US1456187A - Cast-steel tire mold - Google Patents

Description

May 22, 1923.

J. H. MULLOY CAST STEEL TIRE MOLD Filed June 10, 1921 7 Sheets-Sheet 1 INVENTOR. John H. Mulloy BY I W [HIS ATTORNEY.

May 22, 1923. 1,456,187

J. H. MULLOY I Filed June l0. 1921 7 Shlee She at 2 M 9- a INVENTOR.

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May 22,- 1-923. 1,456,187

J. H. MULLOY CAST STEEL TIRE MOLD Filed June 10. 1,921 '7 SheetsSheet 3 .3/ I I V g INVENTOR. Jalzn H.Mulloy H13 ATTORNEY.

May 22, 1-923. 1,456,187

J. H. MULLOY CAST STEEL TIRE MOLD Filed June 10. 1921 '7 Sheets-Sheet INVENTOR. John [7. Hal lay H13 ATTORNEY.

May .22, 1923. 1,456,187

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Patented May 22; 1923.

UNITED STATES PATENT OFFICE.

JOHN H. MULLOY, OF DETROIT, MICHIGAN, ASSIGNOR TO MORGAN & WRIGHT, A COR- PORATION OF MICHIGAN.

CAST-STEEL TIRE MOLD.

Application filed June 10, 1921.

To all whom it may concern:

Be it known that 1, JOHN H. MULLOY, a citizen of the United States, residing at Detroit, county of lVayne, and State of Michigan, have invented a certain new and useful Cast-Steel Tire Mold, of which the following is a full, clear, and exact description:

This invention relates to a cast steel mold and its method of manufacture.

In the manufacture of tires in general and pneumatic tire casings in particular, it is usual to give the exact shape desired to the outer surface of the tire by curing it in sectional metallic molds, the tire being support ed on a core or subjected internally to fluid pressure of around 200 pounds per square inch. In some cases, the green tires are preliminarily subjected to a forming operation in shaping molds while subjected to internal fluid pressure of around 200 pounds per square inch.

Heretofore, tire molds have been made almost exclusively of cast iron. The uncertain and unreliable strength of this metal necessitated making them thick and heavy. Molds of cast iron'were liable to warp and crack, and pitted up to an extent compelling frequent cleaning. But notwithstanding the many objections thereto, cast iron molds have been used for a great many years to the almost complete exclusion of all other types of mold.

Lately, subsequent I believe to my invention, it has been proposed to make tire molds out of forged steel. This is an improvement upon the cast iron mold but, as far as I know, forged steel molds have not been, and cannot be made, as light as the molds of my invention.

My invention aims to provide a tire mold of cast steel that is substantially lighter than any known prior tire mold. capable in some sizes of being made as much as 50% lighter than a cast iron mold of corresponding size.

' Further, it aims to provide a method for casting the molds of steel with low or small margins of tolerance for subsequent machining to exact size; and to provide a method that will insure sound and uniform grain or texture to the metallic body throughout its Serial No. 476,410.

mass as well as at the tire contacting surface of the mold where a smooth machine finish is required. And further, it aims to provide a method that Will insure freedom of the casting from cracks and from strains which in the expansion and contraction incident to curing treatment, are liable to crack the molds. Generally, it aims to provide a practical method of casting annular steel tire mold sections, and one that is economical and requires no extensive outlay in foundry equipment.

Without intention to limit the scope of the invention more than is required by the prior art, it may be described briefly as a cast steel tire mold of substantially uniform wall thickness that is machined from a casting substantially free from flaws, cracks and shrinkage strains and approximating, in the rough, the cross section of the machine finished mold. It is made preferably from a pattern having two substantiallyreinforced parts, each with a face shaped in replica of one side of the tire mold section to be cast. Runner forming projections and core prints are provided on the patterns. From the pattern sand copes and drags are derived and, after their exposed surfaces have been sprayed with a suitable wash, these are baked. After baking, the sand cope and drag are assembled and, into the annular cavity of the shape of a tire mold section defined in the sand mold, metal may be poured and solidified.

A preferred embodiment of the invention is illustrated in the accompanying drawings in which F l is a plan view of a final cure mold section, and

Figs. 2 and 3 are cross sections on the lines 22 and 3-3, respectively, of Fig. 1,

Fig. 4; is a plan view of a preliminary shaping mold, and

Fig. 5 is a cross section on the line 5 Fig. l,

Fig. 6 is a plan view of a core box constituting half of the pattern looking at the sand shaping face.

Fig. 7 is a cross section of the drag forming core box on the line 77 in Fig. 6,

Fig. 8 shows the drag core box rammed with sand and having imbedded reinforcing hoops.

Fig. 9 is a plan view of a core box from which the sand cope is derived,

Fig. 10 is a cross section of the cope forming core box on the line 10-1O Fig. 9,

Fig. 11 is a plan view of a sand mold ready for pouring,

Fig. 12 is a cross section on the line 12-12 Fig. 11,

Figs. 13 and 14 are fragmentary cross sections on the lines 13-13 and 14;-14, respectively, Fig. 11.

Figs. 15 and 16 are cross sections of a filial cure. tire mold and of a preliminary shaping tire inold on an enlarged scale, the rough cast steel shells from which they are machined being indicated in dotted lines.

Figs. 17 and 18 are a cross section and fragmentary side elevation, respectively, of a ribbed type of cast steel mold, and

Fig. 19 is a perspective view of a sectional type of sand-copefor1ning core box,

Fig. 20 is a cross sectional detail of an expedient for casting centering ribs on the sections.

The cast tire mold section desired may be of any suitable shape to meet the fancies of different manufacturers, but the two forms shown in Figs. 1 to and 1 and are re spectivcly typical of final cure and preliminary shaping tire molds. The final cure casting 1 of a tire mold, shown in Figs. 1 to 3, has a concave tire engaging or inside face 2, and an outer face 3 approxii'nating the contour of the inside. Flanges 4; and 5 are formed on the inner and outer periphery, respectively, the former being substantially circular excepting for bolt slots 6, bosses 7 and 8 (for tong holes and dowel pins, respectively,) and the latter, i. e., the inside flange 5, being interrupted as indicated at 9. Bolt receiving slots 10 and lug flanges 11 projecting inward are provided at intervals on the inner periphery. But, of course, the flanges f and 5 may be left plain and unbroken if desired.

The preliminary shaping mold 12 of Figs. 4 and 5 is of like form in cross section excepting that the inner flange 13 is continu ous and located on the outside rather than towards the inside face. On its outer perimeter, it is provided with lugs and bolt slots of the same form as in the final cure mold but a greater number of slots are provided.

According to my invention, I first make a pattern for the desired casting. Preferably, I make this pattern in two parts resembling core boxes, one, indicated by the numeral 14; and shown inFig's. 6 to S, for the sand drag, and the other, indicated by the nuinera-l 15 and shown in F igs. 9 and 10, for the sand cope. The illustrated pat-tern parts 14' and 15 are shaped to form the tire mold section 1 shown in Figs. 1 to 3, but it is to be understood of course that these pattern parts could be variously shaped to suit the type of tire mold wanted.

The pattern part 1 1 for forming the sand drag 16 (from which the inside face 2 of the steel casting is shaped) is carved in intaglio as indicated at 17. The carved out annular groove 17 is flanked by a circular projection 18 which gages the depth or thickness of the outer flange of the casting, and this projection 18 is surrounded in turn by a higher flange 19, being separated therefrom by a relatively deep groove 20 for forming the upstanding flange 21 of the sand drag 16 and also by a cut-out 22 which forms a portion 23 in the sand that constitutes the outer rim of the casting cavity which is indicated by the numeral 24 in Fig. 18.

On the pattern part 1 1, which. may be designated as a circular core box, preferably, but not necessarily, radial pattern prints are fashioned to form runner cavities indicated at 26 in Fig. 14. The several pattern prints radiate from a common center or block indicated at 28 which, of course, forms the bottom of the pouring hole in the sand mold. These pattern prints may extend: to either the outside or inside peripheries of the casting cavity, the former arrangement being preferred for open-hearth steel and the latter for crucible steel. Curved core pattern prints 27 are inserted or fixed between the pattern prints 25 if they extend to the outside of the casting cavity and fit snugly into the hollow 17.

The pattern part 1 1, with its carved face iiippermost, is rammed with sand, reinforc-- ing hoops 29 and 30 being preferably imbedded therein to withstand the hydrostatic pressure. After being leveled off, it is covered with a follow plate 31 Figs; 12 and 13 and inverted. The core box part 1541 is then removed, suitable draft being provided, as indicated, to prevent disruption of the sand drag. Separately formed and dried segmental core blocks 27 are, then mounted in the sand drag 16-, as indicated in Figs. 12 and 14:, in the spaces left by the pattern prints 27 (if the same are used) and the thus completed sand drag is sprayed with a suitable smoothing or finishing wash, such as silica. On its follow plate 31, the sand drag 16 is introduced in an oven and baked. in this manner it is completed, read-y for reception of the sand cope, without seam or break in the portion of its surface which defines one wall of the casting cavity, except ing, of course, where the runner cavities 26 coinn'iunicate therewith as they do at the point 32 adjacent the outer periphery of the casting cavity in the pouring arrangement shown iii Fig. 12. K i

The sand cope 33 in 12 is formed in the pattern part or core box 15 illustrated in Figs. 9 and 10. The wall of sand which gives shape to the outer surface 3 of the casting, shown in Fig. 2, is derived from the carving in relief indicated at 34: in Figs. 9 and 10. This core box 15, like its mate, has a flanking circular flange 35 suitably drafted on its inner wall so that the sand cope will fit into the sand drag. Pattern prints 36 provide cavities for the bolt lug cores 37 in Fig. 12 which preferably are reduced slightly to leave a space 37 for a thin bridge of metal across the outside bolt slots 6 in the rough casting. Pattern prints 38 provide cavities for the flange cores 39 in dicated in Fig. 18. Riser openings 40 in Fig. 12 are provided for by prints 41 Fig. 9,

' and a central pouring sprue 42 is provided such as a silica wash. The sand cope is then baked in an oven.

The separately shaped and baked sand cope 33 and sand drag 16 are then assembled, the latter still resting on its follow plate 31. Runner, 45, and riser, 416, sleeves are then registered over the openings in the cope. These, as well as the cope itself, are suitably weighted down and molten cast steel is poured into the central sprue 12.

The metal flows from the central pouring hole more or less radially through the several runners into the casting or molding cavity. It may enter the same adjacent either the inner or outer peripheries, but the latter method is preferred, inasmuch as the cavity is filled with metal at a more nearly uniform temperature, consequently, the shrinkage is more nearly uniform, and as the risers may be somewhat reduced either in size or in number. And the sand walls of the casting cavity are less likely to be scoured when the metal is poured to the outside periphery than when it is poured to the inside periphery of the casting cavity. And still further, conducting the metal through the several runners to the outside periphery of the casting cavity permits the gases and vapors to be driven off better and there is less likelihood of draws and pipes than in pouring to the inside periphery. It is to be distinctly understood, however, that both methods of entering the molten metal into the casting cavity may be employed, satisfactory results being obtainable with either crucible or open-hearth steel if sufficiently nular casting cavity it would be preferable therefore to locate the risers about or at the outside periphery.

The foregoing relates largely to the preferred method of operation. As before intimated, the shape in cross section of the cast tire mold halves may be varied widely if desired but generally it will be most advantageous to make the wall thickness approximately uniform and to very closely approximate the outline of the finished or machined steel tire mold sections which are shown in Figs. 15 to 18, inclusive. Obviously, the less the amount of metal ma chined off of the rough cast steel to make the finished section, the greater the economy.

Some of the advantages of the invention would obviously be realized by casting the steel shells hollow side up instead of hollow side down but as the impurities in the molten metal tend to rise, the tire engaging face wouldnot be as sound and uniform. Also, the sand. cope might be derived from the sectional form of core box shown in Fig. 19, composed of a plurality of sectors 47 each suitably proportioned and shaped so that the derived sand sectors may be fitted together to form a complete circular sand cope o1- disc. The sections may be baked either separately or in assembled relation after being slicked and having their exposed surfaces sprayed with a silica wash.

In Figs. 15 to 18, inclusive, three different forms of finished tire molds are illus trated. Figs. 15 and 17 show different forms of a final cure mold. These are of a type adapted to receive a sealing ring in the slots indicated at 18 on which sealing ring the green tire has its beads mounted and suitably sealed to enable the interior of the carcass to be subjected to fluid under relatively high pressure, thereby to compact or densify the wall structure and force the rubber during the cure to take the exact form of the machined tire mold cavity. In Fig. 15 provision for stacking the molds one upon an other is afforded by relatively flat surfaces indicated at 19. In Fig. 17 stacking of the molds flatwise upon one another is permitted by more or less non-radial ribs 50 whose outerfree edges 51 are machined co-planar. In Fig. 16 a tire shaping mold is illus trated in cross section and it is likewise pro vided with parallel fiat outer surfaces 52 and with an interior tire receiving cavity defined by the walls 53 which is preferably of the proportions shown, being a little less in height but the same in width as the cavity in the final cure molds.

The machined sections of the molds preferably have cei'itering ribs 54 and grooves The latter are preferably cut out of the solid metal but the former are most desirably cast in the rough and machined to fit into the grooves 55. For this last named purpose the core box 14 on the surface 18 may have an upstanding annular ring (not shown) integral therewith (in which case separate male and female core boxes are required) or, as shown in Fig. 20, the core box 1 1 may be provided with inserts or an inlaid metal ring 56 to which a projecting metal ring 57 may be dotachably secured. By omitting the ring 57, the same core box pattern may be used for deriving the female cast shell.

The shape of the rough cast steel shell from which the final-cure and shaping tire molds, respectively, of Figs. 15 and 16, are machined is illustrated therein by the superimposed heavy dash lines. From these it will be clear that there is little waste in the necessary machine work, the slots 48 necessitating the greatest loss. lVhere the tire is cured on a metal core, this source of waste is reduced, or eliminated, no slots 48 being required in conjunction with a core.

The cast steel tire mold of the present invention may be made very much lighter than a serviceable and repeatedly usable mold can be made of cast iron. The comparative weights of cast steel and cast iron tire molds having two substantially counterpart sections for receiving a tire and in the various sizes are indicated in the following table Weight 01 two halves.

Size In the rough. gfi gfig c. s o. I o. s 1.1.

655 1,377 i 420 1,095 770 1, 580 1 488 i, 210 947 1,779 567 l 400 080 1, 808 1,370 2, 520 2, 185 3,300 2,ss1 4, 365

These figures are illustrative only of the material reduction in weight that may be effected. The invention is not to be understood as limited thereto. The figures given are for cast steel molds obtained from open hearth and crucible steels of usual or ordinary compositions. By varyingthe composition of the. steel, as by using a large percentage of manganese,- say 2030, or other well-known materials of a similar character, a further reduction in weight may be effect ed. It will be noticed that in the smaller sizes, the reduction in weight is about that of cast iron molds of corresponding size. Possibly it may be found advantageous in order to secure greatly increased strength not to reduce the weight of the cast steel mold more than 20%. The invention contemplates any reduction between 1O and 80% that of a cast iron tire mold of corresponding tire size, type and inside shape.

In addition to the saving in Weight, there are other advantages in cast steel molds over cast iron molds. Their relatively thin walls enable more molds to be stacked in a vulcanizing press. Tires may be cured more quickly and with less consumption of steam. And cracking, warping and pitting are less likely, if not eliminated.

The pattern parts 14, 15, and 17, are of a core-box type of construction, and thus clearly distinguishable from an ordinary wooden pattern that is usually split to permit of obtaining a mold cavity in green sand copes and drags. In each of these patterns of the core-box type, the sand-molding face is substantially reinforced by wood in rear of the sand-shaping faces on the side thereof opposite that which is backed up by wood in a. split type of pattern. In the claims, the expression pattern of the core-box type is employed to define this feature of the invention.

This invention is believed to be broad in scope and to comprehend a variety of changes or adaptations and reference should therefore be made to the accompanying claims for an understanding of its scope.

Having thus described my invention What I claim and desire to protect by Letters Patent is: i

1. A pattern of the core-box type for annular castings of tire mold sections having at least two substantially rigid parts for separately deriving shapes in complementary sand copes and drags defining when assembled a molding cavity, one of said parts being provided with an annular groove approximating the shape of the inner face of the tire mold section and the other being provided with a projection approximating the shape of the outer face of the tire mold section. b

2. A pattern of the core-box type for annular castings of tire shaping mold sections having at least two parts each faced in replica of a side face of a tire mold section and each substantially reinforced in rear of its sand-shaping face.

3. A pattern of the core-box type for annular castings of tire shaping mold sections having at least. two parts each faced in replica of a side face of a tire mold section and each of wood substantially thicker than the casting to be made.

4. A section pattern of the core-box type for casting a sectional annular tire shaping mold, each section having a relatively stiff body portion, a circular flange rising from said body portion, and a sand shaping face carved in replica of a face of the desired casting and located below the free edge of said flange.

5. A sand mold comprising interfitting circular baked cope and drag portions formed to define when assembled together a casting cavity for an annular tire mold section.

6. A sand mold comprising baked and assembled cope and drag portions having spaced walls defining in relief and in intaglio respectively an annular casting cavity for a tire mold section which is bowed in cross section.

7. A sand mold comprising baked and assembled cope and drag portions formed to define a casting cavity for an annular tire mold section approximately convex in cross section, said drag portion being provided with a plurality of runners extending from a central point underneath the casting cavity and communicating therewith adjacent its outer perimeter, and a plurality of separate core blocks intermediate the casting cavity and bridging the several runners.

8. The process of pouring steel castings for annular tire mold sections of bowed form in radial cross section, which consists in introducing the molten metal into the center of the mold, and running it simultaneously a in several radial directions into the mold cavity whereby after pouring the metal filling the casting cavity is at a substantially uniform temperature and the shrinkage between the outer and inner peripheries is equalized so as to free the product from intolerable stresses.

9. That method of making sand molds for tire shaping mold sections which includes, forming and mating sand parts which when assembled define an annular cavity partly curved in cross section and approximately uniform in depth or thickness, providing radial runner cavities which communicate with the annular casting cavity at a plurality of points adjacent its outer periphery, introducing formed core segments to bridge the runner cavities underneath the casting cavity, applying a smoothing wash to the exposed surfaces or" the casting cavity,

and finally baking the sand mold parts.

Signed at Detroit, Michigan, this 7th day of May, 1921.

JOHN H. MULLOY.

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