Improving The Wear Resistance of Mechanical Harvester Basecutter Blades by Surface Engineering. Kavian Cooke and Gossett Oliver: Mechanical Engineering Department, University of Technology, Jamaica Andrew Lyle: Sugar Industry Research Institute, Factory Services Division
Overview Introduction Materials Experimental Procedures Results and Discussions Cost benefit analysis Conclusions & Recommendations Questions
Introduction The objective of the study was to improve the wear and corrosion resistance of mechanical harvester blades The first step was to carry out a situational analysis How are base cutter blades used? By what mechanisms are the blades losing mass?
Introduction From the situational analysis conducted it was found that the causes of material loss were: Corrosive wear Abrasive wear Impact wear Using thermal spraying to combat these problems. Why thermal spray coatings? The flexibility of using in expensive parent material (toughness) The hard outer coating provides the required wear and corrosion resistance properties.
Thermal spray processes Both process operate on the same principle i.e. require material is melted and projected towards the parent material. It forms a mechanical bond with the surface and solidifies to form a coating Schematic of the high velocity oxy-fuel spray process Schematic of the electric wire arc-spray process
Materials Arc spraying Variables Chemical composition AI 1800 6.03Al,87.7Ni,6.03Mo other 0.28 Flow density/spray rate size 61b/3.0kg 1.6 mm diameter HVOF Variables Chemical composition WC-NiMoCrFeCo agglomerated sintered powder - WC- Ni Mo Cr Fe Co Particle size 45 microns to + 15 microns Powder flow: 5 lb/hr
Specimen Preparation Specimens used in microscopic examination was Prepared according to ASTM standards. Untreated blades were grit blasted prior to application of the coat and subsequently tested. (a) (b)
Testing This aspect of the research was divided into two areas: Laboratory testing Impact and Abrasive wear Corrosive wear Microscopic examinations Field Testing The blades are placed into operation and the performance evaluated over a seven day period.
Abrasive wear testing Equipment designed to simulate the abrasive wear of mechanical harvester blades. reverse off forward Switch Drill press Spindle How does the equipment work? Board Container What test materials were used? Basecutter Blades Bagasse Sand particles composition of abrasive material Clay Drill press table Silt How was the mass loss evaluate? Drill press base
Testing done to assess corrosive behavior of mechanical harvester blades Corrosion Testing How does the equipment work? What test materials were used? A static potential test was used
Microscopic Examinations These examinations included: Porosity measurements Hardness Microstructure evaluation Hardness was measured using a Vickers Micro-hardness tester at a load of 0.3Kg The Micro-structural examination and porosity measurements were evaluated using a Zeiss Microscope.
Results: Microscopic Examination These defects are represented in the form of dark grey spots, which from X-ray analysis using an SEM appears to be silicon particles. Dominant elements of untreated blade Si Mn C Fe 1.94% 0.93% 0.4% 96.68% Surface of base cutter blade material
Material Microstructures HVOF coating had compact microstructure Separation at the coating/substrate interface for AS coatings. Spherical porosity Microstructure of WC-NiMoCrFeCo Microstructure of the AI 1800 coating
Microscopic Examination Coatings are compared on the basis of hardness and porosity. HVOF coating had a more compact microstructure than AS coatings Tungsten based coating had highest hardness 1400 1200 Hardness ( HV) 1000 800 600 400 untreated WC AI1800 200 0 Blade type
Untreated Blade The material was immersed in simulated sugar cane juice. Corrosion test results The results indicate that the blade was highly corrosive and not suitable for operation in an acidic environment. Figure 4: surface of untreated blade immersed in simulated sugar cane juice of ph 4.0 As the blade corrodes silicon fall out particles leaving pits.
Corrosion test results The untreated blade experience extensive corrosion The coating surface appears to have good corrosion resistance The interface experienced extensive corrosion due to the differences in corrosion rate between the substrate and the coatings.
Micrographs of surface Surface of WC-NiFeCrCoMo Coating/substrate interface
Micrographs of surface Surface of AI1800 coating Coating/substrate interface of AI1800 coating
Results: Abrasive Wear Cumulative mass loss of coated blades. 250 200 WCNiCrFe CoMo Untreated AI800 150 100 50 0 untreated double side Coating position
HVOF blades tested in field conditions untreated blade tested in the field single side bottom cavity WC-NiCrMoFeCo blade double side WC-NiCrMoFeCo blade
Arc Spray coated blades AI1800 coated blade double side untreated blade tested in the field
The life span of each coated blade relative to the life span of the untreated blade 12 Mass loss of untreated blades (g) 10 8 6 4 2 9.7 2.3 0 WC AI1800 Mass loss of coated blades (g)
Cost Benefit Analysis Blade Life Blade Type Number blades per crop Cost per blade Cost per crop n = 1 Untreated 2360 $1050 $ 2,501,600 n = 9.7 WC-NiFeCoCrMo 244 $1450 $353,800.00 n = 2.3 AI1800 1027 $1400 $1,437,800.00
Conclusions The HVOF coating presented a denser microstructure with less porosity and better adhesion to the substrate material than the Arc spray coatings. The surface of all coating tested appeared to provide good corrosion resistant. However the interface between the coating and the substrate material experienced corrosion resulting in delamination of the coating. The primary mechanism of material loss during operation is abrasion. Hence the effect of corrosive wear forms only a fraction of the total material lost by each blade.
Recommendations Other surface engineering techniques: case hardening using blue mountain coffee shells. Exploration of brazing a harder piece of material unto the cutting blades could further improve its performance. The influence of coating variables such as voltage, current, gas, gas pressure, and spray distant has not been assessed for the HVOF process. Optimization of the base cutter angle and blade positioning.
Questions