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MODERNIZATION OF SEALING UNITS OF OIL-FILM BEARINGS FOR WORK STANDS OF BAR AND WIRE MILLS

Conventional sealing units of oil film bearings for the work stands of bar and wire mills, which contain reinforced radial seals in combination with axial seals, having the form of textolite or bronze rings spring-loaded against the end faces of a roll barrel, have proved to be quite ineffective under present-day operating conditions.

Protective seals in the form of spring-loaded contact rings are unserviceable and practically inoperable at high running speeds, while reinforced radial seals rapidly lose their tightening properties due to intensive hydro abrasive wear of seal lips and of respective contacting surfaces of oil film bearing. This results in increased consumption of liquid lubricants and their water contamination causing the rupture of loaded lubricant film and the «hot seizure» of bearings.

A distinctive feature of the modernized sealing units is the presence of specially developed axial-type and combined lip seals, contacting the hard antifriction surfaces and capable of acting as oil-retaining tightening elements as well as protective elements repelling the main flow of cooling liquid and scale.

Figure 1 shows a type design of the modernized sealing unit for oil film bearings of high-speed stands of bar and wire mills.

Fig.1. Sealing unit of the oil film bearing «ПЖТ-220» for the horizontal finishing stand of a wire mill

Here, the tightening function proper is performed by a double axial seal 6 of TД type, which is fastened in the back cover 5 of the chock 3 and contacts with its lips the hard ground counter faces of the clamping sleeves 4 and 8 fitted over the bearing sleeve 2. The flows of cooling water and scale are expelled by the РНСТ type seal 7 having a radial outer lip and a nongliding fixed axial lip. The axial lips of the seal 7, squeezed between the end faces of the clamping sleeve 8 and the roll barrel 1, prevent the ingress of water and scale at the tapered bearing sleeve 2 and the roll 1. The radial lip of the seal 7 repels the major part of the cooling liquid flow, while the particles of water and scale which have found their way into the space between the seals 6 and 7 are removed through a drain hole in the lower part of the cover 5. In so doing, water and scale do not practically reach the counter faces of the axial seal 6, which provides favourable operating conditions and reduces the seal wear.

Sealing units for oil film bearings from «ПЖТ 300» to «ПЖТ 450», used, as a rule, in bar mill stands running at speeds of 10 … 12 m/ps, may have a simpler design as compared to oil film bearing for high-speed stands. An example of such sealing unit is shown in Figure 2.

Fig.2. Sealing unit of «ПЖТ 450» for the roughing horizontal stand of the mill 350

Here, the tightening function is performed by V-ring seals 4, which are mounted on the clamping sleeve 3 fastened on bearing sleeve 2 of the roll 1 and contact the flat surface of the back cover 5. As in the case of sealing units of oil film bearings for high-speed stands, cooling liquid flows are kept out by means of the seal 6 of РНСТ type.

It is actual also modernization of the oil film bearing sealing units for vertical stands (especially for bottom chocks).

The design of sealing unit of «ПЖТ 220» for the bottom chock of V320 stand of the bar mill 300 («Uzmetkombinat») is presented on Figure 3.

Distinctive feature of this sealing unit in comparison with sealing units of horizontal stands is existence of a special reflector 4 between a protective seal 2 (of РНСТ type) and a seal 5 ( of ТД type) which at the expense of centrifugal forces rejects to the periphery to radially focused drainage openings of cover 6 water which can pass through a protective seal 2.

There have also been developed modernized sealing units of oil film bearings for prestressed stands of bar mills (Figure 4). Their feature is the possibility of axial as well as radial displacements of the rolls 1 (with bearing sleeve 2 and clamping sleeve 8) relative to the chock 3 (with covers 4 and 5) during the adjustments of bottom and top rolls respectively. This is made possible owing to the use of specially designed floating double axial seals 6 (of TПД type) and λ-shaped seals 7. Due to considerable precompression of axial seal lips, created during assembly, and to their compensating properties, the effectiveness of presented sealing units is not practically influenced by any possible misalignments, radial or axial shifts of oil film bearings.

Fig.3. Sealing unit of «ПЖТ 220» for bottom chock of vertical stand V-320 of the mill 300 (UzMK):
1 – work roll; 2 – seal РНСТ-255; 3 – clamping sleeve unit ; 4 – repeller;
5 – seal ТД1-210; 6 - cover; 7 – bearing sleeve; 8 – bushing; 9 – bottom chock.

 

Fig.4. Sealing unit for «ПЖТ 220» for the prestressed stand 330 of a bar mill

Due to reduction of leakage and water contamination of working fluid, its consumption is decreased by about 30-40%, while the failure of oil-film bearings caused by hot seizure is reduced at least by 15-20%.

The modernized sealing units have been successfully tested on oil film bearings of bar and wire mills of the metallurgical enterprises in Chelyabinsk, Yenakiyevo, Krivoy Rog ets.

The most representative realization of the modernized oil film bearings sealing units was executed at the bar mill 300 of «Uzmetkombinat». The units mounted in February 2005 and in February - March 2008 successfully work at a bar mill now, providing considerable economy of working liquid and increase of reliability of units.