Carbon brush for miniature motor and manufacture thereof

The invention generally relates to a carbon brush for Small engines with a permanent magnetic field, and the particular a brush coated with metal-graphite, which is produced in that a fibrous material the metal-coated graphite powder obtained by loading layers of graphite powder with a metallic Layer is formed, is added, followed a mixture of metal coated graphite powder and the fibrous material is compression molded and GE is sintered.

Carbon brushes for small motors are far in the way been manufactured in that a binder of the graphite powder is added, the purified to about 98%, or 99.5% was that the solidified mixture crushed and ge was screened out, and in that a metallic powder with the milled and sieved mixture was mixed to the desired electrical conductivity to obtain whereupon the resulting mixture is compression molded and was sintered.

In order to avoid the use of the binder is other than which a brush coated with copper graphite be known. This copper-plated graphite brush is as by made that particles of graphite powder was purified to about 99%, coated with copper who to, whereupon the copper-plated graphite powder without compression molded adding a binder and is sintered.

In all cases remain pockets in particle size 1 to 100 microns, for example, SiO₂, Al₂0₃, Fe₂0₃. MnO, MgO and TiO, back in the graphite powder.

<b>Fig.</b> 7 is a photomicrograph of the particles, the structure of the ashes is mainly composed of SiO₂ , and which are contained in the graphite powders. The Photomicrograph shows that the ash different have particle sizes and can be sized large.

Carbon brushes with ashes in particle sizes above 50 microns tend the commutation to ver deteriorate because the ashes during the rotation of the motor between the carbon brushes and the commutator occur whereby the engine can fail in extreme cases.

To avoid this, the applicant of the present Patent Application already carbon brushes for small motors proposed, the production process a cleaning includes reporting process, wherein the graphite powder to a purified ash content of less than 0.05 weight percent becomes.

In experiments, it was determined that a brush for Small engines, the metal-coated graphite powder, the ge in the above-mentioned cleaning process has been cleaned, prepared, after which the powder is pressure-molded and sintered (Japanese patent cation No. 1 03 201/1989) lower mechanical noise ent developed and improved commutation has, However, a considerable abrasion is subject, as in <b>Fig.</b> 3 (test no. 1) is shown, which further un th is explained in more detail.

In order to improve the wear resistance, has the on detectors of this patent application in the japa African patent application no. 1 03 201/1989 a carbon brush provided for small engines and their method of preparation propose, in the oxides the graphite powder is added, which has been previously cleaned in the cleaning process, so as another carbon brush for small engines and their Manufacturing process in Japanese Patent Application No. 2 47 114/1989, in the same way an elec trically conductive material is added.

Tests have shown that the above-mentioned coal brushing, which oxides as the electrically conductive material is added, improved wear resistance have, however, that it be a low dimensional stability sit.

Object of the present invention, it is, this Pro problems to solve.

This object is achieved according to the characteristics in sign of the claims 1 to 4 indicated Watch male dissolved. Advantageous embodiments of the invention are characterized in the dependent claims.

The carbon brush according to the invention for small engines is produced by using a graphite powder gerei to less than 0.05 weight percent ash content nigt, where 0.1 to 12.0 weight percent of a fiber like material with particle sizes below 40 microns added and lengths less than 50 microns demGraphitpulver are.

Further features, advantages and details emerge from the following description and with reference to the Drawing. They show:

<b>Fig.</b> 1A is a schematic representation of the principle carbon brushes for small motors in accordance the invention;

<b>Fig.</b> 1B is a diagram for explaining a inven to the invention manufacturing process;

<b>Fig.</b> 2 is a schematic representation of a Fri schungs- or cleaning furnace, which in a used cleaning process according to the invention becomes;

<b>Fig.</b> 3 is a diagram for explaining the loading relationship between the type of when gungs the substance and the degree of wear;

<b>Fig.</b> 4 is a diagram for explaining the loading relationship between the mixing amount of the fibrous material and the wear degree according to the invention;

<b>Fig.</b> 5 is a photomicrograph of the particles, the structure of glass fibers shows that inventions be accompanied by formation of the carbon brush;

<b>Fig.</b> 6 is a diagram for explaining another Embodiment of the invention and

<b>Fig.</b> 7 is a photomicrograph of the particles, the structure of mainly of SiO₂ consist the ashes shows the ent in graphite powder are met.

<b>Fig.</b> 1 illustrates the inventive principle, wherein <b>Fig.</b> 1A schematically illustrates the principle of the invention and <b>Fig.</b> 1B show the manufacturing process.

In the figure, reference numeral <b>1</b> a commu tator, <b>2</b> a commutator segment, <b>3</b> a rotor, <b>4</b> a Carbon brush and <b>5</b> an elastic brush part.

In <b>Fig.</b> 1B, the reference numeral <b>20</b> graphite powder which is purified, for example to about 99%, <b>21</b> a cleaning process according to the invention, <b>22</b> a Fiber material admixture process, wherein 0.1 to 12.0 Weight percent of a fibrous material (glass fiber, alumina fiber, silica fiber, Zirkoniumfaser, Carbon fiber, whiskers, etc.) in particle sizes of we niger added than 40 microns and lengths of less than 50 microns are joined, <b>23</b> a metal-plating process, <b>24</b> a Pressure molding process and <b>24</b> a sintering process.

The carbon brushes <b>4</b> are electrically conductive Brush spring parts <b>5</b> maintained and in such a way supported so that it is in sliding contact with the commutator segments <b>2</b> to stand. The carbon brush<b>4</b> is to a swept T-shape sintered, their longitudinal web of the Brush spring part <b>5</b> held as <b>Fig.</b> 1A-1 in a perspective view shows. The bottom surface of the to swept T-shape is slightly curved and is in sliding contact with demKommutatorsegment <b>2</b>,

As <b>Fig.</b> 1B, the brush is carried out execution of the cleaning process <b>21</b>, The fiber material Incorporation process <b>22</b>, The metal-coating process <b>23</b>. the pressure molding process <b>24</b> and the sintering process <b>25</b> of the graphite powder <b>20</b> produced.

A copper-plated or -plattierte carbon brush, the forth by coating graphite powder with copper is detected, is generally known. The present Invention is characterized in that the graphite powder is purified so that it has an ash content of less than 0.05 weight percent in the Reinigungspro process <b>21</b> replaced so that the ash content of the produced carbon brush <b>4</b> is less than 0.05 weight percent. This be indicated that the carbon brush inventive magnificent P designated commutation due to the extreme never has drigen ash content of the brush.

The addition of 0.1 to 12.0 weight percent of above-mentioned fibrous material with a part size of from less than 40 microns and lengths from we niger than 50 microns in the fibrous material admixture process <b>22</b> contributes to the dimensional stability and the abrasion strength improve.

In addition, almost the same treatment as in the Manufacturing processes of the prior art in the Metal plating process or metal Plattierunsprozeß <b>23</b>. the compression molding process <b>24</b> and the sintering process <b>25</b> out out that in <b>Fig.</b> 1B are illustrated.

<b>Fig.</b> 2 is a schematic representation of a Fri Research furnace cleaning or furnace used in the inventions to the invention the cleaning process is used. The Be numeral <b>20</b> in the figure, graphite powder, <b>30</b> an oven, <b>31</b> a transformer, <b>32</b> a halogen pipe and a heater 33.

In the cleaning process <b>21</b> be ash constituents of the graphite powder <b>20</b> using a halogen releasing substance such as CCl₄ or CCl₂f₂ away, halogen which substances at high temperatures in an inert gas such as nitrogen or argon full constantly release. The graphite powder<b>20</b> is in the oven <b>30</b> filled, wherein the halogen gas pipe <b>32</b> in the graphite powder <b>20</b> is arranged. If the tempera ture in the furnace due to the heating device <b>33</b> to about rises to 1800 ° C, CCl₄ saturated in the inert Gas by the halogen tube <b>32</b> supplied. This Too level can be assumed that in the oven, the fol lowing reactions occur.

CCl₄ → C + 2 Cl₂

3 C + Fe₂O₃ + 3 Cl₂ → 2 FeCl₃ + 3 CO

When the temperature further rises to 1900 ° C, CCl₄ by Cl₂F₂ replaced, and the cleaning process is continued for 4 hours at about 2500 ° C. In the following cooling process is to rinse with a inert gas such as nitrogen or argon maintained to to avoid a reverse diffusion of the ash content and discharge the halogen.

This cleaning process is a purity of Graphite about 99.95% and an ash content of less obtained as 0.05 weight percent.

presented the assignee of the present patent application Brushes coated with copper graphite with Ver use the following steps in addition to the cleaning process forth to the purity of the graphite, the used in the metal-coated graphite brushes was to improve, and carried out experiments on engines these brushes are made of.

i) Physical Cleaning

Graphite was separated from ashes in the flotation process, the differences in physiochemical surface self uses properties of solid particles. The physical cleaning process treated particles of about 300 microns in size. Due to the fact that graphite with air bubbles ge can be separated, graphite powder was added to a mixture imported from oil and air bubbles and collected by the graphite particles in the floating bubbles to adhered. This process can not have a purity of less than 98% and less than 99.5% can be achieved. This means that 0.5 to 2.0% of ash in demGraphit powder contained.

ii) Dry Cleaning

The ash content of the graphite powder was highly concentrated trated acid and alkali solutions dissolved, and the solu solutions were heated (at 160 to 170 ° C) and under Print set (5 to 6 atms). This treatment is commonly called autoclave process, the main of the following reactions is:

Fe₂O₃ + 6 HCl → 2 FeCl₃ + 3 H₂O

2 SiO 4 + NaOH → 2 Na₂SiO₃ 2 H₂O

This chemical treatment purities of not less than 99% and less than 99.9%, it aims, with contaminants from not less than 0.05% and about 1.0%, the graphite powder to be in the back stay.

<b>Fig.</b> 3 shows experimental results of the coal There have been brushing, namely at a brush, of the oxides is added, a brush, of a electrically conductive material has been added, a Brush without Bemischungsstoff and an inventive Brush, all by the production process with was made the cleaning process, the graphite, the powder to less than 0.05 weight percent ash content purified as mentioned above. are test no. 1 the results for a carbon brush again, the had no admixture, test no. 2 relates to a Carbon brush, an electrically conductive material (SiO₂) Was added to a small particle size, Test No. 3 is a carbon brush, the electrically initiate the material (TiC) added a small particle size was, and experiment no. 4 A carbon brush in accordance with the prior invention, of a fibrous material (glass fiber) was added. <b>Fig.</b> 3 shows the Versuchser results in a maximum of 80 hour-long tests 10 brushes, each the test numbers 1 to 4 ent speak. The size of the addition of SiO₂ and TiC was each 1.0 weight percent, with particle sizes below 40 microns. In the case of the experiment no. 4 was 1.0 Ge weight percent glass fiber having a particle size below 40 microns and lengths of less than 50 microns added. The Column "term until engine failure" in <b>Fig.</b> 3 shows that the carbon brushes of the test numbers 1 to <b>4</b> have successfully survived the 80-hour test. The column "wear amount" at the end of the 80-hour However, testing shows significant differences in the Wear. That is, the wear test was at the No. 1 is greatest, while in the experiments <b>2</b> and <b>3</b> had already improved. When trying Nr. 4 (vorlie lowing invention) was the degree of wear strong ver repaired.

Moreover, the activities carried out by the Applicant showed Tests indicate that the degree of wear in a close relationship related to the amount of the attached fibrous material. The relationship between the degree of wear and the size the incorporation of the fibrous material (glass fiber) is in <b>Fig.</b> shown. 4 The glass fiber, in which the the tests used carbon brush has been added, has particle sizes below 40 microns and lengths under 50 Micron. The test results in<b>Fig.</b> 4 relate to each Weil's 10 brushes for each test number, which the brushes have a 80-hour test subject. The x-mark indicates the date on which a brush precipitated.

Out <b>Fig.</b> 4 it can be seen that the blending amount the glass fiber in the range of 0.1 weight percent (Test no. 1) to 12.0 percent (experiment no. 7) must be maintained in order to reduce the degree of wear. Ie., At a mixing amount of 15.0 Gewichtspro cent (experiment no. 8) resistance no carbon brush a 80-hour operation, but fell after average maturities of 64 hours.

<b>Fig.</b> 5 is a photomicrograph of the particles, the the structure during the manufacturing process of it inventive carbon brush added fiber shows. From the micrograph it can be seen that the particles used according to the invention, the glass fiber nearly uniform in size and shape. As described above, the particle sizes of glass fiber less than 40 microns and lengths of less than 50 Micron.

Further up is the carbon brush according to the invention be wrote that in accordance with the <b>Fig.</b> 1B Her shown setting process was prepared. The invention is but not limited to. The order of Manufacturing process in accordance <b>Fig.</b> 1B can also following be reasonably: cleaning process <b>21</b> → metal Überzogprozeß <b>23</b> → fibrous material admixture process <b>22</b> → pressure molding process <b>24</b> → sintering process <b>25</b>, This may be the same Effects are obtained as in the case of a carbon brush, pursuant to the manufacturing method <b>Fig.</b> 1B ago was provided.

Regarding <b>Fig.</b> 6 is a further inventive Production process of the carbon brush described. The numeral <b>26</b> in the figure, a binder treatment process, GE wherein in the cleaning process solidified purified graphite powder with a binder becomes, <b>27</b> a grinding and sieving, in which the in which Binder treatment process <b>26</b> solidified with a binder is crushed and sieved graphite material. The remaining Reference numbers correspond to those in <b>Fig.</b> 1B.

In <b>Fig.</b> 6, the graphite powder <b>20</b> in the cleaning process <b>21</b> cleaned. The purified Grahitpulver<b>20</b> is with a binder in the binder treatment process <b>26</b> solidified. The solidified material is graphite in the grinding and screening process <b>27</b> crushed and sieved.

Then 0.1 to 12.0 weight percent of a fibrous material with particle sizes below 40 microns adds and lengths less than 50 microns and with the zer -ground and sieved graphite material in the Faserma terialvermischungsprozeß <b>22</b> mixed. Then, the Graphite material the pressure molding process <b>24</b> and the Sin terprozeß <b>25</b> for producing a carbon brush <b>4</b> among discarded. The fiber mixing process<b>22</b> in <b>Fig.</b> 6 can with the binder treatment process <b>26</b> be combined. Ie., That in the purification process <b>21</b> purified graphite powder can be subjected to a binder treatment process be after the fibrous material added and was mixed with the graphite powder.

Above, with respect to <b>Fig.</b> 6 shows a further Her setting process of the carbon brush according to the invention described. The method according to the<b>Fig.</b> 6 ago Asked carbon brush can achieve the same effects such as those wherein one by Herstellungsver driving under <b>Fig.</b> receive 1B carbon brush produced will.

The present invention provides a carbon brush with improved dimensional stability and wear resistance prepared by graphite powder is purified so that it less than 0.05 weight percent ash as impurities contains, and the graphite powder from 0.1 to 12.0 weight percent fibrous material is attached, the particles sizes below 40 microns and lengths of less than 50 microns has.