GB2233840A - Electrical fuse - Google Patents

Abstract

The high speed fuse employs stamped end bells (12) and terminals (14) rather than forged or machined parts. A slot (16) for the terminal is punched through each end bell. The terminal is inserted into the slot in the end bell and staked in position. This ensures a strong tight fit without requiring welding or soldering. One end of each terminal has coined ridges (44) to facilitate automatic welding of the fuse link (30) to the terminals. Round balls (18) are used to seal the fill holes (20) for the arc quenching material. Metal pins (41) secure the end bells within the fuse housing (40) but are not electrically connected to the terminals if the end bells are made of electrically insulating material. <IMAGE>

Description

1 v HIGH JPEED JESIS This is a continuation-in-part of copending

applications serial number 071344,796 filed Apri 24, 1989; aerial number 071344j718 filed April 24, 1989; aerial number 071344.719 filed April 24, 1989 and serial number 07/344,717 filed April 24, 19896 This invention relates ' in general to fuses and more particularly to high speed fuses.

High speed fuses have been used for a number of years for the protection or isolation of semiconductor devices such as diodes and thyristors. There is very little safety factor in these semiconductor devices and they can fail quickly when subjected to overcurrents, Therefore, a fuse designed to protect semiconductor devices must open quickly. High speed fuses have very little thermal capacity, and in general open in the order of,001 to 004 seconds when interrupting short circuits.

Problems exist with high speed fuses currently on the market because these fuses have been developed over time to meet specific applicationst resulting in a large number of different fuses made in different sizes and shapes to satisfy the voltage and amperage ranges expected to be encountered. Several hundred different parts and subassemblies. for these fuses may be required. Thus, it would be desirable to be able to manufacture fuses having standardized parts to reduce the total number of parts that need to be stocked in order to manufacture a complete line of high speed fuses.

Many applications for high speed fuses require the use of a plurality of fuses usually mounted side by side in close proximity of one another. many users wish to mount multiple fuses as close together an possible. Prior art high speed fuses have metal end bells which are mechanically and thus electrically connected to the mounting terminals hold to the insulating tube with metal pins which are exposed flush with the tube surface and are not sealed. Consequently, when in use in an electrical circuit, the pins are at the- same electrical potential as the terminals and and bells. Typically, three phase electrical applications use a fuse in each phase mounted adjacent to each other and - as close as possible to conserve space within the equipment. Industrial standards govern minimum spacing between eectrically hot parts and dictate the minimum distance between live or "electrically hotH parts through air an a function of stand-of f voltage. since the pins are. electrically hot and exposed to the tube surface, this minimum distance in measured between adjacent tube surfaces# an opposed to terminal distances.

Yet another difficult7y in encountered in manufacturing high speed fuses in that the and bell, must be joined to the terminal for mechanical strength of the fuse package and, in most designs, 2 f '.

for the electrical connection between the current carrying fusible elements within the fuse and the vounting terminal. Prior art high speed fuGGG accomplished this by'brazing, welding or soldering the teminal to the and bell or machining the and bell and terminal from g solid piece of metal or by pressing the metal pine through the tube and and bell and into the mounting terminal. All these techniques are labor intensive.

A further problem is encountered with and bell@ in that these circular pieces of metal are most often forged or machined from rod stock and coined, drilled, and sized. This again requires extra time and additional labor and in thus more expensive.

Yet another manufacturing problem in encountered in making high speed fuses. These fusear in general, are filled with &and or other arc quenching materials. This material in added through a hole in the and bell after the and bell is assembled to the fuse tube. Various methods of plugging the hole have been used, but all suffer from various limitations. For ex&?nple, costly knurled plugs are used which require excessive pressure to insert the plug into the hole in the and bell. A more economical means to close the sand hole is required.

The present Invention employs stampod and bells and terminals rather than forged or nachin4 parts. A Cot for the terminal is punchod through the end ball. The terminal is Inserted into the &lot in the and ball and staked in position. This insures a strong tight fit without requiring welding or ---soldering. One and of each terminal has coined ridges to facilitate automatic welding of the fuse link to the terminals. Round balls are used to seal the fill holes for the arc quenching material. Alternatively, the end balls may be molded of plastic. Metal pint occur the and ball within the fuse housing but are not electrically connected to the terminals because of the insulative end bells.

In the accompanying drawings:

Figure 1A shows 4 Perspective view partially cut away of & prior art fuse:

Figure 1B shown a perceptive view partially in section and exploded of a fuse according to the present Invention; Figure 2 shows a top view of a terminal of the fuse shown in Figure 1; rigure 3 shown a front view along the lines 3-3 of the terminal shown in Figure 2; Figure 4 shows a complete end bell assembly; Figure 5 shows a aide cross-sectional view of the assembled fuse of Pigure 1; Figure 6 is a top cross-sectional view of the fune shown In Figure 1; Figure 1 is a partial crost-sectional view of the ineallation of the ball In a sand hole as shown in Figure S; Figure a It a cross-soctional view along the lines 8-8 in Figure 7s and Figure 9 shown the cross section of two adjacent fuses Illustrating positioning distance.

Figure 1A show a prior art high speed fuss 9. metal and balls 13 with terminals 15 are housed within the and of an insulating tub 40. It Is seen that the terminal 15 is welded or brazed at 17 onto the metal end bell 13. Thus the and bell 13 is electrically hot when the fuse in mounted in an electrically energized circuit. The end bell is hold In place in insulating tub 40 by metal pins 41 which are also.at the same voltage level as the and bell 13, Thusi as shown in 1Pigure 9, the minimum distance OF" that prior art high speed fusis can be placed adjacent to each other, an dictated by industrial standardsi la governed by the distance betwoon the electrically hot pins 41 of adjacent fuses.

In the fuse according to the present invention shown in Figures 15# 5 and 6 and referred to generally by numeral 8, an end ball assembly of an and ball 12 and terminal 14 are adapted to be received in &eh and of Insulating housing or tube 40. The and bell 12 and terminal 1 4 are stainped from a piece of material 1 and a lot 16 In punched In the end ball 12. The terminal 14 Is inserted into the &lot 16 until shoulders 48 engage the and bell 12. The terminal 14 is then staked at 46 or coined or mechanically upset in position as shown in Figure 4 to attach terminal 14 to end ball 12, Thus the terminal and the and bell are joined without brazing. welding or soldering,, and without complicated mechanical assembly using additional components. it in more cost efficient to produce the part by stamping rather than by forging. stamping provides a scrap reduction over making the parts from forging and also allows the selection of appropriate material tor the and bell 12 and terminal 14 which can be of dissimilar materials such an plastic and metal.

An shown in Figures 2 and 3, a eerie of small rectangular cross-oectioned ridge&. weld pad& or projections 44 are embossed on the inner and of terminal 14 during fabrication for welding terminal 14 to one and of a fuse element 30g preferably by resistance welding. These weld projections 44 may be coined or machined into terminal 14. The height of each of weld projections 44 is the am& over the entire weld area. The number of projections 44 Is determined by the width of terminal 14. The size and shape of the pads may vary from terminal to terminal depending upon the size of fuss element 30 and and bell 12. A saw tooth pattern may also be usad in some application&.

The pitch and depth of the saw tooth will vary with link thickness.

An advantage to using weld projections 44 on the terminal 14 in that it improves the welding'of the fusible element 30 to the terminal 14. Weld projections 44 provide consistent weld quality and welded surface area resulting in consistent heat transfer and electrical conductivity through the welded joint between the fusible element 30 and the terminal 14 of fuse 8, This results in more reliable fuss performance and reduction in costs because all welds can be made simultaneously. Thisprocedure also reduces maintenance of the weld electrodes because both electrodes are flat blades an compared to small pointed electrodes. This typo of construction is also very useful for automating welding and results in a more consistent weld than that afforded by prior art spot welding techniques. Direct labor is reduced because multiple welds can be made with each electrode closure. Thus, the time required to weld the strip to the terminal in reduced, the consistency of the weld area is improved, and the electrical conductivity and heat transfer from terminal- strip to fuse element is consistent.

The fuse element 30 is preferably of a standardized planar. design using an accordion shape which allows for the use of an element having a substantially longer overall effective length than can be achieved with a straight through element an in most prior art high speed fumes. The Increase In off6tive length enhances the ability of the fuss, to clear lower level overcurrent situations, specially on DC circuits. As shown In Figures 5 and S# a fuse element 30 may be welded to both sides of terminals 14 to provide a multiple clamant fuse.

Referring now to Figure 9, since the terminal 14 projects through tha front face and back face of the and ball '12, the fusible element 30 may be electrically connected directly to the terminal 14, Thus, the end ball 12 does not need to be made of electrically conducting material, and may be made of plastic or other non-electrically conductive materials. End balls 12 of insulating material, such an plastic, are less expensive than metal and belle and can be moldod Instead of machined allowing for the use of more Intricate shapes when necessary. The Insulating end balls 12 not only serve their normal function of closing off the ends of the Insulating tube 40 of fuse 8 and provide the required structural integrity to the fuse package, their us results In the metal pins 41, which secure the end bell 12 within the tube 40, being insulated from the electrical circuit passing through terminal 14 and fusible clamant 30.

An advantage of using plastic or other non-electrically conductive material for the and bell 12 is that pins 41. designed to project through ths insulating tube 40 into the end ball 12, are not energized since the and ball is not electrically 1 I conductive. Since holding pins 41 are not "electrically hot" when mounted side by side, fuses can be positioned closer together thus conserving panel board space in equipment. in the prior art fuse where the metal pin in electrically hot, the adjacent fuses cannot be mounted aid& by side in close proximity more than the distance "FY shown in Figure 9. The separation between the fuses is governed by the distance between the terminals which are electrically hot. However, when mounted in an electrical circuit, high speed fuses manufactured according to the present invention may be positioned closer to one another since the minimum distance 'IF" is measured between the electrically hot terminals 14 and not the pins 41 as shown in Figure 9.

As the fuses are assembled, a first terminal is joined to a first and bell, a second terminal is joined to a second end bell, and the fusible element 30 in welded between the two terminals. Because of the weld projections 44 on the terminal 14, the welding of the fusible element may be done by projection welding.

- Referring now to Figures 5-8, the assembly of the end bell assemblies welded to the ends of the fusible element 30 is slipped into the insulating tube 40 and the and balls are hold in popition within tube 40 by pins 41 which are inserted- into aligned apertures in tube 40 -and and balls 12. Aligned aperture@ are placed in the end balls 12 and tube 40 by drilling just prior to Insertion of pins 41. An are quenching inaterial 4# shown in Figures 5 and 6# typically special sand# Is poured into sand holes 20 in the and ball 12. After the high speed fuse 8 to filled with sand. the holes 20 are closed using a solid spherical ball 18. These round balls 18 may he steal or other material and are slightly larger than the hole 20 in the and bell 12. The ball 18 in prevented from misalig=ent because It in guided by Its own natural radius into the hole 20. The balls 18 are thus sslf-centering and art held in place by frictional force. ' Alternately, particularly where and bells 12 are metal, such as brass, the and hole 20 may be coined after insertion of the ball 18 to hold the ball In. The balls 18 are forced _or pressed Into the end bell 12 by an insertion tool 45. The ball 18 to trapped between three small pins 47 which displace the metal -49 of the metal end ball 12 over the ball 18 while the final insertion is being accomplished. The flat bottom of the insertion tool 45 provides automatic Insertion depth. Over Insertion in prevented by the design of the Insertion too.1 45. Using balls 18 has several advantages. The hardened steel ball 18 provides a low costo self-aligningi easily Inserted means of plugging the fill hole 20 in the end ball 12 of a fuse 8. The steel ball 19 requires less force to insert and tands to be selflooking. This Is significantly easier than prior art processes - 10 which often used pinal hollow closed-and Cylinders, or screws to seal the holes. it in seen that high speed fuses manufactured according to,the present invention are easier to construct, require lose labor and are consequently less expansive to manufacture and# in one embodiment, can be used closer together, when mounted adjacent to one another# with reduced danger of shorting from fuse to fuse.

1 - 11 m 11 CLAiMS A fuse comprising; a first and bell having a first terminall a second end bell having a second terminal; a fuse element electrically connecting said first and second terminalsy a housing receiving said end belle, terminals and fuse element; said first end bell having at least one aperture with a circular cross-section therethroughl a spherical solid ball having a cross-section greater than said cross-section of said aperture for insertion into said aperture, said ball self-centaring as said ball is inserted into said aperture and frictionally held within said aperture; said housing having a plurality of circumferentially spaced holes in each and of said housing; said first and second and bell having a plurality of bores circumforentially spaced around the periphery thereof adapted for alignment with said holes; said first and second and bells being made of a nonelectrically conductive materialt and metal pins received within said aligned holes and bores for scouring said end bell# within said housing, said pins 12 1 1 1 I in non-electrical contact with said terminals and fuse element.

2. A fuse comprising: a first end bell having an opening therathrough; a first terminal having an inner and extending through said openiq and projecting from said first end bell; said Inner end having weld projections; a second end ball having a second terminal; a fuse element having one end welded to said weld projections on said first terminal and another and welded to said second terminal; a housing receiving said end bells, terminals and fuse elomenti said first end bell having at least one aperture with a circular cross-section therathrough; and a spherical solid ball having a cross-section greater than said cross-section of said aperture for insertion into said aperture, said ball self-centering as said ball is inserted into said aperture and frictionally hold within said aperture. A fuse comprising: a first and bell having an opening therethrough; a first terminal having an inner end extending through said opening and projecting from said first end bell; - 13 m maid Inner and being staked to attach said first terminal to said first and bell; a second and ball having a second terminals a fuse cloyAcint electrically connecting said first and second terminalc a housing receiving said and bellai terminals and fuse elements said first end bell having at least one aperture with a circular cross- section therethrough; and a spherical solid ball having a cross-section greater than said cross- section of said aperture for insertion into said aperture,, said ball self-centering as said ball in inserted into said aperture and frictionally held within said aperture.

4. A fuse comprising:

first and bell having an opening therethrough; first terminal having an inner and extending through. said opening and projecting from said first and bell; said inner and having weld projections; a second and bell having a second -terminal i a fuse element having one end welded to said weld projections on said first terminal and another end welded to said second terminal; - 14 J 0 a housing receiving said end bells, terminals, and fuse element; said housing having a plurality of circumferentially &paced holes in each end of said housing; said first and second end balls having a plurality of bores circumferentially paced around the periphery thereof adapted for alignment with maid holes; maid f trict and second and bells being made of a nonelectrically conductive material; and metal pins received within said aligned holes and bores for &curing maid end balls within said housing, &aid pins In non-electrical contact with maid terminals and fuse element, 5. A fuse comprising: a first end bell having an opening therathrough; a first terminal having an inner and extending through said opening and projecting from said first end bell; &aid inner and being staked to attach maid first terminal to said first and bell; a second and bell having a second terminal; a fuse element electrically connecting said f irst and second terminals; a housing receiving said and bell%, terminals and fuse element; said housing having a plurality of circumforentially spaced holes in each and of said housingi said first and second and bell& having a plurality of bores circumferentially spaced around the periphery thereof adapted for alignment with said holes; said f irst and second and bells being maae of a nonelectrically conductive materiall and metal pins received within said aligned holes and bores for securing said end bells wihin said housing, said pins in non-olootrical contact with said terminals and fuseelement. A fuse comprising:& first and bell having an opening therethroughi a first terminal having an inner and extending through said opening and projecting from said first and bell; said inner and being staked to attach said first terminal to said first and bell; said inner end having weld projections; a second and bell having a second terminal; a fuse element having one end welded to said weld projections on said first terminal and another and welded to said second terminaly and a housing receiving said and bells, terminils, and fuse element.

1 i 1 7. A fuse comprising: a first end bell having an opening therethrough; a f irst terminal having an inner and extending through said oening and projecting from said first and bell; said inner end being staked to attach said first terminal to said first and bell and having weld projections; a second end bell having,& second terminal; a fuse element having one end welded to said weld projections on said first terminal and another and welded to said second terminali a housing receiving said end bells, terminals and fuse elemental said first and bell having at least one aperture with a circular cross-section therethrough; a spherical solid ball having a cross-section greater than said cross-section of said aperture for insertion into said aparture, said ball self-cantering as said ball is inserted into said aperture and frictionally hold within said aperture; said housing having a plurality of circumferential ly spaced holes in each end of said housing; said first and second and bells having a plurality of bores circunferentially spaced around the periphery thereof adapted for alignment with said holes; maid first and second and balls being made of a nonelectrically conductive material; and metal pins received within said aligned holes and bores for. scouring said and balls within said housing. said pins in non-cloctrical contact with said terminals and tune element.

2. A fuse as in claim 11 2 or 3 wherein maid first end ball Is coined around said aperture after said ball in Inserted into &aid aperture.

9. A fuse an in claim 2g 4o 6 and 7 wherein said weld projections are parallel with the longitudinal axes of said terminals and said fuse element.

10. A fuse as in claims 2i 4# 6 and 7 wherein maid weld projections have a longitudinal length substantially the distance said Inner and of said first terminal projects from said opening.

11. A fuse as In claims 2, 4, 6 and 7 wherein said weld projections are disposed on both sides of said inner end of cald first terminal.

12. -A fuse an In claims 2# 4# 6 and 7 wherein said weld projections are alternating ridge# and grooves around said inner end with said grooves and said ridges being In alignment on each side of said inner end.

- is - 13. A fuse an in claims 2, 4# 6 and 7 wherein said weld projections are altornating ridges and grooves.

14. A fuse as in claims 21 4# 6 and 7 wherein said weld projections and alternating ridges and grooves and said grooves have a depth loss than one-half the thickness of said first terminal.

15. A' fuse as in claims 2, 4# 6 and 7 wherein said weld projections are alternating ridges and grooves and said ridges are rectangular In crosssection forming a flat projecting surface.

16. A fuse an In claims 2, 4, 6 and 7 wherein said well projections are alternating ridges and grooves and maid grooves have a bottom perpendicular wall.

17. The fuse an in claim 15, wherein maid and balls and terminals are stampings.

18. A fuse an in claim 1 wherein said first end ball has a rectangular slot therathrough for receiving said first terminal, maid terminal being rectangular In cross section and having a portion thereof projecting through said slot into the Interior of the fuse. maid projecting portion of said terminal Is staked to said first and ball to secure said terminal to said and ball.

19. A fuse as in claim 18 wherein said projecting portion includes a reduced width portion forming a shoulder, maid projecting portion passing through said slot until,zaid first and bell engages said shoulder, said projecting portion having a weld projection on its terminal and, said weld projection being staked to said and bell and adapted for connection to said fuse elarent. 20. A fuse as in claim 18 wherein said staking is the sole connection between said first terminal and said first and bell.

21. A fuse an in claims 1, 2# 3, 41 51 6, or 7 wherein said fuse element is an elongated planar element having an accordion shaped cross section.

22, A fuse as in claims 2. 4# 6 or 7 wherein said weld projections are coinod onto said first terminal.

23. A fuse as in claims 4, 5, and 6 wherein said first end bell has at least one aperture with a circular cross-section thorethrough; and a spherical solid ball has a cross-section greater than said crogs- section of said aperture for insertion into said aperture, said ball selfcentering as said ball in inserted into said aperture and frictionally held within said aperture.

24. A fuse as in claims 2, 3, and 6 wherein said first and second end belle having a plurality of bores circumforentially spaced around the periphery thereof adapted for alignment with said holes; said first and second end bells are made of a nonelectrically conductive material; And metal Pine are received within said aligned holes and bores for securing said end bell& 1 within said housing, said pins being In non-eloctrical contact with maid terminals and fuse element.

Publilied 19533 at The 11alen, 01 Ill c - Slii, lifiti, 66173 1 flul, HoP3orn. L)ilclcii WC1r, 4TP- Funlier copit., ni.n 1)e ol)ldilled troni The flaieni Ofix c Sale, Bran(h. S,, (-ri. K, ill 13R5 Priwed by M ill' I llc! Si Cr.n. hent Co] l 1 IF, 7