US2219951A - Casting method - Google Patents

Description

06L 29, 1940. Q N I 2,219,951

CASTING METHOD Filed May 6, 1938 2 Sheets-Sheet 1 v INVENTOR. fi/VOEEN C. Du/v/v BY ATTORNEYS.

AQc. DUNN 2,219,951

CASTING METHOD Filed May 6, 1938 2 Sheets-Sheet 2 INVENTOR. Du/vN fl/vp/e EW C AWL ATTORNEYS Patented Oct. 29, 1940 UNITED. sTATES;

' ATEN OFFICE.

This invention relates to casting methods and more particularly to a method of castinga relatively thin shell around a preformed metal body.

In casting metal around preformed bodies a I 5 great deal of difiiculty has been encountered in getting the metal to flowproperly around the body without chilling sufficiently to' prevent proper flow. This difiiculty is particularly pronounced where the mass of cast metal is relatively small and it has been proposed to preheat the body prior to pouring the metal around it to reducethe chilling effect. However, preheating is expensive and slow and it is therefore OneOf a the objects of the present invention to provide a casting method .in which no preheating is necessary. a

Another object of the invention is to provide a casting method in which molten. metal is poured into the top of a mold cavityaround a preformed body. With this arrangement the molten metal falls rapidly to the bottom of the mold cavity before it has time to chill sufiiciently to interfere with proper flow so that the cavity will be completely filled.

Still another object .is to provide a method of casting relatively light cylinders or the like impervious to fluid pressure.

Still another object is to provide a method of casting .a .shell around a' preformed tube or cylinder for decorative or mounting purposes,

Other objects and advantages of the invention will be apparent from the following description when read in connection with the accompanying drawings, in which: Figure 1 is a central section of a door silencer constructed according to the invention;

Figures 2 and 3 are sections through molds illustrating steps in the method of manuiacturing the silencer of Figure 1;

Figure 4 is a partial view similar to Figure 2 of a modification; and Figures 5 and 6 are views similar to Figures 1 and 2 respectively showing a further modification. 7

Figure 1 illustrates a novel door silencer constructedlaccord'ing to the invention and constituted by a relatively thin metal tube H! formed with a roughened portion H adjacent one end and external screw threads at the other end. A relatively thin cast metal body I2 is cast about one end of the tube and adheres to the outer surface of the tube throughout approximately two thirds ofits length, the body 12 torming an end closure 13 for the tube, The opposite end of the tube I is closed by a cast metal cap 14 having an internally threaded sleeve l cast therein for engagement with the screw threads on the end of the tube and a mounting bracket It 'for mounting the silencer. r

' A piston llis s'lidably mounted in the tube and .has' a piston rod; 18 extending out through the capM and a spring I9 act'ing between the closure l3 and the piston l! to urge the piston towardthe "A suitable check valve 2!! which maybe of the type more fully described and claimed in my prior Patent No.- 1,966,956 is mounted in the end closure l3 to control the ingress and egress of air.

In use the silencer is mounted adjacent a door on the'brac'ket l6 with the piston rod It in the screw threads at the other end. A suitable core 12] ,of core; sand having the desired configuration for the end closure i3 is then formed in the end of'the tube adjacent the roughened portion II and is baked in place.

The operator may then take a suitable pattern, not shown, which is formed substantially in the same shape as the cast body l2, invert it on a mold board, place the drag of a sand molding flask around it and pack the flask with sand. When the sand is packed, the flask is inverted and the tube. H] is placed in the pattern, a ring 22 preferably being screwed on the end of the tube to assist in holding it in the mold. A'suitable gate 23 is'preferably cut in the drag portion of the mold, it being noted from 'Figure- 2 that thegate' discharges substantially horizonremoved from the drag, and the mold put back together,

Instead of forming the molds singly as described above, a plural pattern or plate carrying a number of projections each shaped in the same manner as the single pattern may be employed. In this way a plurality of cavities will be formed in the sand each time and a plurality of units can be cast simultaneously in the same flask. It will also be noted that many of the advantages of my method are obtainable with permanent mold casting.

Figure 2 illustrates the mold with the tube in place ready for pouring. The mold is preferably formed entirely in the drag 24 and the tubelfl is supported in the cope 26 with a portion thereof projecting into the mold. .Molten metal is;

now poured through the gate 23, striking avertical side wall of the tube Ill at substantially right angle and flowing down-into the moldto fill the same. As the metal flows into the mold and hardens it will adhere firmly to the tube I0 but will not melt it since the heat will be conducted away with sufiicient rapidity to maintain the tube I0 below its melting point. If desired, the tube I0 may be formed of a material having a higher melting point than that of the body I2 but I have found that this is not essential, satisfactory results being obtained with a soft steel tube I0 and a cast iron body I2.

According to the invention, the casting of the relatively thin shell I2 around the tube In is made possible by pouring the molten metalinto the top part of the mold and by correctly prov portioning the mass of cast metal to the metal in the tube. It is desired to make the shell I2 thin to reduce the size andweight of the completed device and I have found that if this shell is less than three times the thickness of the tube wall the metal cannot be flowed up from the bottom of the mold cavity around the tube due to chilling and setting of the metal before the cavity is filled. However, when the metal is poured into the top of the cavity it will flow rapidly to the bottom before it chills and the cavity will fill properly and completely even though the cast shellis considerably thinner than three times the tube thickness.

As the mass the metal in the exposed part of the tube and in the cast shell become morenearly equal or the mass of the tube predominates, the mold cavitywill still fill but the cast metal will be chilled to a greater extentand will tend to become hard and brittle. I have found that when the tube and shell are of the same thickness the shell is apt to be very hard and somewhat porous due to chilling. Therefore, I prefer to make the shell substantially twice the thickness of the tube, which'results in a light, small device and a uniform good casting.

When the casting has hardened it may be removed from the mold with the tube I0 firmly embedded therein and the gate may be removed. It will be noted from Figure 2 that the upper edge of the casting will be formed with a taper 'away from the tube, as indicated at 21, which facilitates machining a smooth shoulder on the edge of the casting without cutting into the tube I0. This machining operation could be omitted if a smooth shoulder were not desired but where it is performed it is the only machining operation necessary aside from tapping a hole for the valve 20 and any desired exterior finishing for the sake of appearance, the tube I0 presenting a smooth inner surface for forming a sliding lit with the piston I'I.

In forming the cap I4, an internally threaded the core 28 inserted in the pattern with the I shoulder 32 resting on a sloping shoulder at the outer edge of the pattern and the cope 34 of the mold is rammed up with the sand surrounding the'portion 3| and holding the core in the cope. The cope may be removed taking the core with it, the pattern removed from the drag, a suitable gate 35 cut, a core 36 for the bracket I6 placed and when the cope and drag are reassembled the mold is ready for pouring. It will be noted that when molten metal is poured inthe gate 35 it will surround and adhere to the sleeve I5 thus, permanently fixing the sleeve in the cast cap. The groove 29 will form an internal annular projection and the sloping shoulder 32 will form a tapered edge to facilitate finishing.

In casting this cap the relationship between the thickness of the sleeve I5 and of the casting is the same as described above, the casting being substantially twice as thick as the sleeve. It will be noted also that the molten metal is poured into the top of the mold cavity so that it will flow down around the sleeve to fill the cavity properly.

When the metal has hardened it may be removed from the mold, the outer end finished off to abut the end of the body I2 squarely and a suitable hole drilled for passage of the piston rod I8. The cap is then ready for use aside from any exterior finishing which may be desired.

Figure 4 illustrates a slightly modified arrangement, parts therein corresponding to like parts in Figures 1 and 2 being indicated by the same reference numerals primed. As shown in this figure the end of the tube I0 is spun over as indicated at 3B and a sleeve 31 is secured thereto by crimping or the like as indicated at 38. v The sleeve 31 is internally threaded to receive a valve such as 20 in Figure 1 and is closed during the pouring operation by the core 2I'. Preferably this core extends into a suitable cavity in the mold to assist in centering the tube in the mold cavity.

Figures 5 and 6 illustrate a further modification, parts therein corresponding to like parts in Figures 1 to 3 being indicated by the same reference numerals plus 100. In this form the end of the tube H0 is completely closed at I39 and the valve I20 is placed in the piston rod II8 which is hollow and has a suitable air outlet outside of the tube. The valve is formed by a tube screwed into a reduced portion of the piston rod H8 and having an air inlet opening I40 in its end and an air outlet MI in one side. The opening I40 is controlled by a check valve I42 and a spring pressed valve I43 is arranged to seat just to the right of the port I4I to close off the port.

When the piston is moved to the left both valves I42 and I43 will be unseated and air will be admitted freely behind the piston. If a sudden force is applied to the rod H8 as when a door is closing fast and strikes it,-the valve I 43 will be seated against its spring to trap air to the right of the piston thereby to stop movement thereof. As the sudden'force is relieved and becomes a lighter, relatively. steady force the valve I43 will be unseated and air will bleed out through the port MI. The end of the valve is preferably provided with a screw-driver slot so that it can be adjusted to cover partially the port I4 I' thereby to regulate the speed of movement of the piston.

In forming the device of Figure 5 the tube H0 is supported in a mold cavity as described in connection with Figure 2 with the closed end I39 down and spaced from the bottom of the cavity. Molten metal is then poured into the top of the cavity through the gate I23 and flows down around the tube and across the closed end to form the shell i 2. In this form as with those described above, the shell 12 is substantially twice the thickness of the tube.

While several illustrative methods have been described in connection with the making of door silencers it will be understood that the invention may be modified in various respects and applied to the manufacture of other articles. .Thus the invention is particularly applicable to the manufacture of fluid pressure cylinders of all types in which the tube provides not only a smooth inner surface but also a relatively thin impervious wall and the cast shell provides a decorative exterior and a convenient method of mounting as by integrally cast brackets. Reference will therefore be had to the appended claim for a definition of the limits of the invention.

This application is a continuation in' partof my prior application Serial No. 29,609 filed July 3, 1935.

What is claimed is: v V

The method of casting an iron shell around a steel tube having walls relatively thin as com-.

against a vertical wall of said tube and down around the tube.

ANDREW C. DUNN.

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