The abrasives recovery

Objective
The abrasives used in cabins, some of them are very expensive, before being unsuitable for a work profitable by destruction or wear, are recycled several times. This contributed to the generalization of the floor recovery systems of the cabin, not only to avoid the loss of a product sometimes expensive, but also and above all for two essential aims:
1) Avoid wasting time, because of the collection, it is difficult to invoice the time wasted according to the m2 treated.
2) Avoid an additional and useless fatigue for the operator, which could be at the origin of injuries or various pains.
There are 3 versions of floor recovery: (see typical schematics)
- the localized recovery,
- the partial recovery,
- the total recovery.
One will try, as far as possible, to do a recovery whose surface will be as big as possible, with ideally a total surface for which the return on investments is immediate.

Recovery versions

Principles
Localized recovery:
Situated in an angle of the cabin or at the bottom of a wall, it is constituted of a pit hopper, with reduced dimensions, covered by floor gratings and feeding directly the foot of an elevator. In some cases, it can be under the form of a low width gutter crossing the cabin.
Constraint: the operator sweeps or scrapes the floor of the cabin but does not raise the abrasive.
Partial recovery:
It is generally made of one or two recovery lengthways corridors coming to flow into a transverse collector which carries the abrasive at the bottom of the recycling system. The solution with two side corridors is preferable to the one with a unique central corridor because the abrasive projected settles at the bottom of the walls after its rebound cushioned by the rubber curtains.
Constraint: according to the version, the sweeping or scraping operation is significantly reduced.
Total recovery:
All the surface of the ground is covered by a recuperator which collects the abrasive and carries it, in masked time, towards the recycling and treatment unit during the shot blasting operations.
Constraint: any, all the time is spent shot blasting (see typical schematics).

Recovery systems

Hoppers
One or several hoppers situated in the basement feed a helical screw, a band conveyor or any other similar device, which carries the abrasive at the bottom of an elevator.
Drawbacks:
The main drawback of these kinds of installation is that they require great pit depths under the cabins in order to put the recovery set. This is why they know a lack of interest today. They give way more and more to more compact systems called "with low civil engineering" or "without civil engineering" made of very flat "recovery floors" whose thickness ranges from 130 and 300 mm. The last-mentioned have the advantage of minimizing and even removing the heavy work, reducing thus the creation cost and allowing the possible removal of the cabin.

Floors
The conveyors recoveries floors can be classified in 3 common categories:
1) the suction systems,
2) the jolts systems,
3) the scraping systems.

Suction systems
Under the floor gratings of the cabin floor, a vast number of small hoppers of 30 to 40 cm of height and side, run into triangular pipes linked to a collector connected to the aspiration circuit. The dusty air, the abrasive and the waste are sucked up towards a set of separation, filtration and storage.
Advantage: the system is also used for the enclosure ventilation and does not include any mechanical part in abrasive atmosphere. It allows a complete draining of the installation in the case of an abrasive change.
Drawbacks: the performances are limited for the recycling of high density abrasives. It requires a good protection of the surfaces of the conveyance circuit in contact with the abrasive passage.

Jolts systems
A set of U-shaped gutters collect the abrasive that went through the floor gratings. Each trough is activated by a pneumatic jack that gives it a slow advance vertical movement, an abrupt stop and a quick return. The abrupt change of direction and the speeds difference give inertia to the abrasive mass which is moving ahead while sliding along the trough bottom.
Advantage: the system allows a complete draining of the only floor in case of a change in the abrasive type.
Drawbacks: the performances are limited for the recycling of high density abrasives. It requires a good sealing between the troughs, their guides support and the civil engineering.

Scraping systems
1) with stiff strips
The scraping units look like ladders whose strip-shaped rungs would be pivoting and not fixed rungs. They are laid flat on rollers on the floor which are activated by a rectilinear to and fro so that the scrapers work as a tool of a shaper. They are jammed in vertical position in one direction and free in the other. The strips push the abrasive on their way on and retract on the wave on their way back. The strips articulations can be mechanical or elastic.
Advantage: The system is not very cumbersome (150 mm) and can be framed in a rail thickness and allow an installation without civil engineering.
Drawbacks: This system is a bit noisy and the mechanical articulations are fragile.

2) with supple strips
The striping units look like ladders whose rungs, in the form of fixed rakes, are lined with a rubber strip. They are laid flat on rollers on the floor which are activated by a rectilinear to and fro. They are jammed in vertical position in one direction by the rake teeth and are free in the other. The strips push the abrasive on their way on and retract on the wave on their way back.
Advantage: identical to the previous one, with noiseless working.
Drawback: does not withstand the selective excess loads of abrasive.

The other systems
Other solutions are still used such as:
- scraping by a mini motorized truck moving under the floor gratings along the length of the cabin,
- scraping through stiff strips fixed on supple bands and driven by a motorized drum,
- conveyance through a rubber band on out-of-control rollers and driven by a motorized drum,
- conveyance through helical multi-screws fed by several mini hoppers.
These mechanical solutions, too bulky, do not have the advantages of the recovery floors.