DE102008035849A1 - Method for coating a brake area of brake disks or other friction elements of brakes, comprises applying a wear-resistant coating on the brake area through thermal injection - Google Patents

Abstract

The method comprises applying a wear-resistant coating on the brake area through thermal injection. The brake area is roughened before applying the coating through radiation with a hard material granulates. A radiation nozzle is moved for spraying the hard material granulates in an interval from the brake areas linearly over the brake areas. The brake areas are hardened on a surface roughness of 20-30 mu m. The hardened break areas possess a profile extension of 70-90%. The brake disk is heated at 120-150[deg] C before applying the coating. The coating is applied by electric arc spraying. The method comprises applying a wear-resistant coating on the brake area through thermal injection. The brake area is roughened before applying the coating through radiation with a hard material granulates. A radiation nozzle is moved for spraying the hard material granulates in an interval from the brake areas linearly over the brake areas. The brake areas are hardened on a surface roughness of 20-30 mu m. The hardened break areas possess a profile extension of 70-90%. The brake disk is heated at 120-150[deg] C before applying the coating. The coating is applied by electric arc spraying in which the free ends of the wires made of metallic materials are melted in an electric arc and the melt is injected with pressure gas on the brake area. The coating is applied through high speed flame injection in which a powdery material is melted in flame and injected with ultrasonic speed on the brake area. The material comprises oxide-free ceramic material and metal. The ceramic material is metal carbide, tungsten carbide. The metal is cobalt or nickel. The coating is polished on a layer thickness of 0.2-0.4 mm after the application. The coating is polished up to its surface possesses a surface roughness of less than 2 mu m, and a profile extension of more than 99%. An independent claim is included for friction element for a brake disk.

Description

The The invention relates to a method for coating braking surfaces of brake discs or other friction elements of brakes, in which a Wear-resistant coating on the braking surfaces is applied. The invention further relates to a friction element a brake, in particular a brake disc, with at least one Brake surface and one applied to the braking surface wear-resistant coating.

The DE 698 12 344 T2 already discloses a method for coating a brake element with a friction material in the form of a wear-resistant ceramic-metal composite, in which a ceramic preform of B ₄ C, AlB ₂ , Al ₄ BC, Al ₃ B ₄₈ C ₂ , AlB ₁₂ and / or AlB ₂₄ C _{4 is} infiltrated with metal and the preform is then subjected to a heat treatment before it is laminated, for example by gluing on the brake element. However, it is considered disadvantageous in the known method that it is very lengthy and, moreover, very complicated.

outgoing This is the object of the invention, a method and to improve a friction element of the type mentioned in the introduction, that in a simpler way one on its braking surface or its braking surfaces with a wear-resistant Provided coating provided friction element for brakes can be.

These The object is achieved according to the invention that the coating by thermal spraying on the braking surface is applied.

It has been shown that the friction surfaces of friction elements for brakes and in particular of brake discs by thermal Syringes can be provided with a coating, which ensures that the friction surface in interaction with the friction surface of a further friction element of the brake, like a brake shoe, has a good grip, taking itself after a long period of use no noticeable scoring is recorded in the braking surfaces of the brake disc and wherein the heat dissipation through the coating itself is sufficient for heavy use, in order for excellent To ensure braking characteristics.

by virtue of the great hardness and wear resistance the coating is in the inventive In addition, friction elements almost no wear Abrasion recorded. Thus, virtually no brake dust is generated, which not only reduces the particulate matter problem in road traffic contributes, but also especially in motorcycles Annoying caking of brake dust on shiny chrome Prevents surfaces near the brakes.

If it is according to a preferred embodiment the invention in the friction element to a conventional brake disc made of steel, which is usually two opposite relatively has smooth braking surfaces on which thermally sprayed Coatings adhere poorly, sees a preferred embodiment the invention, these braking surfaces before application roughen the coating to increase the adhesion of the coating improve. The roughening of the braking surfaces is advantageous by blasting the brake disc with a blasting material in the form of a Hard material granules, preferably granules of aluminum corundum used with a grain size of about 180 mesh becomes. The jet nozzle used for blasting is preferred at a distance of about 150 to 200 mm from the roughened braking surfaces and at an angle of about 10 to 20 degrees, preferably from about 15 degrees, linear to the axis of rotation of the brake disc moves the braking surfaces away, while the hard material granules is ejected from the spray nozzle with the aid of compressed air. To avoid unwanted oxidation of the blasted disc to prevent the radiation serving as carrier gas, suitably under a pressure of 5 to 9 bar standing Compressed air is advantageously pre-cleaned to complete it to get rid of dust, oil or moisture.

The type and grain size of the blasting material and the pressure of the compressed air are suitably coordinated so that the braking surfaces after blasting have a surface roughness Rz between 20 and 30 microns and a t-bearing component t _p of 70 to 90%, resulting in optimal adhesion of most thermally guaranteed sprayed coatings.

A further measure to improve the adhesion of the coating on the metallic friction element is that the latter before the application of the coating is heated appropriately, preferably at a temperature between 120 and 150 ° C, to widen the grain structure.

One of the two preferred thermal spraying methods is arc spraying, in which the free ends of two wires from a metallic material forming the subsequent coating are melted in an arc and the melt is injected onto the respective braking surface with the aid of compressed gas. For coating of brake discs made of steel by arc spraying is preferably used as a wire material, an iron alloy, which advantageously contains more than 70 wt .-% iron. Three iron alloys particularly suitable for coating brake discs are Fe 18 Cr 8 Ni 2 Mn, Fe 13 Cr 0.5 Si and carbon steel with a C content of more than 0.35%. In addition to the above-mentioned alloying components Cr, Ni, Mn and Si, the iron alloys may contain small amounts of other alloying components, such as traces of phosphorus P and sulfur S.

The Another of the two preferred thermal spraying methods is this High-speed flame spraying, in which a burner system with a powdery material used for coating in a carrier gas and with a combustible gas mixture, preferably an acetylene-oxygen mixture, is applied. The carrier gas with the powdery carried by him Material and the combustible gas mixture are so in the burner system fed to that when burning the combustible gas mixture generated hot combustion gases together with the carrier gas the powdery material up to supersonic speed accelerate and at the same time for a partial melting the same worry, so that it is the impact of the molten material particles on the roughened braking surface to a mechanical clamping comes between the material particles and the friction to be coated.

Of the used for high speed flame spraying of brake discs Material is preferably a ceramic-metal composite material of a oxide-free ceramic component and a metal component, from the former suitably a metal carbide contains and preferably consists of tungsten carbide (WC) while the latter expediently consists of either a cobalt or nickel alloy or pure cobalt (Co) or nickel (Ni) consists. While by cobalt (Co) the Verscheißfestigkeit the Ceramic-metal composite can be improved is through Nickel (Ni) the thermal conductivity, adhesion on the friction element and the adhesion within the applied ceramic-metal composite improved. Overall, there is the ceramic-metal composite preferably more than 80% of the ceramic component and to less than 20% of the metal component.

There coatings applied by thermal spraying a very have large surface roughness that is not because of a too low supporting content of the surface suitable for friction elements of brakes, the surface roughness be reduced before the use of the friction elements. This is the coated with a layer thickness of 0.4 to 0.6 mm appropriate to about half of this Layer thickness, d. H. abraded to about 0.2 to 0.4 mm. Thereby Heat dissipation can pass through the coating in the Friction element improves and so the risk of unwanted Cracks in the coating or flaking of the coating due to different thermal expansion coefficients of the friction element on the one hand and the coating on the other hand can be reduced.

According to one Another preferred embodiment of the invention is the coating convenient with a diamond-containing abrasive, For example, diamond grinding paste ground until its surface a surface roughness Rz of less than 5 μm and preferably between 0.5 and 2 μm, which is by using a diamond grinding paste with the finest grain size, for example, reach D-126, in the last sanding cycle.

investigations at Reibflächen paver, as previously described by thermal Spraying coated brake discs made of steel showed that the Brake discs a very good thermal shock resistance had, since after heating in a vacuum oven on more than 1000 ° C and a subsequent quenching in cold water, no cracks or spalling of the coating were to be determined. In addition, in these investigations found that the friction surfaces after coating and grinding a hardness between 1200 and 1300 HV01 who also after heating and deterring during the Thermal shock test essentially unchanged remained.

By grinding the coating is also compared to an uncoated metallic brake disc with the same surface roughness of Rz <5 microns, the profile bearing component t _{p of} the braking surface to DIN increased from about 50% to almost double, namely to about 99.9%.

If the friction element is a steel brake disk, which is intended for use conditions under which the Brake disc is heated to high temperatures, the brake disc can appropriate before applying the coating provided in the region of the friction surfaces with openings be, for example, by laser cutting in the brake disc be introduced.

in the The following is the invention with reference to some preferred embodiments explained in more detail:

Embodiment 1

The braking surfaces of a commercially available steel motorcycle brake disc were first roughened by blasting with a shot of aluminum corundum particles having a grain size of 180 mesh to avoid subsequent adhesion of the Be stratification. The surface roughening was carried out by applying each of the two braking surfaces with a mounted rotary disc successively from an injector jet nozzle with aluminum corundum particles ejected from the Injektorstrahldüse with pre-cleaned, oil, dust and moisture-free compressed air under a working pressure of 5 to 9 bar were. The pre-cleaning of the compressed air was used to prevent oxidation of the surface. When blasting, the blasting nozzle was guided linearly over the braking surface to be coated at a pitch of 150-200 mm and at an inclination angle of the beam axis to the rotational axis of the brake disk of about 15 degrees. After blasting, the braking surface was determined to determine surface roughness DIN 4777 measured and DIN, wherein _p yielded a value of 70 to 90% for the surface roughness of a value of Rz = 20 to 30 microns and the bearing ratio t.

Subsequently were the two braking surfaces of the brake disc successively in a coating system for thermal coating by arc spraying coated with Fe 18 Cr 8 Ni 2 Mn. These were two wires made of Fe 18 Cr 8 Ni 2 Mn, which is energized and connected to the free ends were merged to intervene an electric arc to melt the free wire ends to create. The melting temperature was about 3500-4000 ° C. during the generation of the arc were the free Wire ends of the side facing away from the brake disc side with Compressed air is applied to molten particles from the wire ends to solve and accelerate to about 700-800 m / s and they are in liquid or partly liquid state to squirt on the brake surface to be coated, which is a mechanical clamping of the molten particles with the material the brake disc has the consequence. The coating was in one Layer thickness of 0.6-0.7 mm applied to the brake disc.

After cooling the brake disc, the raised coating was sanded on the two braking surfaces successively on a plane surface grinding machine with a diamond or corundum abrasive to a layer thickness of 0.3 to 0.4 mm to achieve a high degree of smoothness of the braking surfaces. For the final touch, a diamond paste D-126 was used. Subsequently, with a roughness meter according to DIN 4777 the surface roughness Rz and with the Tastschnittverfahren according to DIN 4768 determines the surface profile and the profile bearing component t _{p determined} the ground brake surface. For the surface roughness, a very low value of Rz <2 μm was consistently determined, while a very high value of 99.9% was determined for the profile bearing component t _p , which is approximately twice the profile bearing component t _{p of} an uncoated braking surface with the same Surface roughness is.

Subsequently, an adhesion test was after DIN EN 582 with a coating adhesion of 2 275 N / cm ² and 3 300 psi, respectively.

After that became the thermal shock resistance of the brake disc tested for which purpose this in a vacuum oven at 1050 ° C, d. H. until red hot, heated and then in one Container with 10 liters of water at a water temperature quenched from 15 ° C. A subsequent review revealed that no cracks or other surface defects were.

Embodiment 2

The braking surfaces of a commercial steel motorcycle brake disc were pretreated as in Embodiment 1 and coated by the arc spraying method under the same conditions as Embodiment 1, but using two wires made of Fe 13 Cr 0.5 Si. After application of the coating, the latter was also abraded to a layer thickness of 0.3 to 0.4 mm. After the last grinding cycle, the braking surfaces had a surface roughness of Rz <2 μm and a profile-bearing component t _p of 99.9%.

One subsequent adhesion test and an exam the thermal shock resistance of the brake disc, as described above, led to similar results as in the brake disk of the embodiment 1.

Embodiment 3

The braking surfaces of a commercially available steel motorcycle brake disc were pretreated as in Embodiments 1 and 2 and coated by arc spraying under the same conditions as in Embodiments 1 and 2, but using two wires of alloyed carbon steel having a carbon content of about 0.35 % and other alloying components in the form of Si, Ni, Mn, P (trace) and sulfur (trace). The applied coating was again ground down to a layer thickness of 0.3 to 0.4 mm in order to provide the braking surfaces with a high level of flatness and a surface roughness of Rz <2 μm and a profile carrying ratio t _p of 99.9%.

A subsequent adhesive pull test and a test of the thermal shock resistance of the brake disc, as described above, led to similar Results as in the brake disc from the embodiments 1 and 2.

Exemplary embodiments 4 to 7

In a further series of experiments, the braking surfaces of several commercially available brake discs made of steel were coated by high-speed flame spraying in the HVOF (High Velocity Oxy Fuel) method with various powdery materials, after previously by blasting with an aluminum corundum-hard material in the same manner as in the preceding embodiments. Granules were pretreated to provide a surface roughness of Rz = 20 to 30 microns and a profile bearing ratio t _p of 70 to 90%.

To the Coating was the powdered material in one Carrier gas together with an acetylene-oxygen mixture fed into a burner system, through the material the carrier gas and the generated when burning the gas mixture hot combustion gases at supersonic speed to accelerate and at the same time for a partial melting of the same material.

The coating was applied in all tests in a layer thickness of 0.3-0.4 mm and then ground down to a layer thickness of 0.2-0.25 mm to create a flat braking surface with a high degree of flatness. Again, a diamond grinding paste with the finest grain size was used in the last grinding cycle to achieve a uniform surface roughness of between 0.5 and 1 μm over the entire braking surface and a high profile bearing ratio t _p of 99.9%.

To The grinding of the coating was the hardness in the range the braking surfaces before and after a thermal shock test measured at which the brake discs heated in a vacuum oven to 1200 ° C. and then in water with a water temperature of 15 ° C were quenched.

Embodiment 4

A The pretreated brake discs were treated with WC Co 10 4 Cr powder coated after a previous warming of the Brake disc at 120 to 150 ° C at a speed of more than 2.5 to 3 and at temperatures of more than 3 000 ° C in a layer thickness of 0.3 to 0.4 mm on the pretreated Brake surfaces was sprayed.

Embodiment 5

A other, intended for use in a motorcycle wheel brake Brake disc was also after a warm up with toilet Co 12 coated, with the process parameters and the sprayed Layer thickness of those in the previous embodiment 4 corresponded.

The measured before or after the thermal shock test Hardness of the WC Co 12 coating was 1250 HV01, with no appreciable decrease in hardness due to the thermal shock test was detectable.

Embodiment 6

A other, intended for use in a car wheel brake Brake disc was coated after heating with WC / Ni, the process parameters and sprayed layer thickness being those in the foregoing embodiments 4 and 5 corresponded.

The measured before or after the thermal shock test Hardness of the WC / Ni coating was 1210 HV01, with no noticeable decrease in hardness due to thermal shock test was detectable.

Embodiment 7

Yet another, intended for use in a car wheel brake Brake disc was replaced with WC / Ni with agglomerated WC / Ni powder coated, the process parameters and the sprayed layer thickness those in the previous embodiments 4 to 6 corresponded.

The measured before or after the thermal shock test Hardness of the WC / Ni coating was 1280 HV01, with no noticeable decrease in hardness due to thermal shock test was detectable.

The high-speed flame spraying applied coatings compared with those applied by arc spraying Coatings have higher thermal shock resistance, as in the thermal shock test before quenching a heating up to temperatures of up to 1 200 ° C without any negative effect on the coating possible was.

brake discs therefore, these coatings are likely to be suitable for the use in races on short courses or similar Operating conditions with high temperatures and / or temperature fluctuations a longer shelf life.

For a use under normal conditions of use in traffic However, all the brake discs described above are well suited.

at Trials with the coated brake discs were found that these brake discs in cooperation with commercially available brake shoes for a good grip and excellent braking conditions made sure that even after prolonged use under hard conditions no noticeable scoring was, and that heat dissipation passed through the coating in the brake disk was sufficient, even under heavy use the brake disc to a chipping or damage prevent the coating leading heating.

About that addition was also after a long period of use at the coated brake discs to determine almost no abrasion, so that virtually no brake dust is generated, for one thing in consideration the growing importance of fine particulate matter in road traffic is of great advantage and secondly especially with motorcycles near the brakes to a significant decrease in the caking from hot brake dust to shiny chrome Surfaces leads.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 69812344 T2 [0002]

Cited non-patent literature

• - DIN 4777 [0019]
• - DIN 4777 [0021]
• - DIN 4768 [0021]
• - DIN EN 582 [0022]

Claims (32)

Method for coating braking surfaces of brake discs or other friction elements of brakes, in which a wear-resistant coating is applied to the braking surfaces , characterized in that the coating is applied by thermal spraying. Method according to claim 1, characterized in that that the braking surfaces before applying the coating be roughened. Method according to claim 2, characterized in that that the braking surfaces by blasting with a hard material granules be roughened. Method according to claim 3, characterized that a jet nozzle for spraying the hard material granules at a distance from the surface to be roughened linear over the braking surfaces is moved. Method according to one of claims 2 to 5, characterized in that the braking surfaces on a Surface roughness Rz roughened between 20 and 30 μm become. Method according to one of claims 2 to 6, characterized in that the roughened braking surfaces have a profile bearing component t _p of 70 to 90%. Method according to one of the preceding claims, characterized in that the brake disc before applying the coating is heated. Method according to claim 7, characterized in that that the brake disc before applying the coating to about 120 to 150 ° C is heated. Method according to one of the preceding claims, characterized in that the coating by arc spraying is applied by the free ends of two wires be melted from metallic materials in an arc and the melt injected with compressed gas onto the braking surface becomes. Method according to claim 9, characterized in that at least one of the materials consists of an iron alloy. Method according to claim 10, characterized in that the iron alloy contains more than 70% by weight of iron. Method according to claim 10 or 11, characterized the iron alloy contains between 10 and 20% by weight of chromium. Method according to one of claims 10 to 12, characterized in that the iron alloy contains more than 0.35% carbon contains. Method according to one of claims 10 to 14, characterized in that the iron alloy is nickel, manganese and / or Contains silicon in a total amount of less than 15 wt .-%. Method according to one of claims 1 to 8, characterized in that the coating by high velocity flame spraying is applied by a powdery material in melted a flame and at supersonic speed is sprayed onto the braking surface. Method according to claim 15, characterized in that that the material is an oxide-free ceramic material and at least includes a metal. Method according to claim 16, characterized in that that the ceramic material is a metal carbide. Method according to claim 16 or 17, characterized the ceramic material is tungsten carbide (WC). Method according to one of claims 16 to 18, characterized in that the metal contains cobalt (Co) or cobalt (Co). Method according to one of claims 16 to 18, characterized in that the metal contains nickel (Ni) or nickel (Ni). Method according to one of the preceding claims, characterized in that the coating after application is abraded. Method according to claim 21, characterized that the coating sanded to a layer thickness of 0.2 to 0.4 mm becomes. Method according to claim 21 or 22, characterized that the coating is ground until its surface a surface roughness Rz of less than 5 μm, preferably less than 2 μm. Method according to one of claims 21 to 23, characterized in that the coating is ground until its surface has a profile carrying portion t _p of more than 95%, preferably of more than 99%. Friction element for a brake, in particular Brake disc, with at least one braking surface and a wear-resistant coating applied to the braking surface, characterized in that the wear-resistant coating is thermally sprayed onto the braking surface. Friction element according to claim 25, characterized in that that the wear-resistant coating is a ground Has surface. Friction element according to claim 26, characterized in that that the ground surface has a surface roughness Rz of less than 5 microns, preferably less than 2 microns has. Friction element according to claim 26 or 27, characterized in that the ground surface has a profile load share t _p of more than 95%, preferably more than 99%. Friction element according to one of claims 25 to 28, characterized in that the wear-resistant coating has a layer thickness between 0.15 and 0.3 mm. Friction element according to one of claims 25 to 29, characterized in that the wear-resistant coating has a hardness between 1200 and 1300 HV01. Friction element according to one of claims 25 to 30, characterized in that the coating of an iron alloy consists. Friction element according to one of claims 25 to 30, characterized in that the coating of an oxide-free Ceramic material and at least one metal.