This section is from the book "A Practical Treatise On Friction, Lubrication, Fats And Oils", by Emil F. Dieterichs. Also available from Amazon: A practical treatise on friction, lubrication, fats and oils.
When a cylinder becomes partly worn, or ridges and scars are cut on its bright surfaces, or a partial wearing of the piston rod takes place, it is absurd to lay such results to the oil. Oil cannot cut metal, the cause of such injuries being a purely mechanical one; some parts are loose or out of line or otherwise defective in construction, and no amount of oil or fat of whatever quality is capable of preventing gradual increase of the injury and final necessity for extensive repairs.
No kind of oil or fat can cut ridges or scars in metal. It requires metal or inert substances, such as silica, lime, emery or mica to do it. They do it suddenly and violently when dry and by themselves, and they do it slowly and silently when intermixed and saturated with oil or fat. The idea that mixing silex, sulphur or plumbago (graphite), etc., with oils or fats, to give them increased lubricating power, is erroneous. These inert matters have nothing whatever to do with the lubricating, which is alone done by the oily part of the compound, leaving the inert matter behind, to accumulate on the bearings, and with every new application, by and by will fairly choke the cylinder and the valve-chest.
All fatty oils and fats, without exception and of however excellent quality, either alone or compounded with mineral oil, when applied as lubricants, are decomposed by the steam and by the frictional heat they absorb, and their lighter constituents vaporize and leave the heavier ones to form gummy deposits with the fine metallic particles, the result of abrasion, and with the impurities in the water used.
Such deposits cause dragging of the machinery and waste of power, accumulate gradually in crevices and fill the smallest interstices in the surface of the metal; they settle all around the joints and are found in abundance behind the rings and piston.
The injurious action from the use of tallow in cylinders is well known. The action of the stearin on the metal increases the abrasion, and injury is wrought slowly but entirely uniformly, and by no means in cutting ridges and scars in the iron.
When tallow or very impure fatty oils have been used, or they have been further compounded with inert matter, such as plumbago, etc., the accumulations are still more abundant and detached parts are frequently found worked into marble-like balls by the continuous churning motion of the piston ; they dry against the heated metal and gradually assume the hardness of stone or iron.
Lubricating oils which are not so constituted as to decompose readily and form gummy deposits, are capable of softening and gradually dissolving such hardened deposits. Some particles partly dissolved become detached and get between the piston and the cylinder and commence cutting and scraping into the smooth sides of the latter. A groaning noise gives audible warning and, if the impediment is not removed or relieved by speedy softening and dissolving with more copious application of better oil, the injury inflicted may become very serious and may necessitate the stopping of all machinery and require expensive repairing.
There are also numerous instances on record where small particles of metal broke off from worn-out springs with too sharp and not properly rounded edges, or from careless keying of the valves, and finding their way between the sides of the cylinder and piston, cut heavy ridges in the iron. It is ridiculous to blame the oil for it.
Another source of injury in cylinders, otherwise perfectly clean, arises often from the use of poor packing, overdone with sulphur or overheated in vulcanizing, which has become brittle from exposure and age, or being burnt from long contact with the heated metal. The ragged edges of such packing will become detached, contaminate the oil, and cause injury.
If a babbit or other metallic lining has been placed in a bearing in a bungling manner, or small particles of the metal have broken loose from a raggedly bored hole through which the oil is to be applied, and such particles find their way between the moving parts, cutting and scarring of the metal cannot be prevented with the best of lubricants.
If an employee forgets and fails to apply oil in proper time, and the parts run dry, get heated and cutting takes place, the trouble is generally attributed to the lubricant, but all this proves that it is impossible for an oil to "cut metal," but that impurities in oils, accidentally or intentionally combined with inert matter, will do it.
Acid in oil is often regarded as the cause when cutting of metal has taken place. That can be the cause when fatty oils are used for lubricating as they are liable to absorb oxygen from the atmosphere and, becoming rancid, develop their constituent fatty acids which act injuriously on metal. But acid cannot be in petroleum oils unless left there from faulty washing, or when having been compounded with crude fatty oils. By the process of the manufacture of the Valve-Oleum oils, these fatty acids fixed to a base have thereby been rendered innocuous.
The parts of machinery where oil is used for lubricating should be kept clean and carefully examined, to see if they are in proper condition; that no foreign matter has by chance got between the moving parts or is liable to do so; that keys on wristpins and bolts on bearings, hangers, etc., have not gradually been loosened by the constant jarring of the machinery; that flooring has not settled under heavy weight and thereby the shafting, attached to it, been put out of line or otherwise interfered with.
All these points are generally only thought of after some accident has happened or warning is given by a groaning or squeaking noise, and when some parts are found heated and cut, and the blame is unjustly laid to the oil, until investigation reveals the real cause.