Stations design

Definition
We call improperly "sand blasting stations" the small and medium surfaces treatments cabins in which the operator is outside the enclosure and handles the abrasive jet through the accesses provided. These free jet machines are also called "sleeves cabins" because of their design. The dimensions, the shape and the projection principle of a station vary according to the kind of parts to treat, the treatment sought and the production considered.
Some equipments of handling and automatism of the jets can be adapted to these stations, turning them into real small mechanized machines in which the operator intervenes rarely.

Design
The same as for the free jet shot blasting installations or the blast wheels shot blasters, there are "4 constitutive sets of the distinct functions which are:
1) - the treatment caisson or projection chamber.
2) - the abrasive recovery and conveyance system.
3) - the abrasive recycling and treatment system.
4) - the set of ventilation and filtration of dusty air.

Treatment caisson
It is made of a kind of "glove locker" similar to the ones used in laboratories, fitted with a glass to look through in order to control the operations and two or several over sleeves fitted with gloves for handling. The caisson is covered inwardly of rubber protections and lighted by a unit situated outside. The parts access is generally made from the front or from the side through rocking or pivoting doors. The caisson has to be tight because of the external projections that could cause injuries to the operator who is not protected.

Abrasive recovery
It is generally made of a hopper situated at the bottom of the caisson and which collects the abrasive in order to recycle it. This hopper is fitted with feet which hold it and which heighten the caisson for good ergonomics. When the stations are very small, they can be directly put on the work surface where the operator can work in a sitting position (picture 1).

Abrasive recycling
The abrasive is generally collected at the bottom of the hopper through the projection system, (suction, pressure or wet way: see below) and driven to the nozzle without any particular treatment. The waste retaining is made through a removable sifter situated in the hopper and the abrasive purification through the caisson dust collecting.
For some specific applications, a machinery of "mechanical" or "cyclonal" recycling can be installed foe a better treatment of the abrasive (see types machinery)

Ventilation-filtration
In order the dust does not go out the station, the ventilation system must always maintain the work caisson in depression. To this effect, the speed of the air coming through the caisson openings has to range between 3 and 5 m/s.
In order to calculate the outflow to extract, one will take 20 renewals/ minute to which will be added the quantity of air brought by the projection nozzle(s). The dusty air is sucked up and carried to a filter generally dr (see heading filtration) in order to remove the dust before throwing it back to the atmosphere. The ventilation is imperatively controlled by the lightening and the putting on of the jet and is maintained during the loading or unloading operations in order to avoid the spreading of dust outside.

Kinds of projection

Suction station
It is also called "depression station" and uses the "GIFFARD" effect for the transport of the abrasive from the low storage hopper to the projection gun. This technique is based on the creation of a partial vacuum caused by the passage of the compressed air through an injector in the gun body. The suction generated makes the abrasive grains going up to the pipe up to the projection nozzle. (see heading suction)
The output of this system is relatively low knowing that this is the diameter of the injector and not the one of the nozzle which determines the output of compressed air consumed and thus the one of the abrasive projected (picture 2). It is often used for operations of fine and qualitative shot blasting, with low density and granulometry abrasives. It is a material simple, cheap and easy to maintain.

Pressure station
It is also called "super pressure station" and uses the propulsion of the compressed air coming out of a pressurized pot in order to convey the abrasive contained in the pot through a pipe up to the projection nozzle (see heading pressure).
In this system, there is no more injector. This is the diameter of the nozzle which determines the compressed air outflow and thus the one of the abrasive projected. The output is high and it is possible to use all kinds of abrasives with various granulometries and densities. It is used for operations of stripping, decarbonisation or surfaces preparation before the final coating (picture 3).

Wet way stationIt is similar to a suction station, that is to say the abrasive is mixed up with water in a low hopper and the projection is made thanks to a gun. The transport of the abrasive up to the nozzle can be made through GIFFARD effect (suction) or through a picking up pump which feeds the gun. The mix transported is propelled by a compressed air jet through the nozzle. We are still in front of a gaseous vector system (see heading wet way).
The outflow is very low but the quality of the treatment is very soft.
This process makes it possible to use extremely fine and low density abrasive for very high precisions works with a lower damaging of the parts (picture 4). It is the only one which can use siliceous products forbidden in a dry way process.