 232 causing its contacts 232-1 to close after a suitable delay, typically two seconds. The reason for using the delay 232 is to avoid a false indication of the onset of the release of latent heat when the meter pointer 234 initially sweeps up the dial and momentarily interrupts the coupling between the oscillator coils 238. When the cast metal is being cooled, the meter pointer 234 remains at the temperature of latent heat release for several seconds, and the delay 232 therefore closes its contacts 232-1 approximately two seconds after the onset of release of latent heat.

In keeping with the invention, cooling of the cast metal pipe by the interior cooling spray system 210 continues for a substantial portion of the period during which the metal releases its latent heat but with a provision being made to reduce the rate of cooling before the metal has released all of its latent heat of fusion so as to prevent the continuation of high rate cooling of the metal after the metal has begun to solidify. In keeping with this feature of the invention, means are provided for maintaining the flow of coolant to the internal spray unit 210 for a predetermined time after the cast metal pipe has begun to release its latent heat, this time being calculated to occur before the metal has liberated all of its latent heat. For this purpose, a reset timer 233 is energized from the supply lines X1 and X2 through the delay contacts 232-1. A pair of normally closed contacts 2331 of the timer 233 are connected in series with the lock-in contacts CR212 of the control relay CR21 so as to cause the relay CR21 to drop out when the timer 233 runs down and its contacts 233-1 open.

After the time required by the metal to release its latent heat under the cooling action of the internal cooling spray unit 210 has been determined either empirically or by calculation, the timer 233 is set to time out just before total release of latent heat is expected to occur. This time will, of course, take into account the initial delay introduced by the delay unit 232. Thus, shortly before the cast metal pipe has given up all of its latent heat of fusion, the reset timer 233 times out, its contacts 233-1 open, the relay CR21 drops out, its contacts CR213 open, the control valve 211 is closed and the metal cooling spray is shut off. Very shortly after this event, the flow of heat energy which is now from the cast metal into the mold 32 raises the mold temperature to 350 F. (FIG. 11, point b) causing the mold cooling spray units to be turned on by their temperature controls 200 as the mold temperature sensors 127 detect the rise of the molds above the 350 limit. The mold cooling sprays remain on for the balance of the pipe cooling cycle under the control of the temperature sensors 127 and mold temperature control units 200.

The rate at which heat is removed from the cast pipes within the molds in the cooling station under the action of the mold cooling sprays is governed by the maximum cooling which the cast metal can tolerate after it has solidified without chilling. For cast iron this rate is 15 F. per second. Consequently, the discharge rates of the mold cooling sprays 122 in the cooling stations E and F are set to remove heat at such a rate as to force cooling of the cast pipe at a controlled rate not greater than 15 F. per second (FIG. 12, zones FG).

To recapitulate, the cast metal pipe in a mold located in the cooling station is first cooled at a high rate by means of the pipe interior cooling system and is then cooled at a lower rate by the mold exterior cooling system associated with the cooling station. Thus'the mold cooling system and the pipe interior cooling system may indeed be considered as a single system for cooling the pipe, with the system cooling the metal at a high initial rate (while the pipe interior cooling system is turned on) and at a lower subsequent rate (when the pipe interior cooling system is turned off).

It will be apparent to those skilled in the art that the reduction in the rate of cooling may be achieved by a different control sequence than that described above. For example, where for some reason cooling of the mold per se is not desired, the pipe may be cooled exclusively by the pipe interior cooling system throughout the cooling cycle, and the reduction in the rate at which heat is extracted from the metal may be reduced by merely reducing the rate at which coolant is sprayed into the pipe by the pipe interior cooling system.

(3) The metal composition control system In the description of the metal cooling system in section B-2 above, it was assumed that the metal used for casting the pipe was eutectic so that the metal had a single welldefined temperature of solidification. Iron which is substantially silicon free is eutectic when it contains 4.3% carbon. If the iron contains less than 4.3% carbon, it is called hypoeutectic, while iron containing more than 4.3% carbon is called hypereutectic. The terms hypoeutectie and hypereutectic signify that portions of the iron composition will begin to freeze at a temperature that is higher than that at which eutectic iron would solidify. In hypoeutectic iron, carbon-free iron will begin to solidify over a range of temperatures higher than the eutectic freeze point, leaving behind liquid iron and carbon. This process

Images