Good dust extraction shroud design is especially important
with hand held concrete grinders which are angle grinders
fitted with diamond grinding wheels because their high speed
operation can cause a hazardous airborne dust cloud in
seconds which contributes to the disease silicosis.
To
lower the risk of silicosis it is better to prevent concrete
dust escaping at the source than it is to rely on personal
protective equipment.
When a hand held angle grinder is used as a concrete
grinder or for polished concrete a well designed dust
extraction shroud can increase productivity by removing all
the dust as it is produced which will eliminate costly clean
up afterward.
Using a suitable vacuum dust collector the dust is not
only prevented from entering the surrounding air, it is also
picked up and deposited in a receptacle for easy disposal
which saves sweeping or floor vacuuming.
Flexible shrouds are less efficient
Dust extraction shrouds that have holes in the top to
allow air to enter are generally less efficient and harder
to operate because the holes are there to stop suck-down or
vacuum- stick which is common when these flexible shroud
bodies touch the floor around the perimeter. Without those
holes the perimeter of the shroud will pull down onto the
floor making it impossible to move. The holes are supposed
to produce a balance between enough airflow to hold the
perimeter against the floor without pulling it down too
tightly. This only causes premature wear of the shroud body
around the perimeter and uneven suction pressure as the dust
collector filters vary in airflow because their filters
gradually block over.
The other problem is that the air entering the top of the
shroud does nothing to contribute to the removal of dust at
floor level. All the air that enters these holes is
immediately directed across the inside top of the shroud to
the outlet where the dust collector hose is connected
without aiding the pick up of dust from the floor where it
is being generated.
The best shrouds for hand held concrete grinders have all
the airflow directed under the shroud walls close to the
floor through a constant gap so that the high speed airflow
enters at floor level to pick up the concrete dust where it
is generated and keep the dust in suspension as it flows
through to the outlet. Nothing should touch the floor except
the grinding wheel and this system will effectively remove
dust without allowing it to escape even with a widely
varying range of airflow due to the dust collector filters
gradually blocking over. Suck-down is never a problem
however a fixed gap height is not as good as an adjustable
seal gap.
Steel shrouds with an adjustable seal are better
When a shroud is tightly fixed to the grinder and the
body is made of rigid, long wearing steel an adjustable
rubber seal can be used where the height can be selected for
optimum performance. These steel shrouds are the most
efficient and the seals are long lasting.
These dust extraction shrouds are used more now as
polished concrete becomes popular and the edges of walls are
hand ground with each new finer diamond grinding step of
which there are about ten to achieve the best result.
10/06/2009 2:00 PM
