Retreatment of Polymer Wastes by Disintegrator Milling

Global introduction of waste utilization techniques to the polymer market is currently not fully developed but has enormous potential. Before reintegration of used material into a new product, it normally requires grinding, that is shredding, crushing, or milling. In traditional grinders, the generated stresses in the material to be ground are equal to or less than the strength of the material. If by traditional methods, the stresses generated are compressive + shift, so by milling based on collision are tension + shift. Due to the high stress-material strength ratio at collision, it is possible to crush not only brittle materials but also ductile materials. This process allows easily combining the grinding of composite materials with their separation into individual constituents. In the current study, the mechanical recycling of the following groups of polymer materials was studied: pure brittle and soft polymers (PMMA, HDPE and IER), blends of plastics (ABS+PMMA, PC + ABS), reinforced plastics (PMMA+GFP); elastomers (rubber and tyres), and printed circuit boards (PCB)

Using small punch testing method for the analysis of creep behaviour of Al-Al 4 C 3 composites

Abstract. Mechanical alloying and mechanical attrition are both processes based on the imparting of a severe plastic deformation using high-energy ball mills. The experimental material, dispersionstrengthened aluminium with Al 4 C 3 particles, was prepared by mechanical alloying of aluminium powder (< 50 µ m) with different types of carbon. Creep behaviour of the composite, based on aluminium matrix, reinforced by 4 vol% Al 4 C 3 , was studied at temperatures from 623 to 723 K by small punch testing with a constant force. The time dependence of the central deflection was registered and the minimum deflection rate was determined. The dependence of this quantity on the applied force can be described by a power function with relatively high value of the power. The dependence can be rationalized by an analysis in terms of the threshold concept. Analytical procedure for comparison of the threshold force in small punch experiments and threshold stress in conventional creep testing are given

Decarburisation Effect on Hardened Strip Steel Fastening Components

Heat treatment is widely used for high reliability fastening components such as buckles and brackets. The current study focuses on mass production of safety components which are fineblanked from sheet metal, austempered and chromium electroplated. Electroplating together with stamping defects may lead to unexpected brittle failure of the component. It is widely known that during austenitisation, decarburisation could avoid brittle failure and, therefore, slight decarburisation is recommended. There is little information how much mass production is influenced by decarburisation and where the limits are. The current study has two goals. The first one focuses on the extent of decarburisation effect on the part properties, and the second aims to find the optimum furnace setting for the product type used in the study. Also, it is necessary to choose a reliable decarburisation control method for austempered components. The effect on material grades was analyzed by using three steel alloys with carbon content of 0.37 wt.%, 0.47 wt.% and 0.62 wt.%. The specimens were austempered to hardness 45 – 51 HRC under endothermic protective atmosphere. To gain different decarburisation levels, two gas set-ups were used. Infrared gas analyzer was used to measure CO and CO2 content in the furnace gas. Three characteristics of the specimens were evaluated: hardness, rupture strength and brittleness. The depth of the decarburisation was determined by three different approaches according to standard EN ISO 3887. Based on the results, the spectrographic method is the most reliable for determining the depth of decarburisation. This study reveals that higher surface decarburisation has a positive effect on the ductility and no effect on the rupture strength of the component. The material with carbon content of 0.62 wt.% is the most sensitive to decarburisation. During mass production, the inaccuracy of hardness measuring raises which results in the inaccuracy of salt bath temperature regulation. For the used thermal cycle, the furnace gas carbon potential 0.30 – 0.40 has to be used to ensure expected performance of fastening products

Comparative Study of the PVD Coatings on the Plasma Nitrided Steel

In the current study, the cracking, impact and sliding wear resistance of the PVD single layer TiN (I generation), multilayer (Ti,Al)N-ML (II generation), gradient (Al,Ti)N-G and multilayer nanocomposite FiVIc® (both – III generation) coatings on the nitrided low alloy steel 42CrMo4 are analysed. The cyclic indentation test (normal load 50 N, 10 000 cycles) was carried out to determine the cracking resistance of the coatings. Impact wear test was performed at the normal load 16 N, strokes’ frequency 25 Hz, 104 – 107 strokes. Sliding wear test was applied, using the block-on-plate scheme, Ø 10 mm Al2O3 ball as the counterbody, at the normal load of 10 N, the frequency 5 Hz, the amplitude 10 mm and the test duration 10 min. Best resistance to cracks’ formation is demonstrated by the gradient (Al,Ti)N-G coating, showing medium radial cracks’ formation, whereas delamination of the coating can be observed in other cases. 1.6 – 1.7 times higher impact wear resistance is shown by the TiN coating in comparison with the other coatings. The FiVIc® coating demonstrates lightly better resistance to sliding wear in comparison with the TiN and (Ti,Al)N-ML coatings due to a lower coefficient of friction. The worst sliding wear resistance is observed in the case of the (Al,Ti)N-G coating due to a high affinity of the coating’s and counterbody’s materials.DOI: http://dx.doi.org/10.5755/j01.ms.18.1.1339</p

Metal-Matrix Hardmetal/Cermet Reinforced Composite Powders for Thermal Spray

Recycling of materials is becoming increasingly important as industry response to public demands, that resources must be preserved and environment protected. To produce materials competitive in cost with primary product, secondary producers have to pursue new technologies and other innovations. For these purposes different recycling technologies for composite materials (oxidation, milling, remelting etc) are widely used. The current paper studies hardmetal/cermet powders produced by mechanical milling technology. The following composite materials were studied: Cr3C2-Ni cermets and WC-Co hardmetal. Different disintegrator milling systems for production of powders with determined size and shape were used. Chemical composition of produced powders was analysed.  To estimate the properties of recycled hardmetal/cermet powders, sieving analysis, laser granulometry and angularity study were conducted. To describe the angularity of milled powders, spike parameter–quadric fit (SPQ) was used and experiments for determination of SPQ sensitivity and precision to characterize particles angularity were performed. Images used for calculating SPQ were taken by SEM processed with Omnimet Image Analyser 22. The graphs of grindability and angularity were composed. Composite powders based on Fe- and Ni-self-fluxing alloys for thermal spray (plasma and HVOF) were produced. Technological properties of powders and properties of thermal sprayed coatings from studied powders were investigated. The properties of spray powders reinforced with recycled hardmetal and cermet particles as alternatives for cost-sensitive applications were demonstrated.DOI: http://dx.doi.org/10.5755/j01.ms.18.1.1348</p

Comparison of Plasma Transferred Arc and Submerged Arc Welded Abrasive Wear Resistant Composite Hardfacings

EComposite hardfacings produced by Plasma Transferred Arc Welding (PTAW) and Submerged Arc Welding (SAW) possess a good combination of hardness, wear resistance and fracture toughness, thus providing high wear resistance. Although they cannot substitute and be compared with conventional WC-Co based hardmetals, still they can be used in many applications where high wear resistance, hardness and toughness are in great demand. In this study two different hardfacing production technologies PTAW and SAW, were used to produce the hardfacings for abrasive wear conditions. In both cases hardfacings were welded on the top of low alloy steel using different proportions of disintegrator milled hardmetal WC-Co powder of different fractions as a reinforcement and self-fluxing alloy as a matrix. They were analysed in regard to Rockwell and Vickers hardness, wear behaviour, and microstructural analysis. SAW hardfacings were subjected to Rockwell hardness test after process and after two cycles of tempering; secondary hardness effect was detected as increment of hardness values from 39 HRC to 58 HRC after first cycle of tempering. High Vickers hardness values did not correlate with wear results, as it commonly shows hardness of hardmetal particles. Dissolution of hardmetal particles in the matrix was observed in both PTAW and SAW hardfacings with higher amount in the later. This amount correlated with heat input during welding process. Wear test results in abrasive emery wear (AEMW) and abrasive wheel wear test (AWW) showed almost analogous tendency, with slightly lower wear in later. Both types of hardfacings have shown promising results in intensive wear conditions. DOI: http://dx.doi.org/10.5755/j01.ms.24.2.19121</p

Research of abrasive erosion wear for Fe-C-Cr-B hard layers

This study presents the research related with abra-sive erosion wear of electric-arc welded hard layers. It is estimated, that when the abrasive particles affect the hard layers surface at oblique angle the wear by microcutting prevails, when they strike perpendicularly – the wear is caused by microfatigue processes. Under abrasive erosion conditions the wear of electric arc welded hard layers is lower if compared to Hardox 400 up to 31% at the abrasive particles impact angle of 30°, and only up to 4% at the perpendicular particles impact. Under the abrasive particles stream impacting the surface at oblique impact angle the most resistant to wear are the layers alloyed with 1.6-1.9% carbon and 4-8% chromium while under the normal impact the most resistant to wear are the low carbon layers alloyed with 0.15% C and high chromium layers alloyed with 15% Cr