US2237876A - Method of venting sand molds and molds produced thereby - Google Patents

Description

April 8, 1941. F. L AUB 2237.876

METHOD OF VENTING SAND MOLDS AND HOLDS PRODUCED THEREBY Filed Nov. '7, 1939 Patented Apr. 8, 1941 METHOD OF VENTING SAND MOLDS AND MOLDS PRODUCED THEREBY Frank L. Daub, Akron, Ohio, assignor to The Akron Standard Mold Company, Akron, hio, a corporation of Ohio Application November 7, 1939, Serial No. 303,242

3 Claims.

This invention relates to the venting of sand molds in metal founding. Where the cast article has a bottom concavity formed by an upward convexity of the molding sand in the drag, and also when the sand has a pocket adjacent to the convexity, it is observed that the adjacent metal often exhibits porosity which is highly objectionable in many articles including vulcanizing molds for pneumatic tires, where the metal of the molding cavity wall is cut away to forma smooth rubber surface. I attribute such porosity to the sealing of voids in the molding sand by the molten metal, allowing insufficient opportunity for downward escape of the gases and causing them to be forced into the casting.

The object of this invention is to improve the bottom venting of molds of the character referred to.

Of the accompanying drawing, which illustrates the invention as applied to the production of an annular casting such as one-half of a tire vulcanizing mold, although it is not wholly confined to that use, Fig. l is a partial top plan view approximately on the line ll of Fig. 2 and partly broken away, showing a sand mold constructed according to my invention.

Fig. 2 is a vertical section, approximately on the line 2-2 of Fig. 1.

Fig. 3 is a partial section illustrating preliminary steps in the preparation of the drag, in an inverted position.

Fig. 4 is a similar view illustrating later steps in such preparation.

In the drawing, II] is a drag flask having a temporary bottom board I l for supporting, in an inverted position, the pattern or patterns, core or cores and the sand for forming a mold having a cavity of the desired shape and venting it according to this Invention. The main pattern 12 in this case is shaped like one-half of a pneumatic tire mold having a concavity l3 and the usual inner and outer peripheral flanges I4, l5 under which are placed flat annular baked sand core plates or rings l6, l1. I8 is fine moist molding sand mixed with the usual other materials to make it close packing.

When the drag has been filled and rammed to about the level of the plane l9, there is laid thereon a wooden or other suitable auxiliary pattern ring 20 which has a relatively-wide top base portion 2| to make a correspondingly-shaped sand cavity or depression, and a narrower gas-channel forming portion 22, together with a suitable number of pairs of side-channel forming elbows 23 attached, as by means of nails 24, to the body of pattern 20. Molding sand is then placed around the pattern 20 and may be rammed up to its top level, after which it is withdrawn, leaving a body print, an open annular venting channel 25 and iliary pattern 20 is filled with an annular cover plate 28, preferably of metal, formed over the annular trunk channel 25 with a circumferentially distributed series of perforations 29 of fairly large diameter. After that, or previously if desired, the molding sand is further built up at 30, marginally over the main pattern to form the outer limits of a bed for a layer 3| of dry, coarse or open-grain venting sand, and in turn that is covered to the top of the flask with a rammed further filling of molding sand as shown at l8 in Fig. 2. At a suitable preliminary stage, the drag portion of a vertical gas channel 32 is formed near the center of the mold but somewhat eccentrically to avoid the hub of the cope frame, by means of any suitable pattern which is then withdrawn.

Following the preparation of the inverted drag, there is applied over the top thereof a follow-board 33 which is to become the bottom wall or closure of the drag flask as shown in Fig. 2, the drag is reverted into casting position and the original bottom board I l is removed, leaving a smooth upper parting surface at 34. The flange cores l6, ll are then temporarily removed and the main pattern l2 is withdrawn to leave a moldirg cavity 35 which includes a downwardlyvented annular pocket 35 inwardly adjacent to the convexity hi after which said flange cores are restored.

The mold is finally completed with a cope 36 having a flask 31 with the usual skeleton inner frame 38 and molding sand 39, applied over the drag. Said cope is prepared with a riser channel portion 40 in line with the drag channel portion 32 near the center, other vertical riser openings 4| for gas and sprue metal, and a pouring gate riser 42 continued downwardly into the drag at 43 and laterally at 44 into the molding cavity The complete mold having been prepared as described, the metal is then poured through the gate 42 into the cavity 35, whose outer marginal portions find suificient venting through the bottom and top molding sand and the risers 4 I. The molten metal flowing over the convexity I8 and into the pocket 35 ordinarily finds insufficient venting through the bottom sand from any molding cavity having the illustrated or an equivalent shape. According to the present invention the gases are freely vented through the perforations 21 into the lateral channels 26 and trunk channel 25 under the cavity floor, and from thence through the layer of coarse dry sand 3| and the riser 32, 40 to the top of the mold.

It will be understood that the invention could be variously modified within the scope of the claims, particularly as to the specific provision for final escape of the bottom-vented gases.

I claim:

1. A method of preparing a sand casting mold comprising, a mold cavity in a layer of packed sand, forming an open-face channel in the sand above the mold cavity, forming a plurality of relative minute passageways in the sand, extending from the channel substantially to the mold cavity, covering the open face of the channel with a perforated rigid protecting member, applying a layer of relatively coarse material to the sand and protecting member, inverting the unit, applying a cope thereto, and extending an exhaust passageway from the layer of coarse material to the exterior of the mold.

2. A sand casting mold comprising a layer of packed sand having a mold cavity, a layer of coarse material beneath said layer of sand, there being a second cavity at the junction of said layers, said sand having a plurality of relatively minute passageways extending from the second cavity substantially to the mold cavity, and means including a perforated metal plate arranged and adapted to keep the coarse material out of the second named cavity.

3. A sand casting mold comprising a layer of packed sand having a mold cavity, a layer of coarse material beneath said layer of sand, there being a second cavity at the junction of said layers, said sand having a plurality of relatively minute passageways extending from the second named cavity substantially to the mold cavity, means comprising a perforate ring forming the bottom Wall of the second named cavity and arranged and adapted to prevent any substantial amount of the coarse material from entering said second named cavity, said means comprising a substantially rigid metal member provided with perforations larger in cross-sectional area than the cross-sectional area of the passageways extending through the sand to thereby permit the flow of gases from the second named cavity into the layer of coarse material and to prevent contact between the coarse material and the passageways in the sand, and a venting conduit leading from said layer of coarse material to the exterior of the mold to discharge the exhaust gases.

FRANK L. DAUB.

Images