Simulation and Optimization of the Fluid Solidification Process in Brazed Plate Heat Exchangers

When a brazed plate heat exchanger is used as an evaporator,the working mass in the channel may undergo soli-dification,thereby hindering the refrigeration cycle.In this study the liquid solidification process and its optimi-zation in a brazed plate heat exchanger are investigated numerically for different inlet velocities;moreover,different levels of corrugation are considered.The results indicate that solidificationfirst occurs around the con-tacts,followed by the area behind the contacts.It is also shown that deadflow zones exist in the sharp areas and such areas are prone to liquid solidification.After optimization,the solidification area attains its smallest value when a corrugation spacingλ=4.2 mm is considered.

MONOBRAZE单层翅片箔与三层复合翅片箔耐腐蚀性能对比研究

采用金相显微镜、电位计、EPMA和SWAAT腐蚀试验等手段,研究了分别采用三层复合翅片箔和MONOBRAZE单层翅片箔钎焊后的两种冷凝器接头断面形貌、微观组织、元素扩散、电极电位和耐腐蚀性能。结果表明:与热轧三层复合翅片箔相比,MONOBRAZE单层翅片具有同样的钎焊连接效果,而且钎焊后强度更高、无明显熔蚀、翅片厚度无明显减薄,为MONOBRAZE翅片进一步减薄、大面积替代复合翅片、降低热交换器制造成本创造了有利条件。同时,采用MONOBRAZE单层翅片钎焊后的冷凝器有着更优良的耐腐蚀性能,MONOBRAZE翅片优先被腐蚀,可以对MPE管起到更好的牺牲阳极保护作用,大幅提高热交换器整体寿命。

Research on the heat conduction mechanism of induction brazecoating

Induction brazecoating technology is an important means to improve the surface properties of materials.In this paper,copper plate and corundum are selected as substrates for induction brazecoating respectively.The temperature variation of powder and paste coating is systematically studied,and the heat conduction mode and path in the brazecoating process are analyzed.The results show that rise of the coating temperature mainly depends on the heat absorption from the substrate.The liquid-solid interface conducts heat violently and advances step by step,which promotes the melting spread of metal filler metal.The powdery brazecoating material is in a free state,and there is a gas insulation film between the powder particles and the diamond,making it difficult for substrate to conduct heat to the coating.The binder not only assists forming,shell making and oxygen isolation,but also plays an important role during melting.

Sawing Performance Comparison of Brazed and Sintered Diamond Wires

Great attention has been paid on fabricating diamond wire by using the brazing diamond because of its strong chemical bonding strength and controllability of grits distribution. Although several serving performances of brazed diamond wire have been reported, seldom do these studies refer to its process characteristics. Sawing performances of a brazed diamond wire are investigated and compared with those of a sintered diamond wire on a wire saw machine. The surface topographies of beads selected from the two wires are micro observed before sawing. The sawing tests are carried out in constant feed rate feeding（CFF） and constant normal force feeding（CNFF）. In CFF test, sawing force, power, and the cut depths of positions on contact curve are measured. Then, coupled with the observations of beads topographies, sawing force and its ratio, relations of power against material removal rate, and contact curve linearity are compared and discussed. In CNFF test, the sawing rates of the two wires are investigated. The results indicate that the brazed wire performs with lower sawing force（less 16% of tangential force and 28% of normal force）, more energy efficiency（nearly one-fifth of sawing power is saved）, at a higher sawing rate （the rate is doubled） and with better contact curve linearity as compared with the sintered wire. This proposed research experimentally evaluates the sawing performances of brazed diamond wire from the aspect of process parameters, which can provide a basis for popularizing the brazed diamond wire.

Theoretical study and numerical simulation of the stress fields of the Al_2O_3 joints brazed with composite filler materials

Non-linear finite element code MSC. Marc was utilized to analysis the field of stress of the Al2O3 joints brazed with composite filler materials. The properties of the filler materials were defined by using the mixing law, method of Mori-Tanaka and theory of Eshelby to ensure the accuracy and reliability of results of finite element method （FEM）. The results show stress in brazed beam is higher than that in base material. The maximal stress can be found in the interface of joint. And the experimental results show that the shear strength of joints increases from 93.75 MPa （ Al2O3p Ovol. % ） to 135.32 MPa （ Al2O3p 15vol. % ） when composition of titanium is 3wt% in the filler metal.

Al2_3/Al2O3 Joint Brazed with Al2O3-particulate-contained Composite Ag-Cu-Ti Filler Material

Microstructure and interracial reactions of Al2O3 joints brazed with Al2O3-particulate-contained composite Ag-Cu-Ti filler material were researched by scanning electron microscopy （SEM）, electron probe microscopy analysis （EPMA）, energy dispersive spectroscopy （EDS） and X-ray diffraction （XRD）. The interracial reaction layer thickness of joints brazed with conventional active filler metal and active composite filler materials with different volume fraction of Al2O3 particulate was also studied. The experimental results indicated although there were Al2O3 particulates added into active filler metals, the time dependence of interracial layer growth of joints brazed with active composite filler material is t^1/2 as described by Fickian law as the joints brazed with conventional active filler metal.

Fabrication of in-situ synthesized ceramic reinforced Ni-based alloy composite coatings by reactive braze coating processing

In-situ synthesized ceramic such as TiC,Cr7C3 and Cr5B3 reinforced Ni-based alloy composite coating was fabricated on the surface of mild steel substrate by reactive braze coating processing with colloidal graphite,Cr,Ni,ferro-boron,Si and titanium powders as the raw materials at low temperature of 1000℃,and a new kind of coating materials was developed.By means of SEM,EDS,XRD and surface hardness tester,the microstructures,phases,hardness and wear-resistance of the coating were analyzed,respectively.The results revealed that the coating was mainly composed of the ceramic in-situ synthesized reinforcement phases of TiC,Cr7C3 and Cr5B3 and the binder phases in-situ synthesized of Ni31Si12 and(Ni,Fe)solid solution;The ceramic reinforcement phases of TiC,Cr7C3 and Cr5B3 were randomly distributed in the binder phases of Ni31Si12 and(Ni,Fe)solid solution;The coating had about 15vol%pores and can possibly be applied as a self-lubrication coating;The coating and the substrate were integrated together by metallurgical bonding;The coating had a hardness up to 91-94HR15N.

Defect detection in brazed weldment with lattice structure using ultrasonic Lamb wave technique

In this paper, defects detection in brazed weldment with lattice structure is studied using ultrasonic Lamb wave. Based on the ultrasonic guided wave theory, the frequency dispersion curves for phase and group velocity of I Cr18Ni9Ti are obtained by solving the Rayleigh-Lamb equation. The incident angles of different modes are determined through theoretical calculation and experimental analyses. Artificial defects of through-wall slots with different dimensions are made and tested. Experimental scattering effects of the fundamental symmetric mode S2 and asymmetric modes A1 and A0 are analysed and compared. The results show that mode Ao is suitable for detecting artificial defect, and the amplitude of the received signals are in good agreement with the defect size. Brazed weldment specimen containing lack of brazing with certain dimensions is made. Using the same methodology, scattering effects produced by weld defects are measured. The results show that the clutter wave brought about by the filler metal will certainly disturbs the identification of defect signal. But, when the defect is 3.0 mm in width, the presented mode Ao could be used potentially.

Electron beam braze-welding of vanadium alloy to stainless steel with electroplated Cu/Ag coatings

Cracks may easily occur in the fusion weld between vanadium alloys and stainless steel due to the brittle intermetallics and welding stress. The high vacuum electron beam braze-welding has been successfully used to join vanadium alloy（V-5Cr-STi） to stainless steel （HR-2） with electroplated Cu and Ag coating. To investigate the effects of electroplated coating on the weldability, the joint appearaace, the microstrueture and the mechanical properties of the joints have been thoroughly analyzed. The results show that the joint surface configuration was good and root reinforcement was full and smooth. A reaction zone （RZ） was gained on the interface between the V-5 Cr-5 Ti alloy and HR-2 stainless steel base metals. The width of reaction zone at the top of the joint was up to O. 65 mm, wider than that in the bottom of the joint （ 0.46 mm）. The reaction zone consisted of considerably smaller dendritic structures with an average grain size of less than 10μm. Element Ag and Cu almost enriched the interface between V-SCr-5Ti alloy substrate and RZ, serving as a physical barrier which decreases or avoids the formation of intermetallics. The maximum tensile strength of vanadium alloy^stainless steel dissimilar alloy joint was more than 300 MPa. The joint was defects free.

Microstructure and Strength of Brazed Joints of Ti_(3)Al Base Alloy with Cu-P Filler Metal

Brazing of Ti3Al alloys with the filler metal Cu-P was carried out at 1173-1273 K for 60-1800 s. When products are brazed, the optimum brazing parameters are as follows： brazing temperature is 1215-1225 K; brazing time is 250-300 s. Four kinds of reaction products were observed during the brazing of Ti3Al alloys with the filler metal Cu-P, i.e., Ti3Al phase with a small quantity of Cu （Ti3Al（Cu）） formed close to the Ti3Al alloy; the TiCu intermetallic compounds layer and the Cu3P intermetallic compounds layer formed between Ti3Al（Cu） and the filler metal, and a Cu-base solid solution formed with the dispersed Cu3P in the middle of the joint. The interracial structure of brazed Ti3Al alloys joints with the filler metal Cu-P is Ti3Al/Ti3Al（Cu）/TiCu/Cu3P/Cu solid solution （Cu3P）/Cu3P/TiCu/Ti3Al（Cu）/Ti3Al, and this structure will not change with brazing time once it forms. The thickness of TiCu＋Cu3P intermetallic compounds increases with brazing time according to a parabolic law. The activation energy Q and the growth velocity/to of reaction layer TiCu＋Cu3P in the brazed joints of Ti3Al alloys with the filler metal Cu-P are 286 kJ/mol and 0.0821 m2/s, respectively, and growth formula was y2=O.O821exp（-34421.59/T）t.Careful control of the growth for the reaction layer TiCu＋Cu3P can influence the final joint strength. The formation of the intermetallic compounds TiCu＋Cu3P results in embrittlement of the joint and poor joint properties. The Cu-P filler metal is not fit for obtaining a high-quality joint of Ti3Al brazed.

Ultrasonic C-scan inspection of brazed joint in thin panel honeycomb structure

The non-destructive testing of brazed joint in honeycomb structure with thin panel （ thickness ： 0. 2 mm） was studied by ultrasonic C-scan method. Samples with different types of artificial defect were designed; the characteristic signal and the main parameters of the test were determined by the pre-experiment, and then parameters were optimized by orthogonal design, finally the optimum process was verified by a single panel sample. The multiple reflection echoes were chosen as the characteristic signal. The optimal C-scan results were achieved when the 20 MHz focus probe was used, and the pass band range for received signal were selected as 8 - 17. 5 MHz. The defects such as incomplete penetration and core damage can be detected with ultrasonic C-scan, and the detection accuracy can reach to 1 ram.

Fabrication of Ti-Ni-Mo-Si composite coating by reactive braze coating process

Ti-Ni-Mo-Si composite coating was fabricated on mild steel by reactive braze coating process with Ti61. 9Ni24. 6Si4. 411409.1 （ wt. % ） powders as the raw materials. Microstr^cture of the coating was characterized by optical microscopy, scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy and micro-hardness tester. Results indicate that the Ti-Ni-Mo-Si composite coating is metallurgically bonded to the mild steel substrate and has high hardness. The microstructure of the coating consists of the reinforcement of Ti5 Si3 and Mo9 Ti4 particles and the matrix of eutectic NiTi2. Due to the poor wettability of NiTi2 liquid at low temperature, TisSi3 and Mo9 Ti4 do not uniformly distribute in the NiTi2 matrix.

Defect detection in brazed weldment with lattice structure using acoustic shadow technique

Brazed weldment with lattice structure has been widely used in aerospace industry. The non-destructive testing is often difficult because of the poor inspection accessibility. The present paper illustrates how the plane-like defect lack of brazing can be detected rapidly in this kind of structure by using ultrasonic Lamb wave. Experimental weldments are prepared and weld defect are tested using S2 mode Lamb wave. Acoustic shadow technique is employed based on Lamb wave testing method. The character of the tested D-scan image and A-scan signal is studied. The experimental results show that acoustic shadow based Lamb wave testing method is effective in detecting through-wall lack of brazing. Meanwhile, the D-scan tested data can be rapidly collected and easily interpreted compared with pulse echo bused Lamb wave testing method.

A study on reactive braze coating of (TiC+Cr_3C_2)/Fe composite coatings

A new hardfacing process, reactive braze coating process (RBCC) was studied, and (TiC+Cr_3C_2)/Fe composite coatings were prepared by RBCC using carbon, Cr_3C_2, iron, ferrochromium and titanium powder as the raw materials in vacuum braze furnace. The results show that TiC is in-situ synthesized in the coatings. The methods of introducing Cr_3C_2 have great effects on the distribution of TiC. Adding Cr_3C_2 directly to the raw materials for coatings, fine TiC particles aggregate into discoids parallel to the coating surface, whereas, in-situ synthesizing Cr_3C_2 in coatings, the aggregations of TiC are lumpish. During braze coating, Cr_3C_2 particles directly added dissolve and precipitate to become needle-shaped. The coatings have an even and smooth surface and are combined with their mild steel substrates by a metallurgical bonding.

Reasons and countermeasures for “marking problem” during the production of double-walled copper-brazed steel tubes

This study explores the reasons underlying the frequent appearance of ＂marking problem＂ during the production of double-walled copper-brazed steel tubes. To this end, we compared two types of copper-coated steel strips, of which one has almost no problem during production, whereas the other has higher number of incidences of ＂marking problem＂. We analyzed the chemical composition,mechanical properties,the cross-sectional metallographs, and surface quality of the trimmed edge in both types of specimen. After the roll forming process, the bonding condition between the steel layers of the tubes before and after brazing process has also been examined. Results indicate that the chemical composition and mechanical properties of the two kinds of strips are similar; however, the edge quality of the trimmed strips is significantly different. It is believed that the irregular shape of the edge portions in the strips will be more pronounced during the bevel treatment. Consequently, smooth and tight seams cannot be guaranteed by such uneven beveled edges,which lead to higher number of incidences of ＂marking problem＂ during production.

CMT Braze+焊接工艺在白车身焊接中的调试应用

CMT Braze+焊接工艺因其快速的焊接速度、较低的热量输入、良好的外观质量及其相对于激光钎焊有较大的成本优势,在汽车行业内高端车型被逐渐开始使用,但其由于本身焊接工艺存在特殊性,其调试方法与经验参数与传统的弧焊工艺有很大区别,往往在调试中给使用方造成很大的困扰,本文主要结合现场焊接设备的安装、调试验证与参数、质量验证来阐述此焊接工艺的经验参数与安装、调试方法。

伏能士CMT Braze+技术带来更快的钎焊速度

在与奥迪公司焊接技术部门的合作中,伏能士在CMT钎焊工艺中取得了重要的进展。配合其新专利的气体喷嘴,CMT Braze＋使钎焊速度上有了更快的可能。在奥迪公司车身应用的新工艺中已经证明,即便在正常的量产条件下,高达3m/min的机器人钎焊速度亦是可行的。且由此带来的焊缝规整、干净,这使得CMT Braze＋尤其适合对焊缝外观要求高的应用领域中。

Microstructure and shear strength of the brazed joint of Ti(C,N)-based cermet to steel

Firm joins were obtained between Ti（C,N）-based cermet and steel with Ag-Cu-Zn-Ni filler metal by vacuum brazing. The effects of technological parameters such as brazing temperature, holding time, and filler thickness on the shear strength of the joints were investigated. The microstructure of welded area and the reaction products of the filler metal were examined by scanning electron microscopy （SEM）, metallographic microscope （OM）, energy-dispersive X-ray analysis （EDS）, and X-ray diffraction （XRD）. The brazing temperature of 870℃, holding time of 15 min, and filler thickness of 0.4 mm are a set of optimum technological parameters, under which the maximum shear strength of the joints, 176.5 MPa, is achieved. The results of microstructure show that the wettability of the filler metal on Ti（C,N）-based cermet and steel is well. A mutual solution layer and a diffusion layer exist between the welding base materials and the filler metal.

Microstructure and properties of the joints of ZrO2 ceramic/ stainless steel brazed in vacuum with AgCuTi active filler metal

The ZrO2 ceranfic was successfully jointed to stainless steel by vacuum brazing with active filler metal. The AgCuTi active filler metal was used and the joining was performed at a temperature of 850 ℃ for 10 rain. The microstructures of the joints were characterized by metallographic microscopy, scanning electron microscopy （SEM）, and energy dispersive spectroscopy （EDS）. Metallographic microscopy analysis shows that the morphology of the cross section was a sandwich structure and the TiO is observed in the surface of ZrO2/ stainless steel. The diffusion and enrichment of the elements are the key roles in the brazing of ZrO2 ceramic and stainless steel. The formation of TiCu compounds inhibited the further diffusion of titanium into stainless steel or the ZrO2 ceramic to form TiO compound. In the experimental conditions, the average tensile strength is 80MPa for the joint of ZrO2 ceramic / AgCuTi/ stainless steel systems. A complete joint is formed between the ZrO2 ceramic and stainless steel with the leakage rate at the degree of 10 ^-12 Pa · m^3/s.

Interfacial structure and mechanical property of Al2O3 and Invar brazed joint

This paper introduces a brazing process between Al2O3 ceramic and Invar alloy.Al2O3 can be brazed with Invar effectively.The interfacial structure of Al2O3/Invar joint can be expressed as：Invar/Ag（s,s）＋Cu（s,s）＋Fe2Ti（zone Ⅰ）/Ag（s,s）＋Cu（s,s）＋Fe2Ti＋NiTi＋Cu3Ti（zone Ⅱ）/Ag（s,s）＋Cu（s,s）＋Cu2Ti＋Al（s,s）＋TiC＋TiO（zone Ⅲ）/Al2O3.The maximum shear strength of 139 MPa was measured for as-brazed Al2O3/Invar joint brazed at 850℃ for 25 min or 900℃ for 15 min.