Riveted on the inner surface of the drum are blades (see Plate 6, at right), set at an angle to the central axis of the drum, so that they not only pick up and turn over the materials, but at the same time create an alternating sidewise movement of the contents towards and over the center of the drum. The blades are so placed that no one of them abuts against another blade or surface to form a pocket. In operation, such pockets invariably become filled with concrete, rendering the blades useless and necessitating chisel-work to clean the machine. The blades are arranged spirally in such a position as to cause the materials to flow down the inclined surface of the blades and away from the shell. This materially lengthens the life of the drum.
The spiral arrangement of blades, combined with the double conical shape of the drum, pro duces an alternating, sidewise movement of the materials, simultaneous with the rolling move ment of the batch.
The power is transmitted by a miter gear upon the main driving shaft, to a spur-bevel gear upon the cross-shaft. The spur of the last-men tioned gear, meshing with the gear encircling the drum, causes the drum to revolve.
A feed spout of sheet steel forms a part of the standard mixer equipment. This spout is supported by rods, and by an A-shaped bracket attached to the base of the swinging frame. This bracket carries adjusting screws, by means of which the lower end of the spout can be raised or depressed to avoid contact with the shell of the drum.
Means are provided for lubricating all bear ings without stopping the machine.
The "Koehring" Mixer is illustrated in Plate 7 (at the left). The particular machine shown is mounted on a truck with small steam engine for power, and is equipped with an elevating charging bucket and with an automatic water measuring tank of the cylindrical type. In the same plate (at the right) is also shown a water measuring device of the square tank type.
The "Koehring" mixer is of the cylindrical drum type, but, unlike many others of this class, it does not tilt to discharge. Any desired quan tity of concrete up to the batch capacity of the machine can readily be taken out. Loading and unloading may be done while the mixer is in operation.
The drum is made with rounded corners or rounded edges to prevent clogging. The blades and scoops are riveted to the cylinder of the drum, and rounded in the same manner as the corners. The blades are placed diagonally across, and throw the material in opposite direc tions. The scoops pick up the material and
throw it onto the discharge chute, which in turn throws it back into the drum, or out of it, de pending upon the way the discharge chute is inclined. The arrangement of the blades gives the material an end-to-end mixing. They carry the material alternately from end to end of the drum and break it over against the heavy heads. This effects a constant lifting and pouring from the sides, in addition to the longest possible end to-end mixing. Between the end of each blade and the head of the drum, there is sufficient clearance to prevent pocketing of the material..
The discharge chute is made in two sections, and is sufficiently high from the ground to clear the ordinary wheelbarrow. The section outside the drum is stationary; that inside tilts upward when the material is not wanted, and is con trolled by a lever. To discharge the contents from the drum, it is only necessary to pull the lever which gives the discharge spout a down ward incline, and any quantity of material can be obtained. To stop the flow, simply release the lever, and the discharge is shut off.
The elevating charging bucket is a substitute for the ordinary platform from which materials are dumped into the mixer. The bucket can be filled while a batch is being discharged from the drum; and as soon as the drum is empty the bucket is hoisted into a discharging position, and the entire batch emptied into the drum.
As shown in the illustration, the bucket is elevated by means of two wire cables fastened to its extreme outer corners and passing over sheaves to the winding drums. These drums are keyed onto a shaft, which is driven by gearing from the main driving shaft, and operated by a friction clutch.
The "Koehring" Batch Mixer shown in Plate 10 (lower left figure) is a type of machine com bining the features of dry mixing in the drum and adding the water in the trough. It is especially designed to meet conditions requiring the dry mixing of cement with other materials, such as coloring or waterproofing. In such cases the cement and waterproofing or coloring can be dumped into the drum and allowed to mix, then the sand or gravel added and mixing allowed again to proceed as long as desired. When the material is wanted, it is necessary only to push a lever and open the water-supply valve.