3o4 FIELD OPERATIONS 



are built hopper shaped. In one of these bins is stored 

 cement, in another sand, and in the third, broken stone. 

 These bins, although hopper shaped, have no bottoms. They 

 are closed at the bottom by the cylinder c, which is of 

 sufficient diameter to act as a practically flat bottom to the 

 bin. In the front of each hopper there is a door b that may 

 be adjusted by a weight, as shown in the figure. The cylin- 

 der c is turned by a man at the handle d. As the cylinder 

 revolves, it carries with it a layer of cement, sand, and broken 

 stone. The amount of each material carried forwards is con- 

 trolled by adjusting the gate at b. As the wheel revolves, 

 the materials finally slide off into a conveyer or directly into 

 the mixer. The faster the operator revolves the cylinder, 

 the more materials he will discharge, but they will always 

 be discharged in the same proportion. 



OPERATION OF MIXERS 



A concrete mixer may be operated by a steam engine, a 

 gas engine, or an electric motor; also, where the water-power 

 is available, it can be operated by an impulse wheel or by a 

 turbine; or, if the power is available from shafting in an 

 adjacent building, the mixer may be operated by a chain or 

 belt drive. 



The superintendent or foreman of a reinforced-concrete 

 job should take good care of the machinery in his charge. 

 It'is well for him to obtain from the manufacturers written 

 directions as to the use and operation of their machines. 

 Usually, these directions are explicit and are based on 

 experience with the particular machine in question. As an 

 example, the directions published by the Ransome Machinery 

 Company are given in part as follows: 



"Rules for Operating a Mixer. If the machine is mounted 

 on wheels, see that the weight is first taken off the wheels 

 and carried on suitable sills, as shown in Fig. 8. The points 

 of support should be beneath each of the roller shafts, 

 beneath the bed of the engine, and beneath the boiler. The 

 mixer frame should be carefully leveled in both directions. 

 Remove the hook bolts that hold the drum to the frame. 



