20
Remanufacturing and Advanced Machining
of the box. In that case, there is no need for a third pipeline to be connected to the
pressure distributor (3).
When above atmospheric pressure is applied to the sand, the film (5) may be
blown up at the initial stage of the process. In the event, another protective film with
small perforations displaced from the perforations in the first film is recommended.
Then the excessive air may leave the box, while under vacuum the films are forced
to the sand surface. After several cycles, however, the pressed sand prevents the air
from blowing through and the films remain fastened to their surface permanently.
This phenomenon helps visual assessment and regulation of the vibration frequency
and other working parameters. After regulation, the film must be either motionlessly
tightened to the sand surface or damped oscillations must be produced that finally
lead to a tight adherence of the film to the sand surface. When the latter state is
reached, it indicates the prevalence of pressing phenomena in the upper sand layers,
where compaction of the sand prevents the air from penetrating it. Simultaneously,
lower sand layers reduce gas permeability and redistribute the pulsation energy of
the airflow to lower cavities, thus intensifying the shaking process.
On the other hand, the proposed technology may be further developed to achieve
improved results and repeatability through full automation of the pressing process. In
particular, Rusakov and Shinsky (2014) described the method of three-phase power
activation to obtain a combined effect of vacuum, vibration, and gas pulses. The
method divides each cycle into three stages of different gas states in the molding box.
At the first stage, the gas pressure is changed to produce a vacuum of 40–10 kPa. At
the second stage of each cycle, a control receiver of a certain volume and pressure is
connected, so that equilibrium pressure is reached between the box and the receiver.
The third stage provides the atmospheric pressure to the box. During the cycle, the
pressure is measured both in the sand and in the receiver, and from the measured values the overall void volume in the sand is calculated. The data is analyzed to assess
the effectiveness of compaction and to determine the finishing time of the process.
The system is able to generate vertical vibrations of the molding box with frequencies from 5 to 100 Hz and vertical acceleration between 0.5 and 0.95 g. The control
and diagnostic system includes a frequency generator, gasodynamic vacuum block
and gas pulse generator, and an automatic system for adaptive control. Data collection and diagnostics are performed by sensors and executive modules connected to
a computer system. When the program identifies unchanged void volumes in subsequent cycles, the system performs the last cycle to stop vibrations and eliminate
resonant states.
An additional advantage of the gasodynamic processing of sand molds is its suitability for cooled or heated gas, or even gas with liquid components. Some examples
can be found in the literature (Doroshenko and Berdyev, 2013). In the case of ice
patterns, cooled nitrogen may be applied and the molding sand may be sprayed with
liquid nitrogen. To heat the ice pattern before melting in the mold, a gaseous heat
carrier can be added, or gaseous reagent in the case of СО 2 process. These gases
may be supplied to the molding box at the final moment of the compaction process
through the distributor (8) or the valve (11) as shown in Figure 1.4. However, if gas
Remanufacturing and Advanced Machining
of the box. In that case, there is no need for a third pipeline to be connected to the
pressure distributor (3).
When above atmospheric pressure is applied to the sand, the film (5) may be
blown up at the initial stage of the process. In the event, another protective film with
small perforations displaced from the perforations in the first film is recommended.
Then the excessive air may leave the box, while under vacuum the films are forced
to the sand surface. After several cycles, however, the pressed sand prevents the air
from blowing through and the films remain fastened to their surface permanently.
This phenomenon helps visual assessment and regulation of the vibration frequency
and other working parameters. After regulation, the film must be either motionlessly
tightened to the sand surface or damped oscillations must be produced that finally
lead to a tight adherence of the film to the sand surface. When the latter state is
reached, it indicates the prevalence of pressing phenomena in the upper sand layers,
where compaction of the sand prevents the air from penetrating it. Simultaneously,
lower sand layers reduce gas permeability and redistribute the pulsation energy of
the airflow to lower cavities, thus intensifying the shaking process.
On the other hand, the proposed technology may be further developed to achieve
improved results and repeatability through full automation of the pressing process. In
particular, Rusakov and Shinsky (2014) described the method of three-phase power
activation to obtain a combined effect of vacuum, vibration, and gas pulses. The
method divides each cycle into three stages of different gas states in the molding box.
At the first stage, the gas pressure is changed to produce a vacuum of 40–10 kPa. At
the second stage of each cycle, a control receiver of a certain volume and pressure is
connected, so that equilibrium pressure is reached between the box and the receiver.
The third stage provides the atmospheric pressure to the box. During the cycle, the
pressure is measured both in the sand and in the receiver, and from the measured values the overall void volume in the sand is calculated. The data is analyzed to assess
the effectiveness of compaction and to determine the finishing time of the process.
The system is able to generate vertical vibrations of the molding box with frequencies from 5 to 100 Hz and vertical acceleration between 0.5 and 0.95 g. The control
and diagnostic system includes a frequency generator, gasodynamic vacuum block
and gas pulse generator, and an automatic system for adaptive control. Data collection and diagnostics are performed by sensors and executive modules connected to
a computer system. When the program identifies unchanged void volumes in subsequent cycles, the system performs the last cycle to stop vibrations and eliminate
resonant states.
An additional advantage of the gasodynamic processing of sand molds is its suitability for cooled or heated gas, or even gas with liquid components. Some examples
can be found in the literature (Doroshenko and Berdyev, 2013). In the case of ice
patterns, cooled nitrogen may be applied and the molding sand may be sprayed with
liquid nitrogen. To heat the ice pattern before melting in the mold, a gaseous heat
carrier can be added, or gaseous reagent in the case of СО 2 process. These gases
may be supplied to the molding box at the final moment of the compaction process
through the distributor (8) or the valve (11) as shown in Figure 1.4. However, if gas