A technique for selection and design of magnetic clutches with highly coercive permanent magnets (barium oxide magnets or magnets produced from such alloys of rare-earth elements as samarium-cobalt and neodymium-iron-boron) for sealed machines (pumps, compressors, mixers) is presented.Magnetic clutches are intended for contact-free transmission of rotary motion across a fixed partition through the interaction forces of permanent magnets. With the use of highly coercive barium-oxide magnets and magnets produced from rare-earth alloys (samarium-cobalt, neodymium-iron-boron), it becomes possible to decrease the overall dimensions of magnetic clutches (Figs. 1, 2). Magnetic clutches are used in sealed machines in dangerous industries. The design of such machines and apparatuses is a difficult procedure in view of the absence of criteria for the selection of magnetic clutches according to basic parameters. The objective of the present article is to develop a technique for selecting and designing magnetic clutches with highly coercive permanent magnets produced from barium oxide and rare-earth alloys.Initial data in the selection and design of magnetic clutches: kinematic circuit of machine; clutch ratio of drive and driven elements of machine; nominal rotational speed of asynchronous electric motor; characteristic of load moment on working unit as a function of rotational speed; mechanical characteristic of asynchronous electric motor constructed from reference data; reduced moments of inertia of rotation for drive and for driven parts of machine; requirements imposed on construction materials and characteristics of working medium; gauge or vacuum-gauge pressure in working cavity of machine or apparatus. Determination of Geometric Dimensions of Clutch with Tight Packing of Barium-Oxide Magnets [1]1. It is recommended that the length l m of the magnets (Figs. 3, 4) be set equal to 10-12 mm with gaps between the drive and driven half-clutches δ < 4 mm and equal to 15-16 mm with δ > 4 mm.2. The gap δ is selected on the basis of the thicknesses Δ 1 and Δ 2 of the protective shells of the half-clutches, the thickness δ s of the wall of the airtight shield and the assured air gap between the wall of the shield and the protective shells (at least 0.5 mm).3. The maximum value of the coefficient K 0 for a given gap and a value of the dimensionless coefficient q 0 that assures the greatest torque of the magnetic clutch corresponding to K 0 are selected (Table 1).4. The width τ of the band of the magnet (not final, since an even number of magnet poles is determined), m: τ = 2δ/q 0 , where δ is the gap between the half-clutches relative to the magnets, m, is selected.5. The maximum torque of the magnetic clutch is specified (at the present stage, it is set equal to the maximum moment of the asynchronous electric motor).6. The following are determined: for a cylindrical clutch, the outer diameter of the internal half-clutch,

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The basic aspects of use of magnetic clutches and magnetic systems in sealed machine designs are examined. The investigation results are reported and recommendations are offered for their application.Magnetic clutches are used widely in sealed machines and apparatuses employed in nuclear and several other branches of the industry. In the nuclear industry, magnetic systems are used essentially in sealed transporting and lifting devices.Distinctive aspects of use of magnetic clutches and magnetic systems in sealed machines and apparatuses. 1. The transferring torque of a cylindrical magnetic clutch for a specific sealed machine or apparatus can be calculated by the formulas given in [1], but for making such a clutch, the active length of the magnet along its rotation axis is sometimes comprised of lengths of several magnets varying in length. At the junctions of the magnets, the operating magnetic induction is found to diminish, so it is necessary to perform a check calculation of the transferring torque of the cylindrical magnetic clutch with its component magnets, i.e., it is necessary to calculate the torque for each length of the magnets being components of the common active length and their summation. If the transferring torque of the clutch in the sum is less than the required, the magnets must be replaced by stronger ones, i.e., by magnets with greater residual magnetic induction.Let us examine this peculiar aspect with reference to the sealed pump of the trademark VGM-3/30 (Fig. 1) being operated at the Mayak Industrial Association. In principle of operation, the VGM-3/30 pump relates to vortex pumps with a closed-type impeller. The major components of the pump are an operating head 8, a plug 4 with an intermediate shaft passing through it, a casing 5 with a cylinder 12 supported on the inner projection of the casing, and a motor 1 (asynchronous or dc electric motor). The leak tightness of the pump is ensured by a magnetic clutch 7 that imparts rotary motion through a screen made from a weakly magnetic material, namely, 12Kh18N10T steel. The driving half-clutch of the magnetic clutch is fastened to the intermediate shaft and the driven half-clutch, to the shaft of the operating head. The operating head shaft rotates on sliding bearings made of siliconized graphite, which are lubricated by the fluid being pumped.The basic difference of the VGM-3/30 pump from other types of sealed pumps manufactured by Russian Federation plants is the presence of a magnetic clutch (Fig. 2) and a protective plug. The maximum torque transferable by the clutch must be greater than the torques acting during operation due to resistive forces (friction, load, and inertia), otherwise the magnetic link between the half-clutches may break, i.e., the magnetic clutch will not be able to transfer the torque.For making such a clutch, magnets with an active length l (Fig. 2a) are required, but sometimes there are magnets with a different length (fraction of l), i.e., the magnetic clutch is made with magnets of length l/2 (Fig. 2b) (the tot...

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In this work, a study has been made of the influence of various types of high-coercivity permanent magnets on the key parameters (misalignment angle of half-clutches, power loss in current-conducting screen, screen temperature exceeding ambient temperature, liquid flow rate required to cool the screen with water, and forces of attraction between half-clutches) of a sealed equipment having an end magnetic clutch with retention of its basic parameter, namely, the value of the transferring torsional moment (torque). The overall dimensions of the magnetic clutch and half-clutches where various types of magnets are used remain unchanged.In [1], a study was made of the influence of type of high-coercivity permanent magnet on the characteristics of a cylindrical magnetic clutch (MC). End MCs having high-coercivity permanent magnets (barium oxide magnets or magnets from alloys of rare-earth elements samarium-cobalt (Sm-Co) and neodymium-iron-boron (Nd-Fe-B)) are used also in sealed (leak-proof) equipments operating in atomic, chemical, and other branches of the industry. Sealed equipments and end MCs are manufactured at specialized enterprises. In the manufacturing process, it is often necessary to use in the same MC different types of magnets while keeping the basic parameter, viz., the value of the transferring torsional moment of the MC, unchanged. Let us examine on an example the influence of various types of magnets on the key parameters of a sealed equipment having a magnetic clutch: misalignment (mismatch) angle of half-clutches, power loss in current-conducting screen, screen temperature above ambient temperature, liquid flow rate required to cool the screen with water, and forces of attraction between half-clutches.As an example, let us consider a sealed labyrinth screw pump of the trademark LG-1/20 (head 20 m and volume delivery 1 m 3 /h) [2] made by Sverdlovskii Research and Design Institute of Chemical Machine Building (SverdNIIkhimmash) for radiochemical plants.The general view of the pump is shown in Fig. 1. On the axis 1 of the casing 2 is mounted on the sliding bearings 15 the driven (slave) end magnetic half-clutch 4 assembled with the screw bushing 11. The axis 1 is secured between the flange 14 and the screen 9 by the bolt 5. The sleeve nut 12 is immovably fixed in the casing 2 and fastened to the flange 14 by dowels (pins). The electric motor 6, with the driving end magnetic half-clutch 8 fastened to its shaft, is mounted on the support 7.The support 7, the casing 2, and the flange 14 are braced together by the dowels 10. The material of the sealing gaskets is fluoroplastic-4 (Teflon). The casing 2 of the pump has a suction (intake) pipe 13 and a delivery pipe 3.