The Pros and Cons of Moving Floors
Page 34
Page 35
If you've noticed an error in this article please click here to report it so we can fix it.
Precis of a Paper by C. H. Davison, Garage Superintendent of Poplar, Who Has Tried
Many Types
THE inherent good features and simplicity of maintenance of the moving-floor principle have constituted one of the most outstanding developments towards hygienic refuse collection which have occurred during recent years. The mechanism of devices using this method is based on simple engineering principles which have stood the test of time in other branches of industry.
When these floors were first introduced to the refuse-collection vehicle, certain difficulties were encountered, one obvious disadvantage being the embodying in a specialized vehicle of a proprietary unit designed for general haulage and the need to conform to its existing limitations.
NVith the earnest desire to produce a co-ordinated product, manufacturers commenced to adopt floors of their own design, with the result that to-day there is quite a number of different types manufactured, although the mechanical principles may be closely akin.
The principle has eradicated the disadvantages of sideand plain barrier-loading vehicles, the method being briefly as follows:— The moving floor is moved to the rear of the body so that the barrier is about three feet from the tailboard. The body is then loaded and when this space is full the floor is moved forward, the refuse travelling with it, leaving an empty space at the rear of the vehicle. This process is followed until the moving-floor barrier gradually comes to the front of the vehicle and the body is fully packed. By trimming and the use of a rake the refuse can be well packed up to the roof of the body.
Packing and a slight compression of the refuse can be obtained by winding the moving floor towards the rear of the body, although great care should be exercised in doing this, in order to avoid bulging the rear door.
Results Obtained in Service I think, said the author, it will he more helpful if, instead of dealing with moving floors generally I give a few details of some of the various types cf. floor, each being the result of careful study and experiment, and each having advantages to recommend it.
The Dennis floor is of a type in which instead of winding up on a roller at each end, it passes a large diameter roller at the rear end and along the underside of the superstructure. Another feature of the floor is that the barrier is moved to and fro by means of two endless chains, which take all the strain elf the belt itself.
The floor runs on metal rollers mounted on oilless bushes on spindles, which can be immediately removed from the superstructure, and two operating speeds are provided. It is
fastened to the barrier at one end, whilst the other end is secured to the chains by means of a crossbar. Adjustment of these chains is carried out by a thumb nut on a sprocket and arm.
The bearings for the winding gear are protected by dustproof castings with self-aligning bearings, and a central group of grease nipples permits quick attention to all bearings.
The whole interior of the body. including the roof barrier and tailboard, is constructed of galvanized plate to prevent corrosion.
The floor itself is adjusted by means of a right and left-hand turnbuckle where it is attached to the superstructure of the barrier plate, and the tailboard is fitted with an automatic locking device.
The steps at the rear are of robust construction, and fold.
A Successful Type in Steel The Transport floor is of lightweight steel, the pressed sections being spotwelded together and linked by steel rods. To prevent corrosion the whole floor is sheradized, i.e., zinc coated by an electrical process. It is carried on a series of horizontal cross-members cf channel-section mild steel, the ends of which are bolted to the side members of the body, being so arranged that the floor may pass beneath the bearers when returning.
Conveyor chains, themselves mounted to runners on the underframework of the body, carry the whole of the floor. These chains are rigidly connected to the moving floor at only one point, i.e., at the base of the moving barrier at the front of the body, the other end being held to the chains by springs. These chains are driven by sprockets mounted to the front and rear cross-shafts, which are mounted on ball-bearing journals equipped with independent greasers.
Adjustments for the chains and winding gear consist of elongated slots, self-aligning ball journals and universal couplings.
The tailboard is arranged to rise vertically on rollers and is pulled by cables operating on a reduction drum fitted to the forward end of the body, and rotated by a detachable handle on the near side. A ratchet safety device is provided so that it cannot fall during the lifting process. The loading step is arranged to slide on rollers under the body.
To meet the requirements of those who prefer the rubber floor the Transport concern manufactures one operating on a similar principle.
The Eagle floor is carried on three sets of tubular rollers mounted on ballbearing journals. The front end is attached to a movable barrier, which is .pulled by two chains and operated through sprockets and a two-speed gearbox at the front end of the body. The rear end is attached to the chains, thus removing any stress from the floor during its operation.
The chains are provided with independent adjustments, consisting of turnbuckle bolts, so that any floor twist or chain stretch can be taken up by a very simple operation.
The tailboard is hung from the top and spring loaded to balance in the open position, this being effected by powerful coil springs.
The door is locked by a single catch fastener, and a sliding shutter running into the roof is fitted above it, with spring balancing mechanism to assist opening. The loading step in this instance is of the retractable or hinged type.
The Shelvoke and Drewry floor framing is built of rolled-steel sections, ta which are attached steel rollers carrying ball bearings, these bearings being packed with grease and sealed against the ingress of water, etc. The rollers carry the floor, which is tensioned equally throughout, its whole width being secured to a robust roller at the rear. Turning effort is applied equally to both -ends of this roller.
At the front end the floor is secured to a stout steel plate to which the pull is applied when loading. To this plate the barrier is fitted, and operated through spar gearing on the winding mechanism via twin cables, the whole being of simple construction.
The gears and shafts are mounted on ball bearings, and no adjustments are necessary on the actual gear.
How Distortion is Avoided Any tendency to distortion is obviated by the introduction of bellcrank levers, which constitute a perfect compensating gear. Connected to the bell-crank levers are springs, the function of these being to take up any slackness in the fusee cables when these are not in tension. Fine adjustment for the cable and floor is provided at the rear end by means of adjusting screws and stout coil springs.
There are some unique features embodied in the tail and rear doors, one is the incorporation of split door linkages, so that when discharge takes place and the rear door is open the links push the top part of the door upwards, leaving a practically clear opening during discharge. The loading step is arranged to slide en rollers under the rear of the body.
In mentioning the various makes of moving floor, the particular points to which the author referred are those that he has considered outstanding features and worthy of especial mention. Each has a high and low gear for winding the floor and all have other features too numerous to deal with individually.
The type of floor, i.e., whether it should be of steel or rubber, will always be a controversial subject and advocates for the steel floor will put forward the 'following points against the ruhlier floor:— (1 The strain of the winding operation causes the rubber to Stretch and, because of the uneven nature of the refuse, uneven stretch results, with conserpr Pot troubles.
(2) The rubber floor is liable to be cut and torn by the refuse, with the result that damp penetrates and rots the canvas core. The result being that complete replacement of the floor eventually becomes necessary, thus making maintenance costs rather high.
(3) Ease of operation is hampered by heavy articles of refuse forcing.down the ruhber in the space between the rollers, thus causing heavy friction and consequently greater effort to discharge the load,
For the steel type the following advantages are claimed:— (I) It cannot be damaged by refuse, the floor being linked together in such a mariner that each joint is tight and, whin a load is imposed -upon it, it becomes dust tight and almost water
tight. .
.(2) steel-to-steel joints are not prone to rapid wear by abrasion. It should also be remembered that the floor is not a fast moving piece of machinery. Renewals to the floor itself can very easily be carried out should a slat become damaged it can be replaced.
• What Rubber-floor Advocates Say.
On the other hand, advocates for the rubber floor put forward the following points against the steel door:—
(1) The construction of the floor entails metal-to-metal joints from which dust and grit cannot be excluded; and owing to the subsequent wear liquids cannot be retained. Whilst non-ferrous materials may be employed, rapid wear must result from abrasion by dust or grit.
(2) The effects of rust and corrosion arc always present and must have a deleterious effect on the metal floor, owing to the fact that lubrication for practical purposes is almost impossible.
So one could go on putting forward various points on this controversial subject and therefore, in view of his experience with the rubber floor, he maintains that the type of floor to be selected is a matter of personal opinion.
He has had three Shelvoke and Drewry moving floors in service since 1935, and their performance has been very satisfactory. The following costs in, connection with the mechanism ot floors and rear doors are of note:—
Period June, 1935, to February, 1939:-Wages and materials for three vehicles, el27 3s. 4d. Average cost per vehicle per year, £2 6s. 3d.
Another feature of the moving-floor vehicle is that engine and chassis costs are reduced when compared with vehicles where mechanical tipping is used..
Discharging loads of refuse ny tipping gear which raises the body to an angle of about 40 degrees is a practice which imposes great stress on the chassis at one point. Vehicles fitted with this gear cannot be emptied on uneven ground without the risk of lo Legthl!ii
Considered An Ideal Proposition.
After Ins experience with the moving-floor vehicle, and bearing in mind that the keynote of the manufacturers has been simplicity throughout the design, he is convinced that from the maintenance, load capacity and, most important, the hygienic points of view, it is an ideal proposition.
A very interesting discussion followed this paper. Some of the Allemhers stated that they had had difficulty with refuse getting over the barrier and eventually damaging the rollers and winding gear.
Questions were also raised about the suitability of these vehicles for controlled tipping, the general appearance of the type compared with the side loader, and the preference for L'Ie latter type by the loaders.
It was interesting to note that during the discussion on the most suitable type of material for the floor rubber was said to have given a very high performance, although there is still a lack of similar comparison on this controversial subject.
The author of the paper then stated that he had not experienced any difficulty with the barrier, but after what he had heard during the discussion he was convinced that there was need for an improvement in the barrier and that it was a matter that should be taken up with the man ufactu rers.
As to the suitability of the vehicle for controlled tipping, he felt that it was much more suitable, than a tipping vehicle, particularly on uneven ground, whilst the general appearance was much cleaner and easier to maintain than that of the side loader.
The side loader had numerous advantages to recommend it, but operators had to remember that to-day end loading was held in favour by most people on account of hygiene.
As regards mechanically operated floors, he felt that they were liable to increase maintenance costs, and that the low gear of the hand-operated type could quite easily be used without any undue loss of time.