The Mechanical Handling and Storing of Material

DISCHARGING B Y MEANS OF SKIPS- AND GRABS 393 is illustrated in Fig. 552. These generally consist of a large tub with hinged bottom doors; such appliances were used at the Millwall Docks for unloading grain before the Duckham pneumatic elevator came into use. These tubs have the advantage of being light, as they hold 60 bushels of grain, or nearly 3 cub. yds., and weigh only 5 cwt. The bottom is divided into two halves which are hinged to an iron bar traversing the bottom of the tub, and the lower edge is so contracted as to form a truncated cone 6 in. in height: thus the diameter of the lower portion is 1 ft. less than that of the main portion of the tub. 'rhe lower rim is so machined as to fit the hinged bottom. The bucket is suspended by a length of 3| in. wrought-iron tubing passing through the bearing b, and having a suspending eye at the top and an attachment c for four connecting rods d at the lower end. When suspended from the eye the bottom door supports the shell portion of the tub. When filled the tub is lifted by the crane and deposited on a circular opening in the top of the receptacle where the load is to be discharged, and as the crane continues to lower, after the shell of the tub has reached its seat, the doors open (as shown in the dotted lines) and the grain discharges. The doors shut automatically as soon as the crane lifts the empty bucket off its seat. Self-Discharging Skip of Taylor & Hubbard. —This is similar to the foregoing appliance, as will be seen by Fig. 553. Tt must be filled by hand as is the previous one, but discharges its load auto- matically, after the manner of a single-chain grab described later. The automatic gear a, which is suspended from the jib-head of any ordinary crane, discharges automatically at any predetermined point to which the gear may have been raised or lowered. The mechanical working of this apparatus, which can be operated by one man, is clearly shown in Fig. 553. The flaps forming the bottom of the skip are connected by links f f to the rod G, which is attached to the lifting chain, while the body of the bucket has connected to it a sleeve H, through which the rod G passes, and which has a conical top with a shoulder h2. The automatic gear is Fig. 552. Mechanical Bucket formerly in use at the Millwall Docks. independent of the jib. Bell crank triggers j, adapted to engage the shoulder h2, have projections j1 sliding in slots in the sleeve a, and are normally pulled upwards as shown by springs d. Projections engaging slots in the part a limit the lateral play of the triggers j. On raising the loaded bucket the triggers j are forced apart by the conical end of the sleeve h, and then close under the shoulder h2 as shown. On lowering, the weight of the bucket pushes the triggers down so that their horizontal arms engage projections k1 on the arms k, which are forced inwards by springs, and on further paying out the chain the bottom of the bucket opens. The bucket itself is