[0001] This invention relates to a method of manufacturing slip rings in which an electro-less
plating step is included during manufacture to deposit layers of conductive metal
including a noble metal, and to slip rings produced by such a method.
[0002] An object of the invention is to produce a slip ring which, by eliminating certain
high precision techniques involving highly skilled personnel and time-consuming operations,
is capable of being produced far more economically than conventional slip rings.
[0003] According to one aspect of the present invention there is provided a method of manufacturing
a slip ring including the steps of providing a body of plastics material, forming
a plurality of parallel grooves in a surface of the plastics body, treating the grooved
surface to allow metal to be deposited thereon by an electro-less plating process,
electro-less plating a layer of base metal on the treated grooved surface of the plastics
body including the grooves thereof, removing the plated metal from between adjacent
grooves to define individual tracks of the slip ring and electroplating to overlay
the base metal in the grooves only with a nobl
ie metal.
[0004] According to a further aspect of the invention there is provided a method of manufacturing
a slip ring including the steps of forming a cavity in a slip ring body of plastics
material, forming terminal holes in the body extending between a surface of the body
and the cavity, locating terminal pins within the holes and securing the pins in position
by filling the cavity with an encapsulating medium, forming V-grooves in- said surface
in line with the pins and exposing a portion of a pin at the base of each V-groove,
electro-less plating a base layer of metal on said surface and on the walls of the
grooves, removing said plated metal from between adjacent grooves to define individual
tracks of the slip ring and replating to overlay the base metal in the grooves only
with a noble metal.
[0005] The term 'slip ring' is intended to include discs or cylinders and thus to manufacture
a slip ring in accordance with one embodiment of the method of the present invention
using the electro-less plating method, a cylinder or disc is cast from plastics material
consisting for example of an epoxy base filled resin, and all surfaces are machined
to remove the resin rich skin. The plastics material is then cured and the disc or
cylinder machined to obtain the required external profile leaving sufficient material
to maintain rigidity for subsequent machining operations.
[0006] A cavity for the terminals is then machined in the body of plastics material and
the body drilled with a plurality of holes for the terminals of the rings, each hole-having
for example, a depth of between 0.6 mm and 0.7 mm and each terminal hole extends from
the surface of the body opposite the cavity, through to the cavity.
[0007] Copper terminal pins are located within the holes and cemented in position. The length
of the terminals should each be for example, 70 to 80% of the ring width and project
through the holes in the body of the ring, through the cavity formed in the body and
slightly beyond the cavity extending radially or in any other direction. It is important
to ensure that the ends of the terminal pins remote from the cavity lie flush with
the surface of the plastics material.
[0008] The cavity is then filled with an encapsulating medium to fix the terminal pins in
position.
[0009] With presently manufactured slip rings, square section grooves are machined in the
plastics body in line with each terminal pin and the base of each groove is hand-painted
with silver paint. It is extremely important to ensure that the paint is applied only
to the base of each groove, since when the ring is subsequently placed in a plating
bath, if any silver paint has been deposited on the walls of the grooves, copper from
the materials of the plating bath will tend to be deposited at the nearest point to
the anode of the bath and continue to be deposited from this point in any groove having
silver paint on the walls. Since the object of the plating step is to provide a uniform
deposit of copper in the groove, it will be appreciated that it is important to ensure
that the silver paint is applied only to the base of the groove. This, obviously,
is a highly skilled, precision operation involving the use of highly skilled personnel
and is also obviously time-consuming and accordingly costly, particularly since if
any silver paint inadvertently appears on the side walls of any groove, it must be
meticulously removed manually by means such as a scalpel. The copper deposited in
the square section grooves is finally machined to.form V-shaped grooves.
[0010] In the method of manufacture according to the described embodiment of the present
invention, the hand-painting step is eliminated by introducing an electro-less plating
step and instead of machining square section grooves in the ring, V-grooves are machined
in the plastics material in line with each terminal pin, exposing the head of each
terminal pin only at the base of each V-shaped groove. The grooved body of plastics
material is treated in preparation for plating by an electro-less plating step and
placed in the plating bath and a thin layer of copper is deposited uniformly in the
V-grooves and between adjacent grooves. Peaks of copper may be deposited between the
grooves and these peaks are machined away back to the plastics base to define the
individual tracks of the ring. The electro-less plating step provides a homogeneous
bond between the copper terminal pins and the thin copper skin.
[0011] The ring is finally inserted in an electroplating bath of noble metal e.g. gold where
the copper layer in each V-groove is overlaid with the noble metal.
[0012] The steps of the process are illustrated in the accompanying drawings 1 to 6 in which
in Figure 1, the terminal holes 1, are drilled in the plastics base 2 after formation
of the cavity 3. After cementing the terminals 4 in position within the holes 1, the
terminals 4 are encapsulated within an encapsulating medium 5 which fills the cavity
3, as shown in Figure 2. The V-grooves 6 are machined in the plastics base 2 as shown
in Figure 3 exposing the tips of the terminals 4, and the plastics base is treated
and then inserted in an electro-less plating bath where a thin copper skin 7 is deposited
over the surface of the plastics material and uniformly within the V-grooves 6 as
shown in Figure 4. Peaks such as shown at 8 may be formed during plating and as shown
in Figure 5, the peaks 8 between the grooves 6 are machined away to expose the plastics
material and define the individual tracks of the ring and in Figure 6, the copper
skin 7 in each groove has been overlaid with a noble metal layer 9 e.g. gold in an
electro plating bath.
1. A method of manufacturing a slip ring including the steps of providing a body (2)
of plastics material, forming a plurality of parallel grooves (6) in a surface of
the plastics body, treating the grooved surface to allow metal (7) to be deposited
thereon by an electro-less plating process, electro-less plating a layer of base metal
(7) on the treated grooved surface of the plastics body including the grooves (6)
thereof, removing the plated metal (8) from between adjacent grooves to define individual
tracks of the slip ring and electroplating to overlay the base metal in the grooves
only with a noble metal (9).
2. A method of manufacturing a slip ring including the steps of forming a cavity (3)
in a slip ring body (2) of plastics material, forming terminal holes (1) in the body
(2) extending between a surface of the body (2) and the cavity (3), locating terminal
pins (4) within the holes (1) and securing the pins in position by filling the cavity
with an encapsulating medium (5) forming V-grooves (6) in said surface in line with
the pins (4) and exposing a portion of a pin (4) at the base of each V-groove (6),
electro-less plating a base layer (7) of metal on said surface and on the walls of
the grooves (6), removing said plating metal (7) from between adjacent grooves (6)
to define individual tracks of the slip ring and replating to overlay the base metal
(7) in the grooves (6) only with a noble metal (9).
3. A slip ring produced by the method claimed in claim 1 or 2.
