Permanent Magnetic Couplings and Brakesfor Drive Technology

Tridelta MagnetsystemeA Tridelta Group Company

Raw Materials Magnets Systems and Components

2

Introduction and principals ofconstructionPermanent magnet couplings,clutches and brakes are both safe,reliable and particularly economicalto operate. They work without wearor contact, are virtually mainte-nance-free, operate with low bear-ing friction (concentric ring cou-plings) and, under conditions ofnormal use, have an almost unlim-ited working life. They are particu-larly useful when it is necessary toensure a strict, physical separationbetween the drive and driven side.

Permanent magnetic couplings, clutches and brakes can be dividedinto 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 andbrake the relevant efficiency equati-on is:P1-Pv-P2=0P1 is the influx power from the

drive side,P2 is the transmitted power in the

driven side,Pv is the power loss via the trans-

mission mechanism in coupling,clutches and brakes.

For synchronous couplings Pv=0, asthe slip, S=0 (see pages 6 – 9 forinstructions about applications andinstallation). On the drive and drivensides, permanent magnets are setopposite one another with an equal,

N1 N2

MagnetSoftiron

Non-magnetisablematerial

Fig. 2 Schematic construction of a concentric ring coupling

N1

Magnet

N2

Softiron

Resin

Non-magnetisablematerial

Fig. 1 Schematic construction of a disc coupling

3

even number of poles, mirror bal-anced (disc couplings, fig.1) or arerotationally symmetric (concentricring couplings, fig.2). The magneticrequirements for synchronous cou-plings of • permeability µrev ➝1• coercive field strength and

remanence flux density as great as possible

are best achieved using ceramicbarium, strontium ferrite material,or combinations of rare earth ele-ments and cobalt.

In hysteresis clutches and brakesone half of the synchronous cou-pling – for cooling reasons, the driveside is advised – is replaced by a ringor disc made from a permanentlymagnetic material with relativelygreater remanence and permeabilityand correspondingly smaller coer-cive field strength, so that this halfof the coupling – against some re-sistance – can be magnetically re-versed from the other half (fig. 3). In

eddy current clutches and brakes,Pv>0, as S>0. One of the halves ofthe synchronous coupling – prefer-ably the drive side – is replaced byan iron-backed electrical conductorin ring or disc form (fig. 4).

The standard couplings described intables 1, 2a and b, 3 and 4 are stockranges.

The torque values printed here areminimum values and may be ex-ceeded.

Magnet

N2 N1

Hysteresismaterial

Soft ironResin

NV

Fig. 3 Schematic construction of a hysteresis clutch or brake

Magnet

N2 N1

NV Cu

Soft ironSoft ironResin

Fig. 4 Schematic construction of an eddy current clutch or brake

Synchronous couplings

Disc and concentric couplings de-veloped by us are exceptionally eco-nomical to run, reliable and long-lasting. Successfully deployed innumerous different applications,they have a proven track record ofsuccess. With their relatively smallmagnet size, they transmit hightorque in an enclosed space across aseparating wall without recourse toseals and glands. The particular ad-vantage is that in the right config-uration all couplings, separated byan air gap, operate friction and thuswear-free. In addition, problemswith seal weakness are avoided.

Our disc and concentric ring cou-plings are manufactured and of-fered, 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

4

Magnet

Resin orequivalent

Separating wallfrom non-magnetisablematerial

Iron casing

Fig. 5 The construction of a disc coupling

Tables 1 – 2b contain 3 types of ourdisc and concentric ring couplings.The basic design of these couplingsis illustrated in figs. 1 and 2. De-tailed examples are shown in figs. 5and 6. The technical data includedin the tables on pages 6 – 9 allowsyou to estimate the size of magnetand iron casing needed to producedthe desired torque.

When choosing a coupling typeplease note that at the start of rota-tion, and in some cases throughshock loading, higher torque canoccur than calculated from nominalpower and the number of revolu-tions of the motor. If the coupling is

Magnets and temperatureThe working range of Oxit couplingslies between -30 °C and +100 °C.Temperatures higher or lower thanambient in the factory lead to adecrease or an increase in thetransmitted torque: the relation-ship is linear and approximately 4 . 10-3 K-1 4 %/10 °C. Secolit hasa working range of -190 °C and+250 °C, with an increase or de-

5

Outer magnetIron casing

Separating wall from non-magnetisable materialAdhesive

Inner magnet

Fig. 6 The construction of a concentric ring coupling

not merely run as an overload cou-pling, then possible additional start-ing torque has to taken into consid-eration. The drive gear should eitherbe run up slowly, or a size of cou-pling selected such that the cou-pling moment always exceeds themaximum drive moment. Shouldthe coupling break away no mag-netic changes occur. However, to re-establish synchrony both parts ofthe coupling need to stopped andrun up again.

= ⟨

crease in torque of 0.8 %/10 °C. Atroom temperature couplings recovertheir working values, as the temper-ature effect on torque is reversible.For working temperatures exceeding250 °C we can, on request, develop aspecial coupling made from AlNiCo.This Oerstit type coupling can oper-ate at temperatures up to 400 °C.

6

Magnet

Iron casing

Resin orequivalent

LL

Instructions for application andassembly

Disc couplings The possible uses of disc couplingsare similar to those already de-scribed for concentric ring cou-plings but where the separating wallis flat and level. It should be noted,that relatively high axial power hasto be absorbed by a suitable bearing.Certain precautions should be takenwhen handling loose magnetised

ring magnets supplied by us for theconstruction of disc couplings. Toavoid any loss of magnetic perform-ance, the separation and orientationof the rings as delivered should bestrictly maintained until they areinstalled in the appropriate housing.Where loose rings are supplied, it isrecommended. that the finished

coupling is magnetised. There issome danger of a shortfall in torque(5-10 %) compared to the valueslisted in tables 1 – 2b after installingthe magnets in the iron casing, ordue to their direct contact and mis-orientation with another. Our in-structions are general suggestionsrelating to the materials. They in no

way discharge the user from heed-ing other aspects of construction,which when manufacturing workingcouplings can be unique in everyinstance. We are always available to provide technical advice andassistance.

*) 1 Ncm 100 cmp, 0.00738 ft lbs= ⟨

Disc couplings

= ⟨

Table 1 Disc couplings in Oxit 360 and Secolit

Order-No. Torquein Ncm*)

with air gap LL in mm

1 3 5 10

Axial drive forcein Nwithair gap LL in mm

1 3 5 10

Magnet dimensions

Outer Inner Heightdia. mm dia. mm mm

Dimensions of magnetand iron casing

Outer Heightdia. mm mm

Bore iniron casing

dia. mm

106 070

106 071

106 072

106 073

106 074

106 075

106 076

130 8061)

131 7441)

126 3202)

120 8542)

10 7 5 2

35 23 17 7

80 60 44 24

175 125 100 45

285 240 190 105

780 635 480 260

950 800 600 380

1670 1400 1050 660

2500 2100 1600 1000

500 360 260 120

2800 2200 1600 800

13 8 5 2

50 30 18 5

64 39 26 10

172 113 80 25

210 142 110 54

330 216 180 95

440 310 257 135

778 545 453 242

1182 827 688 367

340 210 135 55

1020 657 427 196

41 ± 0.6 24 ± 0.6 8

53 ± 0.7 23 ± 0.5 8

68 ± 1.5 32 ± 0.7 10

84 ± 4.0 32 ± 1.0 12

100 ± 2.0 50 ± 1.0 15

124 ± 3.0 56 ± 3.0 18

140 ± 2.0 70 ± 1.0 21

180 80 20

214 ± 2.0 68 ± 1.0 20.5

85 ± 1.0 32 10

140 60 ± 0.3 10

50 ± 0.2 9.5 ± 0.15

63 ± 0.2 10 ± 0.15

80 ± 0.25 13 ± 0.2

100 ± 0.25 16 ± 0.2

125 ± 0.25 20 ± 0.2

150 ± 0.3 24 ± 0.2

165 ± 0.3 27 ± 0.2

195 26

235 27 ± 0.3

100 + 0.25 13 ± 0.2

150 + 0.3 16 ± 0.2

–

–

–

–

–

–

–

32

–

32

25 + 0.15

1) Special type in Oxit2) Special type in Secolit

Special types are not held in stock.

7

Concentric ring coupling inSecolitSecolit concentric ring couplingsare particularly useful if rotationalenergy needs to be transmittedthrough a partition without the useof glands. If the partition is electri-cally conductive eddy currents areinduced in the material, represent-ing a loss of energy, which, depend-ing on the r.p.m., leads to a reduc-tion in maximum torque. Further-more, the eddy currents cause heat

loss into the cylindrical air gapspace, so that possibility of coolinghas to be considered. A drive systemmust accommodate such losses,which entails using a larger motorto match the energy dissipated.

H

DD1 dd1

Fig. 7 Concentric ring coupling in Secolit

16

Air gap width [mm]

143210 1513121110987654

2

Ø 300

Ø 250

Ø 200

Ø 150

Ø 100

Ø 75

Ø 50

Ø 25

D – d1

0.1

0.4

Torq

ue [

Nm

/cm

]

0.2

0.60.81

2

4

68

10

20

40

6080

100

( )Fig. 8 Torque per cm axial coupling length as a function of working air gap.

Parameter: outer diameter of inner coupling part (d1). Intermediate dimensions for diameter d1 and larger air gaps are possible, including protection of the inner part.

To estimate the required torquedetailed knowledge of the drivesystem and load characteristics isrequired. Here the user usually hasto rely on trial and error.

If the magnetic couplings are usedfor pumping aggressive media, thenone part of the magnetic couplinghas to be equipped with a protectivesheath. For practical reasons theinner part is best protected, usingeither stainless steel or plastic.

Heating magnetic material leads toa decrease in magnetic flux density,dependent on the material’s tem-perature coefficient, which in turncauses a reduction in torque.

To get the most out of the perma-nent-magnet material, magneticcouplings have to be optimised bycalculation. Fig. 8 shows the resultsof calculations for a several cou-plings, using numerical-field pro-grammes. This data is intended asa rough guide for the user, allowingapproximate estimates of couplingrequirements to be made. The axiallength of concentric ring couplingsshould, where possible, be at leastfour times the air gap length. Asstrong stray magnetic fluxes occurincreasingly towards the end facesthey do not make a full contributionto the torque.

Hysteresis clutches and brakesThe use of hysteresis clutches orbrakes is particularly appropriatewhen constant moment needs to bedelivered through a wide range ofrevs. In the hysteresis clutches andbrakes we produce, for each non-magnetised hysteresis material, e.g.Oerstit 70, there is an opposite,magnetised permanent magnet ma-

8

Relative speed

Torq

ue

Eddy currentclutches

for T =< 50°C

with small air gap

with larger air gap

with small air gap

with larger air gap

Hysteresisclutches

Fig. 9 Torque from hysteresis and eddy current clutches

small. In practice, at relatively highspeeds there is a slight increase inthe moment due to the superimpo-sition of an eddy current moment.Maximum temperature for Oxerstit70 discs must not exceed 100 °C,otherwise irreversible losses occurdue to structural changes.

A schematic illustration of the correlation between torque and relative speed

terial, e.g. Oxit 360. The materialcombinations are varied accord-ing to application and requiredmoment.

The particular torque or brakingmoment for a hysteresis combina-tion is largely independent of rela-tive speed and is sustained even atvery low relative speeds. Fig. 9shows this relationship for two dif-ferent sizes of air gap, large and

9

Hysteresismaterial

Magnet

Iron casing

Resin orequivalent

Hysteresis clutches and brakes

Table 3 Hysteresis clutches and brakes in Oxit 360, Secolit and Oerstit

If necessary, slight control of themoment is possible by axial dis-placement, in other words by al-tering the air gap and thus theeffective flow. It is important toensure that no iron is situated be-hind the Oerstit 70 hysteresis disc,otherwise the transferable torquewill be considerably reduced. Thedistance between hysteresis discand the nearest iron componentsmust be at least 15 mm.

Order-No. Tourquein Ncm*)

withair gap LL in mm

1.0 1.5 2.0

Hysteresis disc dimensions

Outer Inner Heightdia. mm dia. mm mm

Magnet dimensions

0uter Inner Heightdia. mm dia. mm mm

Dimensions of magnetand iron casing

Outer Heightdia. mm mm

Borein iron casing

dia. mm

106 330

106 331

106 332

106 333

106 334

106 335

106 336

129 6381)

123 1901)

106 5421)

123 1912)

128 4782)

124 4982)

1.2 0.7 0.4

2.3 1.9 1.5

9.5 8 6

20 15 12

35 31 27

70 55 42

115 103 90

172 130 100

200 190 177

270 240 220

63 53 44

400 270 110

650 625 600

41 ± 0.6 24 ± 0.6 8

53 ± 0.7 23 ± 0.5 8

68 ± 1.5 32 ± 0.7 10

84 ± 4.0 32 ± 1.0 12

100 ± 2.0 50 ± 1.0 15

124 ± 3.0 56 ± 3.0 18

140 ± 2.0 70 ± 1.0 21

117 42.2 10

180 80 20

212 ± 2.0 68 + 1.0 20.5

85 ± 1.0 32 10

140 60 10

140 60 9

50 ± 0.2 9.5 ± 0.15

63 ± 0.2 10 ± 0.15

80 ± 0.25 13 ± 0.2

100 ± 0.25 16 ± 0.2

125 ± 0.25 20 ± 0.2

150 ± 0.3 24 ± 0.2

165 ± 0.3 27 ± 0.2

117 12.5

195 28 ± 0.2

235 27 ± 0.3

100 ± 0.25 13 ± 0.2

150 ± 0.3 16 ± 0.2

165 ± 0.3 14.5± 0.3

–

–

–

–

–

–

–

40

32 + 0,05

6

32

25+ 0,05

–

42 ± 0.2 6.4 ± 0.2 4 – 0.2

55 ± 0.2 8.4 + 0.2 4 – 0.2

70 ± 0.2 8.4 + 0.2 4 – 0.2

85 ± 0.2 10.5 + 0.2 4 – 0.2

105 ± 0.2 10.5 + 0.2 4 – 0.2

130 ± 0.2 13.0 + 0.2 4 – 0.2

145 ± 0.2 13.0 + 0.2 4 – 0.2

114 45.0 3.5

185 ± 0.3 45.0 ± 0.1 4 – 0.2

215 ± 0.2 6.0 ± 0.2 4

114 45.0 3.5 ± 0.15

143 + 0.1 25.0 14.5

150 – 23.5

*) 1 Ncm 100 cmp, 0.00738 ft lbs= ⟨ = ⟨ 1) Special type in Oxit2) Special type in Secolit

Special types are not held in stock.

Eddy current clutches and brakesIn contrast to the drive and brakeelements already described, themoment in eddy current clutchesand brakes (fig. 4) is first producedby a relative speed between driveand driven sides.

Thus the transferable moment in-creases with relative rpm. Fig. 9shows the moment gradient for twodifferent air gaps. In practice ringsor segments in permanent magneticmaterial, e.g. Oxit 360 are magnet-ised on one side with several polesand are surmounted by copper discs2 – 5 mm thick, which for magneticreasons have a soft iron backing of2 – 6 mm thickness. Table 4 lists thedifferent values of torque estimatedin eddy current clutches and brakesfor 3 different relative speeds andvarious air gaps.

The values were measured at roomtemperature, set by measurementsof corresponding cooling of thecopper discs. In eddy currentclutches and brakes the tempera-ture coefficient of the copper isconsidered along with the tempera-ture coefficient of the magnet.

Eddy current clutches and brakesheat up considerably with increas-ing rpm, due to the development ofeddy currents, causing a sharpdecrease in attainable torque atroom temperature. If no cooling isprovided, then at a relative speed of1000 r.p.m., temperatures in thecopper discs can rise to 200 °C,decreasing the torque by up to 50 %.The losses thus incurred are partlyirreversible. They can only be fullyrecovered by re-magnetisation.

10

Cu Magnet

Iron casing

Resin orequivalentSoft

iron

Eddy current clutches and brakes

If the temperature is kept below50 °C, then the decrease in torqueamounts to approximately 10 %.

Within certain r.p.m. ranges, eddycurrent clutches show a roughlylinearly proportional or constantrelationship between torque andr.p.m. These characteristics makeeddy current clutches suitable foruse in coiling machines, where con-stant band tension and constantband speed are required.

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Table 4 Eddy current clutches in Oxit 360, Secolit and Cu/Fe

Order-No. Torquein Ncm*)

withAir gap LL in mm

0.5 1.0 2.0

Withrelativespeedn

1/min.

Magnet dimensions

Outer Inner Heightdia. mm dia. mm mm

Dimensions of magnetand iron casing

Outer Heightdia. mm mm

Borein iron casing

dia. mm

Eddy current unit

Outer Inner Cu- Fe-dia. dia. thickn. thickn.mm mm mm mm

106 450

106 451

106 452

106 453

106 454

106 455

106 456

123 1921)

120 4061)

123 1932)

123 1942)

41 ± 0.6 24 ± 0.6 8

53 ± 0.7 23 ± 0.5 8

68 ± 1.5 32 ± 0.7 10

84 ± 4.0 32 ± 1.0 12

100 ± 2.0 50 ± 1.0 15

124 ± 3.0 56 ± 3.0 18

140 ± 2.0 70 ± 1.0 21

180 80 20

214 ± 2.0 68 ± 1.0 21

85 ± 1.0 32 10

140 60 10

50 ± 0.2 9.5 ± 0.15

63 ± 0.2 10 ± 0.15

80 ± 0.25 13 ± 0.2

100 ± 0.25 16 ± 0.2

125 ± 0.25 20 ± 0.2

150 ± 0.3 24 ± 0.2

165 ± 0.3 27 ± 0.2

195 28 ± 0.2

235 27 ± 0.3

100 ± 0.25 13 ± 0.2

150 ± 0.3 16 ± 0.2

–

–

–

–

–

–

–

32 + 0.05

–

32

25 + 0.05

50 6.4 2 2

63 8.4 2 2

80 8.4 2 3

100 10.5 2 3

125 10.5 3 4

150 13.0 3 4

165 13.0 3 4

195 45.0 3 4

230 55.0 4 5

100 10.5 3 4

150 25.0 4 6

1.0 0.8 0.6 5002.0 1.6 1.1 10002.8 2.2 1.5 1500

4.9 3.8 2.5 5009.3 7.5 5 1000

13 10.5 7 1500

26 19 14 50047 35 25 100059 47 35 1500

75 56 42 500130 100 75 1000160 120 93 1500

140 120 90 500190 170 130 750230 210 155 1000

450 380 300 500580 500 400 750650 580 470 1000

600 520 400 500760 670 510 750800 700 530 1000

1030 870 670 5001300 1150 870 7501400 1200 900 1000

2300 2220 1800 5002500 2300 1900 7502600 2400 2000 1000

135 110 75 500180 150 105 750200 175 125 1000

1300 1100 650 5001500 1300 850 7501600 1400 950 1000

*) 1 Ncm 100 cmp, 0.00738 ft lbs= ⟨ = ⟨ 1) Special type in Oxit2) Special type in Secolit

Special types are not held in stock.

Technical advice and supply of samplesWe can supply clutches and brakescomplete and ready for installation.However, we can also install mag-nets and magnetise bell housingsand other casings sent to us. Thereare a variety of different ways ofarranging the outer rings of con-centric ring couplings in the hous-ings, independent of form, size andno. of rings in the series. For thisreason, we ask that any enquiry beaccompanied by a drawing showingthe intended receptacle for themagnet rings, so we can establishthe best method of mounting. Theouter diameter of magnet rings isground to an ISO m6 fit, allowingthem to be press fitted. The detailsfor wall thickness of the ironmountings are for low carbon steel,e.g. St 37. In concentric ring cou-plings, the shafts are normally castas an integral part of the inner com-ponents. If possible, each construc-tion project should initially be dis-cussed with us to avoid the disap-pointment and expense of failure.We are always available to provideadvice, supported by the appro-priate computer backup. The production of every permanent

magnetic clutches series is normallypreceded by prototype testing.Prototype testing of eddy current-hysteresis clutches and brakes isadvisable in every case as the torquecurves can alter according to appli-cation e.g. through heating. Themagnet rings and segments of disccouplings, eddy current and hyste-resis clutches and brakes are gluedto iron parts with special adhesiveand the iron casing with specialresin.

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If high chemical and thermal resist-ance is required, we would requestthat the appropriate details be madeavailable. To secure the clutches andbrakes in their iron casings, holesmay be bored to a maximum of theinner diameter of magnet. Counter-balancing is possible by makingholes on the outer perimeter. If careis taken during this work to ensurethat clutches and brakes do notheat above 100 °C, no weakening ofthe transmittable torque will occur.

All data and information in thispublication has been checked andsubject to rigorous controls. How-ever, no liability is accepted forpossible errors or omissions. Weretain the right to make alterationsand modifications appropriate forfurther product development. Thispublication supersedes and invali-dates all previous ones.

Series ProductionOften the demand arises for theseries production of a coupling orbrake design not included amongstthose in this brochure. In this case,adopt the following strategy:

• Assemble pre-magnetised or self-magnetised 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 recom-mend agreed documentation of thetechnical conditions of delivery,stipulating all requirements withrespect to the magnetic, physical,mechanical and chemical propertiesof our products. We can give noguarantee against faults resultingfrom factors other than thoseagreed in the technical conditionsof delivery.

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Quality assurance and deliveryagreementFulfilling and securing the veryhighest standards of quality is fun-damental to Tridelta’s operations.By setting quality targets – fromproduct development and processplaning to careful raw materialtesting and integrate checks duringproduction – Tridelta ensures thequality of product demanded bytheir customers.

The magnetic specifications ofTridelta’s magnet material morethan meet the demands of DIN17410 (permanent magnet materi-als, technical conditions of delivery).In practice, clear definition of thelimits of the application (singlemagnet or magnet system) and afunctional inspection system is re-commended.

The concept of limits of applicationshould also include mechanicalcomposition.

For shape and size tolerances thesubmitted technical drawing is de-initive.

Tridelta Magnetsysteme GmbHOstkirchstrasse 177D-44287 Dortmund

Phone: +49 (2 31) 45 01- 2 15Fax: +49 (2 31) 45 01- 3 96E-Mail: info@tridelta.de

http://www.tridelta.de

Tridelta MagnetsystemeA Tridelta Group Company

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Raw Materials Magnets Systems and Components