Grades for Greases. The National Lubricating Grease Institute has adapted six grade numbers which are an indication of firmness or hardness of the grease, as shown in Table 5–3. The ASTM worked penetration at 77°F. is shown in relation to the NLGI grade number.
TABLE 5–3. GREASE GRADES AND WORKED PENETRATION
| NLGI no. | ASTM worked penetration |
| 0 | 355–385 |
| 1 | 310–340 |
| 2 | 265–295 |
| 3 | 220–250 |
| 4 | 175–205 |
| 5 | 130–160 |
The penetration test consists of dropping a metal cone, of standard size and weight, into a worked grease at a specified temperature (usually 77°F.), and measuring the penetration of the cone after a specified time interval. The consistency or hardness of greases ranges from No. 0, very soft, to No. 5, a very hard grease. The color of greases varies from light red to pitch black according to the ingredients used.
FIG. 5–8. Centralized lubricating system with inset showing essential parts of a central lubricating system. (Alemite Division, Stewart-Warner Corp.)
Methods of Applying Greases. Some greases are applied by hand with a paddle, swab, or brush, to gears, chains, and wire rope. Slow-moving bearings may be lubricated by placing the grease in cups of the screw-down, spring-loaded, and automatic types.
All well-designed modern farm machinery has high-pressure grease fittings at the points requiring lubrication. The grease is applied through the fitting with high-pressure grease guns (Figs. 5–5 to 5-8). Companies manufacturing lubricants have available lubrication guides showing all the points on the machine requiring lubrication and the kind of oil or grease recommended for each fitting.
REFERENCES
Alemite Answers, Alemite Division, Stewart-Warner Corporation, 1945.
American Petroleum Institute, Tech. Letter no. 4–397, 1952.
Clower, J. I.: American Lubricating Greases, Virginia Polytechnic Institute, Engin. Ext. Bul. 35, 1935.
Farm Machinery Lubrication Guides, The Texas Company.
Jones, F. R.: Farm Gas Engines and Tractors, Chap. 23, McGraw-Hill Book Company, Inc., 1952.
Lubricating Greases, Engin. Bul. G-208, Standard Oil Company.
Lubrication Guide for Farm Equipment, Socony-Vacuum Oil Co., Inc., 1951 ed.
QUESTIONS AND PROBLEMS
1. Define friction and discuss its advantages and disadvantages.
2. Enumerate the forms, kinds, and sources of lubricants.
3. Explain the API system of service classification of lubricants for gasoline and spark-ignition engines; name the different kinds of service and give the main features of each service.
4. Explain the API service systems for diesel engines and give the main features of each system.
5. Discuss the SAE grades of engine oils and gear lubricants. What is meant by an EP gear lubricant?
6. Explain the meaning of oil viscosity, and describe how it is measured.
7. Give a definition for grease and list the main types according to use.
8. Explain the NLGI grades of grease.
9. Discuss the various methods of applying greases to farm equipment. What is meant by high-pressure lubrication?
CHAPTER 6
HYDRAULIC POWER LIFTS AND RUBBER TIRES
HYDRAULIC POWER
Farm equipment prior to the nineteenth century era was animal drawn, guided by hand, and lifted manually. Later, when equipment was mounted on wheels, levers were used to raise and lower the working units. The first mechanical power-lift was developed for the trailing-type tractor-drawn plows about 1910 (Fig. 6–1). The tractor power lift was developed about 1930 to raise and lower planters and cultivators mounted on the row-crop tractor. The use of hydraulic power for lifting tractor-mounted equipment was introduced in 1933. Hydraulic power lifts are now used for raising, lowering, and controlling almost all types of field equipment, ranging from the small plow to the platform of a grain combine and the drums of cotton-picking machines. In fact, if it were not for the hydraulic lifts, these heavy units would be extremely difficult to operate.
FIG. 6–1. A mechanical power lift for plow.
The extensive use of hydraulic lifts and controls makes it essential that the operator of modern farm equipment have an understanding of the fundamental principles of power-lift hydraulics.
Fundamentals of Hydraulics. There are several branches of hydraulics, but the branch applicable to farm equipment deals with enclosed liquids under pressure. The fundamental law of hydrostatics, or the mechanics of fluids, was defined by Blaise Pascal1 in 1653 as follows: “Pressure applied to an enclosed fluid is transmitted equally and undiminished in all directions to every part of the fluid and of its restraining surfaces.” The application of this law is shown in Figs. 6–2 and 6–3. In Fig. 6–3 is a 1-pound weight acting on 1 square inch of liquid which is counter-balanced by a weight of 10 pounds on 10 square inches of liquid. There is a 1-pound pressure for each square inch of surface on all sides of the container. The 1-inch piston must move 10 inches to move the 10-square-inch piston 1 inch.
Oil Pumps. Pumps are required in the operation of hydraulic controls to draw the oil from a reservoir and force it into a cylinder. The pump may be of three types, namely, gear, vane, and piston.
FIG. 6–2. How pressure on a liquid distributes pressure in all directions of its enclosure case. (International Harvester Company.)
A typical rotary double-gear pump consists of two closely meshing gears enclosed in a tight, compact housing. There are intake and discharge ports on opposite sides of the housing. When they rotate as indicated in