The Mechanical Handling and Storing of Material

59° THE MECHANICAL HANDLING OF MATERIAL Rigg’s Colliery Tippler.—A tippler Fig. 833. Screen Receiving Tub-load of Coal. Fig. 834. Screen in Stationary Position. released until the tub is inverted over the screen. All these methods are bound to cause a certain amount of breakage, and are therefore superseded in modern collieries by more scientific tipplers. h greatly reduces breakage is that designed by Mr James Rigg, of London. The rotating bonnet which re- ceives the tub is so balanced that the position of the centre of gravity depends upon the tub being loaded or empty, and therefore causes it, under control of the brake, either to tip forward and empty itself, or to return unloaded. Within this bonnet is a horizontal hinged door, which has an important function to fulfil, as at whatever speed the machine may be working, this door will act as a regulator to the flow of coal, while gradually but steadily yielding to its pressure. In reality it com- bines with the shoot in spreading the coal over the screen or sieve, into which it is generally discharged. Fig. 832 gives a perspective view of these tipping machines working in connection with Rigg’s curved balanced screens. The diagram, Fig. 833, shows the screen in its normal position receiving a tub- load of coal, which passes down the incline and is gradually brought to rest under the lower screen bars, as shown in Fig. 834. The brake is again released, and the screen returns to its starting position to receive another load, these operations being effected dur- ing the period necessary for changing the tubs in the tip above. The slack or small coal which has been eliminated by the screen is received in the fixed hopper shown and thus passed into its own trucks. Fowler’s Patent Gravity Tippler.—During the past few years this tippler, which also works by gravity, has come into considerable i than the three-tub tippler (to be next described), and does not require any more height at the rail level than an ordinary power-driven tippler. It was originally built of cast iron, but Messrs Heenan & Froude, Ltd., who have taken up the manufacture, are building it of mild steel for the handling of large materia]. in this country. It is, of course, much smaller