DE4204407A1 - Low resistance commutator brushes - use an additive of micro encapsulated lubricant to allow a lower graphite content to be used - Google Patents

Abstract

Low resistance brushes with low friction are based on a mixt. of graphite, copper and a binder and formed by direct pressing. The feature is that the powdered or granulated starting mixt. contains micro-encapsulated lubricant particles, with a dia. of pref. 1-100 microns, esp. 20-50 microns. The quantity used is pref. 0.005-3% wt., esp. 0.01-1.0% wt. The binder is pref. an organic material which remains in the brush after a hardening or melting process. USE/ADVANTAGE - The use of lubricant capsules allows the quantity of graphite in the formulation of the brushes to be reduced in favour of Cu, which reduces the resistance of the brushes. The reduced resistance also gives a longer operating life. The brushes are used for motors in automotive applications and have a typical max. current density of 25 A/cm2 at max. 30 m/s tangential speed u

Description

The invention relates to low-resistance commutation brushes of copper / gravel type, which are characterized by low friction coefficients th and thus have low wear values in kommu animal operation. The application is given vorran gig in electric motors of automotive electrical. The maximum permissible continuous current density of the brush material ent speaks here conventional conditions up to about 25 A / cm ² at a maximum peripheral speed of 30 m / s.

When operating electric motors in low and low voltage For functional reasons, areas are often metal / graphite brushes used to produce small transient voltages and high To ensure power transmission loss. chief representative This group of materials are copper / graphite systems with specifi rule resistances of 0.2 to 20 μOhm.m. A high performance Transmission without high JOULE losses can thus carry be led. To complain about the life of this system me, since copper commutators are usually used and for a good contact pairing of more similar (metallic) Contact partners so far still no optimal and cost-effective technical solution could be found.

In the manufacturing process of copper / graphite brushes, Mi of a highly graphitized material and electrolyte copper powder with and without organic binders used. Here, the copper content is used to realize a high electrical conductivity and the graphite part to the realisie tion of the lubricity of the brush material on the commutator. The shaping of the brushes is achieved by direct compression molding realized. In this process, the necessary Kontaktie be anchored elements simultaneously in the molding. In order to realize acceptable mileage, me tallhaltige brushes with a minimum of these materials  allowed, which, of course, at the expense of the desired high electrical conductivity goes.

This material-based effect thus runs on egg NEN compromise between a good electrical conductivity and the required service life. At this behavior is thereby relatively little changed, if that may be existing plastic binder in a z. B. nitrogen atmosphere removed by thermal processes from the composite material or is pyrolyzed.

The aim of the invention is that described State of the art adhering to the lack of compromise zwi more efficient power transmission and mileage of the Commutating power transmission system to reduce costs or eliminate.

According to the invention, this object is achieved in that the known microencapsulation processes, e.g. B. from the through Schreibware technique (Dye-Leukobases) and pharmacy (micro / nano-encapsulation of active substances), for encapsulation or particulation of impregnating agents is used and the Microcapsules a copper / graphite composite material for the manufacture tion of low-ohmic commutation brushes are added.

For encapsulation reach such substances, in the usual way by Vakuumimgrägnnierung a large part of carbon brushes mediated. This impregnant particulation, in fol called microencapsulation, allows all known liquid and solid impregnating agent, individually or together and in nearly spherical design and variable sizes education through technological processes. For the Ver Reduction of the coefficients of friction are especially micro capsule diameter from 1 to 100 microns.

These capsules can propro in the case of plastic-bound production, eg B. by direct compression molding on Tablettierautoma or special presses, already in the mass preparation of the Graphite / copper / plastic mixture are added, if the cap  selmaterial is insoluble in the necessary solvent. There a direct and automatic molding always to the use is bound to a suitable granules, there is also the possibility sensitivity, microencapsulated excipients first under the granules mix if the solvents used require this.

From this procedure, it is apparent that the erfindungsge According to low-resistance commutation brushes, not the thermal one Loads in the production process are to be suspended would require a thermal fugacity of the binder phase. These brushes are therefore with a temperature and heat dimensionally stable plastic binding. To the low impedance Properties of the brush material does not worsen The copper content raised accordingly, so that only small men gene of a hochgrafitierten material can be used.

According to the invention, the friction through the microencapsulated Lubricants are reduced. This task was at conven union copper brushes just by this Grafitanteil and thus caused by "dry lubrication".

In the direct shaping process of the brushes, see Be Attention to the tolerance field of the dimensions of the radii and Edge breaks in the mold creates a later rework tion can be omitted. For those contained in the press mixture Microcapsules are virtually iso in the molding process static pressure, which does not destroy the capsules leads. As already mentioned, the reinforcements of the Brushes are involved in this shaping process simultaneously.

The curing temperatures of the plastic binders used are Type-linked to the used thermally reactive system and are directed u. a. even after the use cases of the final Products. When using prepolymerized epoxies Curing can already be successful in the range of 130 to 180 ° C which is also gentle on the microencapsulated material effect. Destruction of the capsule material is in geeigne Material selection and the low curing times excluded sen.  

In the described manner can thus low-resistance commutation be made during the natural Operating wear in t-dimension with the grinding of micro encapsulate through the commutator highly effective lubricant exponie Here a process in a constantly repeating form, the one for the operating condition of the commutator a rule represents the size of the reduction in wear. The lubricating effect This system is also due to the relatively low graphite content supports the brushes. On the different use cases can optimizations of the wear sizes in Wechselbe to the specific resistance of the brush material be guided. Due to the long-term availability of microverkap Rarely lubricant is a high life brushing effective given, even if long-term and thermally exposed Be drive breaks are selected. The friction-reduced brush barrel also has a positive effect on the wear sizes of the commuta tormaterials out.

Essential for the purposes of the invention, the landfill of high effective microencapsulated lubricants in the structure of copper / Gra Fit brushes, even after a simple technology are. Of the numerous processes for the production of Microcapsules are the consequences for the applications mentioned the relevant:

• - complex coacervation between positively and negatively charged Colloid polymers, wherein the reaction conditions over pH Value and temperature settings are effected. (ARNEODO, C., BENOIT, J.-P., THIES, C., S.T.P. 2, 303-306 (1086), BECHARRD, S., McMULLEN, J, N .; Pharm. 31, 91-98 (1986)
• Polymerization to form various wall materials, wherein the capsule formation from internal diffusion processes dissolved monomers to the polar solvent takes place, (HARMIA, T., SPEISER, P., KREUTER, J .; J. Microencapsulation, 3, 3-12 (198S)  
• - Spray drying and similar methods, eg. B. spraying with 3-material nozzle or envelopes by means of a rotating Disc according to DE 27 46 489 (19.4.1979) and DD 2 39 951 (15.10. 1986).

To lower the frictional resistance in the commutative, but also sliding brush contact on commutators and / or Slip rings become the graphite / copper / plastic binder mixture 0.005 to 3% by weight of microencapsulated friction-reducing substances set produced by one of the above methods the. Included here are all known variants except me tallish phases. It would be useful here in hydrophilic and hydro To distinguish phobic lubricant, as in this behavior a technological reference to the type of microencapsulation herge is presented.

On an experimentally based basis, the diameters of the nearly spherical microcapsules to 1 to 100 microns, preferably set to 20 to 50 microns. As a capsule Wall materials are used substances whose temperature or Heat resistance classes to the respective requirements in technological process and operational behavior.

For the phase separation method (complex coacervation) u. a. the following mentioned positively charged colloids gelatin (attention to the isoelectric point) and Citosan, for negatively charged colloids: Arabic gum, Tragacanth, pectin, alkali alginates, polyacrylates (carbopol), agar Agar, carboxyl cellulose, polyvinyl pyrrolidone, polyvinyl alcohol u. a., And the surfactants sodium oleate, sodium alkyl sulfate u. al., glutaraldehyde, glyoxal, cinnamaldehyde, Tannic acid and other aldehydes.

For the polymerization, the wall materials are made Polythiocyanates, polyisocyanates, polyamides, epoxy compounds urea compounds and urethane-epichlorics hydrinsynthese, as well as from methyl and Ethylcyanoacrylaten he testifies.  

On the possibility of using the Fällbadmethoden is on This point only pointed out, since with these procedures in the Usually only coarse-grained particulates can be obtained.

The state, which is characterized by the inventive introduction of microencapsulated lubricants in plastified copper / graphite Brush material systems, is to be described as follows: When commutating the brushes to Cu commutators tre certain wear sizes of the brushes in Tangentialmaß, wherein microparticles are removed. Parallel to this run also chemical oxidation processes, which in the case of Auftre least significantly increased by brush fire. At the Brush fire becomes a plasma state of the ambient medium he testifies, in the course of which also oxygen in its nascent Form and into ozone is transferred and thus the existence stronger Oxidizing agent based in / on the slip plane.

A calm, cool run of the Kommutierungspartner reduces this Effects and increases the life of the commutation apparatus. That's the measure for the low-ohm operation of commuta The subject matter of the present invention is.

embodiment

A ground offset for the production of low-resistance commutation brushes is made as follows:

Basic materials: - High graphitized carbon @ (Electro and / or natural graphite of the grain band 1 to 60 microns): 8.0% by mass - copper powder, fine screening: 86.0% by mass - Microencapsulated paraffin oil (KP <300 ° C): 0.4% by mass Epoxy binder: 5.6% by mass Auxiliary material: organic solvent

After a dry mix of the base materials z. In one Kneading mixer becomes an organic solvent in the Amount added that after a further Walk process a pasty Mixture is achieved. This is determined by means of a FREWITT-Gra nuliermaschine particulates. After expulsion of the solvents phase is carried out a screening on a grain size of 0.5 to 1 mm.

The shaping takes place in the usual way in eccentric presses Füllschuhbetrieb and feeding the contact or Armierungsele preferably in stranded form. Here are the formulas elements, such as running radii, edge breaks and possibly bevels already formed by the tool.

The curing of the binder to impart the necessary mechanical brush parameters are carried out in the circulating air drying cabinet at about 155 ° C, in special cases, this process in Nitrogen atmosphere is made.

It should be noted that by modified thermal Processes on the granulated base material have a positive influence exerted on low geometric tolerances of the moldings can be.

Claims (4)

1. Low impedance commutation brushes with low Reibungsko efficient on the basis of graphite / copper / binder systems, which are prepared by direct compression molding, characterized in that contained in the powdered powdered or granulated Preßmischungen microencapsulated te lubricant to reduce friction. 2. Low impedance commutation brush according to claim 1, since characterized in that the diameters of the microcapsules 1 to 100 microns, preferably 2 to 50 microns. 3. Low-resistance commutation brushes according to claims 1 and 2, characterized in that the Dry mass of the graphite / copper / binder system 0.005 to 3 mass%, preferably 0.01 to 1.0 mass% microencapsulated Lubricants are added. 4. Low impedance commutation brushes according to claims 1 to 3, characterized in that the Bin consists of organic substances and that this after a curing process or remelting process in the Brush structure remains.