IT201900012171A1 - BRAKE DISC COATINGS, WEAR REDUCTION METHOD AND ASSOCIATED BRAKE DISC - Google Patents

Description

DESCRIPTION

of the patent for industrial invention entitled: "COATINGS FOR BRAKE DISKS, METHOD FOR REDUCING WEAR AND ASSOCIATED BRAKE DISC"

Technical field

This description generally relates to coatings for coating brake discs, as well as a method for reducing wear on brake discs and associated brake pads, and the method of using such coatings. The description generally relates in addition to an associated brake disc, a friction surface of which is provided with the linings according to the description.

Technique Note

Coated brake discs are known.

Synthesis

An anti-wear and anti-corrosion coating for a brake disc is disclosed, applicable to at least one friction surface of the brake disc configured to cooperate in use with a braking element such as a brake pad, the anti-wear and anti-corrosion coating being applicable for thermal spray; where the anti-wear and anti-corrosion coating consists of a single layer composed of a material chosen from the group consisting of: chromium carbide (Cr3C2) particles dispersed in a metal matrix consisting of a NiCr alloy; a metal matrix consisting of an austenitic chromium-nickel steel and preferably composed of an alloy of FeNiCrMoSiC (iron-nickel-chromium-molybdenum-silicon-carbon), for example Diamalloy®; their mixing in variable proportions; said anti-wear coating exhibit such plasticity as to have a reduced propensity to form micro-cracks in conditions of tribo-mechanical stress.

An anti-wear and anti-corrosion coating is also described as referred to above, where the said chromium carbide particles or the austenitic steel alloy preferably of FeNiCrMoSiC composition still in the form of metal particles of the individual components of the alloy are applied by thermal spray by means of technology HVOF.

Also disclosed is an anti-wear and anti-corrosion coating as referred to above, which has a thickness of between 20 and 400 micrometers.

Also described is an anti-wear and anti-corrosion coating as referred to above, which, after thermal spray coating and grinding, has a surface roughness of between 0.05 and 2 micrometers and preferably between 0.15 and 0.3 micrometers.

A vehicle brake disc is also described including at least one friction surface intended to cooperate in use with a braking element such as a brake pad, characterized in that at least said friction surface is covered with an anti-wear and anti-corrosion coating according to what indicated above.

A method for the simultaneous reduction of wear on a brake disc and associated brake pads is also described, comprising the steps of:

- prepare brake pads using a friction material formulation of the LS (Low Steel) or NAO (Non Asbestos Organics) type;

- cover at least one friction surface of a brake disc intended to cooperate in use with a brake pad with an anti-wear and anti-corrosion coating with such plasticity as to have a reduced propensity to form micro-cracks in conditions of tribo-mechanical stress consisting of chromium carbide particles (Cr3C2) dispersed in a metal matrix consisting of an alloy of NiCr or of an austenitic chromium-nickel steel and preferably consisting of a metal matrix composed of an alloy of FeNiCrMoSiC (iron-nickel-chromomolybdenum- silicon-carbon), for example Diamalloy®;

- couple the previously prepared brake pads and brake disc.

In the method as above, the anti-wear coatings are applied using HVOF (High Velocity Oxygen Fuel) thermal spray technology.

In the method as above, brake pads made with a friction material belonging to the Copperfree family, in particular of the LS (Low Steel) or NAO (Non-Asbestos Organics) type, are coupled with an anti-wear coating applied to at least one friction surface of the brake disc consisting of chromium carbide (Cr3C2) particles dispersed in a metal matrix consisting of a NiCr alloy or a chromium-nickel austenitic steel and preferably obtained from a combination of several metal materials in order to create a compound consisting of an alloy of FeNiCrMoSiC (iron-nickel-chromium-molybdenosilicon-carbon), for example Diamalloy®.

The use of friction materials belonging to the Copper Free families of the LS type (Low Steel) or of the NAO type (Non-Asbestos Organics) for the manufacture of brake pads in combination with the use of anti-wear anti-wear coatings is also described. -corrosion with such plasticity as to have a reduced propensity to form micro-cracks under conditions of tribo-mechanical stress on at least one friction surface of brake discs operatively associated with said brake pads to simultaneously reduce wear of brake pads and brake discs , said anti-wear and anti-corrosion coating being constituted by a selected combination of chromium carbide (Cr3C2) particles dispersed in a metal matrix consisting of a NiCr alloy or a chromium-nickel austenitic steel and preferably obtained from a combination of several metallic materials in order to create a compound consisting of an alloy of FeNiCrMoSiC (iron-nickel-chromium-molybdenum-silicon-carbon), for example Diamalloy® and applied through the HVOF (High Velocity Oxygen Fuel) hot spray technique.

Also described is a braking system comprising an element to be braked consisting of a brake disc or drum made of cast iron or steel and at least one braking element consisting of a brake shoe or pad, able to cooperate by friction with the element to be braked. , characterized by the fact that, in combination:

- the element to be braked has at least one friction surface configured to cooperate with the braking element, which friction surface is covered with an anti-wear and anti-corrosion coating as described above;

- the braking element includes at least one block of friction material configured to cooperate with the element to be braked, the friction material being of the LS (Low Steel) or NAO (Non-Asbestos Organics) type

Brief description of the Figures

Further characteristics and advantages will appear clear from the following description of its non-limiting embodiments carried out purely by way of example and with reference to the figures of the annexed drawings, in which:

• Figure 1 illustrates the graphs (Fade, oil consumption, friction coefficient trend) obtainable after a standard Fading test performed on a commercial cast iron brake disc, called Cast Iron, using brake pads made with an LS (Low Steel);

• Figure 2 illustrates the same graphs of Figure 1 obtainable after a standard Fading test performed on the same commercial cast iron brake disc of Figure 1, but covered with a coating of WC (tungsten carbide) deposited on a Nickel bed currently on the market and used as a comparison, called Disc A0, using brake pads made with a compound of the LS (Low Steel) type; • Figure 3 illustrates the same graphs of Figure 1 obtainable after a standard Fading test performed on the same commercial cast iron brake disc of Figure 1, but covered with the anti-wear, anti-corrosion coating with such plasticity as to have a reduced propensity to forming micro-cracks produced according to this description, composed of chromium carbide (Cr3C2) particles dispersed in a metal matrix consisting of a NiCr alloy, called Disc A using brake pads made with a compound of the LS (Low Steel) type;

• Figure 4 illustrates an extract of the graphs (Fade, oil consumption, friction coefficient trend) obtainable after a standard Fading test, as in Figure 1, performed on a commercial cast iron brake disc, but covered with the deposited WC coating on a nickel bed currently on the market and used for comparative purposes, called Disc A0, using brake pads made with a compound of the NAO type (Non-Asbestos Organics);

• Figure 5 illustrates the same graphs of Figure 1 obtainable after a standard Fading test performed on the same commercial cast iron brake disc of Figure 1, but covered with the anti-wear, anti-corrosion coating with such plasticity as to have a reduced propensity to forming micro-cracks according to the description, composed of chromium carbide (Cr3C2) particles dispersed in a metal matrix consisting of a NiCr alloy, called Disc A using brake pads made with a compound of the NAO (Non-Asbestos Organics) type;

• Figure 6 compares the thermal conductivities of the brake discs;

• Figure 7 illustrates an extract of the graph obtainable after a standard AK-Master test performed on a commercial cast iron brake disc using brake pads made with an LS (Low Steel) type compound;

• Figure 8 illustrates the same graphs of Figure 1 obtainable after a standard AK-Master test performed on the same commercial cast iron brake disc of Figure 7, but covered in one case (disc A0) with the currently commercially available WC-based coating, illustrated for comparison, and in the lower graph (disc A) covered with chromium carbide (Cr3C2) particles dispersed in a metal matrix consisting of a NiCr alloy, using brake pads made with a LS (Low Steel) compound; • Figure 9 illustrates the same graphs of Figure 7 obtainable after a standard AK-Master test performed on the same commercial cast iron brake disc of Figures 1 and 7, but covered with the coating produced according to the description, composed (upper graph - disc A ) from chromium carbide particles (Cr3C2) dispersed in a metal matrix consisting of a NiCr alloy and (lower graph - disk B) composed of several metal materials in order to create a metal matrix consisting of an austenitic chromium-nickel steel and preferably composed of an alloy of FeNiCrMoSiC (iron-nickel-chromomolybdenum-silicon-carbon), for example the one known with the trade name of Diamalloy®, using brake pads made with a compound of the NAO (Non-Asbestos Organics) type;

• Figure 10 compares the results of a standard wear test carried out on the same commercial cast iron brake disc of Figure 1, respectively: bare (not covered), covered with the coating currently on the market consisting of WC deposited on a bed of Nickel, used as a comparison, and coated with the anti-wear, anti-corrosion coating with such plasticity as to have a reduced propensity to form micro-cracks, of the present description and consisting of chromium carbide (Cr3C2) particles dispersed in a metal matrix consisting of a NiCr alloy, using brake pads made with a compound of the LS (Low Steel) type;

• Figure 11 shows the micrographs of the WC-based coatings deposited on a Nickel bed (coated A0 disc, currently on the market and used for comparison), based on Cr3C2 dispersed in a nickel-chromium matrix according to the description and deposited according to the procedure reported in this description (disk A), and based on several metallic materials in order to create a metal matrix consisting of an austenitic chromium-nickel steel and preferably composed of an alloy of FeNiCrMoSiC (iron-nickel-chromium- molybdenum-silicon-carbon), for example the one known by the trade name of Diamalloy® (disk B);

• Figures 12, 13 and 14 show the characterization of the coatings carried out by means of the micro-hardness measurement technique with a nanoindenter, and highlight a difference in hardness between the toilet coating currently on the market and used for comparison, with the hardness of the coating single layer of the present description consisting of chromium carbide (Cr3C2) particles dispersed in a metal matrix consisting of a NiCr alloy (disk A, fig. 13), or of several metal materials in order to create a metal matrix consisting of a austenitic chromium-nickel steel and preferably composed of an alloy of FeNiCrMoSiC (iron-nickel-chromium-molybdenum-silicon-carbon), for example the one known by the trade name of Diamalloy® (disc B - fig. 14);

• Figure 15 shows the comparison of the state of the surface after test, of the WC-based coating deposited on a Nickel bed, currently on the market and used as a comparative - Disc A0, with the state of the surface after test of the coatings of this description (discs A and B);

• Figure 16 shows the comparison of the surface appearance of the braking surfaces of the discs after a corrosion resistance test, discs which are respectively composed of cast iron, covered by the commercial WC-based coating deposited on a Ni bed. comparative title (disc A0), covered with chromium carbide particles (Cr3C2) dispersed in a metal matrix consisting of a NiCr alloy (disk A) and finally covered with several metal materials in order to create a metal matrix consisting of an austenitic steel chromium-nickel and preferably composed of an alloy of FeNiCrMoSiC (iron-nickel-chromium-molybdenum-siliconcarbon), for example the one known by the trade name of Diamalloy® (disk B); the respective photographs highlighting how the coatings described here have a resistance to corrosion higher than that ensured by simple bare cast iron, and comparable to that ensured by commercial toilet-based coating; And

Figure 17 shows an embodiment of a method of preparing a brake pad and a brake disc system having an embodiment of a coating as discussed here, embodiments of brake pads are prepared, embodiments of brake discs are prepared. The discs are therefore at least partially coated with one or more of the coatings of the present description. Once coated, the brake pads and coated brake discs can be paired.

Detailed description

In some embodiments in the present disclosure, anti-wear coatings for brake discs are described without the drawbacks of the known art. In particular, in some embodiments, the present disclosure describes a method for the simultaneous reduction of the wear of both the brake discs and the brake pads associated with them. Furthermore, in some embodiments exposed a brake disc equipped with an anti-wear coating is described which involves a reduction in the wear of the brake pads compared to an uncoated brake disc.

The following description therefore relates to embodiments of an anti-wear coating for a brake disc, to a method for reducing the wear of both the brake discs and the associated brake pads, and to a coated brake disc itself.

During the running-in period, the friction coefficient can vary considerably, giving the driver of the vehicle a feeling of unsafe braking.

Furthermore, a reduced wear of the brake discs can usually be accompanied by an undesirable increase in the wear of the brake pads.

The description also relates to embodiments of anti-wear and anti-corrosion coating systems for a brake disc, which can entail an increase in resistance to corrosive phenomena of any nature on the disc itself.

The description further relates to coating systems with a plasticity such as to have a reduced propensity to form micro-cracks in conditions of tribo-mechanical stress with a high energy load which leads to a reduction, if not a total disappearance, of the stress phenomena. mechanical cumulated with the creation and propagation of surface cracks in the braking surface.

Furthermore, the use of this anti-wear and anti-corrosion coating is described with such plasticity as to have a reduced propensity to form micro-cracks under conditions of tribo-mechanical stress and to a braking system which can comprise, for example: an element to be braked consisting of a brake disc or drum made of a cast iron or steel, although the particular material is not limiting, and covered at least in part with an anti-wear and anti-corrosion coating with adequate plasticity according to the description. In some embodiments the system can further include at least one braking element which can include a brake pad or shoe, adapted to cooperate by friction with the element to be braked. asbestos and copper or its alloys, generically defined as “Cu-free”, in particular of the so-called LS (Low Steel) type or of the NAO (Non-Asbestos Organics) type.

NAO materials are non-asbestos organics that are usually identified as materials that do not contain Fe-based metals. LS is also identified as an asbestos-free material but with Fe-based metals inside such as metal or iron or powdered steel.

In some embodiments, the braking element may be copper-free. In some embodiments, the braking member may be asbestos-free. In some embodiments, the braking element may be free of copper and asbestos.

The components of the composition or raw blend of the friction material to be coupled with the wear liner according to the description may be the components used in the friction materials. For example, embodiments of the composition may include a fibrous material for example including inorganic and / or organic and / or metallic fibers, excluding asbestos, a binder, a filler or filler, one or more lubricants or friction modifiers, and one or more abrasives.

In some embodiments, one or more elements can be removed as desired.

In particular, the fibers can include any organic fiber or inorganic fiber other than asbestos, or any metal fiber that is commonly used in friction materials. Illustrative but non-exhaustive examples include inorganic fibers, such as glass fibers, rock wool, wollastonite, sepiolite and attapulgite, and organic fibers, such as carbon fibers, aramid fibers, polyimide fibers, polyamide fibers, phenolic fibers, cellulose and acrylic fibers or PAN (Poly-Acrylo-Nitrile). Metallic fibers, such as for example steel fibers, stainless steel, aluminum fibers, zinc, metal alloys such as Iron-Tin etc. can also be used.

The fibers can be used in the form of short or long fibers and the particular length is not limiting.

In order to ensure sufficient mechanical strength, the quantity of fibers can be between 1% by volume and 50% by volume with respect to the total volume of the friction material. In some embodiments they are between 8% and 30% by volume.

According to the description, an organic or inorganic filler or filler can also be used as the raw component in some embodiments.

Numerous materials can be used as organic or inorganic fillers. Non-limiting illustrative examples include precipitated calcium carbonate, barium sulfate, magnesium oxide, calcium hydroxide, calcium fluoride, slaked lime, talc, mica, vermiculite.

These can be used alone or in combinations of two or more of them. The amount of such fillers can range from 1% to 60% by volume based on the total composition of the friction material.

In some embodiments, an organic binder can be used. The organic binder can be any known binder commonly used in friction materials and in general it is a thermosetting resin or a mixture of thermosetting resins.

Non-limiting illustrative examples of suitable binders include phenolic resins, melamine resins, epoxy resins; various modified phenolic resins such as epoxy-modified phenolic resins, oil-modified phenolic resins, alkylbenzene-modified phenolic resins.

Any or combinations of two or more of these compounds can be employed. In order to ensure sufficient mechanical strength and wear resistance, the binder can be included in an amount ranging from 2% to 50% by volume based on the total composition of the raw compound or final friction material obtained. In some embodiments a friction modification may be used. The friction modifier (which may possibly include all or part of the filler or filler) may be an organic filler such as cashew powder, rubber powder (pulverized tread rubber powder), a variety of uncured rubber particles, a variety of vulcanized rubber particles, an inorganic filler such as a barium sulfate, calcium carbonate, a calcium hydroxide, vermiculite and / or mica, an abrasive such as a silicon carbide, alumina, a zirconium silicate, a lubricant such as disulfide of molybdenum, a tin sulfide, a zinc sulfide, iron and non-ferrous sulfides, metal particles other than copper and copper alloys, and / or a combination of the foregoing.

The abrasives that can be used according to this description can be classified as follows (the following list is only indicative, not necessarily exhaustive and not limiting):

• Blandi abrasives (Mohs 1-3): talc, calcium hydroxide, potassium titanate, mica, vermiculite, kaolin;

• Medium Abrasives (Mohs 4-6): barium sulphate, magnesium oxide, calcium fluoride, calcium carbonate, wollastonite, calcium silicate, iron oxide, silica, chromite, zirconium oxide, zinc oxide;

• Strong Abrasives (Mohs 7-9): silicon carbide, zirconium sand, zirconium oxide, zirconium silicate, zirconium, corundum, alumina, mullite.

The content of the friction modifier, according to the desired friction characteristics, can be between 10% by volume and 80% by volume with respect to the volume of the entire material.

In general, the friction material components used according to the description are as follows:

1. binders

2. fillers or fillers

3. lubricants / friction modifiers

4. abrasives (which can be part of the fillers) 5. fibers (inorganic / organic / metallic)

6. any metal powders

However, it is understood that one or more of the above elements can be removed as desired.

Brake pads made with the aforementioned friction materials can be coupled / operationally associated with an anti-wear and anti-corrosion coating, applied on at least one friction surface of the brake discs configured to cooperate in use with the brake pad and consisting of a single layer made with a selected combination of:

• chromium carbide particles (Cr3C2) dispersed in a metallic matrix of a NiCr alloy; and / or

• particles of several metallic materials in order to create a metal matrix consisting of an austenitic chromium-nickel steel and which may include an alloy of FeNiCrMoSiC (iron-nickel chromium-molybdenum-silicon-carbon), for example the one known by the trade name by Diamalloy®. The austenitic steel metal matrix can have a variable chemical composition within the following limits:

35 <Fe <88; 10 <Cr <35; 2 <Ni <18 (proportions in% by weight). In some embodiments, Cr prevails over Ni.

In some embodiments molybdenum from 1.5% to 18% by weight and other alloying elements in lower percentages, such as Si, Mn, B, W, V, C, Cu, Co, Nb, which are added in any case in a total quantity lower than the sum of the content in Fe, Cr and Ni.

In some embodiments the austenitic steel metal matrix can have the following chemical composition:

In some embodiments the coating including metal particles of chromium carbide (Cr3C2) dispersed within a metal matrix of a NiCr alloy has a composition of up to 75% by weight of chromium carbide, the balance being NiCr alloy at 20 or 25% of Cr.

The single layer according to the description, when based on chromium carbides dispersed in a nickel matrix, has a Vickers hardness (Hv) between 500 and 1200. In some embodiments the single layer has a Vickers hardness between 600 and 800 Hv. In some embodiments the single layer has a reduced elastic modulus between 160 and 180.

The single layer according to the description, when based on austenitic Cr-Ni steel, such as FeNiCrMoSiC, can have a Vickers hardness (Hv) between 300 and 800. In some embodiments the single layer can have a Vickers hardness including between 400 and 700 Hv and a reduced elastic modulus between 145 and 160.

The anti-wear and anti-corrosion coatings with adequate plasticity in order to have a reduced propensity to form micro-cracks under the aforementioned tribomechanical stress conditions can preferably be applied by thermal spray using HVOF technology and the chromium carbide particles dispersed in the matrix NiCr metal or those components of the Diamalloy® alloy are used as powders in spheroidal form. However, other methods can also be used to apply coatings with equivalent results, e.g. Plasma Spray, Laser Cladding, Cold Laser Deposition, Laser Spray Deposition.

The anti-wear and anti-corrosion coatings with adequate plasticity in order to have a reduced propensity to form micro-cracks in conditions of tribomechanical stress according to the description have an overall thickness between about 20 and about 400 micrometers and, after spray coating thermal and grinding, have a surface roughness between 0.05 and 2 micrometers.

The use of these selected materials for the brake pads and for the anti-wear coating with adequate plasticity in order to have a reduced propensity to form micro-cracks in conditions of tribo-mechanical stress of brake discs allows to implement a method for the Simultaneous reduction of wear on a brake disc and associated brake pads, including the steps of:

- prepare brake pads using a friction material formulation of the CopperFree family which can be LS (Low Steel) or NAO (Non-Asbestos Organics);

- covering at least one friction surface of a brake disc intended to cooperate in use with a brake pad with an embodiment of the anti-wear and anti-corrosion coating with adequate plasticity of the present description. This may include a selected combination of chromium carbide (Cr3C2) particles dispersed in a metal matrix of a NiCr alloy, and / or particles of multiple metal materials in order to create a metal matrix consisting of an austenitic chromium steel. nickel which may include an alloy of FeNiCrMoSiC (iron-nickel-chromium-molybdenum-silicon-carbon) known by the trade name of Diamalloy®;

- couple the previously prepared brake pads and brake disc.

The anti-wear and anti-corrosion coating is applied using HVOF (High Velocity Oxygen Fuel) thermal spray technology.

In some embodiments, brake pads made of a friction material belonging to the Copper Free family, in particular of the LS (Low Steel) or NAO (Non-Asbestos Organics) type, are coupled with an anti-wear coating applied to at least one surface of friction at the choice of the brake disc consisting of chromium carbide (Cr3C2) particles dispersed in a metal matrix of a NiCr alloy, or of particles of several metal materials in order to create a metal matrix consisting of an austenitic chromium-nickel steel and which can be composed of an alloy of FeNiCrMoSiC (iron-nickel-chromomolybdenum-silicon-carbon), known by the trade name of Diamalloy®.

In this way, a braking system is also implemented including an element to be braked consisting of a brake disc or drum made of a cast iron or steel and at least one braking element including a brake shoe or pad, able to cooperate by friction with the element. to brake. In some embodiments the element to be braked has at least one friction surface configured to cooperate with the braking element, which friction surface is covered with an anti-wear and anti-corrosion coating as described above, while the braking element it comprises at least one block of friction material configured to cooperate with the element to be braked, the friction material of the Copper Free family, in particular of the LS (Low Steel) or NAO (Non-Asbestos Organics) type.

Examples and comparative examples are given here by way of illustration and are not intended to limit the description.

Example 1

Different compositions of friction material of two different types are prepared, as indicated in Table 1. For each of the two families of friction material compositions, indicated as LS and NAO, both known) a friction material is prepared according to the composition note currently in use.

Table 1

In table 1, for mild, medium and strong abrasives, one or more materials are chosen as indicated below: Blandi abrasives (Mohs 1-3): talc, calcium hydroxide, potassium titanate, mica, kaolin

Medium abrasives (Mohs 4-6): barium sulphate, magnesium oxide, calcium fluoride, calcium carbonate, wollastonite, calcium silicate, iron oxide, silica, chromite, zirconium oxide, zinc oxide

Strong Abrasives (Mohs 7-9): silicon carbide, zirconium sand, zirconium oxide, zirconium silicate, zirconium, corundum, alumina, mullite.

Example 2

The compositions of friction material according to Table 1 are printed on identical metal supports and cured in the traditional way, to form identical brake pads, except for the chemical composition of the friction material.

In particular, the molding of the brake pads is carried out at temperatures between 60 and 200 ° C at a pressure of between 150 and 1800 Kg / cm <2> for a time between 2 and 10 minutes or by preforming the mixture in a mold and subsequently printing at a temperature of 130 to 180 ° C at a pressure of 150 to 500 kg / cm <2> (14.7-49 MPa) for a period of 2 to 10 minutes.

The resulting molded article is typically post-cured by heat treatment from 150 to 400 ° C lasting from 5 minutes to 15 hours, then spray or powder coated, oven dried and possibly mechanically processed where necessary to give the finished product.

The effective braking area of each individual pad is 52.6 cm <2>.

Example 3

A series of 18-inch commercial brake discs in lamellar cast iron are purchased, all identical, with the following characteristics: diameter 356 mm; thickness (width along the axis of rotation) 28 mm; a disc is left with bare surfaces; the other brake discs are covered on both opposite faces, defined by the friction surfaces intended to cooperate in use with the brake pads, with anti-wear and anti-corrosion coatings with adequate plasticity so as to have a reduced propensity to form micro- slots, marked as disk A and as disk B, having the compositions and characteristics indicated in Table 2.

Table 2

The coating containing chromium carbide contains a quantity of chromium carbide up to 75% by weight and for the remainder a Ni-Cr alloy with 20% or 25% chromium. In the present example a 75% chromium carbide and 25% NiCr alloy coating was used. The austenitic steel coating has the following composition (percentages by weight): 28% Cr -16% Ni - 4.5% Mo -1.5% Si - 1.75% C - rest Fe. The coatings of table 2 are applied by thermal spraying, using HVOF technology (High velocity oxygen fuel spraying): a mixture of gaseous or liquid fuel and oxygen is introduced into a combustion chamber, where they are burned continuously; the resulting hot gas, at a pressure close to 1 MPa, is emitted through a converging divergent nozzle and travels through a straight section; fuels can be gases (hydrogen, methane, propane, propylene, acetylene, natural gas, etc.) or liquids (kerosene, etc.); the speed of the jet at the exit of the barrel (> 1000 m / s) exceeds the speed of sound. The powdered materials are each time injected into the gas stream, which accelerates the powder up to 800 m / s and the hot gas and powder stream is directed towards the surface to be coated; the powder partially dissolves in the gas stream and deposits on the substrate providing a coating with low porosity and high adhesion strength.

After coating with thermal spray and subsequent rectification of the anti-wear and anti-corrosion coating with adequate plasticity in order to have a reduced propensity to form micro-cracks, it has a surface roughness that can vary from point to point but which is in any case between 0 , 05 and 2 micrometers. The average thickness of the coatings can range from 20 to 400 micrometers and in the present example is about 90 microns.

Example 4

Using the brake discs of example 3 and the brake pads of example 2, different Fading and AK_Master tests are performed, using different disc / pad combinations. The results obtained are illustrated in Figures 1 to 5 and 7 to 9, where the combinations used are indicated:

• Bare cast iron: uncoated brake disc coupled to brake pads made with LS or NAO friction material;

• A0 disc: brake disc coated with WC material deposited on a Nickel bed currently on the market and used for comparison purposes, coupled to brake pads made with LS or NAO friction material;

• Disc A: brake disc coated with an anti-wear, anti-corrosion material with adequate plasticity so as to have a reduced propensity to form micro-cracks according to the invention, consisting of chromium carbide (Cr3C2) particles dispersed in a metal matrix of a NiCr alloy, coupled to brake pads made with LS or NAO friction material;

• Disc B: brake disc coated with anti-wear, anti-corrosion material consisting of an austenitic chromium-nickel steel in an alloy of FeNiCrMoSiC (iron-nickel-chromium-molybdenum-silicon-carbon) obtained starting from powders of the single metallic materials components in order to create a compound consisting of an alloy of FeNiCrMoSiC (iron-nickel-chromium-molybdenum-silicon-carbon), called Diamalloy®, coupled to brake pads made with LS or NAO friction material;

The wear of both the brake disc and the brake pads used in each Fading and AKM test are also evaluated at the end of the test. The results obtained are reported in Tables 3 and 4.

Table 3 - Fading

DISCUSSION OF THE RESULTS

As is evident from what has been described up to now, the materials used for the coating are new in the field of anti-wear coatings for brake discs. In fact, the materials are based on chromium carbides dispersed in a metal matrix of a nickel-chromium alloy, or based on an austenitic chromium-nickel steel and preferably in an alloy obtained from a combination of several metallic materials in order to create a compound consisting, in the examples illustrated, of an alloy of FeNiCrMoSiC (iron-nichrome-molybdenum-silicon-carbon-carbon), known by the trade name of Diamalloy®.

From the comparison of the graphs that can be derived from the Fading test, the best braking behavior is evident, which is reflected in a greater frictional stability, ensured by the brake discs coated with the first material included in this description compared to the bare cast iron, consisting of carbide particles. of chromium applied as per the method reported in the present description (disc A), with both known friction materials tested, belonging to the two most used families of friction materials.

With the further comparison of the AKM graphs, the same or better behavior of the friction material is evident when using the second coating included in the present description, consisting of the Diamalloy® alloy (disc B) compared to both the bare cast iron and the coating material currently in trade (disk A0).

Furthermore, for the coatings of the present description a good maintenance of the friction coefficient during braking results. Therefore, the elimination or, at least, the very strong reduction of the inconvenience consisting in the undesirable lengthening of the "running-in" period of the brake pad / disc coupling coated with traditional anti-wear layers is highlighted.

Then, by observing the wear data shown in table 3, it can be seen that in the face of wear values (measured in mm of pad loss at the end of the Porsche Fading test with respect to the new material) of the brake pads made with the NAO friction compound , coupled to the disc coated in WC deposited on a Nickel bed currently on the market and used as a comparison, when coupled together, of 5.14 mm, while the material of the present description shows the wear of the NAO material at values very similar to those obtained with the bare (uncoated) cast iron disc.

Figure 6 shows the thermal conductivity guaranteed by the coating of the present description based on chromium carbide particles deposited with the method described in the present description, in comparison with the WC coating deposited on a Nickel bed currently on the market and used for comparative purposes, conductivity of the coating according to the description which is close to the values obtained from the bare cast iron disc.

The micrographs of Figure 11 allow to characterize the wear-resistant coatings according to the description. As is evident, thanks to the HVOF spraying technology, the chromium carbide (disc A) or FeNiCrMoSiC (disc B) particles included in the metal matrices ensure good homogeneity and make the coating free of porosity.

The micrographs of figure 15 show the state of the braking surface covered respectively by the coatings in WC (A0), in Cr3C2 (A) and in austenitic steel type Diamalloy® (B), subjected to the Fading test. The two coatings show an evident lower tendency to generate surface cracks, compared to the toilet coating used for comparison. The lower tendency to generate cracks is explained by figures 12-13-14, where the value of the elastic modulus (EIT) of the WC coating is higher than that of the Cr3C2 coating and that of the Diamalloy® type. CORROSION

A corrosion resistance test was performed to evaluate the improvement towards bare cast iron. The different discs chosen are the following:

i) Bare gray cast iron

ii) A0 disc: WC coating, for comparison

iii) Disc A: Cr3C2 coating

iv) Disc B: Diamalloy coating The discs were first subjected to a Fading test as described above. After the bench test, the discs entered the saline chamber with a cycle consisting of: 20% of the time under salt spray at 5% in NaCl, 10% in dry drying and the remaining 70% in the presence of humidity at least 90% %. The discs are left for 1 week, then a visual inspection was done. The bare gray cast iron disc showed a huge amount of rust on the braking track, while the other three with the different types of coating showed a clean surface. Hence, this demonstrates the good corrosion resistance, as extensively described in figure 16.

CONCLUSIONS

All the two types of coatings based on anti-wear material according to the description tested on the same brake discs allow not only to greatly reduce the wear of the brake disc (behavior expected in a certain sense), but above all allow on the one hand to reduce surprisingly also the wear of the brake pads for both families of friction material tested (probably, therefore, for any family of friction material compositions currently in use, given the general composition of the tested friction materials) and, on the other hand, they allow at the same time and quite surprisingly to obtain a good constancy of the friction coefficient.

Finally, still surprisingly, some anti-wear materials and, above all, some specific anti-wear material / friction material couplings, provide significantly higher performance.

From the foregoing description, it will be appreciated that inventive coatings for brake discs and methods for reducing wear have been described. While various components, techniques and aspects have been described with some degree of particularity, it is evident that many modifications can be made in the specific designs, constructions and methodology described above without departing from the spirit and scope of this description.

Some features described in this description in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Further, although the features may be described above as acting in certain combinations, one or more features of a claimed combination may, in some cases, be excised from the combination, and the combination may be claimed as any subcombination or variation of any subcombination.

Also, while the methods may be represented in the drawings or described in the specifications in a particular order, those methods do not need to be performed in the particular order shown or in sequential order, and it is not necessary to perform all methods to obtain desirable results. Other methods that are not described or described may be incorporated into the example methods and processes. For example, one or more additional methods may be performed before, after, simultaneously, or between any of the methods described. Additionally, methods can be rearranged or reordered in other implementations. Furthermore, the separation of the various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the components and systems described can generally be integrated together in a single product or packaged in multiple products. Also, other implementations fall within the scope of this description.

Conditional language, such as "may", "could", "should", unless otherwise specified, or otherwise understood in the context used, is generally intended to communicate that certain embodiments include or do not include certain features, elements and / or steps. Therefore, such conditional language is not generally intended to imply that features, elements and / or steps are somehow required for one or more embodiments.

Subjunctive language such as the phrase "at least one of X, Y and Z", unless otherwise specified, is otherwise understood based on the context generally used to indicate that an element, term, etc. it can be X, Y, or Z. Therefore, such subjunctive language is not generally intended to imply that certain embodiments require the presence of at least one of X, at least one of Y, and at least one of Z.

The degree language used here, such as the terms "approximately", "about", "generally" and "substantially" as used herein represent a value, quantity or characteristic close to the declared value, amount or characteristic that it performs still a desired function or achieves the desired result. For example, the terms "approximately", "about", "generally" and "substantially" may refer to an amount less than or equal to 10% of, within a value less than or equal to 5% of, within a value less than or equal to or equal to 1% of, within a value less than or equal to 0.1% of, and less than or equal to 0.01% of the quantity indicated. If the indicated quantity is 0 (for example, “none”, “having no”), the ranges mentioned above can be specific ranges and not within a particular percentage of the value. For example, within a value less than or equal to 10 wt./vol. % of, less than or equal to 5 wt./vol. % of, less than or equal to 1 wt./vol. % of, less than or equal to 0.1 wt./vol. % of, and less than or equal to 0.01 wt./vol. % of the amount indicated.

All ranges indicated include the upper and lower limits of the range unless explicitly excluded.

Some embodiments have been described in connection with the accompanying drawings. The figures are to scale, but this scale is not limiting, since dimensions and proportions other than those shown are contemplated and fall within the scope of the inventions described. Distances, angles, etc. they are purely illustrative and do not necessarily have an exact relationship with the actual dimensions and layout of the devices illustrated. Components can be added, removed and / or rearranged. Furthermore, the description given herein of any particular feature, appearance, method, property, characteristic, quality, attribute, element or the like in connection with various embodiments can be used in all other embodiments set forth herein. Further, it will be recognized that any of the methods described herein can be practiced using any suitable device for performing the indicated steps.

While a number of embodiments and variations thereof have been described in detail, other modifications and methods of using it will be apparent to those skilled in the art. Accordingly, it should be understood that various applications, modifications, materials and substitutions may be made of equivalents without departing from the unique and inventive disclosure herein or the scope of the claims.

Claims (10)

CLAIMS 1. Anti-wear and anti-corrosion coating for a brake disc, applicable to at least one friction surface of the brake disc configured to cooperate in use with a braking element such as a brake pad, the anti-wear and anti-corrosion coating being applicable for thermal spray; characterized in that the anti-wear and anti-corrosion coating consists of a single layer composed of a material chosen from the group consisting of: chromium carbide (Cr3C2) particles dispersed in a metal matrix consisting of a NiCr alloy; a metal matrix consisting of an austenitic chromium-nickel steel and preferably composed of an alloy of FeNiCrMoSiC (iron-nickel-chromium-molybdenum-silicon-carbon), for example Diamalloy®; their mixing in variable proportions; said anti-wear coating have a plasticity such as to have a reduced propensity to form micro-cracks in conditions of tribo-mechanical stress. 2. The anti-wear and anti-corrosion coating according to claim 1, characterized in that the said chromium carbide particles or the austenitic steel alloy preferably of FeNiCrMoSiC composition still in the form of metal particles of the individual components of the alloy are applied for thermal spray using HVOF technology. 3. The anti-wear and anti-corrosion coating according to claim 1 or 2, characterized in that it has a thickness of between 20 and 400 micrometers. 4. Anti-wear and anti-corrosion coating according to one of the preceding claims, characterized in that it has, after coating with thermal spray and grinding, a surface roughness of between 0.05 and 2 micrometers and preferably between 0.15 and 0, 3 micrometers. 5. Vehicle brake disc including at least one friction surface designed to cooperate in use with a braking element such as a brake pad, characterized in that at least said friction surface is covered with an anti-wear and anti-corrosion coating according to a of claims 1 to 4. 6. Method for the simultaneous reduction of wear on a brake disc and associated brake pads, including the steps of: - prepare brake pads using a friction material formulation of the LS (Low Steel) or NAO (Non Asbestos Organics) type; - cover at least one friction surface of a brake disc intended to cooperate in use with a brake pad with an anti-wear and anti-corrosion coating with such plasticity as to have a reduced propensity to form micro-cracks in conditions of tribo-mechanical stress consisting of chromium carbide particles (Cr3C2) dispersed in a metal matrix consisting of an alloy of NiCr or of an austenitic chromium-nickel steel and preferably consisting of a metal matrix composed of an alloy of FeNiCrMoSiC (iron-nickel-chromomolybdenum- silicon-carbon), for example as Diamalloy®; - couple the previously prepared brake pads and brake disc. Method according to claim 6, characterized in that the wear-resistant coatings are applied by means of HVOF (High Velocity Oxygen Fuel) thermal spray technology. 8. Method according to claim 6 or 7, characterized in that brake pads made of a friction material belonging to the Copper-free family, in particular of the LS (Low Steel) or NAO (Non-Asbestos Organics) type, are coupled, with an anti-wear coating applied to at least one friction surface of the brake disc consisting of chromium carbide (Cr3C2) particles dispersed in a metal matrix consisting of a NiCr alloy or of an austenitic chromium-nickel steel and preferably obtained from a combination of several metallic materials in order to create a compound consisting of an alloy of FeNiCrMoSiC (ferronickel-chromium-molybdenum-silicon-carbon), such as Diamalloy®. 9. Use of friction materials belonging to the Copper Free families of the LS type (Low Steel) or of the NAO type (Non-Asbestos Organics) for the manufacture of brake pads in combination with the use of anti-corrosion anti-wear coatings with such plasticity to have a reduced propensity to form micro-cracks under tribo-mechanical stress conditions on at least one friction surface of brake discs operatively associated with said brake pads to simultaneously reduce wear of brake pads and brake discs, said anti- wear and anti-corrosion being made up of a selected combination of chromium carbide (Cr3C2) particles dispersed in a metal matrix consisting of a NiCr alloy or a chromium-nickel austenitic steel and preferably obtained from a combination of several metal materials in order to create a compound consisting of an alloy of FeNiCrMoSiC (iron-nickel-chromium-molybdenosilicon-carbo-nium), for example as Diam alloy® and applied using the HVOF (High Velocity Oxygen Fuel) hot spray technique. 10. Braking system comprising an element to be braked consisting of a brake disc or drum made of cast iron or steel and at least one braking element consisting of a brake shoe or pad, able to cooperate by friction with the element to be braked, characterized from the fact that, in combination: - the element to be braked has at least one friction surface configured to cooperate with the braking element, which friction surface is covered with an anti-wear and anti-corrosion coating according to one of claims 1 to 4; - the braking element includes at least one block of friction material configured to cooperate with the element to be braked, the friction material being of the LS (Low Steel) or NAO (Non-Asbestos Organics) type.