Structure‐Processibility Relationships During Rotational Moulding of Plastics

Abstract

and 5c. When the sliding propagates to a grain boundary, intergranular cracking is relatively easy to nucleate due to the pile-up of dislocations at the interface, as shown in Figure 5d. Meanwhile, the formation of buckling always accompanies two damage modes, i.e. cleavage fracture and delamination, as illustrated as in Figures 5e and 5f. Also kinking can cause two typical cracks along kinking boundaries and delamination crack, as shown in Figure 5g. Therefore, the plastic strain energy induced by indentation and compression can be absorbed by the multiple deformation and damage mechanisms, including: sliding, buckling, kinking, intergranular and transgraunlar cracking. This often allows a damage-tolerance to long cracks, as in the other brittle ceramic materials.Conclusions: The hardness of Ti 3 SiC 2 crystals shows load dependence in low load range and reaches a nearly constant value of~4 GPa in the high load range. In the low load range, the orientations of Ti 3 SiC 2 crystals also affect the hardness, which ranges from 4 to 8 GPa in the present tests.Ti 3 SiC 2 crystals have a multiple deformation and damage mechanisms. Sliding, buckling and kinking are three basic deformation mechanisms under indentation. Transgranular and intergranular cracking always lead to the local damage in Ti 3 SiC 2 polycrystals. Typical transgranular cracking often displays as the formation of delamination crack and cleavage fracture of deformation bands induced by the severe buckling and kinking. ExperimentalCommercially available Ti (10 lm and 99.9 %), Si (10 lm and 99.9 %) and TiC (2-5 lm and 99 %) powders with a molar ratio of 1:1:2 were selected in the present experiment. Before sintering, the powder was mixed by a Turbular shaker mixer in Ar atmosphere for 24 h, then, was compacted into a graphite mold (50 mm in diameter) and sintered in vacuum (10 -4 Torr) at 1400 C for 60 min by using the PDS technique. The relatively high sintering temperature (1400 C) as compared to the sintering conditions we usually used for Ti 3 SiC 2 synthesis can coarsen the Ti 3 SiC 2 grains. [20] The heating rate was controlled at 50 C/min and the applied pressure was maintained constant at 50 MPa during sintering. The purity of the sintered Ti 3 SiC 2 sample was calculated from the x-ray diffraction result to be~95 wt% with the residual TiC phases through standard additive method. [19] Then, the sample was etched by a solution of H 2 O:HNO 3 :HF (2:1:1) for 5 ± 10 sec to expose the Ti 3 SiC 2 grains. The microstructure of the Ti 3 SiC 2 samples consists of 50 ± 200 lm lath-like structure and 2±10 lm fine grains. Indentation tests were performed to the etched Ti 3 SiC 2 samples in a load range of 0.25 ± 20 N. After tests, the indentations were observed by SEM to reveal the deformation and damage mechanisms at different loads.

Validation of a 1D dynamic thermal finite difference model for the rotational molding of an amorphous polycarbonate resin

“…6,7 The latest trend within rotational molding is to improve process control, efficiency, and automation but also to expand the potential material range to natural fiber reinforced polyethylene (PE), biodegradable polylactic acid (PLA), polyetheretherketone (PEEK), and so on, each having their own challenges to process. 5,[8][9][10][11][12] A rotational molding production cycle typically consists out of four main stages: charging the mold with polymer powder, heating of the mold, cooling, and eventually demolding of the product. 3,13,14 This paper focuses on the heating stage.…”

“…This is mainly because of its high thermal stability, which is needed to cope with the hard to control thermal processing conditions. The remaining 5%–10% is mainly covered by polypropylene (PP), polyvinylchloride (PVC), Polyamide‐6 (PA6), and polycarbonate (PC) 2,3,5 . Recently, more advanced processing equipment like direct heated and actively vented molds in combination with a higher degree of freedom in mold rotations have been developed 6,7 .…”

“…Recently, more advanced processing equipment like direct heated and actively vented molds in combination with a higher degree of freedom in mold rotations have been developed 6,7 . The latest trend within rotational molding is to improve process control, efficiency, and automation but also to expand the potential material range to natural fiber reinforced polyethylene (PE), biodegradable polylactic acid (PLA), polyetheretherketone (PEEK), and so on, each having their own challenges to process 5,8–12 …”

Parametric and mechanical characterization of linear low density polyethylene (LLDPE) using rotational moulding technology

“…In the rotomoulding process, the temperature must be sufficiently high to achieve the correct viscous and elastic rheological characteristics in the polymer to promote the coalescence of granular particles, and for removal of trapped bubbles. The processibility relationship for rotational moulding process between the initial powder temperature (T 1 ) and polymer degradation temperature (T d ) are reported by Abbas Tcharkhtchi & Jacques Verdu (2004). In general, the polymer is processible if T d > T 1 .…”

Bulletin of the Polish Academy of Sciences: Technical Sciences

“…The literature review shows that the process variables play an important role in producing effective and reliable products in rotational moulding; however, no previous studies have investigated the relationship between rotational moulding process parameters and compression behaviour [25][26][27][28][29].…”