US2879196A

US2879196A - Method for metal spray molds

Info

Publication number: US2879196A
Application number: US356759A
Authority: US
Inventors: Brucker Milton
Original assignee: Zenith Plastics Co
Current assignee: Zenith Plastics Co
Priority date: 1953-05-22
Filing date: 1953-05-22
Publication date: 1959-03-24
Anticipated expiration: 1976-03-24

Description

March 24,1959 M. BRUCKER METHOD FOR METAL SPRAY MOLDS 3 Sheets-Sheet 1 Filed May 22, 1953 MILTON BRUCKER,

INVENTOR. HUEBNERJEE'I-LLER,

WORREL 8 HERZ/G, By A TTORNEYS- March 24, 195 9 M. BRUCKER 2,879,196

METHOD FOR METAL SPRAY MOLDS Filed May 22, 1953 3 Sheets-Sheet 2 MIL TON BRUC/(ER,

IN VEN TOR.

HUEBNER, BEEHLER,

WORREL a HERz/c,

A TTORNE Y5.

March 24, 1959 M. BRUCKER 2,879,196

METHOD FOR METAL SPRAY MOLDS Filed May 22, 1953 z Sheets-Sheet s MIL TON 8RUCKER,

INVENTOR.

HUEBNERJEEHLER' WORRE'L 8 HERZIG, By A TTORNEKS'.

United States 7 2,879,196 METHOD FOR NIETAL SPRAY MOLDS Application May 22, 1953, Serial No. 356,759

.6 Claims. (Cl..15,4-110) This invention relates to production molds of a metal spray type, and more particularly relates to a new and improved construction thereof, and method of foirning laminated plastic parts thereon.

It is among the objects of this invention to provide a new and improved metal sprayed mold associated with the means for drawing a vacuum simultaneously upon a molding surface and also upon a back surface of the mold, thereby avoiding vacuum'leakage through the mold body and avoiding undesired bubbling and pitting of the molded parts, particularly the surface adjacent the mold surface.

It has been found in metal sprayed molds of the desired character described that the mold body of sprayed material is, to some extent, porous, so that when a vacuum is drawn so as to evacuate air between a readily yieldable bag in accordance with conventional practice, undesired pitting, blistering, and other malformation of the surface of the molded parts results. It is found that by applying a vacuum to the outer side of the sprayed metal mold, such undesired permeability of the sprayed metal of the mold body is efiectively eliminated as a factor in the molding operation.

It is therefore among the objects of this invention to provide a new and improved apparatus and method for molding in a manner to take advantage of the abovestated discovery and to provide a more uniformly superior molded product.

It is another object of the invention to provide a new and improved means associated with a metal sprayed mold for drawing a vacuum thereon in a vacuum bag type molding operation.

It is also among the objects of the invention to provide improvements over the prior art apparatus and processes heretofore intended to accomplish generally similar purposes, to'improve the vacuum distribution over an enlarged surface area of relatively large parts being molded, and to provide new and improved means for achieving such wide distribution of vacuum so as to obtain a superior molded part.

With these and other objects in view, the invention consists of the construction, arrangement and combinaatent ice Referring more particularly'to the drawings, there is shown by way of illustration but not of limitation, in Figures 1 through 5, successive steps in a preferred procedure for making a mold usable in the practice of the instant invention.

A plaster mold or cast 2% is formed with an upper dome-Shaped portion 21 having an exterior surface con forming to the desired inner contour of the ultimate desired die or mold and an integral base 22 defining an annular flange.

After the plaster mold 20 has been shaped to the desired configuration, the outer surface is sanded and finished to a smooth condition. A light coating 23 of zinc or the like metal is then flash-sprayed over the outer surface of theplaster mold, including the upper surfaces thereof, and the upper flange surface 24 of the base 22.

Next a layer of bronze is sprayed over the zinc to a thickness of approximately one-eighth to one-quarter inch,

as designated at 25 in Figure 2. The bronze coating provides a hard surfaced layer for the interior of the final mold, as will be seen.

Over the outer surface of the bronze coat 25, a coat of aluminum 29 or the like metal is applied so as to give a good bond between the bronze and a resin to be applied over the aluminum. Such aluminum coating is also deposited, preferably by spraying, as stated, to a thickness of approximately one-quarter to one-half an inch. Together the layers25 and 29 constitute a metal mold 58. A coating of wax or paraffin is next deposited, as in a continuous sheet, by daubing, brushing, spraying, or otherwise, over a substantial portion of the surface of the aluminum. For this purpose the aluminum may be formed with a shoulder, as at 26, providing a recess, as at'27, for said wax coating 28 over the corresponding major portion of the mold. Said wax 28 is preferably deposited to a thickness of approximately one-eighth of an inch, although the thickness of the wax layer 28, like the thicknesses of the bronze and aluminum layers, 25 and 29, may vary within limits which are readily, appar ent from a consideration of the particular use to which the mold is to be put, its size, and the like considerations. Over the aluminum coat 29, including the shoulder area 26 and also continuously over the Wax coat 28, a plurality of layers of laminate, preferably of glass cloth, or other reinforcement, impregnated with a suitable resin, such as a polyester, is laid, in intimate contact with said wax and aluminum portions. The resultant mold, with such laminate 30 impregnated with said resin, is then heated to a sufiicient temperature, say 120 F., to cure the reinforcing resin. And in order to insure that such resin cures, preferably at a temperature lower than the melting point of the wax, the resin may be hopped up with suitable accelerators or the like.

tion of the various parts of the device whereby the objects contemplated areattained, as hereinafter set forth, pointed out in the appended claims, and illustrated in the accompanying drawings.

In the drawings:

Figures 1 through 5 are vertical sectional views illustrating the steps of forming a mold of the character most pertinent to the practice of this invention.

Figure 6 is an elevational view of a completed mold as used, parts being cut away.

I Figure 7 is a top view of the mold of Figure 6.

Figure 8 isa'fragmentaryvertical sectional view, enlarged, taken as on a line 8-8 of Figure 7.

Figure 9 is a similarly enlarged vertical sectional view of the lower end portion of the mold of Figures 6 and 7, as used.

After the resin 30 has set so as to provide a firm and rigid backing or enclosure for the metal-layered mold body, the mold-curing temperature is raised to, say F., or in any event to a sufiicient extent to liquefy the wax layer 23, to permit the wax to be withdrawmpreferably under vacuum, so that the cavity 27 formerly occupied by the wax defines a space separating, at least over a substantial portion of its area, the reinforcing laminate 30 and the sprayed

metal mold portions

23, 25 and 29.

It is not essential that the wax be withdrawn at the present stage of operation. It may subsequently be withdrawn as during a first molding operation utilizing the completed mold.

A fiberglass laminated cap or'edging 31 may be used to reinforce and bind the metal portions of the'mold to the laminated backing 30.

Appropriate metal reinforcement, such as a pipe '32,

is also-secured, in "any appropriate manner, to the edge 24 of "the mold to insure dimensional stability of the mold.

The plaster core 20 is broken out at any convenient stage to expose said zinc metal bond coat 23. The inside of the mold is then sanded or dressed out until all of the zinc layer 23 has been removed, exposing the layer 25 of bronze for use as the inner face of the mold.

In the use of the mold, the same, including said reinforcing frame 32, is mounted as upon a suitable strucmm 33, including castors, or the like, 34, to facilitate transport.

In a typical use, a layer of parting agent is applied to the interior surface 35 of the mold, and then a number of layers 36 of resin-impregnated fiberglass cloth are applied thereto. The main body of the part in question is given thickness, strength and rigidity by a layer of fiberglass cloth honeycomb 37. The upper edges of the mold are built up to a corresponding thickness to that of the honeycomb as by a plurality of layers of fiberglass laminate 38 extending to thetop edge 39 of the mold. Another plurality of layers of fiberglass cloth similarly impregnated with resin is applied thereto as at 40, and over the latter, preferably a layer of cellophane, or its like, 41,

is applied.

A layer of industrial mat 42 may be applied as in strips, as shown most clearly in Figures 7, 8 and 9, over another preferably continuous layer 43 of such industrial mat comprising, e.g., an unimpregnated fiberglass material. Said strips 42 comprise bleeder strips which terminate, as at 44, at the upper edge of the mold where a conduit 45 is formed around the upper mold edge circumferentially thereof, most advantageously by means of a wire coil of helical spring shape, the individual coils being in spaced relationship from one another, to permit the free passage of air therebetween.

Over the aboveassemblage a vacuum bag 46 is applied, said bag being preferably of a material such as vinyl alcohol, which is secured in air-tight fashion around the circumferential periphery 47 of the mold, by a suitable seal, such as zinc chromate putty 48.

The upper rim 49 of the mold is drilled, as at 50, and tapped, as at 51, for the threaded accommodation of a metal tubing 52 which makes connection with a similar tubing or pipe 53, similarly drilled and tapped into the bottom of the mold, but only through the resin-reinforced layers 30, so that such tubing 53 communicates inwardly with the wax-formed recess 27.

Suitable conduits 54 interconnect the pipes and

tubes

52, 53 and 54 to a source of vacuum, not shown, by means of a hose or the like 55, in which a resin trap 56 is also connected. A plurality of such resin. traps 56 may be employed, and it is also preferable to provide a plurality of such metal tubing, nipples, or the like, 52, at spaced intervals around the upper edge of the mold. When a vacuum is drawn through the hose 55, and the

several conduits

52, 53 and 54, the poly-vinyl bag 46 is drawn firmly against the underlying bleeder strips 42,

' the layer of fiberglass mat 43, and the upper portions of the coil spring conduit 45. Said nipples 52 are in direct communication through their respective bores 50 with said coil spring conduit 45 so that air is drawn uniformly from the interior of the mold between the bag 46 and the metal mold portion 58.

Previously, that is, without the space 27 and nipple 53, or the like, which serves to draw a vacuum upon the outer side of the metal mold 58, it has been found that the porosity of the metal 58 causes an imperfect surface to form at 35, due to pitting and bubbling occasioned by penetration of air from the metal 58 into the molded parts.

However, by the instant provision of a space, such as 27, between the resin-laminated backing and said metal mold 58, which is porous by virtue of its having been formed by spraying, as heretofore described,any air pressure exerted upon themetal 58, and which would otherwise cause leakage into the mold part is neutralized by the vacuum simultaneously drawn in the space 27. The molded part is thus formed and cured in the mold without surface blemishes, puck-marks, and the like imperfections due to said undesirable air leakage through the por ous bronze and aluminum.

The thickness and rigidity of the metal mold 58 are sufficient, as is the body of the reinforcing laminate 30, to maintain the airspace 27 in an etfectivelyunconstricted condition ,when a vacuum of approximately 18 to 20 inches of mercury is drawn.

The above principles, while illustrated in connection with a female mold, are equally applicable to male molds and may likewise be utilized in the fabrication of any intermediate or varied structure, even including flat parts, or parts which are partially convex and partially concave.

By the use of the coil spring type conduit, vacuum is drawn equally upon all parts of the upper edge and periphery of the molded and laminated parts, thereby materially assisting the removal of air from between the plies of the laminate, as well as beneath the bag 46 to exert any desired pressure upon the parts to be molded. These considerations are advantageous in the instant apparatus and method, so as to materially assist the drawing of a uniform vacuum on the molded part and on the inner and outer walls of the mold through the space 27, or its like.

The above described apparatus and the method also described above are adapted for use in molds of analogous type in order to correct accidentally developed leakages through the body of the mold or in strategic positions or areas of the mold.

Although I have herein shown and described my invention in what I have conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope of my invention, which is not to be limited to thedetails disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent means, methods and devices.

I claim:

l. The method of making a mold comprising forming a first layer of porous metal by spraying said metal on a form, applying a second layer of non-metal to one face of said first layer, and applying a third layer of firm material over said second layer and securing the same to said first layer outside the boundaries of said second layer, and forming a space between said first and third layers by withdrawing said second layer.

2. The method according to claim 1, wherein said second layer has a relatively low melting point appreciably lower than that of said first and third layers, and wherein the withdrawal of said second layer comprises melting said second layer. 7 V

3. The method according to claim 2, wherein said second layer romprises a wax, and said third layer comprises a reinforced resin. 1

4. The method of claim 3 including the steps of applying a moldable body against said porous metal wall, subjecting said body to a vacuum and subjecting said space to a vacuum.

5. The method of claim 4 including the steps of covering said body with an impervious sheet, subjecting the region between said wall and sheet to a vacuum to subject said body to a vacuum. I g

6. A method according to claim 3, wherein said reinforced resin comprises lamina of resin impregnated cloth, and said porous metal is made of material comprising essentially bronze.

(other eferences on following page) 5 6 UNITED STATES PATENTS 2,376,805 Peacock May 22, 1945 1,929,535 Parker Oc 3 9 Vidal er 9 6 2,189,154 Stewart Feb. 6, 1940 2,420,359 Dasher May13, 947 2,264,146 Crane Nov, 25, 1941 2,447,620 Singleton et a1 Aug. 24, 1948 2,280,865 Stossel Apr, 28, 1942 5 2,642,390 Garofano June 16, 1953 2,295,858 McWane Sept. 15, 1942 2,664,593 Larson Ian. 5, 1954 2,370,322 Nebesar Feb. 27, 1945 2,755,216 Lemons July 17, 1956

Claims

1. THE METHOD OF MAKING A MOLD COMPRISING FORMING A FIRST LAYER OF POROUS METAL BY SPRAYING SAID METAL ON A FORM, APPLYING A SECOND LAYER OF NON-METAL TO ONE FACE OF SAID FIRST LAYER, AND APPLYING A THIRD LAYER OF FIRM MATERIAL OVER SAID SECOND LAYER AND SECURING THE SAME TO SAID FIRST LAYER OUTSIDE THE BOUNDARIES OF SAID SECOND LAYER, AND FORMING A SPACE BETWEEN SAID FIRST AND THIRD LAYERS BY WITHDRAWING SAID SECOND LAYER.