Patent Application
20080292393
This invention relates generally to a retainer ring. More specifically, the invention relates to a semi-permanent plastic retainer ring.
Fastener and/or retainer mechanisms are used in a variety of applications and industries in order to prevent undesired movement of a component. If the component is located on a shaft, bar, rod and the like, undesired lateral movement of the component can result in significant damage to surrounding articles, structures and the like.
One type of fastener that can be used on a shaft is a circlip, also known as a snap ring, which consists of a semi-flexible metal ring with open ends which can be snapped into place within a machined groove of the shaft. The snap ring allows rotation of a part on the shaft but prevents lateral movement. Although useful, the snap ring requires a metal stamping operation which increases the cost of the component. In addition, failure of the snap ring during service can result in metal fragments, for example within a gear transmission, that can cause damage, wear, etc. to surrounding components.
Another type of fastener that can be used on a shaft is a cotter pin. The cotter pin is a metal fastener with two tines that are bent during installation. Typically made from a wire with a half-circular cross section, cotter pins are made of very soft metal and can be subject to metal fatigue. Thus, similar to snap rings, failure of the metal wire can result in damage, wear, etc. to surrounding components.
Other methods for securing articles and/or components on a shaft are well known in the art, for example the use of a nut in combination with threads on the shaft. In addition, a washer or plate type structure can be welded onto the shaft in order to prevent undesirable movement of components thereon. However, these securement mechanisms are relatively permanent in nature and do not lend themselves for use when repair of such an article may be needed. Therefore, there is a need for an improved semi-permanent retainer mechanism.
A semi-permanent retainer mechanism for securing a shaft within a component by forming a semi-permanent ridge on the shaft is provided. The mechanism includes a ring made from a heat shrinkable polymer that will heat shrink into a radial groove on the shaft. The heat shrinkable polymer of the ring has a release temperature wherein the ring shrinks in size when heated to a temperature above the release temperature. The ring has a pre-release size that is larger than the radial groove and a release size that is smaller than the outer circumference of the shaft.
In an embodiment of the present invention, a shaft is cylindrical in shape and a radial groove on the shaft has an inner diameter. In this embodiment, the ring is circular in shape and has a release inner diameter that is less than the radial groove inner diameter. Once placed onto the shaft and the radial groove, heating of the ring above the release temperature results in ring shrinkage such that the ring inner diameter and the radial groove inner diameter are in contact with each other. Therefore part of the heat shrinkable polymer ring is within the radial groove of the shaft and part of the ring extends beyond the radial groove. The plastic ring can be removed by cutting the ring with a sharp object and/or prying it off of the shaft with a lever device such as a screw driver. In this manner a semi-permanent retainer mechanism in the form of a securement ridge is formed on the shaft. The present invention also includes a method for forming the securement ridge on the shaft.
The present invention discloses a semi-permanent retainer mechanism in the form of a simple to use plastic retainer ring that prevents undesirable lateral movement of a component on a shaft. As such, the present invention has utility as a retainer ring used to prevent unwanted removal and/or movement of components on a shaft.
The semi-permanent plastic retainer ring of the present invention is made from a heat shrinkable polymer. The ring can include a generally axially oriented split separation which affords for the opening and/or expanding of the ring and subsequent placement onto a shaft. Once placed onto the shaft, the ring can be heated above a release temperature of the heat shrinkable polymer and allowed to shrink onto the shaft. Shrinking of the ring onto the shaft provides a circumferential ridge which can prevent lateral movement of a component on the shaft.
Referring now to
The ring 200, having a thickness in the radial direction and a width in the axial direction, is made from a heat shrinkable polymer which affords for the shrinking of the ring when heated. The heat shrinkable polymers used in the present invention have a release temperature which is defined as the temperature above which the polymer shrinks. The ring 200 has a pre-release inner diameter 222 defined as the diameter of the ring before being heated above the release temperature of the ring, that is, the ID in the pre-shrunk condition. The ring 200 also has a release inner diameter (not shown) which is defined as the inner diameter of the ring after being heated in free space above the release temperature of the polymer, that is, the ID in the post-shrunk condition. The ring 200 can be made from any heat shrinkable polymer known to those skilled in the art, illustratively including fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE), polyolefin, polyvinylchloride (PVC), polyvinylidene fluoride (PVDF) and combinations thereof. The release temperature of a heat shrinkable polymer used in the present invention can range from approximately 100 to 300 degrees centigrade. It is appreciated that the heat shrinkable polymer used to make a semi-permanent plastic ring of the present invention is chosen based on design factors and requirements of a particular application. It is also appreciated that the ring cross-section can be any shape, illustratively including a square, round-corner square, rectangle, round-corner rectangle, circle, hexagon and the like.
In an example of the present embodiment, the prerelease ID 222 of the ring 200 is approximately equal to the diameter 110 of the shaft 100. For the purposes of the present invention, the term “approximately equal to” is defined to mean of equal dimension within a tolerance of +25%. In another example of the present invention, the pre-release ID 222 of the ring 200 is less than the diameter 110 of the shaft 100 and greater than the ID 115 of the radial groove 120.
As illustrated in
In an example, heating the ring 200 above its release temperature results in shrinkage of the ring 200 such that the ID surface 220 is in contact with the radial groove inner surface 122. In another example, heating of the ring 200 above its release temperature results in shrinkage such that the ID surface 220 is not in contact with the radial groove inner surface 122 but has a post-shrunk diameter less than the shaft diameter 110. Therefore, the post-release ring 200 provides a retainer ring in the form of a circumferential ridge along the outer circumference 110 of the shaft 100. Turning now to
Although
Turning now to
A ring 500 has a shape generally matching the end cross-sectional shape of the shaft 400 and includes sidewalls 525 adjoining an inner circumference surface 520 to an outer circumference surface 530. Optionally, a generally axially oriented separation 510 can be included within ring 500. Similar to the embodiment shown in
The semi-permanent plastic retainer ring described above can be used as part of a semi-permanent retainer mechanism that affords for the desired securement of a component on the shaft. For example, components such as gears are commonly located on a shaft wherein lateral movement of the gears along the shaft is undesirable. Using the semi-permanent retainer mechanism of the present invention, a gear is placed onto the shaft, the shaft optionally having a radial groove therein, followed by placement of the retainer ring. Thereafter, a heat source applies heat to the ring and thereby raises the temperature of the ring material above the release temperature of the heat shrinkable polymer. After reaching the release temperature, the ring shrinks and forms a circumferential ridge along the outer circumference of the shaft. Once in place, the gear on the shaft can rotate about the shaft, if desired, but undesirable lateral movement is prevented. If removal of the gear from the shaft is desired, a knife or lever mechanism can be used to remove the ring and thereby allow the gear to be removed also.
The foregoing drawings, discussion and description are illustrative of specific embodiments of the present invention, but they are not meant to be limitations upon the practice thereof. Numerous modifications and variations of the invention will be readily apparent to those of skill in the art in view of the teaching presented herein. It is the following claims, including all equivalents, which define the scope of the invention.
