Lining Materials for Bulk Solids Handling Equipment

Wear & Abrasion

Lining Materials for Bulk Solids Handling Equipment

Selection of Materials for the Iron & Steel Industry – An Integrated Approach
The handling, storage and transportation of raw materials and intermediate products in the preliminary stages of iron and steel production are a cumbersome task, due to their vast amount and abrasiveness. Liners may help to reduce these negative effects.
(ed. WoMaMarcel - 16/12/2014)
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If the influence of temperature and velocity of movement is not considered, the abrasion/erosion wear caused by the main raw materials/intermediate products is as follows: (1) Coke; (2) Sinter; (3) Iron Ore. For the constant height of fall and nominal size ranges, the level of impact encountered by these materials in the order of highest degree is as follows (1) Iron ore; (2) Sinter; (3) Coke.

It is known that the wear resistance of a material can be increased at the expense of resistance to impact and vice versa. It is often required to strike a balance between the wear resistance and resistance to impact of the lining materials to qualify for the suitability under specific application conditions. It is therefore essential to undertake the diagnosis of wear condition existing under the specific situation prior to making a choice of lining materials.

The choice of materials is also governed by the ease of fabrication/forming, ease of maintenance and cost effectiveness. The most popular choices are Quenched & Tempered Medium Carbon Low Alloy Steels, Martensitic Stainless Steel, Mn-Steel, High Cr Iron Alloy (Castings & Composite Plates) and Sintered Alumina.

The complete specifications for these materials, however, need to be drawn after careful consideration of the service conditions and advantages/limitations of the materials under considerations in consultation with expert agencies.

In the iron and steel industry, the two most prominent lining materials for handling of coke, sinter and iron ore are high Cr-Iron-alloy and sintered Alumina.

High Cr Iron Alloy

The high Cr-ironaalloy family encompases a wide range of chemical composition with C in the range of 2.5-3.5 wt.% and Cr in the range of 18-30 wt.% as the main elements, additionally alloyed with Ni, Mo, V, W, Nb etc.. The hardness obtained after heat treatment may vary from 53-67 HRC depending upon the chemical composition and heat treatment. The microstructure consits of mainly a discontinuous network of primary carbides and a martensitic matrix. The chemical composition and heat treatment to suit the application specific requirement can be customized.

The C and Cr contents (wt. %) in the range of 2-2.5 and 20-25 respectively with additional Ni and Mo each in the range of 1-1.5 may be considered for sustaining moderate impact with significant wear resistance. For a hardness of 53-58 HRC and a microstructure consisting of discontinuous network of primary carbides in a tempered martensitic matrix hardening plus tempering may be employed.

The C and Cr contents can be increased to the level of 2.5-3.0 and 25-30, respectively, to increase the wear resistance, if the level of impact is low.

These alloy can be obtained either in the form of castings or in the form of composite plates. The castings can be air hardened at a temperature of 1010 degree C and tempered at a temperature of 400 degree C. The typical microstructure would consist of primary carbides and tempered martensite. The composite plates are based on a hard layer of high Cr iron alloy of suitable thickness with a backup layer of mild steel or sometimes stainless steel. The hard layer could be produced by many methods including weld deposition, composite castin or sintering methods. The microstructure of composite plates typically consits of primary carbide and a carbide austenite eutectic.

These alloys can exhibit 5-6 times superior wear resistance compared to the conventionally used alloys, such as Mn-steel.

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