Compositions – Compositions for coating or impregnating a substrate used...
Reexamination Certificate
2001-03-09
2003-04-22
Gupta, Yogendra N. (Department: 1751)
Compositions
Compositions for coating or impregnating a substrate used...
C208S110000, C428S058000
Reexamination Certificate
active
06551525
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dust-proof element and a method of its use in an electrical hand-held tool for removing an abrasive material, preferably, in a drilling, chiseling, sawing, or grinding tool and with a corresponding working tool.
2. Description of the Prior Art
For minimizing an adverse action of the dust in a tool, usually, the following measures are undertaken, generally, in combination:
the dust is collected at the source of its generation, whereby less dust is released in a space surrounding the source;
measures are undertaken to hinder penetration of the dust into the tool, so that less dust reaches inside of the tool, in particular, less creeping dust penetrates inside the tool; and
measures are undertaken to prevent deposition of the dust inside the tool, whereby less dust remains there. To effect all of the above-listed measures, usually, dust suction devices such as dust filters, dust barriers, and dust traps are used. Dust traps are locally limited and are arranged inside the tools. Dust traps usually represent volumetric or flat objects which serve as dust collectors for dust particles and absorb the dust when the dust constantly penetrates into the tool. Creeping dust, which consists of coagulated, separate, creeping or migrating, dust particles, creeps over free, smooth surfaces because such surfaces do not resist in any noticeable way the movement of the particles therealong. To prevent migration of the creeping dust particles, artificial dust barriers can be used which make more difficult either penetration of the dust particles in the region, where a barrier is provided, or make more difficult for the dust particles to leave the dust barrier region. As dust barriers, volumetric of flat objects are used which prevent dispersion of the dust particles in a direction transverse to a direction in which the particles move along a barrier. The present invention will be described with reference to tools for removing abrasive materials, which removal creates a lot of dust, but the invention is not limited only to this type of tools..
A dust generated during removal of abrasive materials, such as drilling and sawing dust, chips, and the like has particles with a very small size and suitable for being transported, by a moving air, over a distance from several cm to several meters. The particles become adhesively settled on free surfaces of electrical tools and the working tools, in particular, on concave surfaces and in locations where the flow velocity of air is small. Upon treatment of abrasive materials, a possible electrostatic charge contributes to settling of dust particles on dielectrical surfaces along which the particle move. High air humidity also contributes to settling of the dust particles. The dust particles, which settled on smooth surfaces, creep further therealong.
Dust deposits adversely affect, in particular, operation of electrical hand-held tools having an integrated electrical drive and which are, optionally, air cooled. The dust particles increase frictional forces acting on the drive components and reduce the service life of the bearings as a result of their increased wear. With respect to the power electrics and power electronics, the dust facilitate formation of conductive cross-connections which adversely affect the reliability of the operation of a tool and reduce heat dissipation by air convention and radiation which also reduces the service life of the tool, because the tool becomes subjected to higher operational temperatures.
Numerous solutions were proposed for reducing dust accumulation in electrical hand-held tools. Thus, German Publication DE 31 26 511 discloses a dust-proof cup which is connected with an electrical tool, surrounds the working tool, and is sealingly attached to a workpiece. The disclosed dust-proof cup is formed as a transparent bellows, with the dust being removed, during the working of an abrasive material, through suction nipples provided in the bellows and connected with a vacuum apparatuses. According to DE 31 26 511, the generated, during the working of an abrasive material, dust is removed by suction from a space already closely behind the working tool cutters through the hollow working tool.
German utility model DE 298 12 69901 discloses that for removing the cut-off abrasive material from the working tool, chip removing channels are formed in an electrical tool. The removing channels are formed in the outer surface and are subjected to action of an air stream. In order to reduce obstructions, which are formed by accumulation of the removable abrasive material, the surfaces of the removing channels are made with a highest quality and are very smooth. To this end, the surfaces are provided with a metallic or ceramic coating, in particular, a chromium coating. However, the dust, which settles on this smooth surface is still capable of creeping therealong rather well.
Different constructive measures were contemplated to prevent penetration of the dust into the dust-sensitive drive located inside of an electrical tool. E.g., German Publication DE 41 36 584 discloses a locking sleeve for receiving a working tool and connected with the housing of an electrical tool. The working tool is received in the sleeve practically without any clearance. German Publication DE 34 18 882 discloses a dust-proof cap having elastic sealing lips which engage a rotating or swinging working tool. Narrow clearances prevent the penetration of the dust with a movable air, however, the dust still is able to penetrate inside the tool by a capillary effect, i.e., is capable of creeping in. The sealing lips, because they are subjected to wear, can be used as a dust barrier only to a limited extent and are not suitable for a long-lasting prevention of dust creeping in.
A common drawback of all of the above-discussed solutions consists in that they cannot completely prevent penetration of the dust particles with the movable air inside the tool where they coagulated, primarily as a result of humidity inside the tool, and settle in critical locations, which substantially reduces the service life of an electrical tool and operational capabilities of the tool.
European Publication EP 272 514B1 discloses artificial self-cleaning surfaces, which are formed in accordance with so-called “Lotus-effect” and their use for effecting self-cleaning. These surfaces have a hydrophobic microcrystalline pimpled structure that does not hold water. When such as surface is subjected to action of water droplets, the droplets absorb dust particles, which settled on the surface, and carry them away. The water droplets, which are applied in form of rain, provide for effective self-cleaning of such surfaces. European Publication EP 909 747A1 discloses a method of producing such self-cleaning surfaces in form of protective layer which is formed by dispersion of powder particles of a ceramic material in a hardenable silofane solution. This layer is used, preferably, for coating of roof tiles. It is also known to use such surfaces for covering visible inner and outer structures of bins and inner and outer surfaces of pipes to provide for better cleaning of such surfaces with moveable water. It is known to use such surfaces for structures which need be cleaned without any residue remaining thereon by a movable water. Cleaning with movable or running water is not possible in electrical tools for safety reasons. Self-cleaning with a moveable or running water of such surfaces does not suggest the use of the self-cleaning surfaces when the use of the running water is not possible or is not allowed.
An object of the present invention is to eliminate the drawbacks of the known dust protection means and to provide long-lasting dust-proof means that would prevent penetration of creeping dust particles or harmful deposition of dust particles inside an electrical or other tool.
SUMMARY OF THE INVENTION
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing
Hofmann Karl-Heinz
Löffler Alexander
Gupta Yogendra N.
Hamlin Derrick G.
Hilti Aktiengesellschaft
Sidley Austin Brown & Wood LLP
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