US2770857A - Mould for the centrifugal casting of pipes and other pieces - Google Patents

Description

Nov. 20, 1956 P. Bolssou MOULD F'OR THE CENTRIFUGAL CASTING O PIkES AND OTHER PIECES Filed April 20. 1953 Nov. 20,- 1956 P. Bolssou MOULD FOR THE; OENTRIFUOAL CASTING OF PIPEs AND OTHER PIECES 5 Sheets-Sheet 2 Filed April 20. 1953 ammwn Nov. 20, 1956 P. Bolssou 2,770,857

MOULD FOR THE OENTRIFUGAL CASTING OF PIPEs ANO OTHER PIECES Filed April 20, 1953 3 Sheets-Sheet 3 AYHW r/VLLY United States Patent @hice 2,770,857 Patented Nova 20, 1956 2,770,857 MOULD FOR THE CENTRIFUGAL CASTING F PIPES ANI) OTHER PIECES Pierre Boisson, Pamiers, France, assignor to Societe Metallurgique Ariegeoise et Lorraine, Pamiers, France,

a French body corporate Application April 20, 1953, Serial No. 349,605 Claims priority, application France April 21, 1952 7 Claims. (Cl. 22-65) The present invention relates to the centrifugal coating of metal tubular pieces from in particular steel.

In known processes, the molten metal is generally introduced in the form of a jet directly into Ia substantially horizontal mould which is rotative about its longitudinal axis and is open at at least one end. The metal is driven in rotation by the mould and, as it is then subject to centrifugal force, is thrown -against the walls of the mould and is caused to solidify upon contact with these walls.

Owing to its inertia, the rotative movement of the metal varies progressively; `at the commencement of rotation only the metal in immediate contact with the mould is driven in rotation, then this metal in its turn progressivelyl cases, at the start of the centrifugal casting, when the;

metal driven in rotation has not yet attained the upper generatrix of the mould and is, therefore, formed of a closed layer having a circular cross-section, the layer of vmetal falls towards the lower generatrices of Ithe mould and splashes or spatters the metal inside the mold. In any case, the jet form of casting always creates splashing. As a consequence of the foregoing phenomena, a certaink lack of homogeneity in the crystalline structure of the metal in the direction of the thickness of the piece is sometimes to be observed. This may be explained by lthe fact that the solidication of the outer layers had already commenced at the time when the inner l-ayers were not being `driven in rotation at the same speed as the mould. Globular crystals are to be found in the metal, which are larger than normal neighbouring crys-k tals. This, it would seem, is due to the fact that the crests of the crystals whichform during the solidication in a radial ldirection are broken otf by the relative sliding or slip of the interior layers, macroglobulites developing from these broken-off crusts. Furthermore, there are also present in the thickness of the cast piece cold globules which result from the above-mentioned splashing and are embedded in the metal.

In an attempt to remedy the foregoing disadvantages, yit has been proposed to subject the metal to a movement of rotation at a speed at least substantially equal to that of the mould before it is introduced into the mould. This is achieved by placing at the entrance to the mould a rotative distributor which `subjects the molten metal running towards the mould to the desired rotation. In the known devices for putting this method into effect the distributor discharges into the mould through a large central opening through which cold air entering throughy the pouring aperture provided at the entrance ofthe distributor may reach at each `instant during the `entire period of pouring and solidication of the met-al, the

, interior of the mould. From the foregoing it is clear that in the known processes there is a continual renew` ing of the atmosphere inside the mould. Owing to this renewing of the atmosphere the inner surface of the moulded piece is subject to a cooling eect andl is thereby solidified. The moulded piece solidifes, therefore, from its inner and outer surfaces. There results a formation on the inner surfaceof the moulded piece an internal shrinking which in certain cases may bring about a cylindrical separation which produces two tubularv portions one inside theother. In any case, the presence of the two cooling surfaces prevents the total decantation of the inclusions (slag) and the degassing of the molded4 piece which results in the presence of air bubbles.

The invention has for its object to provide an improved rotative mould, this mould being of known rotative type in which the moulding chamber communicates with ak distributor. which forms a chamber provided with an orifice on the upstream side of the feed through which the molten metal is passing and is given thereby a speedof rotation yequal to that of the mould.

According to the invention, the moulding chamber is closed at its end remote from the distributor so that no entry of air can occur and it communicates at its othery end with the chamber ofthe distributor through apertures` provided adjacent the periphery of a transverse 'screen introduced between the two chambers and taking part in their rotation, the points of these apertures the furthermost from the axis of rotation vof thel mould assembly being substantially on al level with the inner surface of the moulding'A chamber and the radial dimension of these` apertures being at the most equ to the radial thickness` of the part of the piece to be cast which is adjacent the screen. As a result of this arrangement, these apertures are hooded or are submerged by the molten metal atl least at the end of the pouring and prevent any entry of cold air from the distributor and its own entry aperture Iso that the poured piece does not tend to cool in the' centrifugal -direction from its central through-bore. In7 other words, during the whole of the cooling period the interiorof the mould has an enclosed atmosphere. v l Other features and advantages Will ybe apparent from.

the ensuing description in which: p

Fig. l is an elevational View of a mould according to the invention,

Fig, 2 is an axial longitudinal section of the mould shown to a larger scale, Y

Fig. 3 is a fragmentary view of the side of the transverse screen provided in the mould, this screenbeing viewed from the side situated in the plane 3 3v1'n Fig. 2 and linthe direction indicated by the arrows.

Fig. 4 is ya radial sectional view of this screen on line 4 4 of Fig. 3,

Fig. 5 is a view of the diffuser from the side thereof situated in the plane 5 5 in Fig. 2,

Fig. 6 is a longitudinal radial section of a modication `of the screen and diffuser,

Fig. 7 is a section of the diffuser on line 7 7 in Fig. 6,

Fig. 8 is a sectional view similar to that in Fig. 6 of another modification of the screen and diffuser,

Fig. 9 is a sectional view on line 9 9' in Fig. 8,V

Fig. l0 is a cross-sectional view of the mould showing a modicatior. of the gas outlet apertures, and y Fig. 1l is a diagrammatic view in partialy Vertical section of a device for casting in an enclosed atmosphere in accordance with the invention.

In the embodiment shown in Figs. l to 5, the'mould` according to the invention comprises a mould body con l stituted by a Vshell l provided on its inner face in this example with a refractory lining 2, for example of sand.

,The surface 2a of the moulding chamber therebykformed, ,l corresponds to the exterior shape of the cast tubular piece to be obtained. The shell 1 is provided externally with two rolling surfaces 3, 3El which rest on two pairs of rollers 4, 4a, each pair being fixed to a longitudinal shaft 5 journalled in bearings 6. One of these shafts is capable of being driven in rotation by any device, for example, an electric motor 5a, so that the mould rotates, for example, in the direction of arrow f. The horizontal axis XX of the mould may be horizontal or preferably make a slight angle of about 5% (4.) with the horizontal, the end situated at the right in Figs. 1 and 2 being in this case the higher.

The shell 1 is closed at one of its ends, i. e. that on the left in Figs. l and 2, by means of a device comprising a cup 7 fixed to the mould by means of screws 8 and provided with an axial aperture 9 in which slides the cylindrical boss 10 of a plate 11 housed in the cavity of the cup 7. This cavity, which faces the moulding chamber, is provided with sand 12 superimposed on the plate 11. A number of longitudinal passages 13 extend through the plate 11 and the sand 12. At the same end of the shell 1 is disposed an end plate 14 held by a number of screws 15. This plate is provided with a tapped hole 16 in which is screwed a rod 17 held to the end face of the head 10 and provided at its other end with a head and radially disposed arms 18. By screwing the screw 17 into the tapped hole 16, the plate 11 is displaced in the mould towards the right. The end plate 14 is also provided with a number of valves 19 which open under the action of a slight over-pressure inside the mould, so that the space enclosed between the end plate 14 and the cup 7 may be put into communication with the atmosphere.

At its other end, the shell 1 is provided with an ex tension which forms the chamber for the prior rotation of the molten metal. This chamber will be termed the distributor in the ensuing description. This distributor D comprises a hollow body 20, preferably of metal, which has a conical or like shape and is provided on its inner face with a refractory lining 21 of, for example, clay. Ihe body is open from one end to the other and its large opening is situated adjacent the shell 1. The small opening, concentric with the longitudinal axis XX of the mould, is in a preferred embodiment provided with a ring 22 of a refractory material such as, for example, Silico-clay.

Between the distributor D and the mould is disposed a flanged ring 23 provided on its inner periphery with an annular rib or wall 24. The inner edge of this wall 24 isprovided with an annular recess or rabbet 25 whose inside diameter is greater than the largest outside diameter of the tubular piece the machine is adapted to mould. A screen E essentially constituted by a detachable disc 26and its refractory covering 29 is housed in this recess 25. The recess is provided on the inside face of the wall 24 relative to the mould so that the disc 26 is free to move towards the left, i. e. towards the shell 1, but is prevented by the facing wall of the recess 25 from moving towards the right. The members 24 and 26 are temporarily held together by means of an alloy key 27 which melts at a much lower temperature than the metal to be moulded. A number of apertures 28 are provided around the periphery of the disc 26; these apertures overlap the annular wall 24 and put the inside of the body 20 into communication with the inside of the mould. The two sides of both the annular rib 24 and disc 26 as well as the apertures 28 are provided with refractory sand 29, which linally reduces the diameter of the apertures 2S to form apertures 288L having a diameter d. As stated, disc 26 and its refractory covering 29 form the aforesaid movable screen E. The apertures 28a are so arranged that they are enclosed within a circle whose diameter is substantially equal to the inside diameter of the moulding chamber in the region of the screen and the diameter d of the apertures is less than the thickness of the piece to be moulded in the machine Whose inner face is represented by the line mm (Fig. 2)` The 4 shell 1, the ring 23, and the distributor D are fixed together by means of bolts 30 and nuts 31.

The lining 21 of the distributor D includes ribs 32 (Figs. 2 and 5 in a number equal to that of the apertures 28 in the screen E and are disposed in front of the solid portions of the screen situated between the apertures 28. These ribs have a radial height lz which is at least equal to the effective diameter a' of the apertures28 and their profile is dissymmetrical, their larger slope being directed in the direction of arrow f.

The machine operates in the following manner:

The mould is rotated about its horizontal axis XX in the direction of arrow f. The molten metal contained in a ladle 33 (Fig. l) is introduced into the distributor D through the ring 22 by means of a pouring gate 34. The feed ow is adjusted in the following manner. At the start of the pouring, the rate of flow is much higher than the flow allowed by the apertures 28a so that the latter are rapidly ooded. The liquid ow from the ladle is then reduced to a ow substantially that through the apertures 28a so as to prevent an overow of the diffuser while maintaining the level of the liquid metal in the distributor above that of the apertures 28a. The

vmolten metal flows along the inner face of the lining 21 of the distributor and is rapidly driven in rotation by the ribs 32 at a speed equal to that of the mould.

Owing to the conical shape of this face, the metal is` subject to a longitudinal component directed towards the 'shell 1. The metal flows, then, towards the interior of the shell 1 through the apertures 28a. Since the metal is driven in rotation in the distributor D, when it enters the shell 1 it is subject, relative to the latter, to only a single component of speed parallel to the axis XX. The metal which liows into the moulding chamber is, then, subject to only the action of centrifugal force and undergoes no peripheral slip relative to the inner face 2a of the mould. There is, therefore, a complete suppression t of splashing inside the molding chamber or, in other words, the metal is turbined in the distributor D at the same speed as the mould before it enters the shelll. It might be mentioned that owing to the fact that the level of the metal in the distributor rapidly exceeds that of the apertures 2S, which, as hereinbefore mentioned, are then flooded, the pouring is effected direct from the molten metal itself thereby preventing the impurities which lloat inside the distributor chamber on the surface of the molten metal from entering the moulding chamber. At the end of the pouring, the metal levels in the distributor and in the moulding chamber equalize along the line mm (Fig. 2).

During the lling of the mould, the air or the gases contained inside the mould heat upon contact with the molten metal, expand, and tend to increase the pressure of the atmosphere inside the mould. These gases escape through the passage 13 and the valves 19. The pouring aperture 22 is practically closed at the start of the pouring by the owing metal and the submersion of the apertures 28a very rapidly completely closes the mould and thereby prevents any entry of air therein. Thus, there is no danger of the inner surface of the molten metal contained in the mould cooling, for the temperature of the air existing in the mould very rapidly attains a temperature very near that of the metal. The only cooling which could possibly occur is that caused by the contact of the metal with the inner face 2a of the mould on the one hand, and the cooling action of the end plate 11 and the screen E on the other hand; these latter are already heat-insulated by the refractory sand lining provided thereon which has such thickness that their cooling effect is negligible relative to that of the inner cooling surface 21 of the mould. The cooling, therefore, progresses radially and in the eentripetal direction from the `outer surface of the moulded piece toward-s the inner surface thereof.

When, as a result of the cooling effect of the mould, the

meta-l completely solidies, the rotation `of the mould is discontinued. During the subsequent shrinkage of the einem metal, the headlsis rotated Vso astourgetheplate 11 toward the right (Fig. 2) andthereby subject.'the endi lof moulded .metal remote from thefplate 11 to alongi'-y tudinal compression. The displacement of the plater 11,

is made possibleV by the breaking 'of the sand lining 12 aground the periphery of the plate. 4By meansy of this compressing operation, they appearance of internal stressesl which often create cracks caused by the shrinkage of the.

piece is prevented. Furthermore, at the pouring headend of the mould, the key 27, which. connects the disc 26 of screen E to the annular wall 24, has, atthe end 'of the moulding operation, already melted under. the action ofl the heat, and the screen E, whiclris heldbetweenfthe` prece `and the dead head, solidified in the distributor and,

by enabling the moulded piece to beexltracted from. the

mould by exerting a pull on the dead head.

During this latter operation, the screen E is withdrawn with the piece. The ring 23 may then be withdrawn by sliding it towards the right. To free thedisc 26 from the piece, it suffices, after having opened 'out thefeed apertures 28a, to separate the dead head fromV the piece by means of a welding torch which cuts` through the cylindrical solidified portions of metal connecting these two parts.

By means of this casting process as hereinbefore explained, the metal that enters the moulding chamber i. e.y

the piece being moulded is driven in rotation yat a periph-y eral speedl substantially equal to that of the mould and there .foccurs no turbulence which would risk causing.

splashing or the format-ion of oxidized cold globulus. Furthermore, there is no relative, concentric, slip'betwen the layers lof metal from which might result ruptures of. the metal crystals during the cooling period. Owing to` the fact that the solidifcation occurs in an enclosed mould wherein there exists absolutely no cooling surface other than the wall of the mould itself, th-is solidiiicati'on occurs only from the exterior towards the interior, thereby eliminating anyy possibility rof a formation of inclusions, blowholes, etc. Thus, the formati-on of macroglobulities is prevented `and the pieces exhibit throughout their thickness an absolutely sound structure devoid of crystal rupture or heterogeneity :of any kind. Moreover, the pouring of the metal from its source eliminatesV any presence in the cast piece lof any impurity or slag. It is noteworthyV that owing to the lackr of slip of the molten metal on the inner surface of the mould, no abrasion of this ,sur-

face occurs, which prevents. any inclusion of Sand in they c-ast pieces, which, when withdrawn from the mould,

exhibit a very clean and regular outer surface.

in the above-described embodiment, the apertures 28.a have their axes disposed parallel to the axis XX of the mould, but they may, of course, be inclined in the direction of rotation or in the opposite direction so as'to accelerate or decelerate the speed `of entry of the molten` metal into the moulding chamber.

According to the modification shown in Figs. 6 and 7v the distributor 3S in the shape of a conical cup comprises on the side of its large base an annular groove 36 constituting a recess in which is housed a screen 37. The unit is located in a machined recess 38 provided at the end of the shell 39, the screen 37 being held between the bottom of this recess and the groove 36 in the distributor 35. Cone-printed screws 40 screwed into the body of the mould shell hold the end unit in place. The refractory lining 41 of the distributor 35 is so shaped that there is provided a ared passage 43 from the pouring aperture 42 and a number of radial passages 44 adjacent the screen. These discharge into an annular passage 45, into` which also discharge radallpassasest lscated in fwn? f apertures 47 provided in the screen,4 The aperturesv 4,7l are providedl'inl the'sand 47a with which the screen is lined and are lined with refractory tubularpieces 47h. Thepasjsages 46 are `disp0sed inthe passage 45 Ibetween' the passages 44. According to this construction the Iassembly of the front part of the mouldis materially simplified." Moreover, before it enters the moulding chamber, the

molten metal undergoes a zig-zag motion whichV helps,

arms 5t). The ring 49 is housed in a recess provided inY the sand 51 forming the refractory lining of the body 52 of the distributor. Owing to this construction, insteadl of having a number of metal feed apertures, the metalvr may be distributed in an even manner practically over,i the whole circumference of the screen. The lining. 51 has of course ribs 53 disposed in front of thearms of the screen. The central part of this screen, includes adja-` cent the moulding chamber a blind hole 54 communieating with pas-sages 55 provided in the arms 5t). These passages are connected to pipes 56 which` are extended alongthe outer face of the extension 52 and discharge inton the atmosphere at SGadjacent the axis of rotation. These pipes are provided for the evacuation of hot air and gases, and in this case the [other end of the mould need not Virl-v clude apertures for this purpose. Owing to this construction, any risk of a projection of molten metal as 'a result of a false move or an accident, is avoided, for the" metal level would be too 'high in the mould anclwouldl'v be thrown out.` The length of the pipes 56 as well as their cooling are such that any meta-l that would attempt to escape therethrough would solidify before having reached the ends of the pipes. i

According to another modification shown in Fig. l0, the Valves 19 provided in the end plate14 may bereplaced4 by radial apertures 57 provided in the wallof the shellv between the cup 7 and the end plate 14 and extended by' short pipes 58 curved to suit the direction of rotation of the mould and which constitute a suction fan. I n 'this arrangement there results a forced suction 'of the gases contained inside the mould. As this mould is closed, as hereinbefore mentioned, at its metal entry end, ai certain depression is thereby produced inside the mould whichl favours the dega'ssing of the molten metal and prevents any formation of blow-holes or gaseousv inclusions inl the cast piece. This device naturally prevents any entry of cold air into the interior of the mould.

As is clear from the foregoing description, the casting is performed in a mould which may be considered completely closed. Thus it is very easy to visualize casting in a controlled inert atmosphere, which is particularly advantageous when easily oxidizable metals need to be cast. To this end there may be provided, as is illustrated in Fig. 1l, a feed pipe 59 suitably insulated at 60 and connected to the lower outlet 61 of a ladle 62. This pipe passes through the aperture 63, and the ladle stopper 64 is provided with an axial through-passage 65 whichcornmunicates at its lower end with the pipe 59 and at its upper end 66 with a bottle containing inert gas (not shown in the drawing). Adjacent the metal entry aperture 63, the pipe 59 is surrounded by an annular sleeve 68 also connected to the bottle containing inert gas and provided with a circular opening 69 which surrounds the pipe 59.A Owing to this arrangement, before commencing the casting operation, the gas may be sent through the passage 65 so as to fill completely the mould, then, after having raised the stopper 64 which opens the opening 61 of the` ladle through which the molten metal 70 flows into` the rotating mould, the mould may be fed with gas through the sleeve 67 so as to provoke between the pipe 50 and the opening of the diffuser a Zone supercharged with this gas and thereby obtain a total superpressure with the surrounding air. In this way, the gas carried with jet into the mould is solely the desired inert gas.

The invention is not limited to the constructional details herein described and illustrated in the accompanying drawings which have been given merely by way of example. The invention is also applicable to vertical or inclined centrifugal casting and is capable of casting tubular pieces having a shape other than those described. Thus, these pieces, instead of being provided with a reinforced or thickened head adjacent the screen E as shown in Fig. 2, may be cylindrical or provided with a thickened head at the detachable end of the mould, etc. It is obvious, furthermore, that the inner face of the mould instead of being lined with sand may be lined with a completely dilerent material such as, for instance, asbestos or paper, etc. This inner face may even be unlined or provided with a metal lining which may or may not be cooled in order to obtain any desired mode or control of cooling depending on the molten metal employed.

Having now described my invention what I claim as new and desire to secure by Letters Patent is:

l. In a mould rotative about an axis of revolution, for the centrifugal casting of an elongated metallic tubular piece with protection against atmospheric air, said piece being susceptible of undergoing a relatively important longitudinal shrinkage, in combination: a rotative tubular mould shell having two ends and an internal surface concentric to said axis, said internal surface emerging at both of said ends and forming a casting chamber; a hollow distributor chamber attached to one of said ends; said distributor chamber forming a passageway for the molten metal to be cast, and being adapted to impart to the molten metal an angular speed of rotation equal to that of said shell before the metal passes from said distributor chamber into said casting chamber; a first transverse plug device, internal to said internal surface comprising a screen disposed between and separating said casting chamber and said distributor chamber; apertures in said screen for the passage of the molten metal and for communication between said chambers, said apertures being so disposed that they are entirely immersed in the molten metal; housing means for said screen, attached to said shell between said distributor and casting chambers, and fusible means disposed between said housing means and the periphery of said screen and adapted to connect temporarily said screen to said housing means, in such a maner that said screen is released at the end of the casting; whereby said screen, then held fast, relative to the cast piece, by the metal frozen in said apertures, is adapted to follow during the cooling of the cast piece the shrinkage of the latter; at the other end of the shell, a second transverse plug device, at least partially movable to close the casting chamber, and a pushing device operable from the outside of said shell and adapted to move said second plug device longitudinally towards said screen during the cooling of the cast piece, whereby the latter is maintained under longitudinal compression in spite of its shrinkage.

2. A mould as claimed in claim l, in which said screen comprises a metal disc having a circular periphery; and said housing means comprise in combination: a ring having an inner circular ange, said flange being provided with an annular inner rabbet facing the casting chamber, the periphery of said disc engaging said rabbet; and said fusible means consist in a metallic alloy key between said ring and said disc, said alloy melting at a lower temperature than that of the metal to be cast, whereby said key forms a temporary bond between said disc and said ring.

3. A mould as claimed in claim 2, in which said disc, saiddange and said apertures are coated with refractory san 4. A mould as claimed in claim 1, further comprising an internal sand coating covering the internal walls of said casting chamber and of said distributor chamber, said screen having its periphery engaged in said sand coating.

5. A mould as claimed in claim 1, in which one of said transverse plug devices comprises at least one exhaust passage in combination with a corresponding valve device, so constructed and adapted that said passage allows the exhaust of the gases and air contained in said casting chamber and prevents the entry of atmospheric air into said casting chamber.

6. A mould as claimed in claim l, in which said second transverse plug device comprises: a double wall consisting in a first internal wall movablelongitudinally within said shell and having at least one gas exhaust vent and in a second outer wall attached to said other end of said mould body; at least one exhaust passage through said second outer wall; a valve device on each said exhaust passage; a tapped axial hole in said second outer wall; said pushing device comprising a screw engaging said tapped axial hole, and abutting said first internal wall, said screw being provided with a driving head outside said shell, whereby the turning of said screw accomplishes said longitudinal compression.

7. In a mould rotative about an axis of revolution, for the centrifugal casting of an elongated metallic tubular piece susceptible of undergoing a relatively important shrinkage upon cooling, said mould comprising an elongated tubular shell having an upstream end and a downstream end, the internal surface of said shell being concentric to said axis and emerging at both said ends and being shaped to form a casting chamber, a distributor attached to said upstream end and provided with a distributor chamber having an upstream intake opening, said chamber being adapted to form a passageway for the metal and to impart to the metal an angular speed of rotation equal to that of said shell, and a screen between said casting chamber and said distributor chamber and internal to said internal surface, apertures in said screen for communication between said two chambers and so disposed that they are entirely immersed in the cast metal, in combination: housing means for said screen, attached to said shell between said distributor chamber and said casting chamber, and fusible means disposed between said housing means and the periphery of said screen and adapted to connect temporarily said screen to said housing means in such a manner that at the end of the casting said screen is free to move inwardly of said casting chamber under the action exerted by the cast piece, said action being an axial traction due to cooling and shrinkage; near the downstream end of said shell, a plug device adapted to close said casting chamber, said plug device consisting in a double wall comprising an inner wall longitudinally movable in said casting chamber and provided with at least one gas exhaust vent, and an outer wall attached to said shell and provided with at least one exhaust vent, closure means on each exhaust vent of said outer wall and constructed and adapted to allow the release of gases from said casting chamber and to prevent the inux of atmospheric air through the exhaust vent of said outer wall; and a pushing device in said plug device, said pushing device being movable relative to said outer wall and being constructed and adapted to engage said inner wall and to displace the latter longitudinally; said cast piece being maintained in said casting chamber under axial compression during its cooling by the inward displacement of said inner wall by said pushing device.

References Cited in the file of this patent UNITED STATES PATENTS 1,377,372 Thompson May 10, 1921 1,466,826 Gordon Sept. 4, 1923 1,636,228 Gray July 17, 1927 2,414,890 Nolan Jan. 28, 1947

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