7. Plants for compressed-air blasting

7.1 Small and medium-sized blasting pots

A blasting pot is the main element for compressed-air blasting. Its volume determines the amount of abrasive being available and thus the blasting time that can be obtained without interruption of the abrasive blasting process. In general, the following volumes have been accepted for the blasting pots.

Filling volume:

30 l
100 l
140 l
200 l
300 l
500 l

The pot containing 200 l is the variant that is used for the most part. For a complete filling, i.e. about 300 kg of slag-abrasive, a permanent blasting time of about 30 – 45 minutes results if an 8 mm venture jet nozzle will be used.

200 l – blasting pot

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7.2 Large blasting pots

Because of the demand for steadily increasing efficiency as regards abrasive blasting methods the time for filling a blasting pot has been included in cost accounting and profitability calculation. The prices per square meter that have to be obtained for blasting and derusting are nowadays considerably lower than in the past. That’s the main reason why a tendency towards the application of large blasting units can be ascertained. Also as regards these units certain sizes have proven to be reliable whereas the number of blasting units that can be connected to a plant is quite decisive for the size of such a unit.

The following sizes result according to the type of application:

Filling volume:

2,500 l
5,400 l
10,000 l
20,000 l
30,000 l

These pressure pots can be used at maximum operating pressures of 12 b or even 25 b. The application of large blasting pots has got the advantage that the abrasive can be filled in and stored completely independent of the weather conditions at the building site (filling is performed by silo wagons).

The number of blasting units to be connected with the pressure pot ranges between 2 and 8. These devices are often installed on running gears so that they can also be optimally used with shortest hose lengths at the place of application.

An interim solution that is considerably more efficient as an investment is the application of silos under which several blasting pots can be put. Each blasting pot will be provided with abrasive from the silo via free outlets which are closed by hand flap. There is no need to close the outlet during operation because of the naturally forming cone of mass.

If one-chamber blasting pots will be used below the silo then these ones will be exhausted via a hand lever from the nozzle with the help of a remote control, i.e. the blaster itself determines when its own blasting unit has to provide it with material.

Large blasting pot on running gear

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Large blasting pot

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7.3 Double-chamber blasting pot

In order to avoid frequent and time-consuming filling periods a system of a double-chamber blasting pot has been developed ensuring a permanent provision of the blasting unit with abrasive. Two pressure chambers being on top of each other enable continuous filling of the abrasive whereas the upper chamber acts as filing chamber and the bottom one as blasting pot. The volume of each chamber is 150 l. 2 mixing valves can be connected without any problems and by this 2 blasting units can also be connected which can even use jet nozzles with a nozzle diameter of up to 20 mm.

Double-chamber blasting pots can be both manually operated, as well as be delivered with remote control and filling control. In case of manual control an operator has to be present at the silo for operation. This operator has to depressurize the upper chamber by opening the air vent and when the abrasive is filled in he pressurizes it again. If the chamber is under pressure again the pressure-force ratio causes the closing cone of the lower chamber to open automatically and the abrasive flows into the lower chamber.

If filling is performed manually there is the risk that the bottom chamber is empty and that the abrasive to be filled in from the top enters the compressed-air flow too late; this would lead to the fact that the blaster at the nozzle only gets compressed air for a short time and no mixture of compressed-air/abrasive. This is avoided at double-chamber automatic pots because the time interval of the filling can be exactly adjusted according to the nozzle size.

The low mobility is a big disadvantage of this system. Comprehensive measures have to be taken to install the pot at a building site and to protect it from atmospheric influences like wind and rain. This will be particularly difficult in case of e.g. moving building site at bridges or tank depots where the location has to be changed several times.

Double-chamber blasting pot

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