The term "solenoid force" refers to the load that a solenoid is able to push, pull, or hold when it is energized. Most solenoids are linear, in which case the solenoid force is applied in a linear motion. In the case of rotary solenoids, a rotary ratcheting mechanism is used instead of a linear armature. Many different factors can affect solenoid force, including the coil design, level of electrical current, and how far the armature needs to move each time it is energized. Increased temperatures typically result in reduced solenoid forces, as do increased stroke lengths.
Solenoids are electromechanical transducers that are capable of converting electrical energy into linear or rotary motion. They typically consist of a stationary electromagnetic coil and a movable metal slug, which is referred to as an armature. When the electromagnetic coil is energized, it generates a magnetic field that causes the armature to move. The movement of the armature results in the force that allows a solenoid to activate an electronic relay, open a mechanical valve, or do other similar work. Solenoids are found in everything from fuel injectors to pinball machines.
There are three main types of force that a solenoid can produce when it is energized, though some solenoids perform more than one function. Push force is achieved when an armature forces a push rod to extend and move a load away from the solenoid. The opposite of that is pull force, which is achieved when an armature retracts and pulls a load inward. Hold force is the third type, and it allows a solenoid to resist any movement when an external load pulls or pushes.
A number of different factors can contribute to the level of force a solenoid is able to produce. The design of the electromagnetic coil is a primary factor, since that dictates the size of the electromagnetic field. In that same vein, the size of the armature and amount of electricity used to energize the coil can also have an effect. Another important factor inherent in solenoid design is the stroke length, or how far the armature needs to move. In order to achieve the highest possible solenoid force, solenoids are often designed with the shortest viable stroke length.
It is also possible for external factors, such as temperature, to affect solenoid force. Higher temperatures are typically associated with a reduction in solenoid force. Since solenoid coils also heat up when they are energized, most units have a maximum stable temperature at which they are rated. That temperature typically factors in both ambient temperature, and the increase associated with an energized coil. After that stable temperature is exceeded, solenoid force can decrease by up to 65%.