The cross-sectional profile of the existing screw rotor has sharp points and the contact line is discontinuous. To solve this problem and simplify the composition of the section profile, this paper uses a sinusoidal helix to smoothly connect the tooth tip arc and the tooth root arc, and then proposes a new type of fully meshed sinusoidal helical screw rotor. The meshing model of the sinusoidal helix and its conjugate curve are proposed, and the equation of the section profile is deduced. The influence of the radius ratios and helical central angle of the new section profile on the performance of the twin-screw vacuum pump is analyzed, and their reasonable value range is given. The results show that the section profile of the as-proposed new full meshing screw rotor is completely smooth, and the spatial contact line is continuous, which is beneficial to improve the performance of the twin-screw vacuum pump.

In the China spallation neutron source（CSNS） large scientific platform, 1.6GeV high-energy protons produced by a high-energy proton accelerator are used to bombard a solid tungsten target. The back neutron beam generated in front of the target returns through the proton channel to the neutron experiment area is called the back neutron source（Back-n）. It has the characteristics of wide energy spectrum（0-200MeV）and large neutron yield（2×10¹⁶n/s）, which is suitable for nuclear data measurement and other high-energy physics research. The Back-n vacuum system consists of a 26m ultra-high vacuum system shared with the high-energy proton beam and a 54m high vacuum system dedicated to the passage of the neutron beam. The two vacuum systems adopt different vacuum acquisition schemes and process routes,and are separated by a neutron beam window. An ultra-high vacuum gate valve is installed on the ultra-high vacuum side to prevent the damage of the neutron beam window from affecting the operation of the accelerator. This article introduces the design and operation of the Back-n vacuum system. The establishment of the vacuum system provides high-quality vacuum conditions for the experimental research of the Back-n.

Nowadays, more and more vacuum test need to detect pressure inside the test specimens. Although direct installation of sensors is the most effective and accurate way to measure the pressure of the test specimens. However sometimes sensors cannot be installed in the test specimens, which makes direct measurement difficult to be realized. In this paper, internal pressure of test specimens under molecular flow was simulated by the method of Monte Carlo. Geometric model of test specimens were established. Material degassing quantity was considered. The variation of vacuum degree with time was calculated under molecule flow. This paper provides a theoretical basis for the pressure prediction of specific location during vacuum test.

A high vacuum chamber suitable for MEMS ion source testing was designed. According to the current research on the high vacuum chamber used for mass spectrometry test, in view of the high vacuum acquiring ability, maintaining ability and the convenience of frequent use, and considering the structural strength, inner wall exhaust and other factors, the cylinder structure which can meet the requirements of both strength and low exhaust rate was selected. Based on ANSYS software, the structural stability and dangerous point distribution of the chamber under high vacuum were analyzed comprehensively. The optimized selection range of wall thickness was determined. This study can provide a theoretical basis for the design of high vacuum chamber.

This paper introduces a set of virtual instrument experiment system for school teaching and enterprise training based on the unity3D platform. With various virtual instruments, the system provides high reality experimental environment with intelligible human-computer interaction and can well simulate the manipulation of the experiment. The as-developed system has two forms, in which one is the realization of VR scenes and the other one is the client APP form. It is suitable for different cenes and meets different teaching and training needs. This paper also provides a reference for the development of such VR platforms.

In order to predict the time of gas pressure drop in the rapid decompression environment simulation system, an approximate theoretical calculation model for rapid decompression was established based on the orifice outflow principle of hydrodynamics, and the numerical iterative calculation method was given. At the same time, the finite element simulation method was used to analyze the pressure balance process, and a set of test system was built. By comparing the results of the two methods with the experimental data, the correctness and feasibility of the calculation method are verified.

In order to improve the service performance of titanium alloy, multilayer films with different R_Cr-CrN:R_Cr-CrAlN modulation ratio were prepared on TC4 titanium alloy by vacuum cathodic arc ion plating. Scanning electron microscope(SEM), X-ray diffraction (XRD), microhardness tester, scratch tester, stress tester and sand erosion tester were used to detect and analyze the cross-section morphology, structure, thickness, hardness, adhesion, residual stress and sand erosion resistance of the multilayer films. The results show that the thickness of multilayer films is 7-8μm, the transition layer is about 1.5 μm, and the thickness of single cycle is 150-200nm. All the multilayer films exhibit (200) preferred growth face centered cubic structure. With the increase of the proportion of Cr-CrAlN layer, the hardness, residual stress and adhesion of the film increase accordingly. The sand erosion resistance of multilayer films with different modulation ratios at 90° angle of attack is more than 3 times that of TC4 substrate before they are completely damaged, and at 30° angle of attack, the sand erosion resistance of multilayer films is about 8 times that of TC4 substrate. When the modulation ratio of R_Cr-CrN:R_Cr-CrAlN is 1∶2, the multilayer films have the best comprehensive properties.

Transition layer is a key factor to improve the film/substrate relationship and increase the quality of the film. In this paper, the epitaxially grown process of Cr, which is a common transition layer material, was simulated using molecular dynamics method. Surface topography, roughness, radial distribution function and adhesion strength was analyzed to study the effect of incident energy on the film quality. The results show that at the initial stage of deposition, the film/substrate interfacial interaction was the main factor affecting the growth mode of the film. As the incident energy increased, the growth mode changed from Frank-Vander Merve to Volmer-Weber. As the deposition process progressed, the film surface roughness gradually raised during low-energy deposition(15-50eV). However, the opposite trend exhibited during high-energy deposition(75eV) because of the etching effect, and the surface roughness decreased gradually. Meanwhile, the film/substrate interface was destroyed by the shallow injection in the lower energy range, which weakened the film/substrate adhesive strength. Further improving the deposition could improve the film/substrate adhesive effect by forming a composition gradient layer. The research results in this paper shows important guiding significance for the thin film deposition process: increasing the incident energy during the deposition process does not meaning a positive effect, and it must be controlled in a suitable energy range.

When using tungsten crucible and electron beam evaporation equipment to evaporate silver thin film, silver is infiltrated with tungsten crucible in the molten state,and the liquid level of molten metal in the crucible is concave. Such concave evaporation sources often lead to poor uniformity of the as-deposited films. According to the principle that the microstructure of the object surface will change the contact angle between liquid and solid, a groove array is fabricated on the smooth inner wall of tungsten crucible by chemical corrosion. By changing the contact angle between the molten metal material and the inner wall of the tungsten crucible, the wettability of liquid silver and the wall of tungsten crucible can be adjusted. The results show that when the groove width is about 1mm,the depth is about 0.5mm and the period is about 2mm, the inner wall of the molten silver and tungsten crucible becomes no longer infiltrated. 100nm-thick silver film is evaporated with unmodified and modified tungsten crucible, respectively, and it is found that the uniformity of the evaporated film can be improved effectively by using the modified tungsten crucible.

To study the application of ITO films in the 1064nm laser window of wide magnetic shielding, ITO thin films were prepared by using dual ion beam sputtering technology under different technological conditions. According to the test results of photoelectric properties of the films,the effects of oxygen flow rate, auxiliary ion source and substrate baking temperature on the transmittance and conductivity of ITO films were analyzed. Using Ti₂O₃ and SiO₂ as high and low refractive index materials and ITO film as electromagnetic shielding film on K9 glass substrate, a 1064nm laser window film with 0°-45° incidence was designed and fabricated for 2-18GHz efficient shielding. The test results show that the thin film prepared under suitable technological conditions has good transmittance and electromagnetic shielding performance, and is suitable as a high-efficient electromagnetic shielding,0°-45° incident of 1064nm laser window film.

In order to study the effect of matrix surface microstructure on the adhesion between coating and matrix, the adhesion between coating and matrix was tested. The hardness of the coating was measured. The interfacial microstructure between coating and matrix,and the matrix surface microstructure were observed. The relationship between adhesion and surface morphology was analyzed. The results show that after water blasting and dry blasting, V-grooves are formed on the matrix surface, which are expressed as type θ₁ and type θ₂ respectively（θ₁<θ₂, θ is the ratio of groove opening width to groove depth）. The matrix surface microstructure can significantly affect the adhesion between coating and matrix. But the phase, density and residual stress of coating are not influenced. According to the nucleation mechanism, the atoms will nucleate and grow at the upper edge of θ₁ “V” groove. A large number of atoms are blocked, resulting in hollow bottom of “V” groove. In θ₂ “V” groove, a large number of atoms enter the groove. With the diffusion of atoms, the almost completely filled“V” groove is formed. As a result,the bonding area of coating and matrix increases, and the adhesion of coating and matrix improves.

The performance of agricultural machinery farming parts is seriously affected due to wear failure, and the development of agricultural mechanization is restricted. Surface modification technology has become an important technical means to improve the wear resistance of farming machine parts owing to its advantages of flexible technology, strong applicability, convenient operation and low cost. The surface modification technology has been widely used in agricultural machinery,such as thermal spraying, spray welding, surfacing welding, cladding and biomimetic technology. The advantages and disadvantages of different technologies and their applicable conditions are different. This paper introduces the research situation of surface modification technology in improving the wear resistance and surface performance of farming machine parts, and puts forward its application prospect and development trend.

An ultrasensitive leak detection technology applied to high pumping speed automatic exhaust system is designed to solve the problem of small leak detection with leakage rate less than 5×10^-12Pa·m³/s in the process of exhaust and sealing off for traveling wave tube. The device is mainly composed of main vacuum system, external vacuum and baking system, cumulative comparison leak detection system, standard gas flow system and electrical control system. The exhaust table has eight stations, whose limit vacuum reaches ultra-high vacuum without load, and the vacuum furnace can be heated to high temperature. The whole process automation of exhaust process is achieved using program control and possessing functions of automatic collection, storage, analysis and transmission. The standard gas flow system can provide a micro flow from 5×10^-7Pa·m³/s to 5×10^-16Pa·m³/s, and the lower limit of cumulative comparison leak detection system reaches 5×10^-16Pa·m³/s, with a combined standard uncertainty of leak detection results less than 15%.

A quadrupole mass spectrometer was used to measure and analyze the residual gas in the vacuum vessel of HL-2M in the process of baking and glow discharge cleaning(GDC), and the pumping performance of the cryopumps for H₂O in the pumping system was studied. After baking with a maximum temperature of 100℃,the partial pressure of 18(H₂O) and 28(CO) were reduced by 47.96% and 17.63%, respectively. The ion current of 18(H₂O), 28(CO) and 32(O₂) during the GDC went down remarkably. And the product of the GDC was exhausted by the pumping system, which effectively reduced impurities such as carbon and oxygen. The partial pressure of 18(H₂O) and 28(CO) were reduced by 3.2×10^-5Pa and 3.7×10^-6Pa, respectively, with four cryopump operation and the steady state vacuum. Mass spectrometry measurement and analytical results provide useful supports for the initial plasma discharge of the HL-2M tokamak.

In order to solve the problem of poor reliability of brazing seal in space environment simulation equipment due to the large installation gap between heat sink and vacuum container, the following methods were adopted. Remove the oxide layer of base metal and solder surface before welding. BAg45CuZn eutectic solder with 45% silver content is selected. The welding heat source with external flame temperature of about 900℃ is used. Heat sink copper pipe and stainless steel pipe with larger wall thickness are selected. The welding gap is controlled in 0.1mm to 0.2mm by welding auxiliary parts. The welding heating time is controlled in 30s. After brazing and sealing of stainless steel pipe and copper pipe with the above processes, the welding test results are good and the welding seam is reliable. Leak detection is carried out by helium mass spectrometer after cyclic impact at low temperature of -186℃ and high temperature of 120℃ on the weld. The leak detection data prove that the sealing performance of the weld meets the use requirements of the equipment.

The cylindrical specimens of a single crystal superalloy with diameter of 15mm and 30mm were prepared using the same melting process and directional solidification process. The stress rupture properties at 980℃/250MPa and high cycle fatigue properties at 800℃ of the alloy with two casting dimensions were tested. Dendrite microstructure, the as-cast γ′ phase, heat treated γ′ phase, micropore, stress rupture and high cycle fatigue fractograph and fracture microstructure of the alloy with different casting dimension were examined by OM, SEM and TEM. The results show that with the increase of casting dimension, the primary dendrite arm spacing, the size of as-cast and heat treated γ′ phase, and the size and volume fraction of micropore increase. The stress rupture properties of the alloy decrease, the fracture mechanism has no obvious change and is dimple model with casting dimension increasing. The quantity and size of micro-crack and the γ′ raft thickness on the stress fracture microstructure increase with the casting dimension increasing, while high cycle fatigue properties of the alloy decrease. At last, the relationship between the property and microstructure of the alloy is discussed.