out door should be provided to enable quick and easy access to the screen areas.
Secondary Attrition Secondary attrition can be employed after the primary
attrition unit to enable further binder removal. Tese units are especially suitable for the alkaline phenolic process and give furan levels of reclaim sand reuse at the mixer. Secondary attrition is not as costly to purchase or operate as thermal reclamation . Te basic principle of secondary attrition is to use a spinning drum at high speed to propel sand against sand at the right force so as to remove binder but not harm the sand grain. RPM can be adjusted to suit different types of sand grain and binder removal levels. Tere are two types of secondary attrition, hard and
soft. Te soft system uses the centrifugal method only and is more suitable for the furan process were not so much binder removal is required. Te hard system uses the centrifugal method as well as pair of squeeze rollers that force the sand grains together to give greater attrition and binder removal. Tis type of unit is more suitable for alkaline phenolic’s, silicate and green sand back to core shop (Fig. 2). It is worth noting that in the case of a hard system, the spinning drum and the squeeze rollers have ceramic outer linings to give a much longer lifetime. Also the pressure of the squeeze rollers can be varied to suit different sand grain structures and different levels of binder removal. Te sand can be passed through the unit up to three times (three separate cells) to further reduce the binder on the sand.
Thermal Reclamation
Te ultimate in sand reclamation has to be thermal, whereby 100% of all binder and other organic material is removed. Te sand is generally better quality than when it was first bought. Typically a thermal unit will
run on gas or electric and operate at temperatures of between 600C and 750C depending on the type of binder used. Te sizes range from 250kg/hour up to 12 tons per hour (Fig. 3).
提供能够快速方便地清理访问到格栅区域。 二次摩擦
二次磨擦可以在初次摩擦单元之后采用，以便进一步 去除粘结剂。这些单元是特别尤其适合用于碱性酚醛工 艺和各级呋喃砂在混砂系统内器的再回用。二次磨擦单 元的购置买或操作也不像热法再生那样昂贵，因此可以 被认为是一个成本效益替代热法再生的工艺。 二次磨擦的基本原理是使用高速旋转鼓，在合适的 力来推动砂撞击砂，以除去粘结剂，但不损害砂粒。 RPM可以调整，以适应不同类型的砂粒和粘结剂去除 水平。
有两种类型二次磨擦，硬和软。软系统只采用离心方 法，更适合为呋喃树脂，,既不需要去除这么多的粘结 剂。硬盘系统采用离心法，以及对挤压辊，迫使沙砂粒 在一起，得到更大的磨擦和除去粘结剂，。这种类型的 单位是更适合于碱性酚醛树脂，硅酸盐和潮模砂回用制 芯。 （图2）
这是值得注意的，在硬盘的系统的情况下，旋转鼓和 挤压辊有陶瓷外衬层，得到更长的寿命。的挤压辊的压 力也可以改变，以适应不同的砂粒的结构和不同的粘结 剂去除水平。砂可以三次通过单元（三个单独的栅格） ，以进一步减少包覆在砂上的粘结剂。
热法再生
最彻底终在的砂再生是热法 再生，由此100％除去所有的粘 结剂和其它有机材料。这使再 生砂子比它被第一次购买时新 砂质量还好。
通常情况下，加热法的单元 靠燃气或电运行，并取决于使 用的粘结剂的类型，在600℃和 750℃之间的温度下进行操作。 尺寸再生能力范围从每小时 250kg到12t每小时（图3）。 对于碱性酚醛树脂系统，一 个特殊的抑制剂必须是预混在 砂中，以防止碱性盐导致低温
Fig. 2. The hard type of secondary attrition unit is more suitable for reclaiming alkaline phenolic, silicate and green sand back to the core shop.
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FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION February 2013
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