Abstract:
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.

Description:
FIELD OF THE INVENTION 
       [0001]    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 
       [0002]    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. 
         [0003]    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. 
         [0004]    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. 
         [0005]    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. 
         [0006]    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. 
         [0007]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    A better understanding of the present invention will be realized from the detailed description that follows, taken in conjunction with the accompanying drawings, in which: 
           [0009]      FIG. 1  is a diagrammatic top view of an apparatus in the form of a container security device that includes a security bolt embodying aspects of the invention. 
           [0010]      FIG. 2  is a diagrammatic side view of the security bolt of  FIG. 1 . 
           [0011]      FIG. 3  is a diagrammatic sectional view taken along the section line  3 - 3  in  FIG. 2 . 
           [0012]      FIG. 4  is a diagrammatic top view of a pin that is a component of the bolt of  FIG. 1 . 
           [0013]      FIG. 5  is a diagrammatic side view of the pin of  FIG. 4 . 
           [0014]      FIG. 6  is a diagrammatic top view of the pin of  FIG. 4 , with the addition of an insulating layer. 
           [0015]      FIG. 7  is a diagrammatic top view of the pin and insulating layer of  FIG. 6 . 
           [0016]      FIG. 8  is a diagrammatic side view of the pin and insulating layer of  FIG. 6 , with the addition of a conductive layer. 
           [0017]      FIG. 9  is a diagrammatic top view of a further security bolt that is an alternative embodiment of the bolt of  FIG. 1 . 
           [0018]      FIG. 10  is a diagrammatic side view of the bolt of  FIG. 9 . 
           [0019]      FIG. 11  is a diagrammatic sectional view taken along the section line  11 - 11  in  FIG. 10 . 
           [0020]      FIG. 12  is a diagrammatic top view of a further security bolt that is an alternative embodiment of the bolt of  FIGS. 9-11 . 
           [0021]      FIG. 13  is a diagrammatic side view of the bolt of  FIG. 12 . 
           [0022]      FIG. 14  is a diagrammatic top view of still another security bolt that is an alternative embodiment of the security bolt of  FIGS. 12-13 . 
           [0023]      FIG. 15  is a diagrammatic side view of the bolt of  FIG. 14 . 
       
    
    
     DETAILED DESCRIPTION 
       [0024]      FIG. 1  is a diagrammatic top view of an apparatus  10  that is a container security device. Devices of this general type are often referred to as bolt seals. The apparatus  10  includes a security bolt  11  that embodies aspects of the invention, and a known type of retaining assembly  12  that is shown in broken lines.  FIG. 2  is a diagrammatic side view of the bolt  11  of  FIG. 1 .  FIG. 3  is a diagrammatic sectional view of the bolt  11 , taken along the line  3 - 3  in  FIG. 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. 
         [0025]    Referring to  FIGS. 1-3 , the bolt  11  has at its center an elongate, electrically conductive pin  16 .  FIG. 4  is a diagrammatic top view the pin  16  by itself, and  FIG. 5  is a diagrammatic side view of the pin  16 . In the disclosed embodiment, the pin  16  is made of steel. However, it could alternatively be made of any other suitable material. The pin  16  is cylindrical along most of its length, except at each end. At one end, the pin  16  has an optional tapered surface  18  of approximately frustoconical shape. The tapered surface  18  facilitates insertion of the bolt  11  into the retaining assembly  12  ( FIG. 1 ). Near the tapered surface  18 , the pin  16  has a circumferential groove  19 . 
         [0026]    At its opposite end, the pin  16  has a flattened head  21 . With reference to  FIG. 4 , the head  21  has approximately an oval shape in a top view, with a length that is greater than the diameter of the remainder of the pin  16 . With reference to  FIG. 5 , the head  21  is generally flat in a side view, with a thickness that is approximately equal to the diameter of the pin  16 . The shape of the head  21  in  FIGS. 4 and 5  is exemplary, and the head  21  could alternatively have any of a variety of other shapes. Although the illustrated pin  16  is generally cylindrical between its ends, it could alternatively have any of a variety of other cross-sectional shapes. 
         [0027]    Referring again to  FIGS. 1 and 2 , the pin  16  is coated over a portion of its length with a layer  26  of an electrically insulating material.  FIG. 6  is a diagrammatic top view of the pin  16  with the insulating layer  26  thereon. The insulating layer  26  completely coats the exterior surface of the pin  16  within the region indicated at  27 . It will be noted that the outer end of the head  21  is not coated with the insulating layer  26 . The insulating layer  26  is, in effect, a sleeve that surrounds the pin  16  over a portion  27  of its length. In the disclosed embodiment, the insulating layer  26  is made from aluminum oxide, also known as alumina. However, in an alternative embodiment, the insulating layer  26  could be made from some other suitable material that is electrically insulating. 
         [0028]    Referring again to  FIGS. 1 and 2 , an electrically conductive layer  36  is provided over part of the insulating layer  26 .  FIG. 7  is a diagrammatic top view of the pin  16 , insulating layer  26 , and conductive layer  36 .  FIG. 8  is a diagrammatic side view of the pin  16 , insulating layer  26 , and conductive layer  36 . The conductive layer  36  coats all exposed surfaces of the insulating layer  26  and the pin  16  in a region of the bolt that is identified at  37 . As shown in  FIGS. 7 and 8 , the insulating layer  26  extends leftwardly a short distance beyond the end of the conductive layer  36 . As shown in  FIG. 6 , and as discussed above, the head  21  has a portion that is not coated by the insulating layer  26 . Thus, with reference to  FIGS. 7 and 8 , it will be recognized that, at the outer end of the head  21 , the conductive layer  36  is in direct physical contact with the conductive pin  16 . The remainder of the conductive layer  36  is electrically separated from the pin  16  by the insulating layer  26 . 
         [0029]    In the illustrated embodiment, the conductive layer  36  is an amorphous metal material that includes iron, chromium, silicon and boron. As one example, the conductive layer  26  may 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 layer  26  can be obtained commercially under the trademark ARMACOR M® from Liquidmetal Technologies Corporation of Lake Forest, Calif. However, the conductive coating  36  could 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 layer  36  could be made from a conductive epoxy or a conductive polymer, either of which could be applied by spraying at room temperature. 
         [0030]    Referring again to  FIGS. 1 and 2 , the exterior surfaces of the conductive layer  36  are completely coated with an electrically insulating outer layer  41  in a region of the bolt  11  that is identified at  42 . The outer layer  41  can be made from any of a variety of electrically insulating materials that are known in the art. 
         [0031]    Referring again to  FIG. 1 , the retaining assembly  12  includes a retainer mechanism that is shown diagrammatically at  51 , and that includes a spring clip  52 . When the free end of the bolt  11  has been fully inserted into the retaining assembly  12 , the spring clip  52  engages the circumferential groove  19  in the pin  16 , in order to permanently secure the bolt  11  within the retaining assembly  12 , so that the bolt cannot be withdrawn. 
         [0032]    The retaining assembly  12  also includes a circuit  56  with two spaced electrical contacts  57  and  58 . When the end of the bolt  11  is disposed in the retaining assembly  12 , and is fixedly held in place by the retainer mechanism  51 , the electrical contact  57  engages the exposed surface of conductive pin  16 , and the electrical contact  58  engages the exposed surface of conductive layer  36 . As explained above, the head of the bolt  11  contains an electrical short between the pin  16  and the conductive layer  36 . Thus, during normal operation, the electrical contacts  57  and  58  will be shorted to each other by the bolt. Assume that a thief cuts the bolt  11 , for example at a location  66  between the retaining assembly  12  and 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 pin  16  and the conductive layer  36 . Consequently, the electrical contacts  57  and  58  will no longer be electrically shorted by the bolt. The circuit  56  can thus detect that the bolt  11  had been cut. The circuit  56  then could, for example, transmit a wireless signal indicating that the security device  10  has apparently been subjected to some form of tampering. 
         [0033]      FIG. 9  is a diagrammatic top view of a bolt  111  that is an alternative embodiment of the bolt  11  of  FIG. 1 .  FIG. 10  is a diagrammatic side view of the bolt  111 , and  FIG. 11  is a diagrammatic sectional view taken along the section line  11 - 11  in  FIG. 10 . The bolt  111  includes an outer layer equivalent to that shown at  41  in  FIG. 1 , but the outer layer is omitted in  FIGS. 9-11  for clarity. The bolt  111  of  FIGS. 9-11  is identical to the bolt  11  of  FIG. 1 , with one difference. In particular, with reference to  FIG. 8 , the conductive layer  36  of the bolt  11  covers all underlying surfaces in the region  37 . In contrast, with reference to  FIGS. 9-11 , the bolt  111  has two conductive layers  136 A and  136 B instead of the single conductive layer  36 . The two conductive layers  136 A and  136 B are provided on opposite sides of the bolt  111 , as best seen in  FIGS. 10 and 11 . The edges of the conductive layer  136 A are thus spaced circumferentially from the edges of the conductive layer  136 B by a gap  141  ( FIG. 10 ). The conductive layers  136 A and  136 B can be made from any of the same materials discussed above in association with the conductive layer  36  of the bolt  11 . 
         [0034]    With reference to  FIGS. 10 and 11 , it will be noted that the conductive layers  136 A and  136 B include respective strips of electrically conductive material that each extend lengthwise of the bolt  111 , and that are spaced circumferentially from each other. As best seen in  FIG. 11 , these strips are each thicker in the middle than at the edges. Although the bolt  111  of  FIGS. 9-11  has 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 strips  136 A and  136 B each extend straight along the bolt  11 , 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. 
         [0035]      FIG. 12  is a diagrammatic top view of a bolt  211  that is an alternative embodiment of the bolt  111  of  FIGS. 9-11 .  FIG. 13  is a diagrammatic side view of the bolt  211 . The bolt  211  of  FIGS. 12-13  is identical to the bolt  111  of  FIGS. 9-11 , except that the conductive layer includes not only the portions  136 A and  136 B, but also an additional portion  136 C that is spaced axially from the portions  136 A and  136 B, and that has one portion disposed on the insulating layer  26  and another portion disposed on the pin  16 . 
         [0036]      FIG. 14  is a diagrammatic top view of a bolt  311  that is an alternative embodiment of the bolt  211  of  FIGS. 12-13 .  FIG. 15  is a diagrammatic side view of the bolt  311 . The bolt  311  of  FIGS. 14-15  is identical to the bolt  211  of  FIGS. 12-13 , except that the conductive sleeve  136 C of the bolt  211  is split into two conductive strips  136 D and  136 E that are disposed on opposite sides of the bolt  311 , with their lateral edges spaced by the gap  141 . 
         [0037]    A number of bolts were built and tested, using different configurations and materials for the conductive layer  36  or  136 , and different thicknesses for the aluminum oxide insulating layer  26 . 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. 
         [0038]    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 location  66  in  FIG. 1 , and then a measurement was taken of the electrical resistance between the conductive pin  16  and each conductive layer  36  or  136 , at locations where the bolt would typically be engaged by the electrical contacts  57  and  58 . 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. 
         [0039]    Turning now in more detail to Table 1, bolt configurations 1-6 all involve an aluminum oxide insulating layer  26  with a thickness of approximately 0.025 inches. The bolts in configurations 1, 3 and 5 each had a conductive layer configured as multiple strips, for example as shown at  136 A and  136 B in  FIGS. 9-11 . The materials used for the conductive layers  136 A and  136 B in these three configurations were respectively ARMACOR M®, 400 stainless steel (400 SS), and nickel. The bolts in configurations 2, 4 and 6 had a continuous conductive layer rather than strips, for example as shown at  36  in  FIG. 7-8 . The materials used for the conductive layers  36  in 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 configurations 1-6 passed the bolt cutting test. 
         [0040]    During fabrication of bolts, the aluminum oxide insulating layer  26  is 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 configurations 1-6 in Table 1, an insulating layer  26  with 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 configurations 1-6 all 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 layer  26 . 
         [0041]    Accordingly, in Table 1, bolt configurations 7-12 are respectively identical to configurations 1-6, except that the thickness of the aluminum oxide insulating layer  26  was 0.012 inches, or in other words about half of the thickness used for bolt configurations 1-6. As shown in Table 1, configurations 7 and 8 each involved bolts with a conductive layer  36  or  136  made of ARMACOR M®, and all bolts with configurations 7 and 8 passed the bolt cutting test. Further, bolt configurations 9 and 11 involved bolts with the conductive layer made of 410 stainless steel or nickel and configured as multiple strips  136 A and  136 B, and all bolts with configurations 9 and 11 passed the bolt cutting test. However, as to bolt configurations 10 and 12, where the conductive layer was made of 410 stainless steel or nickel, and was a continuous layer  36  rather than strips  136 A and  136 B, some bolts with each of these configurations did not pass the bolt cutting test. 
         [0042]    As discussed above, the cost of the aluminum oxide insulating layer  26  increases progressively with increasing thickness. Accordingly, in Table 1, bolt configurations 13-16 are respectively identical to configurations 1-3 and 5, except that the thickness of the aluminum oxide insulating layer  26  was 0.006 inches, or in other words about one-quarter the thickness used for bolt configurations 1-6, and about one-half the thickness used for bolt configurations 7-12. As evident from Table 1, the bolts with configuration 13 all passed the bolt cutting test, in particular where the conductive layer was made of ARMACOR M® and formed as strips (as at  136 A and  136 B in  FIGS. 9-11 ). On the other hand, as to the bolts with configuration 14, where the conductive layer was made of ARMACOR M® and was continuous (as at  36  in  FIGS. 7-8 ), at least one bolt with this configurations did not pass the bolt cutting test. Bolt configurations 15 and 16 each had a conductive layer arranged as strips  136 A and  136 B 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. 
         [0043]    The bolts in configurations 13 and 14 satisfactorily 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 layer  26 . On the other hand, configurations 13 and 14 use 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, configurations 9 and 11 may 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 configurations 1-2, 7-8 and 13-14 that utilize ARMACOR M®. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                   
                 Al 2 O 3   
                 CONDUCTIVE LAYER 36, 136 
                   
               
               
                 BOLT 
                 LAYER 26 
                 (THICKNESS 0.002″ to 0.003″) 
               
             
          
           
               
                 CONFIGURATION 
                 (THICKNESS) 
                 MATERIAL 
                 CONFIGURATION 
                 RESULT 
               
               
                   
               
             
          
           
               
                 1 
                 0.025″ 
                 ARMACOR M ® 
                 Strips 
                 Pass 
               
               
                 2 
                   
                 ARMACOR M ® 
                 Continuous 
                 Pass 
               
               
                 3 
                   
                 400 SS 
                 Strips 
                 Pass 
               
               
                 4 
                   
                 400 SS 
                 Continuous 
                 Pass 
               
               
                 5 
                   
                 Nickel 
                 Strips 
                 Pass 
               
               
                 6 
                   
                 Nickel 
                 Continuous 
                 Pass 
               
               
                 7 
                 0.012″ 
                 ARMACOR M ® 
                 Strips 
                 Pass 
               
               
                 8 
                   
                 ARMACOR M ® 
                 Continuous 
                 Pass 
               
               
                 9 
                   
                 410 SS 
                 Strips 
                 Pass 
               
               
                 10 
                   
                 410 SS 
                 Continuous 
                 Fail 
               
               
                 11 
                   
                 Nickel 
                 Strips 
                 Pass 
               
               
                 12 
                   
                 Nickel 
                 Continuous 
                 Fail 
               
               
                 13 
                 0.006″ 
                 ARMACOR M ® 
                 Strips 
                 Pass 
               
               
                 14 
                   
                 ARMACOR M ® 
                 Continuous 
                 Fail 
               
               
                 15 
                   
                 410 SS 
                 Strips 
                 Fail 
               
               
                 16 
                   
                 Nickel 
                 Strips 
                 Fail 
               
               
                   
               
             
          
         
       
     
         [0044]    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.