CHAIN DRIVING

Evening Star, Issue 19787, 10 February 1928, Page 2

CHAIN DRIVING

POWER TRANSMISSION CLAIMS SUMMARISED While it is admitted that the electric motor may be a very efficient prime mover for driving machines, the best results are not obtained unless the power transmission gear is also of high efficiency. Line shafting, pulleys, and bearings form part of the power system in all factories and workshops, but the most important item in the equipment is the agent employed to transmit the power from the motor to the shafting and thenco to the driven machine. The use of belting is still the nost favored system of transmitting power, probably on account of its lower initial cost and apparent simplicity. There are, however, many cases where it is not only inefficient, but practically impossible to use. Sometimes it is desirable to arrange a drive where two shafts are very close together, or the motor has to be placed either close up to the shafting or the driven machine itself, and belting for such shoit centres is impracticable. This then calls for a system of drive which will satisfactorily solve these problems, and wo may find the answer in the adoption of the chain drive. The true value of chains as a transmission agent is becoming more generally recognised, and its use during recent years has spread rapidly; in fact,_ there are many cases where, in addition to those mentioned above, the only possible choice of power transmission is the chain drive.

Although the utmost caro may have been devoted to the generation of power, the economies thus effected may well bo lost by reason of neglect to fbo power transmission system. If greater care was tifken in this direction, and time devoted to the study of the modern chain as a means of transmitting power, still greater economies arc within reach.

Summarised, the claims for chain driving are; — (I) Security of positive driving, cutting out loss of power through slip. A positive speed ratio is obtained, permitting the driving and driven shafts to operate at all loads at the designed proportional speeds, and this at any reasonable distance between the shafts from approximately the same measurements required by gears Bft or 10ft on big drives. Thus it is possible to effect a great saving of space by using chains for short, centre drives, allowing of the fixing of motors quite close to the shafting or driven machine, and where space is limited this becomes a very valuable feature.

(2) A well-designed chain drive will give an efficiency of from 98 per cent, to 99 per cent., and this efficiency is sustained as the drive ages, by reason of the design of the chain, which, as it wears, lengthens, and adjusts itself to the wheel teeth.

(3) Silent running is desirable in drives, and the, chain drive is far less noisy than ordinary gearing. The writer has had tho_ opportunity of inspecting many chain drives in operation, and in the majority of cases the noise, was but slight. (4) Smooth running is a feature of chain gearing, by reason of the distribution of the load over a number of teeth, the pull being gradually taken by each tooth. (5) Reliability is another claim, as with occasional lubrication the chain is not affected by heat, cold, or moisture. Frequent tightening up to keep the driven shaft up to spe.ed is not necessary, and the bearing surface is such as to give a factor that cuts out the question of chain breakage. (6) Longer life and lower maintenance cost are also claims of the chain drive. From the above it will be seen that the question of chain driving is one deserving of careful consideration. It is not an uncommon experience to meet instances where this type of drive is used where it was originally considered a 10 h.p. motor would suit, and ultimately the motor has had to give place to one of double and even treble horse-power. It is rarely that a now drive will be ordered to take the extra duty. Another driving wheel (if the speed of the motor should be different) represents the limit of expenditure which the user feels disposed to consider, and the same drive has had to do the very much greater duty. This is one of the main advantages of chain drives for such rough-and-ready applications of electric power—i.e., there being no slip and the of safety being so high, the drive will accommodate increases in power over the normal which no belt drive could tackle, on account of slippage even under conditions of considerable tension —which, incidentally, plays havoc with the bearings. This drive is often found extremely useful in locations where it is desirable to put the motor up out of the way by underslinging. The efficiency of the chain drive is such that to all intents and purposes no power is lost at al) in the first stage of speed reduction. Thus one is permitted the advantage of a back-geared motor without the mechanical loss, and at, in general, a lower price. This permits the use of large belt pulleys in the intermediate and final belt drive stages, with a consequent higher all-round efficiency.