Metal working – Method of mechanical manufacture – Assembling or joining
Reexamination Certificate
1999-07-16
2001-10-23
Graham, Gary K. (Department: 1744)
Metal working
Method of mechanical manufacture
Assembling or joining
C015S250430, C015S250320, C264S108000
Reexamination Certificate
active
06305066
ABSTRACT:
BACKGROUND OF THE INVENTION
Prior Art
Support elements of the type under consideration are intended to assure the most uniform possible distribution of the contact pressure, originating in a wiper arm joined to the support element, to the window of a motor vehicle. By means of a suitable curvature of the unstressed support element—that is, when the wiper blade has lifted from the window—the ends of the wiper strip, pressed all the way against the window in operation of the wiper blade, are urged toward the window by the then-tensed support element, even if the radii of curvature of spherically curved vehicle windows vary in each wiper blade position. The curvature of the support element and thus of the wiper blade must accordingly be somewhat greater than the greatest curvature measured in the swept field of the window to be wiped. Thus the support element replaces the complicated support bracket construction of the kind used in conventional wiper blades, with two spring rails disposed in the wiper strip.
A known support element of this type (French Patent FR 21 91 510) is made from a plastic material, such as a polypropylene. However, it has been found that the strength and thus the elasticity of such support elements meet the demands made of them for only a short time, because the aging process that ensues makes the material brittle and causes it to creep. Especially the more markedly curved regions of the window can then no longer be cleaned, or can be cleaned only inadequately.
SUMMARY OF THE INVENTION
In the support element of the invention, the fibers admixed with and embedded in the plastic assure high, durably constant strength and elasticity of the plastic. At the same time, its thermal stability is also improved.
It has proved to be especially favorable if glass fibers or other fibers are admixed with the plastic.
Taking into account the work steps for preparing the plastic that precede the unmolding operation, it has proved to be especially favorable if the fibers have a length between 100&mgr; and 20 mm.
If the fibers have a length between 200&mgr; and 600&mgr;, especially unproblematic filling of the molding tool is possible, and the advantageous properties sought for the plastic material still come fully into play.
To further improve the thermal stability and reduce creepage, it is advantageous if the fiber-reinforced plastic is enriched with at least one mineral filler.
An especially economical design of the support element and thus of the wiper blade is obtained by providing that a connection device for the free end of the wiper arm is integrally formed onto the support element. A time-tested connection device for the wiper arm has two stubs, placed in the center portion of the support element and spaced apart from one another parallel to its length, which are connected to one another via a connection peg oriented crosswise to the length of the support element.
To produce a known support element, the molding tool is often—for example, for the sake of a rapid work sequence—provided with a plurality of injection openings, through which it is simultaneously filled with the plastic material. However, this causes so-called “seam formations”, where the material, arriving from the various openings, converges. At this “seam”, the support element, which in the wiping operation—because of the varying radii of the window—is subjected to uninterruptedly varying changes in shape, is weakened, and in the final analysis this can lead to damage of the support element and thus to a reduction in the wiping quality.
To avoid such “seam formations” and the attendant deficiencies, to produce a plastic support element, the still moldable plastic is introduced via a single opening, discharging into the mold and located in the middle region of the support element to be produced, and from there is forced out to the ends of the support element.
If furthermore fibers of defined length are admixed with the plastic material used for the purpose, the fibers become at least predominantly aligned in the flow direction of the material, and as a result optimal utilization of the fibers in the sense desired is achieved. This advantageous longitudinal alignment of the fibers is attained because, given the extremely slender geometry of the support element, this element practically comprises a pronounced fume layer, which has a very low flow speed, while the layers located beneath it flow substantially faster, and as a result the fibers undergo the aforementioned alignment in the polymer matrix.
It is true that from European Patent Disclosure EP 0 498 802 B1 a support element is known that is produced using fiber material. In it, however, the fibers are processed into strips which after being impregnated in a resin using a core strip are placed in a mold and then compacted. This way of producing support elements is complicated and thus expensive.
In a support element which has two stubs, placed in the center portion of the support element and spaced apart from one another parallel to its length, which are connected to one another via a connection peg oriented crosswise to the length of the support element, especially high strength of the connection peg, which is under high stress during wiping operation, is attained while preserving the aforementioned advantages if the plastic is introduced into a closed mold via a fill opening, characterized in that the fiber-reinforced plastic material is introduced into the mold in the axial direction of the connection peg of the support element to be produced, so that the fiber-reinforced plastic material is forced from there out via the stubs to the ends of the support element. The fibers located in the connection peg, as the mold is being filled, become aligned in the axial direction of the connection peg because of the aforementioned fume layer and the attendant shear flow, so that a substantial reinforcement of the connection peg and its transitions to the stubs is achieved.
Further advantageous refinements and embodiments of the invention are disclosed in the ensuing description of an exemplary embodiment, shown in the drawing, of the support element and of a production method for the support element.
REFERENCES:
patent: 3820188 (1974-06-01), Moorhead et al.
patent: 3837033 (1974-09-01), Van der Berg et al.
patent: 3925844 (1975-12-01), Cone
patent: 4014061 (1977-03-01), Jurowski et al.
patent: 4790992 (1988-12-01), Nishikawa
patent: 0 498 802 B1 (1993-12-01), None
patent: 2 191 510 (1974-02-01), None
patent: 2482540 (1981-11-01), None
Bald Rolf
De Paoli Albano
Just Bernhard
Kotlarski Thomas
Merkel Wilfried
Graham Gary K.
Robert & Bosch GmbH
Striker Michael J.
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