The mixer consists of a trough, with a square shaft, on which are mounted thirty-six mixing paddles, which form practically a continuous conveyor, but, as each paddle is distinct and is shaped like the mould-board of a plow, the mate rial, as it passes from one to the next, is turned over and stirred. Water is sprayed into the mass at the center of the trough, the flow being at all times under ready control. The result is first a dry mix, followed by a wet mix. Machines of this type are regularly equipped with rotary pumps, making them independent of waterworks systems.
To take care of the discharge of material while changing wheelbarrows, a hood is provided on the discharge end of the machine, which can be lowered, and which will hold about a wheel barrow load. The gasoline engine supplying power is shown in its steel housing at the right.
The "Kent" Mixer, of which an example of the stationary type is given in Plate 12 (upper figure), is another continuous, automatically measuring machine. In this—as in all other examples of automatic measuring devices on the market—the material reaches the feeding device by gravity. If the material is damp, it has a tendency to bridge across the hopper, over and out of reach of the feeding device. This diffi culty, however, it is claimed, is overcome in the "Kent" machine by making the feeding device so large that practically all the sand in the hop per is directly suported by it, instead of by the hopper walls.
The feeder is simply a flat plate forming the bottom of the hopper, and having a reciprocating movement edgewise. One end wall of the hopper does not reach down to the feed-plate, thus leav ing a lateral outlet or discharge opening from the hopper. On its outward movement, the feed plate conveys a layer of material from the hop per equal in thickness to the height of this dis charge opening; and on its return or inward movement, as the feed-plate cannot convey the layer of material back into the hopper, it is with drawn from under the layer, which then drops into the mixing trough.
The proportion of cement is varied by chang ing the height of the discharge opening through which it is fed. This height is controlled by a gate arranged to be operated by a hand-lever. As the cement gate may be secured in any de sired position, it can easily be adjusted to meas ure exactly the proportion desired, with prac tically no variation whatever.
The mixing apparatus is of the pug-mill type. The mixing paddles are narrow, so that they chop, stir, and turn the material.
The particular machine illustrated in Plate 12 is one of small capacity designed especially for concrete block, brick, tile, and post work. It has two hoppers—the larger for sand and gravel, and the smaller one for cement. The cement feed-plate is connected to and operated by the sand feed-plate. By changing the position of the hand lever arm which projects from beneath the sand hopper, the operator can adjust the throw of the feed-plates, or the distance they move at each reciprocation, and thus adjust the two feeds simultaneously to deliver any desired output within the capacity of the machine, without changing the relative proportion of the materials and without changing the speed of the driving shaft.. He can also stop the feed entirely without stopping any other part, and thus clean out the mixing trough. This arrangement adapts the machine to be driven by either a variable- or a constant-speed motor.
The principal distinguishing feature of the "Miracle" Continuous Mixer is found in its mix ing device, which consists of ribbon conveyors that throw the material forward, backward, and sideways. There are two of these conveyors side by side in the mixing trough, placed so that they overlap each other. As one is right-handed and the other left-handed, they throw all material toward the center, the narrow ribbons also cut ting under it, turning it backwards, and also pushing it along.
The sand and cement hoppers are placed side by side on one end of the mixing trough, and have their discharge end on the outside, so that the material has a chance to travel the full length of the trough. In the bottom of each hop per is a solid-flight screw conveyor.
To insure that the same amount of material will be dumped at each revolution, each con veyor, before reaching the dump, passes under a hood which allows only the material in the screw to be dumped. The danger of the con veyor being empty through bridging of damp material across the hopper, is provided against by a series of paddles mounted on a revolving shaft over each conveyor. As these revolve, they constantly agitate the material and press it down into the conveyor.