1 Agr. Engin., 34(2):91, 1953; Life, 34(1):62, 1953; 38(1): 54, 1955.
2 U.S. Dept. Agr., BAE.
3 U.S. Dept. Agr. Misc. Pub. 630.
1 Work Simplification News Letter 23, December, 1952.
2 U.S. Dept. Agr. Misc. Rpt. 157, 1933.
3 U.S. Dept. Agr., BAE, F. M. 92, Section 4, 1953.
CHAPTER 2
MATERIALS OF CONSTRUCTION
The strength, durability, and service of a farm implement depend largely upon the kind and quality of material used in building it. There is a tendency in the construction of implements to eliminate as many castings as possible and to use pressed and stamped steel. Where this is done, the cost of manufacturing machinery in quantities is materially reduced. The weight of the machine is reduced, but the strength and durability are retained and often improved. The success or failure of an implement frequently depends upon the material used in building it.
The materials used in the construction of farm equipment may be classified as metallic and nonmetallic. The metallic is further divided into ferrous and nonferrous materials.
NONMETALLIC MATERIALS
The nonmetallic materials are wood, rubber, leather, vegetable fibers, and plastics.
Wood. Iron and steel have practically taken the place of wood. There are, perhaps, two reasons for this: first, steel is more durable; second, it is becoming cheaper than good wood because of the scarcity of the latter.
Rubber. Rubber is both derived from the gum of trees and made synthetically. Special compositions of rubber are developed to obtain the properties desired for a particular application. Design engineers should have a thorough knowledge of the properties of rubber—both natural and synthetic. There are several grades of rubber materials varying in the general properties of hardness, flexibility, bonding properties, and chemical resistance. The leading use of rubber on farm equipment is in production of implement tires and tubes. Much rubber is also used in making flat and V belts and for the insulation of ignition wires. Rubber bushings on suspended oscillating components often give an excellent service life and require no lubrication. Disks of rubber to clasp plants are used on transplanters.
Plastics. A plastic material is an organic solid, polymerized to a high molecular weight, that is capable of being molded, usually with the aid of heat, or pressure, or both. There are many groups and types of commercially available plastics. These are sold under many trade names. Certain types of plastics are used for steering wheels, handles, instrument parts, bearings, washers, tubing, battery cases, bristles for brushes, and windows.
Leather and Vegetable Fibers. Leather is largely a belting material. Vegetable fibers are used in brushes, fabrics, and upholstery padding.
NONFERROUS METALS
The nonferrous metals are copper and its alloys (such as brass and bronze), aluminum, magnesium, lead, zinc, and tin.
Alloy. An alloy is a substance that has metallic properties and is composed of two or more chemical elements of which at least one is a metal. The number of possible alloys is infinite. They are made by the fusion of metals. The most common groups of alloys are bronze, brass, babbitt, alloy steels, and the aluminum alloys.
Copper. In commercial importance, copper ranks next to iron and steel, because of its electrical conductivity and its capacity to form useful alloys. Copper is soft enough to be rolled, or hammered into thin sheets, or drawn into fine wire. It is used for ignition and instrument wires on engines, tubing for conducting fuel from tank to carburetor, and in generator and starting motors.
Brass. Ordinary brass is an alloy of copper and zinc. Some commercial brasses contain small percentages of lead, tin and iron. The percentage of copper in brass may range from 60 to 90 per cent, and the percentage of zinc from 10 to 40 per cent. Brass is used for making radiators, pipe, welding rods, screens for fuel lines, instrument parts, and fittings.
Bronze. Bronze is an alloy of copper and tin. However, zinc is sometimes added to cheapen the alloy or change its color and increase its malleability. The amount of tin in bronze may vary from 5 to 20 per cent. Phosphor bronze, manganese bronze, and aluminum bronze are special copper alloys containing small percentages of tin, zinc, and other metals such as phosphorus, manganese, or aluminum. These are used for bearing bushings, springs, pipe fittings, valves, pump pistons, and bearings.
Babbitt. Babbitt is a tin-base alloy containing small amounts of copper and antimony. Good babbitt for automobile bearings should contain 7 per cent copper, 9 per cent antimony, and 84 per cent tin. It is used mostly as a bearing metal.
Solder. Common solder contains about one part tin and one part lead. Hard plumbers’ solder contains two parts tin and one part lead. Solder is used extensively in joining brass, copper, tin, steel, and cast iron.
Bearing Metals. White metals and bronze alloys are most frequently used for machine bearings, but wood, glass, plastics, rubber, and other materials are also used.
Aluminum. This is a white metal with a bluish tinge. It has a specific gravity of 2.7, a melting point of 658.7°C., and is resistant to corrosion and to many chemicals. It, however, can be dissolved by alkalies and hydrochloric acid. It is frequently alloyed with iron and copper. Aluminum is extensively used to make light castings for certain types of farm equipment.
Zinc. Zinc is a bluish-white, crystalline, metallic element, brittle when cold, malleable at 110 to 210°C. It is used mostly as a coating on sheet iron and die castings, as a protection against corrosion.
FERROUS METALS
The ferrous metals are iron and its various alloys, such as cast iron, malleable cast iron, wrought iron, and steel. There are many others. The best way of forming parts of irregular shape from the ferrous metals is by making a pattern and pouring molten metal into a mold. These are known as castings.
Cast Iron. Cast iron is iron containing so much carbon or its equivalent that it is not usefully malleable at any temperature. The amount of carbon varies from 2.2 to 4.3 per cent, depending on the amount of silicon, sulfur, phosphorus, and manganese also present.
There are two grades of cast iron: gray cast iron, in which the carbon is segregated from the iron in the form of graphite; and white cast iron, which has carbon and iron combined. Another grade is often mentioned, mottled cast iron, which is a mixture of the gray and white. Cast iron is made by combining pig iron and scrap iron and pouring the molten metal into sand molds of the desired shape, where it is allowed to cool. Then, it is cleaned and made ready for use.
Cast-iron castings are generaly large, bulky, and very brittle. They cannot be hammered to any great extent without breaking. They cannot be forged, but can be cemented together by brazing or welding. The brazing process consists of heating the broken parts to a welding heat and applying a brazing compound. Welding is the process of fusing two pieces by heating them with an oxyacetylene-gas flame and applying the proper rod.
Malleable Cast Iron. Malleable iron is annealed white cast iron in which the carbon has been separated from the iron without forming flakes or graphite, as in gray cast iron. It will bend to a limited extent without breaking.
The process of making malleable cast iron consists of melting the white pig iron, with scrap, in the