It is well known that both energy efficiency and productivity are critical for large scale industrial operations. Components such as molds and dies used in powder metallurgy industry and jaws, hoppers, chutes, pumps in mining and cement industry are affected by abrasive wear during raw material handling. Advanced steel grades (with bainite-martensite-carbide microstructure, Hadfield steel) and surface engineering solutions (WC-Co, Cr3C2) offering 10X higher wear resistance have improved productivity and reduced maintenance cost. However, the overall energy efficiency, driven by the electric/diesel power consumed during such operations is ignored. Frictional resistance between raw material and tool interfaces directly affects the power dissipated and energy efficiency.
Figure 1. Schematic (excavator showing operation, abrasive wear interfaces and energy expended)
As an example, excavators digging into soil and ground would require less power if wear resistant materials offering low frictional resistance were used (see Figure 1). A chute or hopper for material handling (see Figure 2) would be more productive if low friction wear resistant liners were used to reduce problems such as bridging due to high wall friction. Dies used during powder metallurgy manufacturing operations (see Figure 3) would require less energy during moulding and demoulding stages if the die material offered lower frictional to powder movement.
Figure 2. Schematic (chute for material handling showing bridging due to high wall friction)
Figure 3. Schematic (dies used during powder metallurgy manufacturing operations).
There is a need to evaluate the friction and wear performance of materials used in similar applications and understand the drivers for high wear and low friction resistance during three-body abrasion.
Ducom Abrasion Tester (ABT-3) with integrated friction measurement system offers the relevant platform for conducting such studies (see Figure 4). In addition, Ducom abrasion tester offers a wide range of test conditions ranging from low stress to high stress abrasion under both dry and wet conditions complying with the ASTM G65, ASTM G105 and ASTM B611 standards. The automated loading module based on the pneumatic system uses an active feedback to maintain constant load irrespective of the contact conditions, extent of wear and vibrations which cannot be met by conventional dead weight loaded systems.
Figure 4. Schematic (Dry and Slurry Abrasion Tester ABT-3 with automated loading and friction force measurement)
Abrasive wear resistance of D2 and H13 steels were tested using ABT-3 as per the ASTM G65 standard (procedure E). These are special tool steels and used as reference materials as per ASTM G65 standard. A load of 130 N load applied on the sample against rubber wheel rotating a speed of 200 rpm. Sand is supplied into the contact interface at a rate of 325 g/min. Mass loss of the sample is measured after 718 m of linear abrasion (1000 revolutions of rubber wheel). The sand used for testing differs in morphology from the AFS 50/70 sand mentioned in ASTM G 65.
Table 1. Material properties.
Figure 5. Volume loss of D2 Steel and H13 Grade Steel.
Visual examination of scar using optical microscope indicates the damage on H13 Grade to be smoother and deeper compared to D2 steel. H13 being relatively softer than D2 steel, experienced greater extent of plastic deformation and continuous rupture due to ploughing by abrasive particles resulting in a smoother surface as shown in Figure 6. D2 on the other hand showed several deep grooves on the abraded surface highlighting a more aggressive material removal mechanism.
Figure 6. Optical images of D2 steel and H 13 Grade steel showing plastic deformation and continuous rupture due to ploughing by abrasive particles of H13 Grade steel.
Figure 7. Friction coefficient of D2 Steel and H13 Grade Steel.
To summarize, D2 showed higher abrasion wear resistance compared to H13 steel due to its higher hardness. However, the same microstructure also lead to 50% higher friction force and energy dissipated during the abrasion testing.
This highlights the importance of evaluating both friction and wear resistance of materials used in industrial processes involving material handling as a precursor to reducing energy consumptions and improving operational efficiency.