IE44068B1 - Capacitor with molded header - Google Patents

Description

The present invention relates to electrolytic capacitors, and particularly though not exclusively electrolytic capacitors incorporating an electrolyte such as dimethylformamide.

Electrolytic capacitors manufactured in the United States have conventionally comprised a capacitor section made up of a series of layers which include a first aluminium foil coated with a layer of aluminium oxide, a paper separator, a second layer of aluminium and a further layer of paper. The layers as assembled are spirally wound to form an elongated cylinder section which is wetted by an electrolyte solution. The elongated section is contained in a housing, normally of aluminium material. A layer of pitch is placed in the housing bottom to protect the capacitor from damage when the capacitor is exposed to shock and vibration forces. The upper end of the capacitor section includes first and second tabs connected respectively to the first and second layers of foil to provide anode and cathode connections. The tabs in turn, are connected inside the housing to terminals which extend through a header which seals off the open end of the capacitor housing. A rubber gasket is normally inserted between the circumferential edges of the header and the capacitor housing, and - 3 44068 after introduction of the capacitor section into the housing, the top end of the open housing is crimped or rolled over to cause the header to be urged into firm contact with a shoulder on the housing thereby to provide a hermetic seal for the housing open end.

In one type of capacitor which has been available in the field for years, the capacitor housing is made of aluminium material, the header is made of phenolic or similar thermosetting material, and the electrolyte is of a glycol type. While such capacitors have performed well over the years, the changing state of the art has resulted in the need and a demand for capacitors of reduced size which are capable Of withstanding the same ripple current as capacitors of large size which use glycol electrolyte.

It is further noted that the conventional capacitor described above is limited in its use to environments in which the temperature is less than 85°C. That is, the glycol type electrolyte which is used in such capacitors requires significant amounts of water, and in the event of the exposure of such capacitors to higher temperatures, the water tends to hydrate the foils, with consequent injury to the capacitor section.

In an attempt to provide a capacitor of smaller size with operating capabilities which are at least the equivalent of the glycol capacitor, the field has turned to the use of new types of electrolytes, one example of which is the group of electrolytes which basically comprise a dimethyl formamide (DMF) solution. Such electrolyte, in addition to having increased stability at higher temperatures, also has the capability of imparting properties to the capacitor which enable the capacitor to accept higher AC ripple currents without experiencing a heating problem (in the order of 3:1 as compared to ripple currents which glycol electrolytes can handle). Capacitors which use such electrolyte have been found to have greater long-term stability, and will operate reliably in environments of higher temperatures. In addition, since the capacitor with such type electrolyte will work at higher ripple currents for a predetermined ripple current specification, the capacitor having a dimethyl formamide electrolyte may be of a smaller size than the capacitor which uses the glycol type electrolytes.

While dimethyl formamide is known to have these inherent characteristics and advantages, it has been found that the phenolic header and the rubber seals of conventional capacitors have a short life when a dimethyl formamide electrolyte is used. In one attempt to solve such problem, certain manufactures have turned to the use of headers made of diallyphthalate (DAP). However, the use of such header material with the dimethyl formamide electrolyte is less than satisfactory because of the tendency of the diallyphthalate material to swell after a period of use at high temperatures and because of the leakage and sealing problems which result as the swelling occurs.

One successful capacitor which was manufactured by the applicant uses an aluminium header having a butyl rubber gasket located between the circumferential edges of the header and the container walls. While such header and rubber material will operate successfully in temperature environments of 85°C., and do withstand the destructive effects of the DMF electrolyte, the capacitor is relatively costly, and it has been necessary to charge a premium price for capacitors of such type. The difference between the cost of an aluminium header and a phenolic header, for example, is significant. Even the smallest saving in the manufactur35 ing cost of a capacitor, as for example, a reduction in 440 68 the cost of the capacitor header, results in a significant advantage because of the relatively high volume of capacitor production.

At least one manufacturer has provided headers for smaller size capacitors, made of polypropylene material. Such headers were of relatively uniform thickness except for the projecting circumferential rings on the upper and lower surfaces, and radial rib members which projected inwardly into the housing to assist in restraining the capacitor section against movement. A similar set of ribs was located at the bottom end of the capacitor. While headers made of polypropylene material were apparently satisfactory for smaller size capacitors, headers of relatively uniform thickness made from such material for larger size capacitors (i.e., two inch diameter and larger) did not satisfactorily withstand the pressures experienced with exposure of the capacitor to temperature conditions in the order of 85°C.

It is an object of the present invention, therefore, to provide a novel capacitor, which is able to provide operating characteristics which are equal to or better than the conventional capacitor, which is of lower cost than the premium type capacitor presently available on the market, and which may in at least some instances withstand the pressures which occur when the capacitor is subjected to temperatures of 8S°C.

According to one aspect of the invention, there is provided an electrolytic capacitor comprising a casing having a closed bottom end and an open upper end, a capacitor section located within said casing, a moulded header, and terminal means in said header connected to said capacitor section, wherein said moulded header is comprised of fibreglass-reinforced - 6 plastics material closing the open end of said casing.

In a preferred embodiment of particular advantage in relation to capacitors larger than 2 in diameter the header includes a bolster ring moulded integrally with said header and extending on the underside of and adjacent the peripheral edge of said header, significant movement or flow of the header material is prevented when the capacitor is subjected to temperatures of 85°C. A plurality of radial rib members may be provided on the underside of the header extending from a central arbor to said bolster ring, together with a plurality of bosses for locating the terminal means, and a circular rib member connecting said bosses. In this case, retainer means may be located at the bottom of said casing, including radial rib members and a central arbor which extends into a central aperture located at the lower end of said capacitor section, the central arbor on said header then extending into a central aperture located at the upper end of said capacitor section, and certain of said rib members on said header extending downwardly into contact with the upper end of said capacitor section.

Thus, a pitchless construction can be provided.

As noted above, conventional electrolyte capacitors use pitch material in the bottom of the container to minimize the possible damage to the capacitor section and/or tabs when the capacitor is used in environments of severe shock and vibration. While such material has performed satisfactorily, the use of pitch material adds a significant cost to the manufacturing operation. That is, it is necessary (a) to provide storage locations for the pitch, (b) to provide machines for heating the pitch and introducing the pitch into the capacitor housing, and (c) to provide storage room for periods of the order of twenty-four hours for the 4 0 68 - Ί capacitors filled with pitch to cool down for room temperature testing. The construction above-described makes the use of pitch unecessary and results in economies in manufacture.

In one preferred embodiment which provided reliable operation and life when used in temperature environments of 85°C, the plastic material comprised fibreglass-reinforced propylene terpolymer injection moulding compound. In embodiments in which the capacitor is subjected to significantly higher temperatures, the plastics material may comprise fibreglass-reinforced polyterephthalate compound or a fibreglass-reinforced nylon, or the like.

According to another aspect of this invention an electrolytic capacitor comprises a casing having a closed bottom end and an open upper end, a capacitor section located within said casing having cathode foils and anode foils, a separator for said two foils, an electrolyte impregnating said foils, a retainer member for fixedly locating said capacitor section, and a moulded header comprising a glass-material-reinforced plastics material for providing closure for the open upper end of said casing.

An electrolytic capacitor in accordance with this invention will now be described, by way of example, with reference to the accompanying drawings, in which:Figure 1 is a transverse sectional view of the capacitor including a header, and with extruded ribs and arbor at the bottom end of the capacitor; Figure 2 is a view from below of the header which is integrally moulded and is used to seal the open end of the capacitor casing; Figure 3 is a view from above of such header; and Figure 4 is a view from above of the bottom of - 8 the capacitor casing.

With reference to Figure 1 there is shown an electrolytic capacitor generally indicated by reference numeral 10. A capacitor header 12 is disposed inwardly of the open end 14 of the generally cylindrical capacitor casing or housing 16 which serves to store the capacitor section 18. The capacitor casing 16 has an annular shoulder 20 which is formed adjacent the open end 14 of the housing. As will be shown, during assembly the shoulder 20 provides a support and reaction surface for the header member 12.

The capacitor section 18 may be of the conventional type comprising a first (or anode) foil made of oxidized aluminium, a second layer of paper, a third layer (or cathode foil) of oxidized aluminium and a fourth layer of paper, all of which are spirally wound to form the elongated cylindrical capacitor section 18 as shown in Figure 1. Flexible tabs 19 and 21 extend outwardly from the upper end of the capacitor section.

The open end 14 of the capacitor housing 16, as shown in Figures 1 and 3, is closed off by the circularly shaped moulded header member 12 which is made from a fibreglass-reinforced plastic injection compound. Header member 12 has a substantially flat outer or top surface 22 (Figure 3) from which project integrally moulded cylindrical bosses 24 and 26, each of which has a metal terminal 28, 30, respectively, moulded therein. A conventional vent hole 32 is also located in the header member 12. The outer circumference of the header member 12 carries an annular lip 36 having a seal projection 37 (Figures 1 and 3) which extends around the periphery of the header member 12 on the lip 36. The diameter of the lip 36 is approximately the same size as the interior diameter of the capacitor casing 12. A relatively wide bolster ring 34 (Figure 2) extends along the under outer circumferential edge of the header member 12 adjacent to and inwardly of the annular lip 36. The inner edge of bolster ring 34 tapers inwardly and upwardly at an angle of approximately 30°, to the thinner areas, such as 39, (Figure 2) of the header member 12.

A central hub or arbor member 40 located on the inner or under side of the integrally moulded header member 12 projects downwardly into the housing, and into contact with the centre portion of capacitor section 18, when the header is assembled with the casing 16. Three compression rib members 42, 44, 46, as best shown in Figure 2, extend radially outward from the hub 40 to the outer peripheral edge of the bolster ring 34. Two of the compression ribs, 42, 44 are spaced from one another by 100°, and each is spaced from the third compression rib 46 by approximately 130°. Terminals 28, 30 are located along a diameter of the header member 12.

Header member 12 in the illustrated embodiment also includes a circular member 47 which is concentric with the circumference and extends through the centres of terminals 28, 30 and vent 32. First and second lugs 52, 56 extend radially inward from the bolster ring to the lower ends 24a, 26a of bosses 24, 26 for terminals 28, 30. A third lug 54 extends radially inward from the bolster ring 34 to a boss 29 which is provided on the under side only of header 12 for vent 32. Two additional minor ribs 60, 62 are located On opposite sides of the rib 46 as extensions of ribs 42, 44 from the hub 40 to the inner edge of bolster ring 34.

Partial rib 65 extends between the arbor 40 and boss 29 for vent 32. A relief groove 41 is located at the point of juncture of the ribs 42, 44, 46 with the arbor 40 to protect against the possibility of shorting of - 10 the anode and cathode elements by the ribs 42, 44, 46 when the assembled section is placed under pressure.

The areas, such as 67, of the header which lie between the circumferential members 47 and the radial ribs, such as 42, 65, etc., have a thinner dimension which is in the order of the dimension of areas 39.

An annular gasket member 64 of butyl-N rubber having a durometer hardness of 65- 70 is placed on shoulder 36 during assembly of the capacitor as will be described, and as thus mounted extends peripherally around the header member to cooperate with the lip 37 in providing a seal for the capacitor housing.

The lower ends 68, 70 respectively (Figure 1) of the metal terminal members 28, 30 which are moulded in the cylindrical bosses 24, 26 on the header 12 project downwardly into the capacitor housing for connection to the flexible anode and cathode tabs 19, 21 respectively on the capacitor section 18. Central recesses 76, 78 in the outer ends of the terminals 28, 30 are threaded to receive fastener screws (not shown) for use in connecting the terminals 28, 30 to other electrical equipment. The cylindrical bosses 24 and 26 extend around terminals 28, 30 both above the upper header surface 22 and below the depressed area 39 to provide increased holding forces for the metal terminal members, the lower or inner ends 24a and 26a of the bosses being of greater diameter than the upper or outer ends. Shoulders 80, 82 on terminals 28, 30 assist in fixedly positioning the terminals 28, 30 within the moulded header 12.

Retainer means 85 located at the bottom of the capacitor housing further retain the capacitor section 18 against movement. In one embodiment such means may be extruded from the bottom surface of the casing 16. Alternatively, the retaining means may be moulded from - 11 plastics material and force fit into the bottom of the housing 16.

In one embodiment of a 3 capacitor the anode member is .09” less in width than the cathode member which is in turn 1/4 narrower than the paper separator, whereby the paper separator extends outwardly 1/8 more than the cathode foil and as assembled the paper separator material is in contact with the capacitor housing.

As shown in Figure 1 and 4, the upper surface of retainer means 85 is shown to comprise a projecting hub or arbor 87, and a plurality of ribs 89, 91, 93 which extend radially from the central hub 87 to the peripheral edge of the casing 16, the ribs being located at approximately 120° relative to one another.

In one embodiment as used in a capacitor having a 3 diameter housing, the section 18 was 4 % in length and the shoulder 20 was nominally 5.344 above the bottom of the casing. The dimension of the ribs from the under side of the lip 36 of the header 12 was .520 inch. The dimension from the top of the bottom ribs 89 to the shoulder 20 was 5.199. With the elements of the three inch diameter capacitor thus dimensioned, when the capacitor was assembled, the pressure exerted on the capacitor section resulted in approximately 5/64 depression of each one of the section ends along the line of contact thereof with the edges of ribs 42, 44, and 89, 91, 93.

The header 12 in such embodiment had a diameter of 3* and the thinnest portions such as 39 of such header were nominally 1/8 thick whereby the ratio of the thickness of areas 39 to the edge thickness of the header was in the order of 1 to 4. Compression ribs 42, 44, 46 had bases which were nominally 3/16 in width and extended inwardly 2 ^/32 the depressed area. The vertical sides of the ribs tapered inwardly 4 0 6® - 12 approximately five degrees to a nominal thickness of 1/8 to terminate at the upper ends in fillets having 1/64 radius. Hub 40 had a base diameter of .45 and extended upwardly at a taper of 5° to a reduced diameter of .260. The outer end of hub 40 had a fillet radius of 1/8.

The bottom surface of bolster ring 34 was nominally .187 wide and tapered inwardly approximately 30 to the depressed area and outwardly at an angle of ° to the bottom of lip 36. The width of the inner surface of bolster ring relative to the header radius was thus in the order of 1 to 8. Lip 36 protruded from bolster ring 34.050 (nominal) and was nominally 1/8 thick. Lugs 52, 54, 56 were 5/32 wide, 1/8 high and 1/4 long and terminated in a radius of 5/64.

Circular rib sections 47 were 5/32 wide, and were 1/8 thick. The inner ends 24a, 26a of the bosses 24, 26 and boss 29, which are joined by the circular rib 47, were nominally the same thickness (1/8) as the ribs 47 and V in diameter. The outer end of the bosses 24, 26 extended 3/16 above the header 12 and were .437 in diameter. The nominal diameter of the inner end of the metal terminals was 3/8 and the upper end portion of the metal terminal located within the outer ends of the bosses 24, 26 was nominally .350 in diameter. The minor radial ribs 60, 62 had a thickness of 3/16, and a width of 5/32. The smaller rib 65 was nominally 5/32 wide and 1/8 thick.

The ribs 89, 91 and 93 had a nominal height of 9/64 measured from the outside bottom of the housing 16, a nominal width of 3/16 and a nominal fillet radius along the upper edge of 1/64. Hub 87 extended 1/2 inch above the top of ribs 89, 91, and 93. The top surface of the hub had a diameter of 1/8, which tapered inwardly to a thicker diameter of (nominally) - 13 .325. The inner ends of the ribs of the retainer means 85 were grooved, as shown at 95, to a depth of 1/16 (nominal) to prevent possible shorting of the anode and cathode elements of the capacitor section when the capacitor was assembled under pressure.

In assembly of the capacitor, a vent plug is inserted in the vent hole 32 in known manner and the tabs 19 and 21 on the capacitor section 18 are fastened by staking or welding, or the like to the inwardly projecting ends 68, 70 of the terminals 28, 30 on the header member 12, and the gasket member 64 is placed on shoulder 36 of the header.

The header member 12 is then moved into engagement with the upper end of the capacitor section, the end portion of the hub member 40 being urged into the central area of the upper end of the capacitor section 18, and the outer fillet surfaces of the rib members 42, 44, 46 being urged against the upper surface of the capacitor section 18.

The capacitor section 18 is then introduced into the capacitor easing 16 to bring the central area of the lower end of section 18 into registration with the locater hub member 87, and areas of the lower end of capacitor section 18 into registration with the upper fillet edges of rib members 89, 91, 93, Such assembly is then placed in a press which urges the header member 12 into capacitor housing 16 until the lower peripheral edge of the lip 36 on the header is brought into engagement with shoulder 20 on the housing 16. At this point the fillet edges of the upper and lower ribs have depressed the respective ends of the capacitor section approximately .08.

The edge of the housing 16 is then rolled over in a conventional manner to apply pressure to the gasket and the header member 12 thereby to cause the rib members 42, 44, 46 to maintain the capacitor section 18 between the upper and lower rib members. The rolling of the upper edge of housing 16 into engagement with the gasket 64 also urges gasket 64 into contact with seal projection 37 on lip 36 to form a hermetic seal for the capacitor.

In one successful embodiment the fibreglassreinforced plastic moulding compound comprises Profil J-6O/4O/E which is a material commercially available from Fiberfil Division, Dart Industries Inc., Evansville, Indiana. Such material may be propylene-ethyleneacrylic acid terpolymer comprised of approximately 90% propylene, 6% ethylene and 4% acrylic acid reinforced with intermediate fibreglass in the order of 40% the acrylic acid providing adhesion in known manner between the fibreglass and the propylene. Other fibreglassreinforced polyethylene materials commercially available and suitable for use in the novel header for capacitor applications in temperature environments of 85°C include Profil j6O/2O/E which is of the same basic composition and includes 20% intermediate fibreglass and Profil J6O/3O/E which has 30% intermediate fibreglass.

Headers for use with capacitors having temperatures higher than 85°C may be made from polyterephthalate compounds, such as are available from General Electric, Mt. Vernon, Indiana, under the tradename Valox, or from the Celanese Corporation, under the tradename Celanex, each reinforced with fibreglass in the manner of the previous examples to provide a plastics material which results in a capacitor header of imrpoved characteristics. A further compound suitable for such use when reinforced with fibreglass in such manner is a nylon compound which is commercially available as Zytel (Trade Mark) 70- G- 33- HSI L, from Du Pont, Wilmington, Delaware.

It was further found that a capacitor 2 or smaller - 15 in diameter, it was possible to use a moulded header of fibreglass-reinforced plastic compound which had a uniform thickness configuration, and the resistance to material flow provided by the fibreglass-reinforced plastic compound even in the uniform thickness configuration was such as to provide reliable use in the field when subjected to temperature environments of 85°C.

As noted above, the novel header moulded from fibreglass-reinforced plastic moulding compound permits the use of eletrolytes, such as dimethyl formamide, in the capacitor, thereby to make possible the provision of a capacitor in small and large sizes having improved ripple current parameters, which may be successfully used in temperature environments of 85°C without experiencing material flow and leakage.

A particular feature of the novel structure is the manner in which the same capacitor header along with a retainer means at the bottom of the casing provide fixed positioning of the capacitor section of an order to withstand the shock and vibration tests which have been established in the field for capacitor units. As noted above, such arrangement eliminates the conventional pitch material and results in a significant reduction in the manufacturing costs.

Xn a further embodiment, the capacitor section 18 is wound to provide a so-called extended cathode configuration wherein the cathode foil extends nominally 1/8 beyond the lower end of the paper separator. As such type section is inserted into the housing, the cathode foil at the bottom of the section is urged into firm contact with the metal rib members located at the bottom of the capacitor whereby heat generated in the capacitor section finds a path over the ribs to the can bottom and can exterior. Tests of a capacitor of the 440 θ8 - 16 three inch size having such construction showed an increase in ripple current capability of approximately 12%, and heat transfer increase at 85°C in the order of 25%.

Claims (16)

1. An electrolytic capacitor comprising a casing having a closed bottom end and an open upper end, a capacitor section located within said casing, a moulded header, and terminal means in said header connected to said capacitor section, wherein said moulded header is comprised of fibreglass-reinforced plastics material closing the open end of said casing.

2. The capacitor of claim 1, further comprising a bolster ring moulded integrally with said header and extending on the under side of and adjacent the peripheral edge of said header.

3. The capacitor of claim 2, wherein said header includes structural members moulded integrally with and located on the under side of said header, and areas located between said structural members and said bolster ring, which are of a thinner dimension than the structural members and said bolster ring.

4. The capacitor of claim 2, further comprising a central arbor on the moulded header, a plurality of radial rib members on the underside of the header extending from said central arbor to said bolster ring, a plurality of bosses for locating the terminal means, and a circular rib member connecting said bosses.

5. The capacitor of Claim 4, further comprising retainer means located at the bottom of said casing including radial rib members and a central arbor which extends into a central aperture located at the lower end of said capacitor section, and wherein the central arbor on said header extends into a central aperture located at the upper end of said capacitor section, and certain of said rib members on said header extend downwardly into contact with the upper end of said 440 68 - 18 capacitor section.

6. The capacitor of Claim 5, further comprising relief sections located between each of said arbors and the ends of the radial ribs adjacent thereto.

7. The capacitor of any one of Claims 4 to 6, wherein said header includes a lip member which extends around the outer circumference of the header to locate a gasket member for use in Sealing said capacitor, and lug members extending between said bolster ring and said bosses, a vent boss which extends downwardly from the under side of said header, and a lug which extends from said bolster ring to said vent boss.

8. The capacitor of any one of Claims 1 to 4, including first retainer means at the bottom of said metal casing comprised of extruded portions of the casing bottom which project upwardly in the housing into engagement with extended cathode foils of said capacitor section, and comprising further retainer means integral with said moulded header for maintaining said capacitor section in pressure contact with said first retainer means to provide an improved heat transfer path from said section to the exterior of the casing.

9. The capacitor of any one of the preceding claims, wherein the moulded plastics header is reinforced with 20%- 40% fibreglass.

10. The capacitor of any one of the preceding claims, wherein the plastics material is a copolymer material.

11. The capacitor of claim 10, wherein said copolymer material is selected from the group consisting of propylene-ethylene acrylic acid and - 19 nylon compounds.

12. The capacitor of any one of claims 1 to 9, wherein said plastics material comprises a polypropylene copolymer material. 5

13. The capacitor of claim 12, wherein said plastics material comprising polypropylene copolymer includes acrylic acid to provide adhesion between the glass material and the polypropylene material.

14. An electrolytic capacitor comprising a 10 casing having a closed bottom end and an open upper end, a capacitor section located within said casing having cathode foils and anode foils, a separator for said two foils, an electrolyte impregnating said foils, a retainer member for fixedly locating said capacitor 15. Section, and moulded header comprising a glass-materialreinforced plastics material for providing closure for the open upper end of said casing.

15. The capacitor of any one of the preceding claims, further including a dimethyl formamide 20 electrolyte.

16. An electrolytic capacitor substantially as hereinbefore described with reference to the accompanying drawings.