US2400482A - Resin casting mold - Google Patents

Description

J. Al.. BRANNQN I :TAL 2,400,482

. May 21, 194e.

RESIN CASTING HOLDS Original Filed Dec. 20, 1958 2 Sheets-Sheet 1 nNvZ @NNW N ,wAM m NR. R o0. `@5A m .NLL Lf sm A E @d Mmmm `AT JS Mvay 2l,v 1946.

J. L, BRANNoN Erm..

i RESIN CASTING HOLDS Original Filed Dec. 20, 1938 2 Sheets-Sheet 2 ATTORNEY Patented May 21,1 14943 UNITED STATES' PATENT- f orner-1 I o RESIN gdgcmonn l original application December zo, 193s, serial No.

246,778. Divided and this application January 2v, 194e, serial No. 428,340

5 Claims.

This invention relates to the casting of resins and molds for that purpose;

In a copending application Serial No. 246,778, Aiiled December 20, 1938, now Patent No. 2,273.,- 926, there is described the preparation of .dip or slush molds by means of arbors, the mold so obtained and the casting of resins therein; the claims of that application` are directed to the arbor. This is a division of that application and is more particularly directed to the molds and the is jarred loose or stripped therefrom to-give a mold commonly called a slush mold.

. As heretofore madereach unit slush mold comprises one or more open top individual forms depending from a plate about which there is anA upstalndingv rim. The presence `of the rimor bounding strip of metal follows from the type of arbor used which consists of a backing plate from which the fingers (or positives) project; in

the dipping or. such anarbor Y1t .is necessary .te ,o partially immerse the backingvplate to'insure a v continuous shelll or negative, and it is the lead which rises around the sides of the backing plate that forms the rim. Suchl a rim varies in height and thickness, depending on the depth and length of time of immersion; but it is usually thin, easily distorted and irregular in shape. In

\ a casting operation the upstanding rim, if it has not become c rimped or bent, serves to conne the resin that necessarily iarbured in excess on the top of the mold; it is therefore regarded as forming an overiiow chamber. l The commercial practice'of casting resins con sists in pouring each unit slush'mold or shell individually from ladies: and lwith such' a' prac tice 'the overflow chamberis useful and necessary for preventing spillage of resin over the sides. 'Ihe excess of resin retained in the overow chamber' is usually scraped over into adiacent unnlled molds during the pouring operation.

Pouring of resin into a hand ladle and then filling the molds individually and scraping'the excess from each, however,jis a slow and tedious of strength of the top section make it almost im' the casting of resin;

A further disadvantage of present commercial practice is that the castings in themolds, after hardening in an oven, must heseparateiy ejected from each mold by hammering. Ejcction in auto-v matic machinery has not been successful because the presence -of the irregular overflow chamber,

the non-uniformity of the molds, and the lack possible to center and support the molds in a press for multiple ejection.

The present invention provides molds which- Acan be handled or made use ofvin ways that are not possible with rim -molds as made heretofore.

Furthermore surprising economies ofoperationY can be obtained; in fact manufacturing costs of o resin castings have been lowered to less than half by their means. In the main the molds are distinctive in having skirts or sides depending from fiat ledges encompassing open top molds, and they possess the three .maior characteristics of a iiat top, uniformity of contour and rigidity or strength; it is these characteristics in combination that in turny have made possible the changes in processing with consequent far reaching economies in producing castings. Arbors for the preparation of such molds are described an @claimed in the parent application.

In the accompanying drawings:

casting molds arranged in a stack orgroup for Fig. 2 is a perspective view partly in vertical section of a unit casting mold and illustrating as.

. well resin castings in the individual forms;

Fig. 3 is a perspective view of a mold similar to that of Fig. ,2 but with a closer spacing tor the Fig. 6 is a perspective view of a gang'eiection means with a mold mounted therein. f

operation; not only does it demand 'considerable manual labor, but'- it delays the pouring while.

all'the time the resin in the kettle is thickeningtomakethepouring andtheremovalofbubbles formed in the castings increasingly dimcult. 55

'straight sidesv or skirts Il, and these A unit mold. as shown inligis. 2 andcm- I prises a fiat top il from'which extend the nega tives or individual casting shells Il. having the open top .molding cavities; the cavities may beof any cross .section as circular. polygonah etc.

Bounding theI edge of the top Il are the ilat are preferreinforcablyofadepthandthicknesstoactas ing beamstothetopwiththemetaibridgingover as at Il between the skirt anda shell to provide a solid structure that resists distortion.

'rae 'meid nu the nai topic and The top il can have a periphery 'of any configuration, but preferably it is a regular polygon in contour-triangular, square,v hexagonal etc.-

i so that a' number of unit molds can' be grouped together to form a composite mold as illustrated in Fig. l.

'Ihe unit molds arey conveniently assembled or racked upon-a large at surface as a table topy or plate 20; because of their regularly contouredilat tops they ilt into each other to form a continuous ilat surface perforated by the cavity openings. About the exposed sides of the assembled molds there can be drawn and secured a strip 22, lsuch as a gum paper, a metal tape or aremovable frame, to form a retaining wall and pre--l the valve is opened for the iiow of resin." Thel resin is first permitted to strike-asclid `part of the top I0. so that it runs by `gravity over the surface into the nearest mold cavities i2; as these cavities become filled; the whole assemblage is slowly rolled under thestill discharge to have al mass of liquid resin on the top owing s thereover and into additional moldcavities.

With the' movement of the assembly,A surplus resin on the top is pushed by the scraper 3l to iiow into uniilled cavities; vby this means-there is no excess of accumulatingl on'the tops il of the molds. 'I'he labor and time for this operation is but` a smallfraction of that demanded by the use of hand ladies and the pour-l ing of the individual molds. i

There are additional advantages in this method of casting. In the of resin bya. ladle` into'the molds, the castings commonly contain bubbles which. have been introduced.v in the pouring operation and .have' not risen'. to the stream of resin directly from the kettle to the molds, the iil'uid mass on the top ilows. by gravity.

assisted by the scraping' action, over the edges into .adjacent mold cavitiesand air bubbles are'y not formed in the castings. Also the more rapid and continuous flow of resin from the still or reaction kettle promotes the"uniformityot\the castings; and the entire still content, which may be as large as several thousandfpoimds, can be utilizedquickly in the one casting operation. Less of resin through spillage is obviated, since the resin does not leak to anylsubstantial extent in' the narrow crevices between the unit molds during the brief period offtime that the resin news or is pushed over the .crevicea A more thorough scraping of the resin from the top of the molds is also made economically practical by.th is method and brings about al further saving of resin. l A form of unit moldis showninll'ig. 8in

' which the mold cavities Il have lolidseparating walls 4|. Thisgives asturdierandlessdistortable meid; and the bottom n is levela'ndevem In Figs. i and 5, a similar ltype `ofmoldbut iaviiigan mee aanwas.

the annular casting cavity Il isenclosed by the external wall Il. and the internal wall l2.y Buch e meid is obtained' with en arbor in wiiieh the depending positives or lingers are tubes.

The molds when illled with the viscous resin" are-placed in ovens and heated at temperatures 5 and for periods of time thatcause the vresin to l0 of castings from the mold can lbe much simpli- "ed. 'The customary methods are manual operations: simple or highly tapered shapes ,are usually hammered out by striking the bottom 6i of the mold cavity with a mallet, and when this is not practical .an air hammer and pin are y commonly used 'to eject each casting separately. Election by a press has heretofore been impractical and generallyv impossible because of the weak upstanding vrim of the overflow chamber, the non-uniformity of the molds and the lack of strengthin the top section; non-uniformity in size and shape interferes with center-v ing and holding the mold for the election pins to strike at the proper points and, since considerable force is required to penetrate the metal, a weak top section oilers insuillcient support. The molds of this invention, however, lend themselves to ejection in a press, for a top section of uniform contour permits inverting a 3g moldand accurately centering it ina frame,

through the metal shell and into each mold cavity; all the. castings of one mold can be ejected in one operation by using a spider having properly located pins. With a. large number of cavities ina mold, it is ierable to stag- 40 gerthe length of the pins so th about six to eight pins are penetrating the metal at one -time because of the force required for penetration; distribution of pins of the, same length in dierent sections of the mold is helpful iep: but by running e continuous bubble-free 4 5 in Preventief! mld dimn muse if elimif' nates excessive stress on any one part -of-the mold. i

1 I of the connguration and size of a mold top `Il provided with theskirt I3. A shoulder 12 extending into the openingforms a seat for the in- .verted mold., Vertical members 13 extend upwardiyirem-'the-iraiiie to heid a spider guide 1I adjustable thereon-andsecured in adjusted position by set screws 1I; the forwardedge ofthe spider-,guide is cut to show channels 1l lfor guiding eiectionpins "I1, The electing spider 00 consists'ofthe pins carried by a plate 1l in proper #Pacing to strike the centerbf the bottom 6| of each moldcavity. The pins are shown of varyins length to avoid simultaneous penetration of all lthe mold bottoms. The assemblage" can be -oli placed in any suitable press, as a hydraulic press, i

arbor vpress or mechanical punchpress, so that the downward stroke of the pren the pins 11 are forced metalbottcmso! thecavities. ll'andthecastingsaredislodgedandforced from the molds; are collected in a receptacle placed beneaththe opening 1|.

-The spider guide "Il, on the verti members |3, alsoacts as astop tolimit any .'ll' u g ardmovement of the mold and freeit from not morethan the ejecting pins on the return stroke of the pr "1; for clarity of illustrationthe spider is shown in its retracted position, and a discharged v casting Il is shown in dotted lines.

What is claimed is: l. A mold for the casting of resins comprising -in combination a flat-surfaced'top member, a

shell depending from the member and providing a casting cavity opening at the surface of the member, and a depending skirt about the periph- ,ery of the top member to-reinforce and .rigidify the top member.

2. A mold for the casting of resins comprising in combination a nat-surfaced top member o f a f regular polygonal contour, a shell depending from the member and providing a casting cavity opening at the surface of themember, and adependlngskirt about the periphery of the top member to reinforce and rigidity the top member.

3. Amold for the casting of resins comprising 20 in combination a flat-surfaced top. member, a

shell dependingfroin the member and=having an open, top casting cavity. a depending skirt aboutthe periphery of the member, and bridging connecting the skirt with the shell for reinforcing and rigidifying the top member.

4. A mold assembly for the casting of resins molds having an open-top casting cavity and a reinforcing skirt depending from the peripheral edge of the top.l

5. A mold assemblyfor the casting of resins comprising in combination a plurality of molds having flat tops of regular contour fitting to each other laterally' and longitudinally ltc form a substantially continuous flat surface, each of said molds having an open-top casting cavity and a reinforcing skirt depending from the peripheral edge of the top, and a retaining wall about. the

mold assembly. c

JAMES L. BRANNON. STEPHEN A. MRAZ.

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