Method to manufacture items from polymer composite materials based on polytetrafluorethylene and device for manufacturing of items

FIELD: technological processes.

SUBSTANCE: invention relates to the field of material science, in particular, to anti-friction polymer composite materials, and may be used in manufacturing of parts of metal-polymer friction units and in general machines of various types of equipment. The method to manufacture items from polymer composite materials on the basis of polytetrafluorethylene consists in the fact that fillers are mixed with polytetrafluorethylene in a mixer with rotation frequency of 2800 min-1, and cold pressing is carried out in a closed die mould. Then the pressed stock is installed into the closed device, and additional pressure of compression is developed in the pressing direction. Besides, the additional pressure of compression is regulated and set within 2.0 - 8.0 MPa.

EFFECT: increased characteristics of mechanical and tribotechnical properties of a composite material based on polytetrafluorethylene.

1 tbl, 1 dwg

 

The invention relates to the field of materials, particularly to antifriction polymeric composite materials (PCM), and can be used in the manufacture of metal-polymer friction and, in General, machines of various types of equipment. The known method of manufacturing products from polymer composite materials based on polytetrafluoroethylene (PTFE) (AC No. 1812190, IPC C08J 5/15) at which PTFE powders, bronze, molybdenum disulfide and chopped carbon fibers are mixed in a mixer with a rotational speed of the knives 2800 min-1pressed preform at a pressure of 100-110 MPa and sintered at a temperature of 360±5°C, aged at this temperature, the rate of 8-9 min per 1 mm of wall thickness of the workpiece is cooled from the sintering temperature to 327°C at a rate of 0.3-0.4 deg./min, 327 to 20°C freely together with the furnace. With chopped carbon fiber is produced from a carbon-based material, stored in liquid freon at least 48 hours. After drying, the material is cut into pieces and ground in a mill in the presence of the PTFE powder at a frequency of rotation of the knives 7000 min-1within 3-9 minutes Known method has the disadvantages of reducing characteristics of the mechanical properties of the composite material and the efficiency of the method. The main disadvantage of this method is that during cold compaction cannot be achieved eno�but dense packing of the particles of the matrix and fillers. In addition, under free sintering the molded workpiece, due to different thermal expansion of the components, their sizes and the amount of PTFE particles and the filler is changed to a different value, which leads to the weakening and destruction of adhesion bonds formed between them at the stage of extrusion, and to the increase of porosity. Upon further cooling with free cooling outside shape level of adhesive interaction and porosity recover slightly, resulting in a reduction of mechanical characteristics and tribological composite properties (tensile strength, wear rate, etc.). Processing of carbon fiber in the liquid refrigerant within 48 hours also provides the solution to this problem, a twofold increase in compaction pressure to 100-110 MPa only partially contributes to the increased packing density of the particles. As a result, the tensile strength and the wear resistance of the composite material are reduced, increasing production costs (spent freon, increase energy expenditure and wear of extrusion equipment) and decreases the performance. Another known method of manufacturing products made of composite materials based on polytetrafluoroethylene with particulate and fibrous fillers, which carry out the mixing of the filler� with polytetrafluoroethylene in a mixer with a rotation speed of at least 2800 min -1, cold pressing in the mould when exposed to pressing punch of energy of ultrasonic oscillations of a frequency of 20±3 kHz within 2-3 min and the amplitude of the oscillations, in the range of 8-12 μm, is heated in a furnace to a temperature of 360±5°C at a rate of 1.5-2.0 deg./min, holding at this temperature for 8-9 min per 1 mm of wall thickness of the product, cooling to a temperature of 327°C at a rate of 0.3-0.4 deg./min to and from 327°C to room temperature - cooling with the furnace (Patent RF №2324708 C2, IPC C08J 5/14, publ. 20.05.2008).

The method closest in its technical essence to the proposed invention, however, it also has its disadvantages, which reduce the mechanical characteristics and tribological properties of the composite material. Practically eliminates the disadvantage associated with the destruction of adhesion between the particles of the components, with free heated, extruded workpieces, since pressing with the imposition of energy of ultrasonic oscillations, increasing the level of adhesion interaction may not affect the difference in thermal expansion of the material of the various components. Consequently, and inevitably, the reduction in mechanical properties of the composite material. In addition, when using ultrasonic compacting is much more complicated technological equipment (optional n�wives ultrasonic generator) and additional tooling in the form of a special waveguide for transmission of ultrasound energy pressing the punch.

The technical result of the invention - improving mechanical characteristics and tribological properties of composite material based on PTFE, and the simplification of process equipment and technology of manufacturing products made of composite materials based on polytetrafluoroethylene.

Said technical result is achieved in that in the method of manufacturing products made of composite materials based on polytetrafluoroethylene, which carry out the mixing of fillers with PTFE in the mixer with a rotational speed 2800 min-1, cold pressing in a closed mold, the installation of the molded workpiece in a closed device, the creation of additional compression pressure in the press direction, according to the claimed invention, additional pressure regulate and compression set in the range of from 2.0 to 8.0 MPa.

The compression pressure, adjustable between 2 and 8 MPa, creates stress-strain state in the volume of the molded workpiece and ensures the preservation and strengthening of adhesion bonds between the components formed during the extrusion of the composition, and significantly improves the characteristics of the mechanical and tribological properties of polymer composite materials.

The minimum value of the compression pressure of 2.0 MPa creates pressure compression and deformation zagotovka�, necessary to compensate for possible volume changes due to thermal expansion of the elements of the closed device and variability of body sizes and punch-defined tolerances in their manufacture.

The maximum compression pressure of 8.0 MPa is determined by the tensile and yield strength of PTFE in compression and recrystallization process, which begins when a certain magnitude of stress and strain.

Review the effectiveness of the claimed method was performed on manufacture and research of PCM following composition: cryptocrystalline graphite 4,5-9,0 masses. %, molybdenum disulfide 1.0 to 2.5 mass. percent, carbon nanotubes of 1.0-2.5 mass. %, PTFE - else (86,0-93.5 masses. %).

Manufacturing (PCM samples for the study of mechanical and tribological properties) was produced as follows. Composition of powders are mixed in a mixer with a rotational speed of the blades is not less than 2800 min-1, extruded workpiece under a pressure of 75 MPa, pressed billet was placed in a closed device, the geometry of the internal cavity of which corresponds to the geometry and size of the workpiece. Using the adjusting screw to set the pressure of 2.0 MPa and sintered at a temperature of 360±5°C for 8-9 min per 1 mm of wall thickness of the product, cooled in the shape from the sintering temperature to 327°C with soon�TEW of 0.3-0.4 deg./min, and then to room temperature free cooling with the furnace.

The invention is illustrated by the attached drawing, which shows the design in the context of a closed device for sintering the pressed blanks. The device consists of a housing 1, a plug 2, a compression spring 3, the support ring 4 and the adjusting screw 5.

After pressing, the billet 6 is installed in the housing 1, the space is closed by a plug 2, by means of a spring 3 and an adjusting screw 5 defines the necessary compression pressure. Mounted in the housing, the workpiece experiences a predetermined compression pressure, wherein in the heating process completely eliminates thermal expansion, since the workpiece is preliminarily subjected to a compression pressure in the entire volume, which is greatly enhanced owing to the difference of thermal expansion coefficients of steel and PTFE at a temperature of 360°C, 25 times). During heating of the workpiece to 360°C compression pressure between the particles increases 3.5 times.

To quantify the effectiveness of the claimed method was carried out tests of samples made by known and declared methods. The definition of the limit of the tensile strength σinand elongation at break δ produced by methods GOST 11262-80, modulus of elasticity by the method of GOST 9550-81. The wear resistance of PCM was determined �about the speed of wear of the friction drive, under the scheme of friction "thumb drive". Fingers with a diameter of 5 mm were made of the test material, the disc (contrale) - made of hardened carbon steel. The test was carried out at sliding velocity of 1.2 m/s and contact pressure of 1.5 MPa. Table 1 shows the mechanical and tribological properties of samples manufactured according to the known and the claimed method with three modes: by mechanical compression pressure of 2 MPa, at a pressure of 6 MPa and at a pressure of 8 MPa. From these data it follows that in the manufacture of samples of the claimed method, the tensile strength is increased to 35%, the modulus of elasticity of up to 41%, the wear rate decreases to 56%, the coefficient of friction is reduced by 17%.

Complex improvement of the mechanical characteristics and tribological properties of the composite material, manufactured by the inventive method, which is expressed in increasing the tensile strength of 24-35% and reducing the wear rate on 42-56%, can significantly improve the performance and significantly increase the life of friction (bearings, sealing devices) machines in various branches of engineering.

Method of manufacturing products made of composite materials based on polytetrafluoroethylene, which carry out the mixing of fillers with policetype�ethylene in a mixer with a rotational speed 2800 min -1, cold pressing in a closed mold, the installation of the molded workpiece in a closed device, create additional pressure of compression in the direction of extrusion, characterized in that the additional pressure regulate and compression set in the range of from 2.0 to 8.0 MPa.



 

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