GB2079550A - Fuse assembly machine - Google Patents

Abstract

A fuse assembly machine comprises a first conveyor 1 having notches in its surface which pass below a hopper 5 feeding cut lengths of glass tube into the notches, a device 8 feeds fused wires through the tubes which are then transferred to a first drum 10 where they are checked, the lower ends of the tubes are then sealed at a station 14, the tubes are filled with anti-flash powder at 15 and the upper ends sealed at 16. The fuses are transferred to a further drum 18 whereon they are allowed to cool and then transferred to a second conveyor 20, electrically tested at 21 and fed to a collection hopper 26. <IMAGE>

Description

SPECIFICATION Fuse assembly machine This invention relates to a machine for assembling fuses. The fuses are of the kind which comprise a length of wire 3-5 cms long with a part of lesser diameter, about 1 cm in length formed of wire filament which provides the fuse which for circuit protection is burned out by overloads well before the main part of the wire. This filament is encapsulated in a glass or quartz tube filled with an anti-flash material such as a refractory powder, and each end of the tube heatsealed to the thicker portion of the wire extending from each end of the tube. A fuse is obtained in this way which is sealed against flash, and can accordingly be used in dangerous environments for circuit protection without fear that fusing will cause a spark which might cause an explosion or fire.

Heretofore, such fuses have been assembled by manually placing the wires, preformed with the fuse filament centrally soldered between two terminal wires, into the glass tubes mounted on a wheel or conveyor, and the conveyor taking the tube and wire assemblies to work stations for heat sealing the tubes and filling them with anti-flash powder, and finally removed manually from the conveyor.

An object of this invention is to provide a machine for assembling fuses; the fuses being of the kind described, wherein all steps are carried out automatically.

According to the invention there is provided a fuse assembly machine comprising means for feeding fuse encapsulating tubes into holders therefore provided on conveyor means, one or more means for feeding lengths of fused wire one into each tube while the latter are carried by the conveyor, means at a first station for sealing the lower ends of said encapsulating tubes, means at a second station for filling the tubes with anti-flash powder, means at a third station for sealing the lower ends of said encapsulating tubes, and means for discharging thus assembled fuses from the conveyor means.

The means for feeding encapsulating tubes to said conveyor means preferably provides a hopper which receives a continuous supply of pieces of glass or quartz tubes cut to the required length which may be cut by a continuous cutting device feeding into the hopper.

The hopper preferably has a chute contoured to feed the tubes one by one into each of a number of outlet orifices which over lie. The paths of series of tube holding recesses in a continuously moving conveyor belt, the tubes falling into the recesses as these pass beneath them.

The means for feeding lengths of fused wires into.the tubes held in their recesses in the conveyor preferably comprises one or more feeders each having a group of wirefeed apertures to which the wires are fed, e.g.

down gravity tubes. The structure containing the apertures has preferably an associated pinretaining plate which is reciprocated to retain the wires until tube-holding recesses are aligned with the apertures, and then allow the wires to drop through the tubes to fall until their ends abut a bottom plate which prevents the wires from falling completely through the tubes, and is provided with a cam portion which partially returns the wire upwards as the conveyor is moved past the feeder so that the fuse incorporated in the wire lies within a respective tube.

The conveyor means preferably comprising not only a continuous chain conveyor passing the tube and wire feeding means, but also a drum associated with the sealing and filling stations, and a second wheel or drum for cooling the fuse assemblies and a second chain conveyor leading to the discharge station. There are necessarily means for transferring the tube and wire assemblies from the first conveyor to the first drum, thence to the second drum and in turn from the second drum to the second conveyor.

The first drum, preferably has checking means before the sealing and filling stations for verifying the presence of tube and wire in turn and rejecting any incomplete units, while the second conveyor may pass and electrical testing station to ensure that the assemblies are electrically conductive -- i.e. that the fuse filaments have not been shattered by mechanical shock for example.

A preferred embodiment of fuse assembly machine according to the invention will now be described by way of example with reference to the accompanying drawings, wherein: Figure 1 is a diagrammatic plan of the machine; Figure 2 is a sectional view of the feed for glass tubes to the conveyor; Figure 3 is a sectional view of the feed for fused wires into the tubes on the conveyor; Figure 4 illustrates the mechanism for effecting transfer of tubes with wires from the conveyor to a drum; and Figure 5 shows a cross section of a completed fuse unit.

Referring first to Fig. 1, the fuse assembling machine according to the invention comprises a conveyor 1, having an endless notched belt 2 running over end rollers 3, 4. Glass tubes for encapsulating fuses are fed one by one from a hopper 5 into the notches on the belt 2. The belt is twisted through 90 by a cam 6, so that the tubes stand on end in the notches and are prevented from falling out by a returner plate 7. The tubes are carried in this attitude past a wire feed station comprising four wire feeders 8. These operate as described in relation to Fig. 3.The conveyor takes the tubes with wire therethrough to a transfer station 9 wherein the tubes are transferred to a working drum or wheel 10 which rotates anticlockwise to take the tubes and wires passed a first checking station 11 wherein a feeler checks for the presence of glass tubes, and a second checking station 1 2 where a further feeler checks for the presence of wires. Tubes without wires are rejected by a lever responsive to the station 1 2 failing to sense a wire through a tube, and sent down reject chute 1 3.

The tubes with wires through are then passed by further rotation of the drum 10 to a station 14 where a heated tool is used to heat seal the lower ends of the glass tubes to the wire. The tubes thus sealed are then passed to a station 15 5 where an antiflask powder (a refractory powder such as MgO) is cascaded over the zone traversed by the tubes. Most of the powder misses the tubes, but enough enters to fill them. The powder is recovered and recycled in an almost closed circuit which only in-frequently requires topping up. The filled tubes then pass to a further heat sealing station 1 6 whereat the tops of the tubes are heat sealed using a similar heated tool to that provided at station 14.

After leaving the sealing station 1 6 the fuse assemblies are complete and are transferred to a second transfer wheel or drum 1 8 at a transfer station 1 7. The assemblies are allowed to cool from the heat sealing steps as they are moved around the drum 1 8 to a third transfer station 1 9 where the assemblies are transferred to a second notched conveyor 20, which runs with the notches directed upwardly at all times, and has a retainer plate 21 for preventing the assemblies from falling out of the notches. The conveyor 20 runs over terminal rollers 22, 23 and leads the assemblies to a test station 24 where the assemblies are tested for conductivity.Any non conductive assembly (usually due to machanical shattering of the fuse wire section by shock) is rejected, by opening a shutter in the plate 21, allowing the assembly to fall out of its notch down a reject chute 25. Finally, the assemblies are discharged over the terminal roller 23 into a collecting bin 26 before being sent for packing.

Fig. 2 shows the hopper 3 for feeding glass tubes 27 to the conveyor 2. The hopper 3 accepts the tubes from a slide 30 which may lead directly from a shearing machine which continuously cuts glass tubes into the lengths required. The tubes are channeled by the side walls of the chute to an aperture 31 of the size to allow a single tube, lying on its side so that it can roll, to pass at a time, The tubes 27 leave this aperture 31 down a slide 32 having an aperture 33 therein which allows tubes which are too short to meet required tollerances to fall through. The remaining tubes fall into notches 34 in the belt 2, and are carried forward by a belt between cam plates 35 over which tubes which are too long to meet required tollerances ride to be rejected.

One wire feeding station 8 of the four is shown in section in Fig. 3. The belt 2 moves continuously under a feed head 36 which has e.g. four wire feed apertures 37 therein alligned with the path of the notches 34 and equi-spaced with them - and a slide 38 which retains wires 39 in the apertures 37 until the tubes 27 and notches 34 are aligned with the apertures 37 and then slides back allowing the wires 39 to fall into the tubes 27. The slide 38 operates in synchronism with the motion of the conveyor, and the four stations 8 operate in turn to ensure that all the tubes 27 are given a wire 39.

A retainer plate 40 below the conveyor prevents the wires 39 from passing completely through the tubes 27, and clear of the head 36 an inclined part 41 raises the wires to the required position for processing i.e.

with the fuse filament within the tube 27 and each end of the wire 39 protruding approximately equally from each end of the tube 27.

The plate 40 then extends along the conveyor to the transfer zone 9.

Zone 9 is illustrated in Fig. 4 which is a sectional view taken from above. The drum or wheel 10 has a flange 42 with notches 43 each spaced with the same linear pitch as the recesses 34 in the belt 2. Each notch 43 is just greater than a half circle, its shape being defined by a major arc of a circle and defining cusps 44 which grip a cylindrical object of similar diameter to the notch when inserted into the notch. The belt 2 is pressed against the drum 10 as the belt moves and the drum rotates. This contact may indeed provide the drive for the drum 1 0. At the same time, the notches 43 and grooves 34 align, and the pressure of the belt on the drum presses the tubes 27, with inserted wires 39, into the notches 43 where they are retained by the cusps 44.

At the transfer station 17, the assemblies which have been formed by the heat sealing steps are levered out of the notches 43 by a tangential blade which has a guide tail which presses them into similar notches in the transfer wheel 1 8. A similar device is used to transfer the assemblies from the wheel 18 to the second conveyor at transfer station 1 9.

Finally, Fig. 5 shows a sectional view of the fuse assembly produced by the machine according to the invention. This comprises a wire 39, composed of end parts 39a, 39b and a mid-length fuse filament 45 soldered at each end to an end of the part 39a, 39b. The fuse filament is encapsulated within a glass tube 27 which is heat-sealed at each end 27a, 27bto the wire end parts. The space within the glass tube is filled with an anti-flask powder, e.g. a refractory powder such as magnesia. Such a fuse assembly can be used for protecting transistor circuits, and in environments where a spark caused by burn out of a fuse element might cause a fire or explosion.

Claims (10)

1. A fuse assembly machine comprising:means for feeding fuse encapsulating tubes into holders therefor held on conveyor means, one or more means for feeding lengths of wire each including a part of reduced cross-sectioned area into each tube while the latter are carried by the conveyor, means at a first station for sealing the lower ends. of said encapsulating tubes, means at a second station for filling the tubes with refractory antiflash powder, means at a third station for sealing the upper ends of said encapsulating tubes, and means for discharging thus assembled fuses from the conveyor means.

2. A machine according to claim 1 wherein said means for feeding encapsulating tubes to said conveyor means comprises a hopper which receives a continuous supply of glass or quartz tubes cut to the required length having a chute contoured to feed the tubes one by one into each of a number of outlet orifices which overlie the paths of respective tube holding recesses in a continuously moving conveyor belt, the tubes falling into the recesses as these pass below the orifices.

3. A machine according to claim 2 wherein the tubes are cut to the required length by a continuous cutting device feeding into the hopper.

4. A machine according to any preceeding claim wherein the means for feeding lengths of fused wire into the tubes held in recesses in the conveyor comprises one or more feeders each having a group of wirefeed apertures to which the wires are fed.

5. A machine according to claim 4 wherein the structure containing said wire feed apertures has as associated pin-retaining plate which is reciprocable to retain the wires until tube holding recesses in the conveyor are alligned with the apertures and then to allow the wires to fall through the tubes until their ends abut a bottom plate which prevents the wires from falling completely through the tubes.

6. A machine according to claim 5 wherein the pin retaining plate is provided with a cam portion which partially returns the wire upwards as the conveyor is moved past the feeder so that the part of reduced cross sectional area lies within a respective tube.

7. A machine according to any preceeding claim wherein the conveyor means comprise a continous chain conveyor passing the tube and wire feeding means, and a drum associated with the sealing and filling station, and a second wheel or drum for cooling the fuse assemblies and a second chain conveyor leading to the discharge station.

8. A machine according to claim 7 including means for transferring the tube and wire assemblies from the first conveyor to the first drum, from the first drum to the second drum, and from the second drum to the second conveyor.

9. A machine according to claim 7 or 8 wherein said first drum has checking means located before the sealing and filling station for verifying the presence of the tube and wire in turn and rejecting any incomplete units, and the second conveyor has an associated electrical testing station to ensure that the assemblies are electrically conductive.

10. A fuse assembly machine substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.