Rope Pulleys*

Paper N o. 735

By JO H N R. W EBSTER

Since electric power transm ission came into com m on use and m otors becam e m ore reliable, the rope drive is no t so com m only used as it once was, but there are still fair quantities of them in use, and as pow er transm ission engi­

neers, it is very seldom indeed th a t the au th o r’s firm is w ithout rope pulleys of some sort in the foundry. A lthough the shape of the groove has changed considerably, yet, on the whole, sizes are sm aller than they used to be. T here are few castings currently m ade which involve so many different designs or lend themselves to so m any different m ethods of m oulding as the rope pulley. The reasons are possibly as varied as the designs themselves. It m ight be profitable, therefore, to consider w hat factors most p ro ­ foundly influence design. As there is seldom m ore than one-off each pulley— unless in ex­

ceptional cases, where the pulley is part of a standard m achine— a whole pattern is too ex­

pensive, and for large sizes, practically im pos­

sible. T herefore, the designer has usually con­

sidered the m ethod m ost suitable for his foundry to produce. This feature probably explains how the m any different types o f arms, the varied m ethods of m oulding grooves, and similar diver­

gencies came into existence. The au th o r’s firm, after trying different designs, finally standardised on the design shown in Fig. 1. This particular pulley is 9 ft. 10 in. dia. over the rope pitch line; it has 17 grooves, and weighs 11,500 lbs.

It was run with fo u r 1J in. down-gates on the nave and the pouring tim e was 1.5 min. This pulley is a good example, though six arm s per set are usually considered am ple. In adopting this design, consideration was given first to appearance, aiming to produce a pulley as artistic as possible, whilst taking cognisance of the cost of production, including patternm aking.

The latter cost is reduced to the m inim um , by having the pattern parts, core boxes, sweeps and groove plates m ade to serve for a wide range of sizes. M oreover, due consideration was given to moulding, dressing and particularly m achining costs, and the m anagem ent was prepared to pay a little m ore in the foundry, if such costs could be recovered in machining.

* T h e A u th o r w as aw ard ed a D ip lo m a fo r th is P ap er.

Working System

W ith this end in view, Mr. H endry F raser produced the system now in use in the foundry, and which has proved most satisfactory. U nder the system all grooves are swept in loam , and necessarily stove dried. This reduces dressing costs, as there are no fins all over the face as there often is when the grooves are cored. It also reduces the machining allowance to a m ini­

mum, as there is no “ siding ” through cores

Fi g. 1.— De s i g n o f Pu l l e y d i s c u s s e d.

being distorted by handling or core box ra p ­ ping. Pulleys with a 12 in. face or less have the inside swept in green sand. Above this dimension, the inside or core is built an d swept in loam. Small diam eters up to about 4 ft. are built on a bottom -plate and stoved. Larger sizes are built in a pit and dried on the site.

Tackle Used

Fig. 2 shows all the tackle set up ready to build the grooves. The spindle is 3 in. dia.

and has a long taper in the footstep to ensure rigidity. T h e usual split collar is provided, on w hich rests an eccentric block w ith 1 in. eccen­

tricity. T he block is held in position w ith a pinching screw fronted with a gunm etal pad to keep the pressure from pitting the spindle.

I t has also a centre line on the top, through the eccentric. Over this, the sw eep-arm works.

The sweep for the grooves is cast iron, 1 in. in thickness. D ow n the length o f the spindle is a line o r m em ber clearly defined approxim ately i s in. wide and a t least the sam e in depth. On the floor is a straight edge w ith a notch cut ou t to accom m odate the spindle, and on the left can be seen a stake driven into the floor and properly plum bed to the vertical. A small straight edge is fixed to the bottom of the

will come in line with the bottom o f the groove.

The cakes are 9 in. square, and the holes in the plate are fo r riveting on the loam . The labourer, w hen the cakes are dry, lifts them out o f the stove, gives them a light ru b w ith a card cloth, and sets them ready for the m oulder who builds them as shown in Fig. 2, setting each cake with the sweep as he proceeds. A fter the m oulder has com pletely built the half pulley, he then loam s up and sweeps the grooves;

loam s up the ends and strikes them off with the straight edge, having a bearing on the spindle and also on the post already mentioned.

This only leaves the ends of the grooves to square off. F o r this purpose two short pieces of groove are provided. This half is now lifted away and placed on the stove carriage, and the

Fi g. 2 . — Ta c k l e f o r Bu i l d i n g t h e Gr o o v e s.

sweep w ith w hich the bed is swept, and after the usual preparation the cope ring is placed in position as shown in the illustration. These plates are necessarily thin, being only } in. thick at the edge tapering back to ab o u t f in. to enable the m oulder to get in the first groove.

This carries all the building.

The back flange which is 5 in. by 3 in. is re­

quired to keep the m ould rigid when stoving.

In the foreground i the cake box. There are different thicknesses o f these for the different sizes o f ropes o r pitch. Inside the box is a m ild steel plate, with six holes punched out. P re­

vious to starting a pulley, a labourer goes into the stove, the floor o f which is plated, and makes as m any cakes off this box as the m oulder will require fo r building the pulley. Each cake has one of these plates bedded-in, so that the edge

other half plate is pu t down on the bed and the sam e process is repeated. H alf-plates are only used fo r the larger sizes, as they can be m ore easily stoved. The m oulder has now swept a half pulley, but he has done m ore than this, for he has swept a h alf pulley, plus f in. a t each end to allow for m achining an d cam ber This

| in. is controlled by the straight edge—the straight edge being | in. back from the centre line of the pulley.

If this pulley h a d been ab o u t 7 ft. o r less in diam eter the plate w ould have been whole instead of in halves. T he procedure then would have been different afte r building the first half.

Two prin t blocks fo r splitting cores H in. thick would have been provided, and w ould be placed against the struck face o f the building. The eccentric block w ould have been turn ed over.

102

and the building proceeded with as before. As there is one inch eccentricity on the block, the m oulder is always sweeping 1 in. off the centre.

T his gives a 2 in. gap between the two halves of the mould, and is used for \ in. machining each side on this size of pulley and 1 in. for cam ber, w hich is insufficient. This finishes the building of the grooves, and as they are now stoved it seems w orth while to exam ine the building o f the inside o r core.

Core Making

It is regretted th a t Fig. 3 does not show m ore of the operation. It would have been better if it could have shown the inside or core of the pulley half built with the arm cores set in position, but an attem pt at rectification will be m ade by description. There can be seen at

A fter drying, it is blackened and is then ready for building in. The other box shown is for m aking the distance piece between the naves of the two sets o f arms. This carries a print for the core through the nave, and also a tee-section- piece, about 2 in. by 2 in. by 1 in., which joins the two naves together. This keeps “ spring ” from affecting the arm s, and as the pulleys are run off the nave the iron flows through these and fills the bottom p art of the mould. The two long pieces shown in Fig. 3 are the patterns for the bolt lugs carrying a print for the splitting core. The sweep for the inside of pulley is in position, and from this view can be seen the arrangem ent for setting.

T he arm is m achined at the neck to a given size from the spindle centre. It is really m achined all along the face and the top edge.

Fi g. 3 .— So m e o f t h e Co r e-m a k in g Ta c k l e Us e d.

the back of the spindle (Fig. 3) the arm core box.

It has a m etal head, m achined at the joints at the correct angle and flanged at the bottom to allow o f the bolting on o f a wood bottom . This is a standard depth, but the depth or thickness of the core is controlled by the length of nave required. It should be noted that this box has a second bottom to m ake it of the necessary depth. The arm is loose, and in the centre of the bed, the section of the nave where it fits into the m itre end, and the end is held in position by the blocks fixed to the side. The arm is tapered and dowelled into the fillet on the back.

A fter the arm is ram m ed up in dry sand and turned over on a plate, the back, with the fillet, comes away. T he arm is then draw n out, and the core is ready for stoving.

On this edge, a plate is fixed projecting about

\ in. over the face, and thus m aking a flange.

To set the sweep, it is put in the arm , close up to the shoulder and against the flange along the top and bolted up; a little “ plum bing ” to guard against any dro o p is all th a t is required.

The patternshop forem an is responsible for sizes, and there are no size sticks used. The crosspiece, on the bottom of the sweep, is for sweeping the bearing for the first set o f arm cores. There is a perm anent plate in the bottom of the pit. This is cleared and the sweep set for height. A single-brick bearing is built round the spindle wide enough to support the tapered end of the arm core, and another a t the centre of the arm and at the rim. On these, when laid down, a facing of loam is swept.

A scertaining th at the eccentric is sound, the process is repeated for the other half, whilst leaving gaps at the sides to accom m odate the bolt lugs.

T he m ould is now ready to receive the arm cores. T he straight edge is again placed in position, using the centre line connecting with the line on the spindle, and weighted down. A templet, the size o f the half nave, w ith a gap to fit the spindle, is placed against the straight edge. The cores are set to this, first the outside ones, the straight edge and tem plet giving the angle for the arm . Then the other cores are fitted in and equally spaced. W hen this is done, the straight edge is lifted aw ay and the arm s on the other half are set. The- only difference here is that, instead o f the straight edge, there is a 1y in. block to place against the arm already

ing upon how much bearing is available. These have to be well secured, as this is the only pos­

sible place fo r iron to escape from the mould.

W hen the building comes up to the crosspiece, a single brick bearing is brought up from the centre o f the arm core, carrying the exact width o f the core, and supporting the centre o f the core on top. This bearing is then loam ed and swept, and the crosspiece is taken off. The next set o f cores is then placed in the same m anner as before, and the building is carried to the top. T hen the bolt lugs are set in posi­

tion, again using the straight edge and a plumb- bob. These are built in. T he bearing for the cope is then set, afte r w hich the face is loamed up and swept. The edge at the top is sharp­

ened up and the bolt lugs draw n out, and the job is ready fo r drying. To effect this, it is

Fi g. 4 .— Sh o w i n g Pr o v i s i o n m a d e f o r Sp l i t t i n g Co r e s.

set. The next arm core is placed against this, the nave tem plet getting the proper angle as before. The block is then w ithdraw n, and leaves the prin t for the nave splitting-core.

T he crosspiece on the bottom is unscrewed and lifted to the next position, form ing the bear­

ing for the next set o f arm cores, and the bo t­

tom nave is now properly finished. T he two distance-piece cores being set, they form a cover core for the bottom nave, and the bottom o f the top one. T he first one is set with the straight edge and a tem plet for the core print;

for the other side, the l i in. block or prin t is again used. T he m oulder now builds in be­

tween the arm cores with brick to form the in­

side o f the pulley. Sometimes he builds brick round the outside of the distance-piece,

depend-covered with plates, an d fires are lit a t four or m ore places according to the size of the pulley. T he fire travels ro u n d slowly, a n d is so stoked th a t it is just burned ou t by m orning.

T he heat is never allowed to be too strong, and the m ould is dry and in a suitable condition for blacking. A fter blacking an d finishing it is given another light firing, and the m ould is as show n in the background of Fig. 3. D uring this tim e, the grooves have been finished, stoved, blackened, and are ready fo r assembly, as are also a cover p la te fo r the rim ; a dry-sand top- p a rt to cover th e nave, w ith the necessary runners, and the cores fo r the split and bore.

In Fig. 4 is show n the space in the grooves for the splitting core. T he p art shown is lowered into the inner p a rt o f the m ould, set

properly, and gauged all round for m etal thick­

ness. T he splitting cores for the bolt lugs are put in from the outside and the back is rubbed up with good stiff loam. The cover plate is placed on the rim; the splitting cores through the nave slipped in and the ends secured; the parts of the core placed in position; the dry sand cover or sometimes a loam plate put in place over the nave, and the assembly is com ­ plete.

“ Cribs ” pu t round the outside are shown at the back of the m ould in Fig. 5; actually they are not deep enough for the pulley illustrated.

A mild steel ring is placed round the bottom and ram m ed. T he crib plates are then pu t in posi­

tion and well ram m ed to the top of the mould.

The inside, w hich is open between the arm cores, is filled in with sand, which is merely tam ped in with a touch round the sides or under

Fi g. 5 .— Mo u l d r e a d y f o r Pl a t e s.

the cores with a shovel shank. The head box is put on and the head m ade up carefully with a skim m er core bedded in ab o u t 8 in. or 9 in.

from the downgates. T he whole is then weighed down, using weights in preference to binders.

T he foregoing is a description of a system of m oulding rope pulleys, and if one considers th at all the pattern tackle is adaptable for m any other sizes; th a t the machining is cut down to a m inim um as the grooves are clean and true; that the dressing costs are negligible, it is obviously a w orth while process. Though the m oulding operations may seem rather in­

volved, they are no t really so. and it is sur­

prising how expert and fast a good m oulder soon becomes on this job.

Inherent Difficulties

There are obviously some difficulties in the m oulding of rope pulleys. The usual practice

until some years ago was to mould the pulley as near the size as possible. It was m arked off and m achined to the given size, due regard being given to strength or rather m etal thick­

ness at the bottom of the grooves, for } in. or fth s of an inch on the diam eter of a 10-ft.

pulley was no t considered a fault.

New conditions arose when an order for a range o f pulleys showed sizes given to two places of decimal such as 59.58 in., 118.38 in., and 63.36 in. over the rope pitch dia. These are three of the actual sizes, and the inspection was to be very exacting. The first pulley of this series, shown in Fig. 1, sent to the m achine shop brought back a report that it would no t machine up to . size. The desired size was 59.58 in. dia. and was to be over size in inside diam eter by | in., but after m ark­

ing off it was m achined to the specified

dimen-Fi g. 6 . — Sh o w i n g Fi n i s h i n g Op e r a t i o n s.

sions. The sweeps were checked and found to be correct to contraction rule of xlf in. per ft.

T est bars showed th at the iron had contracted norm ally. It is thus apparent th at the m ain difficulty to be overcome in pulley m anufac­

ture is th a t o f contraction.

Contraction Problems

T he conclusion reached was that the casting did not contract according to rule, and as the foundry was then m aking another pulley exactly the same size, it was decided to take | in. off the sweeps, which would involve | in. off the diameters, thus reducing the contraction allowance by 50 per cent. The inspector’s report stated pulley was concentric internally but still } in. too large. It was too early at this stage to have a definite opinion, but one could assume that pulleys o f this type cast in loam contracted less than half the norm al allowance

>f 2V iQ- Per ft- T he next pulley, 118.38 in.

R.P. dia. by 12 grooves, was very close to the size o f the one illustrated in Fig. 1. This was the second one cast, and was being m oulded a t the same tim e as the first. T herefore no change had been m ade, and it was produced under norm al practice, with the usual contrac­

tion allowance. The sizes required were 119.63 in. dia. over the flanges, and 114.214 in. inside diam eter. The casting m easured inside the rim from the centre of the nave through the centre

tion allowance. The sizes required were 119.63 in. dia. over the flanges, and 114.214 in. inside diam eter. The casting m easured inside the rim from the centre of the nave through the centre