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    УДК 678.067:621.771
    C.В. Семенов, С.С. Семенов
    ООО «МиниЗавод Промпластик» (Донецк, Украина)
    С.В. Поддубный, Н.В. Гичун
    НИП «Техресурс» (Донецк, Украина)

     

     

    THE NEW PROPERTIES OF THE TEXSTOLITE BEARING BOXES (TRIBOTTEXSTOLITE) FOR THE ROLLING MILL BEARINGS

     

    The article describes the polymeric materials (textolites), which are used for making bearing boxes of rolls of the rolling-mills. The new properties of tribotextolite boxes manufactured byOOO “MINI-STEEL MILL PROMPLASTIC” are presented in the article, they are confirmed during industrial tests and while in operation in the context of the rolling. As bearings of working rolls of rolling mills, the non-metallic textolite boxes are usually used. In the bearings of turning rollers the pressure is 2 … 4 times higher, and the coefficient is 4 … 20 times higher in comparison with bearings of the general purpose vehicles. The small-scale journal and bearings and heavy loads under the rolling impose special requirements to the design and quality of the bearings.

    The bearing life is determined by: the quality of the textolite box, the quality of the greasing substancesupply (usually water and grease), the quality of the bearing journal surface.

    The non-metallic journal bearings have significant advantages over the bronze bearings: low cost, the possibility of water lubrication, good conformability to the journal, the low index of friction and the low consumed powerrequired for rolling. The disadvantages of non-metallic bearings: low conductivity for heat(approximately 100 times less than thermal conductivity of bronze), which requires intensive water cooling; low-level heatproof quality (they are charred at a temperature of 120 … 1500С); significant swelling characteristic(due to the water absorption capacity), which leads to a change in the dimensions of the bearing.

    The types of textolite: textolite from the granulated material, laminated textolite (rolled), tribotextolite. The textolitefrom the granulated material is a plastic obtained by hot pressing of shredded cotton cloth impregnated with artificial resins. The fully molded bearings are made for the small-section and medium-section mills They make all-pressed bearings for small-section and medium-grade mills, with rolls up to 450 mm in diameter.

    The internal structure of the material in the pressed bearings is approximately the same in all directions. This textolite is less consistent and less resistant, than the rolled laminated textolite. The reinforcing of granulated material reduces the stress-related characteristics, reduces the gauge of use the box actuation fluid under the wearing process.

    The laminated textolite is produced in the form of plates and is used for the production of composing bearings for the heavy break-down and sheet mills. It is a plastic obtained by hot pressing of cotton cloth, impregnated with artificial resins, with regular layers. The structure of this textolite is heterogeneous in different directions. The textolite is well processed – grinded, milled, drilled and polished.

    The disadvantages of textolite bearings (sheet): large waste materials of textolite during manufacture, high costs of manual work and machine time for manufacturing and processing bearings.

    The bearings made of plastic have an extremely low coefficient of friction – 10 … 20 times less than bronze bearings, at high speeds and pressures on the journal is almost equal to the index of friction of roller bearings.

    The index of friction of bronze bearings= 0.04 … 0.1. The index of friction of cone roller bearings= 0.002 … 0.005. The index of friction of textolite bearings= 0.004 … 0.006. The use of plastic bearingsprovides a significant reduction of power consumption under the rolling in comparison with metal bearings.

    The new properties of tribotextolite boxes.

    To increase the wear quality of rolling mill bearings at the OOO “MINI-STEEL MILL PROMPLASTIC” tribotextolite boxes developed and put into production, using the modern scientific discoveries in the science of friction (tribology). As a result, a new plastic – tribotextolite – is obtained, it is a directed reinforced polymeric composite specially created for working in highly loaded friction pairs (polymer-metal).

    The tribotextolite meets a number of requirements, which are imposed to the antifriction materials working at high dynamic loads in the context of rolling, which led to a significant increase of wear quality of boxes.

    To increase the durability and tribotextolite life, the reinforcing material is used –“belting” (heavy coarse fabric). According to the structure, this plastic is a frame formed by fabric threads, the spaces between which are filled with resin. The layers of the fabric are placed flat-down against journal, with a maximum breaking tension (30 MPa) in the direction of roller rotation.

    Currently, the following types of materials have been developed and tested under production conditions:

    1. The film-forming textolite (tribotextolite) TP-220 is a material in which the physical and mechanical properties are increased (the rupture limit under compression is 220 MPa instead of 150 MPa according to GOST 5-78).

    Also in this material, the film-forming effect is used, that is the ability to form a transfer filmwith greasy propertieson the friction surface (polymer-metal).

    The wear quality of boxes of this material is 1.5.2 times higher than forstandard boxes (regular).

    1. The film-forming,heat-resistanttextolite (tribotextolite), modified by a combination of layered modifiers TPTS-260 – a material in which the physical and mechanical properties are increased (rupture limit under compression 260 MPa). In the process of friction, under the action of emerging high temperatures in surface microlayers of friction couples, there are significant changes in the properties of materials. In ordinary textolite, on heating to 150 ° C, the physical and mechanical properties deteriorate fourfold. The heat resistance in tribotextolite TPBO-260 is increased to 150 0С without deterioration of physical and mechanical properties.

    The layered modifiers plate the microasperities of the surface of journals and reduce the index of friction. The film-forming effect is also used in this material. The wear quality of boxes of this material is 2.2.5 times higher than for staff (simple) textolite boxes.

    1. The film-forming, heat-resistant textolite (tribotextolite), modified by friction geomodifier(GMT) TPTG-260 – material in which physical and mechanical properties are increased (rupture limit under compression 260 MPa).

    The metallurgical enterprises use GMT to increase the service life of high-loaded mechanisms due to micro-grinding and increasing the microhardness of the friction surface.

    GMT is a complex of milled natural minerals that have undergone mechanoactivation, magnetic separation with the addition of catalysts. Getting into contact zone, GMT make structural changes in the friction surface, which are capable of modifying it in a tribotechnically advantageous direction, while the processed friction units of the mechanisms operate in the normal operation mode.

    The basic material for the production of friction geomodifiers is mineral materials with the maximum content of magnesium oxide, silicon dioxide, tungsten oxides, calcium fluoride and impurities of nickel compound, cobalt, copper, tin, zinc. The tribotechnical composition of GMT makes process of artificial aging of new friction couples and worn-out friction couples of mechanisms being gradual and manageable. The process is accompanied by immunization of sliding surfaces and has a pronounced effect of the consequences.

    The effectiveness of tribotechnical compositions of GMT for increasing theequipmentlife is confirmed by the technical acts of the enterprises: OAO “DMZ”, ZAO “MMZ Istil (Ukraine)”, OAO MK “Azovstal”, OAO “ZMK “Zaporozhstal”, GOAO “Donbass Mine Management”, ZAO “Donetsk high-voltage pylons plant”, OOO “Donetskshsahtometrostroy”, OOO “Mehanic”, OAO “Bastet-Pro”.

    The industrial tests of tribotecostoliteboxes TPTG-260 were carried out in the context of the rolling mill 2300 at OAO “DMZ”. The conducted visual observation and photographic fixation of the journals working surface of the left and right sides of the roller (figure 1) after rolling of 7,500 tons of metal showed: – the surface of the right roller side (standard box) is wavelike, lackluster, rough, with drag lines and sharp edges; – the surface of the left roller side (test box) is clarified as a result of micropolishing due to the action of the GMT modifier, the wave crests are polished, the drag lines are smoothed.

    Figure 1 –The micropolishing the journal surface with box TPTG-260 after rolling 7500 tons.

    Thus, we observe the work of the GMT modifier over the entire surface of the journal surface with the maximum effect at the loaded places, which leads to an additional reduction of the friction coefficient.

    The conducted visual observation and photographic fixation of the standard and test boxes surfaces (figure 2) after the rolling of 7,500 tons of metal showed:

    – the surface of the standard box is porous with microfissures;

    – the surface of the test box is smooth, uniform, with regular wear.

    Figure 2 –The condition of the working surface of the boxes after rolling 7500 tons: textolite (standard box from the left side) and tribotextolite (test box from the right side). In this way, the high physical and mechanical properties and tribotechnicalproperties of tribotextolite TPTG-260 are confirmed.

    The wear quality of boxes of this material is 3.5 … 4 times higher than for standard (regular) textolite boxes. The increase of physical and mechanical parameters was achieved through the use of a new polymer, as well as the application of technology of the reinforcing the boxes actuation fluid with solid belting plates over the full width of 20 … 35 mm (figure 3). Also it allowed the box actuation fluid to be used up to a residual thickness of 8 mm, instead of 12 mm in standard boxes. The sheets are laid in the direction of journal rotation with a base – with maximum breaking properties (30 MPa).

    Figure 3 – Packing diagram of sheets

    The observations during the operation of the boxes showed that the wearing process of the actuation fluid of the standard (textolite) boxes is in the shape of an ellipse (figure 4), that is journal deviates from the vertical in the direction of the horizontal load vector formed at the moment when the stock material enters the rollers. It leads to distortions in the parallel operation of the rollers. The wearing process of the tribotextolite boxes occurs vertically, and it was observed at the rolling mill with the maximum swaging force.

    Figure 4 –The direction of wearing process of the boxes actuation fluid: textolite (standard) – leftward, tribotextolite (test) – rightward

    The analysis of working conditions of rolling mills showed that the wear quality of the boxes is affected by a number of factors:

    – outside temperature;

    – the roughness of journals;

    – feed rate and hardness of the coolant;

    – the oxide scale entering in a friction couple;

    – type of rolled metal (dynamic loads);

    – presence of dense greasing station.

    On the basis of this, the wearing quality of boxes is a relative quantity, depending on the specific conditions of production in which comparative tests of different boxes were carried out.

    The comparative industrial tests of standard and testboxes in various production conditions confirm that the more negative factors are involved in rolling, the higher the relative durability of tribotextolites. That is, at maximum rolling loads, the complex of tribotechnical properties of the boxes shows the maximum relative wearing quality in comparison with standard textolite ones.

    The economic effect of the use of tribotextolite boxes is achieved due to: increasing wearing quality of boxes, obtaining high-quality rolled metalsdue to the stable geometric dimensions, increasing the durability life of the roll necks, saving power consumption, nonstop work of mills, reducing labor intensity in repair work.

    It is planned to carry out the comparative tests of standard (textolite) and tribotextolite boxes in full – on two conjugate rollers:

    – to fix the initial and final roughness of the boxes;

    – to fix the initial and final roughness of the journals;

    – to carry out a wear sensing at control points along the perimeter of the box after rolling;

    – to take photographs of working surfaces;

    – to fix the initial and final hardness of the textolite boxes;

    – to measure vibration parameters.

    Conclusions.

    The conducted industrial tests of standard (textolite) and tribotextolite boxes produced by OOO “Mini-Steel Mill Promplastic”, as well as their operation in the production conditions of various iron and steel companies, showed:

    – the wearing quality of tribotextolite boxes TP-220 is 1.5 … 2 times higher than of standard ones; the wearing quality of tribocostoliteboxes TPTS-260 is 2 … 2.5 times higher than of standard ones;the wearing quality of tribotextolite boxes TPTG-260is 3.5 … 4 times higher than of standard ones.

    To obtain the maximum effect, it is advisable to insert the TP-220 boxes in pairs with the TPTG-260 boxes, as the micropolishing of the journals will increase the durabilityof the TP-220 boxes (taking into account the different wearing quality of the TP-220 and TPTG-260 boxes, their setting is necessaryin the ratio of TP-220 / TPTG-260 – 70% / 30%). In the process of setting pairs of boxes, to maximize the development process of GMT properties, boxes TPTG-260 must be placed in a more loaded place.

    References.

    1. Korolev A.A., NikolaevskyG.N. Machinery of rolling plants. Statetechnologicalpublishing house of literature on ferrous and non-ferrous metals. M.: 1953. p.358
    2. Trofimov N.N., Kanovich M.Z. Fundamentals of polymer composites. Moscow: Nauka, 1999. –pp. 539

    3. GOST 5-78 –Constructive textolite and asbestos-reinforced laminate. Technical conditions

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