• International Journal of Precision Engineering and Manufacturing
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• 제7권4호
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• pp.51-56
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• 2006

This paper proposes a control algorithm, which is verified experimentally, for aspherical surface grinding and polishing. The algorithm provides simultaneous control of the position and interpolation of an aspheric curve. The nonlinear formula for the tool position was derived from the aspheric equation and the shape of the tool. The function was partitioned at specific intervals and the control parameters were calculated at each control section. The position, acceleration, and velocity at each interval were updated during the process. A position error feedback was introduced using a rotary encoder. The feedback algorithm corrected the position error by increasing or decreasing the feed speed. In the experimental verification, a two-axis machine was controlled to track an aspherical surface using the proposed algorithm. The effects of the control and process parameters were monitored. The results demonstrated that the maximum tracking error with tuned parameters was at the submicron level for concave and convex surfaces.

• 한국자원식물학회지
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• 제24권3호
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• pp.309-313
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• 2011

Houttuynia cordata is used as a raw material of oriental medicine to acquire antioxidant and anti cancer effect and to cure a heart disease. Mechanochemical technology not only reduces the size of the object but also changes the chemical properties of the object. Extraction of functional materials from the Houttuynia cordata after grinding as a pretreatment using the mechanochemical technology was conducted in this study to investigate the effect of grinding on the yields and antioxidant activities of the extract. Houttuynia cordata was ground by the planetary ball mill and the morphology was analyzed by SEM. Yields of functional materials were increased from 6.2 g in the sample without grinding to 7.0, 7.8, 8.8 g after grinding of 30 minutes, 1 hour and 2 hours, respectively. Nitrite scavenging abilities were increased from 57-77% to 69-86% as a result of mechanochemical pretreatment. Also, DPPH scavenging abilities for the methanol extraction were increased from 10.01-40.29% to 11.01-49.29% as a result of mechanochemical grinding.

• 대한금속재료학회지
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• 제50권11호
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• pp.855-859
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• 2012

Samples with compositions of 80 wt% Mg-14 wt% Ni-6 wt% $Fe_2O_3$ and 80 wt% Mg-14 wt% Ni-6 wt% Ti were prepared by mechanical grinding under hydrogen (reactive mechanical grinding). Their hydrogen absorptions during reactive mechanical grinding were examined. TGA and BET analysis were employed to investigate the hydrogen storage properties of the prepared alloys. TGA analysis of the $Mg-14Ni-6Fe_2O_3$ showed an absorbed hydrogen quantity of 6.91 wt% while that of Mg-14Ni-6Ti was 2.59 wt%. BET analysis showed that the specific surface areas of $Mg-14Ni-6Fe_2O_3$ and Mg-14Ni-6Ti after reactive mechanical grinding were $264m^2/g$ and $64m^2/g$, respectively. The larger absorbed hydrogen quantity and the larger specific surface area of $Mg-14Ni-6Fe_2O_3$ after RMG than those of Mg-14Ni-6Ti after RMG showed that the effects of $Fe_2O_3$ addition are much stronger than those of Ti addition during reactive mechanical grinding.

• The Journal of Advanced Prosthodontics
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• 제11권1호
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• pp.1-6
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• 2019

PURPOSE. The purpose of this in vitro study was to evaluate the effect of surface grinding and polishing procedures using high speed zirconia diamond burs with different grit sizes on the phase transformation and flexural strength of zirconia. MATERIALS AND METHODS. Forty disc shape specimens ($15{\times}1.25mm$) with a cylindrical projection in the center of each disc ($1{\times}3mm$) were fabricated with 3Y-TZP (Prettau, Zirkonzahn, Italy). The specimens were divided into 4 groups (n=10) according to the grinding and polishing procedures: Control group - grinding (coarse-grit diamond bur), Group 1 - grinding (coarse-grit diamond bur) + polishing, Group 2 - grinding (fine-grit diamond bur) + polishing, and Group 3 - grinding (fine grit diamond bur). Each specimen was analyzed by 3D-OM, XRD analysis, and biaxial flexural strength test. RESULTS. Based on the surface morphology by 3D-OM images, polished specimens showed smoother surface and lower roughness value (Ra). In the result of XRD analysis, partial phase transformation from tetragonal to monoclinic zirconia occurred in all groups. Control group, ground with a coarse grit diamond bur, showed more $t{\rightarrow}m$ phase transformation and lower flexural strength than Groups 1 and 2 significantly. CONCLUSION. The flexural strength in all specimens after grinding and polishing showed over 500 MPa, and those were clinically acceptable. However, grinding with a coarse grit diamond bur without polishing induced the phase transformation and low strength. Therefore, surface polishing is required for the occlusal adjustment using a high speed zirconia diamond bur to reduce the phase transformation and to prevent the decrease of flexural strength of zirconia.

• 한국재료학회지
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• 제31권5호
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• pp.286-295
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• 2021

This study attempts to find optimal conditions of the friction coefficient using a discrete element method (DEM) simulation with various friction coefficient conditions and three different grinding media with various ball sizes in a traditional ball mill (TBM). Using ball motion of the DEM simulation are obtained using the optimal friction coefficient compared with actual motion; photographs are taken by the digital camera and the snapshot images are analyzed. In the simulation, the rotation speed of the mill, the materials and velocity of the grinding media, and the friction coefficient between the balls and the wall of the pot are fixed as the actual experimental conditions. We observe the velocity according to the friction coefficient from the DEM simulation. The friction coefficient is found to increase with the velocity. Milling experiments using a traditional ball mill with the same experimental conditions as those of the DEM simulation are conducted to verify the simulated results. In addition, particle morphology change of copper powder is investigated and analyzed using scanning electron microscopy (SEM) for the milling experiment.

• 한국정밀공학회지
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• 제17권5호
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• pp.131-136
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• 2000

This paper is concerned with the surface roughness and the bending strength of ground workpiece in ZrO2 ceramic grinding. Surface roughness was measured with surface tracer and bending strength value was obtained by three-point bending test on machining center using tool dynamometer. Grinding experiments were carried out to examine the effects of grinding conditions including diamond mesh size, table speed, and depth of cut on ground surface roughness. The correlation between surface roughness and bending strength was also inspected. The experimental results indicate that the rougher surface is produced as the mesh size of diamond wheel is reduced and table speed is increased, but surface roughness is not affected by depth of cut. The values of bending strength decrease as the values of Ra, Rmax and Ku increase.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2000년도 춘계학술대회논문집 - 한국공작기계학회
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• pp.465-470
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• 2000

This paper is concerned with the surface roughness and the bending strength of ground workpiece in ZrO2 ceramic grinding. Surface roughness was measured with surface tracer and bending strength value was obtained by three-point bending test on machining center using tool dynamometer. Grinding experiments were carried out to examine the effects of grinding conditions including diamond mesh size, table speed, and depth of cut on ground surface roughness. The correlation between surface roughness and bending strength was also inspected. The experimental results indicate that the rougher surface was produced as the mesh size of diamond wheel is reduced and table speed is increased, but surface roughness is not affected by depth of cut. The values of bending strength decrease as the values of Ra, Rmax and Ku increase.

• 대한치과기공학회지
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• 제32권2호
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• pp.57-63
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• 2010

Purpose : This study aimed to find out the effects of treatments on the surface of Zirconia. Methods : To this end, we selected six treatments that have been used widely: steam cleaning, 2bar & 6bar sand blasting, grinding by green stone point, grinding by diamond bur, and grinding by diamond bur with water spray. Results : The results of our study showed that monoclinic rate increased from all six treatments. Monoclinic rate varied by treatments, ranged from 0.6% (steam cleaning) to 6.5% (6bar sand blasting). These values from all six treatments were below ISO 13356 standard, which is 25%. Also, we found that two treatments (green stone point and diamond bur) increased roughness of surface of Zirconia. Conclusion : This study concluded that phase changes of Zirconia were not significant by using six treatments we employed.

• Korean Chemical Engineering Research
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• 제55권4호
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• pp.456-466
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• 2017

이 연구는 교반볼밀을 이용한 금속기반 복합재 제조공정에 있어서 분쇄매체의 차이에 의한 입자형상의 변화를 관찰하고, 볼 거동의 DEM시뮬레이션을 행하였다. 교반볼밀에서 볼 거동의 3차원 시뮬레이션을 통해 분쇄메커니즘을 규명하기 위하여 분쇄매체의 힘, 운동에너지, 매체 운동속도 등을 계산하였다. 또한 복합재 제조를 위한 실험조건을 이전의 다른 볼밀에서에 같이 교반볼밀 회전속도를 변화시켰고, 볼 재질, 운동속도, 마찰계수 등도 동일한 조건으로 변화시키면서 투입되는 에너지의 변화량도 계산하였다. 교반볼밀의 회전속도가 증가함에 따라, 분쇄매체와 매체, 매체와 벽면, 그리고 매체와 교반기 사이의 충격에너지가 증가하는 것을 정량적으로 계산 할 수 있었다. 또한 같은 실험 조건에서 입자형상 변화를 명확하게 분석 할 수 있었으며, 볼 거동이 입자형상 변화에 매우 큰 영향을 미치는 것을 알 수 있었다.

• 자원리싸이클링
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• 제28권3호
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• pp.26-34
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• 2019

희토류 영구자석(Rare earth magnet)은 사용량이 급격하게 증가하고 있으며, 이와 맞물려 폐희토류 자석의 발생량도 급격히 증가할 것으로 예측된다. 폐희토류 자석의 재활용은 주로 자석에 포함되어 있는 희토류 원소를 침출/분리하여 회수하는 공정으로 이루어지고 있으나, 침출 공정에 투입되는 폐희토류 자석의 분쇄 특성에 대한 연구는 전무한 실정이다. 따라서 본 연구에서는 폐희토류 자석을 이용하여 효과적인 파분쇄 공정 및 분쇄특성에 대한 연구를 진행하였다. NdFeB 폐자석을 조크러셔로 파쇄한 결과 급격한 산화 없이 효과적으로 입도가 감소는 하였지만, 롤크러셔의 경우 지속적인 압축에 의해 증가하는 표면과 대기 중의 산소가 반응하여 불꽃을 내며 급격한 산화가 발생하였다. 또한 파쇄 공정을 통해 생산된 시료를 볼밀에 투입하여 분쇄 특성을 파악한 결과, 일반적인 광물과 다르게 분쇄가 잘 이루어지지 않고 분쇄 16분 이후에 정상적인 분쇄가 이루어졌다. 또한 일반적인 광물에 비해 매우 낮은 분쇄율(S)과 미분이 발생이 매우 높은 분쇄분포(B)를 보임을 확인하였으며, 이는 향후 NdFeB 폐자석 파분쇄 공정 설계 시 기초자료로 사용될 수 있을 것으로 판단된다.