METHOD AND APPARATUS FOR THE ELECTROLESS PLATING OF A METAL SURFACE OF A HOLLOW CONDUCTOR, HOLLOW CONDUCTOR, STATOR BAR OF AN ELECTRIC MACHINE AND STATOR WINDING ARRANGEMENT OF AN ELECTRIC MACHINE

Abstract: An electroless plating method and apparatus enable electroless plating of hollow conductors and stator bars over an extremely wide range of sizes, in particular such that the relation between length (L) and inner equivalent diameter (IDe) of said hollow conductors ranges up to 5000:l. Furthermore, the method and apparatus are applied to mounted stator bars whereby there is no need to disassemble the hydro- or turbogenerator hence avoiding prolonged outages.

Description: Title: METHOD AND APPARATUS FOR THE ELECTROLESS PLATING OF A METAL SURFACE OF A HOLLOW CONDUCTOR, HOLLOW CONDUCTOR, STATOR BAR OF AN ELECTRIC MACHINE AND STATOR WINDING ARRANGEMENT OF AN ELECTRIC MACHINE." Technical Field The present invention relates to a method for the electroless plating of the inner metallic surface of a hollow conductor with a metal alloy contained in a chemical constitution bath, in particular hollow conductors within the stator bars of a cooling system of an electric machine for power generation without disassembling the hollow conductors themselves and in such a way that individual stator bars may easily be coated on site. The invention also relates to a portable electroless plating apparatus for effecting said method, a hollow conductor with inner boundary surface coated by the method of the invention and more particularly a stator bar comprising any desired number of hollow conductors coated by the teachings of the present invention. A hollow conductor as herein defined also is any tube portion of any desired length (L) and inner equivalent diameter (IDe), for carrying a fluid such that the relation between length (L) and inner equivalent diameter (IDe) is more than 10:1, particularly up to 5000:1. The conductor need not necessarily be straight, the definition including conductors with bends or curves. Thereby conductors and hollow bars can be spare parts for other industrial cooling systems. Some types of electric machines for power generation, in particular hydrogenerators and turbogenerators re- quire their stator bars (so called Roebel type bars) to be water cooled during operation instead of being air cooled. By way of example the inside area of a typical stator bar is traversed by six or more copper hollow conductors each having a flow passage with a squared shape of approximately 2.4 mm x 9.1 mm and a length ranging between 1,000 and 5,000 mm. It will be understood that due to desired heat exchange rates and other design requirements shapes and sizes are variable. When in operation, the cooling water flows through each hollow conductor of the stator bar within a closed cir- cuit in connection with specially designed pumps, particle filters (mechanical filter) and chemical filters (ion exchange system) among other components. These cooling devices are close to the hydrogenerator/turbogenerator and have the function of pumping water of the desired high purity into the hol- low conductors of the stator bars during the operation of said machines. The most common operating problems and stoppages of electric machines arise with the clogging of the hollow conductors within the stator bars of the water cooled stator ar- rangement. The clogging of the water flow passages is caused by corrosion and deposition on the inner walls of the hollow conductors. Corrosion is the most dramatic cooling water problem since it is responsible for numerous failures and system stops due to piping leaks or blocked lines at present. Basically, corrosion is the deterioration of a metal surface because of a reaction with the environment, that is to say, deterioration of the inner boundary surface of a hollow conductor, generally copper or iron in direct contact with cooling water Factors such as low velocity or stagnant water flow allow suspended solids to settle. This settling of solids actually influences corrosion by firstly reducing the contact of corrosion inhibitors with the uncoated metal surface in known hollow conductors and secondly by propagating underdeposit corrosion due to a difference in oxygen concentration. High velocity streams, on the other hand, often cause extreme localized corrosion due to suspended or dissolved solids. An example of a metal that is prone to impingement attack caused by high velocity is copper, even considering that copper is known to resist to most types of corrosion because of his low position in the electromotive series scale. In heat exchangers among other industrial applica- tions, it is normal practice to limit waterflow through copper tubes. Corrosion process causes deposition and deposition can accelerate corrosion by a phenomenon called "underdeposit corrosion" widely detected in stator bars of several hydro and turbogenerators around the world which are equipped with water-cooled hollow conductors made of copper even when using deionised water (that is pure water or high purity water) as coolant liquid. Deposition insulates against heat transfer by re- stricting water flow, thus further reducing the cooling efficiency. Since the known corrosion inhibitors cannot passivate the metal surfaces beneath the deposit the resultant corrosion generates more corrosion products and hence, more deposition. Manufacturers and users of installed electric ma- chines for power generation around the world have been faced with corrosion related problems since the hollow conductors of the stator bars of the prior art are uncoated and invariably constructed from copper or stainless steel in direct contact with the circulating water. copper oxidizes and the oxides accumulate on spots in the hollow conductor thereby obstructing or constricting water flow passages and seriously affecting cooling performance. The flow passage partially or totally clog making necessary long and/or systematic stoppage of electric machines and expensive replacements. Depending on the size of the generator, the time required to replace a stator winding can be up to six months. Although one single blocked hollow conductor is not critical any impairment of the cooling performance of a whole stator bar can lead to damages. Background Art With a view to overcome the aforementioned inconveniences many attempts have been made by suppliers implementing different water treatments, e.g. neutral and low -oxygen, alkaline and low-to-medium oxygen or slightly acid and high oxygen water treatments among other ones. However, no matter how thorough the survey these water treatment programs have failed to ensure unblocked flow passages in hollow conductors of hydro and turbogenerators in almost all electric machines. On the other hand and although the deposition of chemical nickel or electroless nickel onto other metals such as iron, copper, etc is already known, the strict dimensional requirements of the containers and the composition of the coating bath of the coating devices of the state of the art restrict the electroless plating to bodies of commercial shapes and sizes and to relative small or easy movable objects like mounting hardware, fittings, containers, external surface of capillary elements, printed circuits, this is to say, objects which easily are brought to a stationary coating bath or sprayed therewith within a stationary installation. Among the known coating processes USP 3,649,477, assigned to Bart Manufacturing Co. published on March 14, 1972 discloses a process and an apparatus whereby nickel is electroplated onto the interior wall of a large cylindrical vessel such as the tank of a railroad tank car. The electroplating is effected by half filling with the electroplating solution the tank and introducing into and in alignment with the center-line of the tank a pipe which forms part of the anode. The pipe extends along the axis of the tank and is provided with small apertures throughout its length. The electroplating solution during the electroplating process flows into the tank and is projected in streams the apertures by simultaneously rotating the tank. The main limitation of the electroplating process and apparatus of US 3,649,477 is that an anode can not be inserted through the bore of a hollow conductor without making contact with the boundary wall. DR Wirtschaftspatent 90 041 Zobel et Oppermann, filed on 21/09/70 refers to an eletroless Ni plating process for symmetrical containers. The container is half filled with the coating solution, tilted, rotated and heated. Although the process and apparatus of this known art does not require the anode element of US 3,649,477, the object to be plated has to have a symmetrical shape besides the fact that the container requires to be heated and tilted, this not being possible to effect with hollow conductors having variable sizes as already described. EP 0 120 083, international publication number WO 84/01392 of 12.04.84 discloses a method and a device for electrolessly plating circuit boards. The device comprises a rectangular tank for receiving a constituent bath.The storage volume of the tank is defined by two inward facing walls and two tank side portions. The circuit board is disposed centrally within the tank and is immersed to a desired level in the constituent bath which fills the tank between two mutually spaced walls with a plurality of ports therethrough. The device further comprises means adapted to support the printed circuit board and pumping means for delivering the bath through the ports on the circuit board so that it impinges on one surface of the printed circuit board from a location spaced therefrom and sucking away the bath from the opposite surface of the board at a location spaced therefrom while causing an oscillating motion of the board. Notwithstanding the many improvements in the methods and apparatus of the prior art strong limitations still prevail for their application in stator bars of electric machines. The problems in the prior art lie in need of adapting the sizes of an immersion tank so that the object can be immersed. It is to be noted that because of the different ratings of the hydro and turbogenerators shapes and sizes of the stator bar are variable. Another problem which is encountered in the devices of the prior art is that the electrolessly plating of the inner boundary surface of the known hollow conductors and stator bars require a volume of chemical constituent bath which exceeds the storage capacity of the hollow conductor whereby the stator bar cannot be filled with it. Also a further arising problem by the teachings of the prior art is the damage of the electric insulation of the outer wall of the stator bar or any other hollow conductor. Disclosure of Invention Accordingly, a need exists for a simple and inexpensive method and apparatus for electroless plating of hollow conductors and stator bars over an extremely wide range of sizes, in particular such that the relation between length (L) and inner equivalent diameter (IDe) of said hollow conductors ranges up to 5000:1. Furthermore, the method and apparatus should offer the ability to function in mounted stator bars whereby there would be no need to disassemble the hydro- or turbogenerator hence avoiding prolonged outages. Moreover diverging from the known water treatments programs adopted by the suppliers of electric machines of the prior art the method and apparatus of the invention ensure a failure free operation of hydro and turbogenerators by electroless plating with a metal alloy in flowing condition, particularly by Ni coating the inner boundary copper surface of the stator bars regardless of the size and the location of the same within the machine. The objective above is attained by the method of the present invention, which ensures a degree of accuracy and/or precision required for the coating of long hollow conductors and by the apparatus best suited to the electroless coating of inner walls of installed hollow conductors and stator bars on electric machines and other conditions on site. The invention provides an adjustment of the flowing velocity of the controlled chemical constitution bath through each of the hollow conductors and stator bars without disassembling the stator bar arrangement of a hydro or turbogenerator . Since only the inner metallic surface is coated at room temperature conditions and on site the outer wall insulation of the hollow conductor or of the stator bar is preserved. By the method and device of the present invention a desired coating thickness can be achieved by adjusting the flow velocity in response to sensed inflow and outflow temperatures at the hollow conductor. Said coating thickness is re- movable also without damaging the outer wall insulation whenever necessary. Another object of the invention is a quality control method of the coated hollow conductor by placing for flow communication with said hollow conductor a piece of metal for de- termining the coating thickness after conclusion of the coating stage. Another object of the present invention is a portable electroless coating apparatus for effecting said method on already installed hollow conductors and stator bars within a cooling water system by coupling the electroless coating apparatus to both ends of said stator bar by disconnecting the respective hoses in the stator bar arrangement. The portable electroless coating apparatus also can be used for effecting on site the required pretreatment proc- ess, this is to say, causing to flow cleaning solutions through the hollow conductor prior to the coating stage. Another object of the invention is a hollow conductor with an inner boundary surface coated with a corrosion resisting metal alloy. Particularly a hollow copper conductor with a nickel coated inner boundary surface wherein the coating thickness is not less than 30 microns. A further object of the invention is a stator bar of an electric machine for power generation, particularly of a hydro or turbogenerator having a length L and an equivalent inner diameter IDe such that the ratio between said L and IDe is more than 10:1 and typically 5000:1 whereby the inner metal surface is metal coated, in particular Ni coated without prejudice of the outer wall insulation. Brief Description of the drawings Other objects and advantages of the invention will become apparent from the following description and appended claims taken in conjunction with the accompanying drawings in which Figure 1 illustrates the electroless plating apparatus according to the present invention coupled to one stator bar and a detail of a cross-sectional view of a stator bar housing six hollow conductors. Figure 2 is a cross sectional view of the velocity profile homogenization means taken along line II-II of figure 1; Figure 3 is a partial sectional view of a connection side of the stator bar; Figure 4 is a perspective view of a known water cooled stator bar arrangement of an electric machine; and Figure 5 shows an end-winding support of the water- cooled stator winding of figure 4 with the electroless plating apparatus coupled at one end of a stator bar. Best Mode for Carrying Out the Invention Referring to figure 1 of the drawings, the electroless plating portable apparatus of the invention is coupled to both ends of one of a plurality of stator bars 1 which form the stator winding arrangement as shown in figure 4. The outer wall of stator bar 1 bears a high dielectric strength insulation. The cross section of stator bar 1 is shown in detail in figure 1 as containing by way of example six water cooled copper made hollow conductors la,lb,lc,ld,le,lf . The cooling channel cross-sectional area of each of the hollow conductors is reduced approximately 9.5 x 2.4 mm. It is observed that the length (L) and the equiv- alent inner diameter (IDe) of the hollow conductors la to If is such that the L: IDe ratio is greater than 10:1, in particular, L: Ide can be up to 5000:1. Although six hollow conductors are shown in figure 1 stator bars can contain any desired number of hollow conduc- tors, a number of 8 or 12 hollow conductors is usual. A water cooled stator arrangement comprising a plurality of stator bars 1 is shown in figure 5. A flowing stream of pretreatment fluids and chemical constitution bath will pass through each stator bar during the electroless coating process. The portable apparatus comprises a controllable chemical constitution bath 5, an external voltage source 6 with cathode 12 and anode 13 electrodes, a set of coating flow lines 7, 7' ,7", 7'" for connecting within said flow circuit for recirculation of said chemical constitution bath 4 through a stator bar 1 a pump 8, a flow meter 9, a velocity profile homogenization tube 10 and first and second thermocouples 20,21 to be respectively located on inlet and outlet sides 2,3 of stator bar 1. The controllable chemical constitution bath 5 is a coating solution with controlled nickel Phosphor content within a portable container 19 with respective inlet and outlet connections 14,15 and an adjustable exhaust 16. Preferably, container 19 has a 180 liter capacity for coating an arrangement of stator bars of an electric machine on site. The container 19 housing the chemical constitution bath 5 is made of 18/8 stainless steel and protected against deposition of nickel by an electrode inside the bath, which is negatively polarized at a potential of -0.7 V whereby the current may not exceed 100 mA. If current is >100 mA the bath must be pumped out immediately into a plastic container. A pH control means 17, temperature sensor means 18 and a metal alloy content analyzer 19 provide for controlled coating parameters. Cathode electrode 13 is connected to the flat mounting end 2' at inlet 2 of stator bar 1. Anode electrode 12 is connected in flow communication with the flowing stream of the chemical contitution bath 5. Anode electrode 12 is a stainless steel tube inserted into the coating fluid line portion 7" shortly upstream of the non flexible plastic tube element 10. Cathode 12 and anode 13 electrodes of the external voltage source 6 provide for a start of the coating process by means of a current pulse of 1A as in the methods of the known art. Coating flow lines 7, 7',7" and 7"' are preferably flexible silicon tubes insulated against heat loss in order to maintain a required temperature of flowing stream ranging within 88 to 90°C at inlet 2 of stator bar 1. A variable speed membrane or diaphragm pump 8 ensures an accurate preset amount of coating flowing stream ve- locity through stator bar 1. Chemical constitution bath 5 is thereby pumped within a loop, through coating flow lines 7,7' ,7" and stator bar 1 by exiting container 19 at outlet connection 14 and returning via fluid line 7"' through inlet connection 15 into container 19. Flow meter 9 in flow connection with said pump 8 and said stator bar 1 senses the velocity of the flowing stream within a flow range of 0.2 to 0.4 m/sec. A glass rotameter type having a scale mounted next to the tube facilitates flow rate readings and is therefore preferred when used on site for monitoring the flowing stream velocity. Rotameter 9 also can be provided with adjustable alarm contacts for signalling when the rate of flow goes above or below a given setpoint indicative for a desired coating stream velocity. First and second thermocouples 20, 21 are mounted on inlet 2 and outlet 3 of said stator bar 1 for temperature indication of flowing stream temperature during the coating process. A non-flexible plastic tube element 10 is connected at inlet 2 of the stator bar 1 for ensuring a velocity profile homogenization of the flow of the coating fluid. Tube element 10 is preferably about 15 cm length and has a diameter of about 3 cm. Velocity profile homogenization tube 10 ensures a simultaneous coating fluid filled single tubes la,lb,lc,ld,le and If of stator bar 1 therefore preventing of having air en- trapped in the coating fluid circuit. Figure 2 is a cross section view of flow homogenization tube 10 on inlet side 20 of the stator bar of figure 1. Flow homogenization tube 10 comprises a plastic cylinder 21 having a polypropilene filled cross section 22 with through holes 23 which will be flooded by the coating fluid. A removable single tube 24 for flow communication with stator bar 1 is housed within homogenization tube 10. Tube 24 and stator bar 1 have the same cross sectional area and are electrically connected by a cable 25 for the simul- taneous coating start of both tube 24 and stator bar 1. As will be explained later, a desired coating thickness ranging within 15 and 50 microns builds up by adjusting one or a combination of the parameters during operation. It has been found that a nickel coating thickness of not less than 30 microns on hollow copper conductors ensures a coating surface free of pores or any defects. The mounting hardware at outflow connection sides of each of the plurality of stator bars 1 is shown in figure 3. Heat insulating line 7'" of the electroless plating apparatus of the invention replaces the known Teflon hoses of the stator winding and one end thereof is connected on distal end of water chamber fitting 4. Chamber 11 on opposite side of water chamber fitting 4 is adapted for fluid communication with mounting ends of hollow conductors la to If as known for those versed in the art and will be flooded with the coating solution leaving the stator bar through hollow conductors la to If. The other end of heat insulating line 7'"is con- nected to the intake 15 on container 19 whereby the coating solution is pumped back as shown in figure 1. However, the connecting ends of flow paths 7' and 7"' can be inverted so as to direct a coating flow in both directions. Figure 4 is a simplified perspective view of a water cooled stator arrangement internally disposed within a known turbogenerator . The main components of the cooling system comprise a stator winding with a plurality of stator bars 1 cooling water manifold 26, removable teflon hoses 27, expansion tank 28, H2 intake 29, current connection 30 and winding connections 31. The main-casing, end shields, core terminals and hydrogen coolers of the stator are not shown. When in operation the stator winding is cooled by a flow of water which is in direct contact with conductors la,lb,lc,ld,le,lf in stator bars 1. The cooling water for the stator winding is supplied by a circulating pump to manifold tube 26 in the generator from which it is distributed by teflon hoses 27 to the individual stator winding bars 1. All stator bars 1 are fed in parallel with cooling water which leaves the bars, again over Teflon hoses 27, and enters a similar manifold 26 at the other end of the generator. The water returns to the supply unit, flowing over pump and cooler. Thereby the power dissipation in form of heat is absorbed by the cooling water flowing through each stator bar 1 in the known manner for those versed in the art. The portable electroless plating apparatus is connectable to both ends 2,3 of each stator bar 1 by succes- sively replacing respective teflon hoses 27 by fluid lines 7" and 7'" as shown in figure 1. Finally, figure 5 shows one end-winding support of the water-cooled stator winding of figure 4 in a simplified manner with two uncoated stator bars 1A and IB Stator bar 1A is connected by teflon hose 27 at both ends to manifold 26 within the stator arrangement of figure 4. Without disassembling stator bar IB the respective hose 27 is replaced by inflow path 7, 7" of the portable electroless plating apparatus of figure 1 for coating stator bar IB. In a similar manner the other distal connection side of stator bar IB is connected to the outflow path 7"' whereby a closed coating fluid circuit is established. The steps for connecting the electroless plating apparatus of the invention are known to those versed in industrial maintenance. As already mentioned, the required pretreatment also can be effected with the portable electroless plating apparatus of the invention by simply providing a convenient 3- or 5-valves manifold device in flow communication to respective cleaning solutions. As in the prior art, the chemical cleaning of the surface to be coated is required in order to eliminate possible dirt, impurities, fatty materials or even oxides of this metal, with a view to ensure good interaction between the coating nickel alloy and the base metal copper. The pretreatment process must be done immediately before the coating in order to prevent the surface from "re- oxidation" . The pretreatment is done at room temperature (20 to 25°C) and among the many cleaning solutions available the preferred ones are as follows: 1. Degreasing bath ACL 865 3 min 2. Rinsing deionized water 1 min 3. Etching bath 910 10 min 4. Rinsing deionized water 1 min 5. Pickling 5% H2S04 3 min 6. Rinsing deionized water 2 min The cleaning solutions and the rinsing water are located directly beside bar 1. The same pump 8 is to be used for the pretreatment and for the coating. The ends of the flexible tubes 7,7' ,7" are connected to rigid hollow plastic rods not shown in the figures, which are inserted into the respective solution or rinsing water. Advantageously, the solutions for the pretreatment processes are being pumped through stator bar 1 within a loop connected in a by pass and pumped back into the original container . The solutions have to be replaced after some time. In contrast, the rinsing water may be used only once. After each step, the tubes have to be emptied completely by operating pump 8 backwards for some time. In order to ensure an acceptable pretreatment of the inner surface of the hollow conductors copper base ma- terial samples from the pretreatment flow are captured in water chamber 11 for later inspection. Thereby a copper base material content determined by photometric measurements is indicative of a chemical clean internal surface of the hollow conductors la to If. The absence of copper oxides dissolved in the system is thereby verified. A removal rate of at least 1 microns per minute is satisfactory. Immediately after completion or the pretreatment process, the coating process is effected according to the coating flow circuit shown in figure 1 whereby the stator bar 1 firstly is filled with the chemical constitution bath 5. Chemical constitution bath 5 is pumped through coating flow lines 7,7' ,7" and stator bar 1 by exiting container 13 at outlet connection 14 and returning via coating flow line 7"' through inlet connection 15 into container 13. The inflow branch comprises the diaphragm pump 8, rotameter 9 and velocity profile homogenization tube 10 which are connected in series by means of fluid connection tubes 7,7' ,7" to the inlet 2 of stator bar 1. The outflow branch comprises fluid line 7". Sensed inflow and outflow temperatures are read at temperature indicators 21' and 22'. The required 90°C flowing temperature of the coating fluid is maintained by fluid lines 7,7* ,7" ,7"' which are insulated against heat loss or otherwise heated separately. Although the electroless coating process is started by an external battery 6 as in the known art, in the electroless plating apparatus of the present invention, A voltage of 5V is applied for about 30s resulting in a current pulse of about 1A by direct contact of cathode 12 with the flowing stream of the chemical constitution bath 5 in flowing condition through stator bar 1 and anode 13 electrode clamped at inflow connection side 2* of stator bar 1. Thereby, the metal alloy ion is carried to the inner Cu metal surface of each the hollow conductors la to Id of the stator bar 1 to be plated, from the flowing stream of said chemical constitution bath 5 through stator bar 1. The onset of nickel deposition can be seen by the formation of hydrogen bubbles arising in the outlet tube 7"' while the external source 6 is disconnected. However, and for the same purpose of promoting the start of the reactions, a steel piece can also be introduced (high concentration of iron in the chemical composition) at one of the inner surfaces (water chamber) of the stator bar, in order to establish a potential difference also between the metal copper and the iron. The inlet temperature and outlet temperature at respective water chambers 11 of stator bar 1 must be within 88-90°C and the flow temperature during the coating process should be recorded. The temperature monitoring is effected by placing first and second thermocouples 20, 21 for respectively sensing inflow and outflow temperature at said stator bar 1. The variable speed membrane or diaphragm pump 8 ensures an accurate preset amount of a coating flowing stream velocity through stator bar 1 in order to maintain the required inlet and outlet temperatures during the coating process. The membrane of pump 8 serves as a moving partition between the mechanical or hydraulic drive and the coating fluid. Control of pump 8 is done by varying speed of the drive motor or the stoke of the membrane in response to the inlet-outlet temperature differences which are sensed by thermocouples 20,21. By installing a frequency inverter connected directly to the motor which drives pump 8 of the circuit, it is possible, by alteration/variation of the frequency of the motor, to vary the flow discharge of the pump 8 and consequently the circulation of the coating solution within the circuit. In this way, the flow can be gradually reduced until, at a flow of approx. 3.8 1/min, start of the chemical reactions is observed, with appearance/visualization of intense gas bubbles (hydrogen) in the circuit. By connecting flow meter 9 in flow communication with said pump 8 and stator bar 1, the velocity of the flowing stream is easily monitored within a flow range of 0.2 to 0.4 m/sec, thereby properly adjusting the discharge of pump 8. The proper adjustment of the coating solution flowing through stator bar 1 is essential for ensuring a coating thickness as required. If the flowing velocity is too low, deposition at the far end 3 will not occur. If it is too high, coating quality is poor. Furthermore, by properly adjusting the flowing velocity, the coated thickness can be removed at any desired time. The phosphorus content control is also responsible for the quality of the coating thickness. If the phosphorus content is too high, the coating will become brittle which can cause problems during thermal variations. On the other hand a too low content will cause a poor coating quality. The required coating thickness is verified with the aid of sample tube 24 which is placed removably inside homogenization tube 10 as shown in figures 1 and 2 since the streaming velocity through single tube 24 and stator bar 1 is the same. Any desired coating thickness of the hollow conductors is thereby accurately monitored. A control and - if necessary- change of filter element of the container should be effected, as in the known art. As way of example a Degussa Nimuden type 858-AF bath is filled using membrane pump 8. The bath is heated up to 90-91°C. When 90°C are reached, the pH and the nickel-content must be measured in order to verify a pH range of 4.4 to 4.6 and a nickel content of 6+/-0.1 g/1. Preferred chemical constitution bath parameters are as follows: - pH range within 4.4 to 4.6; - bath temperature range within 90° to 91°; - nickel content within 6 +/- 5% or 6+/- 0.1 g/1 of the chemical bath; - Phosphorus content within 10 +/- 10%. Adjusted Phosphorus content within 9 -10.5% provides for an uniform and removable coating thickness. Preferred coating process parameters are as follows: Flow velocity of coating solution: 0.3-0.35 m/sec Pretreatment: 10 min. etching Bath: Degussa-type 858 Phosphorus content: 9-10.5% Coating thickness range: 15 - 50 microns Nickel coating thickness on copper surface: not less than 30 microns Coating time: 120 min Coating temperature: 86-90°C The visual examination in the accessible regions, these being the water chambers 11 at each end of stator bars 1 enable the verification of homogeneous surfaces with appearance, color and brightness characteristic of these types of Ni-P (nickel-phosphorus) coatings. The adequate deposition of self-catalytic Ni-P (nickel-phosphorus) onto the inner surfaces of the hollow conductors and water chambers in electric machines over a wide range of rates and physical sizes can be effected by the teachings of the present invention. Those versed in the art will observe that the electroless plating apparatus also enables the coating of copper made hollow conductors other than those within stator bars since copper tubes are widely used in almost every cooling circuit mainly when in presence of a fluids other than pure distilled water or humid air containing particles of salts. It is to be understood that the method and apparatus of the present invention is by no means limited to the particular installation herein disclosed and/or shown in the drawings, but also comprises any modifications or equivalents within the scope of the claims.

Claims: CLAIMS 1. METHOD for the electroless plating of a metal surface of a hollow conductor with a metal alloy contained in a chemical constitution bath comprising a pretreatment stage characterised by providing for a controlled stream velocity of flow of said chemical constitution bath through said hollow conductor in response to sensed inlet and outlet temperatures at said hollow conductor. 2. Method as in claim 1 characterised by causing to flow through said hollow conductor at least one cleaning fluid providing for a chemical clean internal surface of said hollow conductor. 3. Method as in claim 2, characterised by collecting from said cleaning fluid flowing through said hol- low conductor a base material sample which is indicative of said chemical cleaning of said internal surface. 4. Method as in claim 2 or 3, characterised by said base material sample corresponds to a removal rate of at least 1 microns per minute. 5. Method as in claim 1 characterised by causing to flow in opposite directions through said hollow conductor an amount of flowing stream of said chemical constitution bath within a closed flow circuit. 6. Method as in claim 1 characterised by inducing an electrical starting means between said flowing stream and an external portion of said hollow conductor. 7. Method as in claim 1 or 6, characterised by building up onto the internal surface of said hollow conductor a desired coating thickness of said metal alloy in response to one or a combination of said controlled flow velocity, sensed temperatures, alloy content in said constitution bath and amount of flowing stream. 8. Method as in claims 1 or 7, characterised by adjusting said flowing stream velocity through said hollow conductor in response to a temperature difference between said inlet and outlet temperatures of said hollow conduc- tor. 9. Method as in claim 1 or 6 characterised by connecting first electrode means in-line with said flowing stream and a second electrode means to one end of said hol- low conductor providing for said electrical starting means from an external source. 10. Method as in claim 1 or 7, characterised by a velocity profile homogenization means for providing a fluid filled cross section along said hollow conductor is con- nected at the inlet of said hollow conductor 11. Method as in claim 1, characterised by said flowing stream velocity ranging within 0.2 to 0.5 m/sec. 12. Method as in claim 1, characterised by said flowing stream velocity ranging within 0.3 +/- 0.35 m/sec. 13. Method as in claim 1 or 7, characterised by said pumping time for building up said desired coating thickness be at least 120 min. 14. Method as in any of claims 1, 7 or 8 characterised by a flowing stream temperature range at the inlet of said hollow conductor of 86°C to 90°C. 15. Method as in claim 1 or 13, characterised by a coating thickness range of 15 to 20 micronsns. 16. Method as in claim 1, characterised by said metal alloy comprising Ni and P and the internal surface material of said hollow conductor being Cu. 17. Method as in claim 1 or 7, characterised by maintaining said chemical constitution bath within one or the combination of a pH range within 4.4 to 4.6, bath temperature range within 90° to 91°, nickel content within 6 +/- 5% and P content within 10 +/- 10%. 18. Method as in claim 1 or 17, characterised by a nickel content of 6 +/- 0.1 g/1 within said chemical constitution bath. 19. Method as in claim 1 or 17, characterised by an adjustable P content within 9 to 10.5%. 20. Method as in claim 1 or 7, characterised by connecting for flow and electric signal communication with said hollow conductor a spaced apart tube sample 24 for providing a a simultaneous coating of both said hollow con- ductor and sample tube 24. 21. Method as in claim 1, characterised by coating a hollow conductor of length L and equivalent inner diameter IDe such that the resulting ratio L: IDe is greater than 10:1. 22. ELECTROLESS PLATING APPARATUS for depositing a metal alloy onto a metallic surface of a hollow conductor (1) with inlet (2) and outlet (3) connection sides, comprising a controllable chemical constitution bath (4) an electric starter means (6), further characterised by - a plurality of heat-insulating tubes (7,7 * ,7",7" ' ) for connecting within a flow circuit for re- circulation of said controllable chemical constitution bath (4) through said hollow conductor (1): - a pumping means (8) providing for an adjustable flowing stream velocity within said flow circuit; a flow sensor means (9) for sensing said flowing stream velocity; first and second temperature sensor means (20,21) for sensing inflow and outflow temperatures of said adjustable flowing stream velocity at inlet and outlet connection sides (2,3) of said hollow conductor; providing for a controllable coating thickness of said metal alloy onto said internal metallic surface in response to said adjusta- ble flowing stream recirculation velocity. 23. Electroless plating apparatus as in claim 22, characterised by said starter means (6) comprising an external electric source with first and second electrode means (12,13), said first electrode means (12) flooded with said flowing stream and said second electrode means (13) connectable to one connection side (2) of said hollow conductor (1) providing for a starting electric pulse. 24. Electroless plating apparatus as in claim 20, characterised by said pumping means (8) comprising a vari- able speed positive displacement flowmeter. 25. Electroless plating apparatus as in claim 20, characterised by said pumping means (8) comprising a variable speed membrane pump. 26. Electroless plating apparatus as in claim 20, characterised by comprising a flow conditioner means (10) upstream said one connection side (2) having a filled cross section (22) with through holes (23), electric connection means (25) and adapted for housing a hollow tube sample (24) within one of said through holes (23) when in use. 27. Electroless plating apparatus as in claim 20, characterised by a portable stainless steel container (19) with a variable vapor exhaust means (16) for housing said chemical constitution bath (5). 28. Hollow conductor of length (L) and an equivalent inner diameter (IDe) whereby the resulting ratio L: IDe is greater than 10:1 characterised in that the inner metal boundary surface is coated with a metal other than the base metal of said hollow conductor. 29. Hollow conductor as in claim 28 characterised by said inner boundary surface being coated by the method defined in any of claims 1 to 21. 30. Hollow conductor as in claim 28 characterised by a copper base metal and a nickel coating on the inner boundary surface thereof. 31. Hollow conductor as in any of claims 28 to 30 characterised in that it is a component of a stator bar of an electric machine. 32. Hollow conductor as in any of claims 28 to 30 characterised in that the coating thickness of the inner boundary surface ranges within 07 and 50 microns. 33. Hollow conductor as in claim 28 characterised in that the coating thickness of the inner boundary surface is preferably not less than 30 microns. 34. Hollow conductor as in any of claims 28 to 30 characterised in that it is a pipe portion of a cooling water circuit. 35. Stator bar of an electric machine characterised in comprising a plurality of hollow conduc- tors as defined in any of claims 28 to 30. 36. Stator winding arrangement of an electric machine comprising a plurality of stator bars characterised in that the cooling channels comprise hollow conductors as defined in any of claims 28 to 33.

Inventors: BECK GUENTER, GOMES DE LIMA PAULO, KNOEDLER REINHARD, REISS KARL, VESPOLI MICHELE, BECK, GUENTER, GOMES DE LIMA, PAULO, KNOEDLER, REINHARD, REISS, KARL, VESPOLI, MICHELE
Applicants: ASEA BROWN BOVERI LTDA, BECK GUENTER, GOMES DE LIMA PAULO, KNOEDLER REINHARD, REISS KARL, VESPOLI MICHELE, ASEA BROWN BOVERI LTDA., BECK, GUENTER, GOMES DE LIMA, PAULO, KNOEDLER, REINHARD, REISS, KARL, VESPOLI, MICHELE
Application year: 1996
Main classification: C23C18
IPC codes: C23C18, H02K3, H02K15