High Pressure Coolant Research Articles

COMPARISON OF CONVENTIONAL, COHERENT-JET AND HIGH-PRESSURE COOLANT DELIVERY SYSTEMS FOR PROFILE GRINDING

In this work, conventional (non-coherent), coherent-jet, and high pressure coolant delivery systems are compared for profile creep-feed grinding, under non-continuous dressing conditions. To facilitate this comparison, an analytical method of determining the available flow (coolant that hits the wheel or workpiece) was presented. The coolant delivery systems were compared for five different feed rates. At each feed rate the form error was measured using a coordinate measuring machine at five cross sections along the workpiece. The high-pressure coolant delivery system had the lowest form error and had an available flow of only 1.7 L/min. The non-coherent jet had the second best form error and had an available flow of 17 L/min. The coherent jet had the highest form error with an available flow of 39 L/min.

Pressurizing behavior on ingress of coolant into pebble bed of blanket of Fusion DEMO reactor

In the safety design and technology of blankets for the Fusion DEMO reactor developed in Japan, coolant ingress in the blanket box structure is one of the most important events. Especially, the thermal hydraulics in the pebble bed in the case of the high-pressure coolant ingress is very important to evaluate the pressure propagation and coolant flow behavior. This paper presents the preliminary results of the pressure loss characteristics by the coolant ingress in the pebble bed. Experiments have been performed to simulate the helium coolant ingress into breeder and multiplier pebble beds and to evaluate the pressure loss in the pebble beds. The measured pressure loss is compared with the predicted values by Ergun's equation, which is the correlation equation on pressure loss of the flow through porous medium. Parameter study is carried out and dependencies of pressure loss through pebble bed on pressure and packing factor is evaluated. Method to reduce the maximum pressure in solid breeder blanket after pipe rupture accident is discussed. Enhancement of pressure loss in upstream and reduction of pressure loss in downstream is effective.

Turning performance optimisation of aeronautical materials by using high pressure cooling technology

Machining assisted with high pressure cutting fluid is an effective method in turning operations, which allows to overcome the problems presented in the conventional turning of poor machinability materials. These problems arise as consequence of the difficult evacuation from the heat generated during the cutting process, the premature adhesion of the machined material to the cutting tool and the complex removal of the long chips from the cutting zone. The application of cutting fluid with this technique causes a hydraulic pressure between the chip and the rake face of the tool with very positive effect on machining, as chip size and cutting forces reduction and lower tool wear. Advantages of turning assisted with high pressure coolant (140 bars) in comparison to conventional pressure of 2 bars have been shown in roughing and finishing machining tests carried out on three aeronautical materials: Ti6Al4V, Inconel 718 and Steel MSRR6503 EAK.

Increasing productivity in high speed machining of Ti-6Al-4V alloy under high pressure coolant supply

Cemented carbide tools are the most common tool materials employed in the machining of titanium alloys. Polycrystalline Diamond (PCD) tools can substantially enhance the machining productivity. So, this study investigates the performance of PCD tools when machining Ti-6Al-4V alloy at cutting speeds up to 250 m min-1 with coolant delivered under pressures. The results show that longer tool life can be achieved when machining with high pressure coolant supplies up to 20.3 MPa compared with the conventional coolant flow. Up to three folds increase in cutting speed can be achieved when machining with uncoated cemented carbide tools relative to that currently used for manufacture in industry, while with PCD tools, up to five fold increase in cutting speed is achievable when machining with PCD tools.

High-pressure cooling of face-grooving operations in Ti6Al4V

This paper presents results from an experimental study with high-pressure cooling on the rake face and on the flank face of the cutting tool. The technique was tested in face-grooving operations in Ti6Al4V, which are common and time-consuming turning operations in the aerospace industry. Grooving is a difficult operation because the cooling effect is low, owing to the geometry of the groove and also because of the chips that obstruct the coolant flow. The results show that 10–30 MPa high-pressure cooling on the rake face of the tool can increase tool life by 200–300 per cent as compared with conventional flood flushing. However, when high-pressure rake face cooling is applied, the workpiece surface may be adversely affected by the chip flow. Applying high-pressure coolant to the tool flank face increases tool life by 50–100 per cent relative to conventional flood flushing. No damage to the workpiece surface was observed. It can be concluded that a complete high-pressure cooling system should include options for both cooling methods.

Surface integrity of finished turned Ti–6Al–4V alloy with PCD tools using conventional and high pressure coolant supplies

Surfaces generated when machining Ti–6Al–4V alloy with PCD tools using conventional and high pressure coolant supplies was investigated. Longer tool life was recorded when machining Ti–6Al–4V with high-pressure coolant supplies and the recorded surface roughness R a values were well below the tool rejection criterion (1.6 μm) for all cutting conditions investigated. The micro-structure of the machined surfaces were examined on a scanning electron microscope. Micrographs of the machined surfaces show that micro-pits and re-deposited work material were the main damages to the surfaces. Micro-hardness analysis showed hardening of the top machined surfaces when machining with conventional coolant while softening of the subsurface layer was observed when machining under high-pressure coolant supplies. The later is probably due to lower heat generated, with the consequent tempering action when machining with PCD tools with high-pressure coolant supplies. The microstructure below the machined surfaces had minimal or no plastic deformation when machining with conventional and high-pressure coolant supplies.

Hydrogen Production Using High-Temperature Steam Electrolysis Supported by Advanced Gas Reactors with Supercritical CO2 Cycles

Hydrogen production using high-temperature steam electrolysis (HTSE) supported by a supercritical CO2 (SCO2) recompression Brayton cycle that is directly coupled to an advanced gas-cooled reactor (AGR) is proposed in this paper. The system features and efficiency are analyzed in a parametric fashion. The analysis includes the influence of the major components’ performance and the component integration in a proposed plant layout. The configuration, HTSE-SCO2-AGR, with thermal recuperation from the product gas streams and an intermediate heat exchanger between the turbine exit and the feedwater stream is found to offer excellent thermal efficiency, operational flexibility, and expected cost. The HTSE average process temperature is 900°C, and the hydrogen pipeline delivery pressure is assumed to be 7 MPa for the evaluation of the plant performance. The reactor exit temperature and the SCO2 cycle turbine inlet temperature are the same as those for the SCO2 recompression cycle design: 550 to 700°C. The 900°C at the HTSE unit, which is higher than the reactor exit temperature, is achieved with recuperative and electrical heating. HTSE is assumed to operate within 80 to 90% voltage efficiency at 1 atm to 7 MPa of pressure. A parametric analysis of these operating conditions shows that the system can achieve 38.6 to 48.2% low heating value of net hydrogen production energy efficiency. The extensive experience from commercial AGRs, the compactness of the SCO2 power conversion system, and the progress in the electrolysis cell materials field can help the economical development of a future recuperative HTSE-SCO2-AGR. The major research and development needs for this plant concept are materials processing for the durability and efficiency of the HTSE system, the design update of the AGR with advanced materials to resist high-pressure CO2 coolant, thermal hydraulics of CO2 at supercritical pressures, and detailed component design for system integration.

The Application of Cryogenic Pneumatic Mist Jet Impinging in High-Speed Milling of Ti-6Al-4V

To solve the problems caused by high temperature in the cutting zone during high-speed milling of Titanium alloys, some cooling methods are employed, such as cold air cooling, high pressure coolant jet impinging, MQL, etc. But all have their shortfalls, both in cooling efficiency and environmental pollution. Here a new high efficiency cooling technology-cryogenic pneumatic mist jet impinging (CPMJI) cooling technology is offered. In this technology, a little quantity of coolant is carried by high pressure cryogenic air (-20) and reaches the machining zone in the form of mist jet. This paper mainly focuses on the cooling effects of CPMJI in high-speed milling of Titanium alloy Ti-6Al-4V, as compared with dry, cold air cooling and MQL conditions. CPMJI greatly reduced the temperature in cutting zone and flank wear of tool.

Influence of the direction and flow rate of the cutting fluid on tool life in turning process of AISI 1045 steel

High-pressure coolant (HPC) delivery is an emerging technology that delivers a high-pressure fluid to the tool and machined material. The high fluid pressure allows a better penetration of the fluid into the tool–workpiece and tool–chip contact regions, thus providing a better cooling effect and decreasing tool wear through lubrication of the contact areas. The main objective of this work is to understand how the tool wear mechanisms are influenced by fluid pressure, flow rate and direction of application in finish turning of AISI 1045 steel using coated carbide tools. The main finding was that when cutting fluid was applied to the tool rake face, the adhesion between chip and tool was very strong, causing the removal of tool particles and large crater wear when the adhered chip material was removed from the tool by the chip flow. When cutting fluid was not applied to the rake face, adhesion of chip material to the face did occur, but was not strong enough to remove tool particles as it moved across the face, and therefore crater wear did not increase.

Experimental Study on Creep Feed Deep Grinding Titanium Alloy with Slotted CBN Grinding Wheel

In order to improve the grindability of titanium alloys, the inhibition of chemical affinity between abrasives and titanium alloys and cooling enhancement in grinding zone are carried out in this paper. Slotted electroplated CBN grinding wheels with optimum topography are used, and different grinding fluid supply systems such as conventional tangential spraying coolant supply, inner chamber coolant jet impingement, radial high-pressure coolant jet impingment are employed in creep feed deep grinding experiments on titanium alloy (TC4). The experimental results show that high-pressure jet impingement has remarkable cooling effect. The temperature of the workpiece surface can be steadily kept below the critical film boiling temperature 120~130°C, while the workpiece surfaces is badly burnt with conventional coolant supply. The study will exploit an important research orientation that has great potential in high efficiency grinding. Further perfection of this study will not only enable us to increase the available material removal rate to a new level but also solve the workpiece burn problem of the difficult-to-machining materials in high efficiency grinding.In order to improve the grindability of titanium alloys, the inhibition of chemical affinity between abrasives and titanium alloys and cooling enhancement in grinding zone are carried out in this paper. Slotted electroplated CBN grinding wheels with optimum topography are used, and different grinding fluid supply systems such as conventional tangential spraying coolant supply, inner chamber coolant jet impingement, radial high-pressure coolant jet impingment are employed in creep feed deep grinding experiments on titanium alloy (TC4). The experimental results show that high-pressure jet impingement has remarkable cooling effect. The temperature of the workpiece surface can be steadily kept below the critical film boiling temperature 120~130°C, while the workpiece surfaces is badly burnt with conventional coolant supply. The study will exploit an important research orientation that has great potential in high efficiency grinding. Further perfection of this study will not only enable us to increase the available material removal rate to a new level but also solve the workpiece burn problem of the difficult-to-machining materials in high efficiency grinding.

Study on High Speed Cutting of Bio-Titanium alloy

Using a binder-less PcBN tool, the influences of cutting speed on tool life and wear pattern in turning of Ti-6Al-2Nb-1Ta, which was a vanadium free titanium alloy for a surgical implant material, were investigated. In the condition of feed rate of 0.15mm/rev and depth of cut of 0.5mm with an application of a high pressure coolant, the tool life at cutting speed of 4.2m/s was the longest in the various cutting speeds. In conditions of cutting speed of below 4.2m/s the tool life was determined by chipping and flaking occurring on tool face, on the other hand, smooth wear on the tool face were observed in over 4.2m/s. And, it was confirmed that the smooth wear on the tool face in turning process appeared over 730°C of tool flank temperature , and the promotion of tool wear was so dependent on the cutting temperature. Also, in order to investigate this reaction in the cutting process, the experimental model reaction test between the tool material and the workpiece one by using the SPS equipment were conducted in addition to element analysis of the adhesive on the cutting edge using EDS and XRD. As a result, it was clarified that TiB2 was generated in the interface between the binder-less PcBN and the titanium alloy, and the reaction was sensitive to its temperature.

Machining of nickel-base, Inconel 718, alloy with ceramic tools under finishing conditions with various coolant supply pressures

Machining of Inconel 718 with whisker reinforced ceramic tool gave better performance in terms of tool life under high-pressure coolant supplies up to 15 MPa compared to conventional coolant supplies. The use of 15 MPa coolant supply pressure tend to suppress notching during machining thus improving tool life, while the use of higher coolant supply pressure of 20.3 MPa did not show improvement in tool life due probably to accelerated notch wear caused by water jet impingement erosion. Cutting forces decreased with increasing coolant supply pressure due to improved cooling and lubrication at the cutting interface as well as effective chip segmentation ensured by the momentum of the coolant jet. Surface roughness generated were well below the rejection criteria. This can be attributed to the round shape of the insert which tend to encourage smearing of the machined surface with minimum damage. Microstructure analysis of the machined surfaces show evidence of plastic deformation and hardening of the top layer up to 0.15 mm beneath the machined surface as a result of increase in dislocation density.

Effect of Midpassage Gap, Endwall Misalignment, and Roughness on Endwall Film-Cooling

To maintain acceptable turbine airfoil temperatures, film cooling is typically used whereby coolant, extracted from the compressor, is injected through component surfaces. In manufacturing a turbine, the first stage vanes are cast in either single airfoils or double airfoils. As the engine is assembled, these singlets or doublets are placed in a turbine disk in which there are inherent gaps between the airfoils. The turbine is designed to allow outflow of high-pressure coolant rather than hot gas ingestion. Moreover, it is quite possible that the singlets or doublets become misaligned during engine operation. It has also become of interest to the turbine community as to the effect of corrosion and deposition of particles on component heat transfer. This study uses a large-scale turbine vane in which the following two effects are investigated: the effect of a midpassage gap on endwall film cooling and the effect of roughness on endwall film cooling. The results indicate that the midpassage gap was found to have a significant effect on the coolant exiting from the combustor-turbine interface slot. When the gap is misaligned, the results indicate a severe reduction in the film-cooling effectiveness in the case where the pressure side endwall is below the endwall associated with the suction side of the adjacent vane.

Evaluation of the performance of CBN tools when turning Ti–6Al–4V alloy with high pressure coolant supplies

Cubic Nitride Boron (CBN) tools are generally used for machining harder alloys such as hardened high Cr steels, titanium and nickel alloys. The tools are expected to withstand the heat and pressure developed when machining at higher cutting conditions because of their high hardness and melting point. This paper evaluates the performance of different CBN tool grades in finish turning Ti–6Al–4V (IMI 318) alloy at high cutting conditions, up to 250 m min −1, with various coolant supplies. Tool wear, failure modes, cutting and feed forces and surface roughness of machined surfaces were monitored and used to access the performance of the cutting tools. Comparative trials were carried out with uncoated carbide tools when machining at a speed of 150 m min −1. Test results show that the performance of CBN tools, in terms of tool life, at the cutting conditions investigated is poor relative to uncoated carbide tools, as expected and often, reported due probably to rapid notching and excessive chipping of the cutting edge associated with a relatively high diffusion wear rate that tends to weaken the bond strength of the tool substrate. An increase in the CBN content of the cutting tool also led to a reduction in tool life when machining at the cutting conditions investigated.

Finish Machining of Nickel-Base Inconel 718 Alloy with Coated Carbide Tool under Conventional and High-Pressure Coolant Supplies

Single-point turning of Inconel 718 alloy with commercially available Physical Vapour Deposition (PVD)-coated carbide tools under conventional and high-pressure coolant supplies up to 20.3 MPa was carried out. Tool life, surface roughness (Ra), tool wear, and component forces were recorded and analyzed. The test results show that acceptable surface finish and improved tool life can be achieved when machining Inconel 718 with high coolant pressures. The highest improvement in tool life (349%) was achieved when machining with 11 MPa coolant supply pressure at higher speed conditions of 60 m · min−1. Machining with coolant pressures in excess of 11 MPa at cutting speeds up to 40 m · min−1 lowered tool life more than when machining under conventional coolant flow at a feed rate of 0.1 mm · rev−1. This suggests that there is a critical coolant pressure under which the cutting tools performed better under high-pressure coolant supplies. Cutting forces increased with increasing cutting speed due probably to reactive forces introduced by the high-pressure coolant jet. Tool wear/wear rate increased gradually with prolonged machining with high coolant pressures due to improved coolant access to the cutting interface, hence lowering cutting temperature. Nose wear was the dominant tool failure mode when machining with coated carbide tools due probably to a reduction in the chip-tool and tool-workpiece contact length/area.

Effect of high-pressure coolant supply when machining nickel-base, Inconel 718, alloy with coated carbide tools

Inconel 718 was machined with a triple PVD coated (TiCN/Al2O3/TiN) carbide tool at speeds up to 50mmin−1 using conventional and various high coolant pressures, up to 203bar. Tool life, surface roughness (Ra), tool wear and component forces were recorded. The test results show that acceptable surface finish and improved tool life can be achieved when machining Inconel 718 with high coolant pressures. Compared to conventional coolant supplies, tool life improved as much as 740%, when machining at 203bar coolant pressure at a speed of 50mmin−1. Tool life generally increased with increasing coolant supply pressure. This can be attributed to the ability of the high-pressure coolant to lift the chip and gain access closer to the cutting interface. This action leads to a reduction of the seizure region, thus, lowering the friction coefficient which in turn results in reduction in cutting temperature and component forces. Chip breakability during machining is dependent on the depth of cut, feed rate and cutting speed employed as well as on the coolant pressure employed. Machining Inconel 718 with lower coolant pressures did not produce chip segmentation. Tool wear increased gradually with prolong machining with high coolant pressures. Nose wear was the dominating tool failure mode due probably to a reduction in the tool–chip and tool–workpiece contact length/area.

High speed machining of aero-engine alloys

Materials used in the manufacture of aero-engine components generally comprise of nickel and titanium base alloys. Advanced materials such as aero-engine alloys, structural ceramic and hardened steels provide serious challenges for cutting tool materials during machining due to their unique combinations of properties such as high temperature strength, hardness and chemical wear resistance. These materials are referred to as difficult-to-cut since they pose a greater challenge to manufacturing engineers due to the high temperatures and stresses generated during machining. The poor thermal conductivity of these alloys result in the concentration of high temperatures at the tool-workpiece and tool-chip interfaces, consequently accelerating tool wear and increasing manufacturing cost. The past decade has witnessed a radical approach to product manufacture, particularly in the developed economy, in order to remain competitive. Modern manufacturing philosophies, principles and techniques geared primarily towards reducing non value added activities and achieving step increase in product manufacture have been widely adopted. Recent advances in the machining of aero-engine alloys include dry machining at high speed conditions, the use of high pressure and/or ultra high pressure coolant supplies, minimum quantity lubrication, cryogenic machining and rotary (self-propelled) machining technique. Tool materials with improved hardness like cemented carbides (including coated carbides), ceramics, polycrystalline diamond and polycrystalline cubic boron nitride are the most frequently used for high speed machining of aero-engine alloys. These developments have resulted to significant improvement in the machining of aero-engine alloys without compromising the integrity of the machined surfaces. This paper will provide an overview on these recent developments and their application in the aerospace industry.

Application of Probabilistic Safety Assessment to the Pipe Rupture Incident at Hamaoka Unit-1

On November 7, 2001, a pipe rupture occurred in the steam condensation line of the residual heat removal system at the Hamaoka Unit-1 while operating at rated power, resulting in steam release with radioactivity into the reactor building and the high pressure coolant injection being unavailable. The reactor was manually shut down immediately after the pipe rupture and there was no radioactive release into the environment. Although this incident was not safety significant, the type of rupture was unprecedented. Thus, the regulatory body, the Nuclear and Industrial Safety Agency (NISA), investigated event causes and examined corrective actions for preventing recurrence, and issued the report describing the investigation results, on May 13, 2002. At the NISA's request, the Nuclear Power Engineering Corporation (NUPEC) evaluated the safety significance of the incident and the effectiveness of corrective actions from the risk point of view by carrying out the Probabilistic Safety Assessment (PSA), that is, the estimation of the core damage frequencies (CDFs). The results showed that the incident has no risk significance and that the individual corrective actions would not lead to any significant increase in CDFs. The present study is the first PSA application to the regulatory decision-making process in Japan.

High Speed Machining of Bio-Titanium Alloy with a Binder-Less PcBN Tool

Using a binder-less PcBN tool, improvement of processing efficiency was tried in machining of a vanadium-free titanium alloy, Ti-6Al-2Nb-1Ta which was recently applied for a surgical implant material. The tool which is prepared through the direct conversion sintering of h-BN under both high pressure and temperature, exhibits an improved high thermal durability. It was confirmed that a binder-less PcBN tool exhibited lower flank wear and kept sharper cutting edge compared to the tools made of materials such as sintered carbide, conventional PcBN and polycrystalline diamond with Co-based binder, after turning in cutting speed of 4.2m/s, feed rate of 0.15mm/rev, depth of cut of 0.5mm under an application of a high pressure coolant. Also, milling tests were conducted with a radius end mill tool whose tip was made of the binder-less PcBN material. As a result, the possibility of high speed milling at cutting speed of 8.3m/s was found.

Application of Probabilistic Safety Assessment to the Pipe Rupture Incident at Hamaoka Unit-1

On November 7, 2001, a pipe rupture occurred in the steam condensation line of the residual heat removal system at the Hamaoka Unit-1 while operating at rated power, resulting in steam release with radioactivity into the reactor building and the high pressure coolant injection being unavailable. The reactor was manually shut down immediately after the pipe rupture and there was no radioactive release into the environment. Although this incident was not safety significant, the type of rupture was unprecedented. Thus, the regulatory body, the Nuclear and Industrial Safety Agency (NISA), investigated event causes and examined corrective actions for preventing recurrence, and issued the report describing the investigation results, on May 13, 2002. At the NISA's request, the Nuclear Power Engineering Corporation (NUPEC) evaluated the safety significance of the incident and the effectiveness of corrective actions from the risk point of view by carrying out the Probabilistic Safety Assessment (PSA), that is, the estimation of the core damage frequencies (CDFs). The results showed that the incident has no risk significance and that the individual corrective actions would not lead to any significant increase in CDFs. The present study is the first PSA application to the regulatory decision-making process in Japan.