Hot-pressing Pressure Research Articles

Highly strong aluminum via ball milling and high pressure hot press

As-received and ball-milled powders are used to prepare Al via high pressure hot pressing. The density of Al varied between 96.19 and 99.70 % of theoretical density. The Al prepared using ball-milled powders exhibited significant improvement in the yield strength (from 74 to 308 MPa) nearly by 416 %, compression strength (203.3–526.5 MPa) and reduction in strain (90.62–46.52 %) when compared to Al processed with as-received powders. The present study determines that ball milling and high pressure hot press is advantageous in improving mechanical properties of Al.

Effect of hot isostatic pressing processing parameters on microstructure and properties of Ti60 high temperature titanium alloy

Hot isostatic pressing parameters are critical to Ti60 high temperature titanium alloy castings which have wide application perspective in aerospace. In order to obtain optimal processing parameters, the effects of hot isostatic pressing parameters on defects, composition uniformity, microstructure and mechanical properties of Ti60 cast high temperature titanium alloy were investigated in detail. Results show that increasing temperature and pressure of hot isostatic pressing can reduce defects, especially, the internal defects are substantially eliminated when the temperature exceeds 920 °C or the pressure exceeds 125 MPa. The higher temperature and pressure can improve the microstructure uniformity. Besides, the higher pressure can promote the composition uniformity. With the temperature increases from 880 °C to 960 °C, α-laths are coarsened. But with increasing pressure, the grain size of prior-β phase, the widths of α-laths and α-colony are reduced. The tensile strength of Ti60 alloy is 949 MPa, yield strength is 827 MPa, and the elongation is 11% when the hot isostatic pressing parameters are 960 °C/125 MPa/2 h, which exhibits the best match between the strength and plasticity.

Controlling grain size, morphology and texture in additively manufactured β-titanium alloy with super transus hot isostatic pressing

Titanium alloys produced by Additive Manufacturing (AM) are often characterised as having coarse columnar grain structures on account of the prevailing thermal conditions at the time of solidification. This work investigates whether thermal post processing treatments above the β-transus temperature at both standard atmospheric pressure and 1500 bar pressure (Hot Isostatic Pressing – HIPing) can refine the columnar morphology in the high strength Ti-3Al-8V-6Cr-4Mo-4Zr (Beta-C/ASTM Grade 19) alloy produced by AM. Heat treatment at standard atmospheric pressure was ineffective in modifying the coarse columnar microstructure but HIPing was found to promote new equiaxed grains and significantly refine the grain size by up to 72.5% compared to the as-built component. The strong dominant <001> texture characteristic of the as-built (and heat treated) alloy was weakened and shifted towards <103> with a 5-fold reduction in texture intensity after the HIPing process. EBSD analysis reveals evidence of grain recrystallisation processes including but not limited to discontinuous dynamic recrystallisation (DDRX) which may be associated with pore collapse. Primitive columnar grains were also shown to contain numerous substructures which may have formed through dynamic recovery (DRV).

Preparation and characterization of birch plywood prepared by hot-pressed peanut meal adhesive

The preparation of birch plywood by hot-pressed peanut meal (HPM) adhesive was studied using response surface methodology. The effects of hot-pressing temperature, hot-pressing time, and hot-pressing pressure on the boiling water strength (BWS) were investigated. The BWS of birch plywood was significantly affected by hot-pressing temperature and hot-pressing time. The optimal preparation conditions for maximizing the BWS were: hot-pressing temperature of 120 °C, hot-pressing time of 80 s mm −1 and hot-pressing pressure of 1.2 MPa. Under these conditions, the BWS was 1.21 ± 0.02 MPa. The thickness expansion rate of water absorption (TS) and the wood compressibility were 6.39% and 15.8% respectively. Characterization of birch plywood showed the chemical reactions between hydroxyl of plywood, and the amino, carboxyl and azacyclobutane structures of peanut protein, forming a dense bonding surface and resulting in the higher BWS of birch plywood. This work provided an important reference for the application of HPM adhesive in the production of wood-based panels. • High value utilization of hot-pressed peanut meal was improved. • Chemical reaction between hot-pressed peanut meal adhesive and birch veneer. • The hot processing has strong universality and birch plywood has no formaldehyde. • The boiling water strength of birch plywood reached the national class I standard.

Optimizing The Hot-Press Procedure Of High-Temperature Proton Exchange Membrane Fuel Cells For Adhesion Strength And Conductivity

As society considers alternatives to energy systems based on fossil fuel combustion, high-temperature proton exchange membrane (HT-PEM) fuel cells may play an important role in our future energy and transportation portfolio. When compared to low-temperature proton exchange membrane (LT-PEM) fuel cells, HT-PEM technology offers enhanced electrode kinetics, simplified water management, and most notably increased tolerance to fuel impurities such as carbon monoxide. However, compared to more conventional LT-PEM systems, less is known about the durability, performance, and fabrication of HT-PEM materials. Comprised of multiple layers, the membrane electrode assembly (MEA) is a fuel cell’s central component. In a fabrication process similar to LT-PEM MEAs, the proton-conducting membrane, electrodes, gas diffusion layers and sub gaskets are usually hot-pressed together. The parameters surrounding the hot-pressing operation can have a significant impact on the ultimate performance of the fuel cell, in addition to influencing process reliability and repeatability. In the current research, measurements of MEA thickness, impedance, and adhesion strength were obtained for samples over a range of conditions to optimize for the most suitable processing parameters. Testing in this study quantified the effects of hot-press time, temperature and pressure, within ranges of 1-10 minutes, 140 – 200oC, and 7.72 – 92.67 MPa (1120 - 13440 psi), respectively. After hot pressing, the MEA samples were tested for resistance with a 1260a Solartron impedance gain phase analyzer in tandem with a Solartron Ametek 12962a sample holder, and with a Scott internal bond tester for adhesion strength. Based on the results of these tests the optimal hot-press parameters were established, four 25 cm2 MEA were built and tested for performance with post-mortem analysis conducted utilizing scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). These measurements enabled interrogation of potential sources of conductivity loss associated with material layer delamination and/or dehydration of phosphoric acid in the polybenzimidazole (PBI) membrane. In this case, all tests were conducted at 140oC and the resulting material assembly was allowed to cool to room temperature in a nitrogen glove box prior to executing conductivity measurements (i.e., inverse of resistance). Our results have demonstrated that the optimal conditions for MEA hot-pressing for the HT-PEM system are around 170oC and 23.1 MPa for 5 minutes. Each curve in Figure 1 represents the performance of in-house MEAs, prepared using the optimized hot-pressing condition, with variation of platinum-on-carbon content (Pt/C) and total Pt loading. The data presented in Figure 1 demonstrate the effect of varying electrode thickness on MEA performance. Figure 1

Optimizing The Hot-Press Procedure Of High-Temperature Proton Exchange Membrane Fuel Cells For Adhesion Strength And Conductivity

High-temperature proton exchange membrane (HT-PEM) fuel cell systems are under active development for a variety of mobile and stationary power applications. Measurements of membrane-electrode assembly (MEA) thickness, impedance, and adhesion strength were obtained for samples fabricated over ranges of conditions to optimize for the most suitable processing parameters. Testing quantified the effects of hot-press time, temperature, and pressure, over ranges of 1-10 minutes, 140 – 200oC, and 7.72 – 92.67 MPa, respectively. After hot pressing, MEA samples were tested for resistance with a Solartron impedance analyzer, and for adhesion strength with a Scott internal bond tester. From these results, optimal hot-press parameters were established and four 25 cm2 MEAs were fabricated and tested. Post-pressing analysis of MEAs was conducted using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. Our results demonstrate that the optimal conditions for MEA hot-pressing for the HT-PEM system are around 170oC and 23.1 MPa for 5 minutes.

Effect of Different Hot-Pressing Pressure and Temperature on the Performance of Titanium Mesh-Based MEA for DMFC.

The hot-pressing process of the membrane electrode assembly (MEA) is one of the research hotspots in the field of the fuel cell. To obtain suitable titanium mesh-based MEA hot pressing process parameters, titanium mesh was used as electrode substrate material. The anode and cathode of MEA were prepared by the drip-coated method, and the titanium mesh-based MEA was prepared under different hot-pressing pressure and temperature, respectively. The performance of titanium mesh-based MEA was studied by morphological observation, elemental analysis, thickness measurement, single cell test and numerical fitting analysis. The results demonstrated that: with increasing hot-pressing pressure from 0 MPa to 10 MPa, the forming thickness of titanium mesh-based MEA is getting thin gradually, and the peak power density of titanium mesh-based MEA first increased and then gradually decreased; with increasing hot-pressing temperature from 115 °C to 155 °C, the peak power density of titanium mesh-based MEA enhanced at the beginning and then also gradually decreased. Under the premise of a hot-pressing time of 180 s and the optimal operating temperature of DMFC of 60 °C, the appropriate hot-pressing process conditions of titanium mesh-based MEA are a hot-pressing pressure of 5 MPa and a hot-pressing temperature of 135 °C. The results can provide a technological reference for the preparation of titanium mesh MEA for DMFC.

Enhancement of electrical and thermal conductivity of low-cost novel Cu–Ag alloys prepared by hot-pressing and electroless plating from recycled electrolytic copper powders

In this study, electrolytic copper powders (ECs) were fabricated by electrolysis method using scrap copper pieces as the main material. Copper-silver bimetallic powders (ESCs) were obtained by electroless silver coating process. Then, copper-silver layered materials (ESC materials) with different process parameters were fabricated by using the hot-pressing method. The effects of hot-pressing temperature (25, 200, 400, 500 and 550 °C) and pressures (400, 500 and 600 MPa) on the properties of ESC materials were investigated. Morpholological examination of ECs and ESCs and microstructure examination of layered copper-silver materials was performed using scanning electron microscopy (SEM). Electrical and thermal conductivity, hardness and density of the materials produced with different hot-pressing parameters were examined. According to the results, it was determined that materials with the best physical and mechanical properties were obtained when the temperature used in hot- pressing was 500 °C and the pressure was 600 MPa. In materials produced at higher temperatures and pressures, a decrease in electrical and thermal conductivity values was determined as a result of the increase in deformation.

Hot-pressing polyelectrolyte complexes into tunable dense saloplastics

Salt-plasticized polyelectrolyte complexes of sodium polystrenesulfonate (Na-PSS) and polydiallyldimethylammonium chloride (PDADMAC) were found to be fully dense (non-porous) when hot-pressed under optimal conditions. The quality of these saloplastics is determined by the molecular weights of polyelectrolytes, the salt type and concentration, as well as processing conditions like pressure and temperature. Higher molecular weights give more compact precipitates that are easy to process while decreasing the molecular weight led to particulate ones. Both the type and concentration of salt on complex formation and doping are explored and are found to play an equally important role. The effects of individual hot-pressing parameters, namely, pressure and temperature are studied thoroughly, facilitating the formation of uniform free-standing films over a wide range of thicknesses from 8 μm to 1 mm. For the first time, saloplastics were studied as free-standing films that are dense even at the nanometer scale. In their dry states, they were brittle and strong, showing a uniform Young's modulus over a range of relevant thicknesses, while the wet states were rubbery and elastic, showing a decreasing trend with thickness. In the wet state, the inverse trend is due to the quicker drying of thin films. Within a single hot-pressing step, protruding shapes and structures from the surface were efficiently made at different length scales. Moreover, saloplastics were also successfully reinforced with thin woven and nonwoven fibers for enhanced tensile strengths, higher than conventional thermoplastics. Overall, this work demonstrates an easy approach to fabricate dense saloplastics and their unique mechanical properties.

Microstructural development of platelet alumina while hot-pressing to transparency

Transparent alumina specimens were produced using non-pre-aligned (NPA) and pre-aligned (PA) platelet alumina powder and hot-pressing at several different pressures. The effects of powder alignment and pressure on the crystallographic orientation, relative density, microstructure, and optical properties were studied. Additionally, samples were quenched at certain times during the hot-press run to investigate the microstructural evolution of the specimens. No significant trends were observed with increasing hot-pressing pressure. However, it is shown that while the pre-alignment procedure results in a higher degree of crystallographic orientation, the aligned platelets of the PA specimens result in a higher starting relative density, which causes faster densification to occur, yielding more grain-growth, porosity, and a lower final relative density. This ultimately results in minimal improvements in the in-line transmission compared to the NPA specimens, illustrating the importance of both high relative densities as well as crystallographic orientation for transparent alumina.

Preparation of lightweight glass microsphere/Al sandwich composites with high compressive properties

Glass microsphere/Al sandwich composites were manufactured by hot pressing to investigate their microstructure and compressive properties depending on the hot-press pressures (10–20 MPa). At the proper hot-press pressure, the composites had the highest dynamic compressive properties and maximal peak stress at quasi-static compression. Compared to aluminum foam with similar density, glass microsphere/Al sandwich composites had better compressive properties mainly due to additional reinforcement with microspheres and the formation of a regular cellular structure.

Thermomechanical stability and inelastic energy dissipation as durability criteria for fuel cell gas diffusion media with pre-assembly effects

In this article, pre-assembly hot-press pressure and thermal expansion effects in gas-diffusion layers (GDLs) are addressed to explore the practicalities of the constitutive model reported in the companion article. A facile technique is proposed to include deformation history dependent residual strain effects. The model is implemented in the numerical environment and compared with widely followed conventional models such as isotropic and orthotropic material models. With the normal and accelerated thermal expansion effects no significant variation in stresses or strains is reported with the compressible GDL model in contrast to the conventional incompressible form of the GDL model. The present work identifies the critical differences with advanced and extended variants of the model along with conventional GDL material models in terms of planar stress/strain distribution and the membrane response. Finally, the model is simulated for micro-cyclic stress loads of varying amplitudes that imitate the real working conditions of fuel cell. The inelastic energy dissipation in GDLs is predicted using the proposed model, which is utilized further to distinguish the safe (elastic) and unsafe (inelastic shakedown) operating limits. The inelastic collapse of GDLs is shown to be a active function of high amplitude micro-cyclic load with high initial clamping load.

Optimizing The Hot-Press Procedure of High-Temperature Proton Exchange Membrane Fuel Cells for Adhesion Strength and Conductivity

As society considers alternatives to energy systems based on fossil fuel combustion, high-temperature proton exchange membrane (HT-PEM) fuel cells may play an important role in our future energy and transportation portfolio. When compared to low-temperature proton exchange membrane (LT-PEM) fuel cells, HT-PEM technology offers enhanced electrode kinetics, simplified water management, and most notably increased tolerance to fuel impurities such as carbon monoxide. However, compared to more conventional LT-PEM systems, less is known about the durability, performance, and fabrication of HT-PEM materials. Comprised of multiple layers, the membrane electrode assembly (MEA) is a fuel cell’s central component. In a fabrication process similar to LT-PEM MEAs, the proton-conducting membrane, electrodes, gas diffusion layers and sub gaskets are usually hot-pressed together. The parameters surrounding the hot-pressing operation can have a significant impact on the ultimate performance of the fuel cell, in addition to influencing process reliability and repeatability. In the current research, measurements of MEA thickness, impedance, and adhesion strength were obtained for samples over a range of conditions to optimize for the most suitable processing parameters. Testing in this study quantified the effects of hot-press time, temperature and pressure, within ranges of 1-10 minutes, 140 – 200oC, and 7.7 – 92.7 MPa (1120 – 13,400 psi), respectively. After hot pressing, the MEA samples were tested for resistance with a 1260a Solartron impedance gain phase analyzer in tandem with a Solartron Ametek 12962a sample holder, and with a Scott internal bond tester for adhesion strength. Based on the results of these tests the optimal hot-press parameters were established, two 45.2 cm2 MEA were built and tested for performance with post-mortem analysis conducted utilizing scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). These measurements enabled interrogation of potential sources of conductivity loss associated with material layer delamination and/or dehydration of phosphoric acid in the polybenzimidazole (PBI) membrane. Figure 1 shows the effect of hot-pressing time and pressure on the resistance of MEA samples for one representative temperature condition. In this case, all tests were conducted at 140oC and the resulting material assembly was allowed to cool to room temperature in a nitrogen glove box prior to executing resistance measurements (i.e., inverse of conductivity). Each point in Figure 1 represents a single hot-pressed sample, with each sample undergoing three consecutive measurements that were then averaged; standard deviations of triplicate measurements ranged from 0.1 to 3.6%. Our results have demonstrated that the optimal conditions for MEA hot-pressing for the HT-PEM system are around 170oC and 23.1 MPa for 5 minutes. Research is ongoing to evaluate the impact of hot-pressing conditions on fuel cell performance and durability with both hydrogen and reformate fuels. Figure 1 – Selected measurements of HT-PEM resistance with variation of hot-press time and pressure at 140oC Figure 1

High-performance para-aramid paper strengthened by ultrafine fiber pulp of polyphenylene sulfide

Owing to its excellent heat resistance, lightness, insulation, and mechanical properties, aramid paper has been widely used in aerospace, rail transit, military, and other high-tech areas. With the rapid development of modern industries, para-aramid paper-based materials have become the development direction and trend of the specialty paper industry. In this study, para-aramid chopped fibers/polyphenylene sulfide (ACFs/PPS) composite paper sheets were fabricated by modern wet papermaking. The tensile strength, tensile index, and tear index of the hot-pressed ACFs/PPS composite paper sheets were substantially improved, reaching 103.5 MPa, 80.9 N m/g, and 119.1 mN m2/g under optimal speed of hot-pressing roller (0.2 m/min), hot-pressing temperature (310 °C), hot-pressing pressure (0.2 MPa), and ACFs content (70 wt%). The mechanical properties of hot-pressed ACF/PPS composite paper were markedly superior. Besides, the dielectric constant of the composite paper remained stable even when the temperature reached 100 °C. Briefly stated, ACFs/PPS composite paper exhibits desirable mechanical performance, thermostability, high breakdown strength, and low dielectric constant, delivering great potentials in the high-tech areas.

Study on Response Surface Optimization of Hot-pressing of Multi-layer Plywood via Soy-based Adhesive

Eucalyptus veneers were applied to fabricate multi-layer plywood with soy-based adhesives as the glue. Prior to optimization, single-factor experiments were performed to select the proper range of each factor. Furthermore, effects of adhesive amount, hot-pressing time, hot-pressing pressure, and hot-pressing temperature were investigated via response surface methodology (RSM). Through RSM optimization, optimum hot-pressing conditions were obtained. To verify the optimized conditions, validation test was carried out. The result presented that the error rate between the predicted value and the measured value was 1.2%, which was reasonable for prediction.

Influence of needle-punching treatment and pressure on selected properties of medium density fiberboard made of bamboo (Dendrocalamus strictus Roxb. Nees)

ABSTRACT In this study, Medium Density Fiberboard (MDF) was manufactured from bamboo (Dendrocalamus strictus Roxb. Nees) fibers and phenol-formaldehyde (PF) resins at different hot-pressing pressures using a novel needle-punching treatment to improve the properties of the panel. One-, two-, three- and four-time needle-punching treatments (1TP, 2TP, 3TP, and 4TP) were used in this work. Laboratory MDF panels were prepared by mixing bamboo fibers with 10% of PF resins. The needle-punching treatments were applied simultaneously on resinated bamboo fibers during the mat formation. The MDF mats were then hot-pressed at 14.0, 17.5, 21.0 kg/cm2 and at 150 °C for 15 min. Thereafter, the physical and mechanical properties of MDF panels were evaluated as per Indian Standard (IS) specification IS: 12406. It was observed that the combination of novel needle-punching technique and hot-pressing pressure enhanced the physical and mechanical properties of MDF panels. Statistical analysis suggested that a combination of 3TP and 21.0 kg/cm2 of pressures produced the MDF panel with satisfactory results. The research indicated that a combination of needle-punching treatment and hot-pressing pressure could be an excellent technique to improve the properties of the MDF panel.

Multiwall carbon nanotube reinforced HA/HDPE biocomposite for bone reconstruction

The healing of bone fractures naturally occurs without surgical intervention. Some damage and fractures in bone tissue are complex and leave remnant deformation, and this requires the use of bone replacement material. Hydroxyapatite (HA) is the main element of the bone mineral form and consider as a bioactive material which supports bone growth. Nevertheless, the HA has poor mechanical properties, such as low tensile strength. Thus the applications in bone replacement have been limited, especially in high load-bearing applications. A Carbone nanotube has newly obtained considerable concern because of their mechanical properties, potentially enhancing the bone implant's clinical efficiency. This study attempted to explain the effect of adding Multi-walled carbon nanotubes MWCNT Nanoparticles to the HDPE/HA bio-composites. Two groups of the composites samples were produced 20HA/80 HDPE and 40 HA/ 60 HDPE with adding (0.6, 1, 1.4, 2) % weights of (MWCNT) to each group. The composites were fabricated using a hot pressing technique with various pressing pressures (29, 57, 86, and 114 Mpa) at a compounding temperature of 150 C° and a holding time of 15 minutes. To evaluate samples' characteristics and performance, X-ray powder diffraction (XRD), surface topography by Field Emission Scanning Electron Microscopy (FE-SEM), tensile strength and, microhardness test were investigated. The results showed that the hybrid bio-composites demonstrated excellent structural integrity, homogeneous with the fibrous structure, and improved mechanical properties. When increasing in MWNT additions and increasing hot-press pressure, enhancing the composites' fracture strength and microhardness is beneficial. The excellent properties of hybrids bio-composite (HA/HDPE/MWCNT) samples for homogeneous fibrous structure and high mechanical properties could be applied in bone tissue engineering for bone reconstruction.

Manufacture and Properties of Metasequoia-Based Three-Layer Parquet Flooring

Abstract Metasequoia-based three-layer parquet flooring (MPF) was prepared under the following conditions: hot-pressing temperature of 95°C, hot-pressing time of 7 minutes, hot-pressing pressure of 9 kg·cm−2, and addition of 200 g·m−2 urea-formaldehyde resin adhesive. The results showed that the moisture content, density, formaldehyde emission, static bending strength, and elastic modulus of the three kinds of parquet flooring were not much different than poplar-based multilayer parquet flooring (PPF) or fir-based three-layer parquet flooring (FPF) on the market. The thermal conductivity of the MPF was 0.195 W·m−1·K−1, which was the lowest among the three kinds of parquet flooring. The sound absorption coefficient of MPF under 11 frequency conditions in the range of 0.2 to 2 kHz was higher than that of PPF and FPF under the same frequency condition. The research results provide a reference value for the efficient use of low-quality M. glyptostroboides wood.

Preparation and properties of adhesive-free double-sided flexible copper clad laminate with outstanding adhesion strength

In this paper, the synthesized thermoplastic polyimide (TPI) precursor is coated on both surfaces of the surface-treated polyimide (PI) base film, and the TPI/PI/TPI multilayer films is obtained by thermal imidization. The mechanical properties, heat resistance, water absorption of the multilayer film and the interface between the TPI and the PI base film were investigated in detail. Then, multilayer film-2 (MF-2) with excellent comprehensive performance and the two copper foils were pressed together to prepare a double-sided flexible copper clad laminate (FCCL) by thermal lamination method, and the properties of FCCL were studied in detail. The results show that the FCCL has a high peel strength of 1.22 N/mm, passed a solder bath test of 288°C, and the surface condition was good under hot-pressing temperature of 360°C, hot-pressing pressure of 15 MPa and hot-pressing time of 60 s. In addition, the SEM and EDS spectra of the stripped copper foil confirmed that the TPI layer was immersed into the interstitial space of the Cu nodules, forming a strong physical bite with the copper foil. The current work provides a promising solution for the design and fabrication of multilayer printed circuit boards with excellent performance.

Optimization of hot-press parameters for plywood with environmental aluminophosphate adhesive

An aluminophosphate adhesive was used as the binder in plywood. The hot-pressing parameters of aluminophosphate adhesive-based plywood (APPs) including hot-press temperature (A), time (B), and pressure (C) were optimized using response surface methodology. Results indicated that the hot-press temperature was the most dominant factor. The maximum bonding strength of 1.98 MPa was found with an optimal parameter of 171 °C (hot-press temperature), 7.5 min (hot-press time), and 1.0 MPa (hot-press pressure). Additionally, the chemical reaction mechanism between aluminophosphate adhesive and wood fibers was characterized by X-ray photoelectron spectroscopy (XPS). Results showed that good interaction was generated between wood fibers and adhesives through their surface functional groups. In conclusion, the optimized pressing conditions of plywood significantly improved bonding strength of APPs.