Continuous Grinding Research Articles

국내 자생 식물자원을 이용한 셀룰로오스 나노섬유의 제조 기술 개발

본 연구에서는 국내산 리그노셀룰로오스 자원을 이용하여 기계적 처리를 통해 나노섬유를 제조 후, 형태학적 특성 및 고강도 시트로의 응용 가능성을 평가하였다. 그 결과, 연속식 분쇄 처리는 세포벽의 구조를 느슨하게하고 분쇄 소요 시간이 증가함에 따라 나노스케일에 가까운 섬유가 관찰되었다. 재료의 미립화 정도를 증명하는 여수시간은 모든 공시재료에서 분쇄 소요시간이 증가함에 따라 직선적인 증가 경향을 나타내었다. 셀룰로오스의 상대결정화는 기계적인 해섬처리 정도에 따른 차이를 보이지 않았으나 탈리그닌 처리에 의해 크게 증가하였다. 셀룰로오스 나노섬유 시트는 기계적인 분쇄 소요시간이 증가함에 따라 인장강도가 증가하였고 옥수수줄기를 이용한 시트에서 특히 높은 인장강도가 측정되었다. 상기와 같은 결과는 국내 자생 식물자원을 활용한 셀룰로오스 나노섬유 제조 기술의 유용한 기초자료로 활용될 수 있을 것으로 판단된다. This research has been carried out to investigate the characteristics of cellulose nanofibers manufactured from domestic lignocellulosic materials by mechanical grinding method. The continuous grinding process was effective for loosening cell wall structure, with increasing grinding time, much smaller nanofibers were observed. Filtration time was linearly increased with increasing grinding time for all experimental materials. Relative crystallinity of cellulose was not changed by grinding process, but increased by delignification treatment. Tensile property of fiber sheets was drastically improved with increasing grinding time. Fibers sheets obtained from delignified cone stalks showed an excellent tensile strength. Consequently, it is considered that this study presented some effective information for manufacturing cellulose nanofibers with domestic plantation resources.

Evaluation of a laboratory rod mill when grinding bituminous coal

Laboratory testing was conducted to evaluate the breakage of bituminous coal in a rod mill. A Pittsburgh seam coal, which had been obtained from the product stream of an operating coal cleaning facility, was used as the feed material. This material had an ash value of 6.7% and had been crushed to a nominal −6.35mm. Grinding tests were carried out on a mono-size (2.38×1.68mm) fraction. The tests were conducted using a 193.5mm diameter and 245.0mm long laboratory rod mill, which contained steel rods at a volume loading of 23%. The mill was operated at 70% of critical speed for various grind times. A locked-cycle test was also performed to simulate continuous grinding conditions.The grinding was characterized using the population (or size–mass) balance model. The breakage distribution and rates of breakage were determined from the grinding data. The results indicated first-order breakage. The locked-cycle results indicated that steady state was achieved in several iterations. The simulated results matched the experimental results very well.

Performance of Laser Brazing Diamond Grinding Wheel in Face Grinding

A new technology kind of brazed monolayer cup diamond grinding wheel was developed via laser in an argon atmosphere. Grinding performances of this kind of brazed wheel in the surface grinding of the granites were studied. The experiment results show that the normal grinding forces and wear of diamond grits become higher with the increasing of the accumulated removal volume during grinding granites process. When continuous dry grinding was employed, the grits of the brazed diamond grinding wheel fail mainly in attired wear mode other than pull-out ones in conventional electroplated and sintered diamond tools, which indicates that the strong retention of brazing alloy to the diamond grits and longer service life of this kind of wheel.

AHerschelresolved far-infrared dust ring around HD 207129

Dusty debris discs around main sequence stars are thought to be the result of continuous collisional grinding of planetesimals in the system. The majority of these systems are unresolved and analysis of the dust properties is limited by the lack of information regarding the dust location.vThe Herschel DUNES key program is observing 133 nearby, Sun-like stars (<20 pc, FGK spectral type) in a volume limited survey to constrain the absolute incidence of cold dust around these stars by detection of far infrared excess emission at flux levels comparable to the Edgeworth-Kuiper belt (EKB). We have observed the Sun-like star HD 207129 with Herschel PACS and SPIRE. In all three PACS bands we resolve a ring-like structure consistent with scattered light observations. Using {\alpha} Bo\"otis as a reference point spread function (PSF), we deconvolved the images, clearly resolving the inner gap in the disc at both 70 and 100 {\mu}m. We have resolved the dust-producing planetesimal belt of a debris disc at 100 {\mu}m for the first time. We measure the radial profile and fractional luminosity of the disc, and compare the values to those of discs around stars of similar age and/or spectral type, placing this disc in context of other resolved discs observed by Herschel/DUNES.

Dexterous space optimization for robotic belt grinding

Industrial robots are recently introduced to the belt grinding of complex shaped surfaces to obtain high productive efficiency and constant surface quality. The volume of dexterous grinding workspace is a key factor the grinding robot, in which the gripped workpiece could obtain continuous grinding path and constant surface quality. This paper proposes a new structure of a robotic grinding system in which a new robot frame including active work piece frame {W} and passive tool frame {T} was presented. It shows that the dexterity of the system, which is indexed by the volume of dexterous workspace, is affected by the position of the contact wheel relative to the robot. Based on pattern search method, a strategy to optimize the grinding robot position with respect to the grinding wheel is put forward to obtain the desired dexterity grinding space.

Investigation on Crushing Kinetic Equation of Ball Milling of Quartz Powder

The kinetic equation of ball milling of quartz powder was deducted. by grinding quartz experiments in a intermittent ball mill. The results showed that: (1) Conventional first-order kinetic equation which describe the velocity of quartz grinding is not concordant with theory. Dynamics parameters are not constant, but time-related. (2) The kinetic equation of time correction can more clearly express their grinding speed. Fitted regression equation has a more accuracy prediction for the instantaneous concentration of particle size, and obtain the dynamics constants. (3) The grinding speed has a maximum value over time because of the particle size distribution and grading comminution. (4).The time index is not only related with the material nature and conditions of the grinding, but also with the particle size distribution. To predict accurately, the grade range should be narrow. (5). Different grinding time distribution of particles in the ball mill should be measured in the continuous grinding process. The comminution results can be predicted by the kinetic equation mentioned above.

Mechanically activated minerals as a sink for CO 2

CO 2 removal from exhaust gasses from burning of fossil fuels is a political issue. If undertaken on a large scale, enormous amounts of carbon dioxide will have to be taken care of. This paper investigates how mechanical activation of olivine and other Ca or Mg containing silicates can increase the mineral’s reactivity. Tests by grinding in a planetary mill have been done to investigate the effects of mechanical activation and other surface changes. The reactivity towards HCl and CO 2 has been determined as a function of grinding variables. Prolonged dry milling of olivine resulted in highly aggregated products, which were more reactive with respect to dissolution in acid than their respective BET surface areas would suggest. The initial breaking of bonds appears to give more reactivity on an energy usage basis than longer time activation. Most mechanical activation testwork so far has been carried out in batch mode. The result is diminishing effect of activation with increased grinding time. Continuous grinding and simultaneous reaction with some sort of classification may offer a chance of removing reaction products as soon as they are formed, giving a more energy effective process.

ダイヤモンドテーパワイヤを用いたジルコニアキャピラリの内径研削(機械要素,潤滑,設計,生産加工,生産システムなど)

A zirconia capillary is a key component of an optical fiber connector. Center holes of zirconia capillaries have been conventionally finished in loose abrasive process using a long taper wire. In this process both the productivity and the defect rate were very low. In order to overcome the problems, internal grinding utilizing an electroplated diamond taper wire was attempted. In the condition that the grain depth of cut was large, the diamond grains were stuck to the workpiece and the diamond wire was easily twisted off. Then low-frequency vibration was added to the workpiece and continuous grinding was stably enabled when the amplitude of the vibration exceeded 3mm. At the same time the length of a taper section was clarified to be important and a taper section longer than 60mm was desirable. Continuous grinding over 60 pieces was accomplished with high throughput within 30 seconds.

Influence of grinding procedures on the flexural strength of zirconia ceramics

The surface of zirconia may be damaged during grinding, influencing the mechanical properties of the material. The purpose of this study was to compare the flexural strength of zirconia after different grinding procedures. Twenty bar-type zirconia specimens (21 x 5 x 2 mm) were divided into 4 groups and ground using a high-speed handpiece or a low-speed straight handpiece until the bars were reduced 1 mm using two different grinding times: continuous grinding and short-time grinding (n=5). Control specimens (n=5) were analyzed without grinding. The flexural strengths of the bars were determined by using 3-point bending test in a universal testing machine at a crosshead speed of 0.5 mm/min. The fracture load (N) was recorded, and the data were analyzed statistically by the Kruskal Wallis test at a significance level of 0.05. In the test groups, high-speed handpiece grinding for a short time had produced the highest mean flexural strength (878.5 ± 194.8 MPa), while micromotor continuous grinding produced the lowest mean flexural strength (733.8 ± 94.2 MPa). The control group was the strongest group (928.4 ± 186.5 MPa). However, there was no statistically significant differences among the groups (p>0.05). Within the limitations of the study, there was no difference in flexural strength of zirconia specimens ground with different procedures.

Calculation of Some Integrals Arising in Heat Transfer in Grinding

We calculate some integrals involved in the temperature field evaluation of a workpiece during the grinding process. For the case of dry continuous grinding, this calculation allows a faster computation of the temperature field on surface and inside the workpiece.

An analysis of the temperature field of the workpiece in dry continuous grinding

The recent model for heat transfer during intermittent grinding described in Skuratov, Ratis, Selezneva, Pérez, Fernández de Córdoba and Urchueguía (Appl Math Model 31:1039–1047, 2007) is considered. This model is particularized to the case of continuous dry grinding, where an alternative solution is obtained in the steady state. This alternative solution is analytically equivalent to the well-known formula of Jaeger (Proc R Soc NSW 76:204–224, 1942) for the steady–state temperature field created by an infinite moving source of heat and proves to be very useful for evaluating the maximum point of the temperature.

Mathematical Models for a Closed-Circuit Grinding

New continuous and discrete mathematical models are elaborated for describing some types of closed-circuit grinding mill-classifier systems. Based on the discrete model computer simulation is also developed for investigation of grinding processes. The starting point in developing the model is the continuous grinding equation for the open-circuit grinding which is a partial integro-differential equation describing axial mixing and breakage of particles in the grinding mill. The convective flow in the mill is modeled as particle size-dependent process. The boundary conditions at the inlet and outlet of the mill, the initial conditions, and the equations describing the operation of the classifier and its mass balance are the additional equations of the model. The properties and capabilities of the new computer model are demonstrated and analyzed by simulation developed in Matlab environment. The effects of all parameters of the grinding process, among others of parameters of the classifier, are studied via simulation. The main statistical characteristics of the steady states, the hold-up of the grinding device and the operation of the classifier are also studied. The models presented appear to be very flexible and useful tools for analysis and design of closed-circuit grinding processes, and are suitable for the deeper understanding of the aimed processes.

Design of continuity processes of electrochemical finishing and grinding following turning

A newly designed finishing process utilizing an effective electrode and a grinding tool to execute the continuous electrochemical finishing and grinding processes following turning is described in this paper. The proposed process can be used for a variety of turning operations. Electrochemical finishing and grinding can be performed following the finishing process on the same machine by using a simple attachment. The factors affecting electrochemical finishing, grinding performance, and electrochemical finishing are discussed. The electrode was tested with both continuous and pulsed direct current. A higher work piece rotational speed produced a better finish. Changing the electrode design from a semicircle to a wedge form with a small end radius caused the electrolytic products and heat to dissipate more rapidly and provided the best finishing. Pulsed direct current finishing was slightly better than using continuous direct current finishing. However, the use of pulsed current would increase machining time and cost.

Gear finishing by abrasive processes

Based on the position of hard finishing in the process chain of gear manufacturing, the dominant processes with a geometrically non-defined cutting edge are analysed. While processes like continuous profile grinding and discontinuous generating grinding with double cone discs became less important in the last couple of years, the processes continuous generating gear grinding, discontinuous profile grinding and honing of tooth flanks gain rising importance. The analyses of the processes include functionality, the development status, respectively, maturity as well as identifiable trends. Process superior aspects like dressing of the grinding wheel and honing rings and the problem of grinding burn will be considered and evaluated separately.

Evaluation of continuous grinding tests on some marble and limestone units with silicon carbide and diamond type abrasives

This paper deals with the results of continuous grinding tests carried out with two different grinding machines on some marble and limestone units with silicon carbide and diamond type abrasives. The results showed that the relationship between the surface roughness and the surface glossiness of stones with homogeneous structure are independent of abrasive types. However, this argument is not valid for stones giving orange peel effect and not going through entire ductile behaviour due to their softer mineral and other materials content. Appropriate series of abrasives and operational conditions should be chosen for obtaining desired surface quality. For this reason, the results of surface quality measurements should be used in conjunction with stone properties.

Mid-Infrared Resolution of a 3 AU Radius Debris Disk around ζ Leporis

We present subarcsecond-resolution mid-infrared images of the debris disk surrounding the 230 Myr old A star ζ Lep. Our data obtained with T-ReCS at Gemini South show the source to be unresolved at 10.4 μm but clearly extended at 18.3 μm. Quadratic subtraction of the PSF profile from that of ζ Lep implies a characteristic radius for the dust disk of 3 AU, which is comparable in size to our solar system's asteroid belt. Simple models suggest that the 18 μm flux is well approximated by two contiguous annuli of mid-infrared-emitting dust from 2-4 and 4-8 AU with a 3 : 1 flux ratio for the annuli, respectively. We consider two scenarios for the collisions that must be resupplying the dust population: (1) continuous steady state grinding of planetesimals and (2) an isolated cataclysmic collision. We determine that radiation pressure and subsequent collisions are the dominant determinants of the disk morphology in either case and that Poynting-Robertson drag is comparatively insignificant.

Continuous Grinding Kinetics of Ethenzamide Particles by Fluidized-Bed Jet-Milling

ABSTRACTContinuous grinding kinetics of Ethenzamide powder, as a model active pharmaceutical ingredient (API) was investigated by fluidized-bed jet-milling. Because the oversize fractions after the classification were well fitted by a modified Rosin-Rammler distribution function, an equation of grade efficiency curve was obtained, which was also characteristic of API. A continuous grinding model was developed on the basis of a batch model by using 1st Kapur function relating grinding rate, the grade efficiency curve, and the overall process flow model consisting of grinding, classification, and mixing zones. The residual ratio obtained was well fitted to the experimental results except for the particle size range smaller than 4 μm and larger than 100 μm. Furthermore, because the volume of the active grinding zone adopted as the fitting parameter was found to be 5 cm3 in all experiments and the value was considered to be appropriate dimensionally, this result supports the reliability of the model.

Discrete model for analysis and design of grinding mill-classifier systems

Discrete mathematical and computer models are developed for the simulation of grinding mill-classifier systems on the basis of distributed parameter models of continuous grinding processes. The discrete model is derived from the partial integro-differential equation describing axial mixing and breakage of particles in grinding mills. The convective flow and axial dispersion in the mill are modeled as particle size-dependent processes, while the recirculation line is described as plug flow of the classifier rejected material involving also some time delay. The resulted set of recursive linear algebraic equations was the basis of computer model developed in MATLAB environment. The capabilities of the computer model are demonstrated by presenting and analyzing results obtained by numerical experiences. The influence of both the kinetic and process parameters of the mill-classifier system on the size distribution of the ground material as well the dynamic behavior of the system are presented and analyzed. The computer model is suitable for designing the configuration and operational conditions of both open- and closed-circuit grinding mill-classifier systems efficiently.

Numerical Analysis Of States Of StrainAnd Stress Of Material During MachiningWith A Single Abrasive Grain

In papers [4, 7], a mathematical model was derived of a single-grain machining process in conditions of centreless continuous grinding. This model comprises discrete equations of the object’s motion and heat transfer together with initial and boundary conditions. In this paper, an effective solution of these equations has been presented. The manner of a partial linearization of the incremental motion equations has been shown, which allows for an application of an explicit method of integration, which makes use of an approximation with the method of central differences. As a result of this, it is possible to calculate vectors of displacements and temperature at the end of a given step on the basis of values concerning the previous step. For this method, an adequate algorithm of the solution of motion equations has been developed with the assumptions of Rayleigh’s proportional damping. Its application has been developed in the system of the ANSYS finite element method, which allows for a complex time analysis of the states of displacements, strains and stresses occurring in the set (which consists of an object, an abrasive grain and a binding agent, both for spatial and flat states). Numerical computations of the process of the object’s material strain have been conducted with the use of two methodologies. The first one requires an introduction of boundary conditions for displacements in the contact area determined in modeling investigation, while the second requires a proper definition of the contact zone through the introduction of finite elements of TARGET and CANTACT types, without the necessity of introducing boundary conditions. It is evident from the analyses conducted that forecasting of the physical properties of the surface layer in the centreless continuous grinding processes may occur on the basis of analyses of thermal phenomena and the state of strains in the machining zone. An analysis of machining with a model abrasive grain is the first stage towards a proper design and control of this complex technological process. Computer Methods and Experimental Measurements for Surface Effects and Contact Mechanics VII 57 © 2005 WIT Press WIT Transactions on Engineering Sciences, Vol 49, www.witpress.com, ISSN 1743-3533 (on-line)

Development of Conductive Rubber-Bond Wheel by ELID Grinding(Nanoprecision Elid grinding)

In the aim to fabricate high quality ground surfaces efficiently by ELID grinding, investigations were conducted on the grinding system, grinding wheel, grinding fluid, and electrolytic power supply system. As part of this study, we developed a conductive rubber-bond grinding wheel for ELID grinding. The grinding wheel is composed of rubber, carbon, and abrasives, and was designed to demonstrate ELID effects (continuous grinding ability) by the excellent finishing effects of rubber and conductivity ensured by carbon. The prototyped grinding wheel was a #120 conductive rubber-bond grinding wheel using Al_2O_3 abrasives. Using this wheel, the electrical dressing characteristics and grinding characteristics were investigated. The experimental results show that a non-conductive coating was formed on the wheel surface by electrical dressing, and this coating has greater frictional coefficient and wear amount than the bonding matrix. Grinding experiments of mono-crystalline silicon were also carried out using this grinding wheel, and it was found that stable grinding without loading can be realized by adding ELID grinding.