Bolt for security seal

A seal bolt includes: an elongate and electrically conductive part with a portion extending between first and second locations lengthwise of the bolt; an electrically conductive layer that, between the first and second locations, is spaced from the elongate part; an electrically insulating layer that, between the first and second locations, is disposed between the conductive layer and the elongate part; and structure that electrically couples the elongate part and the conductive layer at a third location, the second location being between the first and third locations. In one configuration, the insulating layer includes aluminum oxide. In another configuration, the conductive layer is one of an amorphous metal and stainless steel. In still another configuration, the conductive layer includes a strip that, from the first location to the second location, has a width less than a circumference of the elongate part.

FIELD OF THE INVENTION

This invention relates in general to security seals of a type that can be used with cargo containers and, more particularly, to security bolts that are components of certain security seals.

BACKGROUND

A variety of different products are shipped in cargo containers. Products are typically packed into the container by a shipper, and then the container doors are closed and secured. The container is then transported to a destination, where a recipient opens the container and unloads the products.

The shipper often finds it desirable to have some form of security and/or monitoring in place while the container is being transported. For example, the cargo within the container may include relatively valuable products, such as computers or other electronic devices. Thieves may thus attempt to break into the container and steal these products if the container is left unattended during transport. It is not cost-feasible to achieve suitable security and/or monitoring by having a person watch the container at all times during transport. Accordingly, various devices have previously been developed to provide some degree of security and/or monitoring. Although these pre-existing devices have been generally adequate for their intended purposes, they have not been satisfactory in all respects.

For example, one pre-existing container security device is commonly referred to as a bolt seal. It includes an elongate bolt or pin with a head at one end. The bolt is inserted through aligned openings in a latch mechanism on the container doors, and then the free end of the bolt is inserted into a retaining assembly. The retaining assembly mechanically and permanently grips the bolt, so that the bolt cannot be withdrawn. The bolt has an electrically conductive core and an electrically conductive sleeve that are separated by an electrically insulating layer, except that the core and sleeve are in an electrical contact in the region of the head of the bolt. The retaining assembly has a circuit with two electrical contacts that respectively engage the conductive core and the conductive sleeve. Since the core and sleeve are electrically shorted at the head of the bolt, the two contacts of the circuit are also electrically shorted during normal operation.

If a thief cuts the bolt at a location between the head and the retaining assembly, the removal of the head eliminates the internal electrical short between the conductive core and the conductive sleeve. Since the core and the sleeve are no longer shorted, the contacts of the circuit are also no longer shorted, and thus the circuit can tell that someone has tampered with the bolt. The circuit can optionally include a radio transmitter, and the radio transmitter can then transmit a wireless signal indicating that the circuit has detected tampering.

In practice, devices of this type do not always operate in this intended manner. As one example, pre-existing bolts often have a conductive sleeve made from nickel, which is a relatively soft material. When a thief cuts the bolt, the jaws of the bolt cutter can smear the nickel material in a radially inward direction as the cut is made. When this smear occurs, it creates an electrical short between the conductive sleeve and the conductive core. Thus, even though the original internal short is eliminated with the removal of the bolt head, it is effectively replaced by an equivalent short in the form of the nickel smear. Due to this new short, the contacts of the circuit in the retaining assembly remain electrically shorted. Consequently, the circuit does not detect the fact that tampering has occurred, and does not take appropriate action.

In terms of testing a bolt configuration, several bolts with that configuration may each be subjected to a “loose cargo test” conforming to a well-known standard defined by MIL-STD 310F, and then a bolt cutting test of the type discussed above. Pre-existing bolt configurations tend to fail rapidly in the loose cargo test, without ever making it as far as the bolt cutting test.

DETAILED DESCRIPTION

FIG. 1is a diagrammatic top view of an apparatus10that is a container security device. Devices of this general type are often referred to as bolt seals. The apparatus10includes a security bolt11that embodies aspects of the invention, and a known type of retaining assembly12that is shown in broken lines.FIG. 2is a diagrammatic side view of the bolt11ofFIG. 1.FIG. 3is a diagrammatic sectional view of the bolt11, taken along the line3-3inFIG. 2. The drawings of the present application are not drawn to scale in all respects. As one example, the thicknesses of some layers have been exaggerated for clarity.

Referring toFIGS. 1-3, the bolt11has at its center an elongate, electrically conductive pin16.FIG. 4is a diagrammatic top view the pin16by itself, andFIG. 5is a diagrammatic side view of the pin16. In the disclosed embodiment, the pin16is made of steel. However, it could alternatively be made of any other suitable material. The pin16is cylindrical along most of its length, except at each end. At one end, the pin16has an optional tapered surface18of approximately frustoconical shape. The tapered surface18facilitates insertion of the bolt11into the retaining assembly12(FIG. 1). Near the tapered surface18, the pin16has a circumferential groove19.

At its opposite end, the pin16has a flattened head21. With reference toFIG. 4, the head21has approximately an oval shape in a top view, with a length that is greater than the diameter of the remainder of the pin16. With reference toFIG. 5, the head21is generally flat in a side view, with a thickness that is approximately equal to the diameter of the pin16. The shape of the head21inFIGS. 4 and 5is exemplary, and the head21could alternatively have any of a variety of other shapes. Although the illustrated pin16is generally cylindrical between its ends, it could alternatively have any of a variety of other cross-sectional shapes.

Referring again toFIGS. 1 and 2, the pin16is coated over a portion of its length with a layer26of an electrically insulating material.FIG. 6is a diagrammatic top view of the pin16with the insulating layer26thereon. The insulating layer26completely coats the exterior surface of the pin16within the region indicated at27. It will be noted that the outer end of the head21is not coated with the insulating layer26. The insulating layer26is, in effect, a sleeve that surrounds the pin16over a portion27of its length. In the disclosed embodiment, the insulating layer26is made from aluminum oxide, also known as alumina. However, in an alternative embodiment, the insulating layer26could be made from some other suitable material that is electrically insulating.

Referring again toFIGS. 1 and 2, an electrically conductive layer36is provided over part of the insulating layer26.FIG. 7is a diagrammatic top view of the pin16, insulating layer26, and conductive layer36.FIG. 8is a diagrammatic side view of the pin16, insulating layer26, and conductive layer36. The conductive layer36coats all exposed surfaces of the insulating layer26and the pin16in a region of the bolt that is identified at37. As shown inFIGS. 7 and 8, the insulating layer26extends leftwardly a short distance beyond the end of the conductive layer36. As shown inFIG. 6, and as discussed above, the head21has a portion that is not coated by the insulating layer26. Thus, with reference toFIGS. 7 and 8, it will be recognized that, at the outer end of the head21, the conductive layer36is in direct physical contact with the conductive pin16. The remainder of the conductive layer36is electrically separated from the pin16by the insulating layer26.

In the illustrated embodiment, the conductive layer36is an amorphous metal material that includes iron, chromium, silicon and boron. As one example, the conductive layer26may include 26% to 31% chromium, 1.2% to 2.7% silicon, and 3.3% to 4.1% boron, with the remainder being iron. One suitable material for the conductive layer26can be obtained commercially under the trademark ARMACOR M® from Liquidmetal Technologies Corporation of Lake Forest, Calif. However, the conductive coating36could alternatively be made from other suitable materials, including but not limited to stainless steel or nickel. ARMACOR M® and stainless steel are not as soft as nickel, and are thus less likely to smear radially when a bolt is cut. As still another alternative, the conductive layer36could be made from a conductive epoxy or a conductive polymer, either of which could be applied by spraying at room temperature.

Referring again toFIGS. 1 and 2, the exterior surfaces of the conductive layer36are completely coated with an electrically insulating outer layer41in a region of the bolt11that is identified at42. The outer layer41can be made from any of a variety of electrically insulating materials that are known in the art.

Referring again toFIG. 1, the retaining assembly12includes a retainer mechanism that is shown diagrammatically at51, and that includes a spring clip52. When the free end of the bolt11has been fully inserted into the retaining assembly12, the spring clip52engages the circumferential groove19in the pin16, in order to permanently secure the bolt11within the retaining assembly12, so that the bolt cannot be withdrawn.

The retaining assembly12also includes a circuit56with two spaced electrical contacts57and58. When the end of the bolt11is disposed in the retaining assembly12, and is fixedly held in place by the retainer mechanism51, the electrical contact57engages the exposed surface of conductive pin16, and the electrical contact58engages the exposed surface of conductive layer36. As explained above, the head of the bolt11contains an electrical short between the pin16and the conductive layer36. Thus, during normal operation, the electrical contacts57and58will be shorted to each other by the bolt. Assume that a thief cuts the bolt11, for example at a location66between the retaining assembly12and the head of the bolt. When the thief cuts the bolt, the head of the bolt becomes separated from the rest of the bolt, thereby eliminating the internal short between the pin16and the conductive layer36. Consequently, the electrical contacts57and58will no longer be electrically shorted by the bolt. The circuit56can thus detect that the bolt11had been cut. The circuit56then could, for example, transmit a wireless signal indicating that the security device10has apparently been subjected to some form of tampering.

FIG. 9is a diagrammatic top view of a bolt111that is an alternative embodiment of the bolt11ofFIG. 1.FIG. 10is a diagrammatic side view of the bolt111, andFIG. 11is a diagrammatic sectional view taken along the section line11-11inFIG. 10. The bolt111includes an outer layer equivalent to that shown at41inFIG. 1, but the outer layer is omitted inFIGS. 9-11for clarity. The bolt111ofFIGS. 9-11is identical to the bolt11ofFIG. 1, with one difference. In particular, with reference toFIG. 8, the conductive layer36of the bolt11covers all underlying surfaces in the region37. In contrast, with reference toFIGS. 9-11, the bolt111has two conductive layers136A and136B instead of the single conductive layer36. The two conductive layers136A and136B are provided on opposite sides of the bolt111, as best seen inFIGS. 10 and 11. The edges of the conductive layer136A are thus spaced circumferentially from the edges of the conductive layer136B by a gap141(FIG. 10). The conductive layers136A and136B can be made from any of the same materials discussed above in association with the conductive layer36of the bolt11.

With reference toFIGS. 10 and 11, it will be noted that the conductive layers136A and136B include respective strips of electrically conductive material that each extend lengthwise of the bolt111, and that are spaced circumferentially from each other. As best seen inFIG. 11, these strips are each thicker in the middle than at the edges. Although the bolt111ofFIGS. 9-11has two of these strips, it would alternatively be possible to provide only one such strip, or to provide three or more strips that are circumferentially spaced and that extend lengthwise of the bolt. It will also be noted that the strips136A and136B each extend straight along the bolt11, parallel to the centerline of the bolt. However, these strips could alternatively be arranged in various other configurations. For example, the strips could be arranged so that they each extend along and around the bolt in a spiral, while still remaining circumferentially spaced from each other.

FIG. 12is a diagrammatic top view of a bolt211that is an alternative embodiment of the bolt111ofFIGS. 9-11.FIG. 13is a diagrammatic side view of the bolt211. The bolt211ofFIGS. 12-13is identical to the bolt111ofFIGS. 9-11, except that the conductive layer includes not only the portions136A and136B, but also an additional portion136C that is spaced axially from the portions136A and136B, and that has one portion disposed on the insulating layer26and another portion disposed on the pin16.

FIG. 14is a diagrammatic top view of a bolt311that is an alternative embodiment of the bolt211ofFIGS. 12-13.FIG. 15is a diagrammatic side view of the bolt311. The bolt311ofFIGS. 14-15is identical to the bolt211ofFIGS. 12-13, except that the conductive sleeve136C of the bolt211is split into two conductive strips136D and136E that are disposed on opposite sides of the bolt311, with their lateral edges spaced by the gap141.

A number of bolts were built and tested, using different configurations and materials for the conductive layer36or136, and different thicknesses for the aluminum oxide insulating layer26. Several bolts of each configuration were initially subjected to a “loose cargo test” that conformed to a well-known standard defined by MIL-STD 310F. A bolt configuration was deemed to have passed the loose cargo test if all of the tested bolts with that configuration passed the loose cargo test. Table 1 below identifies 16 bolt configurations that all passed the loose cargo test, where each row of the table represents a respective different bolt configuration. Table 1 summarizes additional testing that was carried out on each of these bolt configurations, in the form of a bolt cutting test that tests bolts for a false tamper signal, or in other words an undesired electrical short.

In more detail, for each bolt configuration in Table 1, 25 to 50 bolts with that configuration were subjected to the bolt cutting test. In particular, standard bolt cutters were used to cut each bolt approximately at location66inFIG. 1, and then a measurement was taken of the electrical resistance between the conductive pin16and each conductive layer36or136, at locations where the bolt would typically be engaged by the electrical contacts57and58. If a bolt exhibited a relatively high resistance that effectively represented an open circuit, then that particular bolt was deemed to have passed the bolt cutting test. Conversely, if a bolt exhibited a relatively low resistance that effectively represented an electrical short, then that particular bolt was deemed to have failed the bolt cutting test. For a given configuration/row in Table 1, if 100% of the tested bolts with that configuration each passed the bolt cutting test, then that configuration was deemed to have passed the bolt cutting test. Conversely, if just one of the tested bolts with that configuration failed the bolt cutting test, then that configuration was deemed to have failed the bolt cutting test.

Turning now in more detail to Table 1, bolt configurations1-6all involve an aluminum oxide insulating layer26with a thickness of approximately 0.025 inches. The bolts in configurations1,3and5each had a conductive layer configured as multiple strips, for example as shown at136A and136B inFIGS. 9-11. The materials used for the conductive layers136A and136B in these three configurations were respectively ARMACOR M®, 400 stainless steel (400 SS), and nickel. The bolts in configurations2,4and6had a continuous conductive layer rather than strips, for example as shown at36inFIG. 7-8. The materials used for the conductive layers36in these three configurations were respectively ARMACOR M®, 400 stainless steel (400 SS), and nickel. As evident from Table 1, all of the bolts in each of configurations1-6passed the bolt cutting test.

During fabrication of bolts, the aluminum oxide insulating layer26is formed by a plasma process. The larger the thickness of the insulating layer, the longer the plasma process must be performed in order to produce that thickness. The plasma process uses a significant amount of energy, due in part to the fact that it is performed at a high temperature, and due in part to the energy needed to form the plasma. Consequently, with reference to bolt configurations1-6in Table 1, an insulating layer26with a thickness of a 0.025 inches is relatively expensive, because of the amount of energy required to produce that thickness. Accordingly, while the bolts in configurations1-6all exhibit excellent performance in both the loose cargo test and the bolt cutting test, it is desirable to consider whether their cost could be reduced by reducing the thickness of the aluminum oxide insulating layer26.

Accordingly, in Table 1, bolt configurations7-12are respectively identical to configurations1-6, except that the thickness of the aluminum oxide insulating layer26was 0.012 inches, or in other words about half of the thickness used for bolt configurations1-6. As shown in Table 1, configurations7and8each involved bolts with a conductive layer36or136made of ARMACOR M®, and all bolts with configurations7and8passed the bolt cutting test. Further, bolt configurations9and11involved bolts with the conductive layer made of 410 stainless steel or nickel and configured as multiple strips136A and136B, and all bolts with configurations9and11passed the bolt cutting test. However, as to bolt configurations10and12, where the conductive layer was made of 410 stainless steel or nickel, and was a continuous layer36rather than strips136A and136B, some bolts with each of these configurations did not pass the bolt cutting test.

As discussed above, the cost of the aluminum oxide insulating layer26increases progressively with increasing thickness. Accordingly, in Table 1, bolt configurations13-16are respectively identical to configurations1-3and5, except that the thickness of the aluminum oxide insulating layer26was 0.006 inches, or in other words about one-quarter the thickness used for bolt configurations1-6, and about one-half the thickness used for bolt configurations7-12. As evident from Table 1, the bolts with configuration13all passed the bolt cutting test, in particular where the conductive layer was made of ARMACOR M® and formed as strips (as at136A and136B inFIGS. 9-11). On the other hand, as to the bolts with configuration14, where the conductive layer was made of ARMACOR M® and was continuous (as at36inFIGS. 7-8), at least one bolt with this configurations did not pass the bolt cutting test. Bolt configurations15and16each had a conductive layer arranged as strips136A and136B made of either 410 stainless steel or nickel, and at least one bolt in each of these configurations did not pass the bolt cutting test.

The bolts in configurations13and14satisfactorily passed both the loose cargo test and the bolt cutting test, and also have the thinnest layers of aluminum oxide. Thus, they involve the lowest cost for fabricating the aluminum oxide layer26. On the other hand, configurations13and14use ARMACOR M®, which is a relatively expensive material in comparison to either stainless steel or nickel. Depending on factors such as production quantities, the differential cost of using ARMACOR M® instead of stainless steel or nickel can exceed the differential cost of forming 0.012 inches of aluminum oxide, rather than just 0.006 inches. Thus, for applications where it is important to minimize cost, configurations9and11may provide suitable performance at the lowest overall cost. Conversely, where cost reduction is not a primary goal, other configurations may represent appropriate choices, for example any of the configurations1-2,7-8and13-14that utilize ARMACOR M®.

Although selected embodiments have been illustrated and described in detail, it should be understood that a variety of substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the claims that follow.