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A shot blasting machine is a cleaning machine for casting products with a steel ball shooting mechanism from the impeller/blast wheel rotation's centrifugal force. As the main machine in the final process of casting production activities, the decrease in machine reliability has a negative impact on the production system. Currently, the production equipment maintenance strategy at PT ABC is still implementing corrective maintenance, which is unplanned and reactive when a machine malfunction occurs. It resulted in high production loss and increased maintenance costs. Therefore, the shot blasting machine's maintenance strategy should be changed to a type of preventive maintenance. This study aims to plan preventive maintenance (PM) system for the shot blasting machines of PT. ABC, such as creating PM schedule, calculating machine downtime, and technician needs for each PM activity. PM system planning is achieved using the ISMO (Inspection, Small repair, Medium repair, and Overhaul) method. Its method was conducted in several stages, which start with identifying machine objects, making PM work specifications, determining the value of mark complexity and maintenance cycle, calculating machine downtime and technician needs. Then making schedules annual and monthly, and several other maintenance documents. The mechanism for determining the complexity value is determined based on the similarity of the HP Garg methodology's machine specifications. Finally, The planning of the shot blasting machine PM system has been successfully done, some of the PM information obtained are (i) the machine maintenance cycle is C - I1 - I2 - S1 - I3 - I4 - M1 - I5 - I6 - S2 - I7 - I8 - M2 - I9 - I10 - S3 - I11 - I12 - C, (ii) the time interval between maintenance activities is one month, (iii) machine downtime for each shot blasting machine, (iV) the number and level of maintenance technicians required in every ISMO activity for drum shot, batch shot and hanger shot machines. The calculating verification of the shot blasting machine's availability value on the proposed PM schedule shows that machine availability increased to more than 80%.

The results of studies of shot blasting as one of the methods of mechanical cleaning for surface hardening (peening) of parts are presented. The simulation in the QForm-3D (VX) software environment of high-speed impact of spherical particles on the metal was carried out and the stress–strain state of the metal in the impact hardening zone was revealed. It was shown that friction losses are proportional to the squared velocity of the particles of the shot blasting machine, and a decrease in the value of the contact friction coefficient will accordingly reduce the frictional work and increase the blades resource. Calculations and studies have established the basic laws of the shot blasting process conditions influence on the surface geometry and the metal surface layer properties.

Aim: to evaluate the shear bond strength of zirconia bonded with two self etch adhesive resin cements Panavia F2.0 and Bistite ΠDC using two surface treatment techniques:sand blasting and silica coating using Cojet system. Materials & Methods: Twenty rectangular samples with dimensions (14.5×13×3.6mm) and twenty samples with dimensions (7.2×6×3.6mm) were cut from three zirconia ceramic blocks. Sandblasting was done using air blasting machine with 110 µm AL2O3 particles and Silica coating surface treatment was done using Cojet system with 30 µm SiO2 particles. Half of the small sandblasted zirconia samples were cemented to half the sand blasted large samples using PANAVIA F 2.0 adhesive resin cement and the rest were cemented using BISTITE ΠDC adhesive resin cement. Also, half of the small silica coated zirconia samples were cemented to half the silica coated large samples using both cements. Thermocycling were done for 5000 thermal cycles. The shear bond strength was tested using a computerized universal testing machine. Results: Zirconia specimens cemented with Panavia F2.0 showed higher shear bond strength than specimens cemented with Bistite ΠDC and the zirconia surfaces treated with silica coating and sand blasting surface treatments Conclusion: Panavia F2.0 resin cement and silica coating surface treatment could be the best cement and surface treatment for zirconia and sand blasting could be a promising alternative surface treatment.

New micropowder blasting system with controlling a mask temperature was proposed to realize a control of cross-sectional shape of the processing channel on a glass substrate. From an analysis of processing temperature dependence of dynamic viscoelastic properties of the commercial mask material for micropowder blasting, temperature control system which can be set to the micropowder blasting machine was designed. An erosion of the mask during micropowder blasting depends on the loss tangent in dynamic viscoelasticity, and showed maximum value at the mask temperature of 100°C. Moreover, we confirmed that changing the processing temperature can be control the processing line pattern profile on the glass with the mask, and a small width channel was realized the processing temperature of 109°C.

Shot blasting is an important means of metal surface treatment, and the fracture of rotating blade is the main reason for the abnormal operation of shot blasting machine. In order to prolong the service life of the equipment, the dynamic fatigue characteristics of the blade are studied in this paper. A three-dimensional model of the blade is established and its constraint modal are analyzed by both simulation and experiment. The results show that the deformation of blade is proportional with the increase of natural frequency, and the stress concentration is easy to occur at the root of blade. Meanwhile, the dynamic fatigue test of the blade is carried out, and it can be found that the root of the blade breaks at the rotational speed of 750r/min, which verifies the correctness of simulation results. Therefore, it is necessary to effectively adjust the control speed to ensure the normal rotation of the blades and reliable operation of the machine.

Accurate prediction of the remaining useful life (RUL) of machines is becoming mandatory in exploiting the asset in an efficient and secure way by avoiding the unplanned downtimes. In this paper we present an approach to the RUL prediction developed for a shot blasting machine by analyzing the recordings from inexpensive vibrational sensors. The key idea consists of (i) employing generalized Jensen-Renyi divergence (JRD) as a measure of change in the vibrational pattern (ii) exploiting the monotone relationship between JRD and the abrasive wear in rotor blades and (iii) using a Markov model to describe wear dynamics. The unknown parameters of the Markov model are obtained by expectation-maximization approach. Prediction of the remaining useful life is done by executing Monte Carlo simulations on the updated model and evaluation of the first passage time of the JRD index. The approach is validated experimentally by running the machine up to the failure, hence allowing for naturally evolving wear progression.

Besides ground vibrations, air transmitted vibrations or airblast overpressures (AOp), are also generated during blasting operations. Mae Moh coal mine, Thailand, has been concerned about both ground and air vibrations because the residents nearby are located less than 2 km to the southeast of the mine. Most previous studies mainly focused on the air blast prediction by using from basic generalized equations to the sophisticated Artificial Intelligence (AI) techniques. In addition, many controllable and uncontrollable parameters that affect AOp were extensively studies. Blasting operation unit at the mine uses a sequential blasting machine to detonate electrical detonators with a variety of delay time between rows and blasting directions. The wavefront reinforcement model was selected to test its theory that the levels of AOp will increase at the locations where wavefronts are reinforced and, at the same time, to recommend an appropriate delay time between rows and blasting directions that may reduce AOp. The wavefront reinforcement model accounts for input burden, spacing, and sequential delay time from blastholes to generate air wavefronts transmitted out in all directions. The overall 54 blasts were conducted and recorded AOp in dB(L) unit to test the model. Only 37 blasts that had one seismograph placed at the wavefront reinforcement area and another one placed at the non-reinforcement area could be compared. The results indicated that AOp levels were higher in areas of wavefront reinforcement compared to non-reinforcement in 29 (78.4%) of all valid blasts. Most air wavefront reinforcement occurred at in front and to the back of the blasting direction. The blasting patterns of the mine were studies and indicated that the delay time between rows or circuits should be nearly 200 ms to minimize the wavefront reinforcement areas. Graphs of cube root scaled distance were provided to illustrate the effect of blast direction on the increasing of AOp.

Dry ice blasting is a highly efficient and environmentally-friendly method for cleaning of contaminated surfaces. The method is widely used in many industries, such as automotive, machinery and food industry. Dry ice blasting is a technology that requires large amounts of compressed air which is among the most expensive forms of energy currently employed in industries. Compressed air (air of high pressure and volume) accelerates particles of dry ice during the blasting. Our paper presents a comprehensive overview of saving measures which can greatly help decrease energy intensity of the blasting. Technology of dry ice blasting comprises four key elements: a compressor (generator of compressed air), a blasting machine, transport of pellets, and a blasting nozzle. Our team successively analysed these four key aspects of the technology and designed relevant savings measures, which results in identification of minimum, theoretically attainable energy consumption. Experiments and operational tests proved that application of all available savings measures may decrease energy consumption by 87% compared to current industry standards. It is possible to evaluate current technologies for dry ice blasting in terms of performance of the blasting machine and its functional properties. So far, there has been no method for evaluation of energy parameters of the technology. This paper presents a novel quantity which helps quantify and evaluate energy consumption of dry ice blasting. Main benefit of the quantity called “specific energy consumption of dry ice blasting” is the fact that it allows to compare energy consumptions of various blasting systems. For the purposes of this paper, the novel quantity is especially used to quantify the impact of recommended savings measures.

The research of the eff ect of installing the redesigned iron curtains in the turbine of the shot blasting machine (SBM) for notch of the work rolls surface was carried out for the temper mills “1700” and “2500” of sheet rolling shop – 5 of OJSC “MMK”. Curtains were installed in a plane perpendicular to the plane of rotation of shot blast wheel mounted in a turbine. The sizes of the curtains and place of the installation were determined, providing increased density of shot torch at notch of rolls with minimal shielding action of split shot bounces off the iron curtains. The researches have shown that a fraction speed after collision with a curtain changes not only the direction but also the magnitude. Change of direction and speed reduction of the shot after the collision with the curtain depends on the friction conditions between the shot surface and curtains, as well as the angle of attack. Shot blasting machine modernization provided opportunity to increase the density of shot torch peaks on the surface of work rolls of temper mill, and thus to increase also the density of a trained metal peaks at 1.22 times compared with metal, trained before the improvement of shot blasting machine design.

In a metal casting industry, Hanger Shot Blast KAZO machine plays a very vital role for blasting. The downtime equipment data for the last five years, 2013 to 2017, shows that the hanger shot blast KAZO is the machine which frequently encounters downtime with the number of 503,75 hours. As the only blasting machine with 2 (two) tons of load capacity, the issues of hanger shot blast KAZO affect to the targeted production process of company. Moreover, it increases risk of safety for the workers surround the machine. The purpose of this current research is to find out the reliability value of the item/ component of hover shot blast KAZO machine using Reliability Analysis method. The malfunction of its component is reviewed by FMEA (Failure Mode and Effect Analysis). While the risk assessment is obtained from RPN (Risk Priority Number) calculation - MTTF value and reliability value R(t). The result of this current study found that there are 21 malfunctions on hanger shot blast KAZO machine. MTTF analysis shows the highest MTTF value is 9195,324 hours for bearing impeller component and the lowest is 3498,997 hours for motor components. Meanwhile, reliability analysis shows that the largest reliability value with 0.999915 is encountered by motor contactor of crane, while with a value of 0.26385, hanger rotator motor contactor component encountered the lowest reliability value.

The contribution deals with the evaluation of wear blades continuous blasting machine. The current state of wear of blades and a description of the blasting process is analyzed. In the experimental part of this work the quality of the blades is evaluated by measuring the hardness of materials, chemical analysis of the samples and their structural analysis. Abrasive wear was evaluated in loose fill abrasive and in the environment with firmly bonded abrasives. The results of the measurements showed that the material of the blades is hypoeutectic white cast iron with different carbon and alloying, especially Chromium.

The design of a small road surface shot blasting cleaning machine, using the motor driven wheel blasting high-speed rotation, the pellet material (steel shot or sand) at high speed and certain Angle to throw, throw rock formed certain fan type flow, impact to the road to play the role of a blasting and removing the effect of the residue .Then, projectile and dust into the separator, separator will be tiny and dust separation, dust into the dust collector, and the projectile into the shot blasting machine to recycle. Complete road surface shot blasting cleaning machine of shot blasting machine, sand pill purification plant design. By using solid works 3D drawing software of 3D modeling and virtual assembly.

Industrial robots with advantages of highly flexible, high positioning accuracy, high-efficient production, continuous operation capability in the harsh environment, can effectively replace all kinds of complex operations and high-intensity labor which cant be completed by the existing manual operation. The structural characteristic and use of the catenary abrator is described in this paper. Based on the current production status, catenary shot blasting machine workpiece handling methods are elaborated. This paper describes the use of the robot which can work quickly and efficiently loading and unloading.

This article discussed the compound impact-abrasive wear behavior of shots impeller pair in shot blast cleaning. The shots impeller pairs were fabricated by investment casting processing. The predominance and shortcoming of investment casting for high chromium wear resistance materials used in shot blasting machine were also analyzed. Using investment casting technology, the high-Cr iron casting would be improvement in interal and explicit quality. And, owing to different included angles of shots, the blade show different wear behavior. The ideal included angle of shots is 12o. Increase in the angles leads to decreases of the wear resistance.

This paper was based on many pre-existing or being successful tunnel projects for study. Through in-depth investigation and analysis of the action mechanism on rock and the construction control under complex geological conditions, the author synthesized the technical advantages of the drilling-blasting method and tunnel boring machine technology into integration as a new drilling-blasting machine method applied in tunnel (lane) excavation. If this method intended by conventional process, it’s difficult to realize mechanized continuous excavating. In this problem, the author put forward two new technologies named helicoid tunnel face and shallow blasthole close blasting to improve. Respectively from the theory, economic, technology and safety, the paper demonstrates the feasibility of drilling-blasting machine method.

According to the use, design and research of shot blasting machine equipment for years, combined with the company's actual production, the processing technology of fender has been optimized is the wearing part of shot blasting machine in the casting room, the service life of fender have more than doubled in the original ones by the actual use proof, greatly reducing the replacement frequency of fender for the company to save a lot of money.

The level of mobile shot blasting machine analysis, a mechanical model of the projectile with the blade and shot rounds of dynamic simulation model, the model by imposing constraints and external forces, analysis of air resistance, friction, blade length and projectile diameter of throw playing speed. Played by the speed of analysis can throw further analysis of various parameters on the effect of throwing fight.

A three-dimension discrete element model of the shot blasting machine has been established to study the principles of shots flow motion in shot blasting machine. The three-dimension discrete element method (EDEM) was used to analyse the shot-motion process inside the shot blasting machine. The dynamic law of shots motional process inside shot blasting machine was shown through simulation.

Sandblasting machines are widely used in chemical, mechanical and other engineering fields. The internal flow field of the sandblasting machine belongs to a complex gas-solid two-phase flow, and impact by the continuous abrasive sand can cause the machine to wear or even fail. In this study, the EDEM-FLUENT coupling method was used to calculate the transient flow field of the gas phase and the motion, dynamic and collision characteristics of the sand. Air in the sandblasting machine was treated as the ideal gas and the continuous phase. The sand was regarded as the discrete phase solid in the computation. Using the Archard wear model, the wear amount of the sandblasting machine was calculated and the wear law was analysed, to provide a theoretical basis for optimising the design and operation method of the blasting machine.

Japanese Specification for Highway Bridges [1] revised in 2002, which first stated that degradation of bridge members, including those of weathering steels, to occur in prolonged period of time must be taken into account, invoked wide scope of discussions. The final goal of these activities is to realize ultra long term durability of steel infrastructures with minimized maintenance costs. For this value creation, one should take risks which can be controlled without difficulties. Note that risk is different from crisis or failure: To take risks with adequate assessment means to enhance secureness of the structures. To reduce riskiness of anomalous rusting to occur on weathering steel, the author et.al. developed a computerized corrosion prediction system [2,3], which is now used as a corrosion controlling tool on the planning and designing stages of weathering steel structures [4]. Visual as well as instrumental rust monitoring methods and their criteria were already established as reported elsewhere [4, 5]. Unlike organic or inorganic materials, weathering steels do not deteriorate internally. Therefore, all corrosion risks can be monitored by inspections of steel member surfaces. A management system for secureness enhancement for weathering steel bridges is already available as listed in references [6, 7]. Applying these recently advanced methods according Secureness Enhancing System (SES) as depicted in Fig.1 to various stages servicing, riskiness in terms of damage due to anomalous corrosion on weathering steel bridges became much lower than ever: i.e. Weathering steel now became low risk-high return material. However, riskiness cannot be zero due to uncertainty in terms of unpredictable environmental change, breakage of upper concrete deck, human error in designing stage, etc., which might cause water leak from upper part of structures. Also, attachment of large amount of air born salt by stormy weather happened during fabrication and/or transportation might cause anomalous rusting of unpainted weathering steel parts. To cope with such risks, one must carry out corrosion monitoring using above mentioned methods [4, 5, 6]. Although anomalous state is detected, it is neither failure nor end-of-life for the weathering steel structure. Based on accurate cause analyses, one can take an appropriate maintenance. Since it has been pointed out that adherent thick rust on weathering steel is very difficult to remove, the authors have created a novel power tool and high performance zinc rich paint as additions to our contingency plan. In Fig.2, the developed stainless rotor covered with numerous diamonds [8] is shown as an example, which facilitates otherwise inefficient and ineffective surface preparation processes. This method is useful to treat such surfaces as in a place where one cannot operate a blasting machine, which generates large amount of dust influencing onto surrounding environment.

This paper describes the influence of shot peening on of the peened surface and fatigue strength. Shot peening was performed by a wet blasting machine with a wide nozzle. At first, influences of particle size and geometry on characteristic values such as surface roughness, residual stress, FWHM, and Vickers hardness were examined, and then fatigue strength was studied on the peened materials. The material is a medium carbon steel (C:0.45%, 180HV) and the peening particles are alumina and glass beads. The following results are shown in this paper: (1) On the specimen a width of 83% of the wide nozzle is peened uniformly judging from chatterings of FWHM, compressive residual stresses and surface roughness. (2) Surface roughness, compression residual stress, FWHM and the maximum hardness increase with increasing particle size except for the case of 57μm particles; the maximum values are 0.52μm, 390MPa, 2.15deg, 205.6HV respectively. (3) Fatigue strength is improved using alumina and glass beads by 20% and 15%. (4) The peening process using a wide nozzle can effectively improve fatigue strength.

The number of impeller head is short in the original shot blasting machine, and the distance between the pretreatment of steel plate is too far to have enough rust removal ability. Based on these problems, researchers respectively added one impeller head both on the top and bottom of the machine, shortened the underside installation height, and adjusted the angle of impeller heads. The practice proved that the new improved shot blasting machine was satisfied with the requirement of the pretreatment.

The formation of titanium oxide layer with micro and nanotube arrays on titanium substrate was investigated by grit-blasting and anodic oxidation treatment. Micro rough surface can be formed by grit-blasting and nanotube arrays can be formed by anodic oxidation. The morphology of the hybrid surface(micro and nanotube arrays surface) can be affected by the mechanical conditions (grit size, grit material, blasting pressure, nozzle tip of blasting machine, distance nozzle tip and specimen, blasting time) and electrochemical conditions (applied potential, electrolyte concentration and anodizing time) used. Such micro pore and nanotube arrays of titanium oxide can be useful for well-adhered bioactive surface layer on Ti implant metals for orthopedic and dental implants, as well as for photo catalysts and other sensor applications.

An oxide scale layer covers steel wire rod produced by hot rolling. This oxide is often removed by pickling before wire drawing; otherwise, hard oxides will be impressed into the wire surface and give an inferior surface quality. Stricter pollution regulations increase the incentive to replace pickling with mechanical descaling. This paper gives results from tests on carbon steels by using shot blasting to descale wire rod. The tests include: (i) shot blasting experiments in an industrial full-scale in-line shot blasting machine, (ii) laboratory drawing experiments on shot blasted wire rod, (iii) industrial trials on shot blasted wire rod at the drawing plants. There are differences in the appearance of surfaces between shot blasted and pickled wires, but no differences in the drawing process were observed in the laboratory experiment. In the industrial trials the wear of dies were more severe when drawing shot blasted wire of one of the steel grades. In the downstream processes, problems were recorded with the cleanness of the surface of another grade and adhesion of copper coating on a third grade.

Purpose : A new device was made that can produce a high-speed jet of either water (water jet) or abrasives mixed with water (abrasive jet). This paper reports on the ability of this device to remove investment and metal oxides from cast alloy surfaces.Materials and Methods : Two gypsum blocks, three investment blocks before and after heating, and three cast metal plates were tested with the newly produced device. The pressure of the jet was 4 or 8 MPa, and two types of abrasives (#400 and #1500 SiC and glass beads) were used. After treatment, the surface quality was observed with a charge coupled device camera. The concave depths of the investments were measured with a laser displacement meter and the alloy surfaces evaluated with a surface texture measuring apparatus. The concave depths of the investments and the surface roughness (Ra) were statistically analyzed with two-way ANOVA and Tukey's test using data from ten points.Results : After heating, the investment was removed by a 4 MPa water jet ; the concave depth of the investments was from 0.7 to 8.2 mm. The gypsum was removed by the abrasive jet. The oxide films were removed by the 4 MPa abrasive jet using the abrasive agents.Conclusion : This study examined the potential use of a new laboratory tool. It demonstrated that a water jet could remove investment after heating. Gypsum, adhered investment, and metal oxide were removed with an abrasive jet. This new device can be used effectively as a laboratory tool for removal of unwanted surface materials.

The improvement on an existing powder blasting machine is presented and characterised in this paper. The original prototype suffered from irregular powder clogging during real time utilisation, especially with very fine particles. Moreover, the fluctuations of the flow of particle generated were not ideal for micro-machining purposes. We demonstrate that the re-engineering of the original reservoir used with freshly dried powder brings reliability and more consistency in the powder flow rate. This improvement is easy to implement in the original design and does not need to re-engineer the entire machine. For this study, very fine powder with average particle diameter of 9 µm was used.

Several experiments were run to clarify the stock removal mechanism of grit blasting. Factors of the mechanism are treated on surface roughness, work-hardening, residual stress and weight of removed chip. Grit blasting was performed on commercially pure titanium (Ti : 99.4%) and carbon steel (C : 0.45%) by centrifugal blasting machine. Stock removal decreases with the increase of work-hardening and increases with the increase of the surface roughness. The mechanism of stock removal was mainly consisted of the work-hardened brittle layer. Stock removal is closely related with the machinability of the work material.

A comparative study of the degradation of S-460 shot due to target hardness was carried out by impacting the shot against white and gray cast iron targets in a laboratory testing machine and against a gray cast iron hydrant in a WTB6 production blasting machine. The hardness of the white cast iron target was 65 HRC while that of the gray cast iron targets was 22 HRC. A total of 500 impacts (cycles) were run during the three experiments and samples for metallurgical investigation were taken after every 50 impacts. Shot damage was analyzed by measuring the shot fragmentation and stereology and the chemical degradation of the shot. Characteristic failure mechanisms are found for shot impacted against soft and hard targets. Evidence indicates that the present laboratory shot-life-testing machine for peening and/or cleaning applications with a hard target cannot reproduce the breakdown characteristics of shot impacted against a soft target. A new laboratory testing machine is proposed.

• A number of electronic detonators up to 1600 • 2-wire parallel bus with serial protocol • connector for attaching the detonator to the bus • logger • blasting machine • robust against ESD, RF, EMI, blast transients and mechanical shock • field programmable timing delay up to 10,000 ms in 1 ms increments The SDI Electronic System contains a robust serial protocol exhibiting great ease in field usability and deployment. The electronic detonator comprises an Electronic Ignition Module (EIM), shell, primary and base charges, leadwires and end plug resulting in a smart programmable detonator. An ASIC chip is contained within the EIM electronic board together with a firing/energy reserve storage capacitor, additional electronic components, a connection to each legwire and a connection to an initiator bridgewire. The bus communications consist of a 2 parallel wire bus(polarity independent) between the EIMs and a logger or blasting machine. The bus protocol is serial and contains command, data bytes and cyclic redundancy check(CRC) for error checking.

This paper presents a purely mechanical means of producing highly concentric spherical lenses at the endfaces of optical fibers. The production process has two stages. First conical lenses are produced in a grinding process that ensures excellent concentricity. Then the conical lenses are transformed to spherical lenses using a novel process called loose abrasive blasting. The cone grinding is carried out on a micro-grinding machine that has a sophisticated control system that enables the production of precision conical lenses. The blasting is carried out on a diamond blasting machine. Plots showing automatic centering performance of the micro-grinding machine and scanning electron microscopy photographs of the conical and spherical lenses are presented.

The experimental study is conducted to estimate fracture process of the cylindrical rock specimen. In this experiment, an explosive is used as the explosion source, and a pipe filled with water is arranged between the explosive and the cylindrical rock specimen. The main purpose of this fracture test is to collect the experimental data on the behaviors of the dynamic fracture of the rock. In addition, one of the aims of this test is to estimate the dynamic tensile strength of the rock in wide range of strain rate utilizing Hopkinson's effect. Therefore, during the fracture process of the rock, the free surface velocity and the fracture part near the free surface were observed by a laser vibration meter and high speed camera. The precise detonator was used to control the initiation time of the explosive by using an accuratley controlled blasting machine. The results of the fracture test for Kimachi sandstone and the validity of this test are discussed. In order to understand the relationship above fracture condition and the incident underwater shock wave into the rock specimen, the numerical simulation is carried out. The 2D hydrodynamic code based on ALE finite difference scheme is employed. In the case of the fracture test with 50 mm water pipe, the incident underwater shock wave into the cylindrical rock specimen has irregular pressure distribution near the shock front.

A high accurate blasting machine which could control 1 microsecond(s) was developed. At first, explosion of a bridge wire in an electric detonator was observed and next the detonations of caps were observed with a high speed camera. It is well known that a compressed stress wave reflects at the free face, it propagates to the backward as a tensile stress wave, and cracks grow when the tensile stress becomes the dynamic tensile strength. The behavior of these cracks has been discussed through the observation of the dynamic photoelastic high speed photography and the three dimensional dynamic stress analysis.

Several experiments were run to compare steel shot with glass shot on the characteristics of shot peened surface and surface layer. Shot peening was performed on steel (0.45%C) by an air blasting machine. The results obtained from experiments are as follows : diameter of dent, surface roughness, hardness distribution, half width and surface residual stress produced by steel shot are from 5 to 70% more than by glass shot. The maximum hardness and the depth of work hardened layer by steel shot are from 4.4 to 8.7% and from 20 to 30% more than by glass shot respectively. Surface residual stress by glass shot is from -260 to -390 MPa and by steel shot is from -350 to -420 MPa.

As the first approach to study on grit blasting, basic characteristics of grit blasted surface and surface layer are described, measuring such factors as average dent size, surface roughness, hardness distribution, harf width and surface residual stress. Grit blasting was performed on steel (C:0.45%) by centrifugal blasting machine. The results obtained from experiments are as follows : (1) Average diameter of dent is in proportion to size D and root of velocity V of grit. (2) Surface roughness is in proportion to D and V. (3) Maximum hardness on the blasted surface is about 15% more than that of shot peened and the depth of work hardened layer is 40-50% less than shot peened. (4) Residual stress on blasted surface is compressive and the value is 12-35% less than shot peened.

A machining method which can obtain a high precision of a grit blasting is presented in this paper. To clarify the fundamental characteristics of a blasting process, the wall pressure and profile of machined surface were measured. Furthermore, the girt recovery system with vacuum nozzle was adopted in the blasting machine to keep the flow at a steady state. From the result, the removal rate is closely related to the flow pattern of impinging jet, and the condition of two-phase flow of grains and air has a significant effect on its accuracy. It is confirmed that the grit blasting can apply to the precision surface machining and it can effectively finish the brittle material such as engineering ceramics.