• Organic core materials. • Southern clays, western clays and inorganic additives. During the CERP research testing where seacoal was
present, the material contributed 56-75% of the CO emis- sions, depending on the mold configuration. In order to reduce its CO emissions levels, the Nether- lands-based ferrous facility eliminated the use of seacoal over a period of one year, gradually replacing the material with a blend of inorganic additives and processed carbon. Te facility obtained a significant reduction in the quantity of CO found in its cooling and shakeout areas (Fig. 1). Between April 2007 and February 2011, the iron caster’s CO was reduced from approximately 40 ppm to 15 ppm. Te amount of CO allowed in that part of Europe is 30 ppm.
Overcoming Seacoal Loss
The application of seacoal in green sand facilities has been understood for many years. It is generally accepted by metalcasting industry researchers that seacoal (Fig. 2): • Reduces the wetability of molten metal by the precipi- tation of lustrous carbon onto the mold face.
• Produces a reduction atmosphere inside the mold cav- ity for the prevention of oxidation defects.
• Seals mold surfaces and reduces compressive stresses inside the mold (reduces mold wall movement) through the softening of the coal to form coke. The reduction of seacoal to control emissions in green
sand can have an adverse effect on casting quality. How- ever, it has been observed through loss on ignition test- ing that many metalcasting facilities in North America have an excess of carbonacious materials in their mold- ing sand. While every metalcasting facility is unique, a reduction of loss on ignition by 15-20% generally can be accomplished without impacting the castings produced. When a facility goes beyond this level of reduction, materials substitution is the only method that can be used to reduce emissions. Tests have shown the addition of graphite to green sand molds can be effective in combination with seacoal reduction to reduce CO emissions associated with pouring, cooling and shakeout. Graphite can be introduced into the green sand molding mixture in one of three ways: • Integration of graphite onto the surface of bentonite. • The use of graphite-coated green sand molds. • Suspending graphite in a green sand mold release agent. Testing of these methods has shown the combination
of seacoal reduction and graphite addition decreased both CO emissions and smoke in the metalcasting facility. Results from the tests indicate the methods are capable of yielding quality castings in a production environment. Both the Netherlands-based ferrous metalcaster
and Pride castings have lowered measured CO levels and smoke during their pouring, cooling and shakeout operations through the reduction of seacoal. In the final tabulation of its results, Pride determined it had lowered its coal tar pitch by about 0.2 mg/m3, enough to bring it in line with OSHA regulations.
• 南方粘土、西方粘土和无机添加剂 根据提供给CERP研究测试期间的煤粉样本的模型 组合情况，由材料排放的CO量在56~75%。 为降低它的CO排放水平，荷兰那家铸铁厂在为期 一年内取消了煤粉的使用，并逐步用无机混合材料 和加工碳粉取而代之。结果发现，该工厂冷却和落 砂区的CO排放量明显降低（见图1）。2007年4月 至2011年2月，其铸铁连铸机的CO量从40ppm降 到15ppm，而在欧洲国家这部分的CO排放量允许 值是30ppm。
克服减少煤粉的不利
许多年来，在湿型砂工厂中，煤粉的应用已被广 为了解，铸造行业研究人员公认的煤粉的有利之处 （见图2）： • 通过光亮碳在模型表面的沉积来减少熔融金属的 浸润性
• 为防止氧化缺陷，在型腔内部形成还原气氛 • 密封模型表面并通过将煤炼成焦炭来降低型腔内 的压应力（减少型壁移动）
在湿型砂中减少煤粉使用来控制排放会对铸件 质量带来不利影响。然而，通过点火测试的损失显 示，北美地区的许多铸造厂在他们的型砂中都使用 了过量的含碳材料。虽然每个工厂都是独特的，但 降低点火损失的15~20%一般都是能够做到的，并 且不会影响铸件生产。当某个铸造厂超出了这个降 低量水平时，材料替代是用来减少排放量的唯一方 法。
测试显示，在湿砂型中添加石墨对综合减少浇 注、冷却和落砂过程中的煤粉使用量以降低CO排放 量是有效的。在湿砂型中引入石墨的方法有三种： • 膨润土表面上石墨的集成 • 湿砂型石墨涂层的使用 • 在湿砂型脱模剂中悬挂石墨
这些方法的测试结果表明，降低煤粉和增加石墨的 组合减少了铸造厂的CO排放量和烟气。测试结果指 出，这些方法是能够在生产条件下产出品质铸件的。 荷兰的铸铁厂和Pride 公司都已经通过减少煤粉 降低了他们浇注、冷却和落砂操作中的CO和烟气测 量值。在其结果的最后列表中可见，Pride 公司的 煤沥青由大约0.2 mg/m3降低到足以符合OSHA法 规的限定线。
May 2013
FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION | 29
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