Effects of surface hardening on hardness and tensile strength of locally manufactured feed mill hammers

Abstract

Animal feed is a major production cost of raising livestock and accounts for about 65 - 68 % of the total production cost, mainly ingredients and processing costs. During feed manufacturing, a hammermill is required for the grinding process to produce quality feed. However, the absence of durable hammers on the local market in Ghana and the high cost of imported hammers compels feed producers to resort to locally manufactured hammers which wear fast due to poor quality of the material. This study considers the application of two surface hardening techniques: (i) carburizing (charcoal and Barium Carbonate (BaCO3) as activator) and (ii) carbonitriding (charcoal, NPK fertilizer as a nitrogen source and Barium Chloride (BaCl2) as activator) in combination with three different quenching media (water, air and oil), to improve the material properties of locally produced hammermill hammers. The surface hardening experiments were performed at 900 oC for 3 h after which the samples were quenched. Tempering was performed afterwards at 160 oC for 1 h. Carbonitriding and water quenching treatment had the best effect on hardness and tensile strength of all the treatments. It yielded the highest surface hardness and tensile strength of 410.06 HV and 768.79 MPa, respectively, representing about a 218 % increase in hardness and a 47 % increase in tensile strength compared to the control sample, which were 128.92 HV and 522.41 MPa, respectively. The result implies hammers produced with this carbonitriding surface hardening and water quenched technique would have improved hardness and wear resistance compared to untreated hammers.