[1,2,3,4]. Since the mechanism that keeps the MF seal tight differs considerably from that observed in other types of seals, opinions can be found that the use of MF seals is limited mainly to precise machines. These opinions are claimed to be justified by specific properties of magnetic fluids, the necessity of use of high-energy permanent magnets, and relatively high precision required during production of the MF seals. These factors decrease the permissible pressure limit to about 1.0 MPa, at the corresponding critical temperature of the magnetic fluid not exceeding, approximately, 200°C. Moreover, extremely high prices of high-dispersion magnetic fluids (nanomagnetic fluids) and the abovementioned required precision of machining are the reasons why MF seals are not in common use at present.However, despite the above difficulties, obvious advantages of these seals, including excellent tightness and low resistance of motion, are the reasons why growing interest is observed towards their use in difficult operating conditions, where they are mainly used as so-called protective seals. This refers to such machines as reactors used in the chemical, biochemical, POLISH MARITIME RESEARCH 3(57)
The centrifugal magnetic fluid seals have important advantage over the conventional centrifugal seals. They maintain very good sealing capacity at static, medium and high speeds of shaft rotation, with the increased seal lifetime, and minimum torque and static friction. These seals are particularly useful in cases when the angular shaft velocity varies and sometimes decreases to nearly or exactly zero, such as in flywheel applications, ship propeller main shafts, etc. Unique properties of the magnetic fluid give rare opportunities for application in marine design, where perfect sealing together with reliable lubrication are required.
The paper presents a typical design and operation principle of a centrifugal magnetic fluid shaft seal, along with new design solutions. Not only in ocean technology and underwater robotics. Some cases of application of centrifugal magnetic fluid seals in modern sealing technology are included.
The edge criteria for magnetic-fluid seals durability research are critical for the seal’stechnological usefulness. The magnetic fluid seal technology in water is much moredifficult technological problem in comparison to gas or vacuum environment. There isalways problem with immediate contact between magnetic fluid and the environmentaluninspected liquids. In the paper are presented ways of experiments definitions carried outwith multi-stage rotating magnetic fluid seal operating in permanent contact with utilitywater. The special test procedures have been elaborated and practically used, with theaim to define main characteristics of magnetic fluid seals. These characteristics were: critical pressure,critical motion velocity and working life of the seal. Some grades of commercial, silicon based magneticfluids of hydrophobic properties were tested in sealing system. The test stand and its features as well asresults of tests are presented in the form of tables, cross section draws and diagrams. In conclusion onecan see that multi-stage magnetic-fluid seals could be efficiently used in water for rotating shaft seals ina limited range of motion velocity and work lasting.
The aim of the study is to analyse shape memory alloy (SMA) pipeline joints in limited space applications for all kinds of ships. Generally, the space available in various areas on ships is strictly limited and service works usually meet many obstacles. If we consider a pipeline, the flange joints always require a larger free space around the pipe than the pipe alone. A simultaneous problem can occur with the propeller shaft line coupling between bearings. SMA couplings require less space around the pipe and service should be easier, e.g., insulation fixing, painting and so on. SMA couplings last for a lifetime and there is no need for periodical seal replacement. Herein, some proposals among other unpublished data are discussed. There is a significant technological interest in the use of SMAs for applications not widely used yet. A wide variety of alloys present the shape memory effect and many generate an expressive restitution force considerable for commercial interests.
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