Operator
The operator must:
- wear a suitably designed protective helmet, which protects him from any abrasive bounces and allows him to breathe in an environment with very high dust density. The protective helmets are normally fed with compressed air suitably treated with filtration systems or generated by compressors operating without lubrication.
- wear overalls and gloves
- almost always also have hearing protection.
As regards the noise level, it is necessary to check the installation site as the intensity of the noise varies according to the piece to be sandblasted, the working pressure, the nozzle and the type of abrasive used.
Unfortunately it is not possible to intervene on the cause of the noise source as it is generated by the sandblasting work.
Working, for example, with a medium-sized machine, with a capacity of 120 litres, with a nozzle of 7x70 mm diameter which determines an air consumption of about 4000 lt/min at a pressure of 7 bar, on an average support at a distance of 5 metres from the sandblaster, in the vicinity of the operator, a noise level between 95 and 105 decibels is detected.
- have a remote-control device available to start and stop the sandblaster. This device is of great importance as, as it is easy to guess, an accidental or unexpected start can also cause serious damage both to the operator and to any other people around the area where the sandblaster is positioned.
Since January 1995, with Italy's adaptation to the Machinery Directive and the consequent CE marking, each manufacturer has been forced to take into account, in the design phase of a machine, not only ease of use and maintenance but also the analysis of any risks deriving from its use.
Before that date and unfortunately very often still today, models with manual control are used in the shipbuilding industry. The starting and stopping of these machines is performed by a person other than the operator who uses the sandblasting jet and therefore from a first risk analysis, this system is to be considered absolutely unacceptable.
This model of machine, in fact, is built and sold without the CE mark as it is considered a component that the customer will complete with its own control systems.
It is therefore of considerable importance to be aware of these problems as unfortunately there are unscrupulous traders who reduce the CE marking problem to a simple plate.
Below we discuss in detail the systems we have adopted to adapt to MACHINERY DIRECTIVE 2014/68 / EU
- Remote control system
Applied on all CE marked sandblasters, it is composed of a lever device called “pneumatic throttle valve mod. PRC1 ”which, when lowered or released, allows the blasting cycle to start or stop respectively.
This device is placed near the nozzle holder and can therefore be operated only by the operator who, in order to lower it, must act on a locking system which resets itself automatically each time the lever is released. The locking system can be padlocked as the operator must be able to ensure, in the event of a momentary pause, that no one can start the working cycle.
In case of accidental release of the nozzle holder and therefore of the lever, the sandblaster stops automatically.
The sandblaster can be started by means of the PRC1 lever valve exclusively, while it can also be stopped by means of an emergency control placed on the machine.
The most widely used remote control system is of pneumatic type (up to 60/80 metres) and therefore the connection between the lever valve and the sandblaster is ensured by a double tube which acts on a pneumatic circuit designed in such a way that, in case of choking or accidental cutting of the tube, the sandblaster will stop and not accidentally start.
In case of electric remote control (normally used over 60 / 80mt.), a microswitch is placed under the control lever and is called “throttle valve mod. ERC5. In case of breakage or disconnection of the connection cables, the machine is stopped.
- Locking the sieve
The abrasive is placed in the upper part of the container and is normally screened by a sieve to prevent any bodies larger than a diameter of 3-4 mm from entering the tank and therefore causing problems with the abrasive sliding, inside the valves or in the nozzle.
When the operator starts the sandblaster, the container is automatically closed by a pad valve that allows the tank to be pressurised.
By blocking the sieve, the possibility to access near the plug valve with the hands is prevented to avoid crushing of the fingers if, during the loading phase of the machine by a third party, the operator starts the sandblaster.
- Hose clamping system for abrasive
The abrasive hose is normally connected with a swivel type quick coupling at the outlet of the sandblaster.
Once connected, it is necessary to make sure that the system that blocks its rotation is inserted, because if it unhooks during the extension of the pipe roll, when the impulse for the start of the sandblaster is given, the air-sand jet will come out from the lower part of the machine and not from the nozzle.
This system is used for abrasive tubes having a size equal to or greater than 25x40 diam.
Site installation: useful tips
Therefore, from the situations analysed so far, there are accident prevention problems that concern the staff working on the construction site and in some cases also passers-by, in relation to the installation of the construction site and the environmental impact.
When setting up the site, it is necessary to position the compressor, the compressor-sandblaster connection hose, the sandblaster, the abrasive hose and the abrasive pallets in an adequate and convenient way.
As far as possible, the compressor must be placed in the shade, it must not be hit by the dust generated by the sandblasting work, preferably placed at a distance between 10 and 20 metres from the sandblaster to avoid the following:
- if positioned too close, the compressed air temperature is very high and therefore even if a condensate separator has been installed on the machine, its efficiency is reduced.
- if positioned too far, an excessive pressure drop occurs.
The compressor-sandblaster connection pipe must have an adequate section for the flow rate, must be protected from any crushing and correctly fixed to the fittings.
The sandblaster must be positioned flat, in a cool and dry place, on a surface made of sheet metal, wood or concrete and in any case clean from dust to prevent the exhaust air supplied at the stop of the work cycle from raising dust from the ground. The area around the machine must be cordoned off and accessible only to staff.
The abrasive hose must be protected in such a way that it cannot be crushed, broken or cause gripping. It must be spread in such a way as not to create sharp curves along the path as, in the vicinity of the latter, it can break due to abrasion with consequent leakage of abrasive. This pipe must therefore be checked for wear according to the times indicated in the instruction, use and maintenance manual.
In the event of intervention for any type of maintenance, it is necessary to disconnect the compressed air supply source and, if necessary, electrical energy.
The abrasive pallets will be placed on the ground near the sandblaster and, within a radius of 40 metres it is always convenient to move with the abrasive tube, extending it as needed rather than moving sandblaster and abrasive bags too often.
Finally within a radius of at least 20 metres from the operator, access must be forbidden and the area must be suitably marked and well delimited.
Environmental impact
Let's now analyse the problems related to the types of abrasive, the dust generated by sandblasting and the solutions to be adopted to eliminate, reduce or recover it.
First of all it must be said that in cases where it is possible to use only dry sandblasting, the choice of the type of abrasive is of fundamental importance.
The most used and of course the least expensive still today is silica sand. Unfortunately, this type of abrasive generates dust containing silica, which is harmful to human health because it leads to silicosis. The most damaged, in this case, are the people who are around the area where the sandblasting operations take place, as they do not have the same adequate protections the operator is equipped with.
As an alternative to silica sand, there are abrasives to be used as disposable, more expensive but not containing silicone such as quartz, foundry waste and in the case of very special works, sodium bicarbonate. With the use of these last abrasives, we will have at least less harmful dust formations.
