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SEALING UNITS OF OIL FILM BEARINGS FOR SHEET MILLS BACK-UP ROLLS

Effective and widely realized our development is modernization of sealing units of large-sized oil-film bearings for the sheet mills back-up rolls.

The development of the present design was aimed at the creation of up-to-date sealing units for oil film bearings of existing domestic sheet mills, which would ensure a sharp reduction of consumption and water contamination of working fluids as well as an increase in the reliability of oil film bearings along with simultaneous minimization of modernization expenses.

The design of modernized sealing units for back covers virtually identical to large-size oil film bearings with the bushing bore dimensions from 800 to 1600 mm (or from «ПЖТ 800» to «ПЖТ 1600» in accordance with the CIS standards designations) is shown in the Figure 1 below.

Fig.1. The modernized sealing unit of the back cover of an oil film
bearing for the sheet mill back-up roll

The tightening function proper is effected by V-ring seals 8 contacting the hard ground end-face of a disc 10. The major part of the working fluid flow from the work surface of the buching 9 is thrown off by the repeller of a ring 7 into the drain pipe of the oil film bearing back end-face, while safeguarding against cooling water with scale is ensured by a protective seal 3 of PHCT type, having a radial outer lip and a thrust nongliding fixed lip. The axial lips of the seal 3, squeezed between the end-faces of the clamping sleeve 4 and roll 1, prevent the ingress of water and scale at the tapered sleeve 6 fitted into the roll. The radial lip of the seal 3 repels the major part of water flow from the labyrinth cavity between the back cover 5 and the clamping sleeve 4, while the particles of water and scale, which have found their way into the said cavity, are removed through a drain opening in the lower part of the back cover 5. In so doing, water and scale do not virtually reach the counter faces of the V-ring seals 8, which ensures favourable operating conditions and diminishes their wear to a minimum.

The operation experience shows that the service life of V-ring seals amounts to at least 3600 hours, that of protective PHCT type seals – about 2000 hours, with the mounting and maintenance of modernized sealing units being simplified as compared to conventional designs and causing no troubles to handling labour.

Due to considerable precompression of V-ring seals, created during assembly, and to their compensating properties, the effectiveness of the presented sealing unit is practically not influenced by any possible misalignments, radial or axial shifts of oil film bearings.

The distinctive feature of these modernized sealing units considerably promoting their wide usage,was their relative low cost connected with use of existing base details of unit – a back cover 5 and clapping sleeve 4. Thus the total weight and respectively cost of new details of the modernized unit (positions 2, 7 and 10 at fig.1) made about 30% from general the masses and costs of back cover unit.

Such «low cost» decision of unit wasn´t reflected in its reliability and functionality as existence both the protective and two sealing stages provides, at least, not the worst quality of sealing in comparison with the known Morgan Construction decisions, patented in the USA, Germany, France, Japan and used by leading foreign producers of oil film bearings.

From 1990´s, when we began delivery of these units, and for present tense they are successfully exploited in the oil film bearings «ПЖТ 900», «ПЖТ 1000», «ПЖТ 1120», «ПЖТ 1180», «ПЖТ 1600», «ПЖТ 1800» for back-up chocks of hot strip, cold strip and plate rolling mills at the metallurgical enterprises of Russia, Kazakhstan and Ukraine in Chelyabinsk, Magnitogorsk, Cherepovets, Temirtau, Mariupol, Zaporozhye etc.

Since 2006 we develop and deliver for the oil film bearings of the strip mills back-up rolls the modernized sealing units (conditionally «the second generation»), including new back covers and new clamping sleeves. The example of such modernized unit is presented in Figure 2.

Setting of these units appeared preferable foremost wherein the necessity of changing of worn-out old back covers and back clamping sleeves came to a head. In new units the quantity of details (without considering sealing elements) is reduced to two – a back clamping sleeve 1 (on which V- ring seals 4 are directly established) and a back cover 3 on which contact surfaces both for V- ring seals and for a protective seal 2 PHCT types are executed.

Fig.2. The modernized sealing unit of the back cover of the oil film bearing «ПЖТ 1120»

The rubber reflector 5 established on an internal part of the clamping sleeve 1, carries out simultaneously the function of a seal between the bearing sleeve and the clamping sleeve.

Seals 4 in these units remained the same standard sizes, as in units of «the first generation» (at fig.1), and protective seals 2 are made with the increased dimensions of their sections that increased their firmness.

Besides in these units (at fig.2) there are no fixing elements inside the unit, it still simplifies their assembly and installation in comparison with the described above «first generation» units.

Sealing units of «the second generation» already successfully work in oil film bearings from «ПЖТ 800» to «ПЖТ 1120» of strip mills of Ukraine and Russia (in Zaporozhye, Mariupol, Magnitogorsk, Cherepovets) and are planned to further installation.

In some cases (espacially for superlarge-sized oil film bearings of plate mills back-up rolls) there is a need for ensuring big axial shifts of chocks concerning rolls without danger to damage of seals.

The example of the sealing unit corresponding such requirements and developed specially for plate mill 5000 («Severstal», Sanct-Peterburg), is presented on Figure 3. Here self sealing function carry out by specially developed lip seal 2 with radial external lips (standard size PH3-1910) established on the clamping sleeve 1 and contacted with the boring of the holder 3, fixed in a back cover 4. A protective function as well as in presented above modernized units, the seal 5 (standard size PHCT3-1960) carries out.

Fig.3. The sealing unit of the «ПЖТ 1800» back cover of the plate mill 5000.