In this paper, highly Yb-doped Ca
4GdO(BO
3)
3 (Yb
:
GdCOB) crystals were grown by the Czochralski method. The absorption and fluorescence spectra were measured. The laser of Yb
:
GdCOB crystal was ...demonstrated with different output mirrors when it was pumped by a fiber-coupled laser diode (LD) at the wavelength of 976.4
nm. The lowest pumping threshold was 280
mW, the highest light–light conversion efficiency was 33.8%, and the highest slope efficiency up to 70% was thus calculated from the linear part of the curve. The self-frequency doubling (SFD) green laser output was also observed.
In order to resolve the difficulty of micro abrasive feed continuously and precisely in micro abrasive water jet machining, an installation for precise feed micro abrasive was designed based on ...principle of material conveying by auger mechanism. The auger is driven by DC motor reducer. The abrasive flow rate is controlled precisely by regulating the revolve speed of DC motor. The relationship between abrasive flow rate and voltage of DC motor was linearly fitted based on experimental results. It shows that within 10-24V, the average error and maximum error of abrasive flow rate is 1.3g.min -1 and 1.96g.min -1 respectively, the average relative error and maximum relative error of abrasive flow rate is 0.2% and 1.79% respectively. Therefore it can be used as controlling equation of the installation for precise feed micro abrasive. The experiments on micro abrasive water jet cutting with installation for precise feed abrasive was carried out. It was showed that the surface roughness of the cutting face is greatly improved by 2.64 times in average with respect to traditional abrasive feed system. Therefore the newly installation for precise feed micro abrasive has great application value in micro abrasive water jet precise machining.
In this paper, Er
:
Ca
4YO(BO
3)
3 (Er
:
YCOB) and Er
:
Yb
:
Ca
4YO(BO
3)
3 (Er
:
Yb
:
YCOB) crystals with large size and excellent quality have been grown by the Czochralski method. The absorption ...and emission spectra of Er
:
YCOB and Er
:
Yb
:
YCOB crystals have been measured; the emission spectrum of Er
:
Yb
:
YCOB crystal shows that the strongest emission peak is located at 1537
nm. An output power of about 2
mW at the wavelength of 1553
nm has been obtained under the pumping power of a fiber-coupled laser diode (LD) of 1600
mW at 976
nm, using a
Y direction cut 2.5
mm thick Er
:
Yb
:
YCOB crystal sample.
Steel ladle is the important tool for containing and transiting in steel enterprises. Analysis of tilting torque steel ladle is very important for reasonable design of electric tipping mechanism of ...steel ladle. Based on the ANSYS, the varies of steel ladle total mass, centroid, moment of inertia, tilting torque etc. with tilting angle in steel ladle tipping process are studied. The tipping torque was fitted based on MATLAB. It was showed that maximum torque is 554254N.M when tipping angle is 50°. It has great application value in calculates a variety of mechanical properties of tipping as well as design of steel ladle and electric execute mechanism for steel ladle.
Al-Cr-pillared montmorillonite was synthesized by using bentonite and Al-Cr pillaring solutions as starting materials. The basal spacing and specific surface areas of the materials were significantly ...increased relative to those of untreated clays. When the Al/Cr molar ratio(R) was 0.10, the d(001 ) value and specific surface area of pillared montmorillonite were 1.9194 nm and 165.7 m^2 g^-1 , respectively. Thermal stability of the materials was determined using calcined tests and X-ray diffraction ( XRD ) analysis. The materials formed at different R(0.05;0.10;0.15;0.25) exhibit a high thermal stability at 300℃ , especially at initial R = 0.10, the basal interlayer spacing of materials is stabilized at 1.7313 nm after calcined at 500℃ for 2 h. Adsorption behavior of the materials was studied by adsorption experiments. The results show that the Al-Cr-pillared montmorillonites exhibit much stronger adsorption capacity on Cr^6+ in aqueous solution than untreated clays do.
Numerical simulation of flow field inside abrasive water jet nozzle on steady, turbulence, two-phase flow conditions was carried out based on FLUENT. The main geometric parameters of abrasive water ...jet nozzle were analyzed. The results show that the smaller the contraction angle a of the focusing tube, the better flow field inside abrasive water jet nozzle is. Also smaller contraction angle avoids abrasive gathering at the entrance of the focusing tube. The smaller the outlet diameter of focusing tube, the greater velocity of the abrasive can be obtained. On the other hand, the smaller the outlet diameter of focusing tube is, the smaller negative pressure inside the mixing chamber exists. Consequently abrasive inhalation is not good. Outlet diameter of focusing tube should be in the range of 3 times of the jewel orifice. The results show also that the length of the focusing tube has significant effect on the outlet velocity of abrasive. In order to achieve maximum speed of abrasive, the length of cylinder part of focusing tube should be in the range of 30 times of the outlet diameter. Simulation of flow field inside abrasive water jet nozzle and analysis of parameters of the focusing tube provide basis in design of nozzle for abrasive water jet.
This paper analyzes the Direct Torque Control (DTC) theory. We find that dynamical and stable performance are not hold with traditional voltage switch strategy at the same time. It presents a new ...direct torque control method of brushless DC motor, and introduces a space voltage vector selection table. By the addition of zero vector in the converter control, traditional three order torque control loop translates to five order torque control loop. So torque output have good dynamical and stable response, and stable torque ripple of traditional DTC can be improved. The direct torque control for brushless DC motor is implemented with TI DSP TMS320LF2407A. The experiment results show that the system has very quick dynamic response, low torque ripple and high performance requirements of industrial applications.
The objective is to study the content of element Nb to the microstructure and properties of centrifugal cast binary Ti-Nb alloys in order to develop a new type titanium alloy for dental prostheses ...with better properties than pure titanium (CP Ti). Experimental Ti-Nb alloys (5,10,15 and 20 weight% Nb) were made using an argon-arc melting furnace and cast into a graphite mold using a centrifugal casting machine. The microstructure, phase composition, Vickers hardness and compression strength were studied by means of optical microscopy (OM), X-ray diffraction (XRD), Vickers tester and a Instron 5500 testing machine. Experimental results indicated that crystal structure and morphology of Ti-Nb alloys were sensitive to their niobium contents. Only the α-Ti phase was observed in the XRD patterns of Ti-Nb alloys. Among all Ti-Nb alloys, Ti-20Nb alloy had the highest Vickers hardness (341 HV), the highest compression strength (1522 MPa) and the lowest elastic modulus (23.3 GPa). Ti-5Nb alloy had the highest compression ratio (24.9%). By alloying with niobium, the cast titanium exhibited better mechanical properties. The hardness and strength of Ti-Nb alloys have been improved.
