SOLIDS IN LK SAVE TIME AN VIONEY
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BULK transport of solids and powdered materials often involves terminal handling problems of a more individual character than the haulage of liquids in tanks (with which I dealt last week). The design of the static equipment and that of the vehicle are frequently parts of an indivisible plan. Symptomatic of this co-ordination is that transport costing then becomes as complex as estimating the cost of a particular production process which has necessitated, or is the result of, essential changes in the works organization.
The haulage of cement in bulk is of national importance to any country with a priority building programme and present developments in Great Britain indicate manufacturers' and builders' interest in evolving the most suitable systems.
The storage of cement in silos offers obvious advantages, but requires the use of specialized vehicle equipment. A Hands semi-trailer built for Gibson Readymixed Concrete, Ltd., South Gosforth, Newcastle upon Tyne, carries a total of 101 tons of cement in bulk —31 tons in each of three hoppers—thus dispensing with the troublesome process of bagging. The dry cement is pumped into the hoppers under pressure at the I.C.I. plant, Billingham, the process taking in the region of 15 minutes.
B4 On arrival at Newcastle, the compressor. which is mounted at the front of the semi-trailer, comes into action and feeds . the cement into overhead silos from which • the concrete batching plant is supplied by means of a screW conveyor. Movement of the cement from the hoppers is facilitated by a pressure system which imparts a swirling motion to the contents during the process ot unloading. Coupling up the feed lines, raising the load to the silos, unscrewing and making the semi-trailer ready for departure, occupy approximately 45 minutes.
Every two days the vehicle delivers about 30 tons of cement a distance of 35 miles from the Tees-side area to Newcastle upon Tyne, a total mileage in the period of 210. The tractor is a Commer 10-12-tonner with an Eaton two-speed rear axle. The special containers were supplied by the Yorkshire Engineering Co., Ltd., Bradford.
The use of air pressure for discharging the cement (up to heights of 45 ft.) into silos from hopper vehicles has also been successfully applied by Hall and Co., Ltd., Croydon, and although little official information is available regarding the " air-slide " method, it has been accfaimed by a number of operators after experimental tests.
Tipping vehicles for bulk loads, in place of lorries carrying bagged cement, are being increasingly. necessitated by the requirements of contractors who install bulk-storage plant to ease handling and provide facilities Two dual-purpose vehicles for transporting grain in bulk or in bags, but for very different purposes, are employed by Hovis, Ltd., London, S.W.1, and its associated companies. A 15-ton eight-wheeler is used for a regular delivery of imported grain to mills in Bungay. Suffolk, a distance of 130 miles, and a 7-ton tipper collects English wheat from farms for transport to Westminster and Battersea and to other mills in the Home Counties. Loads of bagged produce are generally collected for the return journeys. The normal daily mileage of the 15-tonner is about 168.
The 15-tonner is based on a Foden chassis, powered by a Gardner 6LW engine, and is fitted with a Duramin light-alloy body with a capacity of 14 tons 9 cwt. This represents a gain of about 25 cwt compared with the use of a composite body.
20 Bushels at a Time Filling is through hatches in the roof from two chutes which are fed from a batch-weighing machine and deliver 20 bushels of grain at a time. The grain is discharged through two panels at the side of the vehicle, and both loading and unloading occupy about 20 minutes, with a total turn-round time of 45 minutes. Rather more than a ton is trimmed from the floor of the vehicle manually after the initial free run-out, the speed of which is determined by the maximum intake capacity of the conveyor at the mills.
Before the adoption of the bulk transport in 1948, a Leyland Beaver and trailer with box-type bodies were employed for the same run, carrying 11 tons 5 cwt. of bagged wheat. The payload gain is, therefore, 3 tons 4 cwt. Added to this is the saving on the labour cost of the driver's mate and a reduction of turn-round time of 11 hours, which is employed by the driver in cleaning the vehicle. The total saving in transport costs is at least 10 per cent. and the internal handling at both terminals is greatly reduced.
Sending a tipper to collect wheat at the farms is a recent innovation and one which meets with the approval of farmers. No percentage figures can be quoted showing the gain compared with collection in bags, which is organized on a different basis, but the method is obviously advantageous. The chassis is a Bedford S-type short-wheelbase unit, on which is mounted a light-alloy body weighing 71 cwt., supplied by a Hovis associate, Locomotors, Ltd., Andover. The vehicle is in the 30 m.p.h. class, despite a payload of 7 tons.
Big Saving in Labour
A feature of the tipper is a worm-operated discharge trap which enables the flow of grain to be accurately controlled according to the capacity of the conveyor. The labour for unloading is reduced from three men to one man, and storage space is saved. The body is filled through the open top, which is provided with a framework for attaching the sheet.
The Hovis transport staff believe that the haulage of flour in bulk would be economic at the present time only in special circumstances, such as would obtain when large deliveries were frequently being made to bakeries with the necessary capacity. So far as present designs have progressed, the weight of the equipment for aerating and discharging the flour reduces a 15-ton payload to below 9 tons, and the complete discharge of flour from the inside of the body presents certain difficulties.
Representative of the ways in which bulking has been adopted to more specialized operations is the transport of milled softwood; or wood flour, and of silica.
136 An interesting application is to be seen in the three Eagle moving-floor semi-trailers employed by the Rothervalc Manufacturing Co., Ltd., Northallerton, for the conveyance of wood flour. The prototype was of 6-ton capacity, but the two later models have inclined floors, which give a slightly greater load as well as facilitating the unloading action.
A special worm rack has been provided for loading the wood flour through the top of the vehicle. Discharge is from the rear orifice into a linen chute which deposits the flour into a trough from which it is removed by a conveyor.
As compared with loading into sacks and transport by platform semi-trailers,. there are vast savings; no labour is involved and the operation is carried out by an electric motor. On arrival the driver couples up the power line and the rest is automatic.
Because wood flour has a tendency to coagulate, a separate motor operates an oscillating screen near the end of the floor, so that difficulties associated with sticking are avoided. The company's principal customers have found the installation of the mating equipment of great advantage, as it not only minimizes labour, but also reduces the time at the loading bay.
Ground Silica in Tankers Special articulated container units for the bulk transport of ground silica are employed by Colin Stewart, Ltd., Winsford, Cheshire, and these are towed by Atkinson prime movers on a run from Coed Talon to Merseyside. The semi-trailers each carry an 8-ton load in a tanker-type container of conical cross-section-in which two full-length worm screws are located to discharge the material. This is performed at the rate of approximately 3 tons an hour direct to the receiving plant, thus obviating the use of a separate means of storage. Electric power for operating the screw is taken from an external supply.
Loading is by gravity into two traps in the top of the tank. Pipes are employed for both loading and discharge, and are positively connected to screwed unions to prevent any loss of silica. The risk of silicosis to the operatives is, therefore, greatly reduced.
The previous method was to bag the powder in paper containers and dispatch by train in loads of 50-63 tons. Loading and unloading required six men, and wastage on account of torn bags was high.
Three semi-trailers are in use and three additional semi-trailers are under construction for the concern. The trailer running gear is supplied by the Eagle Engineering Co.. Ltd., Warwick.
Telescopic Bodies
Many other types of solid, such as granulated products and powders with distinctive characteristics, are being carried in bulk by vehicles having special bodies and equipment. Telescopic bodies built in sections can be used for such goods as sugar-beet and road-surfacing materials/ and in a completely different category is the flotation method of carrying shelled peas in a tanker, which experiments have shown to offer substantial savings.
Even in the conveyance of gravel, solid fuel and so on, from which the term " bulk transport" was derived, means for promoting efficiency and economy have been developed by the production of maximum-load lightweight tippers with capacities up to nearly 24 cu. yd. When measured quantities of a material are required in reduced amounts for separate deliveries tippers are available with hinged partitions, which can be released externally.