An axial load describes a load that creates a force parallel to the axis of an object. When an object spins along a specific line, that line is called the axis. In a manufactured device, the axis typically corresponds to a shaft or rod that holds the spinning part in place. If the shaft was perfectly up and down, any force that pushed from the bottom or top of the object would create pressure parallel to the axis; any force from the side would not.
In order to understand load types, it is necessary to understand spinning objects. If an object spins in a predictable way, such as a top that never stops, it is possible to name parts of it even though the object is in constant motion. A stable object will be symmetrical, meaning any perfect cross section is exactly like any other perfect cross section. When looking at the object, it is possible to define a ‘+’ shaped cross-section where one arm is parallel to the spin and the other arm is perpendicular. The line parallel to the spin is the axis and the perpendicular line is the radius.
Typically, an item can have an axial load, a radial load or a combined load. An axial load creates force parallel to the axis or perpendicular to the radius. A radial load is exactly opposite; it creates force that is parallel to the radius or perpendicular to the axis. This means that as an object spins, the force comes from the sides rather than the top or bottom. Lastly, a combined load is both a radial and axial load.
When a load is perfectly balanced and the spinning object is exactly symmetrical, it creates perfect motion. The force placed on the object will have little impact on the spin and will create little excess wear. In real life, this situation is very unlikely and typically some part of the system is slightly out of balance.
This results in up to three different descriptors. A pitched load forces the axis to move forward or backward in relation to the greater system. Yaw is a measurement of side-to-side movement and roll measures twisting motion. These three terms are especially common when talking about moving vehicles as axles and tires are perfect real-world examples of these types of motion.
Generally, the greater the variance from a perfect radial or axial load, the quicker the part will fail. Even small shifts in weight or angle will have drastic consequences over prolonged use. Unbalanced loads will cause the spinning object to wear evenly over the entire surface, resulting in rapid wear and unpredictable accidents.