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7/30/2019 513 e CA Aachen1 Streb En

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Dr. Rainald Finzel, Wolfgang Weber, Heinz HllerVoith Turbo GmbH & Co. KG, Crailsheim

Water flow-controlled turbo couplings

of the new generation to drive AFCs


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Lecture Aachen 1AFC drive

Content

1 Preamble................................................................................................. 3

2 Requirements for the drive units ......................................................... 3

3 Previous solutions with hydrodynamic couplings ............................ 4

4 Flow-controlled hydrodynamic couplings of the new generation ... 6

5 Design and Functioning........................................................................ 7

6 Coupling function.................................................................................. 8

7 Management of operating medium...................................................... 9

8 Operating behaviour ...........................................................................108.1 Start-up after normal shutdown.................................................... 108.2 Start-up after emergency shutdown........................................... 108.3 Start-up vs. overcharged or blocked conveyors........................... 11

9 Rating.................................................................................................... 12

10 Creep speed .........................................................................................14

11 Short blockage of chain...................................................................... 14

12 Summary ..............................................................................................16

Voith. Lecture 2

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genera

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todrive

AFCs.


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1 Preamble

For decades hydrodynamic couplings have been a major component in thedrive train of AFCs. The paper introduces a further development of thewater flow-controlled turbo coupling for the power range up to 1000 kW andmore and explains its operation. The advantages of the turbo coupling are

to provide smooth start-up, torque limitation and load sharing on account ofits natural characteristic more or less automatically, without controlmechanism it is possible to show that the coupling is extremely water-saving during operation. A very robust and compact design is achieved byomitting bearings and by using simple shaft seal labyrinths.

2 Requirements for the drive units

Modern high-capacity longwall faces distinguished by large conveyingcapacities are increasing in face lengths more and more. Thus, therequirements for the chain conveyors become higher; on the one hand, theyhave a larger power consumption due to the length and the higherconveying capacity; on the other hand, the reduction in the number of minesresults in increasing requirements for the reliability. This paper shall onlydeal with the drive units of these conveyors.

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Fig. 1: Drive unit of a chain conveyor

The most important criterion is the conveyor start-up. It shall be as smoothand as quick as possible to protect the chain, thus enabling a producing astarting torque without jerks.

Voith. Lecture 3

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Usually, low-price asynchronous motors are used to drive chain conveyors.Their characteristic with a significant saddle torque is not well suited for thestart-up of machines with constant torque. Overloaded or even blockedconveyors require a break-away torque which should be considerably


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higher than the rated torque. It would be best to make use of the pullouttorque of the motor.

A high start-up frequency and the possibility of a counterclockwise andclockwise rotation are of advantage of starting an overloaded or blockedconveyor. During operation, the load between the drive units needs to beshared in case of a multi-motor drive; on the one hand, in order to charge allmotors as uniformly as possible but on the other hand, to also avoid a chain

back-up in the return run. The possibility of an inspection or creep speed isoften requested, as well as the protection of the chain in case of the so-called "short blockage" right in front of the main drive.

The general requirements are as follows:

max. mining capability reliability

easy handling

compact construction

3 Previous solutions withhydrodynamic couplings

With the use of hydrodynamic couplings in the drive train of AFCs, it will bepossible to meet most of the requirements of the drive system byuncoupling the motor runup and the conveyor start-up.

Hydrodynamic couplings usually consist of two bladed wheels (pump andturbine) forming a working chamber with an enclosing shell in which the

operating fluid circulates. The mechanical power is transported by thecirculating flow of fluid, with requiring, however, a speed difference betweenthe pump and turbine, the slip.

For approx. 40 years, turbo couplings with constant filling have been usedfor smaller powers which can be operated with the operating fluids oil, HFDor water.

For the motor start-up relief, the coupling is operated with reduced fillingfirst. Part of the operating fluid is temporarily stored in the delay fill chamber.When motor startup is complete, the volume stored will be fed into theworking chamber. Thus, the motor pullout torque can be used to anoptimum extent. The filling partition is controlled by nozzles and speed-

controlled valves.

Voith. Lecture 4

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Fig. 2: Coupling type TVF with constant filling

Advantages of this coupling type:

simple construction easy mounting and removal

no peripheral devices, control systems and similar devices

relieved motor runup

utilization of the pullout torque of the asynchronous motor

automatic load sharing

Disadvantages:

tight thermal limits in case of frequent starts or when starting against theblocked conveyor (spraying-off of coupling)

longer standstill periods for cooling-down and refilling of the coupling

no creep speed is possible

For higher powers, flow-controlled turbo couplings have been used forapprox. 7 years. They are self-supported and are connected, as a separateunit, with motor and gear by means of flexible connecting couplings.

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Fig. 3: Flow-controlled coupling type 562 DTPPWL

An arrangement with 2 circuits back to back reduces the hydrodynamicallyproduced axial forces and also reduces the outer coupling diameter.

Voith. Lecture 5

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A further design variant is on with only a output side bearing arrangement

and a rigid connection of the drive to the motor shaft to reduce the laidlength. This design has been successfully used by "Saarbergwerke".


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More than 150 couplings of both types have been used in the mines ofRBAG and SB, on 315 kW and 400 kW drive systems, in the USA and inAustralia, partially in reinforced design in drives of up to 750 kW.

The advantages of flow-controlled turbo couplings are as follows:

use of water as operating medium

start-up of asynchronous motors with hardly any wear

sequential starting of individual drive systems by variable coupling fillingtimes

automatic torque limitation during start-up, no motor stalling over thepullout torque

smooth and quick torque build up at the chain

start-up against blocked conveyor, with maintaining the motor pullouttorque

possibility of a repeated start-up without any thermal problems afterchange of water

automatic load sharing

possibility of inspection creep speed

possibility of tensioning the chain in connection with a locking brake

easy control since important functions, such as torque limitation and loadcompensation, are automatically effected by the natural couplingcharacteristic

Disadvantages:

chain protection against "short blockage" only with additional safesetcoupling between gear and chain sprocket at the main drive

water consumption which can, however, be considerably reduced by

managing the operating medium accordingly

very long laid length of the drive unit due to the turbo coupling being self-

supported and due to the two flexible connecting couplings

4 Flow-controlled hydrodynamiccouplings of the new generation

For some time, the power requirements of drive systems, imposed by theinternational markets USA and Australia, have increased from 600 to 1000kW and further increases are expected. VOITH TURBO made use of theirexperience to jointly develop a new compact drive system, together with alarge international manufacturer of longwall equipment. The result is a newgeneration of turbo coupling which is only sold on the international markettogether with the partner "Joy Mining Machinery. However VOITH TURBOcan offer this technology to the German Mining Industry without Joy.

Voith. Lecture 6

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Fig. 4: Flow-controlled coupling type 562 DTPKW (new generation)

5 Design and Functioning

The design of the water flow-controlled turbo coupling of the new generationis also of the tunnel type, with 2 symmetrically arranged circuits. The mostimportant difference to the previous coupling type is that they are designedwithout bearings. The pump impellers are directly mounted on the motorshaft, the turbine wheels are directly fitted to the gear shaft. Thisarrangement enables a very compact design. The installation space for thebearings, their sealings and the flexible connecting couplings is no longernecessary.

In case of a power transmission of 1000 kW and more, a considerable heatgeneration in the coupling has to be expected during start-up which may

partially lead to the evaporation of water. In order to avoid any cavitationdamages, the impellers are therefore manufactured of propeller bronze,they can also be made of aluminium for applications at low powers. Housingparts in contact with water are of stainless steel.

The connection coupling to gearbox is designed for being made aboveground. The connection motor to coupling can be made and loosened in thelongwall face. Regarding mounting, a short bell housing is provided on themotor side. A second short bell housing serves to pick up the gearwheel ofthe chain tensioner. The chain tensioner can be mounted left-hand, right-hand or on the top. It is also possible to provide a brake instead of the chaintensioner.

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Fig. 5: Functional sectional drawing of the 562 DTPKW

Voith. Lecture 7

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In order to achieve that the temperature in the coupling working chamber isdistributed as uniformly as possible, the water is fed on the one couplingside and is taken in diagonally opposite position, contrary to the previouscouplings.

The closed outer water circuit was maintained. The flow rate from theworking chamber into the pump shell can be individually adjusted by meansof nozzles. The stationary discharge pump delivers the flow rate through the

valve block back to the working chamber filling point.

Inevitable low water losses at the transfer points are entrained in thehousing due to the outer ventilation of the runners, peeled at the watercollecting pockets and fed again to the circuit through channels. So theconstant filling of the working chamber is ensured.

The management of the operating medium is made by the valve blockmounted on the coupling housing. This valve block includes all requiredvalves and their internal connections from and to the coupling, as well asone pressure and temperature pickup each. Both the coupling supply anddischarge is effected by means of 2 hoses.

6 Coupling function

0 % filling

100 % fillinglongwall characteristic

1

1 1

2

3

0 00,5 0,5

Primary characteristic field Secondary characteristic field

remaining filling inthe runner

typical characteristic ofasynchronous motor

M/MN

n1/nsyn n2/n1

Fig. 6: Primary and secondary characteristic fields

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The turbo coupling transmits the mechanical power of the asynchronousmotor with help of a circulating liquid flow to the driven machine. Thecoupling transmission can be easily, infinitely adjusted via the fill level of theworking chamber. The effective load on the motor during start-up, resultingfrom the countertorque and the masses to be accelerated, is onlydetermined by the turbo coupling, the driven machine is uncoupled. Ontermination of the motor runup, the coupling transmission is only influencedby the fill level of the working chamber.

Voith. Lecture 8

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In order to fully use the max. torque of the drive system (pullout torque)during start-up, the secondary characteristic curve should be as flat aspossible until reaching low slip values. The secondary characteristic fieldshown represents the result obtained from our efforts to reach an optimum


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between the characteristic steepness at min. slip and, if possible, thehorizontal characteristic curve towards the starting point. For this reason,VOITH internally calls this characteristic curve, which was especiallydeveloped for the use of operating medium flow-controlled couplings forchain conveyors, "longwall characteristic curve".

This characteristic is only influenced by the fill level but not by the flow rateof the outer operating medium circuit.

7 Management of operating medium

During each start-up, half of the energy used is converted into heat. Thisheat is produced in the operating medium of the coupling. The advantage ofthe water flow-controlled coupling types is that the operating medium isidentical with the cooling medium which transports the heat away from its

origin. So it is also possible, in case of a blocked output side (100 % slip)and utilizing the pullout torque, to convert a power, which may be four timesthe rated motor power, in the coupling into heat and to dissipate it.

Example:In order to maintain a starting torque of 18,000 Nm over a longer period oftime, a flow rate of 660 l/min is required at a water temperature increase inthe coupling by 60 C, whereby a thermal capacity of 2750 kW istransported.

The dimensions of the outer water circuit have to be determined accordingto the start-up conditions, i.e. the flow rates vary, as a function of the max.torque to be transmitted and the requested maintaining time of the max.

torque, from 180 l/min. (400 kW motor) to 660 l/min. (1000 kW motor).

On account of the new solution with closed loop circuit, the waterconsumption can be considerably reduced at start-up and rating without anyproblems.

Voith. Lecture 9

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Valve blockHeat exchanger

Turbo

coupling

Discharge pump

Scope of supply

Longwall hydraulics Water circuit supply Water discharge

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Fig. 7: Circuit and functional scheme


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The signalling and switching functions required here can be taken from theflow diagram which shows the coupling itself dash-dot, the scope of supplyof coupling and valve block has a bold frame.

The valve block comprises the valves of the fresh water side, the outletside, the pressure and temperature switches as well as the required throttleand adjusting fittings. It is also provided with the connections for the "rampump" and for an optimum heat exchanger.

When using a "ram pump", the fresh water supply can be optimized. The"ram pump" stores an additional volume. If required, in case of a blockedconveyor, a water flow rate corresponding to the circulating flow rate can bedelivered to the coupling short-term. The "ram pump" is driven by thehydraulic fluid of the longwall hydraulics.

8 Operating behaviour

Both the functioning of the coupling and the peripheral units shall bedescribed hereunder, at rating, at automatic load sharing and at creepspeed.

8.1 Start-up after normal shutdown

The coupling working chamber and the housing were fully drained byopening the drain valve, with the motor still running. When the motor isswitched on, it can run up in relieved condition. By opening the filling valve(drain valve closed), the working chamber is filled by the normal fresh water

supply. Thus, the coupling transmission starts from "0", i.e. without any jerksbut quickly, until the break-away torque of the conveyor is reached and theconveyor starts to move.

8.2 Start-up after emergency shutdown

The operating medium was not discharged to the outside. The operatingmedium in the working chamber and outer circuit collects in the couplinghousing, due to gravitation, a minimum residual filling remains in theworking chamber.

During start-up with filled housing, both the filling and the drain valve remainclosed. The motor is only charged by the residual filling in the workingchamber during the runup phase. An outer circuit produces. The decisionwhether to start with filled housing or whether the water should be changedwill be made as a function of the operating medium temperature.

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AFCs.

The water from the coupling housing is fed to the outer operating mediumcircuit by the so-called "adhesion pump" formed by runner and housing.

In case of the decision "water change", the drain valve will be opened andthe hot operating medium will be discharged. Afterwards, the drainedcoupling will be started with fresh water, as described before.

Voith. Lecture 10

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8.3 Start-up vs. overcharged or blocked conveyors

If the start-up procedures described do not lead to the conveyor breaking-away, the water temperature will increase to a value exceeding the limittemperature, water change will be started and the coupling output speedwill be checked. If the output side continues to stand still, the normal waterflow rate will not be sufficient and the water will be changed by the "rampump", with the flow rate being high short-term (same value as the

circulating flow rate).

To do so, a large drain valve must be additionally opened. Owing to this"management", the motor pullout torque can, for example, be maintainedduring 20 seconds at blocked conveyor which can be proven at the testbench.

Fig. 8: Check of ram pump function

[l/min]

[l/min]

[10

4N

m]

CInput speed n_E

562 DTPKW

Q-Circulationtorque built-upwith blocked output

Temperature

Q-supply

torque M_T

Temp.

off

n_

E

flow

Q

Voith. Lecture 11

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9 Rating

Normally, the conveyor already breaks away with partially filled coupling.The closed circuit is supplied with fresh water from the water mains via thefilling valve until the pressure switch in the outer circuit signals its setpressure and the working chamber reaches its nominal filling. Owing to the

nominal coupling slip, the circulating operating medium flow is heated.When the max. temperature limit (e.g. 55 C) in the circuit is reached, waterchange will be started by the temperature pickup in the valve block. First thefilling valve opens, afterwards the drain valve. Medium will be changed untila min. limit of, for example, 20 C is reached, without any power or speedlosses. First the drain valve is closed, and after the set pressure in the outercircuit has been reached, the filling valve closes.The advantage of this system is that the water consumption depends on theload. Low load means a long operating cycle without water change and thusa corresponding low water consumption.

A heat exchanger arranged in the by-pass and supplied with motor coolingwater can still considerably extend the changing cycle.

In case of multi-motor drive, the hydrodynamics offer another significantadvantage owing to the automatic load compensation. Due to the motor sliptolerances (to VDE 0530 20 %), manufacturing tolerances of chains andgears as well as due to the different wear, the load of the individual drivescan considerably vary. The load is automatically shared owing to thecoupling slip. The following figures show that theory and practice matchvery well.

Coupling characteristic curveMotor characteristic curve

Torqu

e

Conveyor speedMotor speed

Tor

ue

Loa

ddifference

Loa

ddifference

Load partition at 2 % speed difference,rigid motor connection

Load partition at 2 % speed difference withadditional turbo coupling

Motor speed

Fig. 9 Theoretical relations regarding load compensation

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Voith. Lecture 12

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auxiliary drive

main drive

TFCPCT F_CV SAMPLE 121 %FLAHFC1PCT F_CV SAMPLE 114 %FLAHFC2PCT F_CV SAMPLE 110 %FLA

AFCSPD F_CV SAMPLE 2 RPM

TFCPCT F_CV SAMPLE 39 %FLAHFC1PCT F_CV SAMPLE 38 %FLAHFC2PCT F_CV SAMPLE 36 %FLA

AFCSPD F_CV SAMPLE 1753 RPM

Fig. 10: Motor currents measured at a chain conveyor with 3-motor drive

Voith. Lecture 13

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10 Creep speed

Usually, inspection or material transport is effected at reduced speed. Withthe coupling working chamber being partially filled, operating points belowthe nominal speed are adjusted. The corresponding coupling characteristiccurve offers stable intersecting points. The open filling valve and the

clocking drain valves guarantee both the partial filling and the thermaleconomy. The following test stand diagram shows that this operating pointis stable regarding temperatures, without any time limitation. The couplingwater supply needs to be usually optimized to this operating point.

Input speed n_E

Creep speed and change of water

Output speed n_A

TemperatureSupply flow Q_Zu

Torque M.T.

Filling valve

Drain valve

562 DTPKW

Fig. 11: Evidence of the function creep speed at stable temperature

11 Short blockage of chain

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In case of a blockage near the main drive, the extensibility of the short chainpart between the point of blockage and the chain sprocket is no longersufficient to absorb the incurring torque peak. As a function of the chainspeed, the blockage can be effected within 30 to 50 milliseconds.

Voith. Lecture 14

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Though the turbo coupling only transmits the torque in conformity with itscharacteristic curve, there will be an additional torque peak due to thesudden deceleration of all rotating parts, from the secondary side of theturbo coupling to the chain sprocket. In order to increase the unit safety, it is

recommended to provide a safeset coupling between the gear output andthe chain sprocket. This safeset coupling mainly consists of a shaft andbush which are held together by a defined oil pressure.


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Fig. 12: Sectional drawing of a safeset coupling

When the slipping torque is reached, the shaft and bush slip together untilthe peak does no longer exist. The diagram hereunder shows a slipping

angle of 20 degrees for the example assumed. After decrease of the peakvalue, the system torque has already been reduced to the coupling torquevalue and the system will become stationary again, i.e. the coupling will limitthe torque again.

Assumption: Power 750 kWInput speed 1480 rpm

Gear ratio 37 : 1Mass moment of inertia 10 kgm

2

Breaking away safeset 740 kNmSliding safeset 629 kNmBlocking time of shaft 0.1 sec

(100 mm)

Safeset sliding torque

Coupling torque

Twisting angle 20 degrees

Input speed(Gear)

TimeOutput speed(Chain wheel)

rpmin %

Fig. 13: Diagram conc. the function of a safeset coupling

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Voith. Lecture 15

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12 Summary

A new drive system with hydrodynamic coupling was presented which wasespecially developed for high-capacity chain conveyors and whichdistinguishes by a compact design being adapted to an operationunderground.

It was possible to show that all requirements to the drive unit of an AFC aremet on account of a perfect operating medium management, the "longwallcharacteristic curve" especially developed by Voith and the use of thesafeset coupling. Owing to the use of the cooling agent 'water' as operatingmedium, water flow-controlled turbo couplings have a pioneer function withregard to mine safety and protection of the environment.

Voith. Lecture 16

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May

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Lec

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May

1997

Voith Turbo GmbH & Co. KGStart-up ComponentsVoithstr. 174564 CrailsheimGermanyPhon (07951) 32-409Fax (07951) [email protected]
mailto:[email protected]:[email protected]

513 e ca aachen1 streb en

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