Magnetic fluid seals have most widely been used for electric motors of various sizes (in general, with vertical shafts) which operate in vertical cooling towers and air cooling apparatuses. Generally, MFS replaced defective standard seals (stuffing box, ring or labyrinth types) of a top bearing unit of an electrical motor to prevent it from penetration of fine dispersive moisture, water fog and other types of contamination inside.
The operational conditions of electric motors are rather unfavourable: there are clouds of large splashes, fine dispersive moisture and fog in cooling towers; heat-exchangers in air-coolers of various technological installations are sprayed permanently or periodically, but often.
The weakest point of this electric motor during operation is exactly the seal of a top bearing unit of an electrical motor which must to prevent the penetration of moisture inside engine.
The experience has revealed insufficient reliability of the seals under the similar conditions both in summer and in winter. Water penetrates into a bearing unit, causes lubrication failure, bearing corrosion, moisture increase in windings, and insulation resistance drop which results in the necessity of winding drying in a specialized bay of an electrical repair shop.
Mechanical contact of a shaft with a stuffing box or ring felt causes its wear, consequent build-up, surfacing or even its complete replacement. Electric motor mounting and demounting at cooling towers and air-coolers (air-cooling apparatuses) are rather expensive operations, because it is only performed by means of a crane truck. MFS application enables to reduce operational costs dramatically.
Durability, better sealing capability, absence of physical contact with a shaft and a radical prolongation of periods between repairs are obvious MFS advantages over a stuffing boxes and rubber armed rings.
MFS reliability in operation is confirmed by the fact that maintenance workers do not demount motors with dry windings and normal insulation resistance in spite of the requirement of the manufacturing plant to replace bearings’ lubrication and perform their revision every year, though previously they had to demount electric motors to dry windings.
MFS were developed for BACO and BACB electrical motors of various sizes (10, 14, 15, 16) and types (BACO-22, BACO-37, 2ACBO, etc.) and for Japanese (TIKK, MLA), French (JSNF/MJUL 180), Czech (ENGV-250, AWM-7110) electrical motors, including explosion-protected modification.
MFS application at BACO engines of dust-ignition proof construction was confirmed by Ukrainian Scientific Research Project-Designing and Technological Institute of Explosion proof and Mining Electrical Equipment with Experimental Production UkrNIIVE without any remarks.
Now these engines are produced by its assignee – “Large-size Electrical Machines Plant” (Novaya Kakhovka, Ukraine).
Besides, “Safonovo Electric Machines Plant” (Russia) releases 2АСВО 710 electric engines both in usual modification and with MFS – under the request of the Customer.
The installation o MFS on the 2ACBO 710 electrical engine provides protection extent not less IP55 according to GOST 17494 that is reflected in specifications on the engine ТУ 16-87 ИАПФ.528622.002 ТУ.
"Privod" Holding Company (Lysva, Russia) has begun production of the new explosion-proof BACO 4-24 engine where the possibility of MFS application is provided at designing. First these engines are in trial operation at “T-Star” deep oil refining complex of "Lukoil-Permnefteorgsintez" Ltd.
“Ferrohydrodynamica" also collaborates with JSC “VNIINEFTEMASH” which develop and deliver air cooling apparatuses. As “VNIINEFTEMASH” on the prescription of Gosgortekhnadzor of Russia carries out the supervision on such equipment, as cooling towers and air cooling apparatuses, then “Ferrohydrodynamica" in collaboration with “VNIINEFTEMASH” developed Technical Specifications for magnetic fluid applied in MFS of electric engines for cooling towers and air cooling apparatuses ventilators, and for the 2АСВО 710 electric engine magnetic fluid seal.
These magnetic fluid seals are designed for seal replacement (labyrinth type, most of all) of separate sliding bearings of large electrical machines and mechanisms which do not always prevent oil fog and droplet ejection from bearings to electrical engines’ windings driving various pumps, turbo compressors at chemical productions, etc. It is often difficult to use contact seals (e.g. ring seals) because of high linear shaft velocities, and, respectively, considerable heat release. Magnetic fluid seals reduce heat release in a sealing device due to the fluid friction. The main problem is to minimize the access of oil droplets to the magnetic fluid of a seal to prevent their mixing at high linear velocities. Therefore the seals of similar units are often of combined types where the specific optimized non-contact seal is the first stage, and the magnetic fluid seal is the second one.
Similar magnetic fluid seals have been installed on bearings of synchronous electrical engines of CДH type driving ЦНД set water pumps (“Azot” Production Association, Cherkassy); on bearings of 2500 kWt GEK – 42585 motors driving a carbon oxide turbo compressor (“Association Azot”, Severodonetsk); on bearings of various compressors (“Sera”, Rozdol; “Concern Stirol”, Gorlovka); on bearings of synchronous electrical engines of CТД-1600-23УХЛ type driving К-250 compressor (“MAZ”, Minsk).
Fig. 3 shows the design of a magnetic fluid seal for СДН 2-16-4-9-6 electrical engine, preliminary oil separating labyrinth seal being mounted near a pole piece.
In 2010 “Large-size Electrical Machine Plant” (Novaya Kakhovka, Ukraine) coordinated the MFS installation on new generation СДН electric motors – СДН4 and included the modification of motor with MFS in the nomenclature directories and questionnaires.
Vacuum seals were used at vacuum inputs of PA “Nikond” metallization units, Central NIITS technological lasers, “Sihi” water ring vacuum pumps at sebanic acid production (“Association Azot”, Severodonetsk). Fig.4 shows magnetic fluid seal design of the “Sihi” vacuum pump. It is specific that a ferromagnetic insert bushing is mounted onto the stainless, non-magnetic pump shaft to close the magnetic field.
It is necessary to note that vacuum magnetic fluid seals are mostly widely used all over the world. They are widely used in electronic industry, especially in vacuum inputs. Silicone-based magnetic fluids are characterized of low vaporability and it results in high vacuum. MFS sizes are mainly small due to low pressure drop (to 0,1 MPa), and anti-torque moment is insignificant due to the fluid friction in a gap.
This magnetic fluid seals foremost are designed for shaft seals of chemical apparatus mixers of various volumes. Their peculiarity consists in its ability to operate at considerable wobbles of a mixer shaft. The design was developed for the shaft seal of the agitated distilling mixer-evaporator (“Crimeasoda”, Krasnoperekopsk).
This magnetic fluid seals foremost are designed for shaft seals of chemical apparatus mixers of various volumes. Their peculiarity consists in its ability to operate at considerable wobbles of a mixer shaft. The design was developed for the shaft seal of the agitated distilling mixer-evaporator (“Crimeasoda”, Krasnoperekopsk).
