Polymer filled capped nut

Capped nuts are provided with an polymer in the top portion of the capped nut. The polymer may be disposed between the inner surface of the cap and a nut body. The polymer may extend into a top opening in the nut body and contact an inner wall of the opening in the nut body.

BACKGROUND

The present invention relates generally to fasteners and more particularly to a nut with a cap secured to a nut body.

A nut is one type of fastener that is commonly used to attach various components together. Typically, a nut has at least an internal threaded portion and one or more external bearing surfaces attached thereto. The bearing surfaces are designed to receive torque from a tool, such as a socket or other wrench, which is used to tighten or loosen the nut. For example, in a conventional nut, the nut may have six bearing surfaces oriented in a hexagonal shape around the internal threads. However, it is possible for nuts to have a different number of bearing surfaces as desired.

Aesthetics is one concern for certain nuts, such as automobile wheel nuts. In particular, many automotive consumers are drawn to the aesthetics of an automobile's wheels, since this is often a distinctive part of an automobile. As a result, wheel nuts have become an integral component of the aesthetics of automotive wheels, and automobiles more generally, because wheel nuts form a highly visible pattern around the center of a wheel.

One approach that has been highly successful in addressing wheel nut aesthetics is stainless steel capped wheel nuts. In this solution, a nut insert is capped with a stainless steel covering. Since stainless steel is resistant to corrosion, durable and visually attractive, stainless steel capped wheel nuts have been capable of addressing a large portion of the demand for aesthetically pleasing wheel nuts. Another advantage of stainless steel capped wheel nuts is that the color of stainless steel, a shiny silverish color, generally matches the color used for most automobile wheels. One disadvantage, however, of stainless steel capped wheel nuts is the cost of manufacturing such wheel nuts.

One problem with conventional capped nuts is that the cap can be damaged by rough handling. Such damage may make a capped wheel nut less aesthetically appealing, and thus, may be rejected by a manufacturer or a consumer. Handling damage usually occurs when capped nuts are shipped in bulk containers with hundreds or thousands of capped nuts mixed together in a container. Because the capped nuts are typically in contact with each other during shipping, rough handling of the shipping container can cause the capped nuts to beat against each other and damage each other.

Accordingly, the inventor believes it would be desirable to provide an improved capped nut that is more resistant to damage.

SUMMARY

A capped nut is described with an polymer inside the cap between the cap and the nut body. The polymer contacts the inner surface of the top of the cap and the inner wall of an opening extending through the nut. One advantage of the polymer is that it increases the damage resistance of the top of the cap. A method for manufacturing the capped nut is also described. The inventions herein may also include any other aspect described below in the written description or in the attached drawings and any combinations thereof.

DETAILED DESCRIPTION

Referring now to the figures, and particularly toFIG. 1, a conventional automotive capped wheel nut10is shown. The nut10includes a metallic nut body12with internal threads14that are threadable onto the external threads of a mating fastener. Preferably, an axial opening16extends through the entire length of the nut body12, although the top portion18of the opening16may be unthreaded18. The nut body12also includes wrenching surfaces20that receive wrenching forces during tightening and loosening of the nut10and transfers the torque to the threaded portion14. The nut body12may have six wrenching surfaces20arranged in a conventional hexagonal shape around the axial opening16and the internal threads14. Preferably, the nut body12has a flange22below the wrenching surfaces20that extends outward from the wrenching surfaces20and has an inward extending step24below the flange22.

The nut body12is inserted into it a cap26that may be made from a metal, such as stainless steel, by stamping. The cap26has corresponding wrenching surfaces28that wrap around the wrenching surfaces20of the nut body12. The lower portion of the cap26preferably forms a skirt30that covers the flange22of the nut body12. The cap26may be secured to the nut body12by welding or other suitable means, but in the preferred embodiment the skirt30wraps around the flange22of the nut body12and engages the step24below the flange22. The top32of the cap26covers the top of the opening16in the nut body12. Thus, the majority of the nut body12, including the top opening16, is not visible to a consumer when the nut10is threaded onto a mating fastener, such as an automotive wheel stud.

In the embodiment shownFIG. 1, the cap26has a raised dome34along the top32. Typically, raised domes34are provided for aesthetic reasons, since it is believed by some that a raised dome34is more attractive than a generally flat or undomed top. Thus, the height of the dome34is usually dictated by aesthetic concerns. In the dome design, a ring portion36of the cap26wraps over the top surface38of the nut body12and is located relatively close to the top surface38of the nut body12. Thus, the dome34forms a circular center portion34that is raised up from the ring portion36.

One particular area of capped nuts10that is more sensitive to rough handling is the top32of the cap26. This is an area of concern for several reasons. The top32of the cap26is less supported than the rest of the cap26because the top32of the cap26covers the opening16through the nut body12. In addition, the top32of the cap26is the most visible portion of the nut10to consumers in certain applications, such as automotive wheel nuts10.

One test that has been developed to test the durability of the top portion32of capped wheel nuts10is a drop test. In the drop test, the capped nut10being tested is placed on a support surface with the top32of the cap26facing upward. Another nut is then raised above the test nut10at a set height and at an angle with one side of the nose40of the nut pointing downwards towards the top32of the test nut10. The raised nut is then dropped so that the angled nose40of the raised nut hits the top32of the cap26of the test nut10. This test is intended to simulate rough handling of capped nuts10when they are packaged in bulk containers with many capped nuts10mixed together in a container. It has been found that capped wheel nuts10in bulk containers typically do not become damaged during normal bouncing that occurs from roadway motion or moving containers from place to place in a staging area. Instead, more significant damage occurs in instances like international ocean shipping when heavy loads are placed on top of a container of capped nuts10and the heavy load crushes the capped nut10container. Thus, damage typically does not occur from capped nuts10jostling against each other during travel motion, but instead, occurs when the capped nuts10are squeezed together by an event that also damages the shipping container.

An example of a damaged capped nut10is shownFIG. 3A. As shown, the conventional capped nut10has a significant dent42along the top32of the dome34. This is the type of damage that would result in the automobile manufacturer rejecting the capped nut10. Because this type of damage is usually caused by an isolated event that affects an entire shipping container as noted above, a large number of capped nuts10in an affected container can be damaged like this. As a result, automobile manufacturers sometimes reject an entire shipping container of capped nuts10instead of trying to sort undamaged nuts10from damaged nuts10. Unfortunately, it is not economical to repair capped nuts10that are damaged likeFIG. 3A, and thus, damaged capped nuts10must be scrapped.

Turning toFIG. 2, an improved capped nut44is shown. A polymer46may be disposed within the opening16and along the inner surface of the top32of the cap26. The polymer46referred to herein has a fluid state and a hardened state. As described further below, the polymer46may be injected into the cap26in the fluid state and thereafter hardens along an inner surface of the cap26. Preferably, the polymer is an epoxy or other adhesive, but may also be other hardenable polymers, such as thermoplastic, thermoset or UV curable polymers. Preferably, the polymer46extends partially into the opening16, and is disposed between the top surface38of the nut body12and the inner surface of the ring portion36of the cap26. Thus, the polymer46fully fills the top area of the inner region of the nut44. While the top portion of the opening16may be threaded, in the embodiment ofFIG. 2the polymer46contacts an unthreaded top portion18of the opening16. The polymer46preferably has a Shore D durometer of 80 or higher. For example, ITW Devcon 1 Minute Epoxy or Resinlab EP1026 may be used.

As shown inFIG. 3B, the polymer46fill provides greater support to the top32of the cap26and increases the resistance of the cap26to damage. Thus, when the same drop test is performed on the improved capped wheel nut46as described above, only a small scratch48or crease48occurs instead of a large dent42as with the conventional nut10shown inFIG. 3A. As a result, the damage resistance of the nut44is greatly improved. Because of the increase in damage resistance, it is also possible that the thickness of the cap26may be reduced to decrease the manufacturing costs of capped nuts44. For example, stainless steel caps26for capped wheel nuts10commonly have a thickness of about 0.018″. However, capped wheel nuts10with larger domes34sometimes require cap thicknesses of 0.020″ or 0.023″. The increased cap thickness for nuts10with larger domes34is primarily due to the need to strengthen the unsupported top32of the cap26. However, it is possible that with the use of the described polymer46, the cap thickness may be about 0.015″ to about 0.018″ for nuts44with the inner surface of the cap26disposed at least 0.180″ above the top surface38of the nut body12. In addition, even for capped nuts44without larger domes34, the cap thickness may be reduced compared to conventional capped nuts10. For example, the cap thickness may be about 0.012″ to about 0.015″ compared to about 0.018″ for conventional stainless steel capped wheel nuts10. Preferably, the cap thickness is within the range of about 0.012″ to about 0.018″.

Turning toFIGS. 4A-4F, the polymer46may be injected into the capped nut44during the manufacturing of the capped nut44. The capped nut44may be manufactured in a multi-station automated assembly machine as schematically depicted inFIGS. 4A-4F. However, the manufacturing method is not limited to a single machine or to a limited number of stations. For example, there may be additional stations between the depicted stations for inspection steps or other purposes and there may be other non-operational stations in the machine.

As shown inFIG. 4A, in the first station50the cap26is placed in a fixture52with fingers54so that the cap26is oriented upside down in the fixture52. In other words, the bottom opening56of the cap26faces upward and the closed top32faces downward.

In the second station58, as shown inFIG. 4B, the polymer46is injected in a fluid state from a nozzle60through the bottom opening56of the cap26onto the inner surface of the closed top32. As a result, a pool of polymer46forms on the inner surface of the top32of the cap26.

In the third station62, as shown inFIG. 4C, the nut body12is inserted into the cap26through the bottom opening56of the cap26with fingers64.

In the fourth station66, as shown inFIG. 4D, the nut body12is pressed into the cap26with a ram68. Although the polymer46may come into contact with the nut body12in the third station62, the pressing in the fourth station66squeezes the polymer46between the inner surface of the top32of the cap26and the top surface38of the nut body12. Excess polymer46flows upward through the opening16in the nut body12and contacts the inner wall of the top portion18of the opening16.

In the fifth station70, as shown inFIG. 4E, the skirt30of the cap26is crimped around the flange22of the nut body12with a die72.

In the sixth station74, as shown inFIG. 4F, the assembled nut44is unloaded from the fixture52with a pin76and is subsequently transferred to a bulk container with other assembled nuts44.

As described above, one advantage of the improved nut44is increased damage resistance along the top32of the nut44. Another advantage is that the polymer46injection can be incorporated into existing manufacturing methods for capped nuts10,44. In particular, by injecting the polymer46into the cap26before inserting the nut body12, the polymer46does not come into contact with the threads14of the nut body12along the bottom portion of the nut body12. The sequence of the method also avoids introducing air pockets into the polymer. In this regard, it is preferable for the polymer46to harden before the nut44is unfixtured and turned upright so that the polymer46remains in the top of the nut44and does not flow into the bottom threads14. Since capped nut44assembly typically involves high volume production, it is preferable for the polymer46to harden within 20 seconds or less. However, it is not necessary for the polymer46to fully harden before the nut44is unfixtured and transferred to a bulk container. The reason for this is that the manufacturing facility is usually a controlled environment and there is little risk of damage to the caps26even in bulk storage in the manufacturing facility. However, it is preferable for the polymer46to fully harden before the capped nuts44leave the manufacturing facility. Thus, it is preferable for the polymer46to fully harden within24hours or less, which is a typical time period that assembled capped nuts44remain in the manufacturing facility before shipping.

While preferred embodiments of the invention have been described, it should be understood that the invention is not so limited, and modifications may be made without departing from the invention. The scope of the invention is defined by the appended claims, and all devices that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein. Furthermore, the advantages described above are not necessarily the only advantages of the invention, and it is not necessarily expected that all of the described advantages will be achieved with every embodiment of the invention.