447,754

PATENT SPECIFICATION

Application Date: Oct. 26, 1934. No. 30817/34.

Complete Specification Left: July, 23. 1935.

Complete Specification Accepted: May 26, 1936.

-------------------------

PROVISIONAL SPECIFICATION

Improvements in or relating to Insulated Electrical Conductors

We, ALAN DOWER BLUMLEIN, a British Subject, of 7, Courtfield Gardens, Ealing, London, W.13, and HERBERT EDWARD HOLMAN, a British Subject, of 4, Fairway Avenue, Garden City, Yiewsley, Middlesex, do hereby declare the nature of this invention to be as follows:-

The present invention relates to improvement in insulated electrical conductors.

It is an object of the present invention to provide a simple method of producing insulated electrical conductors.

According to the present invention to provide a method of coating wire with insulating material wherein the wire to be coated is passed though a tube of insulating material and the tube and wire together drawn out.

Preferably the tube is evacuated before the drawing is effected so that the tube, when drawn, collapses on to the wire.

This method of coating wires with insulating material is clearly not limited in scope by the use to which the coated wire is subsequently put.

The present invention may be carried out in the following way:-

A wire of about 0.05mm. diameter is inserted in a glass tube. The glass tube is heated and is drawn out into a fine capillary tube containing the wire, the diameter of the final glass coated wire being about 0.15mm. The capillary tube is preferably drawn out from an evacuated glass tube, so as to prevent air being trapped between the wire and the glass. Thus the glass tube to be drawn out may be sealed at one end to an evacuated glass vessel in which is mounted a light spool carrying the wire. The free end of the wire is sealed into the free end of the glass tube. The glass tube is heated and as it softens and collapses, is drawn out with the wire inside it. The drawing may be done on a draw bench having a moving carriage which draws out the wire, and by starting with a comparatively long glass tube, a number of lengths may be drawn out before it is necessary to seal in a new glass tube and evacuate again.

Dated this 26th day of October, 1934.

REDDIE & GROSE,

Agents for the Applicants,

6, Breamís Buildings, London, E.C.4.

COMPLETE SPECIFICATION

Improvements in or relating to Insulated Electrical Condensers

We, ALAN DOWER BLUMLEIN, a British Subject, of 7, Courtfield Gardens, Ealing, London, W.13, and HERBERT EDWARD HOLMAN, a British Subject, of 4, Fairway Avenue, Garden City, Yiewsley, Middlesex, do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement:-

The present invention relates to improvement in insulated electrical conductors.

It is an object of the present invention to provide a simple method of producing insulated wire conductors, which is particularly suitable for use with wires of very small diameter.

According to the present invention there is provided a method of coating wire with electrically insulating material capable of being drawn, comprising the steps of surrounding the wire to be coated with a tube of the insulating material, and thereafter evacuating and drawing said tube.

The tube may be evacuated after drawing, and it may be redrawn while it is in an evacuated condition.

According to the present invention in a further aspect, a method of electrically insulating wire with glass comprises the steps of passing a part of a length of wire through a glass tube, sealing the wire to one end of said tube, heating a part of the tube until it becomes plastic, drawing the tube, evacuating the drawn tube, and reheating the redrawing the evacuated tube.

These methods of coating wires with insulating material are clearly not limited in scope by the use to which the coated wire is subsequently put.

The invention will be described with reference to the accompanying diagrammatic drawings, in which

Fig. 1 is a side elevation of a draw bench, and

Fig. 2 is a side elevation of a part of the draw bench of Fig. 1, with an additional element.

In Fig. 1 there is shown a draw bench 1 having an endless belt 4 which passes over pulleys 2 and 3, the pulley 3 being driven by a motor 5 through a clutch mechanism housed in the pulley 3 whereby the belt may be started and stopped by the operator, or stopped automatically at a predetermined point, by control means not shown.

On the left hand end of the bench (as viewed in Fig. 1 is fixed a cylindrical glass chamber 6 having a neck portion 7. A cover 8 makes an airtight closure over the base of the chamber 6. A side tube 9 connects the chamber 6 with a vacuum pump 10 and a manometer 11 is also provided.

The belt 4 is provided with a stud 18 which can engage loosely with a slot in a wooden lath 17 which lies on the belt 4.

The operation of covering a tungsten wire with glass under the registered trade mark "Pyrex" is as follows. A spool 12 of the wire, which in this example is 0.052 mm. in diameter, is rotatably mounted in the left hand end of the chamber 6 on a clip 121. A rubber stopper 13, which is so bored as to be able to receive as a tight fit a piece of the glass tubing 14 is about 5 cm. From the spool 12, and its right hand end projects some distance from the stopper. A piece of stout copper wire is passed down the tube and the tungsten wire 28 is hooked on to it, thus enabling the tungsten wire to be drawn through the tube. The tungsten wire is then sealed into the right hand end of the tube by means of a suitable burner, for instance a Marshall burner 19, having finely adjustable needle valves for regulating the supply of air and gas. The sealed end of the tube 14, while still plastic, is fixed to the lath 17 by means of a clip 16.

The burner is now shifted along the tube 14 slightly away from the sealed end, and the tube is heated until it becomes soft; an indication of the right temperature may be had from the degree of incandescence of the tungsten wire 28 within the tube.

When the tube is hot enough, the burner is removed, the clutch in the pulley 3 is engaged and the belt 4 carried the lath 17 to the right hand end of the bench, and leaves it in a trough 20 provided for this purpose. The clutch is then automatically released.

As the lath moves to the right, it draws out the glass tube into a fine capillary, having inside it the tungsten wire which has unwound from the spool 12. The diameter of the drawn glass is about 0.2 to 0.4mm.

Although the wire is completely covered with glass, this covering is loose on the wire, owing to the film of air which adheres to the wire during the drawing process. The diameter of the glass covering is also uneven.

The glass covered wire is now examined and the end is once more sealed if broken. The vacuum pump 16 is now started to exhaust the chamber 6, and to remove air from inside the glass covering of the wire. The sealed end of the covered wire is fixed to a winding drum 21 mounted on the draw-bench 1. The winding drum is rotted by any suitable means such for example as by a handle 22. The wire is moved clear of the belt 4, for example by displacing the drum 21 and the chamber 6 transversely.

When the chamber 6 has been sufficiently evacuated as indicated by the manometer 11, the wire is redrawn in a manner illustrated in Fig. 2. A Marshall burner 23 is arranged to heat a nickel trough 24. The whole is fitted with a hand 25, so that it may be held in the hand and passed along the glass covered wire, thus heating it locally.

As the glass, here denoted by 14a, becomes heated and softened, it collapses on to the tungsten wire owing to the external atmospheric pressure. The winding drum is rotated, and the glass is extended, the thickness of the glass covering decreasing. Tungsten wire unwinds from the spool 12 and advances through the tube 14a after the firs drawing. The tension required to draw out the glass covering is governed by its thickness, because a thick wall will extend lengthwise more readily than a thin once, since with a thick tube a smaller change in molecular arrangement is required for a given extension than in the case of a thin tube. Hence if the torque on the drum is constant, the drawing will cause a greater reduction of the thick parts than of the thin parts of the covering, thus largely removing variations in thickness which arose during the preliminary drawing. The external diameter of the glass is of the order of 0.08 to 0.11 mm. The stresses wet up by this extension also assist the collapsing of the glass on the tungsten wire.

The redrawn wire, denoted by 14b, most of which is now coiled on the drum, is cut at its junction with the parent tube 14. The tube 14 is resealed at the right hand end, and pulled out from the neck 7 to replace the used-up portion; the process is now repeated.

If desired, the apparatus on the bench may be duplicated, and while one chamber is being evacuated another length of wire may be drawn.

The controls for the clutch mechanism are preferably taken to the left hand end of the bench so that one operator is able to control the whole process.

The covering process may be carried out with various sizes of wire, and various thicknesses of covering may be given by suitably choosing the size of the tube 14 and the extent of drawing. It is found however that as the thickness of covering increases, the variations in size of the finished insulted wire become greater.

The whole process of drawing may be carried out in a vacuum, in which case the stage of redrawing may be dispensed with, when the unevenness of the coating of the wire is not objectionable.

Insulated wires prepared according to the present invention are particularly suitable for use in the manufacture of insulated grids, which may be used in cathode ray tubes, as described and claimed in co-pending Application No. 34772/35 (Serial No. 447,824).

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is:-

  1. A method of preparing insulated electrical conductors in which a wire is coated with electrically insulating material capable of being drawn, said method comprising the steps of surrounding a part of the wire to be coated with a tube of the insulating material and thereafter evacuating and drawing said tube.
  2. A method as claimed in claim 1 wherein said tube is evacuated after drawing.
  3. A method as claimed in claim 2 wherein said tube is redrawn while it is in an evacuated condition.
  4. A method of electrically insulating wire with glass, comprising the steps of passing a part of a length of wire though a glass tube, sealing the wire into one end of said tube, heating a part of the tube until it becomes plastic, drawing the tube, evacuating the drawn tub, and reheating and redrawing the evacuated tube.
  5. Insulated electrical conductors produced by the method claimed in any of the preceding claims.
  6. The method of coating electrical conductors with insulating material substantially as herein described with reference to Figs. 1 and 2 of the accompanying drawings.

Dated this 23rd day of July, 1935.

REDDIE & GROSE,

Agents for the Applicants

6, Breamís Buildings, London, E.C.4.

---------------------------

Leamington Spa: Printed for His Majestyís Stationery Office, by the Courier Press. Ė 1936.