Te fertilizer knife is attached to the Coulter disc to keep the blade free of residue and protect the fertilizer delivery tubes from wear. It creates a 4-in. trench in the soil for fertilizer or ammonia placement. In operation, the knife shatters the trench cavity’s hard side walls to help close it quickly so the liquid nitrogen delivered to the soil via tubes is not exposed to the air to become gas. Te knife’s application requires high wear resistance due to the severe conditions of the application. To achieve optimal performance out of the cast conver-
sion, Yetter worked with Lethbridge to produce prototypes in three materials: 27% high chrome iron, austempered ductile iron (ADI) and carbidic austempered ductile iron (CADI). CADI is a relatively new family of ductile iron that few
North American metalcasting facilities pour. It contains carbides in its microstructure to increase toughness and wear resistance after austempering. Abrasion resistance and hardness increase as carbidic content increases. In field trials, the CADI knife prototype exhibited increased impact resistance compared to the 27% high-chrome iron prototype and superior abrasion and wear resistance over ADI grade 5. Yetter and Lethbridge selected CADI as the production material. Yetter wanted the new knife design to offer better
protection for the assembly’s anhydrous ammonia delivery tubes and beavertail components, which were prone to wear on the original fabrication. Consolidating various parts into a single casting also would eliminate the need for additional part numbers. Other non-critical components could be offered as optional add-ons. Lethbridge produced the final design in green sand
with two cores and supplied it to Yetter as-cast, without any machining required. Shell coring was chosen for the mounting ears and holes, which kept the ears parallel to each other and provided dimensional stability for final assembly. A
肥料刀装在犁刀盘上，保证刀片远离残渣，保护肥 料输送管不被磨损。它在土地里制造了4英尺的沟，放 置肥料或氨水。工作时，刀具粉碎沟槽坚硬的侧壁， 辅助它迅速关闭，这样从管子输送到土壤中的液氮不 会暴露在空气中挥发。由于恶劣的使用条件，刀具需 要较高的抗磨损性能。
为了通过铸造转变实现最佳性能，Yetter和莱斯布 里奇合作生产三种材料的样品：含Cr27%的高铬铸 铁，等温淬火球墨铸铁（ADI）和碳化物等温淬火球 墨铸铁（CADI）。
CADI是球墨铸铁中相对较新的类别，北美几乎没有 铸造厂生产。它在微观组织中包含碳化物，在回火后 提高韧性和耐磨损性能。随着碳化物含量的增多，耐 磨损性能和硬度提高。在现场试验中，同含Cr27%的 高铬铸铁样品相比，CADI刀具样品呈现出更高的冲击 韧性，耐磨度也高出ADI样品5个等级。Yetter公司与 莱斯布里奇公司选择了CADI材质作为产品最终材质。 Yetter希望设计新的刀具，为装配体中的无水氨输 送管和测高天线零件提供更好的保护，它们在初始的 制造中容易磨损。把不同的零件合为一个单体铸件， 也消除了对额外零件的需要。其他不重要的零件可以 作为可选附加装置提供。
莱斯布里奇用砂型铸造制造出最终交货给Yetter的 铸件，使用了两个型芯，不需要任何机加工。使用壳 芯制造吊耳和孔 洞，保证吊耳的 相互的平行关 系，为最终的装
Lethbridge Iron Works produced the cast conversion of the fertilizer knife in carbidic austempered ductile iron, which exhibits excellent wear resistance.
莱斯布里奇钢铁厂生 产肥料刀的改装铸 件，用含碳化物等温 淬火球墨铸铁，呈现 良好的抗磨损性。
May 2013
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