The present disclosure relates to mechanical machine parts and more particularly, but not exclusively, to a type of machine part commonly known as a “spring plunger” or a “ball and spring plunger.”
Mechanical devices known variously as “plungers,” “spring plungers,” “ball and spring plungers,” and “press-fit plungers” are used throughout industry in various applications. Such devices may be used as components of a larger apparatus such as a rotatable work surface to provide a locating feature which allows a user to reliably return the apparatus to a home position, or to provide a positioning feature which allows a user to reliably rotate the apparatus to one of a plurality of predetermined orientations, e.g., a 15 degree angle, a 30 degree angle, a 45 degree angle, etc. Related uses may include indexing, locating, and positioning applications in dies, special tooling, and automatic feed devices. Alternately, such devices may be used as components of an electrical circuit extending between the separable parts of an apparatus. In such uses, the device may be inserted into a conductive socket disposed in the transverse face of a first part, and oppose a conductive contact plate affixed to the transverse face of a second part. In such an arrangement, the device biases a conductive ball or nose against the contact plate, providing a durable electrical contact that is tolerant of reasonable variations in the distance separating the opposing faces of the respective parts. Related uses may include electrical supply or contact sensor applications in dies, automatic feed devices, and other machinery.
Typical constructions of such devices include non-adjustable collared plungers and adjustable threaded plungers. Collared plungers may have a body that consists of a main barrel having an essentially constant outer diameter and a proximal collar surrounding a plunger opening. The collar typically extends laterally outward from the main barrel of the device, and serves to position the device over a blind aperture drilled or otherwise formed in the front or face of a receiving part. Collared plungers may be friction fit into such an aperture, but can loosen or separate from the receiving part in environments that experience substantial vibration and/or thermal cycling because the “tightness” of the friction fit is limited by the force that can be applied to the collar of the device during installation. Such devices are typically inserted into an aperture by lightly hammering or pressing the proximal end of the device, particularly the collar, to drive the device into the aperture, however, when excessive force is applied to the collar it may become damaged. Such damage may include distortion of the outer rim of the collar, which may prevent the collar from sitting flush against the surface of the receiving part, and distortion of the inner rim of the collar, which may prevent the plunger from returning to a fully extended position. Either type of damage may cause the assembly to fail to meet specifications. Typical uses of collared plungers are also restricted by the nature of their construction in that (1) the collar of the device typically rests above the front or face of the receiving part, which exposes the device to potentially damaging strikes from opposing cycling parts or other loose matter and (2) the device must be installed through the front or face of the receiving part, which restricts the range of applications or design configurations that may make use of such a device without substantial design modifications.
Threaded plungers overcome many of the drawbacks associated with collared plungers, but require significant machining and installation preparation. Threaded plungers may have a body consisting of a threaded shaft and a proximal slotted rim surrounding a plunger opening. Such plungers may also include a plastic locking element and/or second slot disposed across a distal wall of the device. Threaded plungers are typically screwed into an aperture that has been tapped to provide complementary threading, and the plastic locking element, if present, serves to frictionally engage the aperture threads to increase the torque that must be applied to install, adjust, or remove the device. Such devices are typically installed by using a plunger wrench that engages the slotted rim of the device while minimizing contact with the plunger, permitting one to screw the device into a threaded aperture in the front or face of a receiving part. Such devices may also be installed by using a narrow-blade screwdriver that engages the second distal slot, if present, permitting one to screw the device into a threaded aperture through the rear of the receiving part. If the device is installed through the front or face of a receiving part with a screwdriver rather than a plunger wrench, the blade of the screwdriver will depress the plunger of the device past the outer surface of the slotted rim during installation. Such excessive travel may overcompress an internal spring, altering the plunger force profile and damaging the device.
Thus there is also a need for a plunger device that may be installed into a drilled or formed aperture through either the front or the rear of a receiving part without additional preparation of the aperture, such as tapping. There is also a need for a non-threaded plunger device that is better able to resist vibration and thermal cycling.