Bushings comprising notched terminal ears

Abstract

A bushing assembly is provided including terminal ears coupled to opposed end walls of the bushing assembly. Each of the terminal ears includes an electrically conductive plate with a first terminal edge (1D) coupled to a bushing first end wall, and extending away from the first end wall to a second, free terminal edge (1A) and having a curved geometry. The curvature, 1/(2R), at any point of the curved second end of the slot is less than the reciprocal, 1/ Wo, of the smallest gap width, Wo, of both slot first open end, W.sub.A, and elongated portion, W.sub.B, where R is defined as the radius at any point of the curved second end.

Claims

1. A bushing assembly (2) comprising terminal ears coupled to opposed end walls (2A) of the bushing assembly, for heating a bushing tip plate and walls, each of said terminal ears comprising an electrically conductive plate (1) comprising a first terminal edge (1D) coupled to a bushing first end wall (2A), and extending away from said bushing first end wall to a second, free terminal edge (1A) connectable to a source of power (5, 6), said electrically conductive plate comprising a slot (3) comprising: (a) a first, open end (3A) of width, W.sub.A, at the second, free terminal edge (1A) of said electrically conductive plate, (b) an elongated portion (3B) extending towards said first terminal edge (1D) of gap width, W.sub.B, and (c) a second, closed end (3C) that has a curvature, separate from said first terminal edge (1D) of one of said terminal ears, and having a curved geometry; characterized in that, the curvature, 1/(2R), at any point of the second, closed end (3C) of the slot is less than the reciprocal, 1/W.sub.o, of a smallest gap width, W.sub.o, of both slot first open end (3A), W.sub.A, and elongated portion (3B), W.sub.B, wherein R is the radius at any point of the curved second, closed end (3C).

2. The bushing assembly according to claim 1, wherein the elongated portion (3B) of the slot has a constant width, W.sub.B.

3. The bushing assembly according to claim 2, wherein the second, end (3C) portion of the slot is circular of radius, R, or elliptical of small radius, R, wherein R is between 5 and 60 mm.

4. The bushing assembly according to claim 2, wherein each terminal ear comprises more than one such slots.

5. The bushing assembly according to claim 2, wherein the electrically conductive plate (1) of the terminal ear is folded over a line substantially parallel to said first terminal edge (1D) and second, free terminal edge (1 A) of the terminal ear.

6. The bushing assembly according to claim 2, wherein the elongated portion (3B) of the slot extends along a direction substantially normal to both first terminal edge (1D) and second, free terminal edge (1A).

7. The bushing assembly according to claim 1, wherein the first, open end (3A) has a gap width, W.sub.A, larger than the gap width, W.sub.B, at any point of the elongated portion (3B).

8. The bushing assembly according to claim 1, wherein the second, closed end (3C) portion of the slot is circular of radius, R, or elliptical of small radius, R.

9. The bushing assembly according to claim 1, wherein each terminal ear comprises more than one such slots.

10. The bushing assembly according to claim 1, wherein the electrically conductive plate (1) of the terminal ear is folded over a line substantially parallel to said first terminal edge (1D) and second, free terminal edge (1 A) of the terminal ear.

11. The bushing assembly according to claim 1, wherein the elongated portion (3B) of the slot extends along a direction substantially normal to both first terminal edge (1D) and second, free terminal edge (1A).

12. A bushing assembly (2) comprising terminal ears coupled to opposed end walls (2A) of the bushing assembly, for heating a bushing tip plate and walls, each of said terminal ears comprising an electrically conductive plate (1) comprising a first terminal edge (1D) coupled to a bushing first end wall (2A), and extending away from said bushing first end wall to a second, free terminal edge (1A) connectable to a source of power (5, 6), said electrically conductive plate comprising a slot (3) comprising: (a) a first, open end (3A) of width, W.sub.A, at the second, free terminal edge (1A) of said electrically conductive plate, (b) an elongated portion (3B) extending towards said first terminal edge (1D) of gap width, W.sub.B, and (c) a second, closed end (3C) that has a curvature, separate from said first terminal edge (1D) of one of said terminal ears, and having a curved geometry; characterized in that, the curvature, 1/(2R), at any point of the second, closed end (3C) of the slot is less than the reciprocal, 1/W.sub.o, of a smallest gap width, W.sub.o, of both slot first open end (3A), W.sub.A, and elongated portion (3B), W.sub.B, wherein R is the radius at any point of the curved second end (3C), and wherein the slot has a keyhole geometry.

13. The bushing assembly according to claim 12, wherein the elongated portion (3B) of the slot has a constant width, We, of between 2 and 50 mm.

14. The bushing assembly according to claim 12, wherein the elongated portion (3B) of the slot has a constant width, We, of between 5 and 20 mm.

15. The bushing assembly according to claim 12, wherein the first, open end (3A) has a gap width, W.sub.A, larger than the gap width, W.sub.B, at any point of the elongated portion (3B).

16. The bushing assembly according to claim 12, wherein the second, end portion (3C) of the slot is circular of radius, R, or elliptical of small radius, R, wherein R is between 5 and 60 mm.

17. The bushing assembly according to claim 12, wherein each terminal ear comprises more than one such slots.

18. The bushing assembly according to claim 12, wherein the electrically conductive plate (1) of the terminal ear is folded over a line substantially parallel to said first terminal edge (1D) and second, free terminal edge (1 A) of the terminal ear.

19. The bushing assembly according to claim 12, wherein the elongated portion (3B) of the slot extends along a direction substantially normal to both first terminal edge (1D) and second, free terminal edge (1A).

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) For a fuller understanding of the nature of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings in which:

(2) FIG. 1: shows a perspective view of a bushing assembly with terminal ears according to the present invention.

(3) FIG. 2: shows a perspective view of a terminal ear according to the present invention.

(4) FIG. 3: shows top views of various embodiments of terminal ears according to the present invention.

(5) FIG. 4: shows a top view of a terminal ear according to the present invention comprising two notches.

DETAILED DESCRIPTION OF THE INVENTION

(6) As illustrated in FIG. 1, a bushing assembly (2) generally comprises two side walls (2B) and two end walls (2A) forming the peripheral walls of the assembly. The side walls (2B) define the longitudinal dimension of the bushing assembly and the end walls (2A) define the transverse dimension. The top surface of the assembly (not shown) is open to bring it in fluid communication with a source of molten glass, typically a furnace. The floor of the bushing assembly comprises a tip plate which comprises a multitude of orifices allowing the glass melt to flow out and be drawn to form fine glass fibres. In some embodiments (not illustrated in the Figures), the floor may be divided in two tip plate portions by a central beam which contributes to the stiffening of the floor in the longitudinal direction. A number of reinforcing ribs (not shown) are also generally distributed along the length of each tip plate portion, extending in the transverse direction to further stiffen the floor. Bushing assemblies are ususally electrically heated, by running current from a source of electrical current (6) electrically connected (5) to a first terminal ear (1) coupled (1D) to a first end wall (2A) of the bushing assembly, through the bushing assembly in the longitudinal direction and out through a second terminal ear coupled to the opposite end wall.

(7) The source of electrical current (6) is connected to the terminal ears through connectors (5) coupled to the free edge (1A) of each terminal ear. The connectors (5) are usually made of copper or other good electrical conductor. In view of the high current density passing therethrough, they need be cooled, generally water cooled, in order to maintain their temperature within reasonable working values, e.g., not more than 150-200 C. The temperature at the opposed edge (1D) of each terminal ear, which are coupled to an end wall (2A) of the bushing assembly is of the order of 1200-1400 C., thus creating huge thermal gradients along the longitudinal direction of the terminal ears which provoke warping of, and build-up of internal stresses within the terminal ears, due to varying magnitudes of the ear thermal expansion along the thermal gradient. The connectors cooling also drives a substantial heat flow running down said gradient which cools the end walls (2A) the terminal ears are coupled to.

(8) As suggested in US2003/0167802, the heat flow cooling the end walls (2A) of the bushing assembly can be somewhat limited by reducing the cross-sectional area of the terminal ears in the longitudinal direction away from the bushing end walls (2A). Care should be taken not to thus generate a steeper heat gradient by requiring more cooling to maintain the connectors at their working temperature, due to the higher current density passing through connectors of smaller dimensions. If this problem can be addressed by calculation, it remains that the V-shaped notch proposed in said document generates important concentrations of internal stresses at the tip of the V-notch, which can lead to the rapid failure of the terminal ears. The same applies to the tip of I-notches as disclosed in US2006/0218972 or CN2516548U.

(9) The terminal ears of the present invention combine the advantages, in terms of lowering the cooling of the end walls (2A), of terminal ears provided with a notch without having the inconvenience thereof in terms of build-up of internal stresses. This is achieved by ensuring that the curved tip (3C) of the notch has a radius of curvature larger than the half-width, W.sub.A, W.sub.B, of the gap at any other point. In terms of curvature, 1/(2R), at any point of the curved second end (3C) of the slot, it must be lower than the reciprocal, 1/W.sub.0, of the smallest gap width, W.sub.0, of both slot first open end (3A), W.sub.A, and elongated portion (3B), W.sub.B, wherein R is the radius at any point of the curved second end (3C). Such geometry permits to distribute the internal stresses generated by the thermal gradient about the low curvature notch end (3C), and also to release internal stresses by allowing the two flaps of the ear flanking the notch to warp in different directions independently from one another.

(10) As illustrated in FIG. 4, a terminal ear can be provided with more than one such notch. It may comprise two, three or more such notches arranged side by side. FIG. 3 illustrates schematically various embodiments of notch geometries according to the present invention. For example, the notch can have a keyhole geometry as illustrated in FIG. 3(a)-(d) with a curved second end (3C) having a substantially circular geometry, and an elongated portion (3B) extending till the open end (3A) either with parallel notch walls like in FIG. 3(a)&(b), or flaring out like in FIGS. 3(c)&(d). It is preferred that the notch comprises no sharp corner (i.e., no discontinuity in the tangents at each point of the notch edges), like in FIG. 3(b)&(d) wherein the corners have been rounded up. FIG. 3(e) shows a keyhole-like geometry wherein the corners have been smoothened substantially. The second, closed end (3X) needs not necessarily be circular, and can have any curved shape. For example, as illustrated in FIG. 3(g)&(h), the closed end (3C) of the notch may have a substantially elliptical shape. The geometry illustrated in FIG. 3(f) is illustrative of how the length of the connectors may be increased to lower the current density passing therethrough, whilst still decreasing internal stress concentration build-up with a low curvature closed end (3B).

(11) The slot preferably extends along the longitudinal direction of the terminal ear, wherein the longitudinal direction is defined by the side walls (2B) of the bushing body. The terminal ears of the present invention are preferably in the shape of a rectangular plate, with one or several slots of geometry as discussed above, extending normal from the second, free end of the ear. In a preferred embodiment, the terminal ears are folded over a line substantially parallel to the first, coupled edge (1D) and second, free edge (1A) of the ear. This geometry increases the bending stiffness of the terminal ear in the transverse direction, which is substantially reduced by the presence of the notch.

(12) A terminal ear according to the present invention must be made of a material which is a good electrical conductor and withstands high temperatures of the order of 1400 C. Precious metals are preferably used for making such terminal ears, such as platinum, rhodium, and alloys thereof.

(13) The present invention has the advantage of decreasing the build up of internal stresses within a terminal ear exposed to steep thermal gradients, whilst giving more freedom of design for attenuating the cooling of the end walls (2A) than henceforth permitted.