This research presents performance of nitrogen gas as a coolant in machining titanium. Compressed nitrogen gas stored in a cylindrical tank is supplied to the cutting zone via the stainless steel tube of 2x8x25mm (inside diameter x outside diameter x length) connected to the flexible hose and specially-designed valve with pressure controller. Machining experiments are carried out on conventional turning center. The cutting tool used is triangular insert of ISO-TPGN160308 with the holder (ISO-CTGPR3232K). The cutting insert grade is KC5010 (TiAlN3 coated carbide) as recommended by Kennametal for machining titanium. During machining, the tube is manually directed to be just-above the tool rake face and the nitrogen gas is supplied with high pressure so that the cutting zone receives an effective cooling as well as the chip brakes easily. The effectiveness of this new cooling strategy is demonstrated by the cutting edge condition and surface finish after machining at various speeds, and also by comparing with performance of conventional coolant. The result is found to be excellent in terms of relative amount of tool wear and surface finish. The cutting insert has surprisingly remained almost intact when using nitrogen gas coolant whereas severe tool wear occurred with conventional coolant even at low cutting speed. This cryogenic strategy also improved machined surface quality greatly.

Vibrational damping behaviors of graphene nanoplatelets (GNPs) reinforced natural rubber/ethylene-propylene-diene rubber (NR/EPDM) were investigated. The nanocomposites were prepared through melt compounding using a Haake internal mixer. In this study, GNPs reinforced NR/EPDM nanocomposites were characterized for damping properties towards the effect of GNPs loading (1, 3 and 5 wt%) and chitosanfunctionalization. The results indicate the addition of GNPs have significantly improved both log decrement and damping ratio values correlated to the enhanced damping property of the nanocomposites. Chitosan-functionalized GNPs seem to slightly hamper the increase of damping properties contributed by incorporation of GNPs in NR/EPDM blends. These findings were further supported by thermal and morphological studies through dynamic mechanical analysis (DMA) and transmission electron microscopy (TEM) analysis. The storage modulus, loss modulus and tan δ showed good agreement with the vibrational damping test. Meanwhile, TEM analysis revealed the existence of intercalated and exfoliated structure of GNPs in NR/EPDM matrix which resulted in improved vibration damping properties of the nanocomposites for the potential used as vibration insulator.

Abstract

A statistical model was developed in this study to describe cure characteristic, rebound resilience and tensile strength of natural rubber/starch composites which was prepared by using a Haake internal mixer. Response surface methodology (RSM) based on central composite centered design (CCD) was employed to statistically evaluate and optimize the conditions for maximum cure characteristic, rebound resilience and tensile strength and study the significance and interaction of carbon black and glycerol on rebound resilience and tensile strength yield. The experimental runs were carried out according to a 22 full factorial design for the two identified design independent variables, namely, carbon black (X1) and glycerol (X2). With the use of the developed quadratic model equation, a maximum rebound resilience 71% was obtained to be a carbon black loading of 50 phr and glycerol loading of 7 %.