AN INEXPENSIVE MECHANICAL STIRRER C. F. KREWSON University of Kentucky, Lexington, Kentucky
T
HE air-driven motor here described is excep- pounds of air pressure, fits into a medium-sized buret tionally compact and efficient and may be con- clamp, and possesses sufficient power to operate, a t structed in several hours a t a cost of no more variable speed, any of the frequently recurring lightthan seventeen cents. This motor runs on a few duty mixing jobs. In this laboratory a stirrer of this
type shows no signs of wear after five hundred hours of service. In ordinary operations a home-made glass propeller is attached by means of a small one-hole rubber stopper. The materials required for the construction of the stirrer are: two roller-skate wheels (F), one skatewheel axle bolt ( A ) with nut (H) and lock-washer (G),
one small piece of galvanized sheet iron for cutting the propeller (D) and the jacket (4,and one short piece of brass tubing (I). This air-intake pipe may he cut from an old blowpipe. Skate-wheels are available in a variety of styles hut
the one-bearing, concave-sided type will produce the most compact unit. The wheel selected for the top is drilled with several holes (C) for air relief and the lower wheel is drilled with one hole to accommodate the air-intake tube. The propeller is conveniently cut of either aluminium or galvanized iron from a disc of such a size as to give the propeller edge-clearance with the upper skate-wheel. The propeller to fit the type wheel here shown is made by scribing three circles of diameters 6.5 mm., 16.0 mm., and 40.0 mm., upon the piece of sheet metal. The area of the inner circle is dnlled out and fits the axle. Guide lines for cutting the propeller blades are obtained by dividing the circumference of the outer and the middle circle into eight equal parts and drawing lines to connect these marked points. After the blades are cut they are bent to resemble those of an ordinary electric fan. The upper unit consisting of the axle-bolt, lockwasher, nut, propeller, and skate-wheel is assembled as shown in the diagram with the lock-washer serving to give added clearance to the propeller in addition to locking the propeller to the shaft. The lower unit consists of the air-intake tube and the other skatewheel. The intake tube is bent a t a forty-five degree angle after it has been inserted in the skate-wheel so that its stream of air will be directed a t the blades of the propeller. It is cut off as short as possible on the inside in order to give the propeller clearance. If this tube is filled with fine sand it may he bent uniformly. The tube is soldered in place to the inside and the outside of the wheel. The outside of the tubing may he bent to any desired shape and cut off a t any convenient length. The length of the galvanized jacket is the same as the circumference of the skate-wheel and its width is about thirty-eight millimeters; that is, a width necesary to have it extend to within two millimeters of the top and two millimeters of the bottom of the assembled unit. The jacket is curved to the shape of the drcumference of a wheel and soldered a t the joining ends to form a seam. If the seam is soldered a t this point in the construction the top and bottom units are then easily inserted and made ready for soldering to the jacket. Before soldering the wheels to the jacket slight clearance is given between the nut (H) and the case (B) of the lower wheel. This will permit the lower wheel to serve as a guide and not require that its hearing he compelled to turn. Soldering all the way around the top and the bottom of the jacket completes the construction and the soldered edges may be ground to give a neat appearance. Acknowledgment is made to Mr. H. C. Young, a student in the College of Engineering, for the drawing.
