ALEX DEN OUDEN
Oude techniek en werktuigbouw,
industriŽle geschiedenis en archeologie
Historical engineering and technology,
industrial archaeology and history
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Could you explain the manner in which the bearings of early steam engines (say, first half of the nineteenth century) were constructed? How they were lubricated?
(1) Bearing design
An excellent contemporary description of early 19th c. bearing design is given in "The Cyclopædia; or universal Dictionary of Arts, Sciences and Literature"; Rees, A.; Longman, Hurst, Rees, Orme & Brown, London; 1802-1820. It is a bit difficult to find, however. The most obvious lemma - "Steam engine" - offers no information at all on the subject .... In fact, you have to turn to the following two lemmata: "Machine" and "Mill". These appear in, respectively, Volume 21, Section II (1812); and Volume 23, Section II (1813).
The construction of bearings, pivots, gudgeons, or centres, or spindles, as they are indifferently termed, is a most important point; these parts being the principal seats of that friction which is the destruction of all machinery.
Pivots are always made of iron or steel. Both because these substances are better adapted for rubbing surfaces, and that their strength admits the pivot being as small as possible. The bearing, or bed, to receive the gudgeons or pivots, should be of a softer material, as brass or tin. The bearing should be kept well supplied with oil when at work. ["iron" here is to be interpreted as a generic term, comprising both cast and wrought iron, as well as soft steel (<0.4 carbon, non-hardenable); while "steel" is to be interpreted as hardenable steel, with >0.4 carbon; "brass", finally, is used to denote the copper-tin alloy we nowadays generally call "bronze"]
Hardened steel is a most admirable substance for pivots, which have a great strain to bear, and a rapid motion. The bearing or bed may then also be made of the same material, and this is the only instance where two bodies, having friction against each other, can with propriety be made of the same substance. Soft steel or iron pivots can not be worked against bearings of the same substance, because it is found that the friction and abrasion are far greater than when a softer material as brass, tin, hard wood, ivory, horn &tc. is used. The great difficulty of making hardened steel pivots is the only reason they are not generally used; but there are some cases, in which nothing else can be employed: where steadiness and accuracy of motion are required, and great velocity at the same time. It is necessary that a hardened steel pivot should be fitted accurately with the interior surface of the hardened steel pivot-hole so as to ensure a sufficient access of oil, to prevent the spindle from burning or heating by the friction, when in rapid motion. Such accurately fitted spindles, if getting heated, tend to become fixed in the spindle-hole, due to thermal expansion. The spindle will then rather twist itself off than turn round in the hole. A failure in the supply of oil, even for a moment, can thus be fatal.
The best form of a gudgeon or pivot, is that of a cylinder, with a flat shoulder, to prevent it from shifting its position endways. This form will bear most fairly and steadily. But it is necessary that the socket, or "brass" which contains the pivot, should be made in two halves, and put together with screws. These so that the halves may be screwed closer as the socket enlarges by wearing. This naturally is only an imperfect method, because the pivot can never fit accurately after wear. When the pivot is given a slightly conical shape, it can always be made to fit a worn hole accurately by pressing it sideways into the pocket. In many cases such sideways drift is not allowable, however. Heavy and slow-moving works, such as the gudgeons of waterwheels, seldom have a top brass screwed down over them, their own weight being sufficient to keep them down. These bearings are always true as they wear away.
The old kind of bearing called "brasses" is shewn in fig. 12. A lump of brass a, with a semicircular notch in it, was let into the piece of timber A, which was to support it; and two screw-bolts b b were fixed through the timber, being half received in notches formed in the sides or ends of the lower brass a. The upper brass b, was exactly similar to the lower, and over it a plate of iron d was placed, with two holes through it to receive the two bolts b b and keep them together. The nuts c c upon the tops of the bolts confined the upper brass down, and made all fast and tight.
This kind of brass is not sufficiently strong or steady for all purposes, and, therefore, the bearing shewn in fig. 13 has taken its place.
In this, a a is a cast iron plate, which is held by two or more bolts r r down upon the timber or framing of the mill. This piece of cast iron has two pieces b b rising up from it, between which a piece of brass l is bedded, and has a semicircular notch in it. Another similar piece of brass is fixed into the cast-iron cap-piece B which is fitted into the space between the two pieces b b and is drawn down by nuts upon the two bolts C C. The brasses are prevented from getting out sideways by small fillets projecting from the middle of them, which are received into proper notches in the cast-iron work. in the same manner, the cap B is fitted between the pieces b b with a tongue or fillet, and groove, so that it cannot deviate sideways, and then the bolts have only to draw the brasses down together.
Sometimes a bearing of this kind is fitted up, so that it is adjustable in its position a little: to adjust two toothed wheels to work accurately with each other; or for other purposes where nicety is required. In this case, an iron plate D is bolted down to the framing and the bearing a a lays upon it, the same bolts r r going through both, and also through the framing beneath. But the holes through which they pass in the piece a a are oblong, to admit the whole bearing being adjusted sideways. This is done by two wedges o o inserted at the end of the piece a a, between the two ends of D which rise up for the purpose, as at n n. The bearing rests upon two wedges at g g and is drawn upon them by the bolts r r. By these two wedges it can be raised up at pleasure, and by the other two, at the ends, it can be adjusted endways; and the bolts r r, when screwed fast, hold all tight.
The best way to make the interior surface of the brasses for a bearing eactly true, is to have them cast solid, that is, the two halves of the brass in one, with a notch which very nearly, but not quite, separates them. In this state, it can be bored or turned out true in a lathe. Then it may be sawn in two halves, and put into its place. [to prevent the upper brass from clamping down on the journal when the cap-bolts are tightened, filler sheets to the thickness of the saw cut have to be placed between the two brasses; these can be partially removed to allow for wear]
For larger brasses, the halves are cast separately and fitted together and screwed down and then bored in situ to the exact dimension required. A borer is used, the same as is employed to bore pump barrels.
Very light spindles can be supported on centres. The axis has a small conical hole made in each end of it; and the supports are formed by sharp conical points, received into the holes. At least one of them must be adjustable by a screw, to make it always fit the length of the spindle. It is however usual to make the conical points on the ends of two scews, either of which may then be adjusted. The same thing may be accomplished by making conical points at the ends of the spindle, and forming the holes for its reception in the ends of the two fixed screws. This is the most perfect of all methods, but it is not adapted to bear any great strain, because the screws will get loose. Also, these constructions do show sideways drift with wear.
The pivot at the lower end of a vertical shaft usually has to sustain a great weight, as in a horsewheel or gin; or in a windmill. Most properly it is made of a hemispherical figure, and received into a properly shaped cavity. These pivots are also made with a cylindrical bearing with a flat end supported on a flat plate. But it is difficult to keep oil supplied to them, as the great weight of the upright axle presses the oil out from between the acting surfaces, and the flat end burns. To avoid this, some mechanics make a spiral cleft across the flat face of the gudgeon. This getting full of oil, is constantly supplied to the acting surfaces.
In Abraham Rees's magnum opus, there's hardly any information to be found on lubrication of bearings as such. Oil is mentioned, of course, particularly for fast-running journals; and tallow for slowly-moving ones. Further details are lacking.
First let's consider the topic of "speed". What kind of engine speeds were common in the early 19th century? What constitutes "fast-running"? Well, most engines then were beam engines and they operated at anything from 15-20 revolutions per minute. Watt's sun-and-planet motion doubled the speed of the main shaft to 30-40 r.p.m.; but by 1800 this mechanism was obsolete and all beam engines had regular crank mechanisms. A second class of engines, beside beam engines, are the small high-pressure direct-acting steam engines, mostly vertical at that time. These run at speeds of up to 30 r.p.m.
Speeds of up to 30 r.p.m. were known long before the advent of the steam engine, in windmills and water mills. Lubrication with ordinary animal tallow was common for these. To improve lubrication, the tallow could be mixed with oil. This however destroyed one great advantage of tallow: its stiffness. Tallow would not easily run out of a bearing. Oil did.
In the early 19th c. beam engines, slow-moving as these were, there was no great need to deviate from mill-practice. Nearly all the engine's bearings were lubricated with tallow, as were the hempen piston and piston-rod packings. Only the main bearings required more advanced techniques. These were lubricated with oil and to this end, they were provided with oil cups, with cotton wicks; or, for larger engines, with oil tanks on top of the bearing caps, with adjustable drip feeds. The small direct-acting engines of the early 19th c. were usually lubricated in the same way as the beam engines and this proved to be one of their weak points. They required (too) much attention and special care from the engineer.
By the way, what kind of oil is Rees referring to? To answer that question, we'll have a look at the lemma "Oil" in the Cyclopædia. This appears in Volume 25, Section I (1813).
Most animals contain oil and fat. The fat investing the kidneys of quadrupeds is called suet or tallow, and is the hardest and most solid of any. The next in hardness is the fat of the bones; and the fat in which the muscles are imbedded is the next in degree. The fat of the hog, called "lard", is the least solid. The fat or oil of fish is almost always fluid at the common temperature.
All the animal oils (and fats) belong to the class of unctuous or fat oils, none of them being either drying or capable of being dried by other substances. They are of very great economical importance. They are used as food, and in medicine as the basis for onguents; they are largely employed in the manufacture of soap; and also for burning either in lamps or in the form of candles. Fish oils always are rancid and mostly thick and glutinous. This renders them less suitable for burning in lamps. [you see, no mention of animal oil for lubricating purposes ....]
Vegetable oils are divided into two classes: (A), Volatile oils and (B), Fixed oils.
Volatile vegetable oils are of great use in medicine and are considered stimulants. They are also used as perfumes; and in the composition of varnishes and paints. [due to their volatility, the essential oils are of no interest for lubricating purposes]
Fixed vegetable oils, in contrast to the volatile vegetable oils, cannot be directly volatilized without decomposition. When these fixed oils are boiled, a vapour is disengaged consisting of oil, carburetted hydrogen and carbonic acid. When finally every thing volatile has been driven off, nothing remains in the vessel but a little charcoal. The oil that was driven off, when condensed, is lighter, less viscous and more volatile than the original oil. By continuing this process of boiling and condensing, all oil can be made to disappear, only some charcoal remaining.
The most common fixed vegetable oils are procured from the cotyledons of rape seed and linseed. The seeds are beaten to a pulp and then heated to a certain temperature. The mass is then subjected to the action of a strong press, to force out the oil.
Fixed vegetable oils are divided into two sub-orders: (a), Drying oils and (b), Fat oils.
Drying vegetable oils, when exposed to the air for a certain time, gradually acquire properties similar to those of horn by the action of oxygen, so becoming a concrete, flexible and hard substance.
The two most important oils of the drying kind are those extracted from lin-seeds and hemp-seeds. Both hempseed oil and linseed oil are of great use for paints and varnishes and making printers' ink. [it will be clear, that drying oils cannot be used in bearings, as they would quickly gum these up]
Fat vegetable oils, when exposed to the air for a certain time, first become viscid, and ultimately concrete, having the appearance of animal tallow and in every respect similar to this substance. The exposed oil will be more or less hard, according to the time exposed; it at the same time acquires a disagreeable odour, to which we give the name rancidity. This change is more rapidly brought about by dilute nitric acid, or any substance which affords oxygen.
Of the fat vegetable oils we may mention the two most important, these being oil from rape seeds, known as rape oil; and that of cole-seeds. Rape oil is used in many instances in bearings to lessen friction. It has however a decided action upon any iron gudgeon, as we see in the axle-trees of carriages. Cole-seed oil is primarily used by wool-dressers, in order to preserve the wool from the attacks of moths; and also by leather-dressers, to make leather supple.
An empyreumatic oil can be obtained from pit-coal by destillation. It has many properties in common with oil of turpentine or the oil of common tar. [this stuff is unsuitable for lubrication due to its volatility]
Oil of the earth, Oleum Terrae, is a thick mineral fluid with the consistence of a thin syrup, very little transparant, and of a strong penetrating smell. It oozes out of the cracks in rocks, in several parts of the island of Sumatra and some other parts of the East Indies, and is much esteemed there in paralytic disorders. [no practical technical application is known at that time; the oil also is very rare in Europe]
So .... we conclude, that Rees was referring to rape oil for the lubrication of bearings.
(3) In the 1860s and 1870s
In fact, this situation (tallow and rape oil) did not change much until the discovery and exploitation of those vast deposits of mineral oils at the end of the 19th and beginning of the 20th century. Take for instance, Grothe's famous "Mechanical Technology" of 1866. The descriptions under the chapter "Oil" are nearly identical to those of Rees ....
The same, however, cannot be said of steam engine design. In the 1820s, a quick evolution sets in and by the 1850s, the design of beam engines has much improved. They now are provided with cast iron beams and frames. They can therefore be run at somewhat higher speeds, say 25-35 r.p.m., depending on size. Direct-acting stationary engines by now are available in several types: vertical (flywheel at top); inverted vertical (cylinder at top) and horizontal. Speeds vary with the type, say up to 45 r.p.m. for vertical; 55 r.p.m. for inverted vertical; and 35 r.p.m. for horizontal engines. In marine practice, there is a wide gap between the behemoths powering gigantic paddlewheels (at less than 10 r.p.m.) and the compact and fast-running inverted vertical screw engines (up to 60 r.p.m.). In locomotive practice, running speeds are still quite low, due to difficult design conditions and maintenance; hence the extremely large "drivers" (driving wheels) with diameters of over 2 metres!
So, all-in-all, speeds of 50-60 r.p.m. were not uncommon. These require oil lubricaton. Rape oil; there wasn't anything else. Although it was not really satisfactory. We'll have a look at two text-books for (aspiring) engineers, dating from the 1860s and 1870s, to sketch the state-of-the-art.
In 1861 ....
Firstly: Bourne, J.; A Catechism of the Steam Engine; Longman, Green, Longman and Roberts, London; 1861.
Question 742: Have you any information to offer relative to the lubrication of engine bearings?
A very useful species of oil cup is now employed in a number of steam vessels, which, it is said, accomplishes a considerable saving of oil, at the same time that it more effectually lubricates the bearings. A ratchet wheel is fixed upon a little shaft which passes through the side of the oil cup, and is put into slow revolution by a pendulum attached to its outside. In revolving it lifts up little buckets of oil and empties them down a funnel upon the centre of the bearing.
Instead of buckets, a few short pieces of wire are sometimes hung on the internal revolving wheel, the drops of oil which adhere on rising from the liquid being deposited upon a high part set upon the funnel, and which, in their revolution, the hanging wires touch. By this plan, however, the oil is not well supplied at slow speeds, as the drops fall before the wires are in the proper position for feeding the journal.
Another lubricator consists of a cock or plug inserted in the neck of the oil cup, and set in revolution by a pendulum and ratchet wheel, or any other means. There is a small cavity in one side of the plug which is filled with oil when that side is uppermost, and delivers the oil through the bottom pipe when it comes opposite to it.
Question 743: What are the prevailing causes of the heating of bearings?
Bad fitting, deficient surface, and too tight screwing down. Sometimes the oil hole will choke, or the syphon wick for conducting the oil from the oil cup into the central pipe leading into the bearing will become clogged with mucilage from the oil.
In some cases bearings heat from the existence of a cruciform groove on the top brass for the distribution of the oil, the effect of which is merely to leave the top of the bearings dry. In the case of fully revolving journals the plan of cutting a cruciform channel for the distribution of the oil does not do much damage. In other cases, as in beam journals, with short stroke reciprocal motion, it is most injurious. The right way is to make a single horizontal (longitudinal) groove along the brass where it meets the upper surface of the bearing, so that the oil may be all deposited on the highest point of the journal. This channel should, of course, stop short a small distance from each end of the brass, otherwise the oil would run out at the ends.
Question 744: If a bearing heats, what is to be done?
The first thing is to relax the screws, slow or stop the engine, and cool the bearing with water, and if it is very hot, then hot water may be first employed to cool it and then cold. Oil with suphur intermingled is then to be administered and as the parts cool down, the screws may be again cautiously tightened, so as to take any jump off the engine caused by the bearing being too slack.
The bearings of direct acting screw engines require constant watching, as, if there be any disposition to heat manifested by them, they will probably heat with great rapidity, from the high velocity at which the engines work. Consequently, every bearing of a direct acting screw engine should have a cock of water laid on to it, which may be immediately opened wide should heating occur. It is advisable to work the engine constantly, partly with water, and partly with oil, supplied to the bearings. The water and oil are mixed by the friction into a species of soap, which both cools and lubricates, and less oil moreover is consumed than if water were not employed. It is proper to turn off the water some time before the engine is stopped, so as to prevent the rusting of the bearings.
In 1873 ....
And secondly: A catechism of High-pressure or Non-condensing Steam Engines; Roper, S.; Claxton, Remsen & Haffelfinger, Philadelphia; 1873.
Rules for the care and management of the steam engine
The oil or tallow should never be admitted to the cylinder until some time after the engine is started and the drip-cocks in the cylinder closed, as the tallow would otherwise be carried out by the condensed water and lost.
All the parts of the governor should be kept perfectly clean and free from the gum formed by the use of inferior qualities of lubricating oils.
No more oil should be used on an engine than is absolutely necessary, as it is not only a loss, but often detracts from the appearance of an engine and greatly interferes with its free and easy movement, from the accumulation of gum and dirt on its working parts.
How to treat your bearings ....
In case the crank-pin should heat -- which is a common occurrence with engines having a narrow bearing on the pin, but more particularly with engines that are slightly out of line -- remove the key and slacken the strap and box of the big end bearing; then pour in some flour of sulphur with a liberal supply of oil; then adjust the key, and the trouble will generally disappear.
If the pillow-blocks of an engine should heat badly, remove the caps and pour in a good supply of pulverized bath-brick and water while the engine is in motion; after doing this for some time, wash out with oil and wipe the bearing clean with cotton waste, and it will be found to give permanent relief.
In case any of the bearings of an engine should heat through the accumulation of matter deposited from the oil used; or sand, grit or whitewash as used in polishing steel engine parts, being dropped into the bearings: use a strong solution of concentrated lye with oil when the engine is in motion.
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