Toru Noguchi

FEM analysis of erosive wear

Abstract Surface damage caused by the impact of dispersed particles in gas or liquid flow is called “erosion”. Much attention has been paid to this phenomenon as one of the most serious problems to be solved, particularly concerning pipe-bends or valves in pneumatic conveying systems. But the phenomena of erosive wear are so complicated and vary depending on the factors of not only the kinds of material, hardness, shapes, sizes and mechanical properties of the particles, but also of blasting angles and velocity. For the purpose of this study, mild steel was prepared and erosion wear tests were carried out. Steel grits were impacted against target materials at different incident angles. The results showed that the wear losses varied markedly as a function of the impact angles, and that the maximum wear occurred at specific angles. Maximum wear occurred at 20–30° for mild steel, and 60° for ductile iron. This impact angle dependence of wear was simulated by Tabor’s theory and FEM which could analyze the plastic deformation of alloy surface as a result of a single particle impact. In the case of both mild steel and ductile cast iron, it was found that the impact angles play a very important and valid role in the corrosion process.

FEM analysis of the dependency on impact angle during erosive wear

Abstract The phenomenon of material surfaces being damaged and removed by particle-impact is called “erosion” and it is a serious problem in transportation by pneumatic conveyance. The erosive wear is complicated, and its behavior changes depending on factors including not only the kinds of material, hardness, shape, size and mechanical properties of the particles but the collision angles and velocity. In this study, mild steel was prepared and erosion wear tests were carried out using steel grits at different impact angles. It was found that the wear losses varied markedly by changing the impact angle and there appeared special angles that showed the maximum wear. They were 20 to 30° for mild steel, 60° for ductile iron, respectively. This suggested that harder the hardness of the alloy, the higher the value of the collision angle of the maximum wear. The dependency on impact angle during erosive wear was simulated by the Tabor [5] theory and FEM (MARC/MENTAT) that could analyze the plastic deformation of alloy surface as a single particle collision. In the case of mild steel and ductile cast iron, the impact angles to have maximum wear were explained successfully. In order to evaluate the plastic strain of the raised part quantitatively, the total corresponding plastic strain within the range of contact depth 0.3 mm and the length 0.6 mm is employed. The frictional coefficient μ is changed as 0.1, 0.3 and 0.7. The sum total of the corresponding plastic strain at this raised part reaches maximum at impact angles of 20 to 30° and appears the minimum value at impact angles of 60 to 90°. This dependency on impact angle agrees quite well with the results by experiments, namely, it can be explained by means of the total sum of corresponding plastic strain by unit particle impact that the reason for the appearance of a peak at impact angles of 60 to 90° for mild steel.

Erosion characteristics of ductile iron with various matrix structures

Abstract Erosive wear tests were performed on austempered ductile iron (ADI), ferritic ductile iron (FDI) and pearlitic ductile iron (PDI) using a shot blast machine. Erosion damage was measured by the removed material volume at impact angles between 10° and 90°. The surface metal flow in vertical sections was also observed. The mechanism of erosive wear, the effect of impact angles, and differences in wear features of specimens were discussed. Experiment showed that, after an initial stage, the eroded volume increases almost linearly with blasting time in ADI, FDI and PDI. The erosion rate for ADI is about 1 10 – 1 25 of that for FDI and PDI. The surface hardness of eroded ADI specimens increased from the initial HV350 to HV700 after 600 s of blasting. The amount of retained austenite was measured as about 40% before the test, but decreased to about 3–5% by transformation of austenite to martensite, hardening the surface and lowering the erosion rate. It was shown that ADI has excellent erosion resistance and it is expected to find wide applications as a wear-resistant material.

Progress of erosive wear in spheroidal graphite cast iron

Abstract To clarify the erosion mechanism of spheroidal graphite cast iron, the authors carried out erosion tests and observed the continuous structural change in the vertical section near the surface. The erosion of spheroidal graphite cast iron progresses as follows: (1) the spheroidal graphites on the surface layer deform gradually; (2) lips grow in the impact direction; (3) they expand and drop off. Although the erosion progresses with the repetition of lip-growth and dropping off, the cycle differs depending on the materials. The wear growth rate, which serves as the standard cycle of lip-growth and drop off, decreases as the pearlite ratio increases and corresponds well to the erosion rate. We also confirmed that our continuous observation method is practical and useful for elucidating the erosion mechanism.

Application of flow and solidification simulation in cast-in insertion processing

Abstract This report examines an application of a flow-solidification simulation system in the cast-in insertion process. This process is effective for producing composite castings, but the bonding state is determined by thermal conditions at the interface, which alter the geometrical condition of the inserts and castings. The bonding state is estimated approximately by geometrical and thermal parameters. However, in practical applications, it is quite difficult to predict the bonding state over the whole interface area. This report applies a flow-solidification simulation system, combined with criteria the authors have established previously, to estimate the bonding state and to optimise the shape and size of insert/casting/gating systems. Several types of gates and insertion settings were examined and bonding and uniformity compared. The effects of the temperature distribution during pouring on the bonding states and ways to optimise the gating system are also discussed. Application of the process to automobile components is also described.

Strength evaluation of cast iron grinding balls by repeated drop tests

Abstract Repeated drop tests were performed on Ni-hard and high-Cr cast iron grinding balls with material toughness varied by heat treatment. Instrumented impact tests and bending fatigue tests were also performed on bar specimens with the same heat treatment, and correlation between drop strength and other strength characteristics were discussed. In the drop tests from various heights, balls fractured by breakage or spalling, with longer life (Nf) at lower drop heights (H) giving H–Nf curves similar to the S–N curves in fatigue tests. Experiments show that drop strength correlated better with fatigue strength and hardness than with impact toughness(KId) in both irons. The stress causing spalling by repeated drops was inferred to be repeated contact stress, and internal tensile stress caused by surface plastic deformation assists the fracture. Breakage from the ball center is caused by cyclic tensile radial stress by impact body force, and is assisted by residual casting stress. Breakage type fracture is possible in as cast or very brittle balls, and with drops from high heights.

Gravity-Dependent Silicon Crystal Growth Using a Laser Heating System in Drop Shaft.

Spherical silicon crystals were grown without a crucible within about 10 s under microgravity in a drop shaft. To perform crystal growth in a short period, a compact crystal growth system which can be installed in a drop capsule was developed. A CO2 laser with the output power of 25 W was focused to approximately 300 µm to heat the crystal seeds. We used silicon crystal rod arrays as seeds and moved the arrays with a motor-driven sliding mechanism. This method allowed us to observe variations of crystal growth when gravity changed successively from 1 G to microgravity in a single drop test.

Accurate Evaluation of the Mechanical Properties of Grey Cast Iron

AbstractGrey cast iron has been regarded, in some circles, as being brittle, low in reliability and one where the usual design equations cannot be applied. The reason is usually attributed to the presence of randomly distributed graphite flakes. This presentation discusses, both experimentally and theoretically, the notch strength, bending strength, and the scattering of tensile strength of grey cast iron, and suggests a new approach based on plasticity theory for the accurate evaluation of these characteristics. Experiments showed that grey iron has a very low notch sensitivity in circumferentially notched bars, but that strength decreases in edge-notched plates. At the temperature of liquid nitrogen, notch sensitivity is very high. In ductile iron, strength increases in notched specimens. These results have been interpreted by the stress distribution, taking into account non-elastic stress/strain behaviour, and using a fracture criteria with an over-stressed depth, δ· The δ is a necessary region for fra...

The enhancing effect of surface coatings on cast-in bonding of steel and titanium inserts in aluminium castings

Insertion bonding of mild steel and titanium pipes in aluminium castings was performed in two ways; either by holding paired pipe and aluminium cylinder specimens at constant high temperatures, or by pouring molten aluminium into sand moulds containing inserts. The surfaces of the inserts were electroplated using Ag or Au, or spray coated with Al-Si alloy. The bonding was evaluated by shear strength measurements and microstructure observations. To verify the effect of surface coatings, the contact between the molten aluminium and the specimens was observed. At constant high temperatures, coated steels showed good metallurgical bonding when they were maintained for about 200 s in contact with molten aluminium. The time necessary for bonding was shorter with titanium inserts. In bonded specimens, alloyed microstructures were observed at the interfaces. There was no bonding with uncoated specimens. All coatings used were effective when poured, but preheating of the moulds was necessary to allow sufficient solidification time for the melt/insert volume ratios which were 32 and 36. Process analysis by the finite difference method showed that bonding required a period of liquid phase contact of the melt with the inserts. Observation of aluminium droplet contact with the inserts showed that uncoated surfaces of steel and titanium are not wetted by the melt due to stable oxide skins. With Ag electroplating, aluminium droplets can make wet contact with the specimens. The contact angle decreased from about 140° in uncoated specimens to 15°-45° with Ag plating. The plating prevents surface oxidation of the inserts and promotes wet contact when the active aluminium liquid surface is exposed. The Al-Si alloy spray coating has some effect in promoting wettability, but it is inferior to Ag plating.

Cast-in insertion of steel pipes in cast iron with internal air and nitrogen cooling

When using cast-in inserts of pipes in molten metal with large melt/insert volume ratios, the pipe may suffer structural damage such as grain growth and excessive diffusion of melt elements, and ma...