SOLDERING APPARATUS

Abstract: The present invention provides soldering apparatus wherein a rotatable shaft (3) which penetrates the surface of molten solder is surrounded by a substantially stationary tube (1) which also penetrates the solder suface, in which a substantially airtight seal (4a) is provided between the tube (1) and the shaft (3) above the solder surface. The formation of toxic dust is thus substantially reduced or almost eliminated. In accordance with a particular embodiment of the present inven­ tion, it is applied to a pump for solder, comprising a screw bladed impellor (2) mounted on the shaft (3), the blade (2) ex­ tending more than 360° around the drive shaft (3). It is preferred to pump solder through a nozzle, by pumping the solder up into the tube to form a constant head device, and feeding solder from the tube, through a conduit to the nozzle.

Description: The present invention relates to soldering apparatus. Such apparatus typically comprises a bath of molten solder from which solder is pumped through a nozzle to form a stream or wave of solder through which components to be soldered or tinned are passed, or into which they are dipped. A skin of oxidised solder will form on the exposed upper surface of the molten solder and this needs to be cleaned off at intervals. Such soldering apparatus may also comprise a pump or stirrer having a rotating shaft which passes through the surface of the solder bath. It has been found that a fine dust, believed to be oxidised solder, tends to accumulate on the surface adjacent the rotating shaft, probably due to shear at the surface. This dust may become airborne, and so represents a potential hazard to operatives when the machine is being cleaned. It has been found that dispersal of this dust may be controlled by surrounding the rotating shaft with a stationary cylinder or tube where it passes through the solder surface. However, a large amount of dust still accumulates inside the tube and needs to be cleaned away periodically. US-A-4437605 discloses soldering apparatus having a pump for pumping solder through a nozzle. The pump has an upright housing which extends through the surface of the solder to isolate the pump shaft from the solder. A small amount of dross is formed about the shaft at the base of the housing and this is allowed to accumulate in the housing until it spills over onto the surrounding surface of the solder bath. JP-A-5994570 shows a pump shaft extending through the upper wall of a housing which is filled with solder. DE-A-1923689 shows a pump shaft having an impeller blade surrounded by a housing which extends above the solder surface. A baffle near the top of the housing inhibits upward movement of the solder, which is pumped through an aperture in the side of the housing. The present invention provides soldering apparatus including a solder bath, a solder pump arranged to be submersed in the solder bath, a generally upright drive shaft for the pump which extends above the surface of the solder, a tube surrounding the drive shaft and having an aperture in communication with a nozzle through which solder is fed by the pump is use, characterized by an airtight seal between the tube and the drive shaft positioned above the surface of the solder in the tube to provide an airtight cavity above the solder in the tube. It has been found that by incorporating an airtight seal between the shaft and the tube above the solder surface, the formation of toxic dust is substantially reduced or almost eliminated. The seal may be formed by a high temperature grease-packed bearing, but as an alternative, a high temperature polytetrafluoroethylene or other plastics seal may be used. In particular, a single or double lip seal, with the lip(s) formed of polytetrafluorethylene or other plastics material, may be utilised to seal against the rotatable shaft. Preferably the tube extends downwards to surround the pump. Very preferably a baffle is provided on the shaft, above the outlet aperture, and below the normal operating height of the solder in the tube. The baffle forms a barrier to solder being pumped up the tube. Hence if the pump speed is increased to increase or pulse the flow of solder through the nozzle, or the flow fluctuates for some other reason such as a momentary blockage, the baffle will limit the rise of solder up the tube, thus allowing greater pump speeds and pressures whilst protecting any bearings or seals at the top of the tube. Hence whilst the tube may act as a constant head device, there is also an action pumping the solder through the nozzle. Preferably the blade is a screw blade, extending 360° or more around the shaft, preferably for two revolutions, 720°. Advantageously, the blade is a close fit in the tube, to a tolerance of a few thousandths of an inch (0.025 mm) in 30mm. Preferably, a lower end of the tube remains immersed in the solder bath, the solder covering at least a lower part of the blade, and preferably all of it. In operation, solder is pumped through a nozzle, by pumping the solder up into the tube to form a constant head device, and feeding solder from the tube, at a fixed level in the tube, through a conduit to the nozzle. The flow of solder through the nozzle may then be kept substantially constant even if the nozzle and tube are moved vertically, the head of solder relative to the nozzle remaining substantially constant. Preferably a valve is provided between the pump and the nozzle to control the flow of solder through the nozzle while maintaining a constant pump speed. Preferably the valve operates by allowing pumped solder to escape into the solder bath, preferably below the surface thereof. The invention will be further described by way of example with reference to the accompanying drawings in which: Figure 1 is a cross-section through a soldering apparatus according to the invention; Figure 2 is a perspective view illustrating a modification of the embodiment of Figure 1; and Figure 3 is a cross-section along the line III - III of Figure 2 showing a valve in position. Figure 1 of the drawings shows a first embodiment of the invention having a circular cross-section tube 1 housing a blade 2 mounted on a driven shaft 3. The lower end of the tube 1 is immersed in a molten solder 9 contained in a bath 10. The shaft 3 is in two parts, a lower part 3a carrying the blade 2 and an upper part 3b. The lower shaft part 3a carries a socket 3c for the upper part 3a and is attached thereto by a lockscrew 3d. The shaft 3 is mounted in bearings 4, 5 at the top and bottom of the tube. Upper bearing 4 is a high temperature grease-packed ball bearing which forms a partially airtight seal to minimise oxidation of the solder within the tube 1. The seal provided by the bearing 4 alone may not be sufficient to keep oxilation to an acceptable level, and therefore two oppositely facing lip seals 4a mounted in collars 4b are also provided. More than two seals, for example 4, may be provided to enhance the effective lifetime of the sealing arrangement. A plain lower bearing 5 supports the shaft 3 and is apertured or spider-mounted to allow solder to flow into the tube 1. The blade 2 is a helical, screw blade and extends for 720° around the shaft beginning and ending in a sharp edge to penetrate the solder and deliver it cleanly at the top of the blade. The blade 2 is a close fit in the tube 1. An aperture 6 is formed in the side of the tube 1 just at and above the top edge of the blade 2. The aperture connects with a socket or union 7 welded to the tube for receiving a conduit 15 to deliver solder to a nozzle. Union 7 has a vertical threaded aperture 14 connected to a bore 15 which is contiguous with side aperture 6. A conduit 15 is swivably mounted on the union 7 by means of a tapering boss 16 which is screwed into aperture 14. A similar boss 17, but relatively upside down, is mounted at the other end of the conduit 15 and connected to a nozzle 18. Such an arrangement is described in EP-0139455. Nozzle 18 may have an elongate aperture for forming a wave or wide stream of solder, or a single or a plurality of tubes forming small streams for soldering difficult. access terminals. A cicular baffle 19 is welded to the shaft 3. The baffle is located below the normal operating height H of the solder in the tube 1. Shaft 3 is rotated by an electric motor using a chain and sprocket arrangement as is known in the art. The motor is mounted on a plate 19 which supports cylinder 1, and hence the conduit and nozzle 15, 18. Plate 19 is supported by a vertical beam 20 which is raised and lowered by a rack and pinion arrangement (not shown) as is known in the art. The shaft 3 is rotated at a constant speed to produce a head of solder in the tube 1 above the aperture 6. The heal relative to the nozzle 18 may thus be maintained substantially constant, even with vertical movement of the lower end of the tube 1 relative to the solder bath as beam 20 is moved to raise the nozzle 18 during a soldering operation, at least the lower end of the tube remaining below the surface of the solder bath. Union 7 may comprise a plate like member 20 ( Figure 2 ) which extends around the tube 1 and has several outlets for connection to conduits 15. Outlets not in use are plugged. Nozzles 18 may be attached directly to the union 7 if desired. Plate 20 may be welded to the tube 1, or cast integrally with the tube, and vertical and radial apertures 21,22 drilled through the plate and adjacent tube wall (see Figure 3). Those apertures not in use may be plugged, or covered by welded on plates. This arrangement also allows a conduit to be mounted below the plate to reduce the required height between the bottom of the tube and the top of the nozzle 18. Figure 3 shows a valve arrangement 23 which may be positioned in aperture 21, controlling the flow of solder through the corresponding aperture 22. Preferably the valve is used in one such port and a conduit 15 connected to another port, hence the valve 23 allows pumped solder to escape into the bath, below the surface, to control the rate of flow of solder through the nozzle 18. Valve 23 comprises an internally threaded cylinder 24, of reduced diameter at its lower end 25 which is received in and projects through aperture 21. The bottom portion of lower end 25 is threaded and a nut 26 secures the valve on the plate 20. Bottom portion 25 has a through aperture 27 which is aligned with aperture 21. A threaded stud 28 is screwed into cylinder 24 and is screwed up or down to open or close the aperture 27, to decrease or increase the flow of solder through the conduit 15 to nozzle 18. It will be apparent that the invention is applicable to soldering apparatus in which the nozzle and/or pump are held stationary. Various modifications may be made within the scope of the invention, as set forth in the appended claims.

Claims: 1. Soldering apparatus including a solder bath (10), a solder pump (2) arranged to be submersed in the solder bath, a generally upright drive shaft (3b) for the pump (2) which extends above the surface of the solder, a tube (1) surrounding the drive shaft (3b) and having an aperture (6) in communication with a nozzle (18) through which solder is fed by the pump in use, characterized by an airtight seal between the tube (1) and the drive shaft (3b) positioned above the surface of the solder in the tube (1) to provide an airtight cavity above the solder in the tube. 2. Soldering apparatus according to claim 1, characterized in that the tube (1) extends downwards to surround the pump (2). 3. Soldering apparatus according to claim 1 or 2, characterized in that the seal comprises one or more lip seals (4a, 4b). 4. Soldering apparatus according to any one of claims 1 to 3, characterized by a baffle (19) mounted on the shaft (3b) above the aperture (6) and below of the surface of the solder in the tube (1). 5. Soldering apparatus according to any one of claims 1 to 4, characterized by an adjustable flow diverting valve arrangement (23) arranged to control the flow of solder to the nozzle (18).

Inventors: CINIGLIO, ALEXANDER JAMES
Applicants: DOLPHIN MACHINERY LIMITED
Application year: 1986
Main classification: B23K1
IPC codes: B23K3, B23K1, H05K3