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By Clyde J. Porter, Wyman Gordon Company, N. Grafton, MA
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Improving air quality and environmental conditions
in a foundry were the objectives for
a recent project undertaken by the Industrial
Hygiene and Safety Department at Wyman
Gordon Company, a division of Precision
Castparts Corporation and a leading manufacturer
of metal forgings and castings for the
aerospace and industrial gas turbine industries.
Airpak, Fluent’s airflow modeling software,
was used to understand better the airflow
patterns and resulting contaminant and temperature
conditions generated by heat
sources, exhaust fans, and replacement air systems.
In subsequent simulations, it was used
to evaluate several exhaust and supply
options so that the best combination and configuration
could be selected and tested without
incurring costly trial and error expenses.
Worker exposure to metal oxide fumes was a problem in the melt shop
when molten metal was poured into molds, even though more than 30,000
cfm of air was being exhausted through fans in the ceiling. Fresh air
was supplied to the foundry primarily through a large door opening on
one side of the shop and directly in-line with the mold pour area. This
air entered at relatively high speed, disturbing the normally buoyant
nature of the metal fumes by forcing them towards the workers’ breathing
zones. Also, a large volume of warm air built up above the workers. Over
time, the exhaust fans expelled most of this warm contaminated air. However,
a portion continued to recirculate into the occupied area, further deteriorating
the working conditions.
Pathlines originating from the heat sources show that airflow patterns
in the original foundry design are dictated by buoyant plumes and by replacement
air currents that enter the shop from the large door opening on the side
(gray)
Pathlines originating from the heat sources show that the low velocity
discharges from the replacement air systems on the side walls (green and
gold) and other changes in the optimized melt-shop layout improve working
conditions in the Melt Shop
The initial analysis confirmed that heat from
two gas-fired furnaces, three electric induction
furnaces, and the hot molds was the key
driving force for air currents in the shop.
It also highlighted the need for considering
alternatives to the existing replacement
air system.
After the initial simulation, an Airpak model
was developed to test whether such changes
as increasing the total exhaust rate, relocating
the ceiling fans, or extending passive vents
from the roof down to the shop floor would
be beneficial. The best configuration was found
to capture the process fumes before they reach
the workers’ breathing zone and minimize
the downward recirculation of hot air. This
configuration consisted of three important
components. Close-capture canopy hoods
were designed for the pour station and the
crucible heating station, one ceiling fan was
relocated to directly remove furnace heat,
and two new systems were designed to provide
replacement air to the shop. The first
replacement air system utilizes a perforated
duct positioned over an aisle to provide 15,000
cfm on the opposite side of the shop from
the pour area, and a second system consisting
of a floor-level perforated plenum provides
an additional 10,000 cfm near the pour
station. Airpak results showed that the lowvelocity
discharges from these supply systems
would not interfere with the local exhaust
systems and would actually enhance a favorable
airflow pattern in the shop.
To gauge year-round performance, models
were run at ambient temperatures of 85°F
for summer conditions and 40°F for winter.
The results provided the basis for specifying
ventilation schemes for each season.
Installation is expected to occur in phases
over the next year. Once again, as seen with
previous Airpak projects at Wyman Gordon,
a key benefit gained from using Airpak is the
ability for management to visualize how proposed
changes will impact existing conditions.
For this project, Airpak results were
instrumental in getting the necessary support
to proceed with the project. In addition,
using Airpak allowed plant management
to choose a strategy that is in keeping with
future plans for the department.
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