evaluate the HAP emission potential of various core- making processes and binder systems. Phenolic ure- thane no-bake and coldbox systems were identified as having the highest emissions, largely due to the sol- vent-based nature of both systems. The binder industry responded with options to replace some or all of the aromatic solvents.
In ferrous applications, the substitution of aromatic sol- vents in Part 1 and Part 2 urethane coldbox resins by methyl esters derived from vegetable oils results in a re- duction of volatile organic compounds (VOCs) of nearly 50% for both parts. These binder versions often referred to as “biodiesel” from the use of methyl esters used to ox- ygenate diesel fuels to render them cleaner burning, can reduce benzene, toluene, xylene, and naphthalene emis- sions at pouring, cooling and shakeout by 20–30%.
Development of resin systems have not been limited to the reduction of VOCs; the reduction of odors from foundries is becoming increasingly important. Foundries have tradi- tionally relied on abatement and/or treatment systems such as scrubber and regenerative thermal oxidizers to eliminate pollutants and odor-causing substances. In nonferrous ap- plications, tetraethyl orthosilicate (TEOS) replaces aro- matic solvents in Parts 1 and 2. Although the VOC emis- sions are similar to traditional aromatic-based solvent res- ins, the primary advantages of this silicate-based solvent are reduced condensate formation and reduced smoke and odor at pouring, cooling and shakeout. This is especially important in lower pouring temperature aluminum semi- permanent molding; excessive smoke and condensate (tar)
formation in the die are not only environmental, but also productivity concerns.
system introduced in the U.S. in 1952 suffered from sensitivity to moisture, low strength, and poor shakeout. The latest generation systems all use some form of alu- minosilicate (Geopolymer) or other inorganic additive to reinforce the water-soluble silicate. These systems have little to no VOCs, are generally non-flammable, generate no odor during mixing, coremaking and shakeout. They generate little to no smoke during casting. While these systems are quite advanced for nonferrous applications, further development for ferrous is required.
Many efforts have taken place to remove core washing from the coremaking process. In many cases, it can successfully be eliminated with improved coreroom process controls, while for other castings it is a necessity. If a core wash is desired, then a novel way to cut core drying costs is to use a color-changing indicator in the core wash to determine when a core wash is dry. Drying time can possibly be cut by 50% and, therefore, gas consumption could be cut by more than 50%. Core ovens are typically very inefficient. Making a number of modifications, like adding air turbulizing devices to break up laminar airflows or introducing air to both top and bottoms of the drying belts, greatly speed up core drying and improve efficiency.
Even with the substitutions mentioned, the continued use of phenolic resins is threatened by lower emission stan- dards. This has given rise to a new generation of inorgan- ic systems such as heat-cured sodium silicates or ester- cured no-bake sodium silicate. The original CO2
gassed
Figure 8. Coldbox core production. 14 International Journal of Metalcasting/Summer 10
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