Vacuum Bag

Silicone rubber vacuum bag tool

Vacuum Bag Abstract:
A vacuum bag tool utilizing a silicone rubber sheet as the bag. The silicone rubber sheet has at least one edge and a strip of silicone elastomer material adhered by curing to a surface of the sheet along each edge. On each strip of silicone elastomer material a further strip of adhesive tape is adhered. With this adhesive tape, the bag is adhered to the base plate of the tool. Thereafter, a vacuum can be established within the bag adhered to the base plate. The tool can thus be used for applying pressure to a layup of composite material place on the base plate and within the bag.

Vacuum Bag Claims:
What is claimed is:

1. A tool for use in applying pressure to a layup of composite material, comprising:

a base plate;

a silicone rubber bag in the form of a sheet having at least one edge, said at least one edge having on the surface of said sheet facing the base plate a strip of silicone elastomer material adhered thereto and a further strip of adhesive tape adhered to the strip of silicone elastomer material, said strip of adhesive tape adhering the at least one edge of the sheet to the base plate; and

means for establishing a vacuum within the bag when adhered to the base plate.

Vacuum Bag Description:
TECHNICAL FIELD
The present invention relates to vacuum bag tools in general and in
particular to silicone rubber vacuum bag tools and to a method of
fabricating the bag for such a tool.
PRIOR ART
Vacuum bag tools for use in fabricating a structure made of composite
material are known. See, for example, U.S. Pat. Nos: 3,146,148; 3,553,054;
3,575,756; 3,666,600; 3,769,133; 3,861,977; 4,065,340; 4,216,047;
4,287,015; and 4,357,193.
The vacuum bags disclosed are typically made of nylon, or a polymeric
material or of rubber, such as silicone rubber. To effect an edge seal
about the bag, a sealant such as zinc chromate is used. In some instances
clamps are also used. I have had extensive experience as have others at
the assignee company of the present invention with the tools using nylon
bags adhered to the base plate of the tool with a sealant tape such as
zinc chromate tape. It has been observedthat the seal provided by the zinc
chromate tape does not exhibit a high degree of effectiveness, i.e.,
leakages occur which result in lose of vacuum in the bag. This was
observed even when C-clamps were added to the sealed edges of the bag. In
a addition, the nylon bags lose considerable resiliency after a single use
and must be discarded.
I have also had extensive experience as have others at the assignee company
of the present invention with the tool disclosed in U.S. Pat. No.
4,287.015. The tool disclosed uses a rubber bag and triangular ribs
extending about the bag at a position inward of the bag edge. Both the
triangular ribs and the bag edge are sealed to the base plate of the tool
by a sealant material. The seal is not established primarily at the
junction of the bag with the base plate, but rather at the engagement of
the bag and the triangular ribs. Leaks have been observed with this tool
as well, due perhaps to the lack of adequate engagement of the bag and
ribbing as well as the lack of adequate adherence of the sealant material
to the bag. C-clamps were added to the bag edges at the base plate. Even
so, leaks were detected resulting in lose of vacuum. The loss of vacuum in
the bag is undesirable since control of the uniform pressure exerted by
the bag on the layup in the bag is lost. Curing of the layup is thus
adversely affected.
There is a need, therefore, for a vacuum bag which can be effectively
sealed to hold a vacuum.
While the tool disclosed in U.S. Pat. No. 4,287,015 exhibits vacuum leak
problems, it is still preferred over the tools using nylon bags because
the rubber bag is reusable. However, the use of such a tool is undesirable
because it requires considerable man-hours just in preparation time
because of the ribbing.
There is a further need, therefore, for a tool which has a reusable bag and
does not require an appreciable amount of man-hours of preparation.
SUMMARY OF THE INVENTION
The present invention was developed to overcome the noted problems. It was
decided to eliminate the triangular ribs and to find more effective means
of adhering the rubber bag to the base plate of the tool.
A silicone rubber bag was chosen since it has sufficient resiliency under
repeated vacuum applications to insure a long service life. Attempts were
made to find a way to adhere the widely used standard sealant tapes, such
as zinc chromate tape, to the surface of the rubber bag. All attempts,
however, failed. Apparently, silicone rubber does not adhere to the
standard sealant tapes. It was found, however, that MOSITE #14206 adhesive
could be made to adhere to the surface of the silicone rubber bag. The
standard sealant tape could then be applied to the MOSITE adhesive for
sealing the bag to the base plate of the tool.
BRIEF DESCRIPTION OF THE DRAWINGS
Three figures have been selected to illustrate a preferred embodiment of
the invention. The figures are schematic in nature. They are, however,
sufficiently detailed to enable the person skilled in the art to
understand and practice the invention. Illustrated are:
FIG. 1, which is a partial cross-sectional view of the tool according to
the present invention;
FIG. 2, which is a set-up for fabricating the bag of the tool of FIG. 1;
and
FIG. 3, which is an exploded view of the set-up of FIG. 2.
DETAILED DESCRIPTION
A tool 10 according to a preferred embodiment of the present invention is
shown in FIG. 1. The tool 10 includes a metal base plate 12, a silicone
rubber bag 14 and a vacuum source 16. The bag 14 has four generally
mutually perpendicular edges on the surface 18 on which facing the top
surface 20 of the base plate 12, there is adhered a strip of silicone
elastomer material 22. In conjunction with each strip of elastomer
material 22 there is associated a strip of adhesive tape 24. Preferably
the strips of adhesive tape 24 match the width of the corresponding strip
of material 22, although they need not, as shown. The bag 14 is adhered to
the top surface 20 of the base plate 12 by the adhesive strips 24 and is
secured against the top surface 20 of the base plate 12 not only by the
adhesive tape strips 24, but also by the pressure force applied by the
external atmosphere when a vacuum is produced within the space 26 defined
by the top surfaces 20 of the base plate 12 and the lower facing surface
18 of the bag 14.
The space 26 is evacuated by the vacuum source 16 through one or more ports
28 in the base plate 12. The connection to the port(s) 28 is conventional.
The base plate 12 is provided with bores 30 along its edges for use with
clamps in clamping the overhanging edge 32 of the bag 14, if desired. The
clamping procedure is also conventional.
The tool 10 is used in the curing process of a layup 34 of composite
material. The layup is placed on the top surface 20 of the base plate 12
and rests in the space 26. A vacuum is produced in the space 26 by the
vacuum source 16 with the bag 14 drawn down over the layup 34. In the
process, the bag applies a pressure against the layup 34. The entire tool
10 is then placed in an autoclave in which the layup is finally cured
through the application of further pressure and temperature.
The bag 14 of the tool 10 can be reused any number of times for subsequent
curing operations by simply removing the strips of adhesive tape 24 and
adhering new strips of adhesive tape 24 to the strips of silicone
elastomer material 22.
It has been found that Mosite #14206 manufactured by the Mosite Rubber
Company of Fort Worth, Tex. is a preferred silicone elastomer material 22.
The Mosite Rubber Company has published the following physical properties
of Mosite #14206