FR2702777A1 - Chemical nickel plating process. - Google Patents

Abstract

The invention relates to a chemical nickel plating process in a bath (1) heated so as to make it active, also implementing localized heating of at least one nickel-plated part (40) so as to create a temperature gradient between the room (40) and the active bath.

Description

CHEMICAL NICKELING PROCESS

  The subject of the present invention is a process for chemical nickel plating in a bath heated so as to

make it active.

  Chemical nickel plating is a nickel deposition process generally combined with phosphorus or boron, and obtained without an external current source. These chemical deposits exhibit qualities of hardness, resistance to wear, to friction, to abrasion and corrosion. In addition, this deposition technique is particularly advantageous in the case of parts with complicated shapes, the thickness being uniform whatever the shape of the parts. The deposits of chemical nickel were carried out on numerous supports, such as cast irons, carbon and alloy steels, stainless steels, aluminum, copper, silver, gold, titanium, nickel and its alloys, etc. There are two main families of deposits, these being distinguished by the type of reducing agent used If the reducing agent used is a boron compound, the deposit obtained also contains boron If the reducing agent used is a hypophosphyte salt, the deposit obtained is based on phosphorus A nickel-phosphorus type deposit having between 9 and 13% of phosphorus has remarkable properties of corrosion resistance, good resistance to wear and abrasion Their use is particularly recommended to achieve nickel plating of the contacts

electrical connectors.

  In the known deposition technique, the bath temperature is maintained at around 900 ° C., for example 880 ° C., and a deposition rate is thus obtained which is at most of the order of 12 to 15

microns per hour.

  As the deposit thicknesses of the order of 20 microns are often necessary, the result is that in practice, a period of immersion of the parts of the order of 1 H 3/4 in a nickel-plating bath is necessary to obtain the desired thickness It will therefore be understood that the cost of the deposition operations is directly linked to the time which is particularly desirable to increase the deposition rate. The present invention therefore relates to a chemical nickel-plating process making it possible to increase the deposition rate and therefore reduce the

cost of such operations.

  The invention therefore relates to a process for chemical nickel plating in a heated bath so as to make it active (that is to say capable by itself of producing a deposit), characterized in that it also implements a localized heating of at least one room to be nickelled so as to create a gradient of

  temperature between the room and the active bath.

  Note also that it is known from the East German patent DD-249,495 (VEB Carl Zeiss JENA), a nickel plating process using a cold bath (not active) Local heating is used so as to locally carry the bath temperature between 60 and 950 C The working temperature of the bath is created directly on the surface of the parts thanks to an induction heating This process makes it possible to reduce the energy consumed, but does not make it possible to increase the speed of deposition of the nickel, nor to decrease

  notably the production costs.

  The method according to the invention can be characterized in that it includes circulating the bath so as to avoid a significant rise in its temperature in the vicinity of a said heated room. Indeed, since, as well as will be explained later, the presence of a temperature gradient between an active bath and a workpiece increases the deposition rate, it appears that, contrary to what the prior art might suggest, any increase in the bath temperature produced by heating the sample tends to

decrease the deposition rate.

  Said circulation of the bath corresponds, according to a preferred embodiment, to a displacement of the order of a few centimeters per

second at said room.

  The bath temperature can advantageously be between 60 and 900 ° C. and the thermal gradient can be understood in the order of a few degrees and 500 ° C. It will be noted that a given thermal gradient brings an increase in deposition speed all the higher that the temperature of the

  active bath is itself higher.

  The thermal gradient can be chosen in such a way that the heating of said nickel plating piece does not produce significant aging of the bath This thermal gradient can be in particular such that the temperature of the nickel plating piece is between 90 and 1100 C. In this case, the local heating of the bath is not likely to bring it to a temperature of chemical decomposition, and this all the more that the temperature of the

bath is weaker.

  The process according to the invention can be characterized in that the temperature of the bath is between 60 and 70 ° C., the temperature of the piece to be nickelled being substantially equal to 90 ° C. In this configuration, the bath is heated to a relatively low temperature. low and sufficient all the same so that it is active enough, and the parts to be nickelled are at a temperature such that the bath cannot in any way be brought to a detrimental temperature since 9 OC corresponds to a conventional treatment temperature. corresponds approximately to a doubling of the deposition rate compared to the prior art, ie approximately 25 to 30 microns per hour under the conditions observed. According to another embodiment, the temperature of the bath is between 85 and 90 C and the thermal gradient is between 1 and 150 C In this configuration, the maximum deposition speed which is sought, this being obtained with a temperature bath of 9 QOC and a thermal gradient of C. Other characteristics and advantages of the invention will appear better on reading the

  description which follows, given by way of example not

  limiting, in conjunction with the drawings which represent: FIG. 1, a general diagram from above of a nickel-plating installation according to the invention, FIG. 2, a device allowing the heating of a piece to be nickelled according to the invention, FIG. 3, different curves illustrating some deposits as a function of the thermal gradient between the part and the bath for different temperatures of

active bath.

  According to FIG. 1, a device for implementing the method according to the invention comprises a tank filled with a chemical nickel-plating solution 1 The level of the nickel-plating bath is detected by a sensor 4 which actuates a filling valve 6 A temperature sensor 7 transmits a signal to a regulator 5 to control the heating of heating resistors 3 placed in the tank and possibly a supply of cold solution (valve 9) The mechanical agitation of the liquid the tank is ensured by a propeller 2 located at the bottom of the tank and in the center of it and actuated by an electric motor The circulation of the bath out of the tank 30 is ensured by means of a pump 14 which takes liquid and restores it

by pre-filtering through a filter 15.

  The purpose of the agitation of the liquid is to homogenize the temperature of the bath and to avoid overheating. The circulation of the liquid also makes it possible to avoid the localized heating of the nickel-plating bath.

  at the level of the rooms which are themselves heated.

  It also makes it possible to renew the electrolyte at the level of the various surfaces to be nickelled, which

  promotes the formation of more homogeneous thicknesses.

  The agitation eliminates the gaseous curtains which slow down the rate of deposition and drives out the bubbles of hydrogen in formation, which prevents the formation of pitting on the treated surfaces. It will be noted that agitation of the liquid can also be obtained by creating a movement.

pieces.

  When the level of the tank drops due to the evaporation of the bath, the sensor 4 causes, thanks to the valve 6, the supply of demineralized water to the bath. The nickel-plating bath is stored in a polypropylene tank which is provided with a filter pump 16 connected to the bottom point of the tank 30 It

  works back and forth with the latter.

  A tank 17 for storage of% nitric acid makes it possible to decontaminate the bath at each renewal. A p H-meter 10 making it possible to actuate a pump 22 for dosing diluted ammonia 14 stored in a tank 19 makes it possible to compensate for the acidification of the bath, that is to say the drop in p H which appears during

the overall deposition reaction.

  In addition, to obtain a good deposit of nickel, the bath must contain precise quantities of nickel (Ni 2 +) and of hypophosphyte (H 22 P 02-), these

  quantities decreasing as depositions.

  The concentrations are regulated using a colorimeter 11 operating on the technique of comparing the color of the bath with a standard color, and actuating metering pumps of nickel in solution 23 from a tank 20, and of hypophosphyte 24 from of a tank 21 The quantities of hypophosphyte and nickel to be injected into the tank being proportional, only the

  nickel concentration measurement is necessary.

  The reference 12 designates a sampling valve making it possible to supply the p H-meter 10 and the colorimeter 11. In FIG. 2, the individual heating of the sample 40 is carried out by an induction solenoid 33 starting from the coated conductor wire of ceramic The solenoid 35 is arranged around a PTFE ring 34 in which is housed the sample 40 taken between two spacers 41 Rings 38 and 39 are held by clamping bars 35 and 36 of plastic material fixed together by tie rods 37 The rings 38 and 39 can also define, as shown, a pipe

  forced flow of bath liquid.

  FIG. 3 gives the curves of the deposition rate in micron per hour as a function of the temperature difference A T between the temperature Tp of the part 40 and the temperature TB of the bath 1 These curves were obtained with a stirring speed

  of the bath at the level of the room 40 equal to 3 cm / s.

  The first curve I corresponds to a bath temperature equal to 60 C (bath not very active);

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  the intercept corresponding to A T = O is 3

  microns / h It is therefore a weakly active bath.

  When t AT increases, the deposition speed increases regularly up to a plateau between values of t T equal to 40 to 50 C. This value of T equal to 500 C is apparently the maximum value not to be exceeded in practice, so as to avoid the problems of chemical decomposition and / or aging of the bath. In addition, as soon as the temperature of the workpiece to be nickelled exceeds 1000 C, there is a possibility of cavitation, in particular if the flow speed bath at room level

nickeler is not enough.

  Curve II corresponds to a bath temperature TB equal to 750 C (moderately active bath) with an ordinate at the origin of 5 microns / h The curve increases in a practically linear fashion up to values of 4 T equal to 450 C , which corresponds to a temperature of the room to be nickelled 40 equal to 1100 C. Curve III corresponds to a very active bath, the temperature TB being equal to 900 C. The curve increases with a higher slope than the two previous curves from an intercept of 12 microns / h to a maximum which is reached for A T equal to 15 'C with a speed

  growth slightly above 55 microns / h.

  These curves make it possible to highlight the importance of the temperature gradient A T For example, curve III shows that for a temperature bath of 880 C and t AT = O (prior art), the growth speed is equal to 12 microns / h On curve I, for a room temperature 40 equal to 880 C, we have AT = 28 C, and the growth speed is close to 24 microns / h, which is double the previous case On curve II for a room temperature 40 equal to 88 'C or i T = 13' C, the speed of

  deposit is also close to 24 microns / h.

  For a room temperature 40 equal to 1000 ° C., on the curve IAT = 40 and a growth speed of 30 microns / h, on curve II, a value of AT = 250 ° C., and a growth speed of about 35 microns / h, and on curve III, a value of at T equal to 120 C, a growth rate

greater than 50 microns / h.

  The conditions should not be such that the heating of the room 40 produces, by heating effect of the bath, a reduction in the temperature gradient AT, since this would have a negative influence on the growth rate It is possible, in practice, with good circulation of the bath, to reduce the localized heating thereof to only a few degrees. There is also an optimal value for the flow which makes it possible to maximize the rate of deposition of the nickel, this speed corresponding to

a few centimeters / s.

  The curve curve III indicates that it is advantageous in terms of speed to use an intrinsically very active bath, for example at a temperature close to 90 ° C. However, in this case, it is advisable to avoid when the temperature of the room reaches 950 C at 100 'C, the bath heats up enough to cause its degradation or aging It is particularly suitable to avoid this phenomenon of increasing the speed of movement of the bath in the vicinity of the room 40 Indeed, repeated overheating of the bath could be harmful to its aging and also cause enough

  quickly a decomposition of it.

  The use of less active baths, for example having temperatures between 60 and C, allows the fact that the bath temperature is moderate, to heat the rooms to higher temperatures without the aforementioned drawbacks, in particular by stirring the liquid within the bath overheating limits The temperature gradient at the room-bath interface is thus higher and gives

  appreciable deposition rates.

  In particular, with moderately active baths (between 60 and 750 C), heating the room by induction makes it possible to raise its temperature to 900 C at the wall of the room, that is to say just the place concerned by the deposit of nickel This allows a gain of energy in heating compared to the prior art, while notably increasing the speed of deposition In particular, the speed of deposition for a bath at 60 C with T = 30 C, is twice the deposition rate for a bath at 88 'C and T = 0

  (best performing prior art).

  The degree of circulation of the bath is also a function of the possible overheating thereof. For a weak or moderately active bath, heating the parts can cause the phenomenon of overheating to appear if the agitation in the parts is not sufficient. , unless the temperature of the part to be coated does not exceed a value substantially equal to 880 C In this case, no problem of overheating on the wall appears because the bath temperature will always be below 90 'C whatever the degree of agitation The agitation of the bath then only has the function of renewing the electrolyte When the part is heated to more than 90 ° C., it is preferable that the agitation is sufficient to avoid overheating, that is to say that is, to maintain the temperature value at the interface equal to 900 ° C., failing which, there is a risk of causing aging of the bath and loss of part of the economic advantages of the process. Other techniques can be used to heat the room 40 For example, electric resistance heating can be used, or alternatively, the room 40 can itself be heated directly by passing it through a

given current.

  It will be understood that the currently known chemical nickel-plating baths can be used in

the scope of the invention.

  As a preferred embodiment, a bath of (Ni SO 4, 6 H 20) at a rate of 20 to 30 g / l, of (Na H 2 P 02, H 20) at a rate of 42 g / l at which optionally, in a known manner, a complexing agent, an accelerator and / or a stabilizer is suitable

particularly.

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Claims (9)

  1 Chemical nickel plating process in a heated bath so as to make it active, characterized in that it also implements localized heating of at least one nickel plating piece (40) so as to create a temperature gradient between the part (40) and the active bath (1).   2 Method according to claim 1, characterized in that it comprises a circulation of the bath (1) so as to avoid a significant rise in its temperature in the vicinity of a said heated room (40).   3 Method according to claim 2, characterized in that said circulation of the bath (1) corresponds to a displacement of the order of   a few cm / s at the level of said part (40).   4 Method according to one of claims 1 to   3, characterized in that the temperature of the bath (1) is between 60 and 90 C.   Method according to claim 4, characterized in that the thermal gradient is included between a few degrees and 50 'C.   6 Method according to claim 5, characterized in that the thermal gradient is chosen in such a way that the heating of said part (40) to be nickelled does not produce significant aging of the bath (1). 12 2702777   7 Method according to claim 5, characterized in that the thermal gradient is such that the temperature of the part (40) to be nickelled is between 90 and 1100 C.   8 Method according to one of claims 1 to   3, characterized in that the temperature of the bath (1) is between 60 and 700 C and in that the temperature of said part (40) to be nickelled is substantially equal at 900 C.   9 Method according to one of claims of   claims 1 to 3, characterized in that the   bath temperature (1) is between 85 and 900 C   and the thermal gradient is between 1 and 15 'C.