US2396195A

US2396195A - Method of making patterns

Info

Publication number: US2396195A
Application number: US569733A
Authority: US
Inventors: Herbert J Pattison
Original assignee: Briggs Manufacturing Co
Current assignee: Briggs Manufacturing Co
Priority date: 1944-12-26
Filing date: 1944-12-26
Publication date: 1946-03-05
Anticipated expiration: 1963-03-05

Description

meh 5p 1946o H. J. PATTlsoN 2,395,195

METHOD OF MAKING PATTERNS Filed neg. 26, 1944 Patented Mar. 5, 1946 UNITED STATES QFFICE BIETHOD F BIAKING PATTERNS Herbert J. Pattison, Grosse Pointe Park, Mich., assigner to Briggs Manufacturing Company, Detroit, Mich., a corporation of Michigan Application December 26, 1944, Serial No. 569,733

12 Claims.

This invention relates to the production of patterns for use in preparing foundry molds utilized in the casting of metals, an object of the invention being to provide an improved method for reproducing or duplicating any existing master pattern, model or article so as to increase the productive capacity of the foundry in casting articles corresponding to the master pattern, model or article.

A further object of the invention is to provide an improved method for duplicating or reproducing a master pattern, article or model while at the same time compensating for shrinkage so that the production castings made from the pattern duplications or reproductions will in no case be undersize and in fact may, if desired, be oversize to any predetermined amount so as to allow for the removal of surface metal in finishing operations.

Another object of the invention is to provide an improved method of making patterns by reproducing an existing pattern, article or model and in such manner that the pattern reproduction will have sufficient oversize to compensate not only for shrinkage of the production casting but also for any machining operations necessari7 for finishing the surfaces of the casting.

Still another object of the invention is to provide a new and improved method of making pat terns for use in preparing foundry molds, in which a plaster or other impression is taken of the article to be reproduced and a pattern casting is made in this impression from a metal or metallic allogghaving the property of growing in size after it Has congealed and stood for a period of time. When the growth of the pattern casting has proceeded to an extent giving the desired oversize, a plaster or other impression is taken of the oversize pattern after which the iinal pattern is cast in this impression resulting in the production of a pattern for use in preparing foundry molds having the required oversize to compensate forshrinkage of the production castings as well as any needed iinishing of the surfaces thereof.

This application is a continuation in part oi' my application Serial No. 510,131, led November 13, 1943.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawing forming a part of this specication wherein like reference characters designate corresponding parts in the several views.

Fig. 1 is a sectional view oi a flask containing a metal pattern or other article to be reproduced and illustrating the step of forming a plaster irnpression within the flask.

Fig. 2 is a sectional view of a iiask containing the plaster impression and illustrating the step of forming a preliminary pattern casting within the flask.

Fig. 3 is a sectional view of a i'lask containing the preliminary pattern casting and illustrating the step of forming a plaster impression within the ask. i

Fig. 4 is a sectional view of a liask containing the last mentioned plaster impression and illustrating the step of forming the final pattern reproduction within the flask. l Before 'explaining in detail the present invention it is to be understood-that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawing, since the invention is capable of other embodiments and of being practiced or carried out in various Ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

In the drawing there-is illustrated, by way of example, a suitable masterv pattern, article of model ID to be reproduced or duplicated so as to provide a pattern which may be used in preparing a foundry mold. Inasmuch as any article, such for example as a iinished production casting or a master pattern or model, may be reproduced in accordance with the present invention, it will be understood that the article l0 may be of any type or category in which backdraft is eliminated so as to permit an impression to be made of the article utilizing suitable moldable material for this purpose, such as plaster or calcined gypsum. In carrying out the first step of the method the pattern or article i0 to be reproduced or duplicated, which may be of metal, wood or other suitable material, is placed within the bottom of a iiask H supported upon a table or other suitable base. Where plaster is used to make the impression of the exposed side of the article I0, the plaster or calcined gypsum is mixed with water to produce a flowable material which is poured into the ask and allowed to set, thus providing a solid mold impression l2. The mold impression is then removed from the flask and allowed to dry.

In carrying out the second step of the invention illustrated in Fig. 2, the plaster impression !2 is reversed and placed upon a supporting plate I3 within a suitable fiask i4 held in position upon the supporting plateby means of locating dowel pins l5. Mounted upon the upper edge of the flask le is a cover plate or closure member I6 notched or grooved along its edges at Il to receive the upper edges of the flask and position the cover plate I6 properly with respectlthereto. This plate is provided with pairs of shrink-control depending ribs i8 extending la suitable distance within the ask and is also provided at one side thereof with an opening or hole I9 through which molten metal may; be poured into the space between thelcover plateu and the plaster impression l2 to provide a cast impression 20 of the upper side ofthe plaster,

The ribs I8 Vattheunclerside:offV the cover plate I6 are bounded bya'groove-or` channel |6a extending around the four sides, of the cover plate providing in the casting 2Q' This marginal rib Y,

member I 2.

a continuous marginal rib 2l. is joined by longitudinal ribs and also byacentral transverse'rib 22 connecting'two opposite sides ofthe ribl 2l. The depending-ribs IS serve to quickly chill the metal within the cavityl by rapidly conducting the heat from the molten metal away, thereby eliminating shrinkage or other defects on the working surfaces of the pattern casting. The ribs '2l and 22 provide ameans by which the casting 20, when inverted, may be supported evenly upon a base in orderto carry out the next step of the method.

The metal employed in forming the/prelimi-v nary pattern casting '20 is preferably alow melting alloy which has very low shrinkage properties when the'metal in molten state congeals o1' solidifies and which' after solidiication will grow in size when allowedtostand for a predetermined period of time. One low melting point alloy. which may be usedfor the purposes of the` present invention, is an alloy of 58% bismuth and 42% lead known commercially as Cerrobase having a melting point of approximately 285 F. A castingY formed from this alloy. such as the pattern casting- 20, will shrink to little or no extent when the molten metal congeals and solidies. However, after the casting has been removedfrom the ask and'allowed to stand for a number of hours; the casting will grow in size; This growthis uniform in alldirections and the amount of oversize may be predetermined by the length of time which the pattern casting 20 is allowed to stand. For example, the casting 2D after removal from the ask I4k may be permitted to erow'to a predetermined amount such as .005 per inch.

When the pattern casting 20 has reached the proper oversize, it'is inverted andmounted within av iiask 23 and awet plaster mix is poured into the ask to produce a mold impression 21S. After the plastermaterial within the ask has set sufciently it is removed therefrom and'thoroughly dried. Thus'. it will be-seen that inthe stepof the method illustratedin Fig. 3 a plaster impression 24 is made of the oversize pattern casting 2li and, hence, the mold impression 2li' As in'. thecase ofthe closure platel 6, the closuremem ber 28 is so constructed as to control the shrink- :the member 28 is formed with a marginal groove or channel 28a extending around the four sides thereof and is also provided with cross-channels or grooves forming intervening ribs 3K) of substantial depth and width. The closure or cover plate 23 is also provided with a. pouring aperture 3l VV.through which molten metal, such as brass, is

poured to produce the final pattern casting 32. This castingywill be provided with a continuous marginal rib 33 extending around the four sides thereof and cross-ribs 3ft.

Assumingvthatthe preliminary pattern casting 2i! 'is allowed to grow to an oversize such, for example as .005 per inch, and also assuming that the allowance necessary for the shrinkage of the metal forming the castingf32 andthe shrinkage of the iinal production casting is in each instance .002 per inch, it will be seen that the mold impression 24 taken of the oversize pattern casting 29 will in effect have a double shrinkage value of .004 per inch plus an additional amount'of oversize of .001 perlinch. Having assumed, for purposes of illustration, that the metal forming the final pattern casting 32 will shrink .002 per inch, then it will be apparent that-this'pattern will be oversize an amount equal 'to .003 per inch. Thus, a production mold of plaster or other molda-ble material formed from the nal pattern 32 will provide a castingv cavity which' will be'oversize an amount equal'to .003 per inch. This oversize will not only allow for the shrinkage of the production casting, assumed lfor the purposes of illustration to be at the rate of .002 per inch, but in addition will allow an amount of metal equal to .001 per inch to be removed from the surface of the production casting in finishing operations. After this amount of metal hasbeen removed in the nishing operations the nal production casting will be substantiallyz the-exact sizeof Ythe master pattern, model or article I!) employed in making the initial mold impression l2.

Thus. it will beseen that by preparing the intermediate vpattern casting 2U from a metal alloy having the property of growing or increasing in sizeafter standing, it is possible to'produce a final production pattern 32 having sufficient oversize to allow for shrinkage ofthe production casting as well as 4the removal of metal in argv machining f operationsy needed to finish the surfaces'thereof.

The allowable growth of the pattern casting 28 may be controlled within exact limit-s in order` to meet requirements and when the predetermined oversize has'been attained the plaster impression 24 is made after which the nal pattern 32 is poured in the flask 26 as previously described.

The example given above is especially applicable to the production of a foundry pattern from an article, such as a production casting, which cannot be practicably used as a pattern in the preparation of foundry molds since such casting has no oversize allowance for shinkage of metal cast in such molds. In the event the article l0 is a foundry pattern, which it is desired to duplicate, and which pattern has an oversize allowance for single shrinkage;v then the amount of growth ofv the pattern casting 2B need not be as great as vwould be necessary in the example given above where itis necessary to provide for double shrinkage. In such instance, assuming the article lil is a production pattern having a single shrinkage allowance, the pattern 20 willl be allowed to grow an amount greater in size than the size of the pattern Hl sufficient to offset the shrinkage of the metal used in casting the final pattern 32 which will then be a duplication in size of the pattern Iii. Additional growth to com pensate for finishing operations may of course be permitted as in the example given above.

I claim:

1. The method of producing a metal pattern, including the steps of making a mold impression of an article to be reproduced, casting a pattern in said impression with a metal having the property of growing in size when allowed to stand, allowing said pattern casting to grow to a predetermined oversize, making a mold impression of said oversize pattern casting, and casting in metal a pattern from said last named mold impression.

2. The method of producing a metal pattern, including the steps of making a plaster mold impression of an article to be reproduced, casting a pattern in said impression with a metal alloy having the property of growing in size when allowed to stand, allowing said pattern casting to grow to a predetermined oversize, making a plaster mold impression of said oversize pattern casting, and casting in metal a pattern from said last named mold impression.

3. The method of producing a metal pattern, including the steps of making a mold impression of an article to be reproduced, casting a pattern in said impression with a low melting metal alloy having the property of growing in size when allowed to stand, allowing said pattern casting to grow to a predetermined oversize, making a mold impression of said oversize pattern casting, and castingr in metal a pattern from said last named mold impression.

4. The method of producing a metal pattern, including the steps of forming from moldable material a mold impression of an article casting a pattern in said impression from a metallic alloy having growth producing properties. allowing said pattern casting after cooling to stand for a predetermined period of time so as to grow uniformly to a size greater than said articlethen making a mold impression from said pattern casting and casting a metal pattern in said last mold impression.

5. The method of producing a metal pattern, including the steps of forming from moldable material a mold impression of an article. castingr a Dai-.tem in said impression from a metallic alloy having growth producing properties and adapted to melt at a temperature below 300 F.. allowing said pattern casting after cooling to stand for a predetermined period of time so as to grow uniformly to a size greater than said article, then making a roold impression from said pattern cast.. ing and casting a metal pattern in said last mold impression.

6. The method oi producing a metal pattern. including the steps of forming from moldable plaster or gypsum material a mold impression of an article, casting a pattern in said impression from a metallic alloy having growth producing properties, allowing said pattern casting after cooling to stand for a predetermined period of time so as to grow uniformly to a size greater than said article, then making a plaster mold impression from said pattern casting and casting a metal pattern in said last mold impression.

7. The method of producing a metal pattern.

including 'the steps of positioningan article'in a flask, pouring a wet plaster mix into the flask to produce a mold impression of said article, drying and positioning said mold impression in a ask, pouring molten metal into said flask to produce a pattern casting from said mold impression. said metal having the property of growing in size when allowed to stand after a casting operation, allowing said pattern casting to stand for a predetermined period of time so as to increase a predetermined amount in size uniformly throughout all dimensions thereof, positioning the oversize pattern casting in a ilask, pouring a wet plaster mix into the flask to produce a mold impression of said oversize pattern casting, drying and then positioning said last mold impression in a fiask and casting a metal pattern in said last mentioned ilask of said last mold impression.

8. The method of producing a metal pattern, including the steps of positioning an article in a flask, pouring a wet plaster mix into the flask to produce a mold impression of said article, drying and positioning said mold impression in a flask, pouring molten metal into said ask to produce a pattern casting from said mold impression, said metal comprising a low melting alloy having the property of growing in size when allowed to stand after a casting operation, allowing said pattern casting to stand for a predetermined period of time so as to increase a predetermined amountl in size uniformly throughout all dimensions thereof up to .005 per inch or less, positioning the oversize pattern casting in a ask, pouring a wet plaster mix into the iiask to produce a mold im pression of said oversize pattern casting, drying and then positioning said last mold impression in a flask, and casting a metal pattern in said last mentioned flask of said last mold'impression.

9. The method of producing a metal pattern, including the steps of making a mold impression of an article to he reproduced, casting a pattern in said impression with a metal having the property of growing or increasing uniformly in size when allowed to stand after a casting operation, allowing said pattern casting to grow an oversize amount necessary to allow for double shrinkage, making a mold impression of said oversize pat tern casting, and casting a pattern in said last mold impression which after shrinkage and cooling has an oversize suflicient to allow for the shrinkage of a production casting made in a mold formed from said last named pattern.

10. The method of producing a metal pattern, including the steps of making a mold impression of an article to be reproduced, casting a pattern in said impression with a metal having the prop erty of growing or increasing uniformly in size when allowed to stand after a casting operation, allowing said pattern casting to grow an oversize amount necessary to allow for the shrinkage of a metal cast in a mold prepared from said pattern casting, making a mold impression of said oversize pattern casting, and casting a metal pattern in said last mold impression.

11. The method of producing a metal pattern, including the steps of making a plaster mold impression of an article to be reproduced, casting a pattern in said impression with a low melting metal alloy having the property of growing or increasing uniformly in size when allowed to stand after a casting operation, allowing said pattern casting to grow an oversize amount necessary to allow for double shrinkage, making a plaster mold impression of said oversize pattern casting, and casting a pattern in said last mold impression which; alter shrinkage; and cooling has an f over-- sizesuiicientzto -allowffon the kshrinkage ofia, production; castingmadepina mold formed from said 1ast1namedfpattern 12. yThey method; ofg producing ametalY pattern, including: the stepsl ofmaking; a plaster. mold impression; of; an article, to be reproduced. castingV agpatterninsaid impression withvalow melting metalalloy havingthe yproperty yof growing lor increasing: uniformlyv in vsize when allowed to stand after .a castingv operation.` allowingy said pattern casting tovgrow` an oversize amount vnecessary to allow for the shrinkage vof a metal cast in a` mold prepared from said pattern casting,. making a plaster mold impression ofv said oversize pattern casting, and,4 casting. a metal pattern inrsaid last mold impression.

HERBERT J. PATTISON.