447,824

PATENT SPECIFICATION

Application Date: Oct. 26, 1934. No. 34772/35.

(Divided out of No. 447,754.)

Complete Specification Left: July 23, 1935.

Complete Specification Accepted: May 26, 1936.

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PROVISIONAL SPECIFICATION

Improvements in or relating to the manufacture of Insulated Electrically Conductive Screens, more particularly for use in Cathode Ray Tubes

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 improvements in insulated electrical conductors.

In co-pending Application No. 22724/34 there is described television transmitting apparatus comprising a cathode ray tube having disposed within its envelope a photo-electrically active mosaic screen. The mosaic screen comprises a metal plate, which henceforth will be called a "grid", pierced with a multiplicity of closely spaced small holes; this grid is coated all over with a thin layer of insulating material and the holes are filled up with metal rivets which pass right through the grid; the surfaces of the rivets on one side of the grid are coated, with photo-electrically active material and on the other side are coated with a non-oxidising metal.

A mosaic screen is also know which comprises a grid in the form of a wire mesh, the mesh being covered with insulating material and the holes in the covered mesh being filled with photo-electrically active rivets of the kind described above.

During the operation of transmitting apparatus of this kind an optical image of the object to be transmitted is projected upon the photo-electrically active side of the mosaic screen, the opposite side is scanned with a cathode ray and picture signals are generated in an external circuit associated with the grid.

Difficulties have been experienced in the construction of mosaic screens of this kind arising out of the fact that the distance between the centres of adjacent holes in the grid must be very small. In the first place it is difficult to coat the grid with insulating material without filling up the holes and this difficulty is enhanced by the fact that, since the insulating material has subsequently to withstand being baked in vacuo and also must be a very good insulator, the insulating materials available are very few. Glass or vitreous enamel has been found suitable, but even with these materials, it is extremely difficult to avoid filling up the holes. Secondly if a grid in the form of wire gauze is used, the weaving of the wires gives a rough final surface which is detrimental to the operation of the mosaic screen.

It an object of the present invention to provide a simple method of preparing an improved mosaic screen of the kind described above.

According to the present invention there is provided a grid of crossed wires, the wires being coated with insulating material and being held together by adhesion between the insulating material covering the wires.

The coated wires may be crossed in any directions and are not interwoven to any large extent. Preferably two sets of wires are used, the wires of any one set being substantially parallel, the wires of one set being perpendicular to those of the other set and the wires of one set lying wholly on one side of the wires of the other set. A small amount of weaving of the wires may be utilised, however, in order to hold the wires together during the construction of the grid.

According to a further feature of the present invention there is provided a method of coating wire with insulating material wherein the wire to be coated is passed through 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.

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

A wire of about 0.05 mm, 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 0.15 mm. 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.

In order to form an insulated grid with the wire so coated, the latter is cut up into equal lengths. The lengths of wire so obtained are preferably graded according to diameter, and a number of lengths of substantially equal diameters are cut off to make the "north and south" wires of a grid. These are then arranged side by side on a metal plate. A further set of wires forming the "east and west" wires are then laid on top of them at right angles, and another plate is laid on top. Alternatively the east and west sires may be attached to the top plate and then placed in position. The combined pile is then heated and pressed until the glass insulation is firmly welded at the intersections.

If the insulated grid so formed is to be used in a mosaic screen the coated wires should preferably be pressed together with sufficient force to make the resultant surfaces flat, as this facilitates the subsequent operation of forming photo-electrically active rivets in the holes in the grid without neighbouring rivets short-circuiting.

In an alternative method of forming an insulated grid, each set of coated wires is laid in grooves in a specially prepared plate. Such a plate has half round grooves of the required radius and pitch formed in it. For instance, to form a 10-cm. x 10-cm. grid with 0.25-mm. pitch, the plate may be about 14 cm. x 14 cm. large, and has one set of 400 grooves extended across it in one direction and a second set of 400 grooves extended across it preferably at right angles to the first set. The outer 2 cm. at the edges is grooved in one direction only, the corners are plain and the centre is grooved in two directions. Such a plate may be prepared from an original wax master which is suitably grooved and plated, and from the master so obtained many duplicate plates may subsequently be made by further plating, the whole process following the technique well known for producing gramophone record matrices. The final plates may be of thin copper, nickel faced, and two such plates are used. Before use, location holes are put in the corners of the plates so that later they may be clamped together with the grooves in one plate exactly registering with the grooves in the other. The glass clad wires are then cut off about 15-cm. long and the 400 north-and-south wires are laid in one set of grooves in one plate. These wires are held in position by cement placed near the edges of the plate, a suitable cement being wax. The second plate is similarly charged with400 east-and-west wires placed in the other grooves. The second plate is then placed on top of the first with the wires in contact and at right angles, and the plates are located so that the grooves register. The plates are then mounted between thick metal plates heated and pressed so that the glass welds. The pressing is preferably continued until the two plates are in contact, so that the lower surface of the upper wires is as near as possible in contact with the lower plate. The resultant grid will then be flat, the north-and-south glass surfaces being almost, or quite co-incident with the east-and-west glass surfaces. In order that this result may be obtained, the initial diameter of the glass-clad wires must be less than the diameter of the grooves, in order to give space to receive the excess glass pressed out of the "cross-overs" where two glass-clad wires will be pressed into the space of one. After cooling the thin mould plates may be removed or dissolved away in acid if they refuse to separate from the glass. Since the resultant grid is nearly or quite flat, rivets may be inserted in the holes (by electro-plating for example) without contact being made between adjacent rivets.

The drawing of the wire in vacuum is not a necessity, but it is advantageous as it prevents air bubbles breaking the insulation when pressing, gives a firmer grip between glass and wire, and for subsequent vacuum work prevents air bubble in the glass covered wire spoiling the vacuum. Similarly, the wires may be insulated by other means such as "sputtering" with glass from a hot flame.

A satisfactory grid may be formed of tungsten wire covered with a coating of glass known and sold under the Trade mark name "Pyrex".

Although the sizes given are suitable for making a mosaic, widely different sizes may be employed, and the ratios of the wire diameter, glass diameter and pitch may be varied widely.

The coated wires may, if desired, be woven to a small extent in order to assist the process of assembling. For instance, the outer wires may be woven by passing above and below the wires of the other set. Such weaving gives slight support prior to pressing. On the other hand, such weaving does not contribute materially to the ultimate strength of the grid, which is derived from the insulation fixing the crosses of the wires.

When finished, the wires of the grid may be stripped of insulation at their ends and connected, as by welding to a suitable frame, which may be in the form of a metal plate having a square hole to receive the grid.

Dated this 4th day of December, 1935.

REDDIE & GROSE,

Agents for the Applicants,

6, Breamís Buildings, London, E.C.4.

COMPLETE SPECIFICATION

Improvements in or relating to the manufacture of Insulated Electrically Conductive Screens, more particularly for use in Cathode Ray Tubes

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 improvements in the manufacture of electrically conductive screens having a multiplicity of closely spaced small holes (which screens will hereafter be called "grids") and coated with electrically insulating material, more particularly for use in cathode ray tubes.

In Patent Specification No. 446,661 there is described television transmitting apparatus comprising a cathode ray tube having disposed within its envelope a photo-electrically active mosaic screen. The mosaic screen comprises a grid in the form of a perforated metal plate coated all over with a thin layer of insulating material; the holes therein are filled with metal rivets which pass right through the grid; the surfaces of the rivets on one side of the grid are coated with photo-electrically active material.

A mosaic screen is also know which comprises a grid in the form of a wire mesh, the mesh being covered with insulating material and the holes in the covered mesh being filled with photo-electrically active rivets of the kind described above.

During the operation of transmitting apparatus of this kind an optical image of the object to be transmitted is projected upon the photo-electrically active side of the mosaic screen, the opposite side is scanned with a cathode ray and picture signals are generated in an external circuit associated with the grid.

Difficulties have been experienced in the construction of mosaic screens of this kind arising out of the fact that the distance between the centres of adjacent holes in the grid must be very small. In the first place it is difficult to coat the grid with insulating material without filling up the holes and this difficulty is enhanced by the fact that, since the insulating material has subsequently to withstand being baked in vacuo and also must be a very good insulator, the insulating materials available are very few. Glass or vitreous enamel has been found suitable, but even with these materials it is extremely difficult to avoid filling the holes. Secondly, if a grid in the form of wire gauze is used, the weaving of the wires gives a rough final surface which is detrimental to the operation of the mosaic screen.

It is an object of the present invention an insulated grid is formed of crossed wires, the wires being coated with electrically insulating vitreous material and being held together by fused joints between the insulating coverings of the wires at the points where they cross.

Preferably two sets of wires are used, each set consisting of substantially parallel lengths of wire, the wires of one set being disposed transversely to those of the other set and the wires of one set lying wholly on one side of the wires of the other set.

In the preferred method of constructing such a grid, the wires required to lie in one direction are placed in grooves in a plate, the wires required to lie in the other direction are placed in grooves in another plate, the two plates are juxtaposed face to face in such a manner that the wires on one plate lie transversely of those on the other plate, the assembly is heated and the wires on one plate are secure to those on the other plate by the fusing together of their insulating vitreous coverings.

Where the finished insulated grid is required to be as flat as possible, each plate is provided with a second set of grooves disposed transversely of the set in which the wires are placed, the plates, after being loaded with the wires, are so juxtaposed that the empty grooves of each plate register with the loaded grooves of the opposite plate, and the plates are thereafter heated and forced together.

In another method of construction a number of lengths of glass-insulated wire are arranged side by side on a metal plate. A further set of wires are then laid on top of them at right angles, and another plate is laid on top of the crossed wires. The combine pile is then heated and pressed until the glass insulation is firmly welded at the intersections.

If the insulated grid so formed is to be used in a mosaic screen the coated wires should preferably be pressed together with sufficient force to make the resultant surfaces substantially flat, as this facilitates the subsequent operation of forming photo-electrically active rivets in the holes in the grid.

The preferred way of carrying out the invention will be described with reference to the accompanying diagrammatic drawings, in which

Fig. 1 is a sectional elevation of parts of two grooved plates, loaded with insulated wires, and nearly juxtaposed,

Fig. 2 is an elevation of a part of a finished grid, with some of the insulation broken away,

Fig. 3 is a section one the line 5-5 of Fig. 2, and

Fig. 4 is an elevation, to a smaller scale, of a finished grid.

In the following description it will be assumed that the insulated wire is coated with glass. A method of coating wire with insulating material is described in our co-pending application No. 30817/34 (Serial No. 447,754), and the glass coated wire used for the preparation of grids in the manner to be described is preferably made by the method set forth in detail in the specification of that application.

Before the wire is used for making wire mesh grids it is cut into the lengths needed for the grids, and graded, by means of a dial micrometer, into two sizes: 0.07 to 0.09 mm., and 0.09 to 0.11 mm., larger and smaller sizes being rejected. The diameter of the wire is taken at 2 cm. intervals. The wire may be inspected under the microscope for faults, and tests may be made on the adhesion of the covering. It is found however, that faulty adhesion is rare.

Referring to the drawings, the two sets of coated wires are laid respectively in grooves in specially prepared plates 26 and 27 (Fig. 1). Each plate has part-round grooves of the required radius and pitch formed in it. For instance, to form a 10-cm. by 10-cm. grid with 0.25-mm. pitch, the plate may be about 14cm. by 14 cm. large and has one set of 400 grooves such as 33a and 33b (Fig. 1) extended across it in one direction and a second set of 400 grooves, such as 34a and 34b extended across it transversely of - preferably at right angles to - the first set. The outer 2 cm. at the edges is grooved in one direction only and the corners are plain, that is to say the plate bears grooves which correspond to the position of the wires in the finished grid. The elevation of the finished insulted grid shown in Fig. 4 indicates the position of the grooves on the plates. Such a plate may be prepared from an original wax master which is suitably grooved and plated and from the master so obtained many duplicate plates may subsequently be made by further plating, the whole process following the technique well know for producing gramophone record matrices. The final plates 26 and 27 may be of thin copper, nickel faced. Before use, location holes are put in the corners of the two plates so that later they may be clamped together with the grooves in one plate exactly registering with the grooves in the other. The glass clad wires are cut into 15 cm. lengths and the 400 north-and-south wires 28a are laid in the grooves 33a in the plate 26. These wires are held in position by cement placed near the edges of the plane, a suitable cement being wax. The plate 27 is similarly charged with 400 east-and-west wires 28b placed in the grooves 34b. The two plates are then juxtaposed face to face with the wires in contact and at right angles, and the plates are located so that the grooves register. The plates are then mounted between thick metal plates which are heated and pressed together so that the glass fuses to form fused joints at the points where the wires cross. The pressing is preferably continued until the two plates re in contact, so that the insulated grid assumes the form shown in Figs. 2 and 3.

In this way there is produced a substantially flat insulated grid, the north-and-south glass surfaces being almost, or quite co-incident with the east-and-west glass surfaces. In order that this result may be obtained, the initial radius of the glass-clad wires must be less than the radius of the grooves, in order to give space to receive the excess glass pressed out of the intersection points, where two glass-clad wires will be pressed into the space of one. After cooling the thin mould plates may be stripped off or dissolved away in acid if they refuse to separate from the glass. Since the resultant grid is nearly or quite flat, rivets can be inserted in the holes (by electro-plating for example) without contact being made between adjacent rivets.

When finished, the wires of the grid shown in Fig. 4 may be stripped of insulation at their ends and connected, for instance by welding, to a suitable frame, which may be in the form of a metal plate having a square hold to receive the grid.

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 way we claim is:-

  1. An insulated grid formed of crossed wires, the wires being coated with electrically insulating vitreous material and being held together by fused joints between the insulating coverings of said wires at the points where they cross.
  2. A grid as claimed in claim 1 wherein two sets of wires are used, each set consisting of substantially parallel lengths of wires, the wires of one set being disposed transversely to those of the other set, and the wires of one set lying wholly on one side of the wires of the other set.
  3. A method of constructing an insulated grid having the features claimed in claim 1 or 2, wherein the wires required to lie in one direction are placed in grooves in a plate, the wires required to lie in the other direction are placed in grooves in another plate by the fusing together of their insulating vitreous coverings.
  4. A method as claimed in claim 3, wherein each of said plates is provided with a second set of grooves disposed transversely of the set in which the wires are placed, said plates, after being loaded with said wires, are so juxtaposed that the empty grooves of each plate register with the loaded grooves of the opposite plate, and said plates are thereafter heated and forced together.
  5. The method of constructing and insulated grid substantially as herein described with reference to the accompanying drawings.
  6. The improved insulated grids substantially as herein described or as shown in Figs. 2 to 4 of the accompanying drawings.

Dated this 4th day of December, 1935.

REDDIE & GROSE,

Agents for the applicants,

6, Breamís Buildings, London, E.C.4.

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