Perhaps the first question that needs to be asked is what criteria will help me to decide which is best for my application?
What disadvantages and advantages does each have?
The concept of a blast room, introduced an area where the abrasive could be recycled, allowing the reuse of abrasive that would otherwise be wasted. This stops the prevents the process from being more expensive and wasteful. In a blast room, dust can be controlled by proper ventilation, proper lighting allows the operator to see clearly, producing a constant work quality and where blasting can be done 365 days a year without being interrupted by weather conditions, dew etc. This can be done with an absolute minimum of manual labour.
To ensure high production and low maintenance from blast rooms, it is essential they are carefully designed. Walls should be constructed from 5mm steel plate suitably stiffened to prevent buckling. All interior surfaces should be free form any protrusion inside the chamber to avoid collecting dust and abrasive.
Lighting is of paramount importance to provide sufficient visibility levels for the operator to easily see inside angles, corners, cleats or around complex fabricated items. Lights should never be mounted inside a blast room. Doors should be open to allow full access to the room to utilise the entire size of the chamber. Floor grating and the associated support structure should be engineered to handle the loading levels necessary. Typically 50 tonne loadings are easily accommodated.
Whether or not your blast facility is going to have a full floor area recovery or just a partial floor recovery, the problem remains that you will need to elevate the grit either before or after it is cleaned (separated) and drop it back into the storage hopper on top of the blast pot. Two methods are common in the industry: bucket elevators or pneumatic (airflow).
Abrasive Separators are necessary at some stage to separate the dust, fines and trash from the good abrasive. There are three main types of separtors used with blasting rooms: pneumatic pipe to a cyclone type separator, underfloor suction units and Air Wash. Each method has its own advantages and disadvantages from running costs to wear on the equipment.
Underfloor recovery systems are installed to recover spent abrasive, convey it to the abrasive separation system and onto storage ready for reuse without any manual labour being required in the case of full recovery, or minimum labour in the case of partial recovery floors.
If you are considering a room with no underfloor recovery initailly and you wish to upgrade later on you will save extra costs by some forethought as to the type, position of various items.
Bear in mind that to be successful, a abrasive recovery system should not require undue labour to upkeep, the aim with recovery floors is to reduce the labour required to recover abrasive to almost nothing if possible. It should always be remembered that abrasives are just that, abrasive. As well, abrasives generally don’t ‘flow’ with sweepers or augers alike, systems do not lend themselves to change from one type or grade of abrasive to another, as considerable quantities are left behind.
Airflow within a blastroom is one of the most important and least understood aspects of designing and building a blast rooms. Planning the airflow within a room should be the next step after determining first the size; the position on the site; then where the dust collector is.
The air should enter the room at one end and exit at the other. If air enters on one long side and exits on the other long side, the speed of airflow will be low, unless you had huge or multiple dust collectors. If air speed is low, dust will settle on the floor. Next time the blast is pointing in the dusty area you will pick it up again, and again, and you will create your own dust storm. This point cannot be stressed enough.
The air inlet vents therefore will be at opposite ends to the dust collector. As it is common for the dust collector to be at the opposite end to the doors, the vents frequently are placed in the doors. This has the advantage of not forming dead spots where airflow is low and dust will settle on the floor. If vents were in the roof just inside the doors you would have a ‘dead’ spot where dust would settle just inside the doors. It is usual for vents to be positioned not far above floor level (up to 3’). Additional vents of course may be necessary and can be either higher up or on each side of doors on side walls. The inlet air vents are best made so that air can pass in without undue restriction, (approx 1000 feet/min but so that baffles precludes abrasives from passing through.
At the heart of a Blast Room Facility is the blast machine itself. This is a pressure vessel with a means of loading abrasive through an opening in the top. An Abrasive Metering Valve on the bottom allows the abrasive to fall by gravity into the airstream from the compressor in the “pusher line”.
The other element of the blast pot is the remote control system. This allows the operator to start the blast by means of a valve (known as the deadman handle) strapped to the blast hose near the nozzle. This valve must by law automatically shut the blast machine down if the valve is released, and lock in the 'off' position. The deadman handle actuates a valve on the blast pot which controls the flow of compressed air to the nozzle and the release of abrasive from the hopper.
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