BLOWING MACHINES. The term blowing machine or blower is applied to various forms of mechanical arrangements employed for the production of artificial currents of air for ventilating purposes, for forced draught for furnaces, etc. They are also employed as ex hausters for the removal of smoke and fumes from smelting works, foundries, etc., for the removal of sawdust and wood planings from saw mills and planing mills, and for handling such material as emery, coffee, metal filings, etc. The various forms of blowers may be con veniently divided into the following general classes: Bellows.— These comprise the earliest forms of blowing machines and are also the most familiar at the present time. In their earlier forms, still used in some Oriental coun tries, they consisted of simple bags of skin each equipped with a valve and nozzle. A more elaborate application of the same principle is found in the ordinary domestic bellows and those used in the blacksmiths' shops.
Piston Blowers.— The simplest form of a piston blower consists of a square wooden chamber with a close fitting piston working within it. When the piston is drawn backward, air is sucked into the chamber through a flap valve, and when the piston is pushed forward this air is compressed and forced out through the nozzle.
Blowing-Engines.— The air pump or air compressor used for producing low pressure represents the modern form of piston blowers. Various types of these machines are extensively used for supplying the air blast to the cupolas of blast furnaces, Bessemer converters, etc. They are driven by either steam, gas or water power, and are then commonly known as blow ing-engines. A machine of this type usually consists of a power cylinder operating a piston either by steam or gas, and an air compressor cylinder which delivers the compressed air into the blast pipes. In the horizontal engines, the two cylinders are placed tandem to each other with the compressor cylinder in front. In the vertical engines, the compressor cylinder is usually placed on top of the power cylinder.
The pistons of both cylinders are carried on a common piston rod, and the engines are usually provided with heavy flywheels to Insure steady operation.
In many forms of steam blowing-engines, the power cylinders are compounded, while those of gas engine installations are often made double-acting, and sometimes two power cylin ders placed tandem to each other and to the compressor cylinder are successfully employed.
The recent discovery of the suitability of blast furnace gas, i.e., the gas which passes out of the top of blast furnaces employed for the smelting of iron ores, has greatly tended to ward the development of large gas engines specially adapted for blowing purposes. Up to the year 1900, the largest engine of this type was a Cockerill engine of about 600 horse power, but since then, the capacities of these machines have been greatly increased, and engine units developing many thousand horse power are being built in the United States and in Europe for this purpose. See INTERNAL COMBUSTION ENGINES.
Rotary Blowers.— This type of machines includes various forms of disc blowers and fans which are_generally used for ventilating purposes. See MINING MACHINERY.
The disc blowers are built in sizes ranging from one to ten feet in diameter, and are ca pable of delivering from 1,000 to 250,000 cubic feet of air per minute, according to their size and the number of revolutions per minute at which they are operated.
Disc blowers are often called fans, but it is well, to understand that in the former the blades are set at an angle to the axle, while in a fan blower proper the blades are set parallel to the axle on radial spokes in a manner similar to the setting of the paddles on a paddle wheel. These blades may be either flat or curved in both cases, and are arranged to revolve in a steel or cast iron casing or shell so designed that the air is sucked in through a larger or smaller orifice at the side and forced out through an outlet leading from the periphery.