GB2206178A

GB2206178A - Impact extruded roll

Info

Publication number: GB2206178A
Application number: GB08715011A
Authority: GB
Inventors: Dhirendra Damji
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1987-06-26
Filing date: 1987-06-26
Publication date: 1988-12-29
Anticipated expiration: 2007-06-26
Also published as: GB8715011D0; GB2206178B

Abstract

A process for manufacturing a developer roll (24) for a magnetic brush development apparatus, comprising impact extruding a hollow cylindrical tube (40), open at one end, and substantially closed at its other end, said substantially closed end forming an end cap (41) of the roll. The tube is formed of a non-magnetic metal or alloy, and its external cylindrical wall is formed with a series of axially extending ridges and valleys (43). <IMAGE>

Description

Impact Extruded Developer Roll This invention relates to a process for manufacturing a developer roll for a magnetic brush development apparatus, and to a developer roll produced by the process.

A magnetic brush development apparatus is commonly used for the development of electrostatic latent images in an electrostatographic imaging apparatus, and typically comprises a hollow cylindrical roll of non-magnetic material, mounted for rotation around a multi-pole magnet arrangement. An example of such a magnetic brush developer roll is described in US-A-4 608 737. Developer material containing magnetically attractable particles is transported by the rotating cylindrical roll in to contact with an electostatic latent image, formed for example on a photoconductive member.

A develper roll in the form of an aluminium alloy tube having a textured surface is described in GB-B-2 126 925. Developer rolls of this kind may be produced by, for example, flow forming, but the roll so produced has a wall at least 1.5 mm thick. This means that the magnets inside the roll are spaced by at least this distance from the magnetic developer particles being transported by the roll, so the magnets have to be relatively powerful.

Furthermore, the basic tube has to be fitted with two end caps to enable it to be rotated about its axis.

It is desirable to reduce the cost of the development apparatus of xerographic copying machines, especially in the case of a machine using a xerographic cassette which includes the development apparatus and which is discarded at the end of its useful iife.

It is an object of the present invention to provide a developer roll which needs less process steps in its manufacture, which needs less material and less individual parts, which has a thinner wall so that less powerful magnets can be used.

The invention accordingly provides a process for manufacturing a developer roll for a magnetic brush development apparatus comprising impact extruding a hollow cylindrical tube, open at one end and substantially closed at the other end, said substantially closed end forming an end cap of the roll.

The invention also provides a developer roll produced by this process.

A process for manufacturing a developer roll and a developer roll produced by the process will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic cross section of a xerographic copier incorporating a developer roll in accordance with the invention; Figure 2 is a longitudinal cross sectional view of a developer roll in accordance with the invention, and Figure 3 is an enlarged section taken on the line A-A of Figure 2.

Referring first to Figure 1, there is shown schematically a xerographic copying machine incorporating the present invention. The machine includes an endless flexible photoreceptor belt 1 mounted for rotation (in the clockwise direction as shown in Figure 1) about support rollers la and ib to carry the photosensitive imaging surface of the belt 1 sequentially through a series of xerographic processing stations, namely a charging station 2, an imaging station 3, a development station 4, a transfer station 5, and a cleaning station 6.

The charging station 2 comprises a corotron 2a which deposits a uniform electrostatic charge on the photoreceptor belt 1.

An original document D to be reproduced is positioned on a platen 13 and is illuminated in known manner a narrow strip at a time by a light source comprising a tungsten halogen lamp 14. Light from the lamp Is concentrated by an elliptical reflector 15 to cast a narrow strip of light on to the side of the original document D facing the platen 13.

Document D thus exposed is imaged on to the photoreceptor 1 via a system of mirrors M1 to M6 and a focussing lens 18. The optical image selectively discharges the photoreceptor in image configuration, whereby an electrostatic latent image of the original document is laid down on the belt surface at imaging station 3. In order to copy the whole original document the lamp 14, the reflector 15, and mirror M1 are mounted on a full rate carriage (not shown) which travels laterally at a given speed directly below the platen and thereby scans the whole document. The mirrors M2 and M3 are mounted on another carriage (not shown) which travels laterally at half the speed of the full rate carriage in order to maintain the optical path length constant.The photoreceptor 1 is also in motion whereby the image is laid down strip by strip to reproduce the whole of the original document as an image on the photoreceptor.

At the development station 4, a magnetic brush developer system 20 develops the electrostatic latent image into visible form. Here, toner is dispensed from a hopper (not shown) into developer housing 23 which contains a two-component developer mixture comprising a magnetically attractable carrier and the toner, which is deposited on the charged areas of belt 1 by a developer roller 24 which is described in more detail below.

The developed image is transferred at transfer station 5 from the belt to a sheet of copy paper which is delivered into contact with the belt in synchronous relation to the image from a paper supply system 25 in which a stack of paper copy sheets 26 is stored on a tray 27.

The top sheet of the stack in the tray is brought, as required, into feeding engagement with a top sheet separator/feeder 28. Sheet feeder 28 feeds the top copy sheet of the stack towards the photoreceptor around a 1800 path via two sets of nip roller pairs 29 and 30. The path followed by the copy sheets is denoted by a broken line in Figure 1. At the transfer station 5 a transfer corotron 7 provides an electric field to assist in the transfer of the toner particles to the copy sheet.

The copy sheet bearing the developed image is then stripped from the belt 1 and subsequently conveyed to a fusing station 10 which comprises a heated roller fuser. The image is fixed to the copy sheet by the heat and pressure in the nip between the two rollers 10a and 10b of the fuser. The final copy is fed by the fuser rollers into catch tray 32 via two further nip roller pairs 31a and 31b.

After transfer of the developed image from the belt some toner particles usually remain on the surface of the belt, and these are removed at the cleaning station 6 by a doctor blade 34 which scrapes residual toner from the belt. The toner particles thus removed fall into a receptacle 35 below. Also, any electrostatic charges remaining on the belt are d.ischarged by exposure to an erase lamp 11 which provides an even distribution of light across the photoreceptor surface. The photoreceptor is then ready to be charged again by the charging corotron 2a as the first step in the next copy cycle.

The photoreceptor belt 1, the charge corotron 2a, the developer system 20, the transfer corotron 7, and the cleaning station 6, may all be incorporated in a process unit 12 adapted to be removably mounted in the main assembly 100 of the xerographic copier.

Referring now to Figure 2, the developer roll 24 comprises a cylindrical tubular part 40 and an integral end cap 41 at one end. The other end is open, as shown, and receives a press fitted end cap to enable the roll 24 to be mounted for rotation about its axis. End cap 41 is provided with a suitable boss 42 for supporting the developer roll on a drive spindie (not shown). A multi-pole magnetic member (not shown) of generally cylindrical shape is mounted within the developer roll.

The outside surface of the roll 24 is provided with a series of axially extending ridges and valleys 43, for example as shown in enlarged form in Figure 3. The thickness t of the walls of the tubular part 40 is less than 1 mm, and is preferably about 0.7 mm, measured from the interior suface of the wall to the bottom of a valley of the exterior suface. The tops of the ridges are approximately 0.24 mm above the bottoms of the valleys.

The developer roll 24 is manufactured by impact extrusion, the internal and exterior surfaces of the die portion and the ram portion of the impact extrusion tool being shaped to form the features of the roll described with reference to Figure 2. Thus the impact tool ram has smooth side walls, whereas the internal surface of the die member is ribbed to provide the ridges and valleys 43. The end cap 41 and boss 42 are formed by an appropriate combination of shapes on the die and ram. In order to produce the roll, a suitable disc-shaped pellet of an aluminium alloy is placed in the die portion of the tool, and is impacted by the ram portion.

The alloy is extruded around the plunger to form, In one operation, both the end cap 41 and the ribbed tubular portion 40.

Impact extrusion is a well-known technique, and its use in the formation of generally cup-shaped members is described, for example, in an article entitled "Can formation by impact extrusion" by S Birch in Sheet Metal Industries, June 1978, p714. Extruded tubular members having a shaped end cap at their 'closed' end are described in an articie entitled "Impact extrusion of collapsible tubes" by J Bennett, in Metallurgia, July 1978, p346.

The developer roll so produced uses less material than previous developer rolls, needs only one additional end cap (not shown) to close the open end of the tube, and has thinner walls than previous developer rolls, enabling the use of less powerful, and hence less expensive, magnets inside it. No separate process is needed to form the ribbed exterior of the roll. In use of the roll, lower start-up torques can be used because of the reduction in the movement of inertia of the roll compared with known rolls.

Claims

Claims:

1. Process for manufacturing a developer roll for a magnetic brush development apparatus, comprising impact extruding a hollow cylindrical tube, open at one end, and substantially closed at its other end, said substantially closed end forming an end cap of the roll.

2. A developer roll produced by the process of claim 1.

3. The developer roll of claim 2, wherein the tube is formed of a non-magnetic metal or alloy.

4. The developer roll of claim 2 or claim 3, wherein the external cylindrical wall of the tube is formed with a series of axially extending ridges and valleys.

5. The developer roll of any one of claims 2 to 4, wherein the external cylindrical wall of the tube is less than 1 mm thick.

6. The developer roll of claim 5 wherein the external cylindrical wall of the tube is approximately 0.7 mm thick.