US2513785A - Method of manufacture of matrices and casting beds - Google Patents

Description

July 4, 1950 T. c. BROWNE 2,513,785

METHOD OF MNUFACTURE OF' MATRICES AND CASTING BEDS Filed April 25, 194e 2 sheets-sheet 1 L?? Tlgi. j;

ufff 1| @ggg TLQE July 4, 1950 T. c. BRowNE 2,513,785

METHOD OF MANUFACTURE 0F MATRICES AND CASTING BEDS Filed April 25, 1946 2 Sheets-Sheet 2 36 30gb l i| 35 33 g%gwwgegg@gvvf 31 Q T F Hoi Air or RadiumL Energy Thermoplastic Diaphragm /4l Inventor Patented July 4, 1.950

METHOD F MANUFACTURE `OF MATRICES AND CASTING BEDS Theodore C. Browne, WinchesjsenvMass., assigner yto Dewey and Ahny Chemical Company, North Cambridge, Mass.,., a corporation of. Massachusetts Application April.25, 1946; Serial No.v 664,931

6 Claims.

My present invention relates to a rapid and e-hcient method of making molds or casting beds.

Heretofore it has been proposed that molds or casting beds for orthopedic impressions, for `inw stance, of feet for corrective lasts and anatomical patterns for the design of chair seats be made by taking the impression upon a bed of sand covered with a flexible diaphragm such as a rubber sheet.

Then, after the impression is made in the sand and while the sand is still under pressure from the pattern, exhausting the air from beneath the diaphragm.

This procedure was based on the discovery that, if air is exhausted from the sand while the sand is under pressure from the pattern and consequently is in close-packed condition, it will retain close-packing land permit the Whole body of sand to `act as a massive solid as long as the Vacuum is maintained. On the release of the vacuum, however, close-packing is no longer maintained, and the whole mass reverts from a solid system toa mobile system. This phenomenon is ordinarily referred to as di1atancy.

Such a procedure has been used electivelyto produce molds or casting beds having rounded or gentle contours. But when the contoursare sharp or `when there are substantial projections, as in the case of type or other sharply -outlined patterns, I have found that sharp denition, if it is initially produced at all, is not maintained.

There may be several reasons for this. First, the diaphragm fails to follow the contours in the sharp indentations of the pattern. Instead, it bridges between the projections. Second, When the vacuum is drawn, the diaphragm tends toipull against what should be the sharp cornersof the sand and tends to round them off. Third, the diaphragm becomes pinched between the projections of the pattern and the sand immediately beneath so that some parts of the diaphragm are tightly stretched and do not follow the outline of 'the relief.

'When gentle contours are reproduced, these difculties do not appear, and the mold or matrix which is produced by using the dilatancy prnciple has considerable stability. But perhaps the most serious difficulty, which prevents theuse of such a molding'bed in pressure moldingoperations, is the lack of lateral strength orthe stability of what may be termed the columns of sand. This possibly occurs because, as the pattern is forced against the diaphragm and down into the sand, the maximum pressure and hence the maximum packing concentrates directly beneath the projectionsof the-pattern while the pressure .in

2 theA low areas (for example, theshoulder areas of type) -is rlow or non-existent. In any event, a molding.compoundl for-ced laterally against a vertical matrix ywall meets small resistance, and the walls collapse.

' M-y -invention isbased` on the discovery that, if the-pressureapplied to the sand is uniform over the wholearea independently of whether or not afprojectionpr a depression is involved, true closepackingisproduced throughout the whole sand mass and the strength of the `mold is thereby greatly-increased,particularly in shear, so that the walls-of the `projections havestability enough to withstand the lateral flowof a molding composition, .and that such uniform pressure maybe obtained by lllrst bringing the diaphragm into full enveloping contact with the pattern, allowing the sand toflll and form a negative pattern contour onthe v`opposite side ofthe diaphragm and then placingthewholebed of sand .under compression. Sincethe l.vv-hole bed ofsand is under uniform compression ,the distribution of ypressure appreaches thehydraulic ideal. Lateral compaction as 1well as column Vpressure is, secured.

.-My .new method also produces the maximum definition in the mold. Because the diaphragm islv moved into full enveloping contact with the pattern and is,l maintained in such contact beforeany pressurewhatever is applied to the sand, I `haveiound that the. process is suitable for the reproduction yof patterns of many descriptions, molded parts, costume decorations, buckles etc., butvfor convenience and brevity indescription and illustration, I describe the process as applied to the reproduction of type.

The invention maybe better understood .by reference to the drawings in Ywhich Figure 1 is a longitudinal cross-section through ,the matrix or sand box;

. ,Figure 2, is arlongitudinal crossfsection through the. pattern 0r, type box; d

Figure 3 is la 4longitudinal cross-section view of Athetvvo,parts,superposed on a press ram before Ath'eiormation, of the matrix;

Figure 4 isy the same longitudinal cross-section Viewv after compression; fand ,Figure 5 is aV fragmentary cross-section ofthe ,completedmatrix ready for subsequent molding operations.

Figure ,6 illustrates a variant of the process shown inFigures 2 and 3, wherein the relative positionsof pattern fchamberand ,sand bed have Albeen reversed.

, The`r apparatus comprises `,a matrix or sand box ,40. Topermit .the `uniform Withdratvall of air,

amres the box I has a step I I formed in its walls I2 upon which is fastened a stiff perforated metal plate I3. Studs 23 stffen and support the plate. A layer of stiff screening I4 is fitted over the plate I3 and upon this is placed a filter pad I5; depending upon the size of the sandv grain, this may be felt, paper, or a ceramic or sintered metal filter plate. wall I2 by a holding fillet I6.

The top surface of the wall I2 terminates in a sofi'l rubber gasket I1, the purpose ofy whichis to prevent cutting and tearing of the thin The lter I5 is sealed to the side duced pressure with respect to the external presrubber diaphragm I8 which is stretched over the f sand S and held in place by a` cord or spring seizing I9 fitting into the groove 20 cut in the Outside of the wall I2. A flexible hose 2| connects the port 22 in the sand chamber Ywith a vacuum pump (not shown).

The pattern or type chamber consists of a sha low box 30 having walls 3| topped by a stiff perforated plate 32, which is also supported by the studs 31. To prevent the type from shutting off the flow of air, the top surface ofthe plate 32 is knurled, or it may be covered with a fine mesh wire screen. An angle iron frame r33 is attached to the plate 32 to provide an abutment for the quoins or to center the chase as the case may be. (For simplicity of illustration the quoins and furniture are indicated by the cross sectioned blocks Q. AA chase has not been shown.) A sponge rubber gasket 34 is mounted around the margin. A flexible hose 35 connects the port 36 in the box 3i! with a vacuum pump (not shown).

The type is mounted in theA type, box in any suitable manner (usually the whole chase is laid in the box). The furniture and quoins are covered with felt, indicated at F in Figure 3, to prevent cutting and injury to the diaphragm, but to allow proper seating, a free space over the quoins and furniture is left to receive the displaced sand. The volume ofthe free space should equal the volume of the plate one intendsr to produce.

In operation, the pattern or type box 30 containing the type T, is placed on the ram 40 kof a press. The sand box IB is then placed on top of the type box 3!A with its diaphragm I8 engaging the'gasket 35 of the type box as shown in Figure 3. Bearers ilI are placed.` between the press platens so adjusted that by compression of the sponge rubber gasket the proper plate thickness will be produced. vFor example, to produce a plate of 0.183 inch thickness, a bearer height is chosen which will project the face of the type 0.183 inch into the sand box when the press is fully closed. Y y

Then the press is closed with just enough pressure to compress the sponge rubber gasket slightly and make an air-tight seal between the parts I0 and 353. Air is now exhausted from the type box Awhile the port 22 leading into the sand chamber is fully open to the atmosphere. This operation forces the diaphragm 'into complete contact with the type, and since the diaphragm is stretchable as well as flexible, it .molds itself about the minute details` of the type, for example, the serifs. Alternatively, air pressure applied to the sand while the pattern box 30 remains at a lower pressure will produce the same result. The sand falls into place. Its proper and uniform rearrangement may be assured by vibrating the sand box with a foundry flash vibrator. Then the press is closed to the bearers, the

This puts a uniform pressure on' the The diaphragm is not moved i or stretched during the compression, and the columns of sand whether rising from the face of the type or from the type shoulder are under equal pressure.

After the press is seated, air is exhausted from the sand box through the pipe 2 I, and thereafter air is admitted to the type box through the port 36. Then the press is opened and the parts I0 and 30 separated.

As long as the sand box I0 remains under resure on its diaphragm, the matrix which the previous operations have formed has considerable rigidity and `may be used for casting, electroplating', or for low pressure molding by procedures which are otherwise conventional and are', therefore, not further described.

Avaluable property of the matrix so formed is its self-destructibility. When the molding or casting operation is complete, the vacuum is turned off and air is admitted through the port 22. The matrix immediately becomes mobile and releases itself from the finest details of the cast or molded materials.

As a variant in the process, the diaphragm may be made of a heat softenable sheet material such as, for example, rubber hydrochloride, poly vinylidine chloride and polyethylene, and the diaphragm uniformly heated before the vacuum is drawn in the pattern box. Extremely delicate castings may be made, for the softened, plastic diaphragm molds itself about the pattern without tension and follows the pattern with microscopic fidelity.

The method of carrying out this variation of the process is illustrated in Figure 6. Some press constructions make it more convenient to reverse the relative positions of the pattern chamber and the sand bed with respect to the press. Whether this is desirableor'not is dictated by the particular press. The drawing illustrates the pattern chamber attached to the upper bolster 42 of a hydraulic press Q3. The sand chamber is shown placed on the press ram 4B. The diaphragm I8a, in this case made of one of the heat-softenable materials as above described, is heated to a liowable, plastic state prior to forcing the diaphragm into contact with the pattern. Preferably this is accomplished by focusing radiant energy derived from a bank of infrared lamps on the surface of the diaphragm. This is preferred because of the ease of adjustment and the uniform radiation pattern which may be secured on the diaphragm. As a further alternate, hot air may be blown against the diaphragm, but is not so convenient because it is harder to obtain a uniform heat distribution. When the diaphragm has been brought to the proper temperature, the press is closed, the air is exhausted' from the pattern chamber, and the process thereafter continues throughout as previously described. The elements of the sand bed and the pattern chamber being the same, the same reference numbers are used. y

The definition which may be secured is vdetermined by the maximum size of the sand grain and the thickness of theV diaphragm if this be flexible and extensible. The ner the grain and the thinner the diaphragm, the greater is the definition. Twenty-four point type can be reproduced effectively with a diaphragm of chloroprene (unloaded save fo-r vulcanizing ingredients) .0035 thick and sand grains passing mesh.

The lword sand has been chosen as a convenient generic word. I have used ne glass beads tic diaphragm into intimate contact with a pattern and then bringing a bed of comminuted material having a fluid between the particles of said material on the other side of the diaphragm into intimate contact with the already shaped diaphragm, subjecting the comminuted material to pressure to cause it to assume a close-packed condition and maintaining said close-packed condition during molding by removing the uid from the bed of comminuted material.

2. The method of molding which includes the following steps: iirst bringing one side of an elastic diaphragm into intimate contact with :a pattern and then bringing Ia bed of comminuted material having a fluid between the particles of said material on the other side of the diaphragm into intimate contact with the :already shaped diaphragm, subjecting the comminuted material to pressure operative laterally within said material as 4well as generally in the direction of the body of the pattern to cause it to assume a closepacked condition and maintaining said closepacked condition during molding by removing the uid from the bed of comminuted material.

3. The method of molding which includes the following steps: softening a diaphragm of a heat softenable substance by heating it, bringing one side of said diaphragm into intimate contant with a pattern and then bringing fa bed of comminuted material having a fluid between the particles of said material on the other side of the diaphragm into intimate contact with the already shaped diaphragm, subjecting the comminuted material to pressure to cause it to assume a close-packed condition and maintaining said close-packed condition during molding by removing the uid from i the bed of comminuted material.

4. In matrix forming apparatus, a sand-bed having a flexible gas-excluding diaphragm, means to remove a gas from the sand-bed, a pattern Chamber having lcompressible walls, means for removing air within the pattern chamber to cause said sand-bed diaphragm to advance into full contact with a pattern contained in said chamber, and means to cause the pattern chamber walls to compress and compact the sand-bed upon the pattern.

5. The method of molding 'which includes the following steps: rst bringing one side of an elastic diaphragm into intimate contact with a patternand then bringing a bed of sand having i a fluid between the particles thereof on the other side of the diaphragm into intimate contact with the already shaped diaphragm, subjecting the sand to pressure to cause it to assume a closepacked condition and maintaining said closepacked condition during molding by removing the fluid from the bed of s-and.

6. The method of molding which includes the following steps: rst bringing one side of an elastic diaphragm into intimate contact with a pattern, removing air from the space between the diaphragm and the pattern, bringing a bed of comminuted material having a fluid between the particles of said material -on the other side of the diaphragm into intimate Contact twith the already shaped diaphragm, maintaining the lair pressure on the pattern side of the diaphragm below the pressure on the opposite side thereof, subjecting the comminuted material to pressure to cause it to assume a close-packed condition and maintaining said close-packed condition during molding by removing the fluid from the bed of comminuted material.

THEODORE C. BROWNE.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 271,494 McClellan Jan. 30, 1883 1,154,255 Landis Sept. 21, 1915 1,737,874 Busch Dec. 3, 1929 2,132,185 Prayale et al.y Oct. 4, 1938 2,172,243 Goodno'w et al Sept. 5, 1939 2,309,865 Reach Feb. 2, 1943 2,326,381 Milligan et al Aug. 10, 1943 2,354,916 Hurt Aug. 1, 1944 2,377,946 Leary June 12, 1945 2,390,129 Shobert Dec. 4, 1945 FOREIGN PATENTS Number Country Date 392,952 Great Britain Nov. 21, 1930

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