CA1047437A

CA1047437A - Method of and apparatus for, local electroplating of strip material

Info

Publication number: CA1047437A
Application number: CA228,533A
Authority: CA
Inventors: Martinus A. M. Bakker; Leonardus H. Klerks
Original assignee: Philips Gloeilampenfabrieken NV
Current assignee: Koninklijke Philips NV
Priority date: 1974-06-07
Filing date: 1975-06-04
Publication date: 1979-01-30
Also published as: SE7506384L; IT1036175B; GB1508826A; NL7407632A; JPS516137A; AT336365B; FR2273884A1; ATA424375A; CH612218A5; DE2523115A1

Abstract

ABSTRACT:
Local electroplating of strip material by means of a cylinder which is non-conductive at its surface and wets the workpiece and by means of at least one separate anode. The strip material is preferably fed in a direction parallel to the axis of the cylinder.

Description

1'~47437 - The invention relates to a method of local electroplating of strip material and to an apparatus for carrying out this method.
Such a method is described,-inter alia in British Patent Specific-ation 14.091 A.D. 1909 in which strip material is electroplated externally of an electrolyte tank and in contact with a rotating cylinder which is continuously wetted with a liquid electrolyte and itself wets the material connected as the cathode with liquid electrolyte. The or each such cylinder is connected as an anode and is covered with a layer of porous electrically non-conductive material capable of absorbing the electrolyte. Because the rotating cylinder is continuously wetted, for example by partly dipping in the tank of electrolyte, the Plectrolyte is continuously renewed and de-position is highly uniform.
This method may be modified so that deposition is effected locally only.
The latter method has become highly attractive owing to the scarcity and cost of some metals, such as gold, platinum, rhodium, and the like, because it provides appreciable saving in such a material. In many types of electric contact springs or contact pins in which a noble metal is . used because of its high resistance to chemical attack, in present-day

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technology the noble metal is pTovided at the contact face only, the remainder of the spring or pin being made of a cheaper material of less high quality. The said contact springs or pins are joined to form a strip, which after the electroplating treatment is divided.
The method described of local electroplating of material was found to have serious disadvantages in practice. The porous anode-cylinder cover which is impregnated with liquid electrolyte proved to provide less renewal than is required for even electroplating.
A very serious disadvantage is provided by the anode products which are produced simultaneously with the desired deposit and may in-admissibly contaminate it so as to adversely affect the properties and/or ,; the appearance of the deposit. In cyanide containing gold baths, for example, products such as cyanates and malonic acid dinitrile may be produced. As a result, the gold coating shows blisters, it becomes porous and less resistant to corrosion. Free oxygen which may be evolved impares the current efficiency and may also spoil the deposit.
Thisinvention relates to a method of electroplating selected portions of a strip material comprising locally wetting the strip material with electrolyte liquid by means of a rotating cylinder which is partly immersed in the electrolyte liquid, which cylinder at least at its surface is electrically non-conductive, at least one anode being submerged in the electrolyte liquid, said anode or anodes being in electrolytic connection ' .

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11~47437 with the cathodically connected strip-material in contact with and via a film of the electrolyte liquid on the cylinder surface above the level of the electrolyte-bath only, the strip material being fed in a direction parallel to the axis of the cylinder across its length.
Obviously in this method, in which the anode is separated from the point of contact of the material with a film of liquid on the surface of the cylinder, the anode products are separately produced and cannot contaminate the deposit on the material. Consequently the product obtained by the method is of particularly high quality. A great advantage is also that high current densities can be used.
In a further elaboration of the method according to the invention the strip material is moved in a direction parallel to the axis of the wetting cylinder. Hitherto the material was fed forward in a direction at right angles to the axis. The advantage of this novel feed in a direction parallel to the axis is that the profile of the deposit can be varied at will with respect to thickness and to location. The strip material is in contact with the film of liquid on the cylinder during a time which depends upon the speed of feed, which enables .

1~47437 the amount of deposit per unit length of the strip to be determined.
The location of the deposit is determined by the choice of the point of contact with the strip. The profile of the deposit can further be influenced by means of the speed of rotation and the direction of rotation of the cylinder and the location of the or each anode.
In the apparatus for carrying out the method according to ; the invention the cylinder, at least at the side at which the strip material is fed forward, has a locally increased diameter. As a result the advancing strip material is wetted by the liquid electrolyte.
m e strip material retains the film of liquid by capillarity at the location at which the cylinder has its normal diameter and hence along this part of its travel is not in direct contact with the cylinder.
m is greatly reduces wear of the cylinder and of the deposit.
An embodiment of the invention will now be described, by way of example, with reference to the accompanying diagram~atic drawings, in which:
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; Figure 1 is a cross-sectional view of an apparatus according to the invention, and Figure 2 is a side elevation thereof.
Referring now to the Figures, a tank 1 is filled with a liquid electrolyte 2. The tank accommodates a rotating cylinder 3 the speed of which is variable and the surface of which consists, for example, of a polyamide or polypropylene. m e cylinder at one end has an edge 4 , lQ47437 of increased diameter. An anode 5 is disposed in the tank. The workpiece to be electroplated, in the case under consideration a batch of contact springs 6 which are united to form a continuous strip, is disposed outside the tank. The rotating cylinder entrains a surface film 7 from the liquid, and between the batch of contact springs 6 and the cylinder a given amount of liquid electrolyte 8 is retained by capillarity.
In a practical embodiment the cylinder has a diameter of 50 mm :
and a length of 1 meter. At one end the cylinder has a raised edge 4 of height 1 mm and length 5 mm. In the apparatus, springs united to form a strip are gold-plated using a current density of about 10 A/cm in a conven-tional gold-plating bath heated at a temperature between 50C and 70C. The speed of the cylinder is 200 revolutions per minute, the speed of the strip is 1 m per minute.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of electroplating selected portions of a strip material comprising locally wetting the strip material with electrolyte liquid by means of a rotating cylinder which is partly immersed in the electrolyte liquid, which cylinder at least at its surface is electrically non-conduc-tive, at least one anode being submerged in the electrolyte liquid, said anode or anodes being in electrolytic connection with the cathodically connected strip-material in contact with and via a film of the electrolyte liquid on the cylinder surface above the level of the electrolyte-bath only, the strip material being fed in a direction parallel to the axis of the cylinder across its length.

2. Apparatus for electroplating selected portions of a strip material comprising an electrolyte tank, at least one anode and a cylinder which is provided with a spindle and a drive, at least the surface of said cylinder consisting of an electrically non-conductive material, characterized in that the cylinder at at least one of its ends has a locally increased diameter, whereby the strip material is wet locally with electrolyte liquid by means of the cylinder which rotates and which is partly immersed in the electrolyte liquid, with at least one anode being submerged in the electro-lyte liquid, said anode or anodes being in electrolytic connection with the cathodically connected strip-material in contact with and via a film of the electrolyte liquid on the cylinder surface above the level of the electro-lyte-bath only, the strip material being fed in a direction parallel to the axis of the cylinder across its length.