Opinions from Others.
Page 14
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Fire-engine Tests at Glasgow.
The Editor, THE COMMERCIAL MOTOR.
11,124] Sir,—With reference to Messrs. Merryweather's letter re the above in your last week's issue, we are quite in agreement with them that it is not desirable to enter into a controversial correspondence with competitors, but there is one point which demands our reply—that regarding the official deep-lifting tests at Glasgow.
Messrs. Merryweather state that " if the Hatfield pump had been filled with water from a priming tank, as Messrs. Halley's was, it would have exceeded the litt which their pump (H alley's) accomplished." The point we specially wish to emphasize is that we do not require to use the water from the priming tank in order to get a deep lift, nor have we ever so done, and, therefore, we must assume that Messrs_ Merryweather are not acquainted with the details of our system. The water tank carried on the Halley machine is not primarily a priming tank, but a first-aid tank, which can be utilized for fire-extinguishing purposes at small fires, at which much time might unnecessarily be lost, and damage caused by the delay due to the coupling of the suction hose to the street ME ins or other source of supply.—Yours faith fully, ALLEY'S INDUSTRIAL MOTORS, LTO.
(ieo. H. HALLEY, Managing Director.
Ball Bearings and Their Lubrication.
The Editor, THE COMMERCIAL MOTOR.
[1,1251 Sir,-Part of Colonel Crompton's reference to this matter in connection with Mr. T. B. Browne's paper is well worth noting. His point,that the sole value of the " lubricant " in the ball bearings is as a preventative against corrosion, and not as a preventative of metallic contact between the halls and ball race, was emphasized several yeare ago by that famous British maker, The Hoffmann Manufacturing Co., Ltd., of Chelmsford, for I have by me ono of that company's old lists, in which it is stated : " Ball bearings require very little lubrication, but it is eetremely important to keep all the hardened and ground 6teel surfaces in contact with grease, as they quickly rust if this is not done. We therefore recommend that the housings of all bearings which are isolated be fitted with a Stauffer lubricator, so that grease can he oceasionally forced into them. This ensures the ball race being kept free from rust, and the grease also acts as a barrier at the sides of the housing to prevent dirt and moisture getting in," This plainly shows that the Hoffmann Co. was -cognisant of the true position at that time.
Tt will be clear to anyone who keeps in mind that t 1 w bearing surface of a true sphere is infinitely small, and who also has a knowledge of the physical properties of lubricants, that no lubricant can prevent the contact of such bearing surface. The load per unit of area of contact is in theory infinitely great, and the question of the elasticity of the ball and of the race is not sufficient in this case to justify departure from the above statement.
Colonel Crompton states that in his opinion the corrosion is due to the presence of water in the form of minute globules_ This, however, I cannot conceive to be possible -at least, except for a very short time, unless water were on purpose or inadvertentlyfrom time to time added to ths lubricant, because, so far as my knowledge goes, no lubricant will in the natural course of things continue to contain water in sueb form. It must be borne in mind that all oils and grease, like most other forms of matter, have the property of taking up water in a true solution (that is to say, not in separate globule form) until they reach a. certain point of saturation, and that any water that is in excess of that point of saturation would in due course evaporate to the atmosphere: in the case of the ball bearing, owing to the rapid changes of the surfaces of grease exposed, such loss of mechanically-present water uld be very rapid. My point is that, even were water purposely churned up with the lubricant, and put into a ball bearing, all that water would evaporate until only the water of saturation was left, and no water in a globular form would remain.
Then, as to the tendency which oils and greases have to take up and to retain such water of saturation. I may say that I have in the past made exhaustive experiments, and have found without exception that fatty oils, i.e., legetable and animal oils, always absorb a greater percentage than do mineral oils; and, a-gain, the mineral oils vary amongst themselves in this respect. For instance, an oil from Texas will absorb 3 or 4 per cent, more than a Rus.sian product having about the same viscosity. As to fatty nits, the greater the amount of free fatty acid present, the greater is the capacity for absorbing water. That is to say, Colonel Crompton's lard oil with 2 per cent, of fatty acid will take up certainly far more water than the ordinary mineral oil, and also more than it would if it contained only 0.2 per cent, of fatty acid. Another objection to the use of fatty oils is that, on exposure to atmospheric conditions, the generation of acid continues, and, quite apart from the affinity which this acid has for water, it gradually exercises a minute etching effect on the metal, and any roughness of surface resulting from such etching allows wear to take place, owing to the crushing of the tiny projections thus formed.
On a ball bearing, I have come across three distinct classes of corrosion: (1) the ordinary brown rust, due to atmospheric influences, and in some eases due to the aecidental or careless admission of water—nut dissolved as water of saturation in the lubricant ; (2) the etching effect, due to the inferiority of the lubricant, such as the presence of free acids; and (3) the peculiar black marking, which starts on the race at some slight distance from the actual point of contact of the ball, and spreads gradually outwards, becoming more intense at its periphery—it is also distinctly noticeable, under the microscope, that this disto!ouration occurs in a ripple-like form, such as one finds when ink has been evaporated, and, in the case of ink, this " ripple " formation is caused by the uneven rateof eveporation, but such cannot be the ease in ball bearings. One would like to be able to say that this last-named clees of marking was due to POMO electrolytic action, but there are not rit present sufficient grounds even to put that forward as a theory, although. from some experiments I have made, it is apparently the case that, where e perfectly-pure hydro-rarhon lubrieant (incapable of being an eleetro medium) has been cmployed, there is no sign of
diseolouration; but, in cases where alkaline salts r nd fatty acids have been present, the trouble is found.
In view of the interest that has been shown in this question, we asked Messrs. Hoffmann to supply us with a considerable number of their bearings for test purposes, and they have kindly supplied all our requirements. I hope I may be successful in obtaining results which will justify us in making some definite statement as to the cause of tile trouble.—Yours faithfully, Millwall, E. A. DI:0E11AM.