Strength and wear of plastic shredder blades based on different orientations and geometries

• Main Author: Wong Jin Hoong
• Format: Thesis
• Language: English; English
• Published: 2023
• Subjects: TD783-812.5 Municipal refuse. Solid wastes
• Online Access: https://eprints.ums.edu.my/id/eprint/40559/1/24%20PAGES.pdf; https://eprints.ums.edu.my/id/eprint/40559/2/FULLTEXT.pdf; https://eprints.ums.edu.my/id/eprint/40559/

Plastic pollution has become a worldwide issue and requires adequate awareness to solve the plastic waste management and disposal processes. Alternatively, recycling initiatives are important. The plastic shredder machine is a preliminary machine for shredding plastic waste before converting it into a functional commodity. Shredder machine designs for industrial, small to medium businesses, or individuals are readily available. However, the shredding output is constrained by the configuration of the blades, where inconsistent plastic distribution was observed. Therefore, certain sections of the blades experience more load compared to others. Shredder blade is the main components of a shredder machine used in plastic recycling. The validation of the shredder blades’ design is essential to justify the suitability and safety of the design for the blade’s installation in the shredder machine. Various edge angle (20°, 35° and 50°) of the shredder blade was analysed. The shredder blade with edge angle of 35° was chosen as it might provide a better shredding performance with larger grabbing curve. The maximum von Mises stress, displacement, and shear stress along with the minimum safety factor of the double and triple edges shredder blade towards the shredding of the Polyethylene Terephthalate (PET) sheet was analysed using Finite Element Analysis by Fusion 360 software. The result based on 1000N reaction force showed the maximum von Mises stress between 159.70 MPa to 184.80 MPa, maximum total displacement deformation of 0.03752 mm – 0.04611 mm, maximum shear stress of 50.85 MPa – 71.86 MPa, and safety factor of 1.95 – 2.25 for both double and triple edges shredder blade. The design of both blades is acceptable and safe since the safety factor is higher than the lowest safety factor standard of 1.5 based on the allowable stress code standard. A performance study was conducted on shredder blade using double and triple edges geometries with three different orientations which are spiral, V-orientation and series to understand its wear and shredding mechanism. Series orientated shredder blades were excluded due to high torsion were created caused the permanent deformation on the shredder machine’s part. Identification of the loading distribution along the shredder blades was observed in different orientations. The microstructure and hardness of the worn cutting edge and as-received shredder blade were characterised by optical microscopy, scanning electron microscopy along with energy dispersive X-ray (EDX), X-ray diffraction analysis (XRD) and hardness testing. Wear mechanism in the shredder blades were categorised as progressive wear. The progressive wear was due to the abrasive, adhesive, and oxidation wear. Abrasive wear as the major progressive wear mechanism has been confirmed based on the shredding mechanism and microstructure analysis on the blades. An increase in oxygen element in EDX and the presence of magnetite and hematite in XRD analysis proven the oxidation wear occurred at the crack and dents on the blades’ surface. Recycling efficiency, shredding efficiency, and percentage retention are the parameters used to evaluate the performance of the shredder blades. The shredding efficiency in all geometries and orientation ranged between 64.83 ± 0.69% to 69.53 ± 1.32% and is highly efficient in recycling of PET plastic with recycling efficiency above 95%. The best combination of the geometry and orientation is the double edges shredder blade with spiral orientation, which exhibited recycling efficiency at 97.39 ± 0.04%, shredding efficiency at 69.53 ± 1.32%, and retention at 2.61 ± 0.04%, along with a fewer number of blades recorded severe wear.