Permanent Magnetic Couplings and Brakes for Drive Technology

Transcription

1 Tridelta Magnetsysteme A Tridelta Group Company Permanent Magnetic Couplings and Brakes for Drive Technology Raw Materials Magnets Systems and Components

2 Magnet N1 Soft iron N2 Resin Introduction and principals of construction Permanent magnet couplings, clutches and brakes are both safe, reliable and particularly economical to operate. They work without wear or contact, are virtually maintenance-free, operate with low bearing friction (concentric ring couplings) and, under conditions of normal use, have an almost unlimited working life. They are particularly useful when it is necessary to ensure a strict, physical separation between the drive and driven side. Non-magnetisable material Permanent magnetic couplings, clutches and brakes can be divided into three basic types: Synchronous couplings, which include disc and concentric ring couplings Hysteresis clutches and brakes Eddy current clutches and brakes For all types of coupling, clutch and brake the relevant efficiency equation is: P 1 -P v -P 2 =0 P 1 is the influx power from the drive side, P 2 is the transmitted power in the driven side, P v is the power loss via the transmission mechanism in coupling, clutches and brakes. For synchronous couplings P v =0, as the slip, S=0 (see pages 6 9 for instructions about applications and installation). On the drive and driven sides, permanent magnets are set opposite one another with an equal, Fig. 1 Schematic construction of a disc coupling Magnet Soft iron N1 N2 Nonmagnetisable material Fig. 2 Schematic construction of a concentric ring coupling 2

3 even number of poles, mirror balanced (disc couplings, fig.1) or are rotationally symmetric (concentric ring couplings, fig.2). The magnetic requirements for synchronous couplings of permeability µ rev 1 coercive field strength and remanence flux density as great as possible are best achieved using ceramic barium, strontium ferrite material, or combinations of rare earth elements and cobalt. eddy current clutches and brakes, P v >0, as S>0. One of the halves of the synchronous coupling preferably the drive side is replaced by an iron-backed electrical conductor in ring or disc form (fig. 4). The standard couplings described in tables 1, 2a and b, 3 and 4 are stock ranges. The torque values printed here are minimum values and may be exceeded. In hysteresis clutches and brakes one half of the synchronous coupling for cooling reasons, the drive side is advised is replaced by a ring or disc made from a permanently magnetic material with relatively greater remanence and permeability and correspondingly smaller coercive field strength, so that this half of the coupling against some resistance can be magnetically reversed from the other half (fig. 3). In Magnet N2 Soft iron Resin N V N1 Hysteresis material Fig. 3 Schematic construction of a hysteresis clutch or brake Magnet N V Cu N2 Soft iron Resin N1 Soft iron Fig. 4 Schematic construction of an eddy current clutch or brake 3

4 Synchronous couplings Disc and concentric couplings developed by us are exceptionally economical to run, reliable and longlasting. Successfully deployed in numerous different applications, they have a proven track record of success. With their relatively small magnet size, they transmit high torque in an enclosed space across a separating wall without recourse to seals and glands. The particular advantage is that in the right configuration all couplings, separated by an air gap, operate friction and thus wear-free. In addition, problems with seal weakness are avoided. Our disc and concentric ring couplings are manufactured and offered, according to the application, capacity and performance required, from the following materials: Ceramic materials (hard ferrite): Oxit 100, 360 Metallic materials AlNiCo; Oerstit 260, 450, 500 Seco materials: Secolit 215 NdFeB material Tables 1 2b contain 3 types of our disc and concentric ring couplings. The basic design of these couplings is illustrated in figs. 1 and 2. Detailed examples are shown in figs. 5 and 6. The technical data included in the tables on pages 6 9 allows you to estimate the size of magnet and iron casing needed to produced the desired torque. When choosing a coupling type please note that at the start of rotation, and in some cases through shock loading, higher torque can occur than calculated from nominal power and the number of revolutions of the motor. If the coupling is Magnet Iron casing Resin or equivalent Separating wall from non-magnetisable material Fig. 5 The construction of a disc coupling 4

5 Iron casing Outer magnet Inner magnet Adhesive Separating wall from non-magnetisable material Fig. 6 The construction of a concentric ring coupling not merely run as an overload coupling, then possible additional starting torque has to taken into consideration. The drive gear should either be run up slowly, or a size of coupling selected such that the coupling moment always exceeds the maximum drive moment. Should the coupling break away no magnetic changes occur. However, to reestablish synchrony both parts of the coupling need to stopped and run up again. Magnets and temperature The working range of Oxit couplings lies between -30 C and +100 C. Temperatures higher or lower than ambient in the factory lead to a decrease or an increase in the transmitted torque: the relationship is linear and approximately K -1 = 4%/10 C. Secolit has a working range of -190 C and +250 C, with an increase or de- crease in torque of 0.8 %/10 C. At room temperature couplings recover their working values, as the temperature effect on torque is reversible. For working temperatures exceeding 250 C we can, on request, develop a special coupling made from AlNiCo. This Oerstit type coupling can operate at temperatures up to 400 C. 5

6 Instructions for application and assembly Disc couplings The possible uses of disc couplings are similar to those already described for concentric ring couplings but where the separating wall is flat and level. It should be noted, that relatively high axial power has to be absorbed by a suitable bearing. Certain precautions should be taken when handling loose magnetised Disc couplings L L Magnet Iron casing Resin or equivalent Table 1 Disc couplings in Oxit 360 and Secolit Order-No. Torque in Ncm *) with air gap L L in mm Axial drive force in N with air gap L L in mm Magnet dimensions Outer Inner Height dia. mm dia. mm mm Dimensions of magnet and iron casing Outer dia. mm Height mm Bore in iron casing dia. mm ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ) ) ± ± ± ) ± ± ) ± ± *) 1 Ncm = 100 cmp, = ft lbs 1) Special type in Oxit 2) Special type in Secolit Special types are not held in stock. ring magnets supplied by us for the construction of disc couplings. To avoid any loss of magnetic performance, the separation and orientation of the rings as delivered should be strictly maintained until they are installed in the appropriate housing. Where loose rings are supplied, it is recommended. that the finished coupling is magnetised. There is some danger of a shortfall in torque (5-10%) compared to the values listed in tables 1 2b after installing the magnets in the iron casing, or due to their direct contact and misorientation with another. Our instructions are general suggestions relating to the materials. They in no way discharge the user from heeding other aspects of construction, which when manufacturing working couplings can be unique in every instance. We are always available to provide technical advice and assistance. 6

7 Concentric ring coupling in Secolit Secolit concentric ring couplings are particularly useful if rotational energy needs to be transmitted through a partition without the use of glands. If the partition is electrically conductive eddy currents are induced in the material, representing a loss of energy, which, depending on the r.p.m., leads to a reduction in maximum torque. Furthermore, the eddy currents cause heat D 1 D d 1 d H Fig. 7 Concentric ring coupling in Secolit Torque [Nm/cm] Fig loss into the cylindrical air gap space, so that possibility of cooling has to be considered. A drive system must accommodate such losses, which entails using a larger motor to match the energy dissipated. Ø 300 Ø 250 Ø 200 Ø 150 Ø 100 Ø 75 Ø 50 Ø Air gap width [mm] D d1 ( 2 ) Torque per cm axial coupling length as a function of working air gap. Parameter: outer diameter of inner coupling part (d 1 ). Intermediate dimensions for diameter d 1 and larger air gaps are possible, including protection of the inner part. To estimate the required torque detailed knowledge of the drive system and load characteristics is required. Here the user usually has to rely on trial and error. If the magnetic couplings are used for pumping aggressive media, then one part of the magnetic coupling has to be equipped with a protective sheath. For practical reasons the inner part is best protected, using either stainless steel or plastic. Heating magnetic material leads to a decrease in magnetic flux density, dependent on the material s temperature coefficient, which in turn causes a reduction in torque. To get the most out of the permanent-magnet material, magnetic couplings have to be optimised by calculation. Fig. 8 shows the results of calculations for a several couplings, using numerical-field programmes. This data is intended as a rough guide for the user, allowing approximate estimates of coupling requirements to be made. The axial length of concentric ring couplings should, where possible, be at least four times the air gap length. As strong stray magnetic fluxes occur increasingly towards the end faces they do not make a full contribution to the torque. 7

8 Hysteresis clutches and brakes The use of hysteresis clutches or brakes is particularly appropriate when constant moment needs to be delivered through a wide range of revs. In the hysteresis clutches and brakes we produce, for each nonmagnetised hysteresis material, e.g. Oerstit 70, there is an opposite, magnetised permanent magnet ma- terial, e.g. Oxit 360. The material combinations are varied according to application and required moment. The particular torque or braking moment for a hysteresis combination is largely independent of relative speed and is sustained even at very low relative speeds. Fig. 9 shows this relationship for two different sizes of air gap, large and small. In practice, at relatively high speeds there is a slight increase in the moment due to the superimposition of an eddy current moment. Maximum temperature for Oxerstit 70 discs must not exceed 100 C, otherwise irreversible losses occur due to structural changes. with small air gap with larger air gap Eddy current clutches for T = < 50 C Torque with small air gap with larger air gap Hysteresis clutches Relative speed Fig. 9 Torque from hysteresis and eddy current clutches A schematic illustration of the correlation between torque and relative speed 8

9 Magnet Iron casing If necessary, slight control of the moment is possible by axial displacement, in other words by altering the air gap and thus the effective flow. It is important to ensure that no iron is situated behind the Oerstit 70 hysteresis disc, otherwise the transferable torque will be considerably reduced. The distance between hysteresis disc and the nearest iron components must be at least 15 mm. Hysteresis material Resin or equivalent Hysteresis clutches and brakes Table 3 Hysteresis clutches and brakes in Oxit 360, Secolit and Oerstit Order-No. Tourque in Ncm *) with air gap L L in mm Magnet dimensions 0uter Inner Height dia. mm dia. mm mm Dimensions of magnet and iron casing Outer dia. mm Height mm Bore in iron casing dia. mm Hysteresis disc dimensions Outer Inner Height dia. mm dia. mm mm ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ) ) ± , ± ± ) ± ± ± ± ) ± ± ± ± ) ± ± , ) ± ± *) 1 Ncm = 100 cmp, = ft lbs 1) Special type in Oxit 2) Special type in Secolit Special types are not held in stock. 9

10 Eddy current clutches and brakes In contrast to the drive and brake elements already described, the moment in eddy current clutches and brakes (fig. 4) is first produced by a relative speed between drive and driven sides. Thus the transferable moment increases with relative rpm. Fig. 9 shows the moment gradient for two different air gaps. In practice rings or segments in permanent magnetic material, e.g. Oxit 360 are magnetised on one side with several poles and are surmounted by copper discs 2 5 mm thick, which for magnetic reasons have a soft iron backing of 2 6 mm thickness. Table 4 lists the different values of torque estimated in eddy current clutches and brakes for 3 different relative speeds and various air gaps. Cu Soft iron Eddy current clutches and brakes Magnet Iron casing Resin or equivalent The values were measured at room temperature, set by measurements of corresponding cooling of the copper discs. In eddy current clutches and brakes the temperature coefficient of the copper is considered along with the temperature coefficient of the magnet. Eddy current clutches and brakes heat up considerably with increasing rpm, due to the development of eddy currents, causing a sharp decrease in attainable torque at room temperature. If no cooling is provided, then at a relative speed of 1000 r.p.m., temperatures in the copper discs can rise to 200 C, decreasing the torque by up to 50%. The losses thus incurred are partly irreversible. They can only be fully recovered by re-magnetisation. If the temperature is kept below 50 C, then the decrease in torque amounts to approximately 10 %. Within certain r.p.m. ranges, eddy current clutches show a roughly linearly proportional or constant relationship between torque and r.p.m. These characteristics make eddy current clutches suitable for use in coiling machines, where constant band tension and constant band speed are required. 10

11 Table 4 Eddy current clutches in Oxit 360, Secolit and Cu/Fe Order-No. Torque in Ncm *) with Air gap L L in mm With relative speed n 1/min. Magnet dimensions Outer Inner Height dia. mm dia. mm mm Dimensions of magnet and iron casing Outer dia. mm Height mm Bore in iron casing dia. mm Eddy current unit Outer Inner Cu- Fedia. dia. thickn. thickn. mm mm mm mm ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ) ± ) ± ± ± ) ± ± ± ) ± ± *) 1 Ncm = 100 cmp, = ft lbs 1) Special type in Oxit 2) Special type in Secolit Special types are not held in stock. 11

12 Technical advice and supply of samples We can supply clutches and brakes complete and ready for installation. However, we can also install magnets and magnetise bell housings and other casings sent to us. There are a variety of different ways of arranging the outer rings of concentric ring couplings in the housings, independent of form, size and no. of rings in the series. For this reason, we ask that any enquiry be accompanied by a drawing showing the intended receptacle for the magnet rings, so we can establish the best method of mounting. The outer diameter of magnet rings is ground to an ISO m6 fit, allowing them to be press fitted. The details for wall thickness of the iron mountings are for low carbon steel, e.g. St 37. In concentric ring couplings, the shafts are normally cast as an integral part of the inner components. If possible, each construction project should initially be discussed with us to avoid the disappointment and expense of failure. We are always available to provide advice, supported by the appropriate computer backup. The production of every permanent magnetic clutches series is normally preceded by prototype testing. Prototype testing of eddy currenthysteresis clutches and brakes is advisable in every case as the torque curves can alter according to application e.g. through heating. The magnet rings and segments of disc couplings, eddy current and hysteresis clutches and brakes are glued to iron parts with special adhesive and the iron casing with special resin. If high chemical and thermal resistance is required, we would request that the appropriate details be made available. To secure the clutches and brakes in their iron casings, holes may be bored to a maximum of the inner diameter of magnet. Counterbalancing is possible by making holes on the outer perimeter. If care is taken during this work to ensure that clutches and brakes do not heat above 100 C, no weakening of the transmittable torque will occur. 12

13 Series Production Often the demand arises for the series production of a coupling or brake design not included amongst those in this brochure. In this case, adopt the following strategy: Assemble pre-magnetised or selfmagnetised rings into a drive mechanism Send us the mountings for the couplings, clutches or brakes and we complete the rest We then produce the finished coupling according to the customer s drawing For series production we recommend agreed documentation of the technical conditions of delivery, stipulating all requirements with respect to the magnetic, physical, mechanical and chemical properties of our products. We can give no guarantee against faults resulting from factors other than those agreed in the technical conditions of delivery. Quality assurance and delivery agreement Fulfilling and securing the very highest standards of quality is fundamental to Tridelta s operations. By setting quality targets from product development and process planing to careful raw material testing and integrate checks during production Tridelta ensures the quality of product demanded by their customers. The magnetic specifications of Tridelta s magnet material more than meet the demands of DIN (permanent magnet materials, technical conditions of delivery). In practice, clear definition of the limits of the application (single magnet or magnet system) and a functional inspection system is recommended. The concept of limits of application should also include mechanical composition. For shape and size tolerances the submitted technical drawing is deinitive. All data and information in this publication has been checked and subject to rigorous controls. However, no liability is accepted for possible errors or omissions. We retain the right to make alterations and modifications appropriate for further product development. This publication supersedes and invalidates all previous ones. 13

14 Tridelta Magnetsysteme A Tridelta Group Company Tridelta Magnetsysteme GmbH Ostkirchstrasse 177 D Dortmund Phone: +49 (2 31) Fax: +49 (2 31) info@tridelta.de Order-No.: E This publication may not be reproduced in whole or in parts without permission. All rights reserved. Printed in Germany. Raw Materials Magnets Systems and Components