Something About Oil Grooves

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Modified on 2015/10/18 08:33 by Joel Havens Categorized as Bearings

» Something About Oil Grooves

By Charles J. Mason

The proper lubrication of the journals and other wearing surfaces of machinery depends on not only upon the quality and quantity of the lubricant which is used, but also upon how well it is distributed over those surfaces in question. With proper distribution, less oil will prove effective than would a greater quantity not so well distributed, and so economy enters into the consideration of the question.

In large power plants, the principal journals and wearing parts of the engines are usually supplied with oil by the gravity system. This consists of an elevated tank which is supplied with oil by a pump especially for the purpose. The oil is conveyed from the tank to the various cups about the engines through a system of pipes. After the oil leaves the bearings it flows into collecting pans, thence into a receiving and filtering tank, whence it is pumped into the elevated tank referred to.

When this system is employed and all the apparatus is free from leaks, very little of the total quantity of oil used is lost, and such loss is replenished by the addition of new oil to the system from time to time. The oil is fed into the cups, and from them to the surfaces to be supplied, in a continuous stream, thus insuring proper distribution. Because of the rapidity, and consequently the quantity of the flow, the oil leaves the bearings almost as clear and clean as when first supplied.

Although such a system as has just been briefly described is efficient in all particulars, it should further be aided by having the grooves which are to conduct the oil over the surfaces, properly cut, both with regard to direction and extent.

In the smaller plants it would be too costly to install and maintain the gravity system of oiling, so instead, the oil cups are filled at intervals by hand from a feeder. By this method the oil is fed from the cups by drops; so many drops per minute, the number being determined by conditions. The oil remains in the bearing for a longer period of time than with the gravity system, and so it does not come out quite as clean.

As before stated, it is of great importance that the oil be properly distributed over the surfaces which are assumed to be in contact with each other, and between which friction exists. In fact, it is to prevent actual contact between the parts that oil is required at all; it should be clear, then, that a proper distribution is necessary to attain the desired end.

The oil grooves in the various parts of engines and other machines are at first cut in the shop in which the machine is built. Although the men who do this work are supposed to understand just how it should be done to attain the best results, it frequently happens that the work is so laid out and executed that the results are far from satisfactory when viewed from any standpoint whatever.

While overhauling and the renewing of parts is going on in a plant, the engineer himself generally desires to have something to say, if not to actually do the work himself, about the cutting of oil grooves. It is natural to suppose that he would know what is required better than the machinist, whose work ends when the machine has been installed.

As all parts of an engine should be made with an eye to symmetry, so, also, should the layout or design of the oil grooves be as neat as is consistent with the other requirements. It is painful to the eye to view a ragged edged, unevenly cut groove in a brass or on a surface, and the fact that the work may be seldom seen is no excuse for the existence of such poor workmanship. Neatness in design and execution counts for a great deal in the mechanical arts in these days.

Just how oil grooves should be cut in the different parts which have them depends upon the direction of motion, whether the surfaces to be lubricated are vertical or horizontal, and the number and location of the cups which are to supply the oil.

We will first consider the journals and bearings of a horizontal shaft, such as those of an engine. Sometimes it is found that grooves are cut in the upper half of the box or bearing only, no such provision having been made for the lubrication of the lower half, reliance being placed on the probability that the oil will work down and around the entire surface. While it is probable that the oil will find its way to the bottom, especially if there be any degree of looseness between the shaft and its bearings, still it is better and safer to have grooves in that part also.

If the bearing has one cup only, which is placed in the center of the cap or binder, the grooves should be laid out and cut as shown in fig. 1. First, a pocket is cut in the sides of the bearing, or box, as it is sometimes called, as shown at A, in fig. 1, to a depth of 1/8 inch, and extending downward to a distance, the proportion of which to the whole bearing is as shown in fig. 1. Although there is no hard and fast rule for the extent of the oil pockets, yet one that will serve the purpose is to cut a strip of tin or other thin metal to a length corresponding to the diameter of the journal, and in width about 1 inch. This strip, shown in dotted lines at B in fig. I, is laid in the bearing equidistant from the sides, the ends of the strip of tin indicating the distance from the edge to where the pockets are to be cut. It can be seen that the two pockets together occupy nearly one-third of the entire surface of the bearing, the remaining portion being sufficient to carry the journal, if it is otherwise properly designed.

Figs. 1 & 2. Forms of Reservoir and Methods of Cutting Them

The outline of the pockets is cut as shown at C, in fig. 2, by using a grooving chisel, the same as used for the grooves themselves. The metal within the bounds of this is removed by using a cape chisel, at shown at D, fig. 2, and finishing with a keen edged flat chisel. A file may be used to give the surface a finish, filing in the direction of the length of the box. Should the box be lined with Babbitt metal, a scraper will serve the purpose better than a file.

It should be observed that the pockets do not extend lengthwise from end to end of the box, a narrow margin being left to prevent the oil from quickly flowing out, confining it instead so that it may be conducted to the lowest part.

The grooves are cut diagonally, as shown in fig. 1, in both top and bottom boxes; the intersection of the grooves in the top box occurring at the point where the oil cup hole is located. These grooves should be cut of ample width and depth, in proportion to the size of the journal; due allowance must be made for the wearing down of the shaft, which of course reduces the size of the grooves, and if at first they were cut too shallow, would entirely obliterate them.

Grooves laid out as just described serve the purpose in every particular in the kind of bearing under consideration. It can readily be imagined that the oil will be carried to every part of the bearing, while at the same time the least possible amount of metal has been removed to accomplish the result. This item alone is worthy of consideration in bearings which are closely designed, requiring all the surface they contain to support their loads without undue friction.

It might be argued, and reasonably, that such a bearing could afford to lose some of its surface in order that a more liberal supply of oil might be fed to it, which would, in effect, more than balance the loss of bearing surface. But it is still true that the less metal removed consistent with conditions, the better will the purpose be served for which the grooves exist.

Cut your grooves as evenly and as smoothly as possible; remove the edges raised by the chisel during the operation. By applying a straightedge longitudinally, or, better still, if the box can be placed on its journal and rocked to and fro, the "high spots" will be revealed. A very thin coating of marking material, such as red lead mixed with lard oil, applied to the journal, will show just where the bearing takes place, and where it should be eased off. A few alternate "tryings" and "scrapings" will soon restore an even surface to the bearing. Sometimes a chamber is cut instead of the pockets before referred to. This method is shown at E, fig. 3. Although not so good as the pockets, it still acts in that capacity, but to a lesser extent. For small bearings, however, the chamfer is sufficient; besides, it does not take so long to cut.

Figs. 3 & 4. Oil Grooves in Top and Bottom Boxes

In quarter box bearings grooves should be cut as shown in fig. 4. The edges of the box should also be chamfered for the purpose explained.

Large bearings are usually supplied with oil through three cups, which require a little different design of groove. In fig. 5 is shown the top half of such a bearing, with the layout of the grooves; in fig. 6 is shown the quarter box with its grooves, which would accompany a three-cup bearing. There should always be a groove leading from each cup, no matter how many there be. Otherwise, in a neat fitting box, the oil will not get away fast enough, and possibly not get away at all until it overflows the cup outlet pipe, which screws into the binder of the bearing, and contains the sight glass.

Figs. 5 & 6. Showing Grooves in Top and Quarter Boxes

We sometimes see boxes with a longitudinal groove cut in them, as shown by the dotted line in fig. 5. Alone, it will not successfully fulfil the purpose for which it is supposed to exist. To add it to those grooves already there would be superfluous, as the oil will naturally flow downward and not along, when there is an outlet such as our grooves afford. Of course there are cases where such a groove is about the only kind that could be conveniently cut, such as in long, solid bearings made in one piece and with small diameter, like those of a fan blower. Better this groove than none at all, for the oil will at least have a chance to wet the surface of the journal as it revolves. A longitudinal groove tends to weaken a box along its line, and under certain conditions the box would crack at that place. Especially is this liable to happen with a box which is further weakened by having three holes drilled for as many cups.

In figs. 7 and 8 are shown respectively a groove cutting chisel, and a half round bent end scraper for touching up the box after the grooves have been cut.

Figs. 7 & 8. Showing Forms of Chisel and Scraper

In a future issue we will take up other parts in which oil grooves are cut.

Oil grooves are the means by which the distribution of oil is accomplished, conducting it from the point of entrance to the furthermost portion to be oiled. With any system of oiling the grooves should be laid out and cut with this object in view, but particularly when the quantity of oil to be fed per unit of time is limited. If care is not exercised in this matter, it is quite possible, under certain conditions, to have one part of a journal well supplied with oil, while none whatever may be reaching some other part, in consequence of which it becomes hot, and will continue so until the proper remedy is applied.

Part 2

Oil grooves for the bearings of vertical shafts and valve stems should be laid out somewhat differently from those of horizontal bearings recently described, because of the direction of the flow of the oil. In this case, the oil is received at the top end of the bearing and flows downward and around the journal until the bottom is reached. A reservoir is bored out at the top, as shown in fig. 1, which represents a half box.

It should be noticed that the grooves do not quite reach the bottom of the box, nor is it intended that they should; for then the oil would not be retained sufficiently long to do its work. In fact, the grooves in any bearing should not entirely run out.

Fig. 1. Oil Grooves in Box for Vertical Shaft

The design of groove in fig. 1 is suitable for a shaft which revolves in either direction, or for valve stems which have a vertical movement only. Sometimes the latter runs through a bush, which is a bearing made in one piece only, instead of two, as is generally adopted. When such a bush is used instead of an adjustable bearing no oil groove is required, because there is always a certain amount of play which will permit the oil to circulate.

Fig. 2. Oil Grooves in Wristpin

It is not desirable to cut oil grooves in the journals of shafts, nor in pairs of any kind unless the bearings of such are of a design which precludes cutting grooves in them. Not because the journal might not run well if a groove were cut in it, but because it is not desirable to break into the enameled surface, and, besides, it would have a tendency to weaken, if ever so little, the part in which it is cut. But in crankpins and crosshead wristpins which are supplied with oil through a hole drilled from the surface radially and meeting a centrally and longitudinally drilled hole, a small groove should be cut to give the oil a start to flow in four directions. Care should be taken, however, to round off the edges of such grooves to prevent any tendency to cut the boxes. Fig. 2, views a and b, shows how these surface grooves are cut in a wristpin, and the general arrangement of the cup and oil holes.

The brasses for crankpins should be grooved to meet conditions as to whether the engine is vertical or horizontal; this also applies to wristpin brasses as well. In the vertical type of engine diagonal grooves for the top and bottom brasses of both pins are all that is necessary to properly distribute the oil.

Fig. 3. Oil Grooves in Brass for Vertical and Horizontal Engines

For horizontal engines, the grooves should be cut as shown in fig. 3, view b; not extending below the center line, for the oil will seek and eventually find its way to the bottom. It should be noticed that the individual channels run diagonally or nearly so. This is as it should be, except where peculiar conditions exist, when the plan may be departed from. But in general, the grooves should not run parallel with the direction of motion, nor even at right angles to it.

As the brasses of vertical engines require differently laid out grooves from those of horizontal engines, so also do the different styles of guides for the crosshead require a particular form of layout for the groove.

Fig. 4. Grooves in Guides and Crosshead Feeds

First, consider horizontal engines: There are three different forms of guides, as shown in fig. 4, a, b, and c illustrating the face and sectional view of each.

In the V-shaped guide, fig. 4, a, the grooves should be cut from the upper edge, or side, to the bottom, and they should run in a direction almost parallel to the center line, longitudinal, of the guide. The idea which I wish to convey is that the groove should be at such an angle to the center line that the oil will have a tendency to remain in it quite a little while, although at the same time it is gradually approaching the bottom. This condition could not be realized if the groove were cut at an angle which approaches a right angle to the center line, because the groove would be so steep that the oil would immediately flow to the bottom.

A portion of the oil is wiped off every stroke the crosshead shoe makes over the grooved surface, and so continually keeps the shoe moist, as long as the supply of oil is kept up.

As shown in fig. 4, a, face view, the grooves are elongated diamonds, the extent of the elongation being determined by the length and width of the guide face. With this form of groove, perfect lubrication is insured, especially if a heavy bodied oil is used, as, for instance, castor oil. I have seen crosshead guides in vertical engines kept cool by using castor oil, when no other kind that was tried would accomplish like results.

In the foregoing paragraphs we have assumed that the crank "runs over"; that is, the crank turns in a direction which causes the crosshead to press harder against the bottom guide than it does against the top guide. An engine "running under" causes the crosshead to press harder against the top guide. It is well understood why the difference exists. Now, should the engine be of the run under type, then the oil grooves should be cut in the face of the upper shoe of the crosshead, instead of the upper face of the guide. By having the grooves in the shoe a reservoir will be formed to retain the oil, which could not be said if they were cut in the guide face.

While it is not absolutely necessary to cut grooves in the bottom guide face of a "run-under" engine, still it is not detrimental to the engine in any sense, to do so. Just as the crank is passing each center the crosshead drops to the bottom guide and then it will be found that grooves in the lower face will materially aid in the proper lubrication of the parts. It is not advisable to cut oil grooves in the crosshead shoe, because, as a general thing, there is none too much surface to spare, all of it being required for wear without undue heat. We have to depart from this suggestion in the case of the upper shoe in the "run under" engine, for the reasons before given.

Seldom, if ever, do we see engines turned out from the works where they are constructed, with the different parts oil grooved, as here described. But that fact in itself is no criterion to be guided by when we look into the governing reasons.

In the first place it is not considered of sufficient importance to spend much time either in laying out or cutting the grooves; very frequently this matter is left entirely to the individual tastes of the persons doing the work, and sometimes the results are far from satisfactory, as many operating engineers have found when taking charge of a new plant. Good machinists are able to construct, erect, and install engines and other machinery, but of the details and requirements of operation of such, it can hardly be said that they arc as familiar as the operating engineers are who make a specialty of such work. The nature of the engineer's duties causes him to be observing of what is taking place around him, and further, to acquire an ability to look into things as well as at them.

The bored out guide, circular in section, shown in fig. 4, b, may be treated in a similar manner to the V guides just described. The grooves can be marked out by using a strip of flexible sheet metal to conform to the surface of the guide and against the edge of which a scriber or other marker is held while tracing the proposed course of the groove. Sometimes a flexible steel scale will answer the purpose better than anything else. In any case the grooves should be neatly laid out and cut in a workmanlike manner so that they will present a good appearance, as well as be sufficient for the purpose for which they exist.

In some makes of engines the guides are flat, as shown in fig. 4, c. The diamond shaped grooves are also applicable to this style of guide. In marine engines of the vertical type the guides are usually flat with housings at the sides, which are secured by screws or tap bolts. With such an arrangement it is possible to plane a number of grooves across the face of the guide, at right angles to its length, and spaced so that the shoe of the crosshead will cover two grooves at least. The grooves may be 1/8 inch deep and from 1/2 inch to 1 inch in width, according to the length and width of the guides. I have been in ships whose engines were equipped with guides like these, and I cannot speak too highly of the method of grooves for distributing the oil.

The oil is fed from the top of guide, fig. 4, E, and flows downward into the cross grooves.

As the grooves become filled to overflowing the crosshead picks the oil up and spreads it out over the entire surface at every stroke. The tendency of the crosshead is to sweep the oil off the surface, but owing to the presence of these grooves the oil is swept into them instead, and of course the surface of the crosshead shoe receives oil while passing over the grooves. As the grooves are always full while the engine is in motion, both surfaces are constantly and thoroughly lubricated. At the bottom end of the guide there is also a box attached which contains oil, and into which is dipped once every revolution, a comb (so called from its resemblance to that article) that lifts the oil from the box and drags it up and over the guide face, depositing a liberal quantity in the grooves. The method of attaching the box and comb is shown in fig. 5. Grooves like these will retain the oil longer than will any other that could be cut, and this is exactly what is required.

Fig. 5. Showing Application of Oil Comb to Crosshead of Vertical Engines

If there were no grooves at all in a vertical guide, the surfaces would have to depend, for lubrication, upon what little oil would work its way down between the shoe and the guide. Even if the oil were supplied top and bottom, as just described, there would still be a portion of the stroke that would be almost dry, especially if the crosshead were neatly fitted between the guides.

We have seen, then, that the proper function of the oil groove is to distribute and retain the oil in bearings and other parts of machinery where friction takes place, and that they should be designed with this end in view.

Information Sources

The Engineer, 01 Oct 1902, pgs. 664 & 665; 15 Nov 1902, pgs. 753 & 754

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