This invention concerns apparatus for blasting with abrasive particles such as shot or grit.

Ordinarily when it is desired to provide for continuous blasting it is necessary for the hopper which contains the supply of abrasive particles to be pressurised.

It is amongst the objects of the present invention to provide blasting apparatus capable of continuous operation without the disadvantage aforesaid.

According to the present invention there is provided apparatus for blasting with abrasive particles comprising a blast pot which is continuously pressurised, a chamber above the blast pot and communicating therewith by means of a first drop valve, a second drop valve in the top of said chamber for establishing a communication between said chamber and an unpressurised supply of abrasive particles and timer means for alternately pressurising and depressurising said chamber, the arrangement being such that when said chamber is depressurized the first and second drop valves are closed and open respectively to allow abrasive particles from said supply into said chamber

and when the chamber is pressurised the first and second drop valves are open and closed respectively to allow abrasive particles from the chamber into the blast pot.

The timer means may change the pressure state of the chamber after every interval of time in the range of from 30 seconds to 2.5 minutes.

The timer means may operate by pneumatic pressure.

Since the blast pot is recharged with abrasive particles at frequent intervals, neither it nor the chamber need be of large capacity and volumes of as little as 2.5 litres are preferred. Thus the apparatus is readily portable and usable at any site where there is a supply of compressed air and abrasive in a hopper or other container beneath which the apparatus can be connected.

The invention will be further apparent from the following description with reference to the single figure of the accompanying drawing, which shows, by way of example only, a vertical section through one form of apparatus embodying same.

Referring now to the drawing, it will be seen that the apparatus includes a blast pot 10 which is kept supplied with abrasive particles. Compressed air passing along line 11 entrains abrasive particles from the pot 10 for supply to a hose and blasting nozzle (not shown) .

Mounted above the blast pot 10 is a chamber 12. A drop valve 13 is provided between the blast pot 10 and chamber 12.

The top of the chamber 12 includes a further drop valve 14 which can be opened to establish a communication between the chamber 12 and a hopper 15 containing abrasive particles beneath which the chamber 12 can be mounted.

Compressed air is supplied through line 16 continuously to the blast pot 10 and through line 17 to chamber 12 when a valve 18 therein is open. The chamber 12 may be exhausted through line 19 when a valve 20 therein is open. Line 19 terminates in the base of the supply hopper 15 above the drop valve 14 to fluidise the abrasive particles in the base of the hopper as the chamber 12 depressurizes.

A pneumatically powered timer 21 controls valves 18 and 20 through pneumatic line 22. The arrangement is such that when valve 18 is open valve 20 is closed and vice versa.

When valve 18 is open pressure in the chamber 12 closes the drop valve 14 and allows the drop valve 13 to open (the pressures in chamber 12 and blast pot 10 being equal) to allow particulate material to fall from the chamber 12 into the blast pot 10.

When valve 18 is closed the drop valve 13 closes and the drop valve 14 opens to allow abrasive particles to flow from the hopper 15 into the chamber 12.

The timer 21 reverses the setting of the valves 18 and 20 at intervals in the range of from 30 seconds to 2.5 minutes .

In this way the blast pot 10 is continuously recharged and it and the chamber 12 can consequently be of small capacity. Each may typically have a height of 15 cm and a diameter of 15 cm.

Solid members 23 providing upwardly directed conical dishes fit into the bottoms of the chamber 12 and blast pot 10 to facilitate particle flow and remove

what would otherwise be dead areas, avoiding the need for dismantling and clearing when changing from one kind of abrasive to another.

It will be appreciated that it is not intended to limit the invention to the above example only, many variations, such as might readily occur to one skilled in the art, being possible, without departing from the scope thereof.