Patent Publication Number: US-6903649-B2

Title: Fuse with fuse link coating

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional of U.S. application Ser. No. 10/672,840 filed Sep. 26, 2003, which is a divisional application of U.S. application Ser. No. 10/302,549 filed Nov. 21, 2002 and now issued U.S. Pat. No. 6,664,886, which is a divisional application of U.S. application Ser. No. 09/549,143 filed Apr. 13, 2000 and now issued U.S. Pat. No. 6,507,265, which claims the benefit of U.S. Provisional Application No. 60/131,550 filed Apr. 29, 1999. 

   BACKGROUND OF THE INVENTION 
   This invention relates generally to fuses for interrupting the flow of current through an electrical circuit upon predetermined overload conditions and, more particularly, to fuses with direct current and alternating current arc interrupting capability. 
   As is well known, fuses are used in electrical circuits to interrupt the flow of current when there is a short-circuit and/or a full voltage overload current event. Fuses typically include one or more fuse elements electrically connected to two end conductors located at opposing ends of the fuse. In the event of a short circuit and/or a full voltage overload, the temperature of the fuse element increases until a portion of the element melts and breaks. The break in the fuse element typically causes an electric arc to be established. 
   Sand is typically used to fill the fuse cartridge to surround the fuse elements to assist in quenching an arc. U.S. Pat. No. 4,656,453 describes cartridge fuses that include end plugs that are used for arc quenching. The fuse element passes through the end plugs adjacent to the end conductors. U.S. Pat. No. 5,280,261 describes a current limiting fuse that includes a short circuit strip that has a plurality of 90 degree angle bends along the length of the strip. The multiple bends in the fuse strip cause the strip to contact or come in close proximity of the inside wall of the fuse body. When a short-circuit arc occurs the fuse strip material burns towards the fuse wall creating an interaction with the fuse wall and an increase in pressure, which extinguishes the arc. However, even with the above noted examples of arc quenching, these fuses may not interrupt the circuit satisfactorily. 
   It would be desirable to provide a fuse that includes arc quenching capabilities during a short-circuit and/or a full voltage overload current interrupt event. It would also be desirable to provide a fuse that reduces arc energy during a short-circuit and/or a full voltage overload current interrupt event. 
   BRIEF SUMMARY OF THE INVENTION 
   In an exemplary embodiment of the invention, a fuse includes an arc energy absorbing coating to reduce arc energy during a short-circuit and/or a full voltage overload current interrupt. The fuse includes end conductor elements, and at least one fuse element secured between and making electrical contact with the end conductor elements. An elongate fuse housing, having a passageway extending longitudinally through the housing, extends between the end conductor elements. The fuse element extends through the housing passageway. The fuse includes an arc energy absorbing coating which at least partially coats each end portion of the fuse element. 
   Prior to assembly of the fuse, an arc energy absorbing coating is applied to the end portions of the fuse element. The fuse element is mechanically and electrically attached to the end conductor elements, typically by soldering, welding or brazing. The end conductor elements are positioned over the ends of the housing and crimped into receiving grooves in the fuse housing. The housing passageway is filled with a filler material, typically prior to positioning the second end conductor element at the end of the housing. 
   The above described fuse provides arc quenching capabilities during a short-circuit and/or a full voltage overload current interrupt event. The fuse also reduces arc energy during a short-circuit and/or a full voltage overload current interrupt event. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional side view of a fuse in accordance with an embodiment of the present invention. 
       FIG. 2  is a cross-sectional view along line A—A of the fuse shown in FIG.  1 . 
       FIG. 3  is a top view of a fuse strip housed within the fuse shown in FIG.  1 . 
       FIG. 4  is a sectional side view of a fuse in accordance with another embodiment of the present invention. 
       FIG. 5  is a top view of a fuse element housed within the fuse shown in FIG.  4 . 
       FIG. 6  is a sectional side view of a fuse in accordance with still another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   FIG  1  is a sectional side view of a fuse  10 , in accordance with an embodiment of the present invention, and  FIG. 2  is a cross sectional view of fuse  10 . Referring to  FIGS. 1 and 2 , fuse  10  includes an elongate housing  12  fabricated from an insulating material. Fuse housing  12  includes an inside surface  14  defining a passageway  16  extending from a first end  18  to a second end  20  of fuse housing  12 . Fuse housing  12  may be any suitable shape, for example, tubular, rectangular, octangular, or hexangular. In the embodiment shown in  FIG. 1 , fuse housing  12  has a tubular shape. 
   A first conductive end cap  22  is positioned over first end  18  of housing  12 , and a second conductive end cap  24  is positioned over second end  20  of housing  12 . End caps  22  and  24  have the same cross sectional shape as housing  12 . End caps  22  and  24  are coupled to fuse housing  12  by flanges  26  and  28  respectively. Housing  12  includes grooves  30  and  32  which receive flanges  26  and  28 . In an alternative embodiment, housing  12  does not include grooves  30 ,  32 , and end caps  22  and  24  are crimped directly onto housing  12 . End caps  22  and  24  and inside surface  14  of housing  12  form a chamber  34  inside fuse  10 . 
   A fuse element or strip  36  extends through passageway  16 . Particularly, fuse strip  36  extends between end caps  22  and  24 , and is electrically connected, e.g., soldered, welded, or brazed, to end caps  22  and  24 . Fuse strip  36  is a strip of conductive metal. Fuse strip  36  may be fabricated from any suitable conductive metal, for example silver, gold, copper, aluminum, and the like, In one embodiment, fuse strip  36  is fabricated from silver. 
   As shown in  FIG. 3 , fuse strip  36  includes a plurality of weak spots  38  located along the length of strip  36 . Each weak spot  38  includes a circular opening  40  and opposing notches  42  adjacent opening  40 . In alternative embodiments, weak spots  38  are formed from alternate shaped openings, for example, squares, ovals, triangles, and the like. Also, in alternate embodiments, weak spots  38  are formed by a plurality of grooves extending across fuse strip  36 . 
   To reduce arc energy during a short-circuit and/or a full voltage overload current interrupt event, an arc energy absorbing coating  44  at least partially coats a first end portion  46  and a second end portion  48  of fuse strip  36 . Arc energy absorbing coating  44  at least partially coats both sides of end portions  46  and  48  and extends partially around openings  40  adjacent fuse end portions  46  and  48 . For optimal performance, openings  40  are substantially free of coating  44 . In an alternative embodiment, arc energy absorbing coating  44  at least partially coats one side of end portions  46  and  48 . Typically, arc energy absorbing coating  44  has a dry film thickness on each side of fuse strip  36  of between about 0.01 inch to about 0.30 inch, more typically between about 0.05 inch to about 0.10 inch. However, thinner and thicker film thicknesses may be used. Arc energy absorbing coating  44  film thicknesses lower than 0.01 inch may not provide sufficient arc suppression, especially in high current rated fuses. In one embodiment, arc energy absorbing coating  44  coats an area on each side of end portions  46  and  48  of about 0.260 inches by about 0.140 inches, and has a film thickness of about 0.08 inch on each side. 
   Arc energy absorbing coating  44  may be, for example, an organo-silicone coating or an epoxy coating. Suitable organo-silicone coatings include, but are not limited to, alkoxy silicone coatings, for example methoxy silicone and acetoxy silicone coatings. Examples of alkoxy silicone coatings include NUVA-SIL 5083, NUVA-SIL 5088, and NUVA-SIL 5091 commercially available from Loctite Corporation, Rocky Hill, Conn. A suitable epoxy coating includes, but is not limited to NORDBAK 7459-9950 commercially available from Loctite Corporation. Coating  44  is applied to fuse strip end portions  46 ,  48  and cured according to known methods and techniques, including, but not limited to UV curing processes, heat curing processes, and moisture curing processes such as atmospheric or humidity chamber curing processes in accordance with the particular coating selected. 
   Referring again to  FIGS. 1 and 2 , fuse strip  36  includes a plurality of bends  50  spaced longitudinally along strip  36 . Bends  50  divide fuse strip  36  into a plurality of substantially straight segments  52 . Each bend  50  has an angle of about  45  degrees to about 120 degrees, typically from about 60 degrees to about 90 degrees. Bends  50  and straight segments  52  are configured to cause fuse strip  36  to contact inside surface  14  of housing  12  at contact points  53 . 
   Chamber  34  is filled with filler material  54 . Suitable filler materials  54  include, for example, silica sand, powdered gypsum, inert gasses, and the like. 
   Prior to assembly of fuse  10 , arc energy absorbing coating  44  is applied to fuse strip  36 . Typically, arc energy absorbing coating  44  is applied before bends  50  are formed in strip  36 . However, bends  50  may be formed in fuse strip  36  before applying arc energy absorbing coating  44 . 
   Fuse strip  36  is mechanically and electrically attached to end caps  22  and  24 , typically by soldering fuse strip  36  to each end cap  22  and  24 . Typically discs of solder are placed inside end caps  22  and  24 , before fuse strip  36  is inserted inside end caps  22  and  24 . Heat is then applied to melt the solder, thereby soldering fuse strip  36  to end caps  22  and  24 . In alternative embodiments, fuse strip  36  is welded or brazed to end caps  22  and  24 . First end cap  22  is positioned over first end  18  of housing  12  and second end cap  24  is positioned over second end  20  of housing  12 . Flanges  26  and  28  are crimped into grooves  30  and  32  respectively to secure end caps  22  and  24  to housing  12 . 
   Chamber  34  is filled with filler material  54 , typically, prior to second end cap  24  being positioned over second end  20  of housing  12 . 
   The above described fuse  10  includes bends  50  which cause fuse strip  36  to contact housing  12  at contact points  53 , filler material  54 , and arc energy absorbing coating  44  which assist in arc quenching during a short-circuit and/or a full voltage overload current interrupt event. Also, because of arc energy absorbing coating  44 , fuse  10  has reduced arc energy during the short-circuit or fill voltage overload current interrupt event. 
     FIG. 4  is a sectional side view of a fuse  60  in accordance with another embodiment of the present invention. Similar to fuse  10  described above, fuse  60  includes an elongate housing  62  fabricated from an insulating material. Fuse housing  62  includes an inside surface  64  defining a passageway  66  extending from a first end  68  to a second end  70  of fuse housing  62 . 
   A first conductive end cap  72  is positioned over first end  68  of housing  62 , and a second conductive end cap  74  is positioned over second end  70  of housing  62 . End caps  72  and  74  have the same cross sectional shape as housing  62 . End caps  72  and  74  are coupled to fuse housing  62  by flanges  76  and  78  respectively. Housing  62  includes grooves  80  and  82  which receive flanges  76  and  78  respectively. In an alternative embodiment, housing  62  does not include grooves, and end caps  72  and  74  are crimped directly onto housing  62 . End caps  72  and  74  and inside surface  64  of housing  62  form a chamber  84  inside fuse  60 . 
   A fuse element assembly  86  extends through passageway  66 . Particularly, fuse element assembly  86  extends between end caps  72  and  74 . Fuse element assembly  86  is electrically connected to end caps  72  and  74 . Referring also to  FIG. 5 , fuse element assembly  86  includes a fuse wire  88  and a substantially flat nonconductive bridge  90 . Bridge  90  includes a first end portion  92 , a second end portion  94 , and an elongate central portion  96 . Elongate central portion  96  includes first and second side sections  98  and  100  extending between first and second end portions  92  and  94  of bridge  90 . First and second side sections  98  and  100  define an elongate opening  102  in bridge  90 . Fuse wire  88  extends between and is coupled to first and second end portions  92  and  94  so that fuse wire  88  makes electrical contact with first and second end caps  72  and  74 . Fuse wire  88  extends through elongate opening  102  in bridge  90 . 
   An arc energy absorbing coating  104  at least partially coats fuse wire  88  and bridge  90  at a first location  106  and at a second, separate, location  108 . At first location  106 , arc energy absorbing coating  104  coats bridge first end portion  92  and wire  88  at end portion  92  and extending into bridge elongate opening  102 . At second location  108 , arc energy absorbing coating  104  coats bridge second end portion  94  and wire  88  at end portion  92  and extending into bridge elongate opening  102 . Bridge first end surface  93  and second end surface  95  are kept free of arc energy absorbing coating  104  to permit an electrical connection between fuse wire  88  and end caps  72  and  74 . Additionally, chamber  84  is filled with a filler material  110  similar to filler material  54  described above. 
     FIG. 6  shows a fuse  112  in accordance with another embodiment of the present invention. Similar to fuse  10  described above, fuse  112  includes an elongate housing  114  fabricated from an insulating material. Fuse housing  114  includes an inside surface  116  defining a passageway  118  extending from a first end  120  to a second end  122  of fuse housing  114 . 
   A first conductive terminal element  124  is coupled to first end  120  of housing  114 , and a second conductive terminal element  126  is coupled to second end  122  of housing  114 . Terminal elements  124  and  126  include end plates  130  and  132  respectively. Elongate terminal blades  134  and  136  extend outward from end plates  130  and  132  respectively. Terminal elements  124  and  126  and inside surface  116  of housing  114  form a chamber  128  inside fuse  112 . 
   A fuse element or strip  138  extends through passageway  118 . Particularly, fuse strip  138  extends between terminal elements  124  and  126 . Fuse strip  138  is electrically connected to terminal elements  124  and  126 . Fuse strip  138  is a strip of conductive metal and may be fabricated from any suitable conductive metal as described above. 
   Fuse strip  138  includes a plurality of weak spots  140  located along the length of strip  138 . Each weak spot  140  includes a circular opening  142  and two notches  144  adjacent opening  142 . In alternative embodiments, weak spots  140  may be formed from alternate shaped openings, for example, squares, ovals, triangles, and the like. Also, weak spots  140  may be formed by a plurality of grooves extending across fuse strip  138 . 
   To reduce arc energy during a short-circuit and/or a full voltage overload current interrupt event, an arc energy absorbing coating  146  at least partially coats a first end portion  148  and a second end portion  150  of fuse strip  138 . Arc energy absorbing coating  146  at least partially coats both sides of end portions  148  and  150 . In an alternative embodiment, arc energy absorbing coating  146  at least partially coats one side of end portions  148  and  150 . 
   Chamber  128  is filled with a filler material  152 . As described above, suitable filler materials  152  include, for example, silica sand, powdered gypsum, inert gasses, and the like. 
   In alternative embodiments, fuse  112  includes a plurality of laterally spaced fuse strips  138 . Each fuse strip  138  includes arc energy coating  146  on at least one side of end portions  148  and  150 . 
   While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.