Typically, apparatus which has parts needing to be cooled, such as the power supply of the apparatus, uses a fan to blow air onto the power supply to cool the power supply, particularly the diodes or thyristors of the power supply.

However, in order for the fan to work, it requires an inlet and an outlet, which in effect means that dirt and dust can get into the apparatus. The dirt and dust can cause the fan to seize and the system to consequently overheat.

The present invention therefore provides an improved cooling system.

SUMMARY OF THE INVENTION According to the present invention there is provided a cooling system for apparatus, which apparatus uses compressed air or induced air flow during its normal operation, the cooling system comprising: at least one heat exchange member in thermal connection with a part of the apparatus to be cooled, the at least one heat exchange member having a passage therein through which air can travel ; and an auxiliary air guide for diverting the air through the passage in the at least one heat exchange member before diverting the air back to the existing piping or tubing of the apparatus, so that the air can subsequently be used for the normal operation of the apparatus.

Preferably, a plurality of heat exchange members are in thermal connection with a plurality of parts of the apparatus to be cooled.

The auxiliary air guide may further divert the air from one heat exchange member to the next before diverting the air back to the existing piping or tubing of the apparatus.

The parts of the apparatus to be cooled may be diodes or thyristors which form part of a diode rectification bridge.

The apparatus may be an arc spraying device.

Preferably, the auxiliary air guide is made from a material which is not electrically conductive.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a part of the cooling system of the present invention; Figure 2 illustrates one of the heat exchange members of the cooling system illustrated in Figure 1; Figure 3 is a schematic illustration of the electrical circuit of the system of Figure 1; and Figure 4 is a schematic illustration of the system of Figure 1.

DESCRIPTION OF AN EMBODIMENT Referring to Figure 1, the prototype of the present invention was implemented to cool the power supply for an arc spray apparatus.

However, it will be appreciated that the present invention could equally be used to cool part of any apparatus which uses a compressed or induced air flow during its normal operation.

The power supply of the apparatus to which the prototype cooling system of the present invention is applied is a 21 kVA three phase transformer system for powering an arc spray gun.

In order to produce an output of 50 volts at 300 amps for the arc, a six diode full wave rectification bridge is used. Alternatively, a variable voltage thyristor system may be used in place of the diodes. It will be appreciated that in such a setup, the diodes or thyristors would get very hot if they were not cooled (typically greater than 200°C).

Each diode 10 is in thermal connection with a heat exchange member in the form of an aluminium block 12. It will be appreciated that any other good conducting metal could be used, for example, copper.

The diodes 10 are connected to aluminium blocks 12 by means of a screw threaded stud 22.

As can be more clearly seen in Figure 3, each pair of diodes 10 are connected to one of the three phases of the transformer and each one of the diodes 10 is connected to either the positive or the negative bar of an output DC bus system 14.

Each of the aluminium blocks 12 has a passage 20 therein through which air can travel via an auxiliary air guide in the form of pipes 16. The passage 20 in the aluminium blocks 12 allows compressed or induced air to flow from one pipe 16 to another pipe 16.

Referring to Figure 3, compressed or induced air enters the first pipe 16 of the cooling system and flows in the direction of arrow A through the first aluminium block 12. The air flows through the passage 20 in the aluminium block 12 and into the second pipe 16, before flowing into the second aluminium block 12.

After flowing through the last pipes 16 and aluminium block 12, the air flows back to the existing air flow passage of the apparatus, in the direction of arrow B.

Because each of the pairs of diodes 10 are connected to a different phase of the transformer, the pipes 16 must be made from a material which is not electrically conductive.

Thermal switches 18 are connected to each of the aluminium blocks 12 and are set to switch the apparatus off if they sense a pre-determined temperature, In the prototype apparatus, the thermal switches are set to switch the apparatus off at 100°C.

In use, the compressed or induced air which is normally used to spray finely atomised particles out of the nozzle of the apparatus is first diverted from the compressed or induced air source (not shown) through the pipes 16 and aluminium blocks 12. This air flow effectively cools the aluminium blocks 12 and prevents the diodes 10 from overheating.

In a test on the prototype apparatus conducted in an ambient air temperature of 25°C, and when the apparatus was fully functional, the diodes only reached a temperature of about 40°C.

Because no inlet or outlet is needed for a cooling fan, the case containing the apparatus and the cooling system of the present invention can be sealed in an air-tight manner. This is obviously very advantageous especially if the apparatus is used in a typically dirty environment, such as is the case with an arc spray apparatus.

Furthermore, although the complete auxiliary air path should ideally not have any air leaks, if there were a small leak along this auxiliary path, the case of the apparatus would become positively pressurised and would further inhibit entry of dust or other particles. This is therefore not entirely undesirable.

In any event, since a fan is not used which requires an inlet and an outlet, dust and other particles are prevented from entering the case of the apparatus. In addition, the prototype of the cooling system has been shown to effectively cool the diodes more effectively than prior art fan systems.