Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a separable contact
joint for use at high-current conductors, particularly at
busbars in electrolytic apparatus.
In large electrolytic plan-ts handling total currents
of 100 ]cA and more, I R ]osses (ohmic losses) which are too
large to be neglected occur in the electric leads and in the
busbars leading to the electrode terminals. A special problem
arises in connection with the joints between metallic leads
and nonmetallic electrodes or easily corrodible metall.ic
electrodes. Soldered joints are often provided for an improved
contact between the lead and the electrode, or said contact
is established by means of noble metal-plated contact surfaces
held in pressure contact by screws, or by means of special
stuffing box contacts. Owing to the requirements of operation
and assembling, the contact joints at the busbars must be
detachable. Currents up to several 100 kA must flow through
these contact joints. The contact joints must be designed
with special care because the voltage drop must not exceed
a few millivolts if an excessive temperature rise and destruction
of said contact joints is to be avoided.
Different materials must often be connected by
contact joints of the kind described. Practical experience
has shown that certain maximum current densities are permissible
for such joints. These maximum permissible current densities
are stated hereinafter together with the voltage drops involved:
Combination Current Voltage drop
of density
materials A/cm _ mV _
Fe/Cu 10 2
Cu/Al 20 2
Cu/Cu 30 1.5
Cu/Ag 60 2
, ~ .
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The contacts forming said joi~ts are usually machined
and smoothened so that they are as planar as possible and can
ensure a large pressure contact surface and an intimate contact.
It has been found in pract:ice that the contact pressure
produced by means of a screw or a c~amping of the contact faces
effected by other mechanical means will not always result in an
intimate contact and the voltage drop may be excessively high.
It is an object of the invention to avoid voltage drops
at contact joints or at separable contacts,or to reduce such
voltage drops.
More particular]y, according to the present invention,
there is provided a separable contact joint for busbars in electrolytic
apparatuses, this separable joint comprising two contact
surfaces, characterized in that at least one of the contact
surfaces of the joint is rough and formed with sharp-edged
peaks having an height of 0.1 to 0.8 mm, and that at least the
contact surface formed with the sharp-edged peaks carries a
coating of noble metal having a thickness of 0.5 x 10 3 to
5.0 x 10 3 mm.
In such contact joints, a reduction of vol-tage drop is
accomplished in that at least one of the contact surfaces of
the joint is rough and Eormed with sharp-edged peaks. Such
peaks may consist of ridges, which may be formed by a cutting,
e.g. of grooves in-to the surface. Alternatively said peaks may
be formed by a filelike structure of a knurled structure or by
spark erosion.
By the provision of such peaks on at least one of the
contact surfaces, an intimate contact between the contact surfa-
ces forced against each other can be ensured and contact
resistances can be avoided. It is assumed that the peaks or
sharp-edged profiles provided in accordance with the invention
can be deformed more easily -than a perfectly planar contact
"f
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surface which apparently has only a few crowned contac-t surface
elements in spite of a substantial machining.
According to preferred embodiments of the invention,
each contact surfaces carries a coating of noble metal, the
noble metal of the two coatings is aifferent, and one of -the -two
contact surfaces is smooth.
For -the purposes of the present invention, the term
noble metals>~ may include silver, gold and platinum metals,
such as osmium, iridium, platinium, ruthenium, rhodium, palla-
dium. The noble me-tals of each coating consist preferably of
silver or platinum. For instance, -the peaked contact surface
may for example carry an electro-deposited silver layer in a
thickness of about 1.0 x 10 3 mm and the smooth contact surface
may be provided with a similar layer in the case it is provided
with a noble metal coating. In accordance with another prefer-
red modification of the invention, the peaked contact surface
may be provided with a silver layer having a thickness of
1.0 x 10 3 mm and the smooth contact surface may carry a pla-ti~
num layer having a thickness of 0.5 x 10 3 mm.
The contact surfaces designed in accordance with the~
invention afford the advantage that losses due to voltage drops
can be drastically reduced and the contact can carry a higher
current.
The invention willbee~plaïned more in detail by way of
example with reference to an Example and Figure 1 of the drawings
which represents a preferred embodiment of separable contact
joint according to the invention.
Figure 1 is a longitudinal sectional view showing a
separable contact ~oint according to the invention. ~usbars 3
consisting, e.g., of copper, are welded to a flat cylindrical
contact element 1, which consists, e.g., of copper and has a
through bore 2. The con-tact surface of the contac-t element
,~ .
3 2 3
1 is rough and formed with peaks ~. The Elat cylindrical
contact element 1 is in contact with the smooth surface of
a cylindrical metal pin 6, which consists, e.y., of copper
and is formed with a tapped bore 7 (the screw threads are no-t
shown). The contact element 1 is i-orced against the cylindrical
pin 6 by a screw, not shown, which extends through 2 and 7.
Noble metal layers are designated 5.
Example
In an electrolytic plant, a screwed contact joint
at a copper busbar (material combination copper/copper) was
designed in accordance with the invention. For this reason,
one of the surfaees was provided with closely spaced eoncentric
grooves having a depth of 0.5 mm. The contact surface provided
with the grooves and sharp-edged ridges was provided with an
eleetrodeposited silver layer in a thiekness of 1.0 x 10 mm.
Under a load of 550 A/cm2, a voltage drop of 5 mV was measured.
This means that such a given voltage drop resulting from four
times the usual load indicates that the contact surface areas
required can be greatly reduced.
