dust

1. Dust measurement and
sampling opk

2. First step
• how much dust is there in the foundary air that is being breathed by the workers
For this purpose there are several methods
• One method - estimates the atmospheric pollution by the amount of straining on a light
coloured filter medium.
• Another is connected with measurement of mass dust particles removed from the air by
filteration
• the third counts or estimates the number of dust particles in the foundary air and which
probably is the best
• Thermal precipitator: this is the most accurate method.
• there is a dust free space around a hot body and a thermal precipitator has its hot body,
• an electrically heated wire placed between the two parallel cover glasses
• The glass slips are placed in such a position that the space between the wire and cover slips
is completely within the dust free zone,
• so that when the dusty air is drawn through the zone,the dust from the air is deposited on
the glass slip.
• The method is tedious and more time consuming.
Owan’s jet counter :
consists of the following parts:
• a damping chamber,
• The head which encloses a cover slip clipped to a rotatable disc which enables the
deposition of dust.
• A hand pump for drawing air into the head.

3. • Dusty air is drawn through a damping chamber which
saturates the air with water.
• The strokes of the pump are standard and valve is
opened, allowing the air to enter the head.
• On passing through the jet, which is in the form of an
oblong slit, a reduction of pressure takes places and
some of the water vapour condense on the dust
particles.
• The stream of air then impinges on the cover slip and a
change in direction takes place.
• The moist dust particles deposits on the cover slip
• due to pressure and temperature rise at this point, the
water evaporates leaving the dust traces on the cover
slip.
• The cover slip is then removed from the head and
mounted on a microscope slide and the counting
operation is carried out.

4. Konimeter:
• it consists of a pump which draws in dusty air so that the air impinges on a
glass cover slip, which is pepared with a sticky substances.
• As the dusty air changes its direction, the dust particles get stuck on the
(sticky) glass cover slip as a dust sample
• this produces a dust spot near the edge of the slip and its size is such that
about thirty dust samples may be taken on one slide.
Comparison of the above method :
• thermal precipitotar is very accurate but the process of counting is very
cumbersome.
• it gives only average results which are generally misleading.
In owan’s jet counter
• the sample collected is too small for analysis.
• the large particles are probably shattered into small particles thereby giving
a high dust count in small size ranges.
Konimeter
• comparatively inaccurate and gives widely varying results with different
operators.
• Besides the above methods, automatic counting devices are now avaliable
in which count accurately the various sized particles: but, they are
expensive and beyond the reach of average foundries

5. • Hexhlet sampler :
• the air to be sampled is drawn through the instrument at a known and
constant rate
• coarse particles which would not reach the lung in normal respiration are
collected in the first stage of instrument, which separates the bigger
paricles;
• while the dangerous dust collected in a paper thimble through which the
air to be sampled is drawn after sampling for a chosen period of time
• the paper thimble is removed from the instrument and the amount of dust
collected can be measured
• The dust can be washed out the thimble by acetone and subsequently
centrifuged and weighed.
• More commonly the thimble containing the dust sample is in sintered at
7000 C and weighed.
• The amount of dust is derived by deducting the weight of thimble ash.
• From the weight of the dust collected, the time of sampling and the rate at
which air is drawn through the instrument, the respirable dust
concentration in the atmosphere is readily calculated.
• The instrument is robust.
• Needs relatively unskilled operator and the sample collected is sufficiently
large for chemical or x-ray

6. • The results obtained by the dust counting methods were not satisfactory;
the reason being , these system extract average dusty air from all over the
room,
• it was decided to develop some visual methods to see actual dust
concentration at a particular place in the foundry room.
• The commonly used methods are given below.
Tyndall beam method
The instrument consist of
• A high intensity length beam.
• A shield placed between the light source and the eye of the observer.
• A relatively dark background for the observer’s eye.
• Because a narrow focused beam of light is employed, the illusion is created
that all the dust is concentrated within the light beam.
• To observe the movement of dust cloud in the vicinity of a dust producing
operation the light beam should be moved into various positions
Method of smoke generation
• Another useful method for visualizing the dust clouds consists in generating
visible smoke.
• The chemical generally used for this purpose is ammonium chloride

7. dust control and dust extraction in foundries
• The dust may evolve during the following foundry operations,
• Furnace work :
• foundry workers are exposed to large amounts of dust when,
– (a) shoveling coke in the hearths
– (b) relining furnaces and fire hearths.
An average of a large number of derterminations of the dust content
associate with chipping out of cupolas in Sweden showed a
median value of 80 and a mean of 130.
Corresponding figure from several American investigations were
88and 124 respectively.
Sand preparation : large amounts of dust arise, when the sand is
mixed or conveyed to the mixer.
To prevent the spread of dust
(a) sand should be moistened before use
(b) mixer can be enclosed
(c) drying and screening of sand should be done in isolated
and well ventilated compartments.

8. • Core making :
• dust evolves in the dressing of dried cores for example during sawing
brushing and polishing.
• Another dust producing operation is the spraying of molded cores with
suspension containing quartz.
• In core making, it is therefore advisable to apply exhaust hood which .if
necessary can be movable.
• Knocking out : the operation is undoubtedly one of the biggest causes of
dust propagation.
• The danger at knock out has been underlined by the new iron and steel
founder’s regulations of 1953 which state, “knock out operation shall be
carried out in separate or suitably separated compartments.
• Suitable local exhaust ventilation and a high standard of general ventilation
should be provided”.
• In order to control dust, a knock out point for small castings is generally
fitted with a water spray in order to suppress the dust spread. Average dust
concentration
(particles per ml)
• Water spray 2400
• No spray 3200

9. • Fettling and dressing : the most dangerous situation comes in the fettling
and dressing shops where the embedded sand particles are removed from
the cast surfaces.
• Local exhaust or low volume high velocity system is perhaps the most
suitable method of dust control during the fettling and dressing operations.
• The low volume high velocity system as applied to the various tools used in
fettling sections is given below:
Pneumatic chisel
• Fine dust could be controlled by handling about (4 to 5 cu ft) 11.3 to 14.2
*10 -2 cubic metre of free air per minute under a vaccum of 250 to 375 mm
of hg, the dust velocity being 370 metres/min.
the ventilation may be applied through,
• I, a separate duct held over the operator’s hand,
• Ii, a duct bonded on the chisel side,
• Iii, a hallow chisel.
• A chisel sleeve may be provided to damp the chisel vibrations and thus help
in a comfortable grip.
• When used on work generating large amounts of dust , a conical rubber
extension duct can be fitted over the sleeve

10. Portable surface grinder
• The dusty air was previously extracted through the ports placed all around the inner edge of
a ring which completely surrounded the wheel.
• The later work suggested, the to allow the the wheel to work close up to projections and in
corners, the ring dust need not encircle the whole wheel the dust can be controlled even if
a section of dust is cut away.
portable grinders
• An extractor head was developed which claimed decided advantages over a peripheral dust.
• In case of extractor head, the maximum amount of wheel face is exposed to the work.
• The head is provided with point on its inner surface to strip the fine dust from the wheel
face.
• The head is provided with a roller devices so that it will run more easily over the work and as
the tangential stream of dust and sparks strike this roller,
• it decelerates and cools them before being collected by the point immediately above the
roller.
wire brushes
• Brushes are frequently used to clean the casting and they produce heavy dust concentration.
• Dust can be extract through the ports drilled at the wooden back of the brush and
connected to a duct to a filter and a vacuum hood.
• Special hoods are sometimes used to catch large amounts of dusts. These hoods may be
fixed against the walls above the machines creating dust or may be placed centrally in rooms

11. dust collecting equipment
• selection of the dust collecting equipment will depend upon the
particle size (1 to 1000 microns)
• shapes,
• density and
• concentration range of the dust to be collected.
The commonly used equipments are
Electronic precipitor :
• they may be of plate type or pipe type.
• The air to be cleanded is passed through a high voltage electronic
field formed by two groups of electrodes (i.e., plates)
• the discharge electrode being negatively charged and the positive
collecting electrode being ground.
• Dust particles receive negative charge while passing through
discharge electrodes and they therefore are attracted by the
collecting electrodes.
• Particles of 100 to 0.05 micron size can be collected and the
equipment has got very high dust collection efficiency.

12. Fabric collectors : dust is collected on the fabric.
• Rate of air flow or air velocity is 0.6 meters/minute.
• These collectors require space, erection cost is high and sufficiently time is
consumed in cleaning the fabrics.
Wet collectors : they employ a multiplicity of methods to wet the
contaminants and remove it from air steam.
Wet centrifugal collectors : they throw the heavier particles against wetted
collector surface by centrifugal force.
Inertial collectors : they depend upon the cyclonic action. The centrifugal force
spins the heavier particles against the conical section of the collector and
forces it out of the chamber at the apex.
Equipment is low in cost.
dust disposal methods
• The dust disposal methods vary with the plant, process, materials, size and
the quantities involved.
• Dry collectors are unloaded continuously or in batches through dump gates
and rotary locks to conveyors or containers.
• Wet collectors are arranged for batch removal of continued rejection of
dewaterd material by flight conveyors or draining as a slurry.
• But, solids carried over in waste water can create stream pollution problems
if waste water is not properly cleaned before draining.