US2372114A - Pad - Google Patents

Description

Patented Mar. 20, 1945 PAD Eugene R. Perry,'Forest Hills, and Henry C. (iuhl, Pittsburgh, Pa., assignors to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 13, 1943, Serial No. 479,048

8 Claims.

This invention relates to pads and in particular to cushioning pads for use in high pressure molding presses. a

In the molding of resinous products, and particularly laminated resinous products formed of fibrous sheet material impregnated with synthetic resins, it has been necessary to back the pressing plates with pads in order to effect an equalization of the applied pressure. As disclosed in Patent No. 1,942,251, issued January 2, 1934, to G. H. Mains, and assigned to the assignee of this invention, one method utilized in obtaining the equalization of pressure was to employ pads constructed of layers of cloth and asbestos between the heating platens and the movable and head castings of the press. Generally pads of cellulosic material such as paper or cloth are thus used by the trade.

It has been found, however, that where the pads of the cellulosic material are used, because of the poor thermal conductivity of the cellulosic material a considerable loss in time and power is encountered in bringing the molding plates up to the molding temperature. Further, the pads have a relatively short life since the cellulosic material employed in making the pads fail in a relatively short period of time under the molding temperatures to which they are subjected during the molding cycle. This short life of the pads makes it necessary to interrupt the molding cycle to change pads with an accompanying loss of time in the operation of the press.

It is an object of this invention to provide a resilient pad having good thermal conducting Figure 1 is a view, partly in section, of a frag I ment of a molding press embodying the teachings of this invention,

1 1. Fig. 2 is an enlarged plan view of the resilient pad utilized in the molding press of Fig, l, 'Fi'g.- 3 is a view in section of the resilient pad taken a'longjthe line IIIIII of Fig. 2.

4 is-a plan view greatly enlarged of a fragment of the fibrous material employed in the pad of Fig. 3,'and a Fig. 5 is another view of a fragment of the fibrous material taken along the line V-V of Fig. 4.

Referring to Fig. 1 of the drawing, a portion of a hydraulic press I0 is shown as having a stationary block or head casting l2 and a lower movable block or casting 14. The head casting I2 is supported by standards or posts l6 which extend from the main frame (not shown) which is suitably secured to a foundation. The movable casting I4 is disposed to be moved upwardly towards thecasting I2 by a force applied to its lower surface as by rams (not shown) which are I hydraulically operated.

Heating and cooling platens l8 and 20 are associated with the castings l2 and M, respectively, being separated therefrom by pads 22 and 24, respectively, of asbestos or other material which is resistant to heat and which is a poor heat conductor. The platen l8 and associated pad 22 are secured to the casting l2 by the bolts 26 and the platen 20 and associated pad 24 are secured to the casting M by the bolts 28. Each of the platens l8 and 20 is provided with pipes "30 through which a suitable heating medium, such as steam, and a cooling medium, such as water, may be selectively circulated. The pads 22 and 24 function to retard the transfer of heat from the platens to the castings.

In accordance with this invention, when the heating and cooling platens I8 and 20 are separated by lowering the casting H, a pad 32 is positioned adjacent to and substantially covering. the surface of the platen 20. The pad 32 is a thin, flat, tubular member or envelope formed of resilient metallic material as will be described hereinafter, which functions to equalize the pressure applied without detrimentally retarding the flow of heat.

As illustrated, a stack formed of an alternate assembly of pressing plates 34 and molding material 36, such as laminated fibrous material impregnated with a synthetic resin, are then disposed onthe pad 32, the alternate assembly terminating with a pressing plate 34. Another pad 32 is disposed between the top pressing plate 34 and the upper heating platen ill to effect an equalization of the pressure applied to the press ing plates.

Referring to Figs. 2 and 3,- the resilient pad members 32 are better illustrated. As shown, the pads are provided with large substantially fiat surfaces 31 and 38 which are of a size substantially equal to the area of the pressing plates 34 with which the pads are to be associated. Each of the pads 32 is preferably formed of two substantially thin rectangular dish-shaped metallic members 40 and 42 having relatively shallow rims 44 and 46 respectively which, when the members are disposed to face each other, will match, whereby when the rims are seated the fiat surfaces 31 and 38 are spaced apart and substantially parallel. The metallic members 60 and 42 of the pads 32 may be of any suitable resilient metal such as hot or cold rolled sheet steel or brass, or of thin spring steel. Preferably the sheet stock used in making the members 40 and 42 has a thickness of between V inch and inch.

As shown, the space between the substantially fiat'sides 3! and 38 of the metallic members 40 and 42 forming the envelope 32 is filled with a pad 48 of a resilientfibrous material. Preferably the fibrous material 48 utilized in forming the filler is of steel wool, it being found that the relatively hard but springy fibers of steel wool gives an unusually long life to the resulting composite Dad when subjected to the temperatures and pres- .sures employed in the molding of resinous products. The steel wool may be in any form suitable for filling the space within the metallic envelope of the pad 32, such as in the form of a. mat having any predetermined density, thickness and width depending upon the requirements, the mat having been formed by any suitable method such as by felting. Since the mats of steel wool do not always have uniformity, it is preferred to employ quilted layers of the steel wool a the filler for the envelope of the pad 32.

Referring to Figs. 4 and 5, there is illustrated the steel wool fibers 50 formed into a quilted pad 48 for use in the metallic envelope. These pads can be formed by laying the fibers of the steel wool substantially parallel, then quilting or retaining them in the substantially parallel relation as by means of weaving fine wires 52 across the pad substantially perpendicular to the direction of the steel wool fibers. The threads 52 of wire are preferably spaced apart. Where pads of the steel wool of th s type are utilized, the filler may be formed of a plurality of the quilted pads, as illustrated in Fig. 5, one layer being superposed upon the other until a predetermined thickness sufiicient for filling the metallic envelope is constructed.

Regardless of the manner in which the fibrous material is formed. after the metallic envelope is filled and the rims of the d sh-shaped members are seated one on the other, the meeting edges of the metallic members are welded as shown in Fig. 3 at 5d. Preferably the envelope is so filled with the'fibrous material a to prevent excessive sideways movement of the fibrous material after the meeting edges of the metallic members are welded. In this form the sealed metallic pad 32 may be likened unto a free edge supported diaphragm being capable of movement similar to such a d aphragm.

With the pads 32 and the alternate assembly of pressing plates 34 and impregnated fibrous material 36 assembled and in position as described hereinbefore, the press is operated through its molding cycle, heat and pressure being applied to cure the molding material between the pressing plates 34. As pressure is applied to the mold elements, the pads 32 function to cushion and to equalize the pressure applied throughout the surface area of the molding plates. In addition to equalizing the pressure, since the pads 32 are of all jected during the molding cycles.

metallic construction and have a good thermal conductivity, the pads function to prevent local .hot spots on the molding or pressing plates, efiiciently distributing the applied heat over the entire surface of the pressing plates. As the press is operated to separate the mold elements, the pads 82 are so resilient as to return to their original shape.

The sealed metallic pads of this invention have an extremely long life a compared to the pads of cellulosic material employed heretofore, it being found that they have a life in excess of thirty times that of the pads of the cellulosic material. Further, because of the materials employed, the pads have a high mechanical strength and high endurance against fatigue for withstanding the pressures of up to 2000 pounds per square inch which are utilized in the molding operations. The metallic pads will not deteriorate or lose strength or resiliency under the high temperatures in the neighborhood of 200 C. to which they are sub- In addition,

' since the pads are sealed, there is no danger of contaiminating the molded plate. It has been especially noted that because of the good thermal conductivity of the pad that time for heating the mold to molding temperature is reduced to threequarters of the time necessary where pads of the cizllglosic material employed heretofore are uti- Although this invention has been described with reference to a particular embodiment thereof, it is, of course, not to be limited thereto except insofar as is necessitated by the scope of the appended claims.

We claim as our invention:

1. A pad for use in a high pressure molding press comprising, in combination, a non-porous, resilient metallic envelope having spaced fiat side walls of sheet metal having a thickness of between and inch, and a fibrous metallic material disposed between the spaced side walls to substantially fill the envelope.

2. A pad for use in a high pressure molding press comprising, in combination, a sealed metallic, non-porous and resilient envelope having spaced fiat side walls of sheet metal having a thickness of between and inch, and a fibrous metallic material disposed between the spaced side walls to substantially fill the envelope.

8. A pad for use in a high pressure molding press, com-prising, in combination, a thin fiat non-porous tubular member of resilient metallic material having spaced side walls of sheet metal having a thickness of between 3 and inch, and a resilient fibrous metallic material disposed between the side walls to substantially fill the tubular member.

4. A pad for use in a high pressure molding press comprising, in combination, a non-porous and resilientmetallic envelope having spaced side walls of sheet metal having a thickness of bebetween V and /64 inch, and a filler of steel wool disposed between the spaced side walls to substantially fill the envelope, the steel wool cooperating with the non-porous, resilient envelope to provide a thermally conducting, resilient pad.

5. A pad for use in a high pressure moldin press comprising, in combination, a sealed envelope of non-porous resilient metallic material having spaced fiat side walls of sheet metal having a thickness of between /14 and it; inch. and a filler of steel wool disposed between the side walls to substantially fill the envelope and resiliently cushion the side walls, the steel wool and-metallic envelope cooperating to provide are'silient pad having good thermal conducting characteristics.

6. A ad for use in "a high pressure molding press comprising, in combination, a pair of substantially thin, rectangular, dish-shaped, nonporous metallic members having substantially fiat surfaces and relatively shallow rims, the metallic members being formed from sheet metal having a thickness of between $64 and "56 inch and being disposed with their rims seating against each other and their fiat surfaces in spaced relation to form a thin fiat resilient tubular member, resilient fibrous metallic material disposed between the flat surfaces to fill the tubular member, and a weld applied to the edges of the seated rims to 15 seal the tubular member containing the resilient fibrous material, the filled and welded tubular member having a good thermal conductivity and being resilient.

7 A pad for use in a highpressure' molding press, comprising, in combination, a sealed envelope oi nonporous resilient metallic material having spaced side walls of sheet metal having a thickness of between ,4 and 3434 inch, and a filler consisting of a quilted pad of fibrous metallic material disposed between the side walls to substantially fill the envelope and resiliently cushion the side walls, the fibrous metallic material and metallic envelope co-operatin to provide a resilient pad having good thermal conducting character

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