Cement Delivered in Bulk Saves £1 a Ton
Page 48
Page 49
If you've noticed an error in this article please click here to report it so we can fix it.
By Anthony Ellis
SINCE bulk delivery facilities were first offered by cement producers in this country they have been used in the main only by the larger builders and contractors. This was a consequence of the deliberate policy adopted by most of the cement manufacturers to confine themselves to the delivery of large loads while building up their bulk fleets.
Cement silos used on site have usually had a capacity of 20 tons or more and deliveries have been made with heavy vehicles capable of carrying payloads of 9 tons and more. Now that the advantages of bulk handling of this commodity are more widely appreciated a demand has arisen from the smaller builder for the extension of this type of operation to suit his requirements.
As a result, silos with capacities of 10-11 tons are now on the market. It is not economic for a customer to take only a part-load and this has brought about the need for smaller vehicles.
Portasilo, Ltd., Blue Bridge Lane, York, who were pioneers in this field with their one-piece, readily portable silos, have met this requirement by producing a cement tanker of 7-ton capacity based on a Thames Trader 108-in.-wheelbase chassis.
I spent a day with this vehicle on delivery work and found that the advantages of bulk handling were readily apparent. Previous insistence on payloads of 8-9-tons and above stipulated the use of heavier and more expensive chassis. Reducing the payload permits the use of mass-produced chassis, such as the Trader, and this greatly lowers the initial cost of the complete tanker.
The Portasilo tanker employs a 209-cu.-ft. drum-shaped container with dished ends at top and bottom. It is of welded construction fabricated from aluminium-alloy sheet.
Cement is loaded into the tank through a manhole and is discharged c12 by air pressure through a 4-in, fullbore valve and hose. The tank has a sub-floor of sandwich construction with a perforated sheet constituting the top layer. During the discharging operation, pressurized air is fed into the space under this sub-floor.
Good dispersion is achieved and the air passes through the perforations to keep the load in suspension and feed it down to the centre of the floor for discharging.
Air for this operation is provided by a Wellworthy-Ricardo 14-cylinder swash-plate compressor driven through a 21to-1 step-up gearbox from a power
take-off mounted on the side of the vehicle gearbox. When operating at 3,000 r.p.m. the compressor absorbs 18.2 b.h.p. and produces 280 Cuft. of air per minute at 12 psi.
The tank is mounted on the chassis frame by four welded-on feet with rubber packing interposed between them and outrigged brackets bolted to the chassis sidemembers. Complete with ancillary equipment it weighs about 16 cwt., making the unladen weight of the vehicle 31 tons.
Collecting the tanker in York, I drove it to the Humber Cement Works of G. and T. Earle, Ltd., at Hull. The complete operation of loading was timed from driving on to the weighbridge on entering the works to repeating this procedure after loading had been completed.
It took 26 minutes, of which time 13 minutes 14 seconds were spent in actual loading, and approximately 6 minutes in obtaining the weight tickets and getting in and out of the loading bay. The remainder of the time was accounted for in cleaning cement dust off the exterior of the vehicle after leaving the loading bay.
Loading, which was effected through art air slide, was controlled by the driver. As no dust or air-extraction equipment was provided in the loading bay it was possible to see when the tank was nearly full, because of " splashing" of cement from inside it.
The weighbridge showed that 7 tons 9f cwt. of cement had been taken on board, which was an overload for the Trader chassis. However, 9.00-20 (12-ply) tyres were fitted and the location of the tank was such that the gross weight of 11 tons 44cwt. was well distributed, with 3 tons 91 cwt. on the front axle and 7 tons 151 cwt.
on the rear. The position for the tank had been recommended by the chassis manufacturer.
According to the yard manager, the average loading time for cement in 1-cwt. bags was a ton a minute with two men and an extensible conveyor. Although this time was, to me, surprisingly fast, it was not at this end of the delivery operation that economies were looked for, but rather during off-loading at the building site.
On the way from the cement works to the site of the new university buildings in Leeds, where the load was to be discharged, it would have been at once apparent, had I not already known, that the weight distribution was near the ideal. Steering was by no means heavy even with a ton overload and the riding qualities of the Short-wheelbase chassis were excellent.
The optional 7.2-to-l-ratio rear axle had been selected for the Trader. think this was a wise choice for a vehicle which is not likely to undertake single journeys of more than 25 miles and will spend much of its time under difficult conditions getting into and out of building sites.
Although the overall height of 10 ft. 6 in. makes the centre of gravity rather high, accentuated roll was not apparent even when taking main-road curves at 40 m.p.h. Helper leaves on the rear springs are probably responsible for this stability. .
A tortuous path to the silo on the Leeds site proved how suited the short wheelbase of the Trader was for this application. I can think of many occasions when a conventional long-wheelbase lorry loaded with bagged cement would be unable to gain access to similar difficult locations.
Having backed the vehicle up o the silo, the power take-off was engaged from inside the cab. The delivery hose was coupled up to the intake on the silo and the hand throttle at the rear of the tanker was set to give a compressor speed of 2,800 r.p.m. while the main delivery valve was opened. The load was discharged into the 28-ft.-high silo in 8 minutes 35 seconds, and the complete operation, from the time of driving up to the time of driving away, was concluded in 18-1 minutes. On inspection, the tank was found to be completely empty.
it is estimated that it takes approximately half a man-hour per ton to unload bagged cement manually without mechanical aids. Had the vehicle been carrying bags, unloading would have taken 31 man-hours. As it is usually the concrete-mixing team which unloads the lorry, thus interrupting the mixing sequence and leaving machinery idle, the saving effected by bulk delivery at this point is substantial.
Tncluding such additional items as wastage and spoilage of cement in bags and the reduced cost of bulk supplies, the average saving, using bulk delivery to the full, can average about £1 per ton of cement.