Modern production equipment has a rather complex structure. Friction mechanisms transmit motion by frictional force. These can be clutches, clamps, unclamps and brakes.
That the equipment was durable, worked withoutdowntime, its materials make special demands. They are constantly growing. After all, technology and equipment are constantly being improved. Their capacities, working speeds, and also loadings increase. Therefore, in the process of their operation, various friction materials are used. Reliability, durability of equipment depends on their quality. In some cases, the security and life of people depend on these elements of the system.
general characteristics
Friction materials are essential elements.nodes and mechanisms that have the ability to absorb mechanical energy and dissipate it into the environment. At the same time, all structural elements should not wear out quickly. For this, the presented materials have certain properties.
The coefficient of friction of friction materials shouldbe stable and high. The durability indicator is also required to meet operational requirements. Such materials have good heat resistance and are not subject to mechanical stress.
To a substance that performs friction functions,It does not cling to work surfaces, it is endowed with sufficient adhesive properties. The combination of such properties ensures the normal operation of equipment and systems.
Material properties
Friction materials have a certain set of properties. The main ones have been listed above. These are service qualities. They determine the performance characteristics of each substance.
But all service characteristics are caused bya set of physico-mechanical and thermostatic indicators. Such parameters change during the operation of the material. But their limiting value is taken into account in the process of selecting a friction substance.
There is a separation of properties into static,dynamic and experienced indicators. The first group of parameters includes the limit of compression, strength, bending and stretching. Also included are heat capacity, thermal conductivity and linear expansion of the material.
Thermal stability and heat resistance are considered to be indicators determined in dynamic conditions. In an experimental setting, the friction coefficient, wear resistance and stability are established.
Types of materials
Friction materials of the brake system andClutches are often made on a copper or iron base. The second group of substances is used in conditions of increased load, especially with dry friction. Copper materials are used for medium and light loads. And they are suitable for dry friction, and with the use of lubricating fluids.
In modern conditions of production, materials based on rubber and resin are widely used. Various metal and non-metallic fillers can also be used.
Application area
There is a classification of friction materials independing on their field of application. The first large group includes transfer devices. These are medium and lightly loaded mechanisms that operate without lubrication.
Further, the friction materials of the brake system for medium and heavy duty mechanisms are distinguished. In these nodes lubrication is not used.
The third group includes substances used in couplings of medium and heavy loaded nodes. There is oil in them.
Also distinguish a separate group of brake materials in which there is a liquid lubricant. The main parameters of the mechanisms determine the choice of friction materials.
In the clutch, the load acts on the system elements for about 1 s, and in the brake - up to 30 s. This indicator determines the characteristics of materials nodes.
Metallic materials
As mentioned above, the main metal friction materials of the clutch system, brakes are iron and copper. Steel and cast iron are very popular today.
They are applicable in different mechanisms.For example, friction materials for brake pads containing cast iron are often used in railway systems. It does not warp, but abruptly loses its sliding qualities at temperatures from 400 ° C.
Non-metallic materials
Friction clutch or brake materials are also made from non-metallic substances. They are created mainly on the asbestos basis (resin, rubber act as binding components).
The friction coefficient remains high enough totemperatures of 220 ° C. If the binder is a resin, the material is characterized by high wear resistance. But their coefficient of friction is somewhat lower relative to other similar materials. A popular plastic material on this basis is retinax. It contains phenol-formaldehyde resin, asbestos, barite and other components. This substance is applicable for knots and brake mechanisms with severe operating conditions. It retains its qualities even when heated to 1000 ° C. Therefore, retinax is applicable even in aircraft brake systems.
Asbestos materials are made by creatingof the same name fabric. It is impregnated with asphalt, rubber or bakelite and pressed at high temperatures. Short asbestos fibers can also form non-woven linings. Small metal chips are added to them. Sometimes brass wire is introduced to strengthen the strength.
Sintered materials
There is another type ofsystem components. These are sintered friction materials of the brake system. That this variety will become clearer from the method of their manufacture. They are most often made on a steel base. In the process of welding, other components are sintered with it. Pre-pressed billet consisting of powder mixtures, is subjected to high-temperature heating.
Such materials are used most often inheavy duty clutches and brake systems. Their high performance in operation are determined by two groups of components that make up. The first materials provide a good coefficient of friction and wear resistance, and the second - stability and a sufficient level of adhesion.
Steel based materials for dry friction
Выбор материала для различных систем carried out on the basis of economic and technical feasibility of its manufacture and operation. Several decades ago, iron-based materials such as FMK-8, MKV-50A, and the QMS were in demand. Friction materials for brake pads, which worked in heavily loaded systems, later began to be manufactured from FMK-11.
MKV-50A is a newer development. It is used in the manufacture of linings for disc brakes. It has an advantage over the FMK group in terms of stability and wear resistance.
In modern production, materials like QMS have become more widespread. They increase the content of manganese. Also included are carbide and boron nitride, molybdenum disulfide and silicon carbide.
Materials on the basis of bronze for dry friction
In the transmission and brake systems of variousappointments have proven themselves materials on the basis of tin bronze. They wear out mated parts made of cast iron or steel much less than iron-based friction materials.
Presented variety of materials usedeven in the aviation industry. For special operating conditions, tin can be replaced by such substances as titanium, silicon, vanadium, arsenic. This prevents the formation of intergranular corrosion.
Materials based on tin bronze are widelyused in the automotive industry, as well as in the manufacture of agricultural machinery. They withstand heavy loads. Included in the alloy 5-10% tin provide increased strength. Lead and graphite play the role of a solid lubricant, and silicon dioxide or silicon increases the coefficient of friction.
Work in the conditions of liquid lubrication
Materials used in dry systems havesignificant drawback. They are subject to rapid wear. At hit in them greasings from adjacent nodes sharply decreases their efficiency. Therefore, recently, materials intended for use in liquid oil have become increasingly widespread.
Such equipment is smoothly turned on, characterized by a high level of wear resistance. It is easily cooled and simply sealed.
In foreign practice in recent times growproduction volumes of a product such as friction sheet material for brakes, clutches and other asbestos-based mechanisms. It is impregnated with resin. The composition includes molded elements with a high content of metallic fillers.
Most often, sintered materials based on copper are used for the lubricating medium. To improve the frictional characteristics, non-metallic solid components are introduced into the composition.
Improving properties
First of all, improvement requireswear resistance, which have friction materials. The economic and operational expediency of the presented components depends on it. In this case, technologists develop ways to eliminate excessive heat on the rubbing surfaces. To do this, improve the properties of the friction material itself, the design of the device, and also regulate the working conditions.
If materials are used in dry conditionsfriction, special attention is paid to their heat resistance and resistance to oxidation. Such substances are less susceptible to abrasive wear. But for systems with lubrication, heat resistance does not matter so much. Therefore, more attention is paid to their strength.
Also technologists when improving qualityfriction materials pay attention to their degree of oxidizability. The smaller it is, the more durable components of the mechanisms. Another direction is to reduce the porosity of the material.
Modern production should improveused additional materials in the manufacturing process of various moving, transfer devices. This will meet the growing consumer and operational requirements for friction materials.
