JPS61266542A - Inorganic friction material - Google Patents

Abstract

PURPOSE:To stabilize the coefft. of friction and to improve the wear resistance by adding prescribed percentages of lubricative glass contg. P2O5, B2O3, Al2O3, etc., graphite and silica or mullite to a matrix of a Cu alloy or the like. CONSTITUTION:An inorg. friction material is obtd. by adding, by weight, 3-10% lubricative glass, 10-20% graphite and 3-20% silica or mullite to a metallic matrix of a Cu or Fe alloy. The lubricative glass contains 25-35% P2O5, 20-30% B2O3, 10-20% Al2O3, 4-10% Na2O, 4-10% Li2O, 2-6% NaF, 1-5% ZnO and 3-15% alkaline earth metallic oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to inorganic friction materials such as metallic friction materials and cermet friction materials that do not contain organic components.

When two objects move while maintaining contact with each other, movement such as sliding or rolling occurs on the contact surfaces,
Frictional force is generated there. Brakes and clutches are mechanical elements that actively utilize this frictional force.

In the case of brakes, the motion of two surfaces sliding in contact is
The frictional force generated between these two surfaces serves to keep it stationary, and as a result, frictional heat is generated on the sliding surfaces. In other words, the brake plays the role of converting kinetic energy into thermal energy through frictional force.

On the other hand, the role of a clutch is to apply kinetic energy to a stationary object by utilizing the frictional force that acts on two surfaces that are in contact with each other. Expressed in another way, a clutch can be said to have the function of transmitting kinetic energy from one surface to the other through frictional force.

From this, the friction material that is incorporated into mechanical elements such as brakes and clutches and constitutes one opposing surface,
The sliding surfaces of the friction material slide against each other while contacting other surfaces, and play the role of generating frictional force there. In this way, friction materials are used to withstand frictional heat and pressure while sliding on a thousand surfaces, and therefore only require a relatively high and constant frictional force or coefficient of friction. Rather, it must be a material that can minimize wear on itself as well as on the other side.

The present invention provides a friction material suitable for use as a friction pad material for brakes, clutches, etc. as described above, and in particular,
This article relates to the improvement of inorganic friction materials such as metallic friction materials and cermet friction materials.

(Prior art) Most of the friction materials that have been used for brakes and clutches have heat-resistant asbestos fibers as an essential ingredient, and depending on the application, carbon powder, metal powder, metal oxide powder, etc. Composite materials were made by adding various powders such as rubber powder and nut shell powder, and hardening them with organic binders (mostly phenolic resins). However, as brakes and clutches become lighter and smaller, and their usage conditions become more severe, these materials are no longer able to adequately meet social needs in terms of heat resistance and pressure resistance.

Therefore, in order to improve heat resistance and increase strength, we developed semi-metallic friction materials that contain a large amount of metal components, metallic friction materials that do not contain any organic components that have poor heat resistance, or cermets that are made of metal and ceramics. Inorganic friction materials such as friction materials have come to be used in parts of brakes and clutches in place of the asbestos-based friction materials, despite their disadvantage in price.

That is, on the contact surfaces between the friction material and the mating material, where the friction material and the mating material slide, there is a significant temperature rise due to frictional heat. On the other hand, when objects come into contact, the contact between both surfaces is not evenly applied to the entire area, but only on a portion of the surface due to the unevenness of one surface.This is the so-called true contact point, and the apparent contact area Rather, the actual contact area has an important meaning. In other words, high temperature and high pressure act on the real contact point during sliding.

For this reason, heat resistance and strength are important in so-called dry friction without oil, which is said to be a harsh sliding process.

This is the reason why metallic friction materials and cermet friction materials that do not contain organic substances are preferred despite their high prices, as is the case with brake linings for aircraft and Shinkansen trains.

The metallic friction materials and cermet friction materials described above all have metal (copper alloy or iron alloy) as the basic material component, and solid lubricant components such as lead and graphite.
It has a structure in which hard, heat-resistant ceramic components such as silica and alumina are dispersed and retained. Among these, cermet friction materials are designed to specifically improve heat resistance by reducing the amount of metal components and increasing the amount of non-metal components with high melting points. Therefore, even though it is called a cermet friction material, it is not fundamentally different from a metallic friction material in terms of material structure.

(Background of the Invention) Based on this recognition, if we pay attention to the role of the solid lubricant component in these materials, its action is due to the excessive increase in the true contact point of the two surfaces interposed in the sliding surface and in contact with each other. It can be seen that the purpose is to prevent increase and adjust the true contact area. Frictional force is the adhesion between two surfaces at the point of real contact,
This is due to the digging action of the protrusions of the other hard surface against one soft surface, that is, ``total frictional force = adhesive friction force + digging frictional force''.

This can be said to be a widely recognized fact.

For friction materials, it is of course necessary to have a high frictional force during sliding, but it is even more desirable that the frictional force be stable and, if possible, constant. A sudden increase in the coefficient of friction immediately before this causes chattering of the brake, which causes abnormal vibrations immediately before the moving body comes to a stop. Further, a similar phenomenon immediately before the relative movement of the two surfaces of the clutch stops is also a cause of clutch shudder and rabbit-flying phenomena.

Therefore, it is strongly desired that friction materials have a coefficient of friction that is stable and has little fluctuation regardless of changes in sliding speed. The solid lubricant component contained in friction materials is an extremely important component added to improve performance.

(Problems to be Solved by the Invention) The most common materials among solid lubricant components are lead and graphite. The lubricity of lead is due to its low shear force as a soft metal and its low solubility properties in metals. On the other hand, the lubricity of graphite is derived from its low shear force based on its crystalline layered structure and its low solubility in copper alloys. In particular, lead exhibits excellent lubricating properties from low temperatures to around 300°C, near its melting point, and graphite exhibits excellent lubricating properties from low temperatures to 1,000°C.
It exhibits a lubricating effect at high temperatures. For this reason, most metallic and cermet friction materials contain lead and graphite, and the lubricity of lead is effective for sliding at relatively low temperatures of around 300°C, but at higher temperatures. , a method has been adopted that relies exclusively on the lubricity of graphite.

Note that technology regarding solid lubricants has recently progressed, and many excellent materials have been developed. In particular, MoS2 and WS
Solid lubricants such as e are used in lubricated parts that cannot be lubricated with oil or in harsh sliding parts.Therefore, these solid lubricants are also applied to friction materials and have achieved good results, but these solid lubricants are expensive. Not only is it disadvantageous in terms of friction material manufacturing process, it also reacts with the metal component that is the main component of the material (for example, in the case of copper alloy, 2 Cu+ MoS 2-h 2
CuS + No), it is difficult to exhibit sufficient lubricating properties, and it also has the drawback of embrittling the metal matrix and deteriorating the strength of the friction material.

However, in the case of heat-resistant cermet friction materials that are used under harsh sliding conditions, if they contain lead, the lead will liquefy at high temperatures of 300°C or higher, causing the metal matrix to liquefy. This has the disadvantage of causing embrittlement and reducing the strength of the friction material.

For these reasons, various attempts have been made to find a solid lubricant that can replace lead and maintain a lubricating effect comparable to lead from low temperatures to high temperatures of 300° C. or higher.

When lubrication is as good as lead, PBO is 30%
Attempts have also been made to incorporate it, focusing on its ability to survive at high temperatures of 0° C. or higher. However, since pbo also reacts with metal components (PbO+ 2 Cu -Pb+Cu20), it was difficult to achieve this goal. In order to prevent the reactivity of pbo, attempts have been made to dissolve 5i02 into PbO and add it as a low melting point PbO-SiO2 glass in an attempt to lower the melting point, but no desired results have been obtained. .

Attempts to use the above-mentioned PbO--SiO□ type glass as a solid lubricant component have since been developed into one variety of glasses. Following the precedent of glass lubricants for hot working of metals, many types of glass have been used. However, since glass acts as extremely hard particles at low temperatures, no solid lubricant has been developed so far that has low-temperature lubricity for friction materials that can be used in practical applications from room temperature to around 300° C., and that can sufficiently replace lead.

(Means for Solving the Problems) This invention focuses on the importance of lubricating components in inorganic friction materials such as metallic friction materials and cermet friction materials, and
The purpose is to improve this. In other words, the purpose is to provide an inorganic friction material that can withstand harsh sliding conditions ranging from mild sliding conditions to high temperatures and pressures, and a wide range of usage conditions, and has a stable coefficient of friction and excellent wear resistance. do.

(Structure) In order to achieve this object, the present invention uses a copper alloy or iron alloy as a matrix, and 10 to 20% by weight of graphite powder is added to the matrix in place of lead contained in conventional materials. Phosphate glass with the structure described below is
In addition, mullite (3AhO3・2S
i02) Alternatively, by containing 3 to 20% silica, a low shearing material that exhibits a favorable lubricating effect on sliding surfaces is formed, allowing a wide range of applications from low to high temperatures, low to high speeds, and low to high surface pressures. The friction material is provided with a stable coefficient of friction and excellent wear resistance over various sliding conditions.

(Action of the Invention) That is, the phosphoric acid glass used in the present invention has a low softening temperature due to the addition of NaF.

Moreover, when the temperature rises to around 600° C. due to the action of Li20 contained, crystal precipitation progresses, thereby preventing the viscosity of the glass from rapidly decreasing as the temperature rises. The lubricating action of phosphoric acid glass with such viscosity characteristics prevents the decrease in the coefficient of friction and increase in wear of inorganic friction materials such as lead-derived metallic friction materials and cermet friction materials, which become noticeable at around 300°C. becomes possible.

Furthermore, due to frictional heat, the temperature of the sliding surface increases to 500~
When the temperature exceeds 600°C, oxidation of both the friction material and the mating material becomes significant. As a result, copper oxide, tin oxide, or iron oxide is formed from the friction material depending on the composition, and iron oxide from the mating material is formed on the respective sliding surfaces.

These metal oxides are mixed and kneaded with the softened phosphoric acid glass, together with the crushed graphite and ceramics that have been abraded and separated from the friction material, to form a low-shear mixture that is present on the sliding surface. This mixture exhibits a lubricating effect due to its low shear properties, and adjusts the true contact area on the sliding surface, thereby helping to keep the coefficient of friction constant.

The sliding conditions have become even more severe, and the sliding surface temperature has reached 1.000℃.
When this temperature is reached, the oxidation of the friction material and the mating material further progresses without waiting for the formation of the mixture, and a large amount of iron oxide, copper oxide, tin oxide, etc. is formed. These metal oxides are exposed to high temperatures and pressures on the sliding surfaces, becoming a fluid metal oxide mixture that also contains worn-out crushed graphite and ceramics, which are components of friction materials. Intake,
A large amount of it will be present on the sliding surface. This means that the sliding surface is extensively covered with a low shear fluid material, resulting in excessive lubrication and a significant decrease in the coefficient of friction. However, the friction material of the present invention In this case, this phenomenon of excessive lubrication does not occur because the phosphoric acid glass with the above characteristics is included as a lubricating component.
A low shear mixture containing phosphoric acid glass formed at temperatures of 0 to 600°C exists on the sliding surface and thinly covers it, preventing the oxidation of both the friction material and the mating material, resulting in the formation of iron oxide, oxidized steel, This is because the amount of produced tin oxide and the like decreases, and as a result, the amount of the fluid metal oxide mixture, which increases as the temperature increases, decreases.

Furthermore, the phosphoric acid glass of this invention has L present therein.
Due to the action of i20, glass crystallization progresses from around 600°C, so the low shear mixture formed on the sliding surface increases in viscosity as the temperature rises, and there is no significant decrease in shear force.As a result, A mixture mainly composed of metal oxides such as iron oxide, copper oxide, and tin oxide, which is formed in the absence of phosphoric acid glass, which is a feature of this invention, is used in large amounts and in addition to all sliding surfaces. A state of excessive lubrication such as coating does not occur, that is, a desirable proportion of the actual contact area is ensured and there is no reduction in frictional force. In other words, the sliding surface is exposed to harsh sliding conditions and
Even if the temperature reaches around 0℃, jI! This makes it possible to prevent a decrease in the coefficient of friction.

(Embodiments of the Invention) In describing the embodiments below, details of the friction material according to the present invention and reasons for selecting the composition range will be described first.

As mentioned above, the inventors used copper alloy or iron alloy as a matrix, and added 10 to 2% by weight to this matrix.
It contains 0% graphite powder and 3 to 10% phosphoric acid glass with the structure described below, and also contains mullite (3AI2o3
・2Si02) or by containing 3 to 20% of silica, it forms a low shear material that exhibits a favorable lubricating effect on sliding surfaces, allowing it to be used in a wide range of applications, from low to high temperatures, from low speeds to high speeds, and from low surface pressures to high surface pressures. They succeeded in providing a friction material with a stable coefficient of friction and excellent wear resistance over a wide range of sliding conditions.

That is, graphite is an extremely important lubricating component in inorganic friction materials that do not contain lead.
By containing 0%, it is possible to reduce the temperature from the low temperature of the static state to 600%.
Not only is most of the lubrication at temperatures around ℃ covered by graphite, but at higher temperatures it also exhibits a lubricating effect in cooperation with phosphoric acid glass, which will be described later.If it is less than 10%, the lubricating effect will be insufficient; , 20% or more, the strength of the friction material itself decreases, the friction coefficient decreases, and the wear resistance also deteriorates.

Precipitable phosphoric acid glass softens from around 400°C and acts as a low-shear lubricating component, and in particular, from around 600°C to 1,000°C, it plays a role in maintaining favorable lubrication performance through cooperative action with graphite. perform. Conventionally, added glassy lubricating components have a pronounced lubricating effect near their softening point, but on the other hand, their viscosity decreases as the temperature rises, so they intervene on sliding surfaces and provide favorable lubrication. It was impossible to keep it working.

In this invention, in order to eliminate the disadvantages of 0 or more, which had disadvantages such as a decrease in the coefficient of friction and an increase in wear at high temperatures, and to exhibit a preferable lubricating effect, in this invention, P20s * B 203 and ' The glass is made up of three components: Al2O, and Na20 is added to lower the softening temperature, and NaF is added to improve the fluidity of the glass so that it exhibits a lubricating effect from low temperatures around 400°C. is now possible. Also, Li2
By adding 0, crystals were precipitated from around 600°C, preventing the viscosity of the glass from decreasing as the temperature rose, and successfully sustaining the lubricating effect at temperatures as high as 1,000°C.

The above-mentioned high temperature lubricity glass components include 25 to 35% P2O5 and 20 to 30% B2O3 at 1% by weight;
Al2o3 10-20%, Na20 4-10%,
Li20t-4~10%, NaF 2~6%, Z
It contains 1 to 5% nO and 3 to 15% of one or more alkaline earth metal oxides.

In the above components, P2O5 is a glass network forming component, and if it is less than 25%, the softening temperature becomes high, and if it exceeds 35%, water resistance deteriorates and practicality is lost. B2O3 is also a glass network forming component. If it is less than 20%, the softening temperature becomes high, and if it exceeds 30%, the water resistance decreases. Al
2O3 is also a network-forming component of glass, and if it is less than 10%, water resistance is insufficient, and if it is more than 20%, the softening temperature increases and fluidity decreases. configured.

The purpose of adding Na20 is to lower the softening temperature, increase the fluidity of the glass, improve wettability to metal surfaces, and improve lubricity, but if it is less than 4%, it has no effect, and if it exceeds 10%, it will reduce water resistance. deteriorates. Li20 is a component that promotes crystallization of phosphoric acid glass, and if it is less than 4%, it has no effect, but if it exceeds 10%, it increases the hardness of the glass and increases the hardness of the glass.
It is undesirable to damage the mating material at low temperatures below ℃.
Further, NaF plays a role in improving the fluidity of glass, but if it is less than 2%, it has no effect, and if it exceeds 6%, the water resistance decreases. Mg as an alkaline earth metal oxide
O, CaO, and BaO are preferable and have the effect of widening the vitrification temperature range, but if it is less than 3%, water resistance deteriorates and 15
%, the softening temperature increases and the lubricating effect decreases.

ZnO stabilizes B203F& in phosphoric acid glass, but if it is less than 1%, there is no effect of addition, and if it is more than 5%, the softening temperature increases and fluidity decreases.

The role of mullite or silica is to contribute to an increase in the coefficient of friction and an improvement in heat resistance due to the digging action of the friction material on the opposing surface. If it is less than 3%, the effect of addition is poor, and if it is more than 20%, it increases the aggressiveness toward the mating material and increases the wear of the mating material, which is not preferable.

Example 1 Copper powder of 200 mesh or less, tin powder of 200 mesh or less, graphite powder of 100 mesh or less.

Lead powder of 100 mesh or less, mullite powder of 100 mesh or less, silica powder of 200 mesh or less, 325
Molybdenum powder with a mesh size or less and various lubricating glass powders with a mesh size or less of 150 meshes were mixed in the proportions shown in Table 1 on the next page, molded under a pressure of 3 t/cm2, and then molded at the maximum temperature in an H2 gas atmosphere. Heated and held at 800°C for 30 minutes, then cooled to room temperature, and then heated to 6 t/cm
Each friction material was manufactured by repressurizing with a pressure of 2.

Comparative Example 1 shown in Table 1 is a typical composition of a friction material for a clutch in which lead is used instead of lubricating phosphoric acid glass (G-3) used in the present invention. 2
is a composition widely used as a friction material for heavy-load clutches that prevents deterioration of high-temperature friction performance due to lead addition. On the other hand, Comparative Examples 3 and 4 have the compositions of prototype products up to the present invention, and both were manufactured under the same conditions as the invented product. In addition, the lubricating glass component G-3 used in this invention and the other lubricating glass component composition table used as a comparative example are shown in Table 2 on page 21. Comparative Example 1 in Table 2 is PbO -9f02 glass, Comparative Examples 2 and 3
This is the prototype glass that was produced before this invention.

Regarding the samples obtained in the examples, cast iron (FC-25 material)
A manufactured disc was used as the mating material, the sliding speed was 20 m/s, the load was 7, and the load was 5 kg/am2. 2 under the condition of sliding temperature 200℃
A friction test was conducted in which a series of operations of sliding for 5 seconds and stopping the sliding for 5 seconds was repeated 50 times, and the performance comparison results are shown in Table 3 on page 18.

As is clear from Table 3, the friction material according to the present invention has a friction coefficient of 0.4 due to appropriate lubrication.
Although it is high at 8, it shows a stable value, and the wear of both the friction material itself and the mating material is low.

On the other hand, the friction material of Comparative Example 1 has a lower friction coefficient due to the dissolution of lead, and also has relatively high wear due to adhesion of the friction material to the mating material. Since it is lead-free, it is heat resistant and has a high friction coefficient, but it lacks lubrication, the friction coefficient fluctuates sharply, and the mating material wears frequently.
Furthermore, in the friction material of Comparative Example 3, the amount of lead added as a lubricating component was reduced to 4%, so lubrication by lead was insufficient in the low temperature range. Furthermore, when the temperature exceeded 300°C, the strength of the friction material decreased due to dissolution of lead. As a result, wear of the friction material increased, the coefficient of friction decreased, and its fluctuations became more severe. That is, PbO-9i02 added to this material
The lubricating action of glass did not have the expected effect. The friction material of Comparative Example 4 had a prototype composition just before reaching the present invention, and the effect of improving lubrication performance by adding phosphoric acid glass was considerably recognized, and the coefficient of friction was relatively high at 0.45, and a stable value was obtained. However, the material remained slightly aggressive toward the mating material (occurrence of scratches), and the amount of wear was greater than expected.

Example 2 Copper powder of 200 meshes or less, tin powder of 20G meshes or less, iron powder of 150 meshes or less, graphite powder of 100 meshes or less, lead powder of 100 meshes or less, molybdenum powder of 325 meshes or less, and the Various lubricating glass powders of 150 mesh or less having the composition shown in Table 2 are mixed in the proportions shown in Table 4 on the next page, and each powder is 3 t/c.
After molding under a pressure of m2, heat and hold for 30 minutes at a maximum temperature of t, o o o °C in an H2 gas atmosphere, and then:
After cooling to room temperature, the material was pressurized again with a pressure of 6 t/cm2 to produce a friction material according to the present invention.

Comparative Example 1 shown in Table 4 on page 24 is an example of a friction material for a disc brake pad in which lead was used in place of the lubricating phosphoric acid glass G-3 used in the friction material of the present invention. Comparative Example 2 is a heat-resistant friction material for a heavy-load clutch that does not contain lead. Comparative amounts 3 and 4 are prototype compositions developed up to the present invention, and both were manufactured under the same conditions as the friction material according to the present invention.

The samples obtained in this example were made of cast iron (FC-
25 material) A friction test was conducted using a disc as the mating material under the same conditions as the test conducted in Example 1, and the performance evaluation results are shown in Table 5 on the previous page. This product aims to stabilize low-temperature friction, but the sliding surface temperature is 30
When the temperature exceeds 0°C, the friction coefficient decreases as in the case of lead lubrication in Comparative Example 1 in Example 1, and transfer of the friction material to the mating material was observed. Comparative Example 2 is a friction material with excellent heat resistance in which lead has been removed and lubricant is only graphite. However, due to the lack of lubricating components, there was a lot of wear on the mating material, and the friction coefficient fluctuated relatively frequently. Comparative example 3 is PbO-
This prototype was designed to improve the lubrication performance using 3i02 glass, but it did not have the expected effect and showed aggressiveness towards the mating material during the initial wear stage, resulting in scratch marks on the mating material. However, the wear of the friction material also increased.

Comparative Example 4 was an attempt to improve the lubrication performance using phosphoric acid glass G-2, which was in the prototype stage, and although there was a considerable improvement effect in terms of the friction coefficient, there was still insufficient lubrication and relatively high wear. , scratches were observed on the mating material. On the other hand, compared to these comparative examples, the friction material according to the present invention had a remarkable lubricating effect due to phosphoric acid glass G-3, and a high coefficient of friction was obtained, and the wear of both the friction material and the mating material was reduced.

(Effects of the Invention) As described above, according to the present invention, a stable coefficient of friction and excellent wear resistance can be achieved over a wide range of usage conditions, from gentle sliding conditions to harsh sliding conditions with high temperatures and pressures. It has now become possible to provide a sliding friction material having the following features.

Claims (1)

[Claims] In a metallic friction material or a cermet friction material in which the metal matrix is made of a copper alloy or an iron alloy, P_2O_5 is 25 to 35% in weight percentage, B_2O_
3 is 20-30%, Al_2O_3 is 10-20%, N
a_2O 4-10%, Li_2O 4-10%, Na
Lubricating glass with a composition of 2 to 6% F, 1 to 5% ZnO, 3 to 15% of one or more alkaline earth metal oxides, 3 to 10% graphite, 10 to 20% graphite, and silica. Alternatively, an inorganic friction material characterized by containing 3 to 20% of mullite.