In one known apparatus for making such handles, extruded clay is injected into a heated die at high pressure. The impact further plasticizes the clay, so that it assumes the shape of the die, and the outer skin of the handle is set by the heat. The die is then opened for the handle to be removed. However, the clay retains a'memory'of its extruded shape, and once out of the die will try to return to it, so that the handle becomes misshapen. Further it can be difficult to predict the effect of the impact for different clay bodies, so that sometimes the clay may not fill the die, or may contain voids. Either of these makes the handle unusable.

According to the present invention, apparatus for making clay handles comprises a die movable between closed and open positions, the die in the closed position having a cavity defining the shape of the handle, with the cavity having an inlet end and an outlet end, means for injecting clay under pressure into the inlet end of the cavity and pressure control means at the outlet end of the cavity on which the clay is adapted to act, the pressure control means being operative to control the pressure of the clay in the cavity and to shut off the clay injection means when the pressure of the clay in the cavity reaches a threshold value.

Controlling the pressure of the clay in the die cavity so that it reaches a predetermined threshold value ensures that the cavity is full of clay at a sufficient level of plasticization. This means that there will be no voids, and thus reduces the number of unusable handles.

The pressure control means preferably comprises a piston working in a cylinder, the piston being acted on at one end by the clay and at the other end being subject to a fluid pressure in the cylinder, controlled by a regulator. Thus, when the clay injected into the cavity reaches the outlet end it acts on the piston in opposition to the fluid pressure in the cylinder. That fluid pressure is controlled by the regulator, and in turn controls the pressure build up of the clay in the cavity. The piston moves from a rest position and continues to move until the pressure control means sends a signal operative to shut off the clay injection means. The regulator may control the fluid pressure in the cylinder to return the piston to the rest position on completion of handle formation.

The regulator preferably comprises a flow regulator which controls the fluid pressure in the cylinder by controlling fluid flow out of it as the piston is moved by the clay. The cylinder is preferably a pneumatic cylinder, connected to a source of air under pressure. Pressurised air can then be introduced into the cylinder to return the piston to its rest position, on completion of handle formation.

On completion of handle formation the die is opened and the handle is separated from the clay inlet and outlet, and removed, preferably by a robotic arm, so that it can undergo further manufacturing processes.

Normally, the clay that has acted on the piston of the pressure control means forms a pellet, separate 3from the handle, and located in the cylinder of the pressure control means. The pellet is expelled from the cylinder by the piston as it returns to its rest position.

The clay injection means preferably comprises a fluid-pressure-operated piston and cylinder injection assembly, with the injection piston acting on

the clay to inject it into the die cavity. The injection assembly may be pneumatic or hydraulic, with its operation controlled by the pressure control means. Conveniently, a clay processing means is provided between the injection piston and the die, to break up and then re-form the clay under pressure. It has been found that this overcomes the problem with the'memory'of the clay, so that the finished handle does not become misshapen.

Preferably, the clay processing means comprises at least one perforated shredder plate, followed by a tapering nozzle. The shredder plate or plates break the clay into separate streams, which then re-form into one stream in the tapering nozzle. There are preferably two perforated shredder plates, each having holes of different sizes. The holes may be circular or of any other appropriate shape.

Conveniently, the injection piston acts on a charge of clay, whose volume is sufficient to sustain a number of machine cycles.

According to a second aspect of the present invention, a method of making a clay handle in a die movable between closed and open positions, the die in the closed position having a cavity defining the shape of the handle, comprises the steps of injecting clay under pressure into an inlet end of the cavity in the closed die, allowing the clay at an outlet end of the cavity to act on a pressure control means, operating the pressure control means to control the pressure of the clay in the cavity, stopping injection of clay to the inlet end when the pressure of the clay in the cavity reaches a threshold value, opening the die and removing the handle.

Where the pressure control means comprises a piston working in a cylinder, the step of operating the pressure control means comprises allowing the clay at the outlet end to act on one end of the piston in opposition to the pressure in the cylinder acting on the other end of the piston, regulating the pressure in the cylinder to control movement of the piston, and thus the pressure of the clay in the cavity.

The step of stopping the injection of clay to the inlet end is preferably performed by a signal from the pressure control means when the piston reaches a given position.

The step of injecting the clay may include passing the clay through clay processing means to break up and re-form the clay under pressure.

An embodiment of the invention is illustrated, by way of example only, in the accompanying drawings in which: Figure 1 is a diagrammatic longitudinal section through apparatus for making clay handles; and Figure 2 is a diagrammatic section on a larger scale of part of Figure 1.

The apparatus shown in the drawings for making clay handles comprises a die 1 movable between open and closed positions, and in the closed position having a cavity 2 defining the shape of the handle. The cavity 2 has an inlet end 3 and an outlet end 4. Clay is injected under pressure into the inlet end 3 by clay injection means 5 acting on a clay charge 6, and clay at the outlet end 4 acts on pressure control means 7, which is

operative to control the pressure of the clay in the cavity 2 and to shut off the clay injection means when that pressure reaches a threshold value.

The die 1 is of two-part construction (only one part being shown in the drawings; the other part being a mirror image). Each part of the die 1 comprises a metal plate 8 attached to a backplate 9 slidable on a pair of rods 10,11 to open and close the die. The backplates 9 are moved by a fluid-pressure-operated means (not shown), which normally clamp the die 1 in the closed position, to define the cavity 2.

The inlet end 3 of the cavity 2 is fed from the clay injection means 5, which comprises a cylinder 12 for receiving the cylindrical clay charge 6, acted on by a piston 13. At the forward end of the cylinder 12 there are two axially-spaced perforated shredder plates 14,15. Each plate 14,15 has circular holes 16 to allow passage of the clay. The first plate 14 has larger holes than the second plate 15. Although the holes 16 are circular, it will be appreciated that they could be of any other appropriate shape.

The front end of the cylinder 12 has a tapering nozzle 17 terminating in an outlet 18 the same size as the inlet end 3 of the cavity 2. The plates 14,15 act to break up the clay into several streams which are re- formed under pressure into a single stream by the nozzle 17, so that these parts form a clay processing means.

The cylinder 12 has an opening 19 for inserting the clay charge 6. The piston 13 is of stepped outline, having a first part 20 of larger diameter working in the cylinder 12, a second part 21 of smaller diameter and a third part 22 of larger diameter working in a second cylinder 23. The third part 22 and the second cylinder 23 form a fluid power drive piston- and-cylinder assembly.

The cylinder 23 is divided by the piston part 22 into two chambers 24,25, each having a respective port 26,27 connected via a respective solenoid-operated valve 28,29 to a source of fluid pressure 30.

Each valve 28,29 is operative to connect the respective chamber 24,25 to the pressure source 30, or to atmosphere, or in a neutral position to neither, in order to maintain the pressure in the chamber. The piston 13 can therefore be controlled as required.

The outlet end 4 of the cavity 2 is connected to the pressure control means 7. This comprises a piston 31 working in a pneumatic cylinder 32, with a single chamber 33. The chamber 33 has an inlet port 34 connected to a source of pneumatic pressure 35 through an inlet valve (not shown).

The chamber 33 also has an exhaust port 36 connected to atmosphere through a flow regulator 37. In the initial position shown in Figure 2, there is a predetermined pressure in the chamber 33, with the connection to the pressure source 35 and the flow regulator 37 both being closed. In operation, the piston 31 is pushed into the cylinder 32 by the clay from the outlet end 4, and the rate of pressure increase in the chamber 33 and thus the rate of movement of the piston 31 is controlled by operation of the flow regulator 37. When the piston 31 reaches the end of its stroke, there will be a predetermined pressure in the chamber 33, and thus the clay in the cavity 2 will also be at a predetermined threshold pressure. At the end of the piston stroke, the piston 31 operates a switch 38, which sends a signal to the clay injection means 5 to hold the pressure in the chamber 25. As explained in more detail below, the piston 31 is returned to its initial position by pressurising the chamber 33 from the pressure source 35.

The method of making clay handles using the apparatus shown in the drawings is as follows. With the pistons 13,31 in the initial positions

shown in the drawings the die 1 is closed and clamped, and the die plates 8 heated to an appropriate temperature. A cylindrical charge 6 of clay is prepared with suitable lubricant, and is then inserted into the cylinder 12 via the opening 19. The charge 6 is of sufficient size to satisfy a number of machine cycles. The valve 29 is operated to pressurise the chamber 25, to advance the piston 13, which presses the clay through the plates 14,15 and into the nozzle 17. The lubricants assist in the homogenisation process of the re-forming of the clay. The clay leaves the outlet 18 under pressure, and enters the cavity 2 at the inlet end 3.

The clay passes through the cavity 2 in the heated die, and comes out at the outlet end 4, where it acts on the piston 31 of the pressure control means 7. The clay pushes the piston 31 into the cylinder 32, and its rate of movement and the rate of pressure increase in the chamber 33 is controlled by operation of the flow regulator 37. At the end of the stroke of the piston 31 there is a predetermined pressure in the chamber 33 and therefore a predetermined pressure of the clay in the cylinder 32 acting on the piston 31, and of the clay in the cavity 2. This is chosen to ensure that the cavity 2 is filled by the clay, and that there are no voids in the clay. At the end of its stroke the piston 31 operates the switch 8, sending a signal to the clay injection means 5 to switch the valve 29 to the neutral position to hold the pressure in the chamber 25. This stops the piston 13, so that no more clay leaves the outlet 18.

The die 1 is then opened, leaving the handle in place. Because the die 1 is heated, the handle does not stick to it, and the outer surface of the handle is set by the heat. The handle is then separated from the inlet and outlet and removed, preferably by a robotic arm (not shown), and taken for further manufacturing steps. The clay that has been through the

cavity 2 and ends up in the cylinder 32 forms a pellet. This is removed from the cylinder 32 as the piston 31 is returned to its initial position, by pressurising the chamber 33 by connecting it to the pressure source 35.

The die 1 can then be closed again, and the chamber 25 connected to the pressure source 30, to advance the piston 13 again to make another handle in the same way. This continues until the charge 6 is used up. The piston 13 is then returned to its initial position by exhausting the chamber 25, and pressurising the chamber 24.

If further charges are required for continuous operation, they are inserted into the cylinder 12, and the process repeated.

Controlling the pressure of the clay within the cavity 2 ensures that the handles have consistent properties. Thus, once the apparatus is set up with the appropriate threshold pressure for a given type of clay body and die, the handles will be made consistently. Further, it has been found that pressing the clay through the shredder plates 14, 15 and then into the tapering nozzle 17, which breaks up and then re-forms the clay, overcomes the problem of the distortion of the clay following its removal from the die.

It will be appreciated that in a modification (not shown) a single charge 6 could feed more than one die, so that several handles can be made simultaneously.