Method for centrifugal casting and articles so produced

Abstract

Tubular metal articles are produced by centrifugal casting in a rotary metal mold lined by centrifugally distributing a quantity of a dry finely particulate free flowing refractory material on the active mold surface with the quantity being in excess of that required for the lining, densifying the layer by rotating the mold at a rate such that the refractory layer is subjected to centrifugal force adequate to establish an equivalent specific gravity of at least 7.5, determined by multiplying the actual specific gravity of the refractory material by the number of gravities of centrifugal force, contouring the densified layer and removing the excess refractory material, rotating the mold at the casting rate and then introducing the molten metal for casting while continuing to rotate the mold at least that rate. articles so cast have relatively smooth outer surfaces which require only finish machining. The invention employs no additives and thus eliminates the need for venting the metal mold, provides a relatively thick lining of predetermined insulating capability so as to control the grain structure of the cast metal, eliminates the usual end cores, and allows the refractory material to be recycled. The invention is particularly useful for casting articles, such as cylinder liner blanks, from grey iron, such articles having an outer enlargement, typically a transverse outer end flange. cast according to the invention, such articles have Type A graphite throughout the entire inner surface and for at least a substantial portion of the thickness of the flange or other outer enlargement.

Description

RELATED APPLICATION

Apparatus disclosed herein is disclosed and claimed in my copending application Ser. No. 89,306, filed Oct. 30, 1979 and now U.S. Pat. No. 4,260,009. ( 0.254 mm.) . Finish machining was accomplished with markedly less tool wear and machining time than for the same part cast in a mold in which the refractory lining was formed on an aqueous slurry of silica sand or of a silica sand-resin composition. The graphite structure was predominantly AFA Type A throughout the entire wall thickness of the main body portion of the article and was AFA Type A at the inner surface and for more than one half of the radial thickness of the end flange enlargement.

The casting was withdrawn from the mold with the aid of a fork truck. A piece of cleaned corrugated metal was placed on the floor below the end of the mold from which the casting was withdrawn and the refractory material which did not fall free was wire-brushed off the casting by hand. The collected refractory material was poured from the corrugated metal sheet through a screen into a container and was reused successfully with fresh make up material to form the lining for another casting operation.

EXAMPLE 2

The procedure of Example 1 was repeated but with silica flour substituted for the zircon flour of Example 1. No carrier liquid or additives were used. The silica flour had a specific gravity of 2.6 and the following particle size distribution:

______________________________________
On 200 mesh (over 74 microns)
1.1%
On 270 mesh (53-74 microns)
2.0%
Through 325 mesh (smaller than 43 microns)
96.0%
______________________________________

The as-cast outer surface of the casting was found to be very rough and was judged to be so rough as to require excessive machining, with a further loss because it would be necessary to compensate for poor dimensional accuracy of the casting.

EXAMPLE 3

The procedure of Example 2 is repeated, except that the rate of rotation of the mold is increased from 800 r.p.m. (50 gravities) to 1180 r.p.m. (107.7 gravities) providing an equivalent specific gravity of 280. The as-cast outer surface of the casting has a smoothness approaching that attained with a conventional lining of silica sand with resin binder.

EXAMPLE 4

The procedure of Example 1 was repeated except that magnesium oxide, purchased commercially as dead-burned magnesite, was substituted for the zircon flour, again with no carrier liquid or additives being used. The magnesium oxide had a specific gravity of 3.58 and all particles were smaller than 74 microns. The casting was found to have an outer surface too rough for desired minimum finish machining.

EXAMPLE 5

The procedure of Example 4 is repeated except that the rate of rotation of the mold is increased from 800 r.p.m. (50 gravities) to 1015 r.p.m. (80 gravities), so that the equivalent specific gravity is 286. The casting has an as-cast outer surface which has a smoothness and dimensional accuracy approaching those obtained with a conventionally produced lining of silica sand with resin binder.

EXAMPLE 6

The procedure of Example 1 was repeated except that mullite flour (calcined kyanite) is substituted for zircon flour, again in the dry particulate form, without binders or any additives. The mullite flour had a specific gravity of 3.0 and the following particle size distribution:

______________________________________
On 200 mesh (larger than 74 microns)
1%
On 270 mesh (53-74 microns)
2%
Through 325 mesh (smaller than 43 microns)
96%
______________________________________

The casting obtained had a very rough as-cast outer surface and would require excessive finish machining.

EXAMPLE 7

The procedure of Example 6 is repeated except that the speed of mold rotation is increased from 800 r.p.m. (50 gravities) to 1100 r.p.m. (95 gravities), providing an effective specific gravity for the refractory lining of 282. The finished casting has an outer surface smoothness approaching that attained with a conventional silica sand and resin binder lining.

APPARATUS EMBODIMENT OF FIGS. 2-8

Apparatus for carrying out the method typically comprises a mold, indicated generally at 1, FIGS. 2 and 5; means 2, FIG. 5, for supporting and rotating the mold; means indicated generally at 3, FIG. 5, for supplying the refractory material to the mold, the supply means 3, FIG. 5, including a combined trough and contouring tool 4, FIGS. 2, 4 and 5, which also serves to recover excess refractory material at the time the refractory lining is established; and the combined casting puller and refractory recovery device indicated generally at 5, FIG. 6. Also employed, but not shown, is any suitable conventional means for supplying the molten casting metal to the mold, typically a pouring "boot" which can be brought into position at the end of the mold from which the castings are pulled.

The body of mold 1 is in the form of a thick walled tube 6 having two axially spaced outwardly opening transverse annular grooves 7 to accommodate the usual supporting and driving rollers 8, FIG. 5. Mold body 1 has a right cylindrical inner surface 9 which is the active surface of the mold. At one end, body 1 is recessed to receive a transverse annular end ring 10 which is secured by bolts 11 with its inner periphery 12 concentric with the longitudinal axis of the surface 9. End ring 10 has a tubular extension 13 embraced by surface 9. The inner surface of extension 13 is formed with transverse annular steps the forward edges 14 of which all lie in a conical plane which tapers outwardly of the mold and toward the longitudinal axis of surface 9 at an angle α which is less than the angle of repose of the particulate refractory material to be used for the mold lining. At its opposite end, mold body 1 is equipped with a second end ring 15 which has a stepped inner surface complementary to that of ring 10, the steps of ring 15 presenting transverse circular edges 16 all lying in a conical plane tapering outwardly of the mold and toward the longitudinal axis of surface 9 at the same angle as for ring 10. The outer surface of ring 15 includes an inwardly tapering frusto-conical portion 17 embraced by a matching surface portion 18 on the mold body 1. Body 1 has an axially extending tubular projection 19 having a plurality of radial bores each accommodating one of a plurality of drive keys 20 dimensioned to force end ring 15 into the seated position seen in FIG. 2. The circular inner periphery 21 of ring 15 is concentric with the longitudinal central axis of surface 9.

Four rollers 8 can be employed in spaced pairs to cradle the mold 1 and are secured to shafts 22, FIG. 5, supported by bearings 23 mounted on stationary frame 24, shafts 22 being driven by a DC electric motor 25 through a conventional V-belt drive 26.

Trough and contouring tool 4, which forms part of the refractory supply means 3, is of such size as to occupy a substantial part of the free space within the mold and must therefore be completely withdrawn preparatory to introduction of the molten casting metal. Accordingly, the combined trough and contouring tool 4 is carried by a car 27, FIG. 5, operating on rails 28 so arranged that the car can be moved to the right (as viewed in FIG. 5) for insertion of the device 4 axially into the mold, and then moved in the opposite direction to withdraw device 4 completely once the refractory lining has been established on active surface 9 of the mold and contoured to the desired form.

As best seen in FIG. 4, device 4 comprises an elongated trough 29 of generally U-shaped transverse cross-section. Rigid transverse partitions 30, 31 are secured within the trough and are spaced apart by a distance slightly less than the space between the inner ends of rings 10 and 15, FIG. 2. Commencing at the partitions 30 and 31, the trough is provided with tapered end portions 29 a and 29b respectively, the angle of taper and the transverse dimensions of the end portions being such that the tapered end portions will not interfere with refractory material overlying the end rings 10 and 15. Additional partitions 32, 33 are secured at the respective ends of the trough. Trunnions 34, 35 are provided at the respective ends of the trough, the inner portions of the trunnions passing through openings in the respective partitions 30, 31 and 32, 33 and being rigidly secured, as by welding, to the partitions. Trunnions 34 and 35 are coaxial and so positioned as to establish an axis of rotation for the trough which is off center, as later described. Trunnion 34 is considerably elongated, so as to be accommodated by two trunnion bearings 36 and 37, FIG. 5, and to project beyond bearing 37. A gear 38 is fixed to the projecting end of trunnion 34 and meshes with a drive pinion 39 fixed to the output shaft of a hydraulic motor 40 powered by a pump 41, the entire assembly being suitably mounted on car 27.

A tapered plain rotary bearing member 42, FIG. 4, is rigidly mounted on the end of trunnion 35 to cooperate with a corresponding stationary bearing member 43, FIG. 5, supported by a pedestal 44. Pedestal 44 has a base 45 slidably retained in a horizontal keyway 46 which extends at right angles to the longitudinal axis of the mold so that, by movement of the pedestal along the keyway, the stationary bearing member 43 can be moved between the active position seen in FIG. 5, in which bearing members 42 and 43 are coaxial, and an inactive position in which pedestal 44 is displaced laterally from the mold to allow free pulling of the casting and to allow the pouring boot (not shown) to be moved to its pouring position. A fluid pressure operated rectilinear power device 47 is provided to move the pedestal between the active and inactive positions.

Device 4 is completed by an elongated contouring blade 48 rigidly secured to and extending along one longitudinal edge 49 of the wall of trough 29. The main body 50 of blade 48 extends throughout the full space between partitions 30 and 31. In the case where the centrifugal casting operation is to produce a tubular blank made up of six cylinder liner blanks of the configuration seen in FIG. 1 joined flange-end-to-flange-end, the active edge of contouring blade 48 is formed with three identical projections 51 each having a profile, as best seen in FIG. 2, identical to that presented by two of the enlargements F joined end-to-end. The remainder of the active edge of the main body of blade 48 is a simple straight edge and is parallel to the axis of rotation defined by trunnions 34 and 35 and their respective bearings. Beyond partition 30, blade 48 continues as a straight edged blade portion 52 secured at one end to the adjacent end of body 50 and at the other end to trunnion 34. Beyond partition 31, blade 48 similarly continues as a straight edged blade portion 53.

As seen in FIG. 3, the transverse cross-section of trough 29 can be generally circular, with the mouth of the trough defined by a plane which is chordal relative to the circular cross-section. Main body 50 of the contouring blade can then be flat and extend in a plane which is essentially tangential to the circular cross-section with the point of tangency being substantially at one edge of the mouth of the trough. The body 50 can be secured to the trough in any suitable fashion, as by an external bridging strip 54 and screws 55. Considering that the trough is shown in its upright position in FIG. 3 with the circular cross-section concentric with the longitudinal central axis of mold surface 9, which is the axis of rotation of the mold, it will be noted that the common axis for trunnions 34, 35 is offset along a line slanting at 45° downwardly and to the left (as viewed) from the axis of rotation of the mold. The trough is thus eccentric with reference to the cylindrical active mold surface, but the extent of eccentricity is such that the outer edge of contouring blade 48 will clear surface 9 when the device 4 is rotated counterclockwise from the position seen in FIG. 3 to the position seen in FIG. 3A.

Since device 4 is eccentric with respect to mold surface 9 there is a given rotational position for device 4 in which the edge of contouring blade 48 is at its point of closest proximity to the mold surface, that position being illustrated in FIG. 3B. The proximity of the contouring blade will determine the thickness of the finished refractory lining and is thus dependent upon the outer diameter desired for the casting. In order that the position of the contouring blade relative to the mold can be predetermined accurately, the transverse horizontal position of car 27 is fixed, the bearings 36 and 37 are mounted on a keyway 56, FIG. 5, for transverse horizontal adjustment by screw 57, with the vertical position of bearings 36 and 37 being adjustable by shimming at 58, and conventional means (not shown) is provided for vernier adjustment of pedestal 44 along its keyway 46 to horizontally adjust the position of bearing member 43. Vertical adjustment of bearing member 43 is accomplished by shimming at 59. Because of wheel play and like variables, rails 28 do not locate car 27 in a precise transverse horizontal position. Accordingly, to achieve a precise horizontal base position for car 27, and thus for trunnion 34, the car is provided with two forwardly projecting locator bars 60, FIGS. 5 and 5A, each located at a different side of the car and each having an outer face which slants forwardly and toward the longitudinal center line of the car. The stationary frame of mold supporting and rotating unit 2 is provided with two locator beams 61 which project toward the location of car 27 on rails 28 and are spaced apart by a distance such that, as the car approaches unit 2, the outer face of each locator bar 60 on the car is engaged by the end of a different one of the two locator beams 61 and the car is therefore constrained to a position centered between beams 61. Unit 2 is so constructed and arranged that the axis of rotation of mold 1 is centered between beams 61. Each locator bar 60 is equipped with an outwardly projecting stop flange 62 disposed to engage the end of the corresponding locator beam 61 when forward motion of car 27 brings bearing member 42 into seated relation with respect to bearing member 43. Movement of car 27 can be accomplished by a rectilinear hydraulic power device in wellknown fashion.

The particulate refractory material is charged to trough 29, uniformly throughout the length of the trough, when car 27 is in a position, as in FIG. 5, such that trough 29 is entirely removed from mold 1. With trough 29 maintained in its upright position, car 27 is then moved to insert device 4 through mold 1, such movement being continued until bearing member 42 is seated in bearing member 43 and locator beams 61 are engaged by stop flanges 62. By operation of motor 40, device 4 is rotated counterclockwise until the position seen in FIG. 3A is reached, with the result that the total quantity of particulate refractory material in the trough is discharged into the mold. According to the method, that quantity of refractory material is substantially in excess, typically 150%, of that required to form the desired lining. Though the initial layer of particulate refractory material can be established with the mold rotating at any practical rate when the particulate material is discharged from the trough, best distribution and lowest cycle times are achieved if the mold is stationary or rotating at a rate providing a centrifugal force not more than 15 gravities at the time the trough is rotated to discharge the material. Using refractory materials, such as zircon flour, which have a relatively high specific gravity, the rate of mold rotation used to distribute the material centrifugally may be adequate to densify the layer of refractory material preparatory to contouring. When the total quantity of particulate material has been distributed in an even relatively thick layer as a result of rotation of the mold, and densification has been accomplished, device 4 is rotated clockwise until, as seen in FIG. 3B, the edge of blade 48 is at its point of nearest proximity to surface 9. With device 4 in that position, the outer edge of contouring blade 48 engages the layer of particulate refractory material on surface 9 at an angle such that the refractory material approaches the side of blade 48 which faces the open mouth of trough 29. Accordingly, the blade deflects all of the excess refractory material back into trough 29, where it is retained by the combination of the trough and the contouring blade, and the ultimate effect is that blade 48 planes the layer of refractory material to the precise thickness and profile (limited only by the angle of repose of the particulate refractory material) desired for the final lining. Thus, the main straight edge portion of blade 48 establishes right cylindrical surfaces on the layer, indicated at 62, FIG. 2A, while portions 51 of the blade established the surfaces 63, 63a and 63b to define the groove for casting of the end flange portions F of the cylinder liner blank seen in FIG. 1. In actual practice, device 4 is rotated clockwise from the position seen in FIG. 3A continuously at a slow rate, in comparison to the rate of rotation of the mold, to the position shown in FIG. 3, so that the contouring blade simply passes through the position seen in FIG. 3B. The excess refractory material returned to the trough 29 by the action of blade 48 simply remains in trough 29, when device 4 is withdrawn from the mold, and constitutes part of the refractory material to be used for the next casting.

When the initial charge of particulate refractory material is delivered to trough 29, the end portions 29a and 29b of the trough receive quantities of refractory material adequate to cover the stepped surfaces presented respectively by end rings 10 and 15. Because the exposed edges 14 and 16 of the steps of rings 10 and 15, respectively, constitute in effect a tapered surface at an angle less than the angle of repose of the refractory material, the material discharged by the end portions of the trough remains in position on the stepped surfaces of the end rings and this material is shaped to provide the smooth frusto-conical surface portions 64 and 65 of the finished lining, as seen in FIG. 2. The excess refractory material from these areas is returned to the respective end portions of the trough by portions 52 and 53 of the contouring blade as device 4 passes through the position seen in FIG. 3B during return of device 4 to its initial position.

It will be noted that provision of the stepped surfaces of end rings 10 and 15, and provision of end portions 52 and 53 of the contouring blade, eliminates the need for inserting the usual pre-formed sand cores to retain the molten casting metal. The refractory lining produced according to the invention is a completely monolithic lining from end ring to end ring, presents no seams or lining joints, is of precisely desired radial thickness, and has precisely the profile presented by the contouring blade.

With a mold dimensioned for the cylinder liner blank hereinbefore described with reference to FIG. 1, the rate of rotation of the mold can be increased to 500 r.p.m. for hardening the refractory lining and then further increased to, e.g., 900 r.p.m. preparatory to introduction of the molten casting metal.

Device 4 having been removed, motor 47 is now operated to move pedestal 44 and bearing 43 away from the end of the mold, and the pouring boot (not shown) is swung into place and the molten casting metal poured through end ring 15 in conventional fashion. The pour is accomplished conventionally, with the mold being rotated at a casting rate, e.g., 800-900 r.p.m., to distribute the molten metal centrifugally. At this stage, lining surfaces 64 and 65, FIG. 2, serve as end dams to prevent escape of the metal from the mold. The casting is cooled conventionally. For cooling, a water spray can be directed against the outer surface of mold by the usual spray means (not shown).

The pouring boot is removed and, with pedestal 44 remaining in its displaced position, unit 5, FIG. 6, is employed to withdraw the casting from the mold and to recover the refractory material of the lining. Unit 5 includes a conventional puller 70 mounted in fixed position with its fluid pressure operated motor 71 aligned coaxially with the mold so that, when the piston rod of the motor is fully projected, puller head 72 is located within one end of the casting, the position of the puller 70 thus being spaced from the mold by a distance somewhat less than the maximum excursion of head 72. Operation of the puller is conventional, and it will be understood that end ring 15 is removed prior to pulling of the casting from the mold.

A car 73 is located between puller 70 and unit 2 and is supported by rails 74 for movement parallel to the longitudinal axis of the mold supported by unit 2. Car 73 carries a refractory collecting unit 75 and two pairs of casting support rollers 76 and 77. Unit 75 comprises a housing 78 having flat end walls 79 and 80, the housing being rigidly mounted on car 73. End walls 79 and 80 are vertical, extend transversely of the central axis of the mold supported by unit 2, and are spaced apart in the direction of that axis. Nearer the mold, wall 79 has a circular opening 81 sized and positioned to slidably embrace the tubular end extension 19 of the mold body. Disposed nearer the puller, end wall 80 has a circular opening 82 which is coaxial with opening 81 and of a diameter significantly larger than the largest outer diameter to be pulled. End walls 79 and 80 are spaced apart by a distance smaller than the length of the casting. Support rollers 76, 77 are located on the side of housing 78 which is nearer puller 70. Rails 83 and 84 are mounted to extend transversely relative to the axis of the mold supported on unit 2 and include cantilevered end portions which project below the path travelled by the casting as it is pulled, rail 83 being between rollers 76 and 77 while rail 84 is between car 73 and puller 70. Rails 83 and 84 are spaced apart by a distance shorter than the length of the casting but longer than the total excursion of support roller pair 77 as car 73 is moved between its active position FIG. 6, and an inactive position (not shown), chosen to make room for the pouring boot and for bearing pedestal 44. When car 73 is in its active position, with wall 79 of housing 78 engaged with the mold, operation of the puller to extend its piston rod causes puller head 72 to pass through openings 80 and 79 and into the adjacent end of the mold for engagement with the casting. When the puller is operated to retract its piston rod, the casting is drawn first through opening 81, then through the interior of housing 78, then through opening 82, thence onto supporting rollers 76 and 77 and, when pulling ceases, onto rails 83, 84.

It is to be noted that, if six cylinder liner blanks such as that shown in FIG. 1 are made in a single casting, with the liner blanks joined flanged end to flanged end, the casting is in the nature of a single pipe-like piece which is of uniform outer diameter save for the three transverse annular enlargement formed by the three grooves in the refractory lining of the mold, the six liner blanks ultimately being separated by cutting the casting at the midpoint of each enlargement and at the midpoint of each body section.

Save for openings 81 and 82, housing 78 is air-tight. The housing projects well above the location of the mold. A rotary brush 85 is supported within housing 78, above the path of travel of castings pulled through the housing, by a shaft 86 journelled in bearings 87, 88 secured respectively to end walls 79 and 80. A drive motor 89 is mounted on the top wall of housing 78 and drives shaft 86 and brush 85, as by V-belt 90 and pulleys 91, 92. As seen in FIG. 7, brush 85 is of the centrifugal bristle type and comprises a hub 93, secured to shaft 86, and two side discs 94 between which a circumferentially spaced series of bristle support pins 95 extend, the support pins being secured to the side discs. Each pin 95 supports a plurality of bristles 96 formed of heavy, stiff but resilient wire, one end 97 of each bristle being bent circularly to loosely embrace its respective support pin. When shaft 86 is rotated, bristles 96 are caused to extend radially from the brush by centrifugal force. The location of shaft 86 and the effective diameter of brush 85 are such that, with motor 89 operated to rotate the brush as the casting is withdrawn, the bristles of the brush impinge upon the outer surface of the casting and dislodge any refractory material which has not already fallen from the casting. Puller head 72 is mounted on the piston rod of puller 70 by means of a rotary connector 97, FIG. 6, so that the puller head is free to rotate about the axis of the piston rod. Pulling of the casting is accomplished while the mold is still being rotated, through at a very slow rate, by support and drive rollers 8. Accordingly, the casting is rotating slowly about its longitudinal axis as it is pulled through housing 78 and past brush 85, and the bristles 96 of the brush thus strike all portions of the outer surface of the casting.

Since the particulate refractory lining material contains no binder material and is itself virtually unaffected at casting temperatures, all of the refractory material is dislodged from the casting by the pulling and brushing operation.

An exhaust duct 100 is connected to an opening in the bottom wall of housing 78 and extends horizontally lengthwise of car 73, being mounted rigidly on the bed of the car, as by brackets 101. A straight portion of duct 100 projects horizontally beyond car 73 and is telescopically engaged within a stationary horizontal duct 102 rigidly secured to the base of the puller unit. A tubular slip seal 103 is provided at the end of duct 102 to seal between stationary duct 102 and movable duct 100. Duct 102 leads to the intake of a centrifugal separator 104, FIG. 8. Air flowing from separator 104 is delivered to the intakes of a conventional bag filter 105, the fluid outlets of which are connected to the intake of a centrifugal blower 106. Solids separated by centrifugal separator 104 and bag filter 105 are combined and supplies to a screen sized to remove debris, such as metal fragments, and the clean recovered refractory material is delivered to storage for recycle.

The air intake for housing 78 is constrained to the interior of the mold and the small space between the wall of opening 82 and the casting. With blower 106 operating to provide a high volume flow rate, air flow through the mold into chamber 78 is adequate to pick up and convey to chamber 78 the greater proportion, e.g., 90% of all refractory material remaining in the mold after pulling of the casting. In this connection, it is to be noted that, as the casting is pulled, the transverse outer enlargements formed by lining grooves 63 tend to scrub the refractory material toward housing 78, and this action also tends to break up any agglomerates or clusters of particles returning the residual refractory material to its free flowing particulate state. Further, since blower 106 can draw air only from the mold and opening 82, the air inflow to housing 78 is generally along the surface of the casting being pulled, and the air flow into the housing therefore tends to scrub the outer surface of the casting.

EMBODIMENT APPARATUS OF FIG. 9

In the method and apparatus embodiments described above, the active surface of the mold is right cylindrical, and the outer enlargement for the casting is accommodated by the thickness of the refractory lining. In some cases, however, it is desirable to contour the active surface of the metal mold, particularly in the case of relatively large castings which should be cast one at a time. Thus, as seen in FIG. 9, the active surface 109 of the mold can be machined to provide a surface portion 109a of increased diameter in the area to be occupied by the outer enlargement of the casting, the smaller diameter right cylindrical main portion 109 and portion 109a being interconnected by a frusto-conical portion 109b. The layer of particulate refractory material to form the refractory lining is then established as described with reference to FIGS. 2-8, with the layer being shaped by a contouring tool so dimensioned and shaped that the portion 110a of the lining overlying mold surface portion 109a is markedly thinner than the main body of the lining. The lining portion 110b overlying mold surface portion 109b tapers in thickness uniformly from that of main body 110 to thin portion 110a. Main body portion 110 of the lining is right cylindrical. Higher heat transfer through the thin portion of the lining is thus preserved, even though the mold has been machined to partially accommodate the outer enlargement of the casting, and the metal in this area will not chill too rapidly or cool too slowly.

Claims

1. In the production of tubular metal articles by centrifugal casting in a hollow metal mold having an active mold surface which is of circular cross-section transverse to the axis of mold rotation, the improvement comprising

introducing into the mold a quantity consisting essentially of a dry finely particulate binderless free flowing milled refractory material, said refractory material being inert at the temperature of the molten metal to be cast and having a melting point significantly higher than the temperature of the molten metal to be cast, a specific gravity of at least 2.25, and a particle size such that at least 95% of the particles have a maximum dimension not exceeding 105 microns;

rotating the mold to distribute said quantity of refractory material centrifugally and thereby establish over the entire active surface of the mold a layer of said refractory material which is thicker than desired for casting;

densifying the layer of refractory particulate material by rotating the mold at a rate such that the particulate refractory material is subjected to centrifugal force adequate to establish an equivalent specific gravity, determined by multiplying the actual specific gravity of the refractory material by the number of gravities of centrifugal force, or at least 7.5; contouring the inner surface of said layer, to the form desired for the article to be cast, by positioning against the inner portion of the layer, while continuing to rotate the mold, a contouring tool having a working edge which extends longitudinally of the mold and which has a longitudinal profile identical with that desired for the article to be cast,

said quantity of refractory material, and the position of said contouring tool relative to the active mold surface, being such that, after contouring, the thinnest portion of said layer will have a thickness equal to at least 5 times the maximum dimension of the particles of the predominent predominant fraction of the particulate material and significantly greater than the maximum dimension of the largest particle in the particulate material ; ,the particles of the layer, after densifying and contouring the layer, being so packed together in the layer that the voids at the surface of the layer are too small to be entered by the molten metal;

rotating the mold at a casting rate such as to apply to the densified and contoured layer a centrifugal force of at least 10 gravities; and

introducing the molten metal for casting while continuing to rotate the mold at said casting rate, rotation of the mold being continued at said casting rate at least until the molten metal has covered the inner surface of the densified layer of refractory material.

2. The method as defined in claim 1, and further comprising

recovering the cast article and said refractory material from the mold;

classifying the recovered refractory material to remove any debris;

and using the recovered refractory material for casting another article.

3. The method according to claim 1, wherein

said refractory material is zircon flour.

4. The method according to claim 1, wherein

the particles of said refractory material are predominantly smaller than 43 microns.

5. The method according to claim 1, wherein

the metal to be cast is iron; and

said refractory material is zircon flour the particles of which are predominantly smaller than 43 microns.

6. The method according to claim 5, wherein

after contouring of the densified layer, the rate of rotation of the mold is increased until a centrifugal force of at least 10 gravities is applied to the contoured layer preparatory to casting, such increased centrifugal force causing the contoured lining to be hardened.

7. The method according to claim 1, wherein

the metal to be cast is iron;

said refractory material is magnesium oxide; and

said step of densifying the layer of refractory material is carried out by rotating the mold at a rate such that the refractory material is subjected to a centrifugal force of at least 24 gravities.

8. The method according to claim 1, wherein

the metal to be cast is iron;

said refractory material is silica flour the particles of which are predominantly smaller than 45 microns; and

said step of densifying the layer of refractory material is carried out by rotating the mold at a rate such that the refractory material is subjected to a centrifugal force of at least 33 gravities.

9. The method according to claim 1, wherein

said quantity of particulate refractory material introduced into the mold is in excess of that required to form the completed mold lining;

the method further comprising recovering the excess refractory material concurrently with said contouring step.

10. The improvement according to claim 1 wherein

the article to be cast includes a transverse annular enlargement;

The contouring tool employed to accomplish said contouring step including a portion providing in the densified layer of refractory particulate material a transverse annular groove conforming to said transverse annular enlargement, the shape and orientation of the contouring tool being such that the portion of said layer at the bottom of said groove has a thickness equal to at least five times the maximum particle dimension of the predominant fraction of the particulate refractory material, other portions of the densified layer having a thickness substantially greater than the thickness of the portion of the layer at the bottom of said groove;

the metal to be cast is iron; and

the cast article is characterized by having AFA Type A graphite distributed throughout its inner surface and throughout at least a substantial portion of the thickness of the transverse annular enlargement.

11. In the production of tubular metal articles by centrifugal casting, the improvement comprising

providing a rotary metal mold having an active mold surface which is of circular cross-section transverse to the axis of mold rotation and which is longer than the article to be cast, said mold being essentially free of vent apertures;

introducing into the mold a quantity consisting essentially of a dry finely particulate binderless free flowing milled refractory material which is inert at the temperature of the molten metal to be cast and which has a melting point significantly higher than the temperature of the molten metal to be cast, a specific gravity of at least 2.25, and a particle size such that at least 95% of the particles have a maximum dimension not exceeding 105 microns;

rotating the mold to distribute said quantity of refractory material centrifugally and thereby establish over the entire active mold surface, including the end portions thereof, a layer of said refractory material which is thicker than desired for casting;

densifying the layer of particulate refractory material by rotating the mold at a rate such that the particulate refractory material is subjected to centrifugal force adequate to establish an equivalent specific gravity, determined by multiplying the actual specific gravity of the refractory material by the number of gravities of centrifugal force, of at least 7.5; and

contouring the inner surface of the densified layer by positioning against the inner portion of the layer, while continuing to rotate the mold at least at the rate employed for densification, a contouring tool having a working edge extending longitudinally of the mold and which includes a main body portion having a longitudinal profile identical with that desired for the article to be cast, and

two end portions each of which slants axially outwardly relative to the respective end of the mold and generally toward the longitudinal axis of the mold at an angle less than the angle of repose of the particulate refractory; ; and, the particles of the layer, after densifying and contouring the layer, being so packed together in the layer that the voids at the surface of the layer are too small to be entered by the molten metal; and

introducing the molten metal for casting while continuing to rotate the mold, rotation of the mold being continued at said rate at least until the molten metal has covered the inner surface of the densified layer of the refractory material,

the densified layer of refractory material including two frusto-conical end portions, formed by the respective end portions of the contouring tool, which confine the molten metal to the contoured surface of the layer of refractory material.

12. The improvement defined in claim 11 and further comprising

recovering the excess refractory material concurrently with said contouring step.

13. The improvement defined in claim 11, wherein

said refractory material is zircon flour the particles of which are predominantly smaller than 43 microns.

14. In the production of tubular metal articles by centrifugal casting, the method for accomplishing casting without the use of end cores, comprising

providing a rotary metal mold having an elongated generally cylindrical active mold surface and, at each end thereof, a generally frusto-conical end ring which tapers axially outwardly and toward the longitudinal axis of the mold;

introducing into the mold a quantity consisting essentially of a dry finely particulate binderless free flowing milled refractory material which is inert at the temperature of the molten metal to be cast and which has a melting point significantly higher than the temperature of the molten metal to be cast,

a specific gravity of at least 2.25, and

a particle size such that at least 95% of the particles have a maximum dimension not exceeding 105 microns,

the angle at which the end rings taper being less than the angle of repose of the refractory material;

rotating the mold to distribute said quantity of refractory material centrifugally and thereby establish over the entire active surface of the mold and said end rings a layer of said refractory material which is thicker then desired for casting;

densifying the contoured layer of particulate refractory material by rotating the mold at a rate such that the particulate refractory material is subjected to centrifugal force adequate to establish an equivalent specific gravity, determined by multiplying the actual specific gravity of the refractory material by the number of gravities of centrifugal force, of at least 7.5 ; and , the particles of the layer, after densifying and contouring the layer, being so packed together in the layer that the voids at the surface of the layer are too small to be entered by the molten metal; and

contouring the inner surface of the densified layer by positioning against the inner surface of the layer, while continuing to rotate the mold, a contouring tool having a working edge which extends longitudinally of the mold and includes a main body portion having a longitudinal profile identical with that desired for the article to be cast, and

two end portions slanting in general conformity to said end rings; and

introducing the molten metal for casting while rotating the mold at a casting rate, rotation of the mold being continued at said casting rate at least until the molten metal has covered the inner surface of the densified layer of refractory material,

the portions of the densified layer which overlie said end rings serving to confine the molten metal within the mold.

15. The method defined in claim 14 wherein

said refractory material is zircon flour the particles of which are predominantly smaller than 43 microns.

16. The method for producing a tubular iron article having a cylindrical main body and an outer transverse annular enlargement by centrifugal casting with the finished article characterized by having AFA Type A graphite throughout its inner surface portion and for at least a substantial portion of the thickness of the transverse annular enlargement, comprising

providing a rotary metal mold having an active mold surface which is of circular cross-section transverse to the axis of mold rotation;

introducing into the mold a quantity consisting essentially of a dry finely particulate binderless free flowing milled refractory material which is inert at the temperature of the molten iron to be cast and which has a melting point significantly higher than that of the molten iron to be cast, a specific gravity of at least 2.25, and a particle size such that at least 95% of the particles have a maximum dimension not exceeding 105 microns;

rotating the mold to distribute said quantity of refractory material centrifugally and thereby establish over the entire active mold surface a layer of said refractory material which is thicker than the radial height of the outer transverse annular enlargement of the article to be cast;

densifying the layer of particulate refractory material by rotating the mold at a rate such that the particulate refractory material is subjected to centrifugal force adequate to establish an equivalent specific gravity, determined by multiplying the actual specific gravity of the refractory material by the number of gravities of centrifugal force, of at least 7.5;

contouring the inner surface of the densified layer to the profile desired for the article to be cast and thereby providing in said layer a transverse annular groove conforming to the shape of the transverse annular enlargement, said layer being substantially thinner at said groove than in the area which is to define the main body of the article to be cast ; , the particles of the layer, after densifying and contouring the layer, being so packed together in the layer that the voids at the surface of the layer are too small to be entered by the molten iron;

introducing the molten iron for casting while rotating the mold at a casting rate, rotation of the mold being continued at the casting rate at least until the molten iron has covered the inner surface of the densified layer of refractory material; and

allowing the iron to solidify by cooling while continuing to rotate the mold, excessive chilling of the iron which fills the groove in said lining being inherently prevented by heat transfer from the main body of the casting to compensate for the more rapid loss of heat through said thinner portion of said layer.

17. The method defined in claim 16, wherein

said refractory material is zircon flour the particles of which are predominantly smaller than 43 microns.

18. The method according to claim 1, wherein the particles of said refractory material are predominantly smaller than 74 microns. 19. An as-cast engine cylinder liner black cast from grey iron according to the method defined in claim 10, the outer surface of the as-cast blank formed by being cast directly against the mold lining being especially smooth and essentially free of embedded refractory particles;

all portions of the as-cast blank not cast against said groove being characterized by predominantly AFA Type A graphite at the inner surface and throughout the radial thickness of the as-cast blank;

that portion of the blank cast against said groove being characterized by predominantly AFA Type A graphite at the inner surface and throughout a major portion of the radial thickness of that portion. 20. An as-cast engine cylinder liner blank cast from grey iron according to the method defined in claim 16, the outer surface of the as-cast blank formed by being cast directly against the mold lining being especially smooth and essentially free of embedded refractory particles;

all portions of the as-cast blank not cast against said groove being characterized by predominantly AFA Type A graphite at the inner surface and throughout the radial thickness of the piece;

that portion of the blank cast against said groove being characterized by predominantly AFA Type A graphite at the inner surface and for more than one-half of the radial thickness of a transverse annular enlargement formed by being cast against said groove.

21. An as-cast tubular blank cast from grey iron according to the method defined in claim 1 to be converted into a completed article by a minimum amount of finish machining, the as-cast blank having a smooth outer surface formed by being cast directly against the mold lining and which is essentially free of embedded refractory particles;

the as-cast blank including a wall portion of uniform radial thickness and the cast iron of that wall portion being characterized by AFA Type A graphite not only at the inner surface but also throughout the radial thickness of the wall portion.