It is necessary to highlight the magnetic fluid ability to eject non-magnetic particles from a working gap (a gap between a shaft and a pole-piece).
Therefore magnetic fluid seal is one of few seal types which operate efficiently under the conditions of high dust content (including abrasive particles) or when granular materials are sealed.
Magnetic fluid seals of BOKД–2,4 ventilator bearing units operating under the conditions of high dust content at dust-entrapping shop of “Zaporozhsky Aluminium Production Plant” are typical examples of magnetic fluid seals of the kind.
BOKД–2,4 large axial ventilators are installed as air exhausters at aluminium electrolysis shops. The air and gases are pumped out from the shop and then purified; they contain a great amount of abrasive dust (aluminium oxides, flux, etc.). Usually either a stuffing box or a profiling rubber cord are used as standard seals, their caps being split-type and consisting of two halves. The oil system of all fans is centralized, and sometimes there is rarefaction in a bearing case.
Under the conditions of high dust content because of abrasive particles and alternating pressure in bearing cases there is the significant wear of shafts’ protective bushing and abrasive dust penetration to bearings which causes oil ejection from bearing units. To replace bushings and bearings it is necessary to demount a fan from a considerable height and to disassemble it completely.
“Ferrohydrodynamica” has developed and installed magnetic fluid seals instead of standard seals. It prevented bearing units from abrasive dust penetration, bushing wear and oil ejection. After successful application of one set of magnetic fluid seals, “Zaporozhsky Aluminium Production Plant” periodically orders them for scheduled repair of fans.
Magnetic fluid seals for larger fans of BOД–30 and BOД–30M types have also been developed and manufactured.
At “Sera” Rozdol State Mining and Chemical Enterprise (Novy Rozdol, L’viv Region) magnetic fuel seals were installed in Raimond mill hangers for sulphur fine dispersive grinding. Sulphur is ground in a mill case, which is filled with nitrogen at 1000C, with rollers on the mill case. Standard seals’ service life was about 100 hours, bearings being jammed at the end of the service life. Maintenance workers tested different seal types but hanger’s service life has not increased considerably.
The consumer wanted magnetic fluid seals for hangers to be executed in accordance with the size of the components of the standard seal consisting of two parts – outer and inner.
During experimental operation, MFS hanger service life is 1600 hrs. At present magnetic fluid seals are installed at almost all mills. “Sera” is planning to completely replace the standard seals of Raimond mill hangers for “Ferrohydrodynamica” magnetic fluid seals.
At the end of 2000 on the order of JSC “Gorlovsky Machinostroitel” which released mine combines, MFS for 1ГШ68 (shaft diameter 160 mm) and P96M (shaft diameter 130 mm) bearing units of turning gear output shafts have been developed. Magnetic fluid seals were made with the dimensions of conventional seals. Initially “Gorlovsky Machinostroitel” has suggested create MFS for bearing units of turning gear output shafts on which milling cutter is fitted for 1ГШ68 mine cleaning combine. It would like to note some features of work on creation of this MFS.
Usually “Ferrohydrodynamica” develops and manufactures seals as a separate unit which is installed either instead of a bearing unit of a protected mechanism or into a specially executed lid.
However, due to the enterprise requirements to sealing strength, conventional seal components completed with magnetic system elements are used.
Seals were designed by “Ferrohydrodynamica” specialists, the adaptation of magnetic fluid seal components to the elements of the design available and the elements themselves were executed by the enterprise experts.
The magnetic fluid seal for combine reduction gear was based on the design of the magnetic fluid seals for electric engine shafts, it proved its reliability and was used at number of plants in Ukraine and Russia.
Its peculiarity is a considerable overall length of a working gap along which a seal is installed, magnetic system dimensions being comparatively small. In the middle part of a magnetic fluid seal, amid a working gap there is a ring-like space filled with porous material which function is to contain magnetic fluid for filling its working gap (See Fig.2).
Sealing in a given magnetic fluid seal is not fitted along a protected shaft but along a cylindrical ridge on a bush flange in a ring-like groove on the end surface of a bearing unit lid, the magnetic field of the magnetic system being closed through the filled gaps of magnetic fluids between the magnetic conductors and the cylindrical ridge.
Some part of a labyrinth seal between lid surfaces and a bush flange is retained and functions as a preliminary seal.
MFS were assembled in the presence of “Ferrohydrodynamica” specialists and fitted to two 1ГШ68У combines. Combine No. 2634 was put into operation at the “Krasnodonugol” USSR 50th Anniversary Mine, combine No. 265 at A.F. Zasyadko mine.
During their service, magnetic fluid sealed combine operation and lubrication purity in rotation reduction gears were controlled both by the mines and plant specialists. 750,000 tons of coal had been excavated by Combine No. 2635 (A.F. Zasyadko Mine) before the face was exhausted. During this period the penetration of coal ore dust into the lubricating system of the rotation reduction gear or oil leakage on the output shaft had not been fixed.
Comparing the operation of magnetic fluid seals and standard rubber collars, of conventional seals, the specialists emphasize that the latter would have been replaced 4 times under the identical mining and technical conditions.
665,000 tons of coal had been excavated by combine No. 2634 (the USSR 50th Anniversary Mine) up November 1, 2003. No failures in magnetic fluid sealed rotation reduction gears had been fixed. Both the mine and the plant specialists state that their resource has not been exhausted and they are able to operate during the whole scheduled period.
Then magnetic fluid seals for РКУ10, РКУ13, КПД, УКД200-250 combines were produced.
Magnetic fluid seal design is being constantly improved and proved to be reliable in mining operations. It is necessary to note that operational conditions differ very much even for the same mine at its different parts, they also depend on the type of a combine (heading and cleaning combines). “Donhyprouglemash” (Design and Experimentation Institute of Complex Mine Mechanization) got interested in the application of magnetic fluid seals. Taking into account new designs of conventional seals and their possible applications at the stage of combine designing, it was decided to carry out tests of a number of seal types including magnetic fluid seals. The tests enable to determine the parameters of seal reliability under identical conditions. To provide reliable testing conditions, the special test rig representing the design of a bearing unit for the output shaft of mining combine turning gear. The magnetic fluid seal for “Gorlovsky Mashinostroitel”-produced УКД 200 – 250 combine was chosen for the tests.
Installed at the test rig magnetic fluid seal has completed the time provided by the program and has not admitted hit of coal ore dust in bearing unit or oil leakage. The collaboration with “Gorlovsky Mashinostroitel” proceeds. Magnetic fluid seal for turning gear output shafts of УКД 200 – 250 combine is shown on fig. 3.
