Vacuum Pressure Impregnation Process Research Articles

Superhydrophobicity wood with reversible photoresponsive property

Superhydrophobic photoresponsive wood (HPW) was synthesized through the vacuum pressure impregnation process with octadecyltrimethoxysilane (OTS), spiropyran, and polyvinyl alcohol (PVA). The process endowed the wood with photostimulation responsiveness and superhydrophobic characteristics. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS), Fourier transform infrared spectroscopy (FTIR), and a contact angle meter were analyzed to determine the micromorphology, chemical composition, and hydrophobicity of the modified wood. The modified wood had a micro-nanometer mastoid structure at the microscopic level, with a large number of hydrophobic groups. The static water contact angle of the modified wood reached 153°, the water absorption rate decreased from 123.28 % to 19.29 %, and the anti-swelling rate was only 1.69 %, showing good hydrophobic and anti-swelling performance. At the same time, color values of the wood L*, a*, b*, and total color difference ΔE*, it was found that spiropyran made the modified wood have a rapid response to light stimulation.

Effect of the second curing cycle on performance of superconducting magnet insulating system

In large-scale, high-field superconducting magnets used for magnetic confinement fusion, high energy accelerators, and magnetic resonance imaging, the insulating system made from glass fiber reinforced resin-based composites is the key component, which mainly plays the role of mechanical support, fixing and protecting superconducting conductors, as well as electrical insulation. Vacuum Pressure Impregnation (VPI) approach is widely used in the manufacturing of the insulation system. The second curing cycle is generally required after the first VPI and curing process. For example, after the superconducting coil is cured in the mold, the de-molding process requires the superconducting coil to be reheated according the curing temperature. Moreover, for large-scale superconducting magnets, the superconducting coil needs to undergo a second VPI process after the first VPI process to fix the coil in the coil case. In this work, the tensile and shear properties of pure epoxy resin and the glass fiber reinforced resin-based composite, were investigated at both room and cryogenic temperatures and the effect of the second curing cycle on the mechanical properties was analyzed. Additionally, the strain evolution of the Nb-Ti superconducting coil during the second curing cycle was measured using the Fiber Bragg Grating (FBG) sensors embedded in the composite. The results indicate that the second curing cycle will not introduce additional strain to the previously cured resin matrix, but the defective or weak parts of the resin matrix may be affected by the new added epoxy resin and a little extra strain has been observed.

Densification of SiCf/mullite composite via vacuum pressure impregnation process towards excellent mechanical and microwave absorbing performance

A simple and low-cost method for preparing SiCf/mullite composites with high density, mechanical, and absorbing performance using a vacuum pressure impregnation (VPI) system has been developed. The densification mechanism of the mullite matrix was investigated, and the effects of impregnation pressures on the flexural strength, interfacial bonding strength, and the electromagnetic wave (EMW) absorbing performance of SiCf/mullite composites were also studied. The dense composite was prepared under 3 MPa pressure with a porosity of 6.23 % and median pore diameters (MPDs) of 13.02 nm. The preparation efficiency was improved with the impregnation circles decreased from 20 times to 13 times. The flexural strength of SiCf/mullite composites prepared by VPI is 297 MPa, which is improved 230 % of the one prepared by the traditional vacuum impregnation method. Benefiting from the synergistic effects of appropriate impedance matching and multiple polarization loss, the effective absorption bandwidth (EAB, RL < −10 dB) of the SiCf/mullite composites increases from 2.17 GHz to 2.80 GHz in the X band.This work has a positive application value for the manufacture of high-strength EMW absorbing composites in terms of significantly reducing the preparation cost and cycle duration.

The Effect of Joint Thickness on Intermetallic Growth in the In52Sn48(Liquid)/Cu(Solid) Diffusion Couple

Intermetallic growth can simultaneously enable low-resistance electrical pathways and determine the lifetime of a solder joint. Motivating this work is a demountable linear bilateral solder joint application, enabled via a vacuum pressure impregnation process. The effect of the initial solder joint thickness δj=25-125\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\delta _j = 25 - 125$$\\end{document}μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mu $$\\end{document}m on intermetallic growth in this configuration is investigated for the In52Sn48\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext{In}_{52}\ ext{Sn}_{48}$$\\end{document}(liquid)/Cu(solid) diffusion couple for temperatures T = 393, 413 and 433 K, in the range just above the In52Sn48\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext{In}_{52}\ ext{Sn}_{48}$$\\end{document} melting temperature of 391 K. It was found that beyond a critical time ∼1-15\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim 1-15$$\\end{document} min into the kinetic reaction, thicker solder joints had more intermetallic growth. There are two intermetallic phases identified in this temperature range: Cu6(In,Sn)5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext{Cu}_{6}\ ext{(In,Sn)}{_5}$$\\end{document} closer to the Cu substrate, and Cu(In,Sn)2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext{Cu(In,Sn)}_{2}$$\\end{document} closer to the solder bulk. The intermetallic growth fits give temporal growth exponents between n=0.25-0.29\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$n = 0.25 - 0.29$$\\end{document}, indicating that grain boundary diffusion rather than volume diffusion is the predominant growth mechanism. Growth in thicker joints is associated with higher temporal growth exponents; this is attributed to suppressed grain coarsening, as there is Cu dissolution from the intermetallic into the solder bulk in the early stages of the reaction, in more highly unsaturated environments. In addition, there is on average a decrease in the intermetallic phase activation energy with increasing joint thickness. In combination with the literature, the results suggest the linear bilateral joint geometry has a growth constraining effect, and the liquid solder phase state strongly affects the morphology and coarsening of grains, leading to the intermetallic growth trends observed.

Research on the Impregnation Process and Mechanism of Silica Sol/Phenolic Resin Modified Poplar Wood

Phenolic resin-modified materials partially reduce the toughness of the wood. In this study, organic–inorganic composite modifiers were used to modify the wood. Silica sol/phenolic resin was prepared through in-situ polymerization, and poplar wood was modified using a vacuum pressure impregnation process, enhancing its toughness. Orthogonal experiments were conducted, and the impact toughness of the modified poplar wood was used as the evaluation index. Through orthogonal experiments, using the impact toughness of modified poplar as the evaluation indicator, it was found that when the average particle size of the silica sol is 8–15 nm, the pressure is 1.2 MPa, and the pressurization time is 3 h, the impregnation-modified poplar’s impact toughness reaches its optimum, improving by 84.1% and 135.4% compared to the raw material and phenolic resin impregnated wood, respectively. The Fourier Transform Infrared Spectroscopy (FT-IR) results indicated that the characteristic absorption peak of Si-O-Si appears in the poplar wood after impregnation, confirming the formation of new silicon-oxygen (Si-O) chemical bonds. X-ray Photoelectron Spectroscopy (XPS) analysis revealed that a chemical reaction occurs between the impregnation liquid and the wood, generating Si-O-C. Subsequently, through Dynamic Mechanical Analysis (DMA) and Thermogravimetric (TGA) analysis, it was understood that this chemical reaction significantly enhances the thermal stability and toughness of the impregnated material, making it superior to the original poplar material. The TGA further unveiled that, compared to untreated poplar, the thermal stability of the impregnated material has been notably improved. Lastly, Scanning Electron Microscopy (SEM) analysis demonstrated that the composite impregnation liquid successfully permeates and fills the interior of the poplar cells.

Numerical Simulation and Experimental Validation of Internal Heating in Vacuum Pressure Impregnation Process for High Field Coil

An experimental system has been built to explore the vacuum pressure impregnation (VPI) technique and internal heating method. The mold with coil and support part is put into the vacuum tank and a novel type of epoxy resin IR-3 is applied for impregnation. The heat transfer models is built to simulate the heating process and calculate the radiation heat leakage and heating power. A shield is made to reduce the radiation heat leakage and two preliminary experiments without impregnation are carried out to verify the thermal insulation effect of the radiation shield. An experiment with impregnation and shield is carried out to identity the temperature rise, the magnitude of current and heating power applied to the coil. The numerical and experimental results showed that the radiation heat leakage is the main way of heat loss during curing process, and the shield can reduce radiation heat leakage effectively, thereby heating power consumption is reduced, meanwhile the coil and resin could not reach the setting temperature when shield is absent. The results obtained in this paper will helpful to manufacture of superconducting coils using VPI technique and internal heating method.

Industrial assays to evaluate the efficacy of vacuum pressure impregnation with commercial wood preservatives to eliminate the pinewood nematode, Bursaphelenchus xylophilus, and other nematodes from Pinus pinaster wood

To demonstrate the efficacy of the vacuum pressure impregnation (VPI) with commercial wood preservative products to eliminate the quarantine organism, pinewood nematode (PWN), Bursaphelenchus xylophilus, and other nematodes from maritime pine (Pinus pinaster) wood, in vitro assays and industrial assays in horizontal industrial autoclave tanks were conducted. In vitro nematicidal activity assays through direct exposure of the PWN 3rd-stage dispersal juveniles, the resistance juvenile stage, extracted from naturally infected P. pinaster revealed 100% nematode mortality with three commercial wood preservatives. Nematode mortality was also assessed in VPI industrial assays with the three commercial wood preservatives using naturally PWN infected P. pinaster experimental units, with various diameters and sizes. After VPI treatment, the nematode mortality ranged from 99.9761 to 100%. After incubation, the mortality of the total number of nematodes increased and, in all sections, the nematode mortality was higher than 99.9981% and in some it was 100% indicating that wood impregnated with preservative products does not constitute an environment favorable to the reproduction and development of nematodes. Overall, our findings demonstrated that the efficiency of the VPI process results from the joint action of the physical effect of pressure and vacuum and of the nematicidal effect of the preservative product. VPI treatment can be considered a valuable approach to eliminate PWN and other nematodes from maritime pine wood avoiding the subsequent application of the heat treatment.

Investigation of heat treatment to remove carbon on alumino-silicate fiber and mechanical and insulation properties of alumino-silicate fiber composites used at Bi-2212 CICC

Bi-2212 superconductor has become an important research object in high temperature superconducting (HTS) magnets due to its excellent performance at low temperatures. The "wind-and-react" (W&R) process of Bi-2212 HTS magnet puts a high demand on the insulating structure. The alumino-silicate fiber was selected as an insulating fiber material, and air heat treatment was carried out to remove carbon. The influence of heat treatment on the physical-chemical properties of alumino-silicate fiber was characterized by means of TG-DSC, SEM, XPS, as well as tensile test. The results showed that the best treatment condition for carbon removal on the fiber surface is 600 °C for 2 h. Based on the optimization of insulating fiber and the exploration of pretreatment methods, the fiber-resin composite material was fabricated by the vacuum pressure impregnation (VPI) process. The insulation performance, mechanical strength including tensile strength, and interlaminar shear strength of the composites were tested, and the failure mechanism was analyzed by observing the microstructure of the failure site. Results obtained showed that after heat treatment at 890 °C, the composite formed by the alumino-silicate fiber still has high strength. It provides a reference for the manufacture of Bi-2212 CICC insulating structures.

Thermal and Electrical Characterization of Polyester Resins Suitable for Electric Motor Insulation

This paper undertakes the thermal and electrical characterization of three commercial unsaturated polyester imide resins (UPIR) to identify which among them could better perform the insulation function of electric motors (high-power induction motors fed by pulse-wide modulation (PWM) inverters). The process foreseen for the motor insulation using these resins is Vacuum Pressure Impregnation (VPI). The resin formulations were specially selected because they are one-component systems; hence, before the VPI process, they do not require mixing steps with external hardeners to activate the curing process. Furthermore, they are characterized by low viscosity and a thermal class higher than 180 °C and are Volatile Organic Compound (VOC)-free. Thermal investigations using Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) techniques prove their excellent thermal resistance up to 320 °C. Moreover, impedance spectroscopy in the frequency range of 100 Hz-1 MHz was analyzed to compare the electromagnetic performance of the considered formulations. They manifest an electrical conductivity starting from 10-10 S/m, a relative permittivity around 3, and a loss tangent value lower than 0.02, which appears almost stable in the analyzed frequency range. These values confirm their usefulness as impregnating resins in secondary insulation material applications.

Developing a Vacuum Pressure Impregnation Procedure for CORC Wires

Superconducting magnets designed for high energy physics and nuclear fusion require mechanical and electrical integrity to perform at high currents and magnetic fields. Vacuum Pressure Impregnation (VPI), a process of curing epoxy in and around the superconducting wires, is often used to support and consolidate a magnet. However, the heat and mechanical stresses associated with the process can degrade the wires, significantly lowering their critical current. This study explores different methods of potting and curing CORC wire with the aim of reducing wire performance degradation to less than 3% measured at 77 K, self-field. The wires were 2.9 mm in diameter consisting of a total of six REBCO tapes (three layers of two tapes). Two bending radii (20 mm and 50 mm) were tested to mimic the winding shape of a magnet. Mix 61 epoxy was used in preliminary tests for potting. For each test, two wires were used, and their critical currents were measured simultaneously in liquid nitrogen at 77 K – in their straight form, then bent, followed by the heat treatment used for Mix 61 but without epoxy and finishing with the full epoxy impregnation test. Later tests were performed using CTD-528 to explore a room temperature cure, limiting possibility of degradation from thermal expansion and prolonged exposure of the REBCO tapes to elevated temperature. Here we report the experimental results with multiple CORC wires and different curing schedules. The results obtained are the first steps toward identifying the VPI process with minimum degradation in critical current to be implemented in high-field magnets using CORC wires.

Optimization of explosive fumes ventilation layout in vacuum pressure impregnation process

Vacuum pressure impregnation (VPI) is a primary process by which epoxy resin is impregnated into the stator windings of large generators and motors to enhance their physical properties. However, the vaporization of epoxy resin generates hazardous resin fumes during the VPI process, and the residual fumes leak into the atmosphere. This leakage is a safety and environmental hazard in the workplace as it can cause fire, explosion, and respiratory diseases. Therefore, it is crucial to reduce the hazard by designing an optimal ventilation system. This study proposed optimization of the explosive fumes ventilation Layout in the VPI process using computational fluid dynamics (CFD). A total of 12 Layouts of the ventilation system was designed according to the air inlet and outlet positions. This investigation used the pseudo transient method and the RNG k–ε turbulence model. An optimal Layout with the highest ventilation efficiency and the shortest LEL arrival time was determined through CFD analysis. In the optimal Layout, the LEL arrival time was 372 s, down about 59% from the model presented in the previous study, and the ventilation efficiency was the highest at 0.962.

Construction of a Phytic Acid-Silica System in Wood for Highly Efficient Flame Retardancy and Smoke Suppression.

The intrinsic flammability of wood restricts its application in various fields. In this study, we constructed a phytic acid (PA)–silica hybrid system in wood by a vacuum-pressure impregnation process to improve its flame retardancy and smoke suppression. The system was derived from a simple mixture of PA and silica sol. Fourier transform infrared spectroscopy (FTIR) indicated an incorporation of the PA molecules into the silica network. Thermogravimetric (TG) analysis showed that the system greatly enhanced the char yield of wood from 1.5% to 32.1% (in air) and the thermal degradation rates were decreased. The limiting oxygen index (LOI) of the PA/silica-nanosol-treated wood was 47.3%. Cone calorimetry test (CCT) was conducted, which revealed large reductions in the heat release rate and smoke production rate. The appearance of the second heat release peak was delayed, indicating the enhanced thermal stability of the char residue. The mechanism underlying flame retardancy was analyzed by field-emission scanning electron microscope coupled with energy-dispersive spectroscopy (SEM-EDS), FTIR, and TG-FTIR. The improved flame retardancy and smoke-suppression property of the wood are mainly attributed to the formation of an intact and coherent char residue with crosslinked structures, which can protect against the transfer of heat and mass (flammable gases, smoke) during burning. Moreover, the hybrid system did not significantly alter the mechanical properties of wood, such as compressive strength and hardness. This approach can be extended to fabricate other phosphorus and silicon materials for enhancing the fire safety of wood.

Design of Ventilation System to Prevent Epoxy Fume Release from Vacuum Pressure Impregnation

In this study, a model for the exhaust of epoxy fumes generated by vacuum pressure impregnation (VPI) was developed using computational fluid dynamics (CFD), and an optimal design for minimizing the fume exhaust time was developed to improve the safety of the working environment. VPI is a process of durability reinforcement by impregnating epoxy varnish insulators to the windings in the stator. In addition, the VPI process can be used for applications such as coating, sealing, and insulating porous parts. The VPI process tanks are composed of a working tank with an inner tank. As the working tank is opened after the vacuum and pressurization to proceed with the final step of the process, the epoxy fumes derived from the resin can leak into the environment. To address these safety and environmental problems, an epoxy fume exhaust process is required. Therefore, a case study was conducted using CFD to validate the exhaust efficiency of epoxy fumes by rearranging different exhaust methods. It was found that the method of using pressurization yielded a higher fume exhaust efficiency (99.46 %) than did the depressurization method (96.42 %).

Realizing Mechanically Robust and Electrically Conductive Wood via Vacuum Pressure Impregnation.

Wood is highly regarded as the most sustainable resource that is widely used in structural applications. To extend its practicality in electrically conductive applications, it is necessary to confer electrical conductivity to the insulating wood. The most common strategy is to derive carbonized wood powder via an annealing process. Even though these carbonized wood powders are electrically conductive, they lost the ancestry characteristic of wood, that is, excellent mechanical properties. As such, it is of great importance to realize the concept of conductive wood while at the same time maintaining or even enhancing its mechanical properties further. By leveraging on the naturally formed transportation channels found in trees, conductive particles can be aligned along these ordered channels. To substitute active transport in living plants, a vacuum pressure impregnation process was used to infiltrate these conductive particles into the transportation channels. As a result, Cu/wood composite, denoted as Cu-SW, exhibited a minimum volume resistivity of 1.366 × 103 Ω cm, which was lower than those of conventional semiconductors. High Cu loading of ∼43.1 volume % of the final product, Cu-SW, was achieved with such technique, which clearly indicates the ability to achieve deep penetration of Cu nanoparticles into the bulk wood. Furthermore, an encouraging mechanical properties improvement of ∼50% was recorded for Cu-SW as compared to the wood matrix. With the enhancement in both conductivity and mechanical properties, Cu-SW could be used in load-bearing application that requires electrical conduction.

Vacuum Pressure Impregnation Setup at CERN for Nb3Sn Coils

The CERN Large Magnet Facility (LMF) is currently producing 5.5 m long 11 Tesla dipole and 7.2 m long MQXFB quadrupole coils for the HL-LHC project. Both coil types are fabricated with Nb3Sn conductor with the so-called wind and react technique. These coils require a vacuum pressure impregnation process to form the final insulation and to give the final dimensions. The paper will present the impregnation process applied at CERN focusing in particular on the hardware. The impregnation process and its reproducibility are shown, together with ongoing developments. Furthermore, the LMF impregnation infrastructure and recent applied upgrades are described, aiming for a reliable process workflow based on a modular hardware with an improved interchangeability.

Effect of conductivity on the thermal and electrical properties of the stress grading system of an inverter-fed rotating machine

The thermal and electrical characteristics of a stress grading system are studied by simulations and measurements of the electric field and temperature distributions in the overhang region of a form wound medium voltage motor coil. Simulations show that a highly conductive stress grading tape (SGT) reduces the maximum electric field in this region but increases heat production and temperature. In contrast, a highly conductive armor tape (CAT) decreases the maximum electric field in this region and also reduces the heat production and temperature in the stress grading system but also produces a slight increase in the electric field in the SGT region. For the simulation studies, accurate measurements of the electrical and thermal conductivities of materials are made, taking into account the effects of the vacuum pressure impregnation (VPI) process, temperature, and tape builds. The electrical conductivity of single and double half-lap layers of CAT and SGT are measured from 30 to 100 °C. For the evaluation of the simulation model, the temperature profile along the stress grading system was measured and simulated under pulsed voltage at room and near typical operating temperatures.

Excitation characteristics of magnets impregnated with paraffin wax

The Superconducting Electromagnetic Iron Separator (SEIS) based on paraffin wax vacuum pressure impregnation (VPI) technology was developed to remove magnetic impurities from coal. The superconducting coil was wound by Cu/NbTi wires. The inner and outer diameter of the coil are 928 mm and 1022 mm respectively. The height of the coil is 355 mm. The magnet generates a 3 T central field at 165 A of operating current.There are three SEIS devices that have been manufactured and tested. All the design requirements are achieved by the first device. However, the others can’t be charged to the design current in 20 min, which is a requirement of coal handing port. This paper presents the details of the VPI process and the charging tests. The excitation characteristics of three SEIS devices are shown in the results.

Properties of red maple laminated veneer lumber impregnated with waterborne micronized and two soluble copper formulations

ABSTRACTCertain important quality parameters of red maple (Acer rubrum) laminated veneer lumber (LVL) impregnated with three waterborne formulations: copper azole (CA-B), micronized copper azole (MicroCA or MCA) and alkaline copper quaternary (ACQ-D) bonded with phenol formaldehyde or cross-linked polyvinyl acetate (XPVAc) adhesives were evaluated. Pre-dipping of veneers before LVL production and two post-manufacturing procedures, viz., vacuum-pressure and post-dipping of LVL, were applied. Maximum copper retention in pre-dip-treated, vacuum-pressure and post-dip-treated LVL was 1.4, 9.7 and 1.7 kg/m3, respectively. Copper retention in MCA-treated LVL was relatively lower than soluble formulations. Various physical, mechanical and bonding properties of treated LVL such as density, water absorption, swelling, flexural properties, hardness, tensile shear strength, delamination and wood failure (%) were studied and compared with untreated LVL. Little to negligible deleterious effect was observed on properties of LVL due to these chemical treatments. Analysis of variance results showed that most of properties of red maple LVL were not significantly different compared with those of untreated LVL. Therefore, vacuum-pressure impregnation process can be used to treat the red maple LVL with novel micronized copper formulations for increasing the service life of such products against biodegradation without affecting techno-mechanical quality parameters.

Modification of Poplar Wood Using Polyhexahydrotriazine and Its Effect on Hygroscopicity

Chemical modification is an efficient method for improving the properties of wood. In this study, poplar sapwood was modified via paraformaldehyde, 4,4′-oxydianiline (ODA), and N-methylpyrrolidone solvents through a vacuum-pressure impregnation process. The poplar sapwood underwent a curing process producing the ODA polyhexahydrotriazine polymer, which is a strong thermosetting material. The results showed that the weight percent gain of the modified poplar sapwood was 223.3%. The density of the modified wood specimen increased from 356.8 kg/m3 to 445.0 kg/m3. The water absorption decreased from 159.6% to 0.9% due to the thermosets penetration into the lumen and the cell walls of the wood. Additionally, condensation reactions occurred between the aldehyde groups of the paraformaldehyde and the hydroxyl groups of the poplar wood. The results showed that the modified wood achieved stronger waterproof properties than the unmodified wood.

Development of Vacuum Pressure Impregnation for Central Solenoid of JT-60SA

The manufacturing of central solenoid (CS) for JT-60SA is in progress. Vacuum pressure impregnation (VPI) process is key technology for large scale magnet and is used for CS. The height of the CS module after vacuum impregnation process is reduced due to the shrinkage of insulation thickness. Large shrinkage results in difficulties in the VPI process because a moving system is required on the VPI jigs. We evaluated the amount of shrinkage by a VPI test of insulation samples. The test results show that the height of the CS module reduces about 15 mm during the VPI process. Improved jig was developed based on this shrinkage. VPI was well performed and validated by a visual check and impulse test. These results suggest that the VPI process and jig were successfully established. In this paper, the detailed procedure of VPI for CS module, VPI test, and developed jig for VPI are described.