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.

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.

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.

Exploratory Pressure Impregnation Process Using Supercritical CO2, Co-Solvents, and Multi-Cycle Implementation

Supercritical carbon dioxide (scCO2) is extensively used for extracting chemicals from materials, but the impregnation of materials with chemicals using scCO2 has received little attention in comparison. To the best of our knowledge, most technologies described in the literature operate by the principle of diffusion, where impregnation yield is limited by solubility. The objective of this exploratory study is to prove the feasibility of an scCO2 impregnation process that can extract solutes from one material and release them into another material through a single extraction/impregnation stage that can be applied in cycles to increase the yield. The feasibility of the concept was proven in the laboratory using radiata pine bark wax as the solute and radiata pine wood as the impregnated material. Extraction/impregnation tests were performed at temperatures between 40 and 60 °C, pressures between 12 and 16 MPa, and with the addition of ethanol and acetone as co-solvents. The study demonstrated the feasibility of multi-cycle scCO2 impregnation of wax into wood, where the novelty of the concept is the implementation as traditional pressure impregnation methods.

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.

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.

Fabrication of highly stable and durable furfurylated wood materials. Part I: process optimization

Abstract In order to improve dimensional stability and durability of wood, furfurylation of poplar and Chinese fir wood using newly developed furfuryl alcohol (FA) formulation combined with a common vacuum and pressure impregnation process was studied. An orthogonal experiment was designed to optimize the furfurylation process for the two wood species. The weight percent gain (WPG), equilibrium moisture content (EMC), anti-swelling efficiency (ASE), modulus of rupture (MOR), modulus of elasticity (MOE), as well as resistance to mold, decay fungi, and termites were evaluated. The results showed that nearly all the properties of the furfurylated wood could be improved to various extents. The average ASE of the furfurylated Chinese fir and poplar could reach as high as 80, 71, 92% and 79, 90, 75% in tangential and radial directions, and by volume, respectively, higher than most previously reported wood modification processes. Furthermore, the modified wood had excellent biological durability, with nearly 100% mold resistance, strong decay and termite resistance. Finally, processing parameters with 50% FA, 105–115 °C curing temperature, and 5–8 h curing time were therefore recommended for pilot-scale production of furfurylated poplar and Chinese fir wood based on range analysis.

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.

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.

Preparation and Property of Insulated Tension Pole for 550 kV GIS Isolation Switch

550kV GIS isolation switch of aramid insulated tension pole was studied in this paper. The aramid fiber fabric and polyester fiber fabric are rolled into the mold in the winding technology. Through the vacuum pressure impregnation process, the epoxy resin, curing agent, accelerator system was filled, the product of the aramid insulated tension pole was obtained after curing and stripping. Meanwhile, the electrical insulation characteristics and mechanical properties of insulated tension rod were performed. The results indicated that the insulated tension pole made in the vacuum impregnation process owned excellent electrical insulation performance and mechanical properties, which was basically able to meet the performance requirements of foreign products.

Outgassing measurements for the turn insulation of CFETR poloidal field coils

China Fusion Engineering Test Reactor (CFETR) is a new tokamak device. The poloidal field (PF) system plays an important role in controlling the location and shape of the plasma. In order to satisfy the electrical and mechanical requirements, the turn insulation shall be applied on the conductor during winding. Before vacuum pressure impregnation (VPI) process, the conductor with dry (un-impregnated) insulation should be leak tested in a chamber, and the material shall be degassed in the VPI mold before impregnation with epoxy. The gas released from the insulation material will affect the vacuum of leak test vessel and VPI quality. In this paper, the dynamic flow method was used to measure the outgassing rate of insulation material in special structure, and the results were shown and discussed.

Flexible epoxy‐silicone rubber laminates for high voltage insulations with enhanced delamination resistance

In this work, functionalized damping layers consisting of crosslinked silicone rubber are incorporated into brittle epoxy‐based composites to improve the delamination resistance of high voltage insulations. Selected functional organosilanes are attached onto the elastomer surface by a two‐step modification to ensure a covalent bonding between the thermosetting resin and the damping layer. Functional model insulations and stator bar prototypes are then prepared with a vacuum pressure impregnation process. The influence of the damping layer on the thermo‐mechanical and electrical properties as well as the delamination resistance is characterized. The results give evidence that the flexibility of the new composite materials can be increased significantly whereas the electrical properties are not affected by the elastomer layer. By evaluating the performance of the stator bar prototypes it can be clearly shown that both delamination resistance as well as high voltage endurance can be enhanced considerably by the application of flexible damping layers. POLYM. COMPOS., 36:2238–2247, 2015. © 2014 Society of Plastics Engineers

Progress of the Design of HTS Magnet Option and R&amp;amp;D Activities for the Helical Fusion Reactor

The high-temperature superconducting magnet option is being explored in the conceptual design studies of the LHD-type helical fusion reactor FFHR-d1. A 100 kA-class conductor is being developed by simply stacking REBCO tapes in a copper and stainless-steel jacket. One of the design options of the HTS conductor includes internal insulation so that the windings do not require vacuum pressure impregnation process. Innovative winding method of the huge helical coils is being investigated based on the segment fabrication of half-helical-pitch conductors by developing a bridge-type mechanical lap joint. A “30 kA-class” prototype conductor sample was fabricated using GdBCO tapes and successfully tested. The critical current was measured at various temperatures at 4.2-40 K and magnetic field <; 8 T. The joint resistance was evaluated by changing the applied stress. These experimental results are boosting the HTS magnet design of FFHR-d1.

Development and Test of JT-60SA Central Solenoid Model Coil

A central solenoid (CS) model coil (CSMC) was manufactured by using real manufacturing jigs and procedure to validate the CS manufacturing processes for JT-60SA. The winding accuracy and the temperature control precision during the heat treatment met the requirements. The vacuum pressure impregnation process was also successfully finished. The cold test of the CSMC was performed as a final check of the manufacturing process. The joint resistance, the Ic, and the pressure drop measurements were conducted as the verification test. The results of verification test satisfied the design requirements. These results indicate that the manufacturing processes of the JT-60SA CS has been established. The manufacturing of real CS pancakes just started after finishing the CSMC test.

Absorption–desorption behaviour and dimensional stability of untreated, CC impregnated and pine oil treated glulam made of Scots pine and Norway spruce

In order to survive, the wood degrading microbes need a moisture content of wood exceeding the fibre saturation point, i.e., 26%–32%, depending on the species. Maintaining wood moisture content below this level effectively prevents biodegradation. This can be achieved either by preventing wood's exposure to liquid water or increasing the hydrophobicity of wood by some impregnation or modification treatment. The objective of the study was to define the dimensional stability in changing environmental conditions, as well as the water absorption and desorption behaviour of untreated, copper-chromium impregnated and pine oil treated glulam. Scots pine was used for pressure impregnated and pine oil impregnated beams while the reference beams were made of Norway spruce, which is the most commonly used species for glulam production nowadays. The 6 inner lamellae of the glulam beams originated from small-sized logs, whereas the surface lamellae were made of larger logs. Beams with 44 × 200 mm cross cut dimensions were glued using melamine-urea-formaldehyde resin, and divided into three treatment groups. Treatment 1 was not impregnated (Norway spruce), treatment 2 (Scots pine) was impregnated with copper-chromium based preservative in commercial pressure impregnation process, and treatment 3 (Scots pine) was impregnated with pine oil using the process of Ekopine Ltd. After the treatments, 20 glulam specimens with dimensions of 44 × 200 × 170 mm (thickness–width–length) were produced from each treatment group. The cross-cut surfaces of the specimens were sealed using waterproof varnish to ensure that the water movement took place only through the side surfaces of the specimens. The air-dry specimens (MC 7.7–12.6%) were immersed into water for 6 weeks, during which period they were weighed repeatedly. After the immersion treatment, they were brought to a standard climate (65% RH, 20 °C temperature). Again, their mass was recorded until it did not change anymore. Then the same specimens were taken into a weather chamber where they were subjected to four 2-week-long test cycles with varying temperature and relative humidity, totalling 8 weeks of artificial weather exposure. Pine oil impregnated specimens resisted the water absorption significantly better than the untreated and pressure impregnated specimens. Due to the low initial MC after the absorption period, pine oil impregnated specimens also dried rapidly below 20% MC, while the drying of untreated and pressure impregnated glulam to the same level took 3–4 weeks in standard climate. The pine oil impregnated specimens had clearly better dimensional stability in the weather chamber, compared with the untreated and pressure impregnated specimens. Also the mass variation of pine oil impregnated specimens was significantly reduced in comparison to the other two treatment groups, indicating lower hygroscopicity for the pine oil treated specimens. To conclude, the pine oil impregnation of wood can be considered as an effective preservation method against moisture exposure. It appears to be a promising method to prevent biodegradation by maintaining the moisture content of wood below the level that enables mould and fungal growth.

Design and Analysis of Impregnation Chamber Used In Vacuum Pressure Impregnation Process

The simple explanation is that in nature and in manufacturing, things leak. Vacuum impregnation stops leak. The ultimate goal of vacuum impregnation is to seal leak/migration paths without impacting the functional, assembly or appearance characteristics of a part. The impregnation chamber which is used in VPI process operates maximum up to 80 to 150 psi.it is important to analyse and design the pressure vessel that will provide safety, durability and serviceability to the company. Accomplishing this task will require a very good understanding of behaviour and a good knowledge of parameters that affecting the pressure vessel due to varying loads, pressure and thickness of shell element. The most important one is that the given geometry of pressure vessel must be analysed to assure it should meet the design standards. Vacuum impregnation as an industrial process has been in commercial use for more than 60 years. For the world's largest manufacturers, it continues to be the preferred process through which to guarantee the pressure-proof, leak-proof, and corrosion-proof requirements of parts and components in critical operations. The ultimate goal of vacuum impregnation is to seal leak / migration paths without impacting the functional, assembly or appearance characteristics of a part. Functional characteristics include the ability for fluids or gasses to flow only where needed in order to enhance in-service performance of the components' design. Assembly characteristics, which must be maintained, include performance of tapped holes; the integrity of mating and sealing surfaces, the elimination of residual internal contamination in water jackets, sockets, surfaces and dimensional areas. Appearance characteristics include oxidation and discoloration. Vacuum impregnation is governed by military standard MIL-STD-276A as well as numerous proprietary and customer specifications. The vacuum component of the process removes the air that occupies the migration path commonly known as porosity in cast or pressed metals. The impregnation component of the process fills the void with a durable and stable material suitable for field of use. These materials can be silicate or epoxies. (7) During normal operation, transformers are subjected to the failure of the insulation system. How long an insulation system will be serviceable depends on the materials chosen and the service environment. Thermal, mechanical, voltage and environmental stresses all combine to reduce the service life of the transformer. Solid- state Controls, Inc. (SCI) manufactures all of its transformers using the Vacuum Pressure Impregnation (VPI) process. This system strengthens the insulation system and extends the service life of the transformer. The VPI process is the most advanced system in use today. The VPI process is the most effective way known to eliminate the dead air spaces that cause hot spots within the transformer coils. These hot spots can be 20 0 higher than the average coil temperature. The VPI process, along with a good resin, provides a low thermal resistance path that lowers the average operating temperature of the transformer.The resin seals the transformer against environmental conditions and bonds all components of the insulation system together for good mechanical strength. This is very effective in reducing mechanical vibrations. This greatly reduces the audible noise level of the transformer. The VPI process and resin also enhances the dielectric capability between windings and between the windings and ground. This allows the transformer to survive higher voltage stress levels without failure. The general VPI process contain following parts In the impregnation chamber (also known as an autoclave, pressure vessel or vacuum vessel) air is evacuated from the leak path in the part by using a deep vacuum. The evacuated leak path is filled with sealant by covering the part with the sealant and applying pressure. More energy is required to penetrate the porosity with sealant than to evacuate the air. In the recovery station (also known as drain station, centrifuge) excess sealant is recovered for reuse. In the wash/rinse station (also known as surge station, rolling rinse or pump over station) residual sealant is washed from the part's internal passages, taps, pockets and features where sealant is undesirable. In the cure station (also known as standing, rolling cure or pump over station) the sealant, impregnated into the walls of the part, is polymerized in the leak path. In general, vacuum impregnation includes four steps.