US2654925A - Precision casting process - Google Patents

Description

Oct. 13, 1953 E E, ENslGN ET AL 2,654,925

PRECISION CASTING PROCESS Filed June 23, 1950 3 Sheets-Shea?l l EEE/VS/G/V T; ET- RA. M4N PlE'Q/TORS ATTO/@Mfrs Oct. 13, 1953 Filed June 25, 1950 E. E. ENslGN ETAL PRECISION CASTING PROCESS 3 Sheets-Sheet 2 EJE E E, E NS /G/V RA. VAN PATTE/VV INVENTORS BY @du ATTORNEYS Oct 13 1953 E, E. ENsIGN ET AL PRECISION CASTING PROCESS 3 Sheets-Sheet 3 rFiled June 23, 1950 RAW/v PATTEN ATTORNEYS Patented Oct. 13, k1953 PRECISION CASTING PROCESS Elbert E. Ensign, Ypsilanti, and Royal Arch Van Patten, Garden City, Mich., assignors to Ford Motor Company, Dearborn, Mich., a corporation of Delaware Application June 23, 1950, Serial No. 170,008

Claims. l

This invention is concerned with the founding industry in general and more specifically with a process for the simultaneous casting of a large number of identical pieces to very close tolerances and at low cost.

The foundry industry has for some time been familiar with a molding procedure referred to as the shell process. This process is described in detail in a publication by the Oiiice of Technical Services of the United States Department of Commerce identified as FIAT Final Report No. 1168, PB81284 bearing the date of May 30, 1947. Brieily this process includes the formation ci molds by contacting a pulverulent molding material with a heated polished metal pattern. The molding material is preferably clean, fine sand with which has been mixed intimately five to ten per cent of an uncured phenol formaldehyde resin containing the usual hexamethyltetraamine as an accelerator. The molding material clings to the heated pattern and the resin partially cures in place by virtue of the heat derived from the pattern. This partially cured mold still on the pattern is now heated in an oven for a short time Ito complete the cure of the resin bond. This yields a mold having remarkable permeability and which imparts a very fine finish to castings. Ferrous and non-ferrous metals may be cast in such molds with equal facility.

This invention is not concerned with the broad ,process above outlined but rather with certain molding procedures appurtenant thereto which are perhaps best understood by reference to the drawings in which Figure 1 is a sectional view of a certain gang pattern enclosed in a container employed for applying the sand resin mixture to the heated poppet valve pattern.

Figure 2 is a plan view of the gang pattern shown in section in Figure 1.

Figure 3 is a plan view of a mold employed to produce a gate plate useful in the molding procedure. This mold is shown with a gate plate in place. i

Figure 4 is a sectional view of the mold shown in Figure 3.

Figure 5 is a sectional view of a completed mold assembly ready to receive the molten metal.

Figure 6 is an exploded perspective view of the runner plate, gate plate and gang mold.

The assignees of the instant inventors are producing by this process exhaust valves for internal combustion engines. These valves are poured from electric furnace steel having about the following analysis:

Per cent Carbon 0.30 to 0.45 Manganese 0.80 to 1.30 Chromium 18.0 to 20.8

5 Nickel 7.5 to 8.5

Silicon 2.75 to 3.25 Phosphorous 0.03 maximum Sulphur 0.03 maximum Despite the high melting point and syrupy consistency of this highly alloyed steel, it has been found possible to consistently produce a high percentage of acceptable castings with an overall yield in excess of 50%. For a casting produced by this process to be acceptable, its nish and dimensional accuracy must be such that the only machining required is a nal grind. In comparison with this performance the usual sand casting procedure gives only about a 33% yield and requires a rough cut and a ne cut to remove the excess metal before the nish grind. The conventional sand castings must, of course, be rattled prior to machining. This rattling is unnecessary when using the shell process.

In the preparation of molds for the casting of valves use is made of a metal gang pattern designated in general by the numeral I0. This gang pattern comprises in this case sixteen. individual valve patterns II arranged in four rows of four valves in each about a central down sprue I 2. These same parts are of course shown in the plan view in Figure 2.

In the preparation of the mold the metal gang mold I 0 is first dipped in a parting composition and then heated to about 300 Fahrenheit. The preferred parting composition is an aqueous emulsion containing about 5% of any of the many commercially available silicones which are marketed as foundry parting compounds. When the mold I0 has been given a coating of parting agent and heated to 350 Fahrenheit, container I3 is rotated on trunnions I4 through 180 from the position shown in Figure 1. This container is partially filled with a molding compound comprising about 7% of an uncured phenol formaldehyde resin intimately ground with fine clean sand. For the sake o-f clarity the molding compound has been omitted from Figure 1. With the container I3 rotated into the position described, the gang pattern I0 is inverted so that the valve stems point 'downward and securely fasten to the open end of container I3 by means of latches I5 (Figure 2). The entire assembly is then rotated through another 180 to the position shown in Figure l and permitted to remain in that position with the entire gang pattern l submerged in the sand resin mixture. The sand resin mixlture adheres in a thin layer to the heated pattern as the resin starts to cure. At the expiration of a predetermined period of time, container I3 with the attached gang mold pattern l0 is again rotated through 180, latches l5 are released and gang pattern lill remnved.

The gang pattern with the= adhering mold is now transferred to an oven maintained at about 650 Fahrenheit and exposed to this temperature for about one minute. This completes the eur.- ing of the mold Which can now be' stripped' from the gang pattern- This stripping is'. accomplished in the instant case by causing the valve patterns` Il lwhich are individually supported on cylinders I 6 to retreat into the surface of the gang pattern.

In the use of the mold so prepared, it has been found helpful to employ a gate plate which lis indicated by the numeral l1 in perspective in Figure 6. The manufacture of this gate plate is bestshown in Eigures and. 4.. This gate plate is produced in a gate plate. moldv |.8 shown. in plan in Figure 3 and section in Figure 4. This. gate plate mold comprises a shallow steel. box.. formed by si'de walls |19 and. bottom. plate 20... The bottom' plate 20A contains. a. plurality of. periorations, one for each of the valves and. one for the" down To form the gate plate the heated gate plate mold 1.8 is filled with the sand. resin mixture and struck od level as shown in Figure 4. When the gateplatemold. I8. is .so-filled and struck ofi', perforations are. formed in the gate plate so molded corresponding to theperforations existing in the gate plate mold I8. This procedure has. the iurther. advantage that these. perforations in. the gate plate assume a conical shape the angle of which isA equal to the angle of repose of the sand resin. mixture. This conical shape is. very useful in` securing. a. clean break. of' the castings from thev sprue as will be brought out below.

Figures. 5 and 6Y are respectively a sectioned assembly and an exploded perspective view of the mold, the, gate platel and the runner plate. In Figure 5 the mold, thev gate plate andthe. runner plate. arev shown assembled in: a box 2 l' which is provided with. angles 22. which serve to hold. the assembly together. The entire. assembly is` mounted upon slab 23. l

For the introduction expeditiously ot the molten metal, runner cup. 24. is-tted. to the top ot down sprue l2. The. use of runner cup` 24 permitsA the workman to fill this cup. with molten metal in one quick operation without the necessity of. awaiting the flow' of. *metal to the many remote sectionsof the mold. The. box 2|` is filled withV sand, spentshot or similar granular metal which serves to support the mold. against` the hydrostatic pressure ofthemetal.A

It can readily be appreciated from a study of Figures 5 and 6 the gate plate l1.- is actually used in a. position which is the reversefof that in which itis produced in thev gate plate mold. This causes the narrow portion of the perforationsl to be ad.- jacent the valve heads. and the. smooth. surface of. gate plate [.1 produced against gate plate mold- |-8s to formv the-upper surfacesA of the'valfve head. This produces. a smooth valve headand perm-its aclean break-off.

This process has been particularly describedin connection with sand-resin mixtures-butitsyscope is notso limited. The process canbe; employed with.`r the conventional drying oil! bound. core lig;

mixes, or any of the other known molding materials.

We claim as our invention:

1. The process of producing a perforated gate plate for use in the production of a number of castings in a single mold comprising applying a layer of molding material and agent to a plate having a'` perforation for each perforation desired in the gate plate, striking off said layer of molding material on said plate and curing the gate plate so produced on said plate whereby a gate plate having truncated conical perforations with their small diameters the same size asthe plate" perforations are produced.

2l The process ofproducing a perforated gate plat'e'fcar use a foundry mold comprising applying. avlayer' of molding material to a plate having a perforation corresponding to the desired perforation in the gate plate, striking off said layer of molding material on vsaid plate and curing the gate plate so= produced. whereby ai gate platehaving atruneate'd conical perforation with its small diameter the same. size as the plate perforation is: produced.

3. The process of producing a perforatedgate plate comprising' applyingV a layer' of. heat settable molding material to a. heated plate having a perforation corresponding tothe desired@ per'- f'oration in the gate plate, striking, oft' said' layer of molding material on said heated plate, further heating the combination of the1 heatedi plate-and the struck oil molding material tocomplete the cure of the molding materiali and freeing' the gate plate from the heated plate to' produce a gate plate having a truncated conical perforation with its small diameter the same size as the plate perforation. i

4. They processor producing a perforated gate plate comprising dipping momentarily a heated plateA intoY an aqueous parting emulsion, applying alayer of heat setta-ble` molding material' td the'` heated plate' having a perforation corresponding to the desired perforationL in the gate plate', striking off said layer of' molding material on said' heated plate, further heating the combination of the heated plate and the struck ofl molding material to complete the cure of the mnlding" ma terial, and freeing the gate platefrom' thei heated plate to produce a gatel plate having a truncated conical perforation 'with its small diameter the same size as thei plate perforation.

5i The process seti forth' in" claim 4 irr which the parting emulsion inciudes a; silicone com:- pound.

References enea; in the fue or this. patent UNITED STATES PATENTS.

Number Name Datei 772,720- Itadwig.. Oct. 18,1 1190.4 1,055,47 9 Longstaff et al Mar. 1.1;.1913 2,0%;? Campbell Get. 26; 1937 OTHER REFERENCES Y FTA-T Final; ReportiNo. 15168, published; April 8, 1948; lvletalV Industcm. Dec.. 19;. 1941,. Precisibn Moulding, pagie1506.` Silicone' Mold. Lubricants-, published: by Gen. Electric; 2Y pages.. Feb. 183.1949..

Molds fromV DurezA Resin and Sand,v 3vr pages,

May 19; 1950;.

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