Downloaded from https://www.everyspec.com FM 1-506 Oil-change intervals for turbine engines vary widely from model to model. They depend on the severity of oil temperature conditions imposed by the specific airframe installation and engine configuration. Follow the ap- plicable manufacturer’s instructions. The term “antifriction” has long been used to dif- ferentiate rolling and sliding bearings. The word is gradually being dropped in deference to the word “roll- ing" to describe ball and roller bearings. The term’’rolling bearings’’ will be used in this manual to describe all bearings consisting of ball or roller elements that roll between concentric inner and outer rings.
The term “plain or journal bearings” will be used to describe two- piece bearings where the two rotating surfaces are sliding with respect to each other. Synthetic oil for turbine engines is usually supplied in sealed l-quart or l-gallon metal cans. Although this type of container was chosen to minimize contamination, it is often necessary to filter the oil to remove metal slivers, can sealants, and so forth, which may occur when opening the can. Rolling Bearings Some oil grades used in turbojet engines may contain oxidation preventives, load-carrying additives and sub- stances that lower the pour point, in addition to synthetic chemical-base materials.
BEARINGS A brief review of history reveals the long gradual development of rolling bearing. They were developed to reduce friction, thereby increasing work output while reducing energy input. Rolling-type bearings changed sliding friction into rolling motion with a greatly reduced friction level. In Army aircraft bearings are found throughout the power train system from the engine to the rotor or propeller. The failure of anyone of these bearings would place the entire aircraft in jeopardy. It is crucial that they be properly serviced and maintained.
In fact, bearings are considered so important that a major air raid was con- ducted at considerable sacrifice during World War II in an attempt to eliminate one of Germany's principal bear- ing manufacturing centers. If the Allies could have destroyed Germany’s capacity to produce antifriction bearings, its entire aviation effort would have come to an immediate standstill. Today, our economy could not func- tion without bearings. Assyrians and Babylonians as far back as 1100 BC used round logs as rollers to move huge monuments and stones. With the rollers placed under the load, it could more easily be pulled.
AS the rollers came out of the rear of the load, they were carried around to the front and placed in the oncoming path of the load The wheel was an extremely important develop- ment; however, it was based on sliding friction. The use of lubricants did reduce friction and increase load and life expectancy of the wheel. But it was not until the axle rested on balls or rollers that sliding friction was finally changed to rolling motion and the fiction level sig- nificantly reduced. Bearings have the following functions. They– Support the load on a shaft. The load may be a wheel, pulley, or gear, or it may be the turning shaft itself. Reduce friction created by turning.
This is ac- complished both by design and by lubrication and is one of the most important functions of bearings. Reduce friction created by thrust. A specially designed bearing is required for this purpose. Hold a shaft in rigid alignment. A high-speed rotating shaft has a tendency to “whip” unless adequately supported by bearings. Provide a place for adjustment. Bearings are classified into two broad categories Friction– also commonly known as a plain or babbitt type; it makes a sliding contact with the shaft. Antifriction– contains rollers or balls; it makes a rolling contact with the shaft. Modern rolling bearing had their origin with the great inventor, Leonardo da Vinci, about 1500 AD.
Many of his drawings show the use of balls and rollers and foreshadow such modem technology as surface finish, raceway grooves, and conical pivots. Rolling bearings are also classified into two types ball and roller. Ball Bearings. The ball bearing is one of the most common used in aircraft. With relatively minor variations it can be adapted to many different uses. It creates the least amount of friction of any common bearing because the ball itself is the best antifriction rolling device known. The ball maintains point contact with the surface it rolls on and reduces friction to a minimum. It is, therefore, best suited to high-speed applications. Roller Bearing.
The roller bearing makes use of a cylindrical-shaped roller between the fiction surfaces. 1-7