Patent Publication Number: US-10790105-B1

Title: DC switching apparatus with auxiliary contact device using microswitch

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Korean Patent Application No. 10-2019-0057455 filed on May 16, 2019, the entire contents of which are herein incorporated by reference. 
     TECHNICAL FIELD 
     The present invention relates to a direct current (DC) switching apparatus (relay) having an auxiliary contact device using a microswitch. More specifically, the present invention relates to a structure of an auxiliary contact device included in a DC high-voltage contact switching apparatus that is applicable to new renewable energy, electric vehicles, DC power control, battery power control, and the like. 
     BACKGROUND ART OF THE INVENTION 
     Direct current (DC) switching apparatuses may be used in new renewable energy (such as, solar energy generation), energy storage devices, and DC transportation systems such as electric bus rapid-charging devices. Recent energy storage devices and recent electric bus rapid-charging systems tend to increase a voltage up to a high voltage of 1000V and gradually increase a current. With this voltage increase, a device that shuts off (+) power and (−) power simultaneously is required for safety. 
     An auxiliary contact device is also required as a contact monitoring device for checking whether a main contact has been operated. The contact monitoring device such as the auxiliary contact device is used to operate the entire system after checking whether the main contact has entered a closed circuit state after applying power to the coil of a switching apparatus, and is also used to check whether the main contact has been properly opened or closed when the operation of the entire system is stopped. The contact monitoring device may also be used to detect a defect when the defect is generated in the main contact due to a short-circuit accident or other accidents while the entire system is being operated. In this case, reliability of the contact monitoring device or the auxiliary contact device is greatly important. 
     In the conventional art, the auxiliary contact device is completed by fixing an microswitch on a PCB to the bottom surface of an arc cover via soldering, taking auxiliary contact terminals out of the PCB via soldering, and guiding the taken-out terminals to an upper portion encapsulated by high-density epoxy to solder connection wires from the outside. At this time, airtight sealing of epoxy is degraded due to soldering, insulation between a main contact and an auxiliary contact is destroyed due to soldering of a covered wire between the externally taken-out terminals of the auxiliary contact, an operation is difficult, the reliability of the auxiliary contact is degraded due to an arc voltage and arc heat, and burning occurs. 
     SUMMARY 
     Technical Problem 
     Provided is implementation of an auxiliary contact of a sealed direct current (DC) switching apparatus capable of stably protecting insulation of a microswitch, which is to be used as the auxiliary contact, and the auxiliary contact in a harsh opening/closing environment of a DC power supply of a main contact, and securing an operational reliability of the auxiliary contact, which transmits an electrical signal, by accurately monitoring an operational state of the main contact. 
     Provided is also a DC switching apparatus having an auxiliary contact device designed to protect an auxiliary contact from arc and arc heat caused by opening/closing of a main contact by securing an insulation distance of a DC power supply, to monitor an operational state of the main contact at a remote distance, and to facilitate utilization of the auxiliary contact for a reliability-secured accurate feedback, and being capable of securing insulation by arranging the auxiliary contact at a farthest location from the main contact, of preventing a malfunction of the auxiliary contact due to arc heat, and of contributing to sealing securement of the inside of a product, productivity improvement, and cost saving. 
     Provided is also a DC switching apparatus having an auxiliary contact device optimally designed to protect a microswitch, which is to be used as an auxiliary contact, from arc generated during opening/closing of a main contact by arranging the microswitch on a bottom surface of a movable iron core in order to secure an insulation distance from the arc and optimally designed to satisfy an international standard by increasing a space distance and a creeping distance. 
     Provided is also a method and apparatus capable of reducing the conventional inconveniences of soldering a microswitch onto a PCB, accurately soldering an externally connected terminal to the PCB, and soldering the terminal to the outside by using a lead line of an insulating wire. 
     Provided is also a method and apparatus capable of minimizing infiltration of a carbon material generated during opening/closing of a contact due to arc and opening/closing of a main contact into an auxiliary contact because the opening/closing of the contact occurs within a small space. 
     Provided is also an auxiliary contact device of a DC high-voltage contact switching apparatus such as battery control, an ESS, an electric vehicle, a charger, a UPS, or a solar-light inverter, which is a DC power supply that blocks a corrosive gas such as oxygen into a product because the inside of a contact portion is completely blocked from the outside and ambient air is completely blocked. 
     Provided is also a DC relay including an auxiliary contact device of a DC high-voltage contact switching apparatus including a reliability-secured auxiliary contact that controls opening/closing of a DC power supply by reducing the size, being mounted under a reducing insulating gas atmosphere to prevent oxidation of a contact, being manipulated under the insulating gas atmosphere, and monitoring a state of a main contact to facilitate remote control via communication, battery management system (BMS) control, or the like. 
     The technical problems of the present invention are not limited to the above-mentioned contents, and other technical problems not mentioned will be clearly understood by a person skilled in the art from the following description. 
     Solution to Problem 
     According to an aspect of the present disclosure, a direct current (DC) switching apparatus having an auxiliary contact device includes at least one pair of stationary contacts; one or more coils; a movable iron core that is driven by the one or more coils; a movable contact table operating in engagement with the movable iron core; and an auxiliary contact device arranged below the movable iron core, wherein the auxiliary contact device includes a microswitch. 
     The auxiliary contact device may further include a cylinder of which a top and a bottom are open, the cylinder including an upper circumferential portion and a lower circumferential portion; and a ceramic base configured to be airtightly bonded with the lower circumferential portion of the cylinder. 
     A terminal of the microswitch may be fitted onto and fixed to an auxiliary contact terminal formed in the ceramic base, and may transmit an electrical signal to the outside by being electrically connected to the auxiliary contact terminal. 
     A first metalized layer may be formed on an outer circumferential portion of the ceramic base, and the first metalized layer and a lower circumferential portion of the cylinder may be bonded with each other via airtight welding. 
     The ceramic base may include a through hole through which the terminal of the microswitch penetrates, and the auxiliary contact terminal may be bonded with the ceramic base via airtight welding by using a second metalized layer formed on the through hole. 
     The microswitch may include an auxiliary contact lever, may monitor a state of a main contact through the auxiliary contact terminal by a lower portion of the movable iron core operating the auxiliary contact lever through a vertical action of the movable iron core, and may be configured to be filled with an insulating gas. 
     The terminal of the microswitch may be coated with a solder and then fitted onto the auxiliary contact terminal, and the terminal of the microswitch and the auxiliary contact terminal may be electrically connected to each other by heating the auxiliary contact terminal from the outside. 
     The auxiliary contact terminal may be formed of oxygen-free copper, and at least a portion of the lower circumferential portion of the cylinder may be plated with nickel, and thus the lower circumferential portion of the cylinder and the first metalized layer of the ceramic base may be bonded with each other via brazing welding. 
     The upper circumferential portion of the cylinder may be formed in an outward direction to be perpendicular to the cylinder, and the lower circumferential portion of the cylinder may be formed in an inward direction to be perpendicular to the cylinder. 
     Effects of the Invention 
     According to the present invention, provided is implementation of an auxiliary contact of a sealed direct current (DC) relay capable of stably protecting insulation of a microswitch, which is to be used as the auxiliary contact, and the auxiliary contact in a harsh opening/closing environment of DC power of a main contact, and securing an operational reliability of the auxiliary contact, which transmits an electrical signal, by accurately monitoring an operational state of the main contact. 
     According to the present invention, provided is also a DC switching apparatus having an auxiliary contact device designed to protect an auxiliary contact from arc and arc heat caused by opening/closing of a main contact by securing an insulation distance of a DC power supply, to monitor an operational state of the main contact at a remote distance, and to facilitate utilization of the auxiliary contact for a reliability-secured accurate feedback, and being capable of securing insulation by arranging the auxiliary contact at a farthest location from the main contact, of preventing a malfunction of the auxiliary contact due to arc heat, and of contributing to sealing securement of the inside of a product, productivity improvement, and cost saving. 
     According to the present invention, provided is also a DC switching apparatus having an auxiliary contact device optimally designed to protect a microswitch, which is to be used as an auxiliary contact, from arc generated during opening/closing of a main contact by arranging the microswitch on a bottom surface of a movable iron core in order to secure an insulation distance from the arc and optimally designed to satisfy an international standard by increasing a space distance and a creeping distance. 
     According to the present invention, provided is also a method and apparatus capable of reducing the conventional inconveniences of soldering a microswitch onto a PCB, accurately soldering an externally connected terminal to the PCB, and soldering the terminal to the outside by using a lead line of an insulating wire. 
     According to the present invention, provided is also a method and apparatus capable of minimizing infiltration of a carbon material generated during opening/closing of a contact due to arc and opening/closing of a main contact into an auxiliary contact because the opening/closing of the contact occurs within a small space. 
     According to the present invention, provided is also an auxiliary contact device of a DC high-voltage contact switching apparatus such as battery control, an ESS, an electric vehicle, a charger, a UPS, or a solar-light inverter, which is a DC power supply that blocks a corrosive gas such as oxygen into a product because the inside of a contact portion is completely blocked from the outside and ambient air is completely blocked. 
     According to the present invention, provided is also a DC relay including an auxiliary contact device of a DC high-voltage contact switching apparatus including a reliability-secured auxiliary contact that controls opening/closing of a DC power supply by reducing the size, being mounted under a reducing insulating gas atmosphere to prevent oxidation of a contact, being manipulated under the insulating gas atmosphere, and monitoring a state of a main contact to facilitate remote control via communication, battery management system (BMS) control, or the like. 
     The effects of the present invention are not limited to the above-mentioned contents, and other effects not mentioned will be clearly understood by a person skilled in the art from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an assembly view for describing the structure of a direct current (DC) switching apparatus having an auxiliary contact device, according to an embodiment of the present invention. 
         FIG. 2  is a cross-sectional view for describing the structure of a DC switching apparatus having an auxiliary contact device, according to an embodiment of the present invention. 
         FIG. 3  is a view for describing the structure of a ceramic base from among the components of the auxiliary contact device according to an embodiment of the present invention. 
         FIG. 4  is a view for describing the structure of a cylinder from among the components of the auxiliary contact device according to an embodiment of the present invention. 
         FIG. 5A  is a cut-away perspective view for explaining the structure of an auxiliary contact device according to an embodiment of the present invention. 
         FIG. 5B  is a cut-away perspective view for explaining the structure of an auxiliary contact device according to an embodiment of the present invention. 
         FIG. 6  is a view for describing a method of manufacturing an auxiliary contact device, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     It will be understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated components, steps, operations, and/or elements thereof, but do not preclude the presence or addition of one or more other components, steps, operations, and/or elements thereof. 
     While such terms as “first”, “second”, etc., may be used to describe various components, such components must not be limited to the above terms. The above terms are used only to distinguish one component from another. In the description, certain detailed explanations of the related art are omitted when it is deemed that they may unnecessarily obscure the essence of the present invention. 
     In addition, the components shown in the embodiments of the present invention are shown independently to indicate different characteristic functions, and do not mean that each component is separate hardware or one software component. In other words, for convenience of description, each component is listed and described as each component, and at least two components of each component may be combined to form one component, or one component may be divided into a plurality of components to perform a function. The integrated and separate embodiments of each component are also included in the scope of the present invention without departing from the essence of the present invention. 
     Hereinafter, the present invention will be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the inventive concept are shown. The configuration of the present invention and the effect of the action thereof will be clearly understood through the following detailed description. 
       FIG. 1  is an assembly view for describing the structure of a direct current (DC) switching apparatus having an auxiliary contact device, according to an embodiment of the present invention. 
     Referring to  FIG. 1 , an electromagnet may be made by winding a coil  01  around a bobbin  02  and connecting a start line and an end line of an electronic coil winding portion to a coil terminal  03 , and a magnet of the electromagnet may be made by fitting a lower core into an inner groove of the center portion of the bobbin  02 . 
     An inner compression spring  19  and an outer compression spring  20  may fit onto a movable table mold  18 , a movable contact table  07  constituting a movable contact may fit onto a movable table holder  21 , a movable pin  06  may fit into a central through hole of a stationary iron core  09  fixed to a yoke plate  04  by welding, a returning spring  12  may be assembled and may be fixed to a movable iron core  10  after adjusting an over travel (O/T), and then the auxiliary contact device may fit onto the bottom of a cylinder  13  and may be airtightly welded. 
     The cylinder  13  may be configured such that a lower circumferential portion of the cylinder  13  may be welded and bonded with a ceramic base  15 , which is an insulator, by being made of a nonferrous metal in the form of a hollow cylinder and penetrating the bottom. Welding portions of the ceramic base  15  and the cylinder  13  may be airtightly bonded with each other by making a metalized layer  15 - 1  on an outer circumferential portion of the ceramic base  15 , plating a penetrated lower circumferential portion  13 - 2  of the cylinder  13  with nickel such that the penetrated lower circumferential portion  13 - 2  may be welded with the metalized layer  15 - 1  formed on the ceramic base  15 , and performing brazing welding by interposing a solder between the plated portion and the metalized layer  15 - 1 . 
     The ceramic base  15  bonded with auxiliary contact terminals  17  formed of oxygen-free copper is airtightly bonded with the metalized layer  15 - 1  via brazing welding, terminals  14  of an microswitch  16  are coated with a liquid solder and fit into the auxiliary contact terminals  17  to be fixed and assembled, and the solder is melt by heating the auxiliary contact terminals  17  from the outside with a certain temperature, thereby electrically completely connecting the auxiliary contact terminals  17  to the terminals  14  of the microswitch  16 . 
     As such, when creation of an auxiliary contact device (assembly)  22  is completed, the auxiliary contact device  22  is fitted onto the movable iron core  10  located below the moving table mold  18  and airtightly welded with the yoke plate  04 , thereby completing an arrangement of an auxiliary contact. 
     When the welding of the yoke plate  04  is completed, a seal cup  05  airtightly welded with the bottom surface of a ceramic housing  08 , which is an insulator of a stationary contact  24 , may be bonded with the yoke plate  04  via airtight welding. At this time, an air-exhaust and air-supply tube may be made by airtightly welding a copper pipe  23  formed of oxygen-free copper with a hole formed in the yoke plate  04 . The inside of the switching apparatus is rendered into a vacuum state by using the copper pipe  23  and is sealed with an insulation gas that maintains external insulation gas with a higher density than the atmospheric pressure such that the switching apparatus is completely blocked from ambient air, thereby manufacturing a DC high-voltage contact switching apparatus having a sealing structure that prevents discoloration of a contact table and a contact surface carbon phenomenon caused by arc. 
     In the present invention, to address conventional problems, the microswitch  16  to be used as the auxiliary contact may be arranged below the cylinder  13  and may be electrically connected to the auxiliary contact terminals  17  welded to the ceramic base  15  of the auxiliary contact device  22 . 
     The DC high-voltage contact switching apparatus manufactured in this way may provide easy assembly of the microswitch  16  and may be protected from an arc voltage and arc heat due to opening/closing of a main contact. In addition, the inconvenience of attaching and soldering a conventional auxiliary contact to a PCB, soldering a terminal connected to the outside on the same PCB and sealing the terminal with epoxy, and then again soldering a lead line formed of an insulation wire, and the difficulty in securing insulation between an externally-exposed auxiliary contact terminal and a main contact may be addressed, and the convenience of having to insulate a soldering result obtained by soldering the external terminal of the auxiliary contact with the lead line nay be reduced. 
     This DC switching apparatus may drive arc by using an arc driving coil in order to extinct arc. In order to secure the reliability of the auxiliary contact that monitors an operational state of the main contact from an arc voltage and arc heat that accompany an operation of opening/closing DC power by driving arc by arranging a permanent magnet, the DC high-voltage contact switching apparatus according to an embodiment of the present invention may provide a structure of arranging the microswitch  16 , which is to be used as the auxiliary contact, below the cylinder  13 , accommodating the microswitch  16  below the movable iron core  10  and spacing the microswitch  16  apart from the main contact in a harsh arc environment such that the auxiliary contact may avoid a direct impact of arc. 
     As such, the present invention relates to a method of implementing an auxiliary contact of a sealed DC contact switching apparatus, and thus may provide a method for stably protecting insulation of an microswitch, which is to be used as the auxiliary contact, and the auxiliary contact in a harsh environment of opening/closing DC power of the main contact and securing reliability of an operational of the auxiliary contact of accurately monitoring an operational state of the main contact and transmitting an electrical signal. 
       FIG. 2  is a cross-sectional view for describing the structure of the DC switching apparatus having the auxiliary contact device, according to an embodiment of the present invention. 
     Referring to  FIG. 2 , because the auxiliary contact device including the microswitch  16  may be arranged in a lower portion of the DC switching apparatus, the auxiliary contact device is a long distance apart from the main contact and thus the auxiliary contact may avoid a direct impact of an arc voltage and arc heat. 
     When coil manipulation power is applied (on) to the coil terminal  03  extending from the excitation coil  01 , the movable iron core  10  is moved to the stationary iron core  09  according to the principle of an electromagnet. At this time, while the lower surface of the movable iron core  10  fixed to the movable pin  06  of a movable mold assembly interlocked with the movable contact table  07  is moving upwards, an auxiliary contact lever  11  formed on the upper surface of the microswitch  16  may be returned to operate the auxiliary contact. 
     On the other hand, when the coil manipulation power is off, the movable iron core  10  is spaced apart from the stationary iron core  09  and moves downwards, in contrast with the above-described operation. At this time, the movable iron core  10  interlocked with the movable contact table  07  may press the auxiliary contact lever  11  and thus the microswitch  16  may be changed to an open-circuit or closed-circuit state. The auxiliary contact lever  11  may be configured as a type where a lever operates to press a button, or may be configured as a type including only a lever or a button. 
     According to this operation, the auxiliary contact device using the microswitch  16  may monitor the operational state of the main contact at a remote distance. 
       FIG. 3  is a view for describing the structure of the ceramic base  15  from among the components of the auxiliary contact device according to an embodiment of the present invention. 
     Referring to  FIG. 3 , the ceramic base  15  formed of an insulating material may have a circular shape, and may include a first metalized layer  15 - 1  formed on an outer circumferential portion of the upper surface of the ceramic base  15 . The first metalized layer  15 - 1  may be bonded with the lower surface of the cylinder  13  via brazing airtight-welding. 
     The ceramic base  15  may also include a plurality of through holes  15 - 2  through which the terminals  14  of the microswitch  16  penetrate. A second metalized layer may be formed on the through holes  15 - 2  of the lower surface of the ceramic base  15 . The auxiliary contact terminals  17  may be airtightly welded to the ceramic base  15  by using the second metalized layer on the through holes  15 - 2  via brazing welding. 
     As such, the ceramic base  15  may include, on the upper surface thereof, the first metalized layer  15 - 1  for airtight welding with the cylinder  13  and may include, on the lower surface thereof, the second metalized layer for airtight welding with the auxiliary contact terminals  17 . 
       FIG. 4  is a view for describing the structure of the cylinder  13  from among the components of the auxiliary contact device according to an embodiment of the present invention. 
     Referring to  FIG. 4 , the cylinder  13  may have a cylindrical shape having an open top and an open bottom, and thus may include an upper circumferential portion  13 - 1  and a lower circumferential portion  13 - 2 . The upper circumferential portion  13 - 1  may be formed in an outward direction to be perpendicular to the cylinder  13 , and may be configured to be airtight welded to and bonded with the yoke plate  04 . The lower circumferential portion  13 - 2  may be formed in an inward direction to be perpendicular to the cylinder  13 . The lower circumferential portion  13 - 2  of the cylinder  13  may be configured to be airtight welded to and bonded with the first metalized layer  15 - 1  of the ceramic base  15 . 
       FIGS. 5A and 5B  are cut-away perspective views for explaining the structure of the auxiliary contact device according to an embodiment of the present invention. 
       FIG. 5A  illustrates a combination of the ceramic base  15  and the microswitch  16  according to an embodiment of the present invention. 
     After the second metalized layer is formed on the lower surfaces of the through holes  15 - 2  such that the auxiliary contact terminals  17  are airtight welded to and bonded with the ceramic base  15 , the auxiliary contact terminals  17  are airtightly bonded with the ceramic base  15 . After the terminals  14  of the microswitch  16  are coated with a liquid solder and are accommodated into the internal holes of the auxiliary contact terminals  17 , the auxiliary contact terminals  17  are indirectly heated from an external source with a certain temperature and thus fixed and electrically connected to the terminals  14  to thereby prevent separation of the assembly. The auxiliary contact terminals  17  may be formed of oxygen-free copper. 
     The terminals  14  of the microswitch  16  may be fitted onto the auxiliary contact terminals  17  and thus fixed thereto. The terminals  14  of the microswitch  16  may transmit an electrical signal to the outside by being electrically connected to the auxiliary contact terminals  17 . 
     In such a method of arranging the auxiliary contact device, the auxiliary contact terminals  17  formed in the ceramic base  15  perform a fixing role such that the microswitch  16  accommodated in the ceramic base  15  may be stably fixed without moving. 
       FIG. 5B  illustrates a combination of the cylinder  13  and the ceramic base  15  according to an embodiment of the present invention. 
     At least a portion of the lower circumferential portion  13 - 2  of the cylinder  13  may be plated with, for example, nickel, and the lower circumferential portion  13 - 2  of the cylinder  13  and the first metalized layer  15 - 1  formed on the outer circumference of the ceramic base  15  may be airtightly bonded with each other via brazing welding. 
     Because contact opening/closing is conducted in a small space within the cylinder  13  through the above-described structure of the auxiliary contact device, infiltration of a carbon material generated during opening/closing of a contact due to arc and opening/closing of a main contact into the auxiliary contact may be minimized, the inside of a contact portion may be completely blocked from the outside, and an auxiliary contact device capable of blocking the inside of a product from a corrosive gas such as oxygen by completely blocking external air may be secured. 
       FIG. 6  is a view for describing a method of manufacturing the auxiliary contact device  22 , according to an embodiment of the present invention. 
     As described above, as shown in {circle around ( 1 )} of  FIG. 6 , the first metalized layer  15 - 1  may be formed on the outer circumferential portion of the upper surface of the ceramic base  15 . 
     Next, as shown in {circle around ( 2 )} of  FIG. 6 , the second metalized layer may be formed on the bottom surface of the through holes  15 - 2  to bond the auxiliary contact terminals  17  to the ceramic base  15  via airtight welding, and then the bonding of the auxiliary contact terminals  17  may be achieved. 
     Next, as shown in {circle around ( 3 )} of  FIG. 6 , the terminals  14  of the microswitch  16  having the auxiliary contact lever  11  are coated with a liquid solder and accommodated into the grooves of the auxiliary contact terminals  17 , and the auxiliary contact terminals  17  are indirectly heated from the outside at a constant temperature and thus fixed and electrically connected to the terminals  14 , and thus the microswitch  16  may be combined with the ceramic base  15  and stably fixed thereto. 
     Finally, as shown in {circle around ( 4 )} of  FIG. 6 , the lower circumferential portion  13 - 2  of the cylinder  13  may be bonded with the first metalized layer  15 - 1  of the ceramic base  15  via airtight welding, thereby completing the manufacture of the auxiliary contact device  22 . 
     The above-disclosed embodiments of the present invention are merely examples, and thus the present invention is not limited thereto. The scope of the present invention should be interpreted by the following claims, and all technologies within the scope equivalent thereto should be interpreted as being included in the scope of the present invention. 
     
       
         
           
               
             
               
                   
               
               
                 DESCRIPTION OF REFERENCE NUMERALS 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 01: coil 
                 02: bobbin 
               
               
                 03: coil terminal 
                 04: yoke plate 
               
               
                 05: seal cup 
                 06: movable pin 
               
               
                 07: movable contact table 
                 08: ceramic housing 
               
               
                 09: stationary iron core 
                 10: movable iron core 
               
               
                 11: auxiliary contact lever 
                 12: returning spring 
               
               
                 13: cylinder 
                 14: micro switch terminal 
               
               
                 15: ceramic base 
                 16: microswitch 
               
               
                 17: auxiliary contact terminal 
                 18: movable table mold 
               
               
                 19: inner compression spring 
                 20: outer compression spring 
               
               
                 21: movable table holder 
                 22: auxiliary contact device (assembly) 
               
               
                 23: copper pipe 
                 24: stationary contact