SPATE CHOMOGISE: 279 
of the Griffin mill, though this objection does not hold for a homogeneous 
material like clinker. The screw conveyor beneath the Griffin mill, to 
be sure, does some mixing, but it may be doubted whether it does enough 
Oetite 
It is also a fact that but few cement mills employ Griffin mills for 
raw grinding. : 
The repair expenses of the Griffin mill are said to be higher than 
those of the tube-muill, although this difference is balanced again by the 
greater mechanical efficiency of the Griffin mill, which requires less 
power than the tube mill, the ratio per unit of cement produced being 
roughly, as 5:7 in favor of the Griffin mill. 
HANDLING DEVICES, 
In the handling of materials by the dry process horizontally and 
vertically the following devices may be used: 
A. Conveyors. 
Belt conveyors. 
Scraping conveyor. 
Pan, plate and bucket conveyors. 
Screw conveyor. 
Jerking troughs. 
Cars. 
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Buaeidlevaronse 
tT. Bucket belt conveyor. 
2. Bucket chain conveyor. 
Belt Conveyors.—Belt conveyors are used more commonly than 
other conveyors for longer distances. It is important that they be of 
good material and first cost should not be made an object in their 
selection. For carrying crushed or ground material the belt is given a 
trough-like shape by conical rollers or two rollers inclining towards 
the middle, the latter being the better way, throwing less wear on 
the belt. It is better to apply the power at the delivery end than at 
the receiving end, and the end bearings should be adjusted so as to take 
up the slack of the belt. These belts work satisfactorily for lengths as 
great as 500 feet and are the most reliable conveyors; average capacity 
about 10 tons per hour. They consume but little power for the work done. 
craping Conveyors.—The scraping conveyor consists of a set of 
scrapers attached to an endless rope running in a steel-lined trough. 
This conveyor works satisfactorily only if the sheave-driving pulleys are 
large in diameter and the rope is run not too rapidly. It takes, however, 
a great deal of power and is noisy. Chains in place of the rope are 
much less satisfactory. 
