Hot Press System Research Articles

Effect of hybrid ratio on shape memory properties of graphene oxide‐carbon/glass fiber composites prepared based on vacuum infiltration hot‐press forming experimental system

AbstractShape memory composites now have a wide range of applications in aerospace, medical devices, and smart structures. Seven graphene‐carbon oxide/glass fiber (GO‐CF/GF) hybrid reinforced shape memory composites were prepared using vacuum infiltration hot pressing system (VIHPS) and the shape memory properties of the materials were investigated in 100°C test. By comparing and analyzing the microstructure and shape memory properties of composites containing different volume fractions of GFs, the mechanism of the influence of different hybrid contents of GFs on the organizational properties and shape memory properties was investigated. The results show that when the reinforcement of the composites were all carbon fibers, the composites had the largest elasticity modulus, harder material and the fixation rate of 77.15%, the recovery rate of 95.17%, the porosity of 0.80% and the shape recovery force of 7.98 N. When the reinforcement of the composites were glass fibers, the composites had the smallest elasticity modulus, softer material and the fixation rate of 94.89%, the recovery rate of 77.21%, the porosity of 13.56% and the recovery force of 2.28 N. The results of this test can lay a foundation for subsequent research on fibers with different mixing ratios.Highlights The GO‐CF/GF/EP prepared by VIHPS has excellent shape memory properties. Fiber hybrid ratio affects the composite's porosity and its properties. Fiber hybrid ratio affects the composite's shape fixation, recovery, and memory force. The shape fixation of G6 decreases the lowest with test cycles. Carbon fiber content changes the zero‐stress plane of GO‐CF/GF/EP.

Superconducting joints of reacted monofilament MgB2 wires sintered by hot uniaxial pressing system

Successful superconducting joints of reacted magnesium diboride (MgB2) monofilament wires are reported in this paper. The absence of a reliable method to develop superconducting joints between reacted MgB2 wires presents a major obstacle to the wider adoption of MgB2 as a material for magnet winding. A hot uniaxial pressing (HUP) system was exploited for sintering purposes since it can facilitate the formation of condensed in situ bulk on the wire filament. The wires were manufactured with an extra thick barrier material to protect the filament from damage during HUP sintering. The sintering temperature and pressure of the HUP system were varied to comprehend the best-performing joint. The performance of joints could be improved by depreciating the pores within the intermediate bulk of the joint. To prove this point, joints were cut to study their morphology. However, due to sintering in pressurised conditions, the reaction of the in situ intermediate bulk was not completed. The x-ray diffraction result detected a significant unreacted magnesium phase in the intermediate bulk. This work obtained joints of reacted MgB2 wires which can be considered for industrial MgB2 magnetic resonance imaging magnets fabrication.

Comparison of phenol formaldehyde with polyvinyl chloride resin as binder bonded NdFeB magnet for axial flux generator

Bonded permanent magnets are made by mixing a magnetic powder material Neodymium Iron Boron (NdFeB) commercial MQP type 16-7 with a polymer material powders phenol formaldehyde (Bakelite) and polyvinyl chloride (PVC) resin. Comparison between the composition of NdFeB powder and the polymer powders were varied at 80:20, 90:10, and 95:5 wt%, respectively. This mixture is then pressed with a hot press system and then carried out magnetic alignment axial flux using a magnetizer machine, Magnet Phisyk-Germany, with an impulse system. Magnetic properties were characterized by permagraph Magnet Phisyk-Germany. The best value obtained for the composition of 95: 5% NdFeB-pvc resin powder to the value of remanence magnet (Br) = 0.604 Tesla (T), the value of coercivity (Hc) = 480 kA/m and maximum energy product (BH)max = 50.05 kJ/m3. Fabrication is done by the size of the magnetic 50 mm diameter, 8 mm thick and was applied to the axial flux generator. The output voltage of the generator has been tested with variations of 50 to 300 rotations per minute (rpm) using a Hantek 6022BE oscilloscope, and the measurement results obtained values of 1.9 to 12.2 Volts.

Influence of extrusion pressures on shape memory properties of carbon fiber/basalt fiber hybrid composites with graphene oxide fabricated by the vacuum infiltration hot pressing system

AbstractThis work investigated the extrusion pressure‐microstructure‐shape memory properties relationship of carbon fiber/basalt fiber hybrid composites with graphene oxide (GO‐CF/BF hybrid composites), and the associated mechanism was systematically discussed. GO‐CF/BF hybrid composites were fabricated by the vacuum infiltration hot pressing system (VIHPS). The critical infiltration pressure of the composite was calculated according to the dynamic infiltration model, and it was 0.09 MPa. The microstructure and shape memory properties were analyzed by scanning electron microscopy (SEM) and a shape memory testing system. The results showed that the shape fixation ratio first decreased and then increased, but the shape recovery ratio and the shape recovery force tended to initially increase and subsequently decrease with the increase in extrusion pressure. This was mainly determined by void defects. When the extrusion pressure was 0.5 MPa, the shape memory properties of the composite were excellent. Furthermore, with the increase in cycle times, GO‐CF/BF hybrid composites were damaged, and the shape memory properties all decreased. When the extrusion pressure was 0.7 MPa, fiber fracture and delamination appeared in composites, and the shape memory properties deteriorated significantly. However, when the extrusion pressure was 0.5 MPa, the fiber was fractured slightly, and the shape memory properties degenerated vaguely.

Effect of layering angles on shape memory properties of graphene oxide/carbon fiber hybrid reinforced composites prepared by vacuum infiltration hot pressing system

Seven groups of different layering angles of Graphene oxide/Carbon fiber (GO-CF) hybrid reinforced shape memory composites are prepared by vacuum infiltration hot pressing system. The layering angles are respectively [0°]4, [±15°]s, [±30°]s, [±45°]s, [±60°]s, [±75°]s, and [90°]4. The shape fixation ratio, shape recovery ratio, and shape recovery driving force of GO-CF hybrid reinforced shape memory composites are investigated. The composite with the layering angle of [0°]4 has the minimum shape fixation ratio of 90.9%, the maximum shape recovery ratio of 97.6%, and the maximum recovery force of 2.83 N. Compared to [0°]4, the composite with the layering angle of [90°]4 has the 9.13% higher shape fixation ratio, but it has 16.1% lower shape recovery ratio and 59.4% lower recovery force. The microstructure of the composites is characterized and the microstructure of seven groups of composites is satisfactory. Therefore, the matrix within each group of composites has a similar effect on the shape memory properties of the composites. With the layering angle increased, the fiber resilience in the axial direction (X-direction) and the accumulated internal stress gradually decrease. With the layering angle increased, the shape fixation ratio and recovery time of GO-CF hybrid reinforced shape memory composites increase, while the shape recovery ratio, recovery force, and recovery rate decrease.

Effect of Four Groups of GO-CF/EP Composites with Ideal Infiltration Structure and Different Layering Ways on Damping Properties.

In this paper, four groups of graphene oxide and carbon fiber hybrid-reinforced resin matrix (GO-CF/EP) composites with different layering ways were prepared by a vacuum infiltration hot pressing system (VIHPS). The damping properties of the specimens with different layering ways were tested by the force hammer method, and the micromorphology of the specimens was photographed by scanning electron microscope. The experimental results showed that the damping properties of GO-CF/EP composites gradually increased with the increase in the number of Y-direction layers. The [XYXYXY]6 has the best damping property, with a damping ratio of 1.187%. The damping ratio is 5.3 times higher than that of [XXXXXX]6 layer mode, and the first-order natural frequency is 77.7 Hz. This is mainly because the stiffness of the X-direction layer is larger than that of the Y-direction layer, and its resistance to deformation is considerable. Therefore, its decay rate is slower. The Y-direction layer has weak resistance to deformation and fast energy attenuation. The increase in the number of Y-direction layers will lead to the overall increase in, and the improvement of, the damping properties of GO-CF/EP composites.

Mechanical properties of surface-compressed wood resulting from the compression ratio and density distribution

Surface-compressed wood, with controllable mechanical properties according to the production process, could be utilized in timber products as a substitute for energy-intensive adhesives, concrete, and metals. The surface compression of wood was carried out in an open hot-pressing system at 180 °C with a compressed thickness of 2 to 18 mm. The surface-compressed wood was treated by atmospheric heat treatment or 0.30 MPa pressurized superheated-steam heat treatment at 180 °C for 2 h. This study investigated the mechanical properties of surface-compressed wood, namely, its bending, compression, and hardness properties. The results showed that the maximum density and average density of the compressed layer surpassed 1.10 g/cm3 and 0.80 g/cm3 when the compression ratio was 33%. Moreover, the surface-compressed wood with a sandwich density structure had properties that were comparable to, or even surpassed, raw wood, traditional compressed wood, and some engineered timber products. The specific strength (179 to 203 × 103 m2/s2) of surface-compressed wood was slightly higher than other wood-based materials (65 to 197 × 103 m2/s2). And the contribution of sandwich structure to MOR and MOE increase was positively correlated with wood surface density. The results obtained from this study could help engineers utilize more fast-growing wood and develop new products and wood connectors. This work may contribute toward the substantial use of surface-compressed wood in the building and construction industries with great benefits to the environment.

Improved optical properties of BN powder shielded Ce:YAG ceramics prepared by hot pressing

Yttrium aluminum garnet (YAG) phosphor transparent ceramics prepared via vacuum hot pressing (HP) suffer from carbon contamination owing to the graphite mould used in the HP system. The conventional method was to dope LiF as a decarburizing agent, but carbon contamination cannot be effectively prevented when preparing Ce:YAG ceramics via a solid-phase reaction combined with HP sintering. In this study, we report the fabrication of highly transparent Ce:YAG ceramics via HP sintering with a flexible hexagonal boron nitride (BN-h) wrapping, which prevents carbon contamination of the samples caused by the graphite mould used in the process. High-transmittance Ce:YAG ceramics were prepared at a medium temperature of 1600 °C and a low vacuum pressure of 10−1 Pa.

Study on the Influence of the New Type of Powder Metallurgy Ti-Al-Nb Alloy Hot Press Sintering Process on the Microstructure

Based on the hot-pressing sintering process, the kinetics of hot-pressing sintering crystal grain growth and the hot-pressing sintering densification kinetics, the mixing ratio of the raw material powder and the hot-pressing sintering system are designed. The pressure is maintained at 30 MPa from the temperature rise to the end of the sintering process, and wait until the temperature reaches the corresponding hot pressing sintering temperature (1200°C~1400°C), keep the corresponding time for 1.5h~4.5h, stop heating and depressurize, and the alloy billet is cooled to room temperature with the furnace. The main phases of Ti2AlNb powder and hot pressing sintering process are TiAl and Ti3Al.

PRESSURE PATTERN IMPROVEMENT OF PROPORTIONAL VALVE APPLICATION ON HOT PRESS MACHINE USING PID

The purpose of this study is to develop a control scheme for the hydraulic proportionalsystem using PID function on Mitsubishi PLC Q series, which can rapidly control the pressurein a hydraulic cylinder with very short stroke. The mathematical model of the control system isestablished according to the principle of the electro-hydraulic system. Considering the mentionedcharacteristics, simulation of the system modelling will be established to know the systemresponse. In order to improve the control precision of the hydraulic hot-press system, theMitsubishi PID controller are designed by selecting appropriate tuning parameters. Their controlperformances are analysed in time domain respectively. The variation of PID controllerconfiguration will be conduct to know the better model for this system controller. The validityof the proposed control scheme is confirmed through the experiments to verify the rationality ofthe theoretical model. The results show that the Mitsubishi PID and the ideal PID give the sameresult for the tuning parameter resulted from simulation. And also the experiment give the betterstability in the 3 different pressure set value that conduct by author.

Comparison of Tensile and Impact Absorption properties of Bio-Inspired Helicoidal stacked with Cross-Ply Stacked Carbon Fiber Laminate

Herrigbone structures are identified on the chitins of the Mantis shrimp. Bio-inspired helicoidal arrangement of composite layers can mimic these herringbone structures. First, the carbon composite samples are fabricated using the hand lay-up method, followed by a curing process using a hot press system. The impact absorption properties of these samples will be analyzed through a series of impact tests. The samples will also be tested for its tensile properties to compare the effect of plies arranged in helicoidal [0,45,90], [0,30,60,90] and Cross-ply orientations to form the laminate structure. The results showed that helicoidal samples have higher penetration tolerance and toughness as compared to Cross-ply samples during impact tests. It is found that the specimen with helicoidal stacking sequence has better debonding resistance and improved damage tolerance. The 6-ply helicoidal samples exhibits higher tensile strength as compared to 6-ply Cross-ply samples due to better fiber to matrix adhesion for helicoidal structure in the direction of pulling force.

Effect of Fe alloying on the thermoelectric performance of Cu2Te

Copper telluride belongs to the “Phonon Liquid Electron Crystal” (PLEC) class of materials owing to its mobile Cu ions which migrate easily inside the crystal lattice. The mobile copper ions scatter phonons and lead to low thermal conductivity making it a suitable choice as a thermoelectric material. However, the formation of copper vacancies results in high hole carrier concentration (∼1021 cm−3) leading to poor Seebeck coefficient and degrades its overall thermoelectric efficiency. In this work, we aim at improving the thermoelectric transport properties of Cu2Te by alloying with Fe. The alloys of Cu2-xFexTe (where x varies from 0 to 0.06) were synthesized via solid-state synthesis followed by compaction in an induction hot press system. The formation of the trigonal phase (space group P3m1) of Cu2Te and the solubility of Fe ∼ x = 0.05 in Cu2-xFexTe is confirmed by means of X-ray Diffraction and backscattered electron micrographs. The decrease in electrical conductivity and the Hall carrier concentration and increase in the Seebeck coefficient with increasing Fe content signifies the compensation of holes by the electrons contributed from the trivalent Fe. The specific heat capacities of the Fe substituted samples were higher than the Dulong Petit limit of 3NkB, which implies that “liquid-like” behaviour of the Cu ions has been suppressed. This is because the Fe atoms act as barriers to the Cu ion diffusion. Due to the maximum power factor (∼0.47 mW m−1 K−2) and minimum thermal conductivity (∼2.19 W m−1 K−1), the maximum figure of merit of ∼0.16 at 750 K was obtained for the sample Fe0.03. It is hypothesized that the substitution of Fe not only helped to control the high carrier concentration but also restricted the cationic diffusion in Cu2Te. Hence, the present study points to a possibility of synergistically improving the thermoelectric properties as well as suppressing the ionic diffusivity in PLEC materials.

Automatic Hot Pressing System for Indium Packaging

Hot pressing is one kind of effective assembly technology to join two parts together. Automatic hot pressing need control both temperature and pressing force precisely and programmable. In this paper, an automatic hot pressing system for indium packaging is presented, the design motivation is to made the system reliable for application in industry and reach the accuracy requirement. A screw jack with servomotor is selected to actuate the hot pressing head to generate the pressing force, a linear encoder is used to detect the displacement of the screw jack to improve its motion accuracy. A force sensor is mounted underneath the 2-D platform to feedback the pressing force in real time. The hot pressing head is made up of four heating rods and a temperature sensor to control the pressing temperature. The exchangeable manipulator is designed to pick up parts with different size and shape. The machine vision is employed to calibrate the first set of parts to make the system flexible to product variety. The experimental results shown that the maximum force error is 9 N at working load of 2000 N and the temperature error is less than ± 0.3°C. The cycle time is 630 s.

Effects of pressurized superheated-steam heat treatment on set recovery and mechanical properties of surface-compressed wood

The recovery behavior and selected mechanical properties were studied for Populus tomentosa wood subjected to surface compression followed by heat treatment. The surface compression of wood was carried out in an open hot-pressing system at 180 °C with compressed thickness of 2 to 18 mm. The surface-compressed wood was treated by atmospheric heat treatment or 0.30 MPa pressurized superheated-steam heat treatment at 180 °C for 2 h. The results showed that the set recovery of compressed wood decreased with increasing compressed thickness before post-treatment. Atmospheric and pressurized heat treatment reduced the average set recovery of compressed wood significantly from 12.9% to 4.1% and 1.5% respectively, after conditioning at 40 °C and 90% relative humidity. Moreover, mechanical properties including the modulus of elasticity (MOE), modulus of rupture (MOR), hardness, and surface hardness increased with elevating compressed thickness. Both atmospheric and pressurized heat treatment reduced the MOR, hardness, and surface hardness of compressed wood. Analysis of variance showed that the effects of heat treatment on mechanical properties was not significant, except pressurized heat treatment decreased hardness significantly. With a compressed thickness of 10 mm, MOE, MOR, hardness and surface hardness were increased by 52.6%, 36.4%, 122.0% and 129.6%, respectively, compared with untreated wood.

Improved wear properties of magnesium matrix composite with the addition of fullerene using semi powder metallurgy

ABSTRACTThe present study aims to fabricate fullerene (C60) reinforced magnesium matrix composite via semi powder metallurgy in hot press system under high purity argon atmosphere. Improvement of wear resistance of pure magnesium with the addition of fullerene is also aimed with this study. Hardness and wear tests at room temperature were performed to investigate the mechanical effect of fullerene nanoparticles. Microstructures of fabricated composites were characterized using Scanning Electron Microscope (SEM). Results clearly show that hardness performance was improved up to 0.5 wt. % fullerene addition directly. A uniform distribution was also achieved according to the mapping and line EDX analysis for the lower content of fullerene. Agglomeration of fullerene was observed for 1 wt. % reinforced composite. Wear performances of pure magnesium were also improved when harder fullerene reinforcements incorporated into the matrix. Abrasion and oxidation were main wear mechanism for unreinforced and fullerene reinforced composites. Enhancement of hardness and wear performances might be attributed to the high specific surface area of fullerene and achievement of uniform distribution of reinforcement in magnesium matrix.

Hot-pressed geopolymer: Dual effects of heat and curing time

Hot-pressed curing of geopolymers introduces an efficient fabrication of almost pore-less and high strength binders with a minimum usage of alkali activator in an extremely short time. This study presents the dual effects of temperature and curing time on kinetics and mechanical properties of VA-based hot-pressing geopolymer. Moreover, the effects of elevated temperature on the aluminosilicate precursors dissolution and the pressure loss of the hot-pressed geopolymer are investigated. It is observed that increment in temperatures and time improves the dissolving trends of the aluminosilicates. Furthermore, pressure loss of the hot-pressing system is associated with the liquid phase removal and gelation of particles; and, a successive repressing of mixture to the initial condition reduces the porosity of the matrix significantly. The increase in curing temperature of the hot-pressing system is the key point in acceleration of the geopolymerization kinetic, however, curing time is essential in stabilization of the reaction.

Karakteristik Papan Partikel Limbah Kayu Mahoni dengan Perlakuan Pengawetan Asap Cair

This research focused on the characteristics of particleboard made from preservation treated-particl es. Mahagony wood bioma ss waste was used as raw material. Liquid smoke at different concentrations (0%, 2.5%, and 5%) was applied for 24hours onto the particles. After dried in air dry condition, the particles were mixed with urea formaldehyde resin (7.5% and15%), and then were pressed using hot pressing system at 150oC for 10 minutes. The result showed that the particleboardusing 15% urea formaldehyde resin and made form 5% liquid smoke treated-particles provided the best performance, thatmet Japanese Industry Standard (JIS) A 5908. The mortality value of dry wood termites Cryptotermes cynocephalus Lightand the weight loss after termite attack at the same condition were 90.67% and 0.408%, respectively.

Transversal mechanical properties of surface-densified and hydrothermally modified needle fir wood

Hydrothermal–mechanical (HTM) treatment is a combined action of temperature, moisture, and mechanical loads. Various kinds of HTM processes have been developed to produce eco-friendly modified wood products. Among these modification technologies, a combination of surface densification and hydrothermal post-treatment is a promising option that can be used to enhance plantation wood properties and generate value-added softwood products. This paper aimed to investigate the transversal dynamic transversal modulus of elasticity (dtMOE) profile and transversal density profile of surface-densified and hydrothermally post-treated needle fir (Abies nephrolepis) wood, and provide a practical guide for the processing optimization of surface-densified and thermally treated low-grade plantation softwood. Needle fir lumbers were surface-densified in an open hot-pressing system, at a compression ratio of 16.1% and two hot-pressing temperatures (160 and 180 °C) for a pressure holding duration of 10 min with a subsequent hydrothermal post-treatment at two temperatures (180 and 200 °C) for 60 min. The transversal dtMOE profiles for six types of specimens (moisture-saturated, conditioned control, and four types of surface-densified specimens) were measured and analyzed by a dynamic thermo-mechanical analysis (DMA) apparatus. A dtMOE gradient variable (G M) was defined herein to quantitatively formulate the dtMOE distribution of the surface-densified and hydrothermally post-treated wood specimens. Upon hot pressing, compressed cell tissues were observed within a 1.0- to 2.0-mm layer beneath the surface of the densified wood. The density peaks of compressed sections were increased to 650–800 kg/m3, compared with the average density of the control specimens being at 350 kg/m3. The dtMOEs of the compressed sections were increased from 650 MPa of the control specimens, to 750–900 MPa, achieving the objective of surface densification. As the temperature of hydrothermal post-treatment increased from 180 to 200 °C, the differences of the dtMOEs between the compressed surface sections and their inner adjacent ones decreased significantly, indicating the effective fixation of the compression deformations. Based on the test results obtained herein, it was concluded that the impact of the hot-pressing temperature and thermal post-treatment temperature over the dtMOE was insignificant. Nevertheless, it was also found that the hydrothermal treatment temperature showed significant influences over the dtMOE difference between the densified surface and its adjacent layer; the possible explanations for these complicated behaviors were also proposed herein.

Rapid consolidation of powdered materials by induction hot pressing

A rapid hot press system in which the heat is supplied by RF induction to rapidly consolidate thermoelectric materials is described. Use of RF induction heating enables rapid heating and consolidation of powdered materials over a wide temperature range. Such rapid consolidation in nanomaterials is typically performed by spark plasma sintering (SPS) which can be much more expensive. Details of the system design, instrumentation, and performance using a thermoelectric material as an example are reported. The Seebeck coefficient, electrical resistivity, and thermal diffusivity of thermoelectric PbTe material pressed at an optimized temperature and time in this system are shown to agree with material consolidated under typical consolidation parameters.

Evaluation of accelerated decay of wood plastic composites by Xylophagus fungi

The resistance to fungal attack of wood plastic composites (WPCs) containing 40% polypropylene and 60% either pine, maple or oak, wt%/wt%, was examined. WPCs specimens were made using the hot press system. Resistance to decay was evaluated using soil block and agar tests. Test specimens were exposed to either white-rot fungi, Trametes versicolor or Phanerochaete chrysosporium, or the brown-rot fungi Gloeophyllum trabeum or Postia placenta for six or 12 weeks. Moisture content and weight loss were used to assess the extent of decay of WPCs. Rates of decay in WPCs exposed in soil-block tests were greater than those exposed in the agar. WPCs containing either maple or oak were more susceptible to fungal attack then those containing pine.