thrust free tailbar for mill drive

8/18/2019 Thrust Free Tailbar for Mill Drive

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FORTY FOURTH

CONFERENCE

Most of us are aware that imponderable forces are developed within the well-

known tailbar and coupling assembly. Such forces are of a thrust and/or radial nature.

and their value depends mainly on the distance existing between the mill and iis gearing

plus the degree of out-of-alignment existing with the tailbar assembly. The paper

Cane Mill Tailbar and Couplings (Power and Clarke, 1977) indicates the levels of

these forces and the steps necessary to overcome such wear patterns.

In an effort to reduce, or if possible remove, these undesirable forces certain design

and constructional changes have been made.

Conventional mill drives use the square tailbar. square ended main shafts and

conventional box couplings whlch are shown in Fig.

1.

Such a design was of particular

value on earlier mills with brass bearings, as faces, to accept the thrust forces, were

easily provided by increasing the diameter of the mill roller shaft. Any increase in this

diameter was of value in its corresponding effect on the size of the square tailbar.

With this older and almost un~versal esign, all the torque for a milling unit was

delivered to the mill top roller shaft by the drlving tailbar. This torque was then

distributed to the other rolls (Fig. 1).This established the need for a large shaft at AA

to enable all of the milling torque to

be

transmitted at this point. The development of

very large mills in recent times has meant that shaft sizes at

A

have become extreme.

Much time and e rt has been placed on the maintenance and lubrication of

tailbar surfaces, in an effort to reduce the extent of these thrust forces. Perfect

alignment of the tailbar and mill rolls is almost impossible to achieve or maintain under

working conditmns.

Knowledge of the problems which exist with presently-used equipment and a

realisation of the

requirements

necessary for roller bearing mills, plus mills with much

Fig l Present mill drive and torque distribution


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248 FORTY FOURTH CONFERENCE 977

larger rollers, has meant development of a new design. Such a design is shown in Figs.

2 and 3 and it can be seen that an entirely new method of torque distribution is

proposed. With the existing design all

of

the mill driving torque must be delivered

through the mill tailbar and into the mill top roller. However, this new method greatly

reduces these figures, particularly those in the top roller shaft. Such distribution

satisfactorily reduces the diameter of each shaft and allows for the direct application of

roller bearings of sensible size to all shafts.

Fig. 2 New design internal gear coupling

Fig. 3 Drive through bolted on square

The basic requirements of this design is the provision of a direct connection,

preferably by a flanged joint, between the mill top roller pinion and the final tailbar

coupling, whether this be of the internal gear type, Fig.

2)

or the flanged square type,

Fig. 3).

The provision of a separate and flanged square, Fig.

3),

which can be bolted onto

the previously mentioned pinion flange allows the use of a replaceable item, having a

higher tensile strength than the original roller shaft. The value of this flanged square

will be immediately apparent to engineers in the mdustry, as it allows maintenance to

be carried out independently of the mill and spare items can be held. However, all

designs which include a square type coupling will still involve thrust and radial forces

dealt with in the earlier paper Power and Clarke,

1977).

Although the torque distribution of these previously-discussed flange pinion

couplings is advantageous with regard to shaft sizes, the existence of tailbar developed

thrust can still be a problem. Hence the development of the new internal geared self-

aligning coupling which is shown in Fig. 2.

Probably one of the greatest advantages of this new design is the ability to use

hardened gears, which resist wear and abrasion. In addition they operate in a fully

enclosed box which will maintain constant lubrication and keep them clean, in the mill

house. The inner section of this coupling has crowned gear teeth and is mounted into an

external section which has st,raight flank internal teeth. 0th sets of teeth are hardened

and are designed to allow for a 2 to 3' float of the tailbar with a great reduction in

separating thrust. The internal section of the coupling is filled with grease or oil and so

further lubrication is not required.


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977 FORM FOURTH CONFERENCE 249

Even though

it

1s believed that this design

is

the ultimate with regard to sugar

mill

drives it does not overcome pricing difficulties and a coupling of this internal geared

type

will

certainly cost more than the old tailbar and coupling arrangement. However,

it will overcome most, if not all, ofthe known thrust forces of the old design and will be

much cleaner to operate.

A

further advantage is the fact that a circular tailbar can be

used in place of the square design now common and this will tend to reduce costs. The

design

is

covered by an application for Patent protection.

The author wishes to thank the management of Walkers Limited for their co-

operation in the production ofth is paper.

REFERENCES

Power C. and Clarke

S

1977).

Proc. Qd Soc. Sugar Cane l echnol.

44th

Conference.

thrust free tailbar for mill drive

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