DD223023A1 - GRINDING BRUSHES FOR ELECTRICAL MACHINES - Google Patents

Abstract

The invention relates to the production of abrasive brushes, preferably of graphite brushes and plastic bound brushes, for reducing the radio interference of commutator machines. The aim of the invention is to reduce brush noise and commutator wear with minimum effort in order to improve the utility value properties of the machines by increasing the service life and reducing the radio interference. The task is to attenuate the causes of the generation and emission of electromagnetic fields by appropriate measures directly at the source of radio interference by changing the Schleifbuersten, in order to reduce the material and technical effort for radio protection measures. The object is achieved according to the invention in that the axial direction of the shaped body of the abrasive brush coincides with the grain orientation of die brushes pressed in the die and lies in the pressing direction and / or the circumferential surface consists of a metallic layer.

Description

Title of the invention

Grinding brush for electrical machines

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Field of application of the invention

The invention relates to the production of abrasive brushes, preferably of graphite brushes and plastic-bonded brushes, for reducing the punk interference of commutator machines.

Characteristic of the known technical solutions

The operation of commutator machines is associated with the emission of electromagnetic fields, the intensity of which is determined by the amount of the disturbance voltage, the interference field strength or the disturbance power. The radio interference is caused to a significant extent in the commutation by the current turning operation and the resulting plasma between commutator and brush. The radiation is also partly through brush and brush guide.

Since the radio interference in the frequency range 15o kHz to looo Mz leads to impairment of the reception of antenna-driven Kommunikationsssysterae, in most industrialized countries machines and devices are subject to state normative to limit the radio interference. Compliance with these government regulations usually requires the use of RFI components, depending on

Disturbing energy and critical frequency range for the abovementioned Punkstörstrahlung are the punk protection circuits (DE-OS 19 59 o37) more or less expensive. The additional expense is caused by material and assembly costs.

In order to comply with the limit levels for punk interference, Derechet punk protection circuits are used especially for the application. But also constructive measures in the design of the machine, in particular the determination of the switching voltage, and constructive technological measures to achieve a high degree of smoothness of the electric machine are practiced »

For smaller and smallest commutator machines, it is common practice to substantially reduce sparking only by brush displacement and a selection of suitable brush qualities. Likewise, one piece pressed carbon brushes for electrical machines, consisting of two brush parts of different composition, known (DE-OS 2o 25 216) _β A brush with a relatively low abrasion at the same time high current density and low contact pressure is proposed in DE-OS 28 17 371 , The abrasive body of this brush contains a plurality of graphite foils of highly graphitized graphite combined into a stack. This graphite material has a high percentage of crystallized graphite. At least one of the two flat sides to at least some of the graphite foils can be provided with a layer of an electrically conductive material, so that the grinding body in the direction of current flow parallel to the film plane is particularly low and its voltage drop is correspondingly low.

It has been shown that even with this brush with increasing peripheral speeds additional contact resistance occur because the rotating slip rings or

Commutators of the machines can never be ideally performed around. The less flexible graphite sheets can then lift off for a very short time. However, even a small lift of just a few micrometers leads to so-called brush fire, which is always associated with increased material removal and is generally difficult to suppress.

Further developments consisted of electrically adhering to the running edge of a block brush a relatively thin layer of a strongly anisotropic material made of carbon fibers (DE-OM 72 76 433), graphitized pyrolytic carbon or expanded and subsequently compressed graphite (DE-GM 77 oil o36). These abrasive brushes have not prevailed in practice. Finally, it is known to metallize the sliding on the brush guide side of the brush to reduce friction and thus improve the thermal conditions (DE-P3 871 o24). This metallization serves to establish a good contact with the metallic brush guide, as well as to reduce the arc bending due to contact separation,

2 iel the invention . "

It is an object of the invention to eliminate the deficiencies inherent in the known designs as far as possible and to reduce the brush and commutator wear with the least expense in order to improve the utility properties of the machines by increasing the service life and reducing the punk interference.

Explanation of the essence of the invention

The invention is based on the object by suitable measures directly at the source of punk disturbances by changing the brushes the causes

for the development and emission of electromagnetic fields, in order to reduce the material and technical costs for radio protection measures.

The above object is achieved in that the axial direction of the PormkÖrpers the brush corresponds to the grain orientation of pressed in the die grinding brush and is in the pressing direction and / or the lateral surface consists of a metallic layer.

The safe contact between the brush and brush guide as a result of the metallic coating, z. B. chemical nickeling serves the same time avoiding 'Abrißfunken with concomitant Punkstörung.

The advantage of the invention is in particular that DaCf by using the existing anisotropic properties of the Biiratenwerkstoffes a reduction of the transition SpanriPripulation between brush and commutator by the semiconductor layer is partially removed on the commutator by the abrasive action of said measures and the discharge of the brush and blade which leads to the ignition of the spark in the ionized charge channel, already takes place at low voltage and so the stored energy is limited to the degradation of the radio interference radiation is recorded,

Outline example . , '

The abrasive brushes, such as graphite brushes or plastic-bound bars are integrally pressed in a known tool. When using brushes made of grain-oriented graphite, these brushes are to be installed so that the pressing direction and the axial direction of the brushes, when pressed in the die brushes, match. The components that clean conventional • ' graphite brushes can be omitted if the brush is given a metallic coating on all sides. These coatings take over the task of the usual cleaning ingredients » ^! -

The application of the all-round metal layer, ζ. 3, nickel layer, by wet chemical deposition with the following steps:

- Washing in acetone - drying

Activation in a PdC / P-containing solution (palladium chloride) Io min at room temperature

- Do the washing up ,,

- chemical nickel plating in one) 3ad of the composition. 2o g / liter IIi50 ₄ .7 H ₂ O (nickel sulfate A). 15 g / liter of NaH ₂ PO 4 .H ₂ O (sodium hypophosphite). 3o g / liter of lactic acid

3 g / liter of propionic acid

1 g / liter of lead nitrate

at a coating temperature of 95 ° C, pH 4.5-4.8

- Rinsing and drying

Claims (2)

Erflndungsänapruch 1. Abrasive brush for electrical machines, preferably integrally pressed graphite brushes and plastic-bonded brushes, characterized in that the axial seal of the shaped body of the abrasive brush coincides with the grain orientation of die pressed abrasive brush and is in the pressing direction and / or the lateral surface consists of a metallic layer, 2, abrasive brush according to item 1, characterized in that the layer is applied chemically and preferably consists of nickel *