The El Tigre mill Forbes type of liners

At the El Tigre mill Forbes type of liners have been found to give better satisfaction than the El Oro liners. The former consists merely of grating plates of chilled iron or manganese steel, which are backed by mild steel plates $>{ Q in. in thickness. "In this way the advantage of a lining in which the pebbles wedge is retained while the backing pieces do not have to be thrown away when the ribs are worn down, with the result that there is a better efficiency in the wear of the iron."

Closely allied to the El Oro lining is that used in the cylindrical portion of the Hardinge mills at Miami. It will be seen from the cut, Fig. 30, that this lining resembles the El Oro but in addition has a lifter bar, which projects about 2J^ in. above the cast-iron ribs and takes much of the wear at the same time providing efficient means for lifting the pebbles without fear of the load sliding.

The Komata lining, Fig. 31, has the advantage that it alters but slightly as regards thickness during its life, it is easily put in place and has shown in some mills a greater grinding efficiency than other liners used. F. C. Brown says:

"I lay the greatest stress upon the movement of the pebbles, my experience being the more movement the more grinding; hence the advantage of the Komata lining, as this permits of no 'dead' place in the mass of pebbles and ore."

From the cut it will be seen that the lining consists of longitudinal angle bars or ribs about 18 in. apart with plates between. The bars lift the pebbles without any back-slip, thus avoiding waste of power. It can be made of cast iron, carbon steel or special alloy steel. At the Waihi Grand Junction mill in New Zealand a set of liner plates 1 in. thick at the center tapering to % m- a^ the edges lasted 75J^ weeks, and the angle bars 60J-2 weeks, before requiring renewal, grinding 76 tons of ore per day. By reason of the decreased amount of space required for this liner the interior of the mill is of larger diameter than when silex is used, more pebbles may be used in the mill with greater grinding effect and the mill may be run slower to compensate for this increased diameter. There may be an increased power consumption even with the slower speed but the amount of grinding will more than compensate for this.

Smooth liners of carbon or manganese steel have found little favor except perhaps in the Tonopah district of Nevada where better results have been claimed for smooth liners on account of the advantage of being able to grind preferentially the heavy sulphides in the ore. At the Extension mill, one tube mill is fitted with ribbed liners for coarse grinding and another with smooth liners for fine grinding.

All-pebble-and-cement liners have been tried and are now used in Hardinge mills at the discharge and feed ends of the cones, Fig. 30. The disadvantage of this lining is that the cement wears away from the pebbles and when the pebbles are over half worn through they drop out requiring frequent renewals and consequent waste of time while the cement is setting. If this class of lining is used, the pebbles should be carefully laid in the cement to present a regular surface and not thrown in, as in concrete.

Fig. 32 shows a cemented flint lining which was finished in four shifts by one man with two helpers. The pebbles were carefully laid in cement mortar made of half sand and half cement with the long axis of the pebbles vertical. The illustration shows the work on the third day with the unfinished lower segment extending the whole length of the mill. After 10 hr. set the cemented flints clung to the shell of the mill without the need of braces of any sort. The mill was run 7 days after the cement work was started but could have been rotated a day earlier.