GB2044986A

GB2044986A - Fluorescent lamp contact pins

Info

Publication number: GB2044986A
Application number: GB8003037A
Authority: GB
Original assignee: LATHAM Manufacturing CO Ltd
Current assignee: LATHAM Manufacturing CO Ltd
Priority date: 1979-03-20
Filing date: 1980-01-29
Publication date: 1980-10-22

Abstract

A method of assembling the tubular contact pins 20 to the conductor wires 12, 14 of a fluorescent lamp tube 10 uses tubular contact pins which are pre-coated with solder internally, and provided with flux, so that after the assembly step soldered joints between the wires and pins can be made merely by application of heat. Figure 4, not shown, illustrates a typical assembly prior to the application of heat. <IMAGE>

Description

SPECIFICATION Improvements relating to fluorescent lamp tubes This invention relates to the manufacture of fluorescent lamp tubes. Such tubes have contacts which consist of single strands of very thin wire and these have to be soldered to contact pins which are tubular and usually made as pressings. The conventional technique for this is to mount the pins in an end cap, assemble the end cap to the tube so that the wires are received in the pins, cement the end cap to the tube, and then lower the tube so that the tips of the pins enter a molten solder bath. Whilst almost if not all other operations in the manufacture of these tubes are effected by automatic machinery, this operation is manual.

It is known from British Patent 1244954 to make an electrical contact terminal from strip rolled into tubular form, and constructed to provide a spring tongue so that when a conductor lead is pushed into the terminal the tongue is deflected and the lead gripped between an interior wall and the tongue.

That wall is provided with a solder coating in the coarse of manufacture of the terminal, and hence heat applied to the terminal can solder the lead to said wall. In addition, a heat shrinkable sleeve surrounds the terminal so that as the heat is applied to effect the soldering the sleeve shrinks to crimp the terminal about the lead.It is doubtful if the terminal of this Patent could be made small enough to use in conventional fluorescent tube constructions where the external diameter of the pins is less than one tenth of an inch, but in any event this construction would not be suitable for the fluorescent tube contacts because the wires are so flimsy, they would not be able to deflect the spring tongue but would buckle, and because the standard fluorescent tube fitting requires an exposed metal contact pin, it would not be possible to use the heat shrink sleeve, which inevitably would be made of an insulating material.

In accordance with the invention a method of assembling a fluorescent lamp tube having flimsy wires projecting from the tube ends comprises providing tubular contact pins assembled to an end cap and mounting the cap on the tube so that the wires are received in the pins, and is characterised in that the pins are lined with flux coated solder prior to said assembly, and have been swaged to provide a hole slightly larger than the wire diameter, and subsequently applying heat to sweat the wires to the pins.

It will be noted that the holes are to be only slightly largerthan the wires. This is important to provide smooth feed-in of wires on assembly and helps to avoid dry joints. Typically the wires are 0.020 inches diameter and the hole measures 0.025 inches diameter.

There are at least two alternatives for providing the solder. Firstly the contacts may be made from blanks pressed out of solder coated strip, or alternativelytwo separate ribbons of metal, one of brass and one of solder may be fed together to a swaging machine so as to form laminated pins where the solder lies inside the brass but is not attached.

The flux may be a solvent dissolved fluX which is deposited on the pins buy a dipping operation, and centrifuging used to remove and evapprate surplus solvent. At that stage the pins have flux coating internally and externally, and this can be a hard resin like coating. The external coating is then removed in a vibratory mass tumbling operation without this affecting the internal coating.

The swaging operation may reduce the overall diameter of the pin and increase the thickness of the metal, including the thickness of the solder. An increase in thickness of the solder qf possibly five times is possible, and the swaging also has the effect of closing the seam so that subsequently, when heat is applied, solder does not leakthrough the seam but flows to complete the joint between the wire and the pin.

Figures 1 to 3 of the accompanying drawings show the conventional arrangement in use at the present time, wherein Figure 1 is a fragementary perspective view showing the end of a fluorescent tube and a cap and pin assembly about to be assembled to the same; Figure 2 is an enlarged scale fragmentary sectional elevation; and Figure 3 is a further enlarged scale perspective view showing one of the contact pins.

Figures 4 and 5 relate to the present invention, wherein Figure 4 corresponds to Figure 2 but showing the present invention in use; and Figure 5 is a further enlarged sectional view on the line 5-5 of Figure 4.

Referring to the drawings and particularly Figures 1 to 3, the tube 10 has projecting flimsy wires 12 and 14to be received in contact pins 20 which are assembled to an insulating material panei 18 held in an end cap 16. As mentioned, the conventional method is to dip the assembly as seen in Figure 2 into a solder bath so that the solder flows to complete the join between the wire 12 or 14 and the pin 20.

Turning now to Figures 4 and 5 the pin 20 is provided with a complete layer or shell of solder 34 on its interior face, this having been provided by pressing rolling and swaging the pin from a solder coated sheet, or making the same from a sheet of brass and a sheet of solder in contact for example.

The solder is internally coated with a layer of flux 36.

The clearance between the wire 12 or 14 and the smallest diameter bore of the pin is small so as to encourage bridging of the solder when heat is applied. The bridging may lead to local voids as illustrated in Figure 5, but this is unimportant. The gap in the wall of the tube as seen in Figure 5 has been exaggerated for the purposes of illustration, but again is bridged by the solder in the heating step.

Figure 4 shows the brass, the solder and the flux as being substantially equal in thickness, but it will be appreciated that in practice there will be substantial difference in thickness.

The heating step may be effected by induction heating, conduction from a heated body, or by a small flame for example. In any of these possibilities, the step may be automated and for example involve axial travel of the assembly in a horizontal plane into abutment with an end stop which comprises the induction heater or the heated body, or which is located closely adjacent to the heat source, and subsequent movement from the heating station, for example laterally from the stop to the next stage in manufacture.

Claims

1. A method of assembling a fluorescent lamp tube having flimsy wires projecting from the tube ends comprises providing tubular contact pins assembled to an end cap and mounting the cap on the tube so that the wires are received in the pins, characterised in that the pins are lined with flux coated solder prior to said assembly, and have been swaged to provide a hole slightly larger than the wire diameter, and subsequently applying heat to sweat the wires to the pins.

2. A method as claimed in Claim 1 characterised in that the pins are made from solder coated strip.

3. A method as claimed in Claim 1 characterised in that the pins are made from sheet brass and sheet solder so that the solder lining is not attached to the pin priorto the application of heat.

4. A method as claimed in any preceding claim wherein the flux is applied by dipping and is subsequently removed from the exterior of the pins.

5. A method as claimed in any preceding claim where the heat is applied by induction heating.

6. A method as claimed in any of Claims 1 to 4 wherein the heat is applied by conduction from a heated body.

7. A method as claimed in any of Claims 1 to 4 wherein the heat is applied by a flame.

8. A method of assembling and soldering the contact pins of a fluorescent lamp tube substantially as herein described with reference to Figures 4 and 5 of the accompanying drawings.