19
Contemporary Machining Processes
film (5) fixed with clips (4). Vacuum is drawn through the ventilation system with a
porous pipeline (6). The molding box is placed on the damper (7), a closed elastic
pipe under pressure, made of 5 to 15 mm thick resin. The damper system is connected to the distributor (8), where the ventilation systems (6), pulse valves (9) and
(11), controlled relays (1), and the pipeline (13) are connected as well. The latter
delivers gas to an airtight cavity between the base (14), damper (7), and bottom of
the molding box (1). The pipeline (13) and other parts are equipped with valves (12)
or gas pressure reductors.
The sand is vibrated by alternating gas pressure in its porous mass. For that purpose, 2″ pulse valves can be applied, but for larger boxes it is better to use 2.5″ and
3″ valves. The valve (9) is connected with the vacuum pump that provides a pressure
of 20 kPa and more. The valve (11), in turn, is connected to a pressured air source.
When the film (5) is absent, the pressure is kept below the critical value to prevent
the airflow with the velocity of hopping motion of sand grains, or the box is covered with a fine mesh to prevent dusting in the working area. Sand densification is
performed through opening and closure of the valves (9) and (11) with the relay (1),
which generates alternating pressure in the distributor (8).
Controlled frequency sinusoidal pressure in the sand generates important phenomena that contribute to high-quality compaction of the sand mold. First of all, the
sand particles experience cyclical pressure that causes reactive forces of compression and expansion in the particle material as well as in the pattern. The pressure
fluctuations affect surface phenomena and promote changes in wetting forces related
to condensating moisture, inner friction, etc. Gas molecules move among the sand
particles and put the finest ones into motion like at the initial stage of air-carried
transportation. Excessive, above atmospheric pressure is limited to prevent gas flow
through the open surface of the molding box, potentially able to generate hopping
movement of the fine sand particles.
The sand is under gravitation force and under the pressing impact of alternating
pressure. Mechanical vibration of the sand with inertia forces and reduced inner
friction promote effective compaction of the sand mass and excellent reproduction
of the pattern surface. When the conditions are maintained, enabling the proper
effect of these factors on the sand mold, it is possible to simplify the equipment
(Doroshenko, 2013). Simplified apparatus may be based on two valves only, connected with a relay, so that alternating pressure is generated both in the molding
box and under its bottom placed on the damper. Connecting the valve (11) with the
atmosphere, so that atmospheric pressure is introduced, is another possibility. Then
the cycle consists of the pressure drop in the sand mass down to its minimal value, its
rise up to maximum, and then decrease to the minimal value again, where the cycle
started. Dampers (8) may be made of any sort of elastic material, but it is crucial to
keep the entire surface integral or tighten it with additional material to ensure a hermetic cavity under the molding box. When the damper is filled with pressured air, as
it is shown in Figure 1.4, it is possible to synchronize sinusoidal pressure changes in
the damper, cavity under the box, and/or sand mass inside the box. The ventilation
system (6) may be connected to the bottom of the box, then the pressure in the sand
and under the box can be synchronized directly through a choke placed in the bottom
Contemporary Machining Processes
film (5) fixed with clips (4). Vacuum is drawn through the ventilation system with a
porous pipeline (6). The molding box is placed on the damper (7), a closed elastic
pipe under pressure, made of 5 to 15 mm thick resin. The damper system is connected to the distributor (8), where the ventilation systems (6), pulse valves (9) and
(11), controlled relays (1), and the pipeline (13) are connected as well. The latter
delivers gas to an airtight cavity between the base (14), damper (7), and bottom of
the molding box (1). The pipeline (13) and other parts are equipped with valves (12)
or gas pressure reductors.
The sand is vibrated by alternating gas pressure in its porous mass. For that purpose, 2″ pulse valves can be applied, but for larger boxes it is better to use 2.5″ and
3″ valves. The valve (9) is connected with the vacuum pump that provides a pressure
of 20 kPa and more. The valve (11), in turn, is connected to a pressured air source.
When the film (5) is absent, the pressure is kept below the critical value to prevent
the airflow with the velocity of hopping motion of sand grains, or the box is covered with a fine mesh to prevent dusting in the working area. Sand densification is
performed through opening and closure of the valves (9) and (11) with the relay (1),
which generates alternating pressure in the distributor (8).
Controlled frequency sinusoidal pressure in the sand generates important phenomena that contribute to high-quality compaction of the sand mold. First of all, the
sand particles experience cyclical pressure that causes reactive forces of compression and expansion in the particle material as well as in the pattern. The pressure
fluctuations affect surface phenomena and promote changes in wetting forces related
to condensating moisture, inner friction, etc. Gas molecules move among the sand
particles and put the finest ones into motion like at the initial stage of air-carried
transportation. Excessive, above atmospheric pressure is limited to prevent gas flow
through the open surface of the molding box, potentially able to generate hopping
movement of the fine sand particles.
The sand is under gravitation force and under the pressing impact of alternating
pressure. Mechanical vibration of the sand with inertia forces and reduced inner
friction promote effective compaction of the sand mass and excellent reproduction
of the pattern surface. When the conditions are maintained, enabling the proper
effect of these factors on the sand mold, it is possible to simplify the equipment
(Doroshenko, 2013). Simplified apparatus may be based on two valves only, connected with a relay, so that alternating pressure is generated both in the molding
box and under its bottom placed on the damper. Connecting the valve (11) with the
atmosphere, so that atmospheric pressure is introduced, is another possibility. Then
the cycle consists of the pressure drop in the sand mass down to its minimal value, its
rise up to maximum, and then decrease to the minimal value again, where the cycle
started. Dampers (8) may be made of any sort of elastic material, but it is crucial to
keep the entire surface integral or tighten it with additional material to ensure a hermetic cavity under the molding box. When the damper is filled with pressured air, as
it is shown in Figure 1.4, it is possible to synchronize sinusoidal pressure changes in
the damper, cavity under the box, and/or sand mass inside the box. The ventilation
system (6) may be connected to the bottom of the box, then the pressure in the sand
and under the box can be synchronized directly through a choke placed in the bottom