US1944460A - Centrifugal casting device - Google Patents

Description

Jan. 23, 1934. R. b. PIKE' CENTRIFUGAL CASTING DEVICE 2 Sheets-Sheet 1 -Fled March 26. 1930 3'5" JNVENTOR.

B l l 71 Y ma ATTORNEYS.

Jan. 23, 1934. R. D. PIKE QENTRIFUGAL GASTINGr DEVICE 2 sheets-sheet 2 Filed Mrch 26. 1930 INVENTOR.

BY f Ma?- A TToRNEYs.

Patented Jan. 23,' 1935l UNITED STATES y 1,944,460 cEN'rnrFUcAL CASTING rmvrcr:r

Robert D. Pike, Piedmont,

Kali! Corporation, Emeryville,

ration of Delaware Calif., assignor to Calif., a corpo- Appiication March ze, 1930. semina. 439,059

3 claims.

My present invention relates to a method and apparatus for making bearing cylinders of an alloy of copper and lead by centrifugal casting.

The object of my invention is to provide an 5 apparatus for producing copper-lead castings whichare free from lead segregation, porosity and aws due to flow lines, and which possess an extremely fine microstructure and have ori their inside face after machining a lead content of from 23% to 26%.

It has hitherto been impossible to make such castings by methods of centrifugal casting be- `cause of lead segregation and porosity in the walls of the casting and because of drainageof lead away from the inside face leaving, after machining the usual machine cut for finishing, considerably less than' 20% lead on the inside face. Furthermore, it has been found to be impossible after many years of practice to cast pure alloys of copper-lead in sand, which are free from porosity and lead segregation. The cylinders made by my process make excellent bearing bushings for heavy duty high speed service and, as they possess properties not hitherto vattainable in castings of similar composition, arev a new article of great importance in the bearing ileld. In consequence of their very fine dissemination of the lead and entire freedom from occasional large masses of lead, they stand up 3 inches, theturbulence of the metal which occurs as the molten alloy takes its position in the wall under the influence of centrifugal force permits the lead to gather together in large masses which results also in the production of porosityfA and in worthless castings. This phenomenav is caused by the free molten lead which separates from the alloy during freezing while the latter is vstill pasty and therefore subject to turbulence under the intense'centrifugal force acting upon. it, the turbulence affording -opportunity for the separate minute particles of molten lead to gather 56 together into larger, masses. I have ,discovered under the most severe pounding at relatively high that if the alloy be owed into-its place in the wall of the casting substantially without` turbulence, the lead remains in situand a fine grained! perfect casting results. One of the principal features of my invention 60 is'the means which I exnployto flow the metal into the wall 'of the casting substantially without turbulence. Another feature of my invention is to counteract the tendency of the lead to flow outwardly radially under the influence of cenc5 trifugal force during the time interval while the casting is still plastic.` I have also discovered that for .each diameter of casting there is an' optimum revolving speed whichV may be described as the result of a compromise between the'need 7 0 for rapidly putting the metal into the wall and the need for minimizing drainage -of lead outwardly. I have also found that the optimum temperature of the centrifugal mold is from\250 to 400 C. These mold temperatures permit the 75l metal to fill out the mold fully and at the same time give a rapid chill t'o the casting which helps Aprevent segregation of lead. However, all conditions being correct,`I have found that it is not possible to prevent a certain amount-of lead 80 drainage and that if I start with a molten alloy containing 27.5% .lead, balance copper, the leadcontent of the inside face of the casting will range from 15% to 20%, which is lower than desirable for a bearing. I have found that I can 35 overcome this diiliculty by pouring a considerable excess of thev alloy and allowing the excess metal in the mold tov accumulate on the inside walls lof the cylinder. By properly choosing the excess metal in each I have found that when the bushing is machined'out to the finished inside diameter, the inside surface will have from 23% to 26% lead and the outside surface, after the normal machining out, will have from 25% to 28% lead. I remelt the excess boring's from the in- 95 side and cast with 'ai subsequent lot of metal.

For a better understanding of 4my invention,

reference should be had tothe accompanying drawings, wherein I have shown by way of illustration andnot ofvlimitation, a preferred em- 100l bodirnent thereof.

In the drawings- Fig. l isa vertical, sectional View of a rotor setup showinga casting in place,

Fig. 2 is a plan view in section taken along 105 line n n of Fig. 1,

Fig. 3 is a schematic diagram showing the radial disposition of the lead in the alloy Ywhen cast in accordance with my invention,

Fig. 4 is a side elevation partly i-.cross section llo of a modification of the bottom plate and vanes, and

Fig. 5 is a plan view thereof. For the purpose of illustrating my invention, I shall describe a method for making a bearing bushing which, "when finished, will have an outis illustrated in my prior application Serial Number 345,707, filed March 9, 1929. When this apparatus I propose to also fill the casting chamber with a hydrogenl and sulphur Afree producer gas, as therein disclosed, before proceeding with the casting.

For the purpose of centrifugally casting a bushing of the above character, I provide a rotor set-up, as illustrated in Fig. 1, in which 10 is a steel shell provided with an inside threaded portion at the top and bottom. The bottom vclosure of the rotor is effected by a threaded cap 11 having a tapered shank 12 through which there is a central longitudinal bore 13. An annular plate 14, preferably made of so-called high temperature alloy of ironnickel and chromium, rests on top of the cap 11 when the latter'has been screwed into place, and a sleeve 15, preferably made of cast iron, rests on the plate 14. The plate 14 is illustratedxas having aY graphite distributor 16, to be described hereinafter, inserted through its center, but this distributor 16 can, if desired, be made integral with the plate 14 and the entire plate and distributor can, if desired, be fashioned out of one piece of graphite or metal. Formed integral with the top of the plate 14, I provide radial vanes 17, of which eight are usually employed. These vanes 17 are preferably made a little higher at their inner than at their outer extremities, and a suitable height is approximately inch at the inside end and 1A inch at the outside end. It is to be understood that these dimensions may be varied over a considerable range at the option of the designer. The outside extremities of the vanes 17 are preferably made to terminate just short-of the nished diameterof the casting. A pouring pipe 18, preferably made of the same metal as the plate 14, is provided to deliver the molten alloy at a point dilrectly above the center of the distributor 16; and

19 designates a casting in place. The dotted lines 2Q in this casting outline the portion of the casting which will be retained after nishing. In other words, the material inside of the inner dotted line and that outside of the outer dotted line is surplus material.

On top of the cylinder 15 there is provided a cast iron washer 21 and the top closure is made by screwing a steel cap 22 into place within the shell 10. The distributor 16, made of graphite or heat resistant steel, is placed in the central hole in washer 14 and preferably held in place by a key (not shown). This distributor 16 is provided with a central conduit 23 and branch conduits 24. It will be apparent from this that a stream of gas flowing up from a pipe 25 will enter the conduit 23 and pass into the rotor assembly through the conduits 24- and then upwardly and out through an opening or clearance 4 26 in the top of the closure member 22.

An alternative type of bottom plate isi'llustrated at 30. In this type'there isprovided a central well 31, into which the metal 'first-drops.

In the center of this well is the projection 32 which'diverts the metal away from the center and away from the gas holes 24.

Surrounding the well 31 are a number of projections 33, usually eight, which form between them the passages 34. These passages may be disposed radially, or semi-radially, or may be curved like the passages in a centrifugal pump. Their length radially is determined by the inside diameter of the bushing.v

The criteria of the design of the bottom plates and vanes, however, worked out in detail, is to uniformly and rapidly project the metal onto the wall of th'e bushing by centrifugal force and with a minimum of turbulence.

In the example cited, wherein I make a casting to finish at 3.5 inches outside diameter and 2.75 inches inside diameter by 31/2 inches long, the inside diameter of the sleeve 15 is made 3.75 inches and its length 3.75 inches. Before the molten alloy is poured, the rotor assembly is preferably heated to 250 to 350 C. in a separate electric resistance furnace arranged for this purpose and the speed of rotation of the assembly is brought to approximately 2050 R. P. M. This will givea centrifugal effect of 2050 X2050X1.875=ab0l1t 7,880,000

Incidentally, this number 4has no absolute numerical significance, but is proportional to the centrifugal force in pounds. This centrifugal eifect is proportional to the centrifugal force in pounds, the formula being E=(R. P. Myx?,

such as E= (R. P. Myx? for determining the centrifugal effect which is proportional to the centrifugal force in pounds but independent of mass. The temperature of the copper-lead alloy is then brought to from '1204 to 1250 C., the alloy being melted preferably in a high frequency induction furnace.

In -making such a casting, I pour suicient of the copper-lead alloy to give a bearing bushing having an inside diameter of about 2 inches. By proceeding in this manner and by starting with an alloy consisting of copper and lead and containing 27.5% lead in the molten condition, I get radial distribution of lead in the rough casting as shown typically in Fig. 3, whereon the distances from the inner face of the casting toward the outside face thereof are represented as absciss and the percentages of lead at such distances are represented as ordinates. It will now be seen that if I bore this casting out to the finished bore of 2.75 inches, the inside face will contain 24.5% lead, which is a desirable content from the standpoint of excellent anti-friction properties. Furthermore, the lead content lines assumes a typical wave form and the maximum lead lcontent is toward, but not at the outside. I now take the turnings from the outside and the bearingsfromtlie inside, pass over amagand remelt and cast into ingots. The latter are analyzed and remelted'with addition of lead or copper to give substantially 27.5%, and recast with a fresh lot of the alloy. The average amount of lead in the casting can be somewhat increased by using a liquid casting alloy containing more lead but *I have found that a suitable content of the liquid alloy used for pouring is 27.5% to 30% lead. The mechanism of lead segregation is well illustrated by the curve of Fig. 3. This shows that the flow of lead outwardly has been arrested by the freezing of the alloy and by the packing together of the coppergrains under the action of centrifugal force.

In making a casting of the above character, I proceed as follows: The rotor set-up is brought, as previously suggested, to a temperature of 250-350 C. and then placed in the spinner. The latter is immediately started and the rotor timed at 2.050 R. P. M. The hydrogen and sulphur free gas is then introduced through the pipe 25 so as to ll the rotor set-up. In the meantime a measured amount of copper-lead alloy is drawn into a suitable crucible and is quickly poured through the pipe 18 into the revolving rotor setup and the latter is then kept rotating for about 30 seconds, when it is stopped, and the rotor setup removed from the spinning apparatus. Under these conditions the molten alloy pouring downwardly out of the pipe 18 impinges upon the distributor 16 and flows in between the varies 17.

These latter vanes are analogous to the vanes of a centrifugal pump and immediately impart to the molten metal the full rotational speed of the rotor set-up. The centrifugal force engendered thereby forces the metal outwardly in a radial direction at high speed and when the molten metal strikes the inner wall of the cylinder 15, it overflows it in a strictly longitudinal direction at high speed. The principal point to be here emphasized is that the' molten metal when it strikes the inner face of cylinder 15 has a rotational velocity almost as high as cylinder l5 and that, therefore, there is but little relative rotational motion between the cylinder 15 and the metal. This results in a speedy, almost instantaneous distribution of the molten metal in a perfect hollow cylinder inside of the cylinder l5 with practically no turbulence. On the other hand, if an attempt be made to cast with a smooth bottom plate, particularly when large masses of metal weighing over 15 pounds are cast, the molten metal will churn around with great turbulence over the bottom plate and as it takes its place in the wall this churning will continue until the friction between the metal and the inside face of the cylinder l5 gradually imparts the full rotational speed to the metal. Furthermore, the churning of the metal greatly lengthens the interval between the striking of the metal on the distributor 16 and its final placing in the casting. The result of these phenomena isthat 'a large casting made without the vanes 17 or 33 is worthless because of lead segregation and porosity whereas the same casting made with the vanes is perfect. The same type of imperfect casting results from pouring the alloy into a horizontally disposed centrifugal casting machine of any well known type and for the same reason. The bottom plate 14, with its vanes 17 or 33, acts virtually as a centrifugal pump which distributes the metal at extremely high velocity and with minimum turbulence into its place in the wall.

After the rotor has been removed from the spinner, about 20 minutes is required for a cooling of the casting. Then the rotor assembly ca'n be disassembled and the casting removed.

By an alloy of copper-lead, I refer principally to the one described above, but it will be obvious that the same principles of my invention will apply to alloys of copper and lead containing other metals in which a phenomena of lead segregation similar to that described occurs, and to otheralloys in which similar difficulties are encountered due to separation of a low fusing point constituent at the freezing ypoint of the alloy.

While I have, for the sake of clearness and in order to disclose my invention so that the same can be readily understood, described and illustrated specific devices and arrangements, I desire to have it understood that this invention is not limited to the specific means disclosed but may be embodied in other ways that will suggest themselves, in view of this broad disclosure, to persons skilled in the art. It is believed that this invention is broadly new and it is desired to claim it as such so that allsuch changes as come within the scope of the appended claims are to be considered as part of this invention.

This application is a continuation in part of my application Serial Number 408,263, filed November 19, 1929, for Bearing bushing, wherein I claim the bearing bushing made in the centrifugal casting device` claimed herein; while in Serial Number 587,464, filed January 19, 1932, for

Method of centrifugal casting, I claim the method involved in the manufacture of such bearing.-

Having thus described my invention, what I claim and desire to secure by Letters Patent isl. For centrifugal casting, a rotatable mold having a plate, upstanding radial-like projections on said plate forming radial-like passages between them and forming a central well, means for rotating said mold, plate and projections at the same speed, an upstanding projection on said plate within and centrally of said well, and means for flowing casting material onto said projection and into said well during such rotation.

2. For centrifugal casting, arnold having an upstanding wall and -a horizontal plate and being rotatable about a vertical axis, upstanding radial-like projections on said plate forming radial-like passages between them and forming a central well, an upstanding projection centrally of, said Well, and means for rotating all said parts at the same speed.

3. For centrifugal casting, a mold having an upstanding wall and a horizontal plate and being -5 ROBERT D. PIKE.

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