PATENT ABSTRACT
Disclosed are a small fuse and a method of manufacturing the same. A cover made from thermosetting resin is coupled with is a base to receive a fusing element therein. The fusing element does not cause damage to the cover even if the fusing element makes contact with an inner wall of the cover due to size reduction of the cover.

PATENT DESCRIPTION
TECHNICAL FIELD 
     The disclosure relates to a small fuse and a method of manufacturing the same. More particularly, the disclosure relates to a small fuse and a method of manufacturing the same, in which the small fuse is mounted on a printed circuit board (PCB) of an electronic product such that a fusing element provided in the small fuse is melted to prevent parts on the PCB from being damaged by shutting off current when over current is applied to the PCB, thereby preventing circuits of the PCB from being damaged. 
     BACKGROUND ART 
     In general, higher voltage may be applied to electronic products, such as communication devices connected to telephone circuits, when surge current caused by induction lightning is applied to the electronic products or telephone lines make contact with power lines. For this reason, a fuse used in the communication device must have time lag characteristics to endure against the surge current caused by the induction lightning as well as current blocking characteristics to block current causing malfunction of the communication device. 
     Recently, as the size of devices has become reduced, the current blocking characteristics and the time lag characteristics are required for the surface-mount type small fuse. 
     The conventional small fuse includes a base, a pair of lead wires extending by passing through the base while being spaced apart from each other, a fusing element for connecting ends of the lead wires to each other, and a cover coupled with the base to receive the fusing element and the lead wires therein. 
     The fusing element and the lead wires are made from an alloy of copper and tin so that they have flexibility so as to be bent easily. The base and the cover are individually manufactured by using thermoplastic resin and then coupled with each other to define a space therebetween to receive the fusing element and end portions of the lead wires adjacent to the fusing element. 
     The small fuse is mounted on the PCB of the electronic product through the lead wires extending out of the base and the fusing element of the small fuse is melted when the over current is applied to the PCB, thereby protecting circuits of the PCB. 
     SUMMARY OF THE INVENTION 
     However, the conventional small fuse represents following disadvantages. 
     Since the size of the small fuse is determined according to the size of the cover and the base, the size of the cover and the base must be minimized to reduce the size of the small fuse such that the size of the electronic product employing the small fuse can be reduced. However, if the size of the cover and the base is reduced, the size of the space formed between the cover and the base to receive the fusing element is also reduced. Thus, if the lead wires adjacent to the fusing element are bent due external impact applied thereto while the base is being coupled with the cover, the fusing element makes contact with an inner wall of the cover. In this case, the cover made from the thermoplastic resin may be damaged by heat generated from the fusing element, so that the small fuse may malfunction. In this regard, it is very difficult to minimize the size of the small fuse. 
     Accordingly, it is an aspect of the disclosure to provide a small fuse, which can be easily manufactured in a small size without degrading the reliability of the product, and a method of manufacturing the same. 
     Additional aspects and/or advantages of the disclosure will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the disclosure. 
     The foregoing and/or other aspects of the disclosure are achieved by providing a small fuse comprising a base, a pair of lead wires extending by passing through the base while being spaced apart from each other, a fusing element interconnecting end portions of the lead wires adjacent to the base, and a cover including thermosetting resin and coupled with the base to receive the fusing element and the lead wires adjacent to the base. 
     The cover is integrally coupled with the base through an injection molding process. 
     The base is formed with a perforation hole positioned corresponding to the fusing element and an interior of the cover is communicated with an exterior of the cover through the perforation hole. 
     The base may include thermosetting resin. 
     The cover is individually formed and coupled with the base. 
     The base may include thermoplastic resin. 
     The cover has a hollow box shape having one end being open and is press-fitted with the base such that the open end of the cover surrounds an outer peripheral surface of the base, and the base restricts deformation of the cover when the base is coupled with the cover. 
     The base is provided at the outer peripheral surface thereof with contraction grooves to induce contraction of the base. 
     The cover has a hollow box shape having one end being open and is press-fitted with the base such that the open end of the cover surrounds an outer peripheral surface of the base, and the open end of the cover is screw-coupled with the outer peripheral surface of the base. 
     The fusing element makes contact with an inner wall of the cover when the lead wires are inclined toward the inner wall of the cover. 
     According to another aspect, there is provided a method of manufacturing a small fuse having a base, a pair of lead wires extending by passing through the base while being spaced apart from each other, a fusing element interconnecting end portions of the lead wires adjacent to the base, and a cover including thermosetting resin and coupled with the base to receive the fusing element and the lead wires adjacent to the base, the method comprising installing the lead wires connected to each other by the fusing element on the base and integrally forming the cover with the base through an injection molding process by injecting thermosetting resin molten material into a cavity of a mold in a state in which the fusing element and a portion of the base adjacent to the fusing element are exposed to an interior of the cavity of the mold. 
     The base is formed with a perforation hole positioned corresponding to the fusing element, the cavity is communicated with an exterior of the base through the perforation hole, and air is injected into the cavity through the perforation hole to prevent the thermosetting resin molten material from approaching to the fusing element. 
     The mold is formed with injection ports to inject the thermosetting resin molten material and the injection ports are arranged to prevent the thermosetting resin molten material from being directly injected toward the fusing element. 
     ADVANTAGEOUS EFFECTS 
     As described above, according to the small fuse and the method of manufacturing the same of the disclosure, the cover made from thermosetting resin is coupled with the base to receive the fusing element therein, so that the cover can be prevented from being damaged by the fusing element even if the fusing element makes contact with the inner wall of the cover due to size reduction of the cover. Accordingly, the small fuse can be manufactured in a small size without degrading the reliability of the product. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the disclosure will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a front sectional view showing the structure of a small fuse according to one embodiment; 
         FIG. 2  is a side sectional view showing the structure of a small fuse according to one embodiment; 
         FIG. 3  is a sectional view showing a preparation step in the manufacturing process for a small fuse according to one embodiment; 
         FIG. 4  is a partially sectional view showing an injection molding step in the manufacturing process for a small fuse according to the one embodiment; 
         FIG. 5  is a front sectional view showing the structure of a small fuse according to another embodiment; 
         FIG. 6  is a side sectional view showing the structure of a small fuse according to another embodiment; and 
         FIG. 7  is a top sectional view showing the structure of a small fuse according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the embodiments of the disclosure, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements. The embodiments are described below to explain the disclosure by referring to the figures. 
     As shown in  FIGS. 1 and 2 , a small fuse A includes a base  10 , a pair of lead wires  20  extending by passing through the base  10  while being spaced apart from each other, a fusing element  30  for connecting ends of the lead wires  20  to each other, and a cover  40  coupled with the base  10  to receive the fusing element  30  and the lead wires  20  therein. 
     The fusing element  30  and the lead wires  20  are made from an alloy of copper and tin so that they have flexibility so as to be bent easily. The base  10  and the cover  40  receive the fusing element  30  therein in such a manner that particles generated when the fusing element  30  is melted can be prevented from scattering toward other parts on the PCB adjacent to the small fuse A, thereby preventing peripheral devices from being damaged when the fusing element  30  is melted. The fusing element  30  can be welded to the ends of the lead wires  20 . 
     The small fuse A is mounted on the PCB of the electronic product through the lead wires  20  extending out of the base  10  and the fusing element  30  of the small fuse A is melted when the over current is applied to the PCB, thereby protecting circuits of the PCB. The lead wires  20  can be soldered to the PCB when the small fuse A is mounted on the PCB. 
     Meanwhile, the small fuse A according to the present embodiment can be manufactured in a small size without degrading the reliability of the product due to the material property of the cover  40 , which will be described below in more detail. 
     According to the small fuse A of the present embodiment, the cover  40  has a hollow box shape, in which one end of the cover  40 , that is, a bottom portion of the cover  40  is open. In order to allow the small fuse A to have a small size, an internal space of the cover  40  has a small size to the extent that the fusing element  30  makes contact with an inner wall of the cover  40  if the lead wires  20  are inclined to the inner wall of the cover  40 . 
     Since the cover  40  substantially receives the fusing element  30  therein, if the internal space of the cover  40  is reduced, the whole size of the cover  40  can be reduced. If the whole size of the cover  40  is reduced, the size of the base  10 , which is coupled with the cover  40 , can also be reduced, so that the whole size of the small fuse A can be reduced. For reference, the virtual line shown in  FIG. 2  represents the fusing element  30  making contact with the inner wall of the cover  40  due to deformation of the lead wires  20 . 
     If the internal space of the cover  40  has a small size so that the fusing element  30  makes contact with the inner wall of the cover  40  when the lead wires  20  are inclined to the inner wall of the cover  40 , the fusing element  30  makes contact with the inner wall of the cover  40  if external impact is applied to the lead wires  20  adjacent to the fusing element  30  while the base  10  is being coupled with the cover  40  or before the base  10  is coupled with the cover  40 . Thus, the cover  40  is damaged by heat generated from the fusing element  30 , so the product reliability of the small fuse A may be degraded. According to the present embodiment, however, the cover  40  is made from thermosetting resin having superior heat-resistant property, so that the cover  40  is not deformed by the heat generated from the fusing element  30 . Therefore, the product reliability of the small fuse A may not be degraded even if the fusing element  30  makes contact with the cover  40 . 
     Although thermosetting resin has superior heat-resistant property as compared with thermoplastic resin, the thermosetting resin represents high rigidity and low flexibility so that the thermosetting resin may be easily broken. Thus, the cover  40  including the thermosetting resin may be easily broken when external impact is applied thereto while the cover  40  is being coupled with the base. To solve this problem, according to the present embodiment, the cover  40  is integrally coupled with the base  10  through injection molding. 
       FIGS. 3 and 4  show the manufacturing procedure for the small fuse A according to the present embodiment. 
     In order to manufacture the small fuse A according to the present embodiment, a pair of lead wires  20  connected to each other through the fusing element  30  are installed on the base  10  as shown in  FIG. 3 , and the cover  40  is integrally formed with the base  10  through the injection molding process by injecting thermosetting resin molten material  40   a  into a cavity  100   a  of a mold  100  in a state in which the fusing element  30  and a portion of the base  10  adjacent to the fusing element  30  are exposed to the interior of the cavity  100   a  of the mold  100  as shown in  FIG. 4 . 
     The cavity  100   a  is open toward the base  10  such that the fusing element  30  and the portion of the base  10  adjacent to the fusing element  30  can be introduced into the cavity  100   a . Injection ports  110  are formed in the mold  100  in opposition to the base  10  such that the thermosetting resin molten material  40   a  can be injected into the cavity  100   a  through the injection ports  110 . 
     Therefore, according to the present embodiment, the thermosetting resin molten material  40   a  for forming the cover  40  directly makes contact with the surface of the base  10  when forming the cover  40  through the injection molding process. Thus, the cover  40  can be integrally formed with the base  10  as the thermosetting resin molten material  40   a  is dried, so that the cover  40  can be prevented from being broken although the cover  40  is made from the thermosetting resin which can be easily broken. If the base  10  comes into contact with the thermosetting resin molten material  40   a  used for forming the cover  40 , the base  10  may be damaged by the thermosetting resin molten material  40   a  having the high temperature. Thus, the base  10  is made from the thermosetting resin having superior heat-resistant property. 
     In addition, if the thermosetting resin molten material  40   a  is injected into the cavity  100   a  of the mold  100  in a state in which the fusing element  30  has been introduced into the cavity  100   a  of the mold  100 , the thermosetting resin molten material  40   a  may stick to the fusing element  30  so that the melting performance of the fusing element  30  may be degraded. In this regard, the thermosetting resin molten material  40   a  is prevented from approaching to the fusing element  30  during the injection molding process. 
     To this end, the base  10  is formed with a perforation hole  11  through which the cavity  100   a  is communicated with the outside of the base  10 . In addition, when the thermosetting resin molten material  40   a  is injected into the cavity  100   a  of the mold  100 , high-pressure air is sprayed toward the fusing element  30  through the perforation hole  11  to prevent the thermosetting resin molten material  40   a  from approaching to the fusing element  30 . 
     Since the fusing element  30  is installed corresponding to the center of the base  10 , the perforation hole  11  is located at the center of the base  10  corresponding to the position of the fusing element  30  in order to prevent the thermosetting resin molten material  40   a  from approaching to the fusing element  30 . Arrows with solid lines shown in  FIG. 4  indicate the injection direction of the thermosetting resin molten material  40   a , and arrows with dotted lines indicate the air supply direction. 
     A gap may not be formed between the base  10  and the cover  40  if the cover  40  is integrally formed with the base  10  through the injection molding. Thus, the perforation hole  11  may substitute for the gap formed between the base and the cover in the conventional small fuse. That is, the perforation hole  11  may serve as a discharge path for explosive pressure occurring when the fusing element  30  is melted during the use of the small fuse A, so that the small fuse A can be stably used. 
     If air having excessive pressure is introduced into the cavity  100   a  through the perforation hole  11 , the thermosetting resin molten material  40   a  may not be easily injected into the cavity  100   a . In this regard, the injection pressure of the thermosetting resin molten material  40   a  introduced into the cavity  100   a  is higher than the pressure of air introduced into the cavity  100   a  through the perforation hole  11  by 10 HPa to 20 HPa. 
     In addition, in order to effectively prevent the thermosetting resin molten material  40   a  from approaching to the fusing element  30 , the injection ports  110  are positioned corresponding to outer sides of the fusing element  30  such that the thermosetting resin molten material  40   a  may not be directly injected toward the fusing element  30 . In order to uniformly maintain the injection pressure in a state in which the injection ports  110  are located at outer sides of the cavity  100   a , other than the center of the cavity  100   a , a plurality of injection ports  110  are formed in the mold  100  such that the thermosetting resin molten material  40   a  can be simultaneously injected to plural portions of the cavity  100   a  while preventing the thermosetting resin molten material  40   a  from being directly injected toward the fusing element  30 . 
       FIGS. 5 and 6  show the structure of a small fuse B according to another embodiment. 
     In this embodiment, the cover  40  of the small fuse B is made from thermosetting resin. This embodiment is different from the previous embodiment in that the cover  40  and the base  10  are individually formed through the injection molding and then coupled with each other. In addition, the base  10  is made from thermoplastic resin having superior flexibility than the thermosetting resin to prevent the cover  40  from being broken while the cover  40  is being coupled with the base  10 . 
     In more detail, according to the present embodiment, the cover  40  has a hollow cylindrical shape having one end being open and the base  10  has a disc shape having predetermined thickness. The cover  40  is coupled with the base  10  in such a manner that the open end of the cover  40  surrounds an outer peripheral surface of the base  10 . That is, the outer peripheral surface of the base  10  is screw-coupled into the open end of the cover  40  such that the cover  40  can be securely coupled with the base  10  while preventing the cover  40  from being broken when the cover  40  is coupled with the base  10 . To this end, a female screw  41  is formed at an inner peripheral surface of the open end of the cover  40  and a male screw  12  is formed at the outer peripheral surface of the base  10 . In addition, explosive pressure occurring when the fusing element  30  is melted can be discharged through a fine gap formed between the female screw  41  and the male screw  12 . 
     According to still another embodiment, as shown in  FIG. 7 , a small fuse C includes the cover  40  made from thermosetting resin and the base  10  made from thermoplastic resin. According to this embodiment, different from the previous embodiment, the cover  40  is coupled with the base  10  through the press-fitting scheme. 
     That is, according to the present embodiment, the cover  40  has a hollow box shape having one end being open and the open end of the cover  40  surrounds the outer peripheral surface of the base  10  when the cover  40  is coupled with the base  10 . At this time, the outer peripheral surface of the base  10  is press-fitted into the open end of the cover  40 . In order to prevent the open end of the cover  40  from being expanded, contraction grooves  13  are formed at the outer peripheral surface of the base  10  to induce contraction of the base  10  when the cover  40  is coupled with the base  10 . 
     The contraction grooves  13  are formed along the outer peripheral surface of the base  10  while being spaced apart from each other by a predetermined distance. Each contraction groove  13  is open toward the outside of the base  10  to induce contraction of the outer peripheral surface of the base  10  when the cover  40  is coupled with the base  10 . According to the small fuse C of the present embodiment, deformation of the cover  40  can be absorbed by the contraction grooves  13 , thereby preventing the cover  40  made from the thermosetting resin from being broken when the cover  40  is coupled with the base  10 . The contraction grooves  13  may have various shapes to the extent that they can restrict the deformation of the cover  40 . In the case of the small fuse C according to the present embodiment, explosive pressure occurring when the fusing element  30  is melted can be discharged through the contraction grooves  13 . 
     Similar to the small fuse A, the small fuses B and C can also be manufactured in the small size without degrading the reliability of the product due to the material property of the cover  40 . 
     Although few embodiments of the disclosure have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the claims and their equivalents.