CONTINUOUS MIXERS.
71
Sutcliffe Mixer.—The principle of this machine (fig. 33) is embodied in
the method adopted for measuring the quantifies of material. The cernent
discharged into the uppermost hopper (fig. 34), the floor of which is a
cylinder with three grooves of equal area and capacity in its surface. The
cylinder is turned by a hand wheel, and an angular displacement of 60°
causes the contents of one of the grooves to be emptied into the lower
hopper where it meets with the proper supply of gravel. The gravel is
discharged from hand barrows, and the cement grooves are so regulated
that one grooveful corresponds to a barrow load. When the lower hopper
is full, the contents are allowed to fall through three trap doors, opened
consecutively, on to a moving band which conveys the dry materials to a
Fig. 33. —Sutcliffe Concrete Mixer—Elevation.
séries of trays at the top of a shoot, water being added from a supply pipe
at the level of the topmost tray. Each side of the machine is symmetrical,
and, by means of an oscillating vane for the deflection of the cement supply,
the machine becomes double acting, so that there is absolutely no break
111the discharge, which takes place from each side of the lower hopper
alternately.
This machine has been very extensively used at the Liverpool Docks
for a number of years. It has proved capable of turning out over 300 cubic
yards of concrete in a working day of ten hours, but the normal rate of
supply lies between 200 and 300 cubic yards per day.
Gravity Mixer.—An American machine in which there are no moving
parts, the whole process of mixing being performed by numerous rows of
pins, which intercept and sift the material during its descent through a
shoot, is effectively illustrated in fig. 35. The ingredients are first deposited
111 measured quantities upon the platform, and then shovelled by hand to