Plastic and nonmetallic article shaping or treating: processes – Direct application of electrical or wave energy to work – Using sonic – supersonic – or ultrasonic energy
Reexamination Certificate
2000-03-06
2002-07-16
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of electrical or wave energy to work
Using sonic, supersonic, or ultrasonic energy
C264S138000, C264S145000, C264S154000, C264S155000, C264S156000, C264S444000
Reexamination Certificate
active
06419872
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the manufacture of plastics material parts having at least one mechanically weakened area forming a hole or a hole precursor.
It is directed in particular, although not exclusively, to the manufacture of plastics material sections incorporating a longitudinal succession of holes or hole precursors intended to enable easy fixing of the sections in use. These sections are advantageously sections constituting or forming part of electrical wiring trunking.
As used herein the expression “hole precursor” (the concept of a “preform” could equally well be used) means a hole that is imperfectly formed, constituted by an area that is mechanically weakened relative to the remainder of the part concerned; a mechanically weakened area of this kind can in particular be a hole formed in only part of the local thickness of the part concerned, a hole having over a portion of its depth a web including a constriction of its cross section which is generally concentric with the hole and intended to be destroyed when a fixing member is inserted, or a mechanically weakened contour separating from the remainder of the part a central portion which is intended to be eliminated in use; the aforementioned features can be combined, for example, with a blind hole including a cross section constriction and the bottom of which has a mechanically weakened contour. The mechanically weakened area can have an oblong section and can constitute a hole with a spot facing.
The benefit of providing a hole precursor in the form of a blind hole, rather than a through-hole, is that the user is free to use only some of the hole precursors to fix the part concerned, for example, without the unused precursors constituting traps for impurities or dust or even compromising the sealing of the internal volume of the part; this benefit is particularly significant in trunking, for example electrical wiring trunking, which is required to be as well sealed as possible from the external environment (this applies in particular to electrical wiring trunking intended for use in wet areas in the home).
If the hole precursor is open, the seal is not preserved so well, but the existence of constrictions in the hole precursors facilitates centering fixing members (usually screws) in the hole precursors which are used in service.
The fact of providing hole precursors constituted of mechanically weakened contours is that the areas of the parts containing the hole precursors that are not used in service are more rigid than if the holes were formed completely, which is combined with facilitating the fitting of fixing members into the precursors that are actually used.
The benefit of oblong hole precursors is that they can have a cross section larger than the cross section of the fixing members eventually used and enable the user to choose the location of the fixing hole within the oblong precursor.
The benefit of spot facings (recessed bearing surfaces which are permanent) is well known; in particular, it enables the head of a fixing screw to be accommodated within the thickness of the part.
2. Description of the Prior Art
The skilled person knows how to make hole precursors or holes with spot facings in plastics material parts. In particular, the skilled person knows how to manufacture parts by injection molding with fixed projections or more usually mobile slides incorporated into the design of the mold parts. However, this approach, whereby the spot-faced holes or the hole precursors are formed as soon as the plastic material is shaped, makes it necessary to design the molds accordingly and is applicable only to injection molded parts whose geometry allows this.
The object of the invention is to provide a method of manufacturing plastics material parts with mechanically weakened areas forming holes or hole precursors (in practice a greater number of such holes or hole precursors than is necessary for using the parts), wherein the mechanically weakened areas are formed esthetically and easily, at moderate cost, after the parts (or at least blanks therefor) are produced, and in a manner that is both reproducible and reliable.
SUMMARY OF THE INVENTION
To this end, the invention proposes a method of manufacturing a part having at least one mechanically weakened area, the method including a step of producing a thermoplastics material part and at least one cycle of steps entailing forming a localized opening through an area of the part, heating the part locally by means of a heating probe so as to render the area of the part plastic, and using a punch to modify the geometry of the area rendered plastic so as to delimit in the part a mechanically weakened area constituting a hole or hole precursor.
Thus, in accordance with the invention, the mechanically weakened area is conformed by deforming a plastic area of the part using a punch whose shape determines the shape of the mechanically weakened area after cooling. The punch causes plastic flow of the material, in practice against a counter-punch which can be flush with the surface of the part on the opposite side to the punch. Thus the part is not punched right through but through only a part of its thickness, there remaining material afterwards in line with the punch (considering its largest cross section).
The benefit of the opening is in particular to avoid the creation of an increase in thickness on producing the mechanically weakened area as the result of displacement of material during punching; the fact that the opening is a through-opening (with a section that in practice is constant) corresponds to a simple and reproducible manner of forming a opening.
For the plastics material to flow in a homogeneous manner, the area rendered plastic is preferably formed around the opening.
The hole precursor can have several conformations.
In a first conformation, the geometry of the area rendered plastic is modified to delimit the mechanically weakened area in the form of a blind hole the bottom of which is constituted of a continuous web. This web guarantees that unused hole precursors are sealed. The web is preferably flush with the surface of the part on the side opposite the punch, in which case it is not necessary to provide a counter-punch of particular shape (a simple plane surface can be used).
In another, advantageous conformation, the geometry of the area rendered plastic is modified to delimit the mechanically weakened area in the form of a through-hole bordered by a peripheral web. The peripheral web may be understood as an incomplete web (in the sense in which this term is used in connection with the first conformation referred to above). It materializes a cross section constriction which is advantageously centered on the remainder of the hole precursor and can be used to center correctly the tool for preparing a fixing hole in the wall to which the part must be fixed, or even the fixing member itself. Depending on its thickness, either the peripheral web is destroyed when fitting a fixing member or remains and constitutes a spot facing.
In a further, advantageous conformation, the geometry of the area rendered plastic is modified to delimit the mechanically weakened area by a contour made up of openings. This corresponds to forming “dashed lines” of openings around the contour of a hole obtained by breaking the residual areas of material linking the inside and the outside of the contour. The contour is preferably formed of through-openings, which facilitates breaking the residual connecting areas. However, the openings materializing the contour can instead be blind openings. In a further variant, the contour can be a contour of constant thickness less than the local thickness of the part (like a groove).
The method of the invention is of particular benefit if the thermoplastics material part is extruded. This is because the extrusion process produces a section of constant cross section and forming hole precursors necessarily requires specific operations.
Mechanically weakened areas can be produced after the
Albert Christophe
Claisse Jean-Jacques
Dumon Paul
Browdy and Neimark , P.L.L.C.
Plant Wattohm
Tentoni Leo B.
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