A Remarkable Brake Lining.
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An Account of the Frood Company's Composition "Ferodo" which is Unaffected by Oil or Heat.
We offer no apology for prefacing our remarks concerning the interesting brake lining manufactured by the Herbert Frood Company, of Chapel-en-le-Frith, with a few words in .explanation of the properties of friction, other than to remind our readers that it is always our endeavour to avoid the presentation of descriptions of mechanical devices and improvements in a maze of technical terms, which are unintelligible to all but men with mechanical training. We have to remember that, although many of our supporters are highly-trained manufacturers and charge engineers, a large number are owners, or prospective owners, with little or no mechanical knowledge.
Efficient braking mechanism is a detail of the design of 'commercial vehicles, in common with other forms of trac,tion, the importance of Which can in no way be overestimated. The arrangements for the mechanism by which the .brakes are to be applied are easily made : the choice of suitable materials for the actual braking surfaces in contact is a much more difficult matter. The principal requirements for such materials in simple terms are : (i) a high resistance to the sliding of one surface over another ; in conjunction with (2) freedom from abrasion of the surfaces when Such sliding is taking place; (3) comparative absence of any tendency for the surfaces to " break up " at the temperatures induced by constant braking, or, as the makers describe it, a high heat limit ; and (4) small fluctuations of the first 'condition mentioned, i.e., the coefficient of friction, due to the occasional presence of oil or other foreign matter between the surfaces.
A full appreciation of the difficulty the Frood Company must have experienced in securing all these conditions, by the employment of one particular material, calls for consideration of the following several points. Friction has been -concisely defined as the resistance to relative motion, of bodies in contact, caused by the pressure between their surfaces. Efficient braking depends chiefly, though not entirely, on the amount of friction—which is a resistance and not a force—induced between two surfaces under reasonable pressures. This friction (17, on the sketch) is, then, automatically opposed to the tangential force (T) given out by the revolving wheel, or drum, whose motion it is intended to retard or arrest. The energy of the moving parts is thus gradually exhausted, until a state of affairs comes into existence where the obtaining friction between the surfaces of the brake and drum is greater than the force with which the wheel, or drum, is attempting to revolve past the brake 'block. A state of rest is therefore secured, until such time as the pressure between the surfaces (P and R) is ;wain retluced, and the corresponding friction (F) falls below the force
• (T) exerted at the rim of the wheel as it attempts to move. The coefficient of friction is a term used to compare the :resistance to movement, across each other, of different surfaces under definite pressures, and expresses, for each pair of surfaces, the relation between the power required just to overcome the friction (T), and the pressure (P or R) between the surfaces, necessary to produce that amount of friction. The limiting friction is expressed by the ratio of the perpendicular to the base (tangent) of the angle formed, in a rightangled triangle, between the hypotenuse and the base, that angle, for any two materials in contact, being the one at which sliding begins on inclination of the supporting plane.
The coefficient of friction of Frood's material is remarkably high. This means that, to attain a high frictional resistance between the surfaces of the block and the wheel, a lower pressure than usual is required. The maker claims the difference as being 2 o per cent, less, for 11;-; blocks, than for the ordinary cast-iron ones. Consequent] greater frictional resistances are attainable for the sam applied brake power. Increased pressures generally resuk in serious abrasion of the working surfaces and, as a resu,t, seizing; but one of the most remarkable features of " Ferodo," which is the name given to the production of the Frood Company, is the fact that very high pressures, and consequently high temperatures, can be employed without any danger of abrasion. Whereas an ordinary block may just sustain a total pressure of 2,000.lb. load, the Frood block, of equal size, suffers no ill-effects when the pressure is raised to a total of 6,000lb. Under such high pressures, the ordinary cast-iron block would jolt and jar unmercifully, but the material of which the Frood block is composed, being non-metallic and of a very ductile nature, secures a continuous retarding effect, in addition to rapidity of action.
Quite the most remarkable claim made by the Frood Company is that the braking efficiency of its strips is not adversely affected by the presence of oil, grease, or water. This is a result for which we are not, at the moment, prepared to offer a definite explanation, because the lubrication of surfaces invariably has the effect of reducing their coefficients. We suggest, however, that the non-abrasive tendency of the material, of which full proof has been secured, allows the film of lubricant to be very quickly squeezed out from between the two surfaces.
The manufacturers make a great point of the fact that their material is very consistent in nature, and that the surfaces of different blocks of " Ferodo" vary but little ; their uniformity is the outcome of prolonged experiment and tests. This is a condition of things it is extremely difficult to secure with chilled cast-iron blocks, so that, more often than not, equal pressures on contiguous blocks produce quite unequal frictional results, owing to the variation in the nature of the metal from unequal cooling, pouring, mix_ ing-, and what not. This equality of the material " Ferodo " should be invaluable to commercial-vehicle builders and users, as it is admitted that many a serious side-slip occurs through one wheel's locking quite readily, while the brake on the other side hardly grips, the difference often occurring from different conditions of brake-block surfaces. The nonmetaflic " Ferodo " abolishes the clattering brake-block and, from experiments within our knowledge on certain of the London tube railways, we are enabled to state that fullpower stops can be made on heavy trains with hardly any noise at all, except a faint hissing which arises from the
air-brake. Many a puzzled garage superintendent will welcome this means of quietening his squeaking brakes. The London General, Road Car and Vanguard Companies, have for some time secured excellent results with Frood's lining for the brakes of several types of motorbases. Experiments are also being conducted with " Ferodo " as a cone-clutch cover, but, as this material cannot be satisfactorily dressed in a lathe after mounting, the care necessary in moulding the cover, in the first place, is likely to. render the first cost higher than that of leather, Most experience has been gained at Edinburgh, as regards the use of ".Ferodo " on clutches.
The claims put forward on behalf of this interesting material are, broadly speaking.: (i) high coefficient of friction ; (2) high heat limit, amounting, in some cases, to 1,800 Cent. duting recent tests on a northern English railway, and possibility of employing high surface pressures ; (3) no danger of abrasion ; (4) smooth and continuous action, and absence of all jar or jolt ; (.5) absence of deleterious effects owing to presence of oil ; and (6) consistency of the material itself. These are all claims which will interest the commercial-vehicle user and driver. We would strongly advise a trial of the composition on certain types of internal brakes, from which it is difficult to keep the grease, whilst its behaviour when embodied as one of the series of plates in a multiple-disc clutch should be interesting. It must be borne in mind that, if manufacturers require a particularly high heat limit, this fact must be mentioned in the order, as the Frood Company makes two distinct qualities.
. We regret that we are under restrictions from Mr. He.rbert Frood, the managing director of the company, which pre1,:ent our describing, at present, the method of manufacture adopted, but we hope to do so before long. We must, therefore, content ourselves with stating that the basis of the material is of cotton fibre, and that, during one of the processes, the material is subjected to a pressure of no less than 400 tons per square inch. A curious commentary on the statement that the material is unaffected by the presence of oil is the fact that a certain amount of oil is actually used in the manufacture.
Extreme business acumen and keen foresight have prevented the company from letting it become known to what an extent its busineSs has developed until such time—recently—as complete success was beyond dispute. It will undoubtedly surprise many of our readers to hear that the Frood Company has supplied many thousand pieces of its composition for the facing of the brake blocks on the horse omnibuses of the London General Omnibus Company, and that, at the present moment, a great number of these blocks are being fitted to trains on the underground electric railways of London. Many of the largest tramway authorities, and almost all the English railway companies, are experimenting with the new composition-pattern brake block. The Company's business is developing so rapidly that not only is it very greatly extending its English factory at Chapel-en-le-Frith, but it is erecting large premises in Germany, under the auspices of the National Bank, Berlin, which is the owner of the German patents. We are able to state that the establishment of other Continental and American factories is contemplated. We understand that the 'chief engineer of the Underground Electric Railways, of London, was one of the first men of standing in the engineering world to recognise the potential possibilities of the Frood material, and we can do no better than conclude with a copy of a small comparative table which has been drawn up to show the relative costs of the old and new fittings. The figures have been compiled from actual tests on the underground electric railway lines, who have now adopted the fibre blocks exclusively.
Cost of Frood's Patent Fibre Inserts.
-Life of inserts on motorcar 12,000 miles.
Do. do. trailers ... 22,000 Average . . 17,000 „ Life of cast-iron shell, motorcars . 24,000 miles.
Do. do. trailer 44,000 o
Average ... ... 34,000 • ,, Cost of fibre inserts= is. 6d. (17,000 miles), per 1,00n miles ... ... ... ... ...1.06d. Cost of cast-iron shell (16 lb.) at ,,..6 12s. 6d. per to11..; 11.36d. (34,000 miles) Cost of cast-iron shell per 1,000 miles ... ... Cost of preparing and fixing fibre inserts, per 1,000 miles at id. per block ... ... ... ... .o6d.
Total cost per block per t,000 miles .. ... . 1-45d• Cost of Solid Chilled Cast-Iron.
Life of cast-iron block ... ... ... ... 8,0oo miles. Cost of cast-iron block per ',coo miles, weight 26 lb.
price ..,.5 mos. per ton ... ... ... ... 2..o6d.
Additional labour (boy wipers) per moon miles ... .12.d. Total cost per block, per 1,000 miles ... .., Brake applications per day ... ... ... 12,710 Do. do. per mile ... ... ... 2.31 NOTE—As many as 600 brake applications are made by some trains per day.
Economy effected per imoo miles by En:rod blocks..73d,