EP0392398B1 - Method for producing and enclosing of miniture and micro fuses - Google Patents

Abstract

The invention relates to a method for enclosing an electrical component, especially a fuse, in which the housing parts (which were previously aligned loosely with respect to one another and were jointed to one another) are pressed onto one another under pressure during extrusion-coating. In this case, extrusion-coating takes place either only of the joint (or joints) or of the complete housing parts, with the exception of those surfaces on which the housing parts have been pressed together by plates or pins. <IMAGE>

Description

The invention relates to a method for producing and closing small and miniature fuses, the housing of which is formed from two parts, encloses a cavity with a fusible conductor arranged therein and is provided with at least two connections for electrical connection, with the method steps of provisionally joining the housing parts and overmolding the housing with a plastic.

Such a method for producing fuses, in particular NH fuses, with a synthetic resin coating is known from DE-A-1 463 530. The connections in the form of contact blades and the fusible link connecting the contact blades are fixed in their mutual position by an auxiliary body of thin wall thickness made of insulating material, which can be attached to the contact blade with elastic deformation, and then sealed with a jacket made of synthetic resin by overmolding, overmolding or casting or the like. The cuboid or cylindrical housing consists of two essentially symmetrical halves which are brought into engagement with one another and with the contact blades of the fuse. In particular if the auxiliary body is made of the same plastic as the sheathing, there is an intimate connection between the outer sheath and the auxiliary body in the production of the synthetic resin sheathing. The cavity of the fuse is filled with quenching sand that surrounds the fuse element all around.

The two housing halves can be manufactured in large quantities on plastic injection molding machines with little effort. The manufacture of the contact knife and the fuse element can also be easily automated. However, the method of assembling the contact blades and the fusible link connecting the contact blades in one of the housing parts necessitates one-off production, since the outlay for automated mass production, as is required for small and very small fuses, is too high. The auxiliary body formed from the two joined housing parts, from which the contact knives protrude as connections on different sides of the housing, is completely encased in synthetic resin, including the areas of the contact knives close to the housing, so that a cartridge body which is sealed around and firmly held together is produced.

The known method for the production of small and micro fuses is also not to be used because the fusible link bridging the contact blades in the cavity of the fuse is easily torn off due to careless handling and assembly.

From FR-A-2 358 253 a method for producing a two-part housing made of plastic is already known, according to which the housing is encapsulated with a ring made of thermoplastic plastic, especially in the area of the parting line, while the two housing halves are pressed together under pressure . However, this method is not used to manufacture and close fuses, in particular small and micro fuses, but to encapsulate sensitive electrical components, in particular capacitors, when these have to be used under unfavorable conditions and therefore need to be protected. This method is therefore about encapsulating or encapsulating a finished electrical component in a hermetically sealed protective container, the electrical connections of the electrical component in question being led to the outside in the parting line of the housing through the thermoplastic encapsulation. According to the method of the invention, however, a small or micro fuse as a chamber fuse in sandwich construction is produced from two housing halves with a flat sheet metal stamping strip carrying the fusible conductor between the two housing halves, as already mentioned, in a manner suitable for mass production by means of housing part strips for the lower and upper housing parts and with a strip-shaped stamped part for the connections.

Fully encapsulating fuses occurs for several reasons. On the one hand, this leads to better protection of a possibly sensitive housing, and on the other hand it is achieved in this way that any leaks are eliminated, so that aging and corrosion are better controlled. If the mold for overmolding the component in the parting line has passages for the connections, which are generally in the form of wires, the overmolding is particularly simple, since the component can be held on the wires with an all-round distance to the mold wall. The finished product is also very easy to print on.

Before overmolding, the housing parts have to be connected to one another in a relatively complex manner, so that there are no larger passages or the like through which the molding compound can penetrate into the interior of fuses. There, it would very easily result in the destruction of the fuse wire, which is often only a few meters thick, and fill in the cavity required for the characteristic of a fuse. The housing parts are therefore welded together, glued or locked together. In any case, the fastening is generally so solid that it would also be sufficient in itself to ensure the safety of the fuse and to offer an appealing lifespan. Ultimately, there is a double effort in overmolding, as far as the quality of the assembly is concerned.

It is therefore an object of the invention to provide a method for producing and closing miniature and miniature fuses, in which the effort for the preliminary assembly of the housing parts can be greatly reduced while maintaining the extrusion coating, in particular taking into account the very small designs and the sensitive fuse element.

To achieve this object, the invention proposes that a strip of housing parts made of plastic for the lower housing parts and a strip of housing parts also made of plastic for the upper housing parts with a strip-shaped stamped part placed between the two housing part strips, in which the connections form a closed one Component are connected and the fusible link bridges the free ends of the connections, positioned with means such as pin and hole pairs to each other and temporarily connected to one another, and that the housing parts with the help of pressure plates or pins or molded surfaces during overmoulding using the pressure plates or pins or the molding surfaces are pressed together as a shaped element and / or modeling the molding compound.

According to the method according to the invention, housing part strips for the lower housing parts as well as for the upper housing parts are thus first produced in a plastic injection molding process in a suitable manner for mass production, whereby, as is also shown in an exemplary embodiment, the housing parts lying one behind the other in the housing part strip are each connected by webs are connected. The connections are produced as components of a strip-shaped stamped part, so that they lie in a predetermined position relative to one another and are bridged by the fusible conductor, which is connected to the connections by soldering, bonding or the like. The sensitive fuse element is not subjected to any further mechanical stress after attachment to the connections, because the position of the connections in the strip-shaped stamped part does not change until the fuse is finally manufactured. A precise positioning of the three strip-shaped parts, i.e. the two housing part strips and the strip-shaped stamped part inserted between the two housing part strips, is brought about and secured by means such as pin and hole pairs during the preliminary connection of the three parts, as will be explained in more detail below.

In the method according to the invention, the housing parts are not left to their own devices immediately before the encapsulation and are therefore dependent on a correspondingly solid design, but rather the housing parts are pressed against one another with sufficient pretension so that a controlled hold is present. It is therefore sufficient if the housing parts are loosely plugged together with the aid of means to be explained or are otherwise precisely aligned with one another. The pressure exerted by the pressure plates or pins or the shaped surfaces ensures that the housing parts abut each other so that gas tightness is usually present at this stage immediately before the encapsulation. The housing parts are made almost without exception as plastic parts, the elasticity of which ensures that the desired tightness is present even with unfavorable manufacturing tolerances.

The pressure plates or pins or the molding surfaces are therefore part of the molding chamber, within which the molding compound spreads during the encapsulation. You thus influence the shape of the extrusion coating, of course by leaving channels or the like

Ribs or other, later projecting designs can be created. Depending on the basic shape of the component, the pressure plates or molding surfaces can themselves be modeled on the shape of the component or can bring about a change in shape overall, for example producing a cylindrical shape if the original shape of the housing which has not yet been overmolded is a cuboid. When pressure pins are used, they later form depressions in the spray skin on the molded housing, which do not cause any further problems. It is only important that the housing parts are pressed together by the pressure or molded parts and so there are areas where there is a system for passing on the contact pressure.

As a result, an overmolding of the parting joint takes place with a more or less strong overlap, which can be particularly supported by designing the housing parts in the region of the parting joint in such a way that the parting joint has the greatest extent and the adjacent areas are continuous or in jumps have a smaller scope. Since two housing halves are used, it is particularly expedient to design the outer contour conically or be beveled in a cuboid, so that, in addition to the shape interlocking in the micro range, the extrusion coating also provides a visible and effective conventional form fit. Due to the pre-tension applied during the encapsulation and the subsequent solidification of the injection molding compound after the encapsulation, the gas tightness existing in the preliminary stage is retained even after the encapsulation, if the pressure plates or surfaces have been removed to form the electrical component.

Due to the overmolding which increases the strength, it is advisable to include the connections of the fuse in the overmolding. Irrespective of the anchoring in the corresponding housing part, bends can then occur on the sections outside the fuse of the connections no longer have any effect inside, it is irrelevant whether deformations of the connections are part of the further production process of the fuse or whether they occur accidentally. A particularly good anchoring can be achieved if the overmolded area of each connection contains an opening penetrated by the spray compound. At this point, there is a weakening of the flat connection material and a continuous plastic connection in the overmolded area.

It was already mentioned at the beginning that simple precautions are sufficient for the provisional assembly of the housing parts before the extrusion coating, so that at least a relatively loose cohesion is achieved.

As already mentioned, several housing parts are strung together with the aid of webs, in which case pin-hole pairs can lie in the region of the webs. The actual housing area then contains no precautions for cohesion, rather the mutually facing surfaces of the housing parts lie flat against one another.

When manufacturing miniature fuses and miniature fuses, it is common for the connections to be molded to be connected to each other to form a self-contained stamped part so that the previously applied sensitive fuse elements at the later connection ends inside the housing are not damaged. If such stamped parts are used, it is particularly clever to place apertured sections of the stamped part, which do not necessarily have the function of connections later, between the web halves, the respective pins for the loose pre-connection passing through a corresponding opening in the section . In this way, a manageable unit is created from the lower housing parts, the stamped part including the connections and the fusible conductors and upper housing parts, which are applied by bonding, for example, and which are plugged together to form a loose connection. After pressing the housing parts against each other by means of appropriate plates, pins or molded surfaces, the encapsulation takes place in the area of the parting line, which can also capture large parts of the housing. Deviating from this, the bars can also be pressed in before spraying. Condition are separated so that the entire joint is overmolded during the subsequent molding. After the encapsulation, the webs are separated, the connections are cut free from the stamped part and, if necessary, bent under the component to form a so-called SMD fuse.

The housing parts can be made of different materials. The material of the molding compound only has to harmonize with the material of the housing, otherwise it can be chosen freely. In this connection it should be pointed out that the encapsulation can also take place at a temperature which can lead to melting of the then thermoplastic material of the housing. In this way, not only does a microscopic and macroscopic form fit occur, but the molding compound even sticks to the component, which further improves the cohesion of the housing.

Fig. 1

eine perspektivische Ansicht eines Sicherungsrohlings nach dem Umspritzen vor der endgültigen Weiterverarbeitung zu einer Sicherung als Vertikalschnitt,

Fig. 2

eine Seitenansicht der aus dem Sicherungsrohling gemäß der Fig. 1 gefertigten Sicherung und

Fig. 3

die auseinandergezogene Einheit aus zwei Gehäuseteilestreifen und einem metallischen Stanzteil als Vorfertigungsstufe zur Herstellung von fünf Sicherungsrohlingen in einem einzigen Arbeitsgang.

The method according to the invention is illustrated below with reference to the manufacture and closing of a miniature fuse, which is shown in the figures of the drawing.
The drawing shows:

Fig. 1

1 shows a perspective view of a fuse blank after the extrusion coating before final processing into a fuse as a vertical section,

Fig. 2

a side view of the fuse made from the fuse blank according to FIG. 1 and

Fig. 3

the exploded unit consisting of two strips of housing parts and a metal stamped part as a prefabrication stage for the production of five safety blanks in a single operation.

The security blank shown in FIG. 1 consists of a housing 2, which is formed from two identical housing halves 3 and 4. Through cutouts 18 (FIG. 3) in the housing halves 3 and 4, connections 5 and 6 made of copper protrude into the interior of the housing 2, to which a fuse element 7 is fastened, for example by bonding. The prefabrication stage consisting of these parts is clamped between the pressure plates 12 (FIG. 2) for the encapsulation, the injection mold forming the encapsulation 8, of course, also being wrapped around this prefabricated securing blank 1. The details of the form are not shown. After the injection of the injection compound, the extrusion coating 8, which can be seen in FIG. 1, is formed, which essentially only covers the flanks of the housing halves 3 and 4 while simultaneously enclosing the connections 5 and 6.

When the housing 2 is closed by the encapsulation 8 according to the invention, it is important to use the pressure plates 12, which are shown only schematically in FIG. The pressure plates 12 press the housing halves 3 and 4 firmly against one another, which, moreover, are pre-positioned relative to one another by means to be explained. The slight inclination of the side walls of the housing halves has two advantages: On the one hand, the incline counteracts the injection forces, which can be considerable. On the other hand, this creates a macroscopic form fit because the parting line between the two housing halves 3 and 4 is the location of the largest circumference and all neighboring areas are smaller in circumference. As a result, the encapsulation 8 sits like a clamp on the two housing halves 3 and 4 and holds them together under the same pretension that was originally given up by the pressure plates 12.

FIG. 2 shows the side view of a finished fuse 10. The connections 5 and 6 are bent under the lower housing half 3, so that a fuse 10 has been created which can serve as an SMD component, that is to say for a fastening technique on printed circuit boards by the reflow process or by the wave soldering process (SMD = surface Mounted Device). The wave soldering process requires the components to be glued to the circuit board. For this reason, a rib 13 can optionally be formed between the ends of the connections 5 and 6, which arises during the encapsulation, by a corresponding shaping of the pressure plate 12 lying on this side, which is indicated schematically in FIG. If it is already clear beforehand that the fuse 10 is fixed exclusively in the reflow process, such a rib 13 is not required. The assigned plate 12 is then designed as well the pressure plate 12 shown in the upper half of the picture, namely with a continuous, flat bottom.

2 shows the halves of a web 11 facing the viewer, which in the preliminary stages of production served to form a row of a plurality of housing halves 3 or 4. It is not a condition that the webs touch the parting joint of a housing half 3 or 4, rather the webs can also run at a distance from the parting joint, so that it is completely closed by the encapsulation 8. In the exemplary embodiment described here, the web 11 protrudes from the extrusion coating, and is therefore not covered by the extrusion coating 8. The protrusion of the web 11 from the extrusion coating 8 is harmless because the separated point lies directly next to the actual housing halves 3 and 4, which are pressed against one another with considerable pretension as a result of the pressure plates 12, and are further exposed to this prestressing pressure even after the encapsulation.

3 shows how a plurality of housing halves 3 and 4 are prepared simultaneously for the extrusion coating. First, housing half strips 15 are mass-produced on automatic sprayers from a plastic. Each strip 15 contains five housing halves 3 or 4, three pins 16 and three holes 17. After selecting two strips, one is used to form the lower housing halves 3 and the other strip 15 to form the upper housing halves 4.

Each strip 15 carries cutouts 18 for receiving the connections 5 and 6 in the area of the housing halves, and a recess 19 is also formed in the area of each pin 16 or each hole 17, which serves to receive a section 21 which is part of a stamped part 20 for Formation of connections 5 and 6 are. The stamped part 20 is shown in its entirety in the lower part of FIG. 3.

When preparing the extrusion coating of five securing blanks 1, which are assigned to a strip 15, the main components shown in FIG. 3 are first put together to form a unit by superimposing them. The pins 16 each protrude through holes 22 in the stamped part 20, which are embedded in the sections 21 within the stamped part 20. The sections 21 serve no other electrical purposes, so they will be fed to the waste treatment later after cutting the fuse blank 1. Incidentally, it should be noted that, of course, fusible wires are already installed between the connections 5 and 6 before the housing parts are placed on them, for example by soldering or bonding.

The layer structure thus formed is placed in the mold for extrusion coating, the loose cohesion which is formed by the pins 16 and the holes 17 being sufficient. Within the injection mold, pressure plates 12 rest against the respective housing halves 3 and 4, and the rest of the mold is also closed. After the encapsulation, the layer structure mentioned can be removed, the cohesion now being final.

Openings 24 are provided in the area of the connections 5 and 6, which are in the area of the encapsulation 8 and improve the anchoring of the connections 5 and 6, which will be bent later. In this way it is reliably prevented that the connections 5 or 6 are pulled out of the closed housing during bending.

The unit is then divided along the cutting lines 25 or along the cutting lines 26 and 27 into individual securing blanks, preferably initially with cuts be placed along the cutting lines 26 and 27. As a result, a very easy-to-use unit of a total of five fuse blanks is retained, which in this form can easily be brought into the shape shown in FIG. 2 by bending the connections 5 and 6. Only then are the cuts made along lines 25, as a result of which the strip-shaped unit breaks down into individual fuses 10.

The representation given in the figures is greatly exaggerated. Even Figure 3 shows the actual backups in double size. The fuse 10, which is finished later, takes up a base area of 4.5 × 4.5 mm and a height of approximately 3 mm. Of course, smaller versions are also possible. The invention is by no means limited to miniature fuses, but can be used with good success on small fuses and even larger units, since the cohesion of the housing parts is excellent, that is, the switching capacity of a corresponding fuse is considerable with the smallest external dimensions.

Before the unit is cut into individual security blanks, it can be labeled, which is preferably printed on. Trademarks or other traits of origin can also be attached, so that a complete identification by origin and type is possible.

Even before the unit is divided into individual securing tube blanks along the cutting lines 25, the units in the form presented can be tinned in a galvanic bath, with of course only the connections 5 and 6 being given a tin coating. This late tinning in the galvanic bath is completely harmless for the unit. However, it does not The advantage is that the cut surfaces also have a tin layer, which often facilitates the flow of solder. Deviating from this, of course, a tinplate strip tinned from the outset can be used, which, however, then has no tinning on the cut surfaces.

Claims (13)

1. Method for producing and enclosing micro and sub-miniature fuses;
      the casing (2) of which is formed by two parts (3, 4) encloses a cavity with a fusible conductor (7) positioned therein, and is provided with at least two conductors (5, 6) for electrical connection;
      comprising the method steps of the preparatory joining of the casing parts and the injection moulding around the casing by a synthetic material;
      characterized
      by the feature that a casing part strip (15) made of a synthetic material for the lower casing parts (3) and a casing part strip (15) made also from a synthetic material for the upper casing parts (4)
      together with a strip-shaped punched component (20) laid between the two casing part strips (15) in which component the connectors (5, 6) are united into a closed unit and the fusible conductor (7) bridges the free ends of the connectors (5, 6) respectively,
      are positioned to each other with the aid of means such as pin and hole connections (16, 17) and connected preparatorily into a unit; and by the feature of the pressing together the casing parts (3, 4) with the aid of pressure plates (12) or pressure pins or mould surfaces during the injection moulding under use of the pressure plates (12) or pressure pins or the mould surfaces as forming elements for limiting and for modelling the injected mass.
2. Method according to claim 1, characterized in that the casing parts (3, 4) are so formed in the area of the joint that the joint area has the biggest circumference and the adjacent areas have a steadily or in steps decreasing circumference.
3. Method according to claim 1 or 2,
   characterized in that the connectors (5, 6) are positioned into the area of injection moulding (8).
4. Method according to claim 3, characterized in that the connectors (5, 6) are positioned in the area of the joint between the casing parts (3, 4).
5. Method according to claim 4, characterized in that each area of each connector (5, 6) being surrounded by injection moulding is provided with an opening (24) transgressed by the injection mass for improving the anchoring.
6. Method according to the preceding claims,
   characterized in that the pins (16) formed to the casing parts (3, 4) for the preparatory joining of the casing parts are placed into holes or bores formed into the casing parts (3, 4).
7. Method according to one of the preceding claims,
   characterized in that several casing parts (3, 4) are connected to each other by web halves (11) which are removed prior or after injection moulding.
8. Method according to claim 6 and 7,
   characterized in that the pins (16) are positioned in the area of the webs (11).
9. Method according to claim 8, characterized in that sections (21) of the punched components (20) provided with holes (22) are laid between the web halves (11) the corresponding pin (16) of which penetrates a corresponding opening (22) in the section (21).
10. Method according to one of the preceding claims,
    characterized in that two casing halves are chosen as casing parts (3, 4).
11. Method according to one of the preceding claims,
    characterized in that the casing parts (3, 4) are formed by different materials.
12. Method according to one of the preceding claims,
    characterized in that the casing parts (3, 4) consist of a thermoplastic synthetic material and that the injection mass is injected under a temperature under which the casing parts (3, 4) are surface molten.
13. Method according to one of the preceding claims with the exception of claim 10,
    characterized in that unidentical components are chosen as casing parts (3, 4).

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