Wire tinning system
United States Patent Trattner et al. 1 Apr. 8, 1975 [5 WIRE TINNING SYSTEM 2.527405 10/1950 Toulmin, .Ir. 118/73 3.383.250 5/1968 Pierson et a]. 117/114 R [751 Imam): h Ram 3.392.055 7/1968 Martin et al. 117/114 R both of Munich Germany 3.730.758 5/1973 Laidman d 117/114 R [73] Assignee: Siemens Aktiengesellschaft, Berlin and Munich, Ger ny Primary Examiner-Mervin Stein Assistant Examiner-Douglas A. Salser [22] Filed 1974 Attorney, Agent, or Firm--Hill, Gross, Simpson, Van [21] Appl, NO; 448,496 Santen. Steadman, Chiara &amp; Simpson [30] Foreign Application Priority Data [57] ABSTRACT Mar. 29. 1973 Germany 2315775 A System timing Wire in which the Wire is drawn through a tinning bath, the tension of the wire in the 52 us. (:1 118/74; 117/47 R; 117/114 R; bath being controlled y a plurality of Wire drawing 1 g 73; 34 rollers, one of the drive rollers preceding the tinning 151 1111. c1. B05c 11/00 bath and the other following the timing hathp 53 ma r Search u 3 72 7 74 419, rate motor means are provided for driving the drawing 1 17 113 1 M R 47 34 7 34 rollers at variable speeds to thereby provide a tension on the wire between the rollers which is dependent on [56] References Ci the difference in the peripheral speeds of the two UNITED STATES PATENTS drawing rollers. Means are also provided for automati- 1,933.40l 10/1933 Ward 118/74 Cally controlling the tension on Said wre. 2.428.523 10/1947 Marshall 118/74 6 Claims, 5 Drawing Figures WIRE TINNING SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention is in the field of continuous tinning of 5 wire such as electrical conductors and is directed primarily to an electromechanical control system for adjusting the tension on the wire as it is being passed through the tinning bath.  
 2. DESCRIPTION OF THE PRIOR ART In one conventional wire tinning system, a copper wire or nickel wire is provided with a coating of a solder layer consisting of tin or a tin alloy by pulling the wire vertically upwardly through a bath containing the tin or tin mixture. At the point at which the wire emerges from the tin bath, the wire passes through an element which serves to control the coating thickness, for example, a nozzle surrounding the wire with a specifled clearance. Next, the wire leaves the solder bath through a stripping nozzle which surrounds the wire with a lateral clearance of a minimum of 0.2 millimeters.  
  In connection with the coating of steel strips or wires with molten metal, it is also known to use outlet or compression rollers mounted in the molten bath and to surround the vicinity of the point at which the strip or wire emerges from the molten metal with a casing containing a fluxing agent which dissolves oxides and serves to wet the surface level of the bath. Zinc chloride is a commonly used fluxing agent. By means ofthis technique, the bath surface is kept free from impurities in close proximity to the point at which the wire emerges from the bath. With this type of system, the outlet rollers employed for coating the wires or strips remain free from impurities.  
  In an earlier application, there is described a device in which the wire passes in a vertical direction upwardly through a solder bath and in which the outlet point of the wire in the solder bath is surrounded by a casing which is partially submerged in the solder bath and forms a protective chamber. A dispensing device conveys the flux to the bath surface and into this protective chamber. The protective chamber serves to maintain the outlet cone constant, this being the conical configuration which forms at the wire outlet point of the tin bath during the passage of the wire. This cone must be maintained in a substantially constant configuration if a uniform tin coating on the wire is to be achieved.  
  It has now been shown that the wire outlet cone which provides a uniform coating of the wire and encases the wire at its point of exit from the tin bath is dependent not only on the nature of the tin coating of the bath but also upon the kinematic behavior of the wire during its passage through the tin bath. Since the tin bath is preceded by a number of treatment stages and the wire is conducted in the tin bath across a number of guide rollers having different guidance characteristics, tension variations occur within the wire which is to be tinned. Such variations lead to transverse vibrations, particularly in the upwardly directed end of the wire in the region of the tin bath. These vibrations in turn influence the outlet cone to thereby change the position of the cone on the surface of the molten tin, resulting occasionally in a non-uniform coating.  
  In the known wire tinning systems, it is not possible to carry out an adjustment or control to achieve the desired thickness of the coating layer. These systems have stripping nozzles which are arranged at the wire outlet point directly above the tin bath but where the wire is subject to vibrations occurring transversely to the drawing direction, the wire is applied off center to the stripping nozzles and the coating layer is not uniform.  
 SUMMARY OF THE INVENTION The present invention provides a wire tinning system which insures a substantially uniform passage of the wire through the tinning section of the tin bath and also permits the thickness of the coating layer to be controlled. The wire tinning system of the present invention is particularly useful in the tinning of electrical circuit wires having a diameter of 0.25 to 1.25 millimeters. In general, the present invention provides a system which includes at least two wire drawing rollers one of which precedes the tinning bath and the second, the main drawing roller, is beyond the tinning bath in the direction of the passage of the wire. The peripheral speeds of these wire drawing rollers are adjustable and different in such a way that the wire being conducted between the drawing rollers is subjected to a tension dependent on the difference in the peripheral speeds of the rollers. The invention also includes a wire centering device under the surface of the tin bath which is posi tioned in the region of the exit point of the wire from the tin bath.  
  As a result of the new tinning system, a substantially undisturbed passage of the wire to be tinned through the molten bath is achieved. The outlet cone which is formed in the region of the exit point of the wire from the tin bath does not change its position on the surface of the tin bath during the drawing process. With the improvements of the present invention, a very uniform coating layer is obtained, the thickness of the coating layer being dependent on the wire drawing speed and also upon the temperature of the bath which itself is correlated to the drawing speed. The melt temperature is also dependent upon the material in the bath. In the case of copper wires with the above-mentioned thicknesses, the temperature of the tin bath is on the average of about 280 C at drawing speeds of 0.25 to 1.25 meters per second. Depending on the selected speed, the coating thickness may run from about 4 to 25 microns.  
  The two wire drawing rollers are provided with an individual drive motor, the drive motor operating the main drawing roller located beyond the tinning bath rotating somewhat faster than the drive motor driving the secondary drawing roller located before the bath. Therefore, the wire passes across the secondary drawing roller and/or across the main drawing roller with a certain amount of slip so that the tension on the wire is a function of the known static friction of the wire on the drawing rollers, and of the variable speed difference between the two drawing rollers. The drive motors for both the secondary drawing roller and the main drawing roller are provided with a reduction gear system and are preferably shunt DC motors, the speeds of which may be controlled by the initial electrical load. The nominal speeds of the two drawing rollers and thus the speed at which the wire is drawn through the bath may be adjusted by means of a common wire drawing control unit. The desired wire drawing tension may be fed to a difference indicator. This difference indicator is connected to the wire drawing control unit and, for example, prior to the motor driving the main drawing roller. The difference indicator increases the speed of the motor which drives the main drawing roller. for example, by reducing its initial load. Slight fluctuations in speed between the two motors driving the drawing rollers or fluctuations in load in the stations preceding the tinning bath can result in variation in the set wire ten sion. The wire tension is adjusted by a measuring roller which is mounted on a doublearmed lever and which is under the influence ofa compensating load acting on the other end of the lever. This double-armed lever cooperates with a measured value converter which converts the mechanical movement ofthe lever into an analog electrical value. This electrical value is fed to a wire tension regulator which cooperates with a diffen ence indicator and which increases the speed of the main drawing roller in the case of a reduced wire ten sion and reduces the speed of the main drawing roller in the case of an increased wire tension.  
  In accordance with a preferred embodiment of the present invention. the main drawing roller is mounted prior to the takeup reel and has its own drive means. The winding reel which takes up its tinned wire also has its own drive means which preferably consists of a series motor whose torque is considerably lower than the slipping moment of the wire across the main wire draw ing roller and likewise that of the motor which operates this roller.  
  The tinning bath contains a guide roller which reverses the direction of the wire passing through the bath. Depending upon the magnitude of the wire tension and upon the characteristics of the guide roller, transverse vibrations ofa relatively high amplitude may occur and affect the outlet cone through which the wire emerges. Transverse vibrations of this type can be avoided by means of a wire centering device which conducts the tinned wire, when it has emerged from the tin bath. centrally into an after heating system. This sys tem may be in the form ofa tube which is held centrally in a protective chamber located in close proximity to the wires point of exit from the tin bath. The wire cen tering device may be in the form of a ring. a U-shaped element or a cross pin. It is essential only that it should intercept the vibrational amplitudes occurring trans verse to the direction of pull of the wire within the molten tin.  
  The tinning system of the present invention is also highly suitable for fire tinning of. for example, nickel alloy wires and may easily be adapted to the particular operating conditions.  
  The pretreatment of the wire to be coated is essential for the production ofa uniform coating thickness. This pretreatment can be carried out thermally or chemically. It is particularly advantageous in the case of copper wires that the wire be first conducted through a degreasing bath, then through a rinsing bath and subsequently through a pickling bath. In order to remove residues of the pickling bath, the wire is again rinsed and drawn through a flux bath. The wire pretreated in this way finally passes to the tinning bath through which it is conducted with a uniform wire tension and without vibration.  
 BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and advantages of the invention will be readily apparent from the following description of certain preferred embodiments thereof, taken in conjunction with the accompanying drawings,  
 although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosure, and in which:  
  FIG. 1 is an overall view ofa tinning system employing the improvements of the present invention;  
  FIG. 2 illustrates the wire [inning section of the system:  
  FIG. 3 is a schematic wiring diagram for the system: and  
  FIGS. 4 and 5 are elevational views of a guide roller assembly used in the tinning bath.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS A copper or nickel wire 2 which is to be tinned is drawn off from a feed reel 1 in the direction of the arrow 3. The wire first passes to a pretreatment station 6 which is composed of a degreasing bath 4, a first rins ing bath 5, a pickling bath 7 and finally a second rinsing bath 5. The wire is pulled through these baths by means of rollers 8 by a secondary drawing roller 9 which is driven by a motor 10 shown in FIG. 2. The wire then passes into a flux bath II in which it is coated with a flux in preparation for the succeeding tinning process. By means of further guide rollers 12 and 12&#39;, the wire then passes into the tin bath 13.  
  As shown in FIG. 2 the tin bath 13 consists of a com tainer 15 which is equipped with an electric heater unit 14 and contains a bath of molten tin. In this container there is mounted a guide roller 16 which deflects the downwardly directed end of the wire and reverses its direction. The wire is pulled out of the tin bath by means of the main drawing roller 17 which is driven by an adjustable speed motor 18. A measuring roller 19 is rotatably mounted on a double-armed lever 20,20. A portion 20 of the double-armed lever remote from the measuring roller 19 is equipped with a compensating weight 19&#39;. The double-armed lever is connected to an electrical measured value converter 21 which converts the movement of the lever into an analog electrical value. The measured value converter is preferably in the form of a potentiometer. The drive of the motors l0 and I8 takes place by means of a wire drawing control unit 22 having a control knob 23 for presetting the desired speeds of the motors and thus setting the peripheral speeds of the secondary drawing roller 19 and the main roller 17. The two motors are provided with reduction gears 10&#39; and [8, respectively. In the position A of the control knob 23. the motors are switched off and in position B. the pull-through speed of the wire,  
 is millimeters per second. The two motors 10 and 18 are of the same type and are connected in parallel to the wire drawing control unit. They are each provided with an equal electrical initial load so that they rotate in synchronism with respect to their nominal speed. The secondary drawing roller 9 is operated at a constant peripheral speed as set by means of the control knob 23, whereas the main drawing roller 17 is set to rotate at a predetermined speed slightly higher than the speed of the secondary drawing roller. The wire tension may be adjusted depending upon the difference between the peripheral speed and the slipping moments of the wire across the drawing rollers. This is effected by a speed control device 24 which has a control knob 25 for setting the speed difference. The control knob controls the energization for the drive motor 18 of the main drawing roller. Any fluctuations in the wire tension still occurring within the end of the wire between the two drawing rollers are established by the measuring roller 19 in combination with the double-armed levers 20,20, and the compensating weight 19. This difference is fed as an analog signal to the wire tension control device 24 which is connected to the speed control device 24. The adjustment is carried out by an additional alteration in the initial load of the motor.  
  FIG. 3 is a wiring diagram of the wire drawing control unit. The motor which operates the secondary drawing roller and the motor 18 which operates the main drawing roller are provided with a common initial load 40 which may be adjusted by means of an arm 23. The operation of the arm 23 causes a change in speed of both motors. The motor 10 also has another constant initial load 41 and the motor 18 has two adjustable initial loads 21 and 42, the magnitude of the initial load 41 corresponding to the maximum initial loads 21 and 42. The initial load 42 may be reduced by means of an arm 25 of the speed control device 24 and the initial load 21 by means of movement of the measuringroller 19 as in the event of a reducing wire tension. In accordance with the position of the sliding components 21&#39; and 42, the motor 18 which drives the main drawing roller 17 will rotate faster than the motor 10 which drives the secondary drawing roller 9. In place of the speed control unit shown schematically in FIG. 3, it is also possible to employ other types of control circuits, in numerous forms, for the adjustment and control of the motor speeds.  
  The wire tension control device, in combination with a wire centering device 33, shown in H6. 4, fulfills the requirement that the outlet cone 26 which encases the wire as it leaves the tin bath should not experience any local change during the drawing of the wire through the tin bath. To avoid surface disturbances within the tin bath and to provide a tension-free surface of the tin bath in the region of the outlet cone 26, there is provided a tube 27. This tube is located in close proximity to the wire outlet point in the tin bath and forms a protective chamber 28. A supply container 29 provides a flux which reduces the surface tension, such as zinc chloride, and the flux is conducted into this protective chamber. The quantity of dispensed flux is controlled by means of a dispensing valve 30 which is operated by a timer (not shown).  
  The tinned wire is taken up by a takeup reel 32 operated by a motor 31, this motor preferably being a series type motor. lts maximum torque is lower than the slip ping moment of the wire across the main drawing roller 17 and less than the torque of the motor 18 which drives the main drawing roller 17 so that the takeup reel 32 does not transmit any, or only slight forces to the main drawing roller 17. The double-armed lever 20,20 which carries the measuring roller 19, together with the feed container 29 with dispensing valve 30 and also the container for the tin bath 13 are secured to a common support 34 of a frame 34&#39; which is shown in broken lines. The motor 18 which drives the main drawing roller 17 of the motor 10 which drives the secondary drawing roller 9 are also connected to the frame 34 by means of flanges 35. The support is provided with guide rollers 37 and 38 on a cross bar 36. Since the operative elements are secured on a common frame,  
 there is no possibility of displacement during the drawing process.  
  As shown particularly in FIGS. 4 and 5 and also in FIG. 2, an adjustable bar 39 projects into the tin bath container 15. The tube 27 and the wire centering device 33 are fixed to this bar. At the lower end, the adjustable bar is bifurcated and a guide roller 16 is mounted on pointed studs 46 extending inwardly from the bifurcated arms 44 and 45. The adjustable bar is mounted to be displaceable in a carrier arm 47 which is connected to the support 34 of the frame 34 and may be adjusted in respect to the immersion depth of the guide roller 16. The immersion depth which will be employed is dependent upon the pull-through speed of the wire. The tube 27 which encases the wire exit point and which forms a protective chamber 28 is displaceable on a holder 51 which is positionable in an adjustable position along the slot 48 by means of screws 49. The wire centering device 33 which is held on a transverse bar 50 is correspondingly adjustable. As a result of this arrangement, it is possible at a given immersion depth of the guide roller 16 to align the wire centering device located within the molten tin and also the protective chamber 28 in accordance with the level of the tin bath. Normally, it is advantageous to make this set- -ting such that the wire centering device lies about 3 centimeters below the level of the tin bath and the tube projects approximately I centimeter into the tin bath.  
  It will be understood that various modifications can be made to the described embodiments without departing from the scope of the present invention.  
 We claim as our invention:  
  1. A wire tinning system comprising a wire feed means for delivering wire sequentially through a cleaning station, a flux applying station and a tinning bath, a guide wheel mounted in said tinning bath, a takeup reel for taking up the tinned wire, at least two wire drawing rollers, one of said wire drawing rollers preceding said tinning bath and the other following said tinning bath, and separate motor means for driving said drawing rollers at variable speeds to thereby provide a tension on said wire between said rollers which is dependent on the difference in the peripheral speeds of the two drawing rollers.  
  2. The system of claim 1 in which said separate motor means have a common wire drawing control unit.  
  3. The system of claim 1 which includes a measuring roller engaging said wire, a double-armed lever carrying said measuring roller and means generating an analog signal in response to the movement of said lever to thereby control the tension on said wire.  
  4. The system of claim 1 which includes a wire centering device within said tinning bath, and a tube adjustably positionable with respect to the surface of said tinning bath, said tube providing a protective chamber for the wire as it exits from said bath.  
  5. The system of claim 4 in which said wire centering device is adjustable relative to the surface of said tinning bath.  
  6. The system of claim 1 in which said cleaning station includes a degreasing bath, a pickling bath, a first rinsing bath after said degreasing bath and a second rinsing bath after said pickling bath.