Title: Container transporter crane
Pages: 66 - 69
Container transporter crane
The crane is manufactured by Stothert & Pitt Ltd. and designed by their design team to the specification of the British Railways Board.
The container revolution in transport has well-established advantages: handling costs are considerably reduced; freight is delivered faster; packaging costs are cut; and pilfering is discouraged. But the capital investment containerisation requires is high: container ships are expensive; special trains and lorries have to be built; handling cranes and other equipment are large and complex; and the containers themselves cost anything up to £1000 each. The revolution is therefore economic only if this capital investment is used intensively, with ships, containers, lorries and trains all moving freight with as little delay as possible for handling. And a system using cranes to shift containers from one form of transport to another is entirely dependent on the reliability of the cranes: if a ship, train, or lorry breaks down, temporary replacements can always be found; but if a crane fails the whole multi-million-pound system will rapidly come to a halt.
Reliability and ease of maintenance are therefore the key factors in the two quayside container transporter cranes which Stothert &Pitt have designed and built to the specification of British Rail for BR's Parkeston Quay container port at Harwich. For these two cranes - first of their kind to be designed and made in Britain - provide the only method of transferring containers from ship to land-based transport in this high-capacity freight link with north-western Europe.
The Parkeston Quay installation is designed for the fast transfer of containers from ship to train or lorry. Specially built ships operate between Harwich and Zeebrugge or Rotterdam, each carrying up to 150 containers and completing one round trip a day. The cranes can unload and reload a ship in as short a time as four and a half hours, the containers being systematically moved from the quayside by lorries which take them to a storage area behind the quay where they are sorted and loaded onto Freightliner trains or lorries as appropriate (two Stothert & Pitt goliath cranes are used in this area). The container transporter cranes have been designed to deal with three ships and to sort containers in a temporary storage area at their base during an 18-hour working day. Operating six days a week it is therefore possible for the cranes to load and unload some 5,000 containers, each weighing up to 30 tons, during a week; and each crane can be operated with just a two man crew.
The 450-ton cranes are each mounted on four sets of bogies running on rails 108 ft apart; this span allows space between the legs of the crane for temporary storage of containers six deep and three high, as well as for road and rail vehicles. The crane boom has a cantilevered outreach of 68 ft and can be retracted to 75 degrees to make room for ships to pass for docking; it can continue moving containers between its legs while the boom is in the stowed position. The front legs of the crane are the more heavily loaded and resist any horizontal forces, the rear legs being pivoted at the junction with the main structure in order to allow for any variation in the laying of the rails. The machinery house is mounted above the rear legs.
A telescopic steel spreader is used to lift the containers; this adjusts automatically to 20 ft. 30 ft or 40 ft at the press of a button in the driver's cab; 10 ft containers can be lifted by lugs beneath the spreader. On each corner of the spreader is a T-shaped twist lock which drops into a casting on the corner of the container and turns through 90 degrees to lock for lifting. Each corner of the spreader is also equipped with flared "gather guides"
which position the spreader accurately as it drops onto the container. The crane drive can use all the guides or any pair so that the container may be lifted even if it is adjacent to other containers; all the guides are retracted for lowering the spreader into the cells in which the containers are housed on board ship, the cell framework itself then acting as a guide for the spreader's accurate positioning.
All of these very complex movements are hydraulically operated, directed entirely from a push-botton control console housed in the drivers cab. Interlocks prevent a container being lifted unless all four twist locks are positively in position and unless sensitive vertical probes at each corner confirm that the spreader is in contact with the container. The spreader is suspended from the traverse trolley by four double-wire ropes to ensure that it is lifted level and to discourage the load from swinging.
The driver's cab has excellent all-round vision - including large windows in the floor and is attached to the traverse trolley so that the driver is always over the spreader and can see clearly where to place it or the container it is lifting. Two joysticks operate all crane motions, their direction being related to the movement required. English Electric Cranestat thyristor convertor control equipment is used for hoisting, traversing and travelling, providing infinitely variable speeds, immediate reversal of direction, and smooth acceleration and deceleration. This equipment enables the driver to move the crane by as little as half an inch and the smoothness of its operation helps to prevent the load from swinging.
(Captions page 67) The two container transporter cranes at Parkeston Quay load and unload three ships and sort containers in the storage area at their base during an 18-hour working day. Operating six days a week, they therefore handle 5,000 containers, each weighing up to 30 tons, during a week.
The crane boom has a cantilevered outreach of 68 f t and can be retracted to 75 degrees to enable ships to pass beneath for docking. It can continue to move containers between its legs while the boom is in the stowed position.
The normal method of working is for a row of cells across the ship to be dealt with at a time; once a cell is empty the crane takes a container from the quay and loads it and then takes the container from the next cell to the quay. The speed of travel of the crane is therefore not critical, the important factor being the traverse and hoist speeds. Fully loaded, the traverse speed is 300 ft per minute and the hoist speed 60 ft per minute; unloaded, the speeds are 400 ft per minute and 120ft per minute.
Because the cranes form a vital link in an expensive system, and because they are called on to operate nearly twice as many hours a year as a conventional dockside crane, reliability and ease of maintenance were prime requirements. The two award winning cranes are designed to the British Standard heavy duty operating specification, with all mechanical parts generously rated. Sealed roller bearings and gears running in oil baths are used extensively to reduce maintenance. The electrical control equipment is built on plug-in boards and has a monitoring system which enables any fault to be located rapidly. Even such infrequent maintenance as the replacement of ropes has been considered, with a special device for speeding rope-changing. The large machinery house provides plenty of room for any part to be removed easily, a machinery hoist being built in. The traverse trolley is floored to make access easy, and hooks are provided on the crane for attaching cradles for painting. The electrical control link between the traverse trolley and the machinery house is unbroken by conventional sliding contacts or brushes, and consists of a continuous catenary cable suspended from sliding hooks, thus getting rid of a possible source of control failure.
The crane has many safety features. For example, a container cannot be lifted unless the spreader has been properly locked, and it cannot be unlocked until the full weight of the container is off the spreader; all controls are fitted with limit switches to prevent overunning, and the driver is provided with a Davy escape apparatus for any emergency exit from his high cab 45 ft above the ground.
One danger with these big container cranes is that they will be blown along the rails by a high wind and derailed; Stothert & Pitt cranes have powerful brakes, are equipped with anchor pins to attach them firmly to the quay when parked, and are designed so that the gearing on the individually powered bogies virtually locks the wheels until the moment when power is switched to the motors.
Stothert & Pitt had been in discussions with British Rail about container cranes in general since 1963, but serious work on the Harwich cranes did not begin until the spring of 1966, with the first entering service some 30 months later. The performance specification was laid down by the Railways Board in consultation with the manufacturer, while the design work was carried out by Stothert & Pitt, drawings being discussed with BR at regular monthly meetings. Both customer and manufacturer formed development teams to carry the contract
through, with such specialist sub-contractors as English Electric and Allen West & Co (who were responsible for the cab control console) being called in when necessary. The first design put forward by Stothert & Pitt was for a lattice structure, but BR turned this down in favour of a fabricated stressed box construction. This meant that Stothert & Pitt had to extend their techniques of structural analysis into a new area, for this thin-wall, internally stiffened construction required methods that are more akin to aircraft manufacture than traditional methods of crane-making.
Other areas for study included the design of the rope system to enable the crane to be used with the boom either up or down: this problem was solved by providing guides which direct the ropes onto alternative pulleys as the boom is lifted. Attention was also given to ensure that the endless traverse ropes are always taut: a measuring and control system is fitted to adjust the ropes in order that very fine control of the traverse position is possible. The problems of erection were also considered. The use of large member sections helped, but the methods to be used for erection were nevertheless checked with a model of the crane made for this purpose.
Design costs totalled about 5 per cent of the £400,000 which was the total cost of the two cranes, with nearly a fifth of these costs being on the control gear; this had not previously been used on this size of crane, although Stothert & Pitt had experience with it on later versions of the DD2 dockside crane which won a CoID Design Award two years ago.
Stothert & Pitt have so far built nine quay side container cranes in Britain, and recently announced a £485,000 order for a large double-lift container crane for the port of Wellington in New Zealand.
(Caption page 69) The driver's cab has excellent all-round vision (cabs of both cranes are visible in the picture oppolite). The cab is attached to the traverse trolley so that the driver is always positioned over the spreader, which lifts the containers, to supervise its operation. He can adjust the spreader at the press of a button to 20 ft. 30 ft or 40 ft. A twist lock on each corner of the spreader drops into a casting on the corner of the container and turns through 90 degrees to lock for lifting. Each spreader corner is also equipped with flared gather guides to position it accurately as it drops on to the container. Operations are hydraulically operated, directed entirely from a pushbutton control console in the driver's cab. The spreader is suspended from the trolley by four double-wire ropes to ensure that it is lifted level and to discourage the load from swinging. The machinery house, right, is mounted above the rear legs.