US20110008557A1

US20110008557A1 - "Compression-molded silicone rubber cap and plug"

Info

Publication number: US20110008557A1
Application number: US12/801,982
Authority: US
Inventors: Frederick W. Zeyfang
Original assignee: Protective Industries Inc
Current assignee: Protective Industries Inc
Priority date: 2009-07-07
Filing date: 2010-07-06
Publication date: 2011-01-13

Abstract

A sealing cap or plug is provided, comprising a base element having top and bottom portions, and a circumferential side wall extending therebetween, the base element having a frusto-conical or tapered shape, with the diameter of the base element at the top portion being greater than the diameter of the base element at the bottom portion; the top portion being open-ended, and the bottom portion being closed ended; the base element having a hollow interior that extends from the open end toward the closed end; a flexible flange extending outwardly from a periphery of the base element, the flexible flange spaced from the bottom portion; the side wall having a thickness in the range of from about 0.020 to 0.040 inch; and the cap or plug being comprised of compression-molded silicone rubber.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority pursuant to 35 U.S.C. 119(e) of U.S. provisional application No. 61/213,725, filed Jul. 7, 2009, the contents of which are hereby incorporated by reference in their entirety.

BACKGROUND OF THE PRESENT INVENTION

The present invention is directed to a compression-molded thin-walled silicone rubber cap and plug.
All tapered caps and plugs for the past 60+ years have been primarily center gated when the plastic injects into the part from the center. In a few other cases the parts are edge gated. However, as a result of such molding, the molded part is inherently unstable due to the presence of highly stressed areas where the plastic enters the mold cavity. 99% of the tapered cap/plugs have been formed from low density polyethylene—a few have been flexible vinyl and even fewer have been molded from high density polyethylene.
It is accordingly an object of the present invention to provide a thin-walled tapered plug which avoids the problems of the prior art which result in the presence of highly stressed areas. It is also an object of the present invention to provide a thin-walled tapered plug having enhanced physical properties in comparison to previous plugs comprised of polyethylene.

SUMMARY OF THE PRESENT INVENTION

The present invention is accordingly directed to a thin-walled silicone rubber tapered cap or plug comprised of compression-molded silicone rubber. The cap or plug has a tapered body having a closed end and an open end, with an outwardly extending flange extending about the periphery of the open end, with the cap or plug having a hollow interior extending from the open end toward the closed end.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the cap or plug of the present invention.

FIG. 2 is a side view of the cap or plug of FIG. 1.

FIG. 3 is a top view of the cap or plug of FIG. 1.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The silicone rubber tapered cap or plug of the present invention will be described in connection with the Figures.
The cap or plug is comprised of a generally frusto-conically shaped or tapered body 1 having an open end 2 and a closed end 4. The body at the open end has an outwardly extending flange portion 8, as well as a side wall 6 and a bottom wall 9.
The diameter of the bottom portion of the cap or plug will generally be less than the diameter of the top portion of the plug to assist in use of the plug. A decreased diameter for the bottom portion assists in initially seating the plug in a hole or bore to be sealed, as well as assisting in insertion of the plug into the hole or bore a sufficient distance. However, it is not required that the cap or plug body be tapered. If desired, the diameter of the open and closed end may each be identical.
The degree of taper of the cap or plug body from the top of the plug body to the bottom of the plug body is preferably 2.5 to 15 degrees relative to the longitudinal axis of the body, with a degree of taper of 3 to 10 degrees having been found to be particularly acceptable, with an average taper per side of 6 degrees being preferable.
A flange 8 extends laterally from a top portion of the plug. The flange 8 preferably extends outwardly from an upper edge of the open end of the plug, although this is not critical. The flange may extend from the plug body in a relatively perpendicular orientation to the plug body as shown in the Figures. Alternatively, the flange may extend at a downwardly-oblique angle relative to the longitudinal axis of the body toward the closed end. The length of the flange is not critical to practice of the present invention, and may be lengthened or shortened as desired depending on the particular end use contemplated.
A bottom or underside surface of the flange may include at least one annular ridge or O-ring that extends downwardly from the bottom surface of the flange. The presence of the annular ridge or O-ring assists in sealing the hole or bore into which the plug is placed.
The annular ridges or O-rings are spaced from the side wall of the plug, and may either be co-extensive with the outermost edge of the flange, or positioned between the end of the flange and the side wall of the plug. Advantageously, multiple ridges or O-rings may be positioned along the bottom surface of the flange. The number and size of the O-rings or ridges depends on the size of the flange, which in turn depends on the size of the cap or plug. Of course, a flange of larger lateral dimension will permit a greater number of ridges or O-rings to be employed. The annular ridge or O-ring may have a variety of configurations, such as circular or pointed (such as the tip of a triangular cross-section thereof).
By way of exemplary dimensions, the thickness of the wall portion of the plug body may range from about 0.020 to about 0.040 inch, with the wall dimension depending upon the size of the plug body and the end use contemplated.
By way of example, a plug which is configured to seal an open end of a 1.5 inch pipe, the plug may have a plug body of about 0.55 inch in length, a diameter of about 1.42 inch, a flange extending about 0.15 inch from the side of the plug, and being about 0.04 inch in thickness at its widest point adjacent the side wall of the plug.
The cap or plug has a hollow interior to permit it to serve a capping function when placed over the end of an object to be capped. The hollow interior extends from the open end toward the closed end. The hollow interior may extend partially or wholly to the closed end.
Advantageously, the cap or plug is formed from silicone rubber by compression molding. Compression molding is a conventional molding method well known to those skilled in the art. In compression molding, a slug of curable silicone rubber composition is placed into a compression mold (or smaller pieces are placed into individual cavities) and the mold is closed, squeezing the material throughout the cavities into each part under heat and pressure. The silicone rubber composition is maintained under heat and pressure for a time sufficient for the desired level of curing to occur.
Compression molding is generally effected at a temperature of from about 100° C. to about 500° C., and at a pressure of from about 300 to 1500 psi. The molding time will generally range from about 30 seconds to several hours. The specific temperature and pressure conditions and compression time employed may be varied as desired.
The silicone rubber composition may include a variety of components as desired, such as inorganic fillers, dispersing aids for the fillers, heat-resistance improvers, pigments, flame-retarding agents, etc. For instance, the electrical conductivity of the cap or plug may be increased by the addition of a suitable filler such as carbon black. Alternatively, the addition of non-conductive fillers may be useful if the resistivity of the cap or plug is to be increased. One of ordinary skill in the art may readily determine whether the presence of one or more of such additives is appropriate for the end use desired.
The cap or plug of the present invention may have any suitable hardness. An exemplary Shore A hardness for the silicone rubber product of the present invention ranges from 10 Shore A to 90 Shore A, preferably from 40 Shore A to 85 Shore A. A plug will typically have a higher hardness than a cap, as the cap generally requires greater stretchability.
Silicone rubber compositions have many advantageous properties, including thermal resistance, chemical stability (oil, solvent and chemicals), etc. Such advantageous properties enable the cap or plug of the present invention to be used in a variety of extreme environments, such as elevated temperatures.
Any commercially available silicone rubber composition can be employed in the present invention. Accordingly, one of ordinary skill in the art can readily select a suitable silicone rubber composition for use in the practice of the claimed invention.
The cap or plug has a variety of end uses. Exemplary end uses include a dust or moisture seal, or as a shipping protector for threads, pipe, tubing ends, etc. The cap or plug may also be used as a masking device for electroplating and spray painting, as well as any other use which requires a bore or hole in an object to be temporarily sealed.
Advantageously, the cap or plug of the present invention may be formed without the need for mold gating (due to the use of compression molding in the present invention), which inherently produces a cap or plug having weak spots due to the use of center gating in the injection molding process. The cap or plug of the present invention avoids such a circumstance, while yielding a cap or plug with improved elongation on the order of up to 600% (in comparison to an elongation of from 20-30% for polyethylene). When used as a cap, the cap may be used with a variety of different diameters due to enhanced elongation, resulting in the need for fewer sizes of caps, and increased flexibility as to the use thereof. The enhanced ability of the cap or plug to function satisfactorily at extreme temperature conditions (up to 600° F.) is also a significant advantage, particularly when used in industrial masking operations for plating and powder coating.
Further, the use of a silicone rubber for the thin walled cap or plug enhances the abrasion resistance for the cap or plug, which is particularly important due to the thin walls employed for the cap or plug. Low density polyethylene, for instance, tends to abrade when inserted over sharp machined edges and ports in hydraulic components, whereas silicone has improved resistance to abrasion, reducing the likelihood of contamination from abraded particles finding their way into the hydraulic system. The use of silicone rubber also enhances the removal and installation of the thin walled cap or plug due to enhanced flexibility of both the flange and the side wall—it is also much easier to pick up the flange which assists in removal. Silicone rubber further enhances the range of fit of the thin walled cap or plug, due to enhanced compressibility, increased elongation, etc. Silicone rubber can also, as discussed above, be easily formulated for enhanced electrical conductivity or insulation by addition of the requisite fillers therein.
In essence, the use of silicone rubber as the formulating component of the thin walled cap or plug enables the cap or plug to exhibit physical properties not heretofore appreciated or expected, yet significantly enhancing the desirability of use of such thin walled caps or plugs.

Claims

1. A sealing cap or plug comprising:

a base element having top and bottom portions, and a circumferential side wall extending therebetween, said base element having a frusto-conical or tapered shape, with the diameter of said base element at said top portion being greater than the diameter of said base element at said bottom portion;

said top portion being open-ended, and said bottom portion being closed ended;

said base element having a hollow interior that extends from said open end toward said closed end;

a flexible flange extending outwardly from a periphery of said base element, said flexible flange spaced from said bottom portion;

said side wall having a thickness in the range of from about 0.020 to 0.040 inch; and

said cap or plug being comprised of compression-molded silicone rubber.

2. The sealing cap or plug of claim 1, wherein said flexible flange extends outwardly from said base element at a position adjacent said open end of said top portion.