MICROSTRUCTURE ANALYSIS AND MECHANICAL PROPERTIES OF Zn-Al ALLOY ROD PRODUCED BY HEATED MOLD CONTINUOUS CASTING

The new technology of continuous casting by heated mold was used to produce directional solidification ZA alloy lines to eliminate the inter defects of these lines and increase their mechanical properties. The results are as follows: (1) The microstruc-ture of the ZA alloy lines is the parallel directional dendritic columnar crystal. Every dendritic crystal of eutectic alloy ZA5 was composed of many layer eutectic β and η phases. The micro structure of hypereutectic ZA alloys is primary dendritic crystal and interdendritic eutectic structure. The primary phase of ZA8 and ZA12 is β, among them, but the primary phase of ZA22 and ZA27 is a. (2) Through the test to the as-cast ZA alloy lines made in continuous casting by heated mold, it is found that the tensile strength and hardness increase greatly, but the elongation decreases. With the increase of aluminum amount from ZA 5 to ZA 12, ZA22 and ZA27, the tensile strength increases gradually. ZA27 has the best comprehensive mechanical properties in these four kinds of ZA alloys. (3) Heat treatment can decrease the dendritic segregation and improve the elongation of ZA alloy, but make their strength decrease slightly.

Study on Numerical Simulation of Mold Filling and Heat Transfer in Die Casting Process

A 3-D mathematical model considering turbulence phenomena has been established based on a computational fluid dynamics technique, so called 3-D SOLA-VOF (Solution Algorithm-Volume of Fluid), to simulate the fluid flow of mold filling process of die casting. In addition, the mathematical model for simulating the heat transfer in die casting process has also been established. The computation program has been developed by the authors with the finite difference method (FDM) recently. As verification, the mold filling process of a S-shaped die casting has been simulated and the simulation results coincide with that of the benchmark test. Finally, as a practical application, the gating design of a motorcycle component was modified by the mold filling simulation and the dies design of another motorcycle component was optimized by the heat transfer simulation. All the optimized designs were verified by the production practice.

Non-uniform heat transfer behavior during shell solidification in a wide and thick slab continuous casting mold

By employing a two-dimensional transient thermo-mechanical coupled finite element model for simulating shell heat transfer behaviors within a slab continuous casting mold, we predicted the evolution of shell deformation and the thermal behaviors, including the mold flux film dynamical distribution, the air gap formation, as well as the shell temperature field and the growth of carbon steel solidification, in a 2120 mm × 266 mm slab continuous casting mold. The results show that the shell server deformation occurs in the off-corners in the middle and lower parts of the mold and thus causes the thick mold flux film and air gap to distribute primarily in the regions of 0–140 mm and 0–124 mm and 0–18 mm and 0–10 mm, respectively, from the corners of the wide and narrow faces of the shell under typical casting conditions. As a result, the hot spots, which result from the thick mold flux film filling the shell/mold gap, form in the regions of 20–100 mm from the corners of the wide and narrow faces of the shell and tend to expand as the shell moves downward.

Numerical Simulation of Heat Transfer and Deformation of Initial Shell in Soft Contact Continuous Casting Mold Under High Frequency Electromagnetic Field

Heat transfer and deformation of initial solidification shell in soft contact continuous casting mold under high frequency electromagnetic field were analyzed using numerical simulation method; the relative electromagnetic parameters were obtained from the previous studies. Owing to the induction heating of a high frequency electromagnetic field （20 kHz）, the thickness of initial solidification shell decreases, and the temperature of strand surface and slit copper mold increases when compared with the case without the electromagnetic filed. The viscosity of flux de- creases because of the induction heating of the high frequency electromagnetic field, and the dimension of the flux channel increases with electromagnetic pressure; thus, the deformation behavior of initial solidification shell was different before and after the action of high frequency electromagnetic field. Furthermore, the abatement mechanism of oscillation marks under high frequency electromagnetic field was explained.

Effect of CeO_2 on heat transfer and crystallization behavior of rare earth alloy steel mold fluxes

To improve the heat transfer capability and the crystallization property of the traditional mold flux, CaF_2 was replaced with B_2O_3. Then, the influences of CeO_2 on the heat transfer and the crystallization of the CaF_2-bearing mold flux and the new mold flux with 10 wt% B_2O_3 were studied using a slag film heat flux simulator and X-ray diffraction(XRD). The results revealed that the addition of CeO2 reduced the heat transfer by increasing the solid slag thickness and the crystallization of two mold fluxes. However, CeO_2 had less effect on the B_2O_3-containing mold flux compared with the CaF_2-bearing mold flux. According to the analyses, the CeO_2 contents in the CaF_2-bearing mold flux and the B_2O_3-containing mold flux should not exceed 8 wt% and 12 wt%, respectively. Therefore, these experimental results are beneficial to improve and develop the mold flux for casting rare earth alloy steels.

Effects of heat treatment on the properties of powder injection molded AlN ceramics

The effects of two different heat-treatment atmospheres,nitrogen atmosphere and reducing nitrogen atmosphere with carbon,on the properties of Y2O3-doped aluminum nitride（AlN） ceramics were investigated.The AlN powder as a raw material was synthesized by self-propagating high-temperature synthesis（SHS） and compacts were fabricated by employing powder injection molding technique.The polymer-wax binder consisted of 60 wt.% paraffin wax（PW）,35 wt.% polypropylene（PP）,and 5 wt.% stearic acid（SA）.After the removal of binder,specimens were sintered at 1850°С in nitrogen atmosphere under atmospheric pressure.To improve the thermal conductivity,sintered samples were reheated.The result reveals that the heat-treatment atmosphere has significant effect on the properties and secondary phase of AlN ceramics.The thermal conductivity and density of AlN ceramics reheated in nitrogen gas are 180 W·m^-1·K^-1 and 3.28 g·cm^-3 and the secondary phase is yttrium aluminate.For the sample reheated in reducing nitrogen atmosphere with carbon,the thermal conductivity and density are 173 W·m^-1·K^-1 and 3.23 g·cm^-3,respectively,and the secondary phase is YN.

Computer Aided Design of Heat Treatment for AISI P20+Ni Mold Steel with Good Machinability

Computer aided design of heat treatment for AISI P20 mold steel with good machinability is attempted to proceed by the commercial software package Thermo-Calc (TCP+DICTRA). Through experimental and theoretical analysis of phase transformation during heat treatment, further knowledge of designing proper heat treatment is obtained. Then the machinability of AISI P20+Ni steel under given heat treatment condition is studied and the influencing factors to their machinability are analyzed. It is shown that heat treatment designed by computer simulation of carbide transformation is applicable to AISI P20+Ni steel with good machinability; AISI P20+Ni steel with tempered sorbite treated by quenching & tempering has optimal machinability; normalizing at the temperature of 910°C & tempering can avoid cracking and result in acceptable machinability in small thickness module.

Effect of SEN structure on the mold level fluctuation and heat transfer for a medium thin slab caster

It is important to select suitable parameters of a submerged entry nozzle （SEN） for optimizing the flow and temperature patterns in a mold. The effect of SEN design on the mould level stability, meniscus steel flow velocity, and heat transfer of the mold of a medium thin slab caster was studied by means of 1：1 water modeling and industrial testing. The advantages of a 2-port SEN compared with a 3-port SEN are the following： more optimal flow patterns with a lower mold level fluctuation and a lower meniscus steel flow velocity; proper powder consumption without slag bears due to a reasonable liquid powder thickness. The argon flow rate can be reduced and the mold average heat flux and temperature near the edges of the copper plate are reduced. At a casting speed of 2.5 m·min^-1, the mold level fluctuation lies within ＋5 mm. In addition, soft cooling of the steel shell in the mold is realized, which is suitable for casting crack susceptible steel grades.

Research on mold flux for hypo-peritectic steel at high casting speed

Mold fluxes having adaptable properties were developed in the laboratory to solve quality defects, such as depressions and longitudinal cracks when casting hypo-peritectic steel at high casting speed. Firstly, the effect of components on the high basicity mold flux properties was first studied using the orthogonal method. In the scope of the studied content, Li2O has the largest effect on the melting temperature, and the least effect on the viscosity; CaF2 has the largest effect on the viscosity, and the least effect on the melting temperature; Na2O and CaO/SiO2 have no obvious influence on the melting temperature and viscosity. Secondly, two powders （Z1 and Z6） have reasonable viscosity-temperature curves, higher solidification temperatures, and porous structure after solidification, but the crystal property of Z6 is worse than that of Z1, and thus Z1 is more suitable for continuous casting hypo-peritectic steel at high casting speed. Thirdly, a higher basicity of powder, a less free enthalpy of crystal compound, and a lower baffle energy are good for a higher tendentiousness of crystal.

Fabrication of micro gear wheels by micropowder injection molding

The micropowder injection molding technology was investigated to fabricate the microsized gear wheels on a conventional injection molding machine. The feedstock comprised of carbonyl ferrum powder and a wax-based thermoplastic binder. Microinjection molding was fulfilled at about 423 K under 100 MPa. The heating system was applied to the die to improve the fluidity of the feedstock and subsequently the cooling system was used to enhance the strength of the green compacts after injection by decreasing the temperature of the die. The gear wheels were realized successfully with their addendum circle diameter ranging from 800 to 200 um and with the center hole as small as 60 um.

State of the Art Treatment of Non-Ferrous Castings 3-in-l Heat Treatment Systems Combine Foundry Processes

The interior of a high-pressure die-casting is of an unsatisfactory quality. Engine blocks made with this die casting process show lower specific engine performance. Pressure die-casting can hardly be heat treated for obvious reasons. PSM (Precision Sand Molds) process uses sand and organic binder to generate a mold and even allows the manufacturing of complex diesel engine blocks in aluminum alloys. Combined technologies are available for semi-permanent mold castings with cores and castings made in Precision Sand Molds with organic binders. Castings are placed into the special heat treatment furnace immediately after pouring without the operations in stand alone machinery. This patented Sand Lion 3- in-1 technology processes hot castings and carries out three (3) foundry processes simultaneously in one (1) automated machine: 1) De-coring and sand removal; 2) Thermal sand reclamation; 3) Solution heat treatment of castings. The combination of several main casting processes is reflected in significant reductions of energy consumption, of production costs, and improving the quality of the castings. Audits in foundries using the 3-in-l process showed an average reduction in production costs of more than 30%.

制造氢气瓶内胆的电加热滚塑工艺参数的优化研究

在static bed模型的基础上为在PID控制模式下制造氢气瓶内胆的电加热滚塑工艺建立了一个传热模型,并通过FLUENT软件来仿真计算模具表面温度和模内温度以及加热时间和加热电能。这些仿真值与实测值都吻合得较好,从而验证了本文传热模型的准确性。然后应用该传热模型计算了在16种情形下停止加热时的模内温度以及加热时间和加热电能,并通过灰色关联度方法分析了PID模式的触发温度和初始加热功率的百分比对加热时间和加热电能的影响程度。结果表明,停止加热时的模内温度随初始加热功率的百分比变化较小,但随PID模式触发温度的升高而降低。加热时间和加热电能都是随着PID模式的触发温度的升高而减少。最优化的工艺参数是PID模式的触发温度取250℃且初始加热功率的百分比取90%。另外,PID模式的触发温度对加热时间和加热电能的影响程度都要大于初始加热功率的百分比对它们的影响程度。

某型直升机超短波电台结构设计

本文开展了适用于某型直升机平台的机载超短波电台结构设计,从结构总体设计、电气互联设计、散热设计、抗冲振性能设计、三防设计等角度,全方位的阐述了设备的结构设计过程,可为同类设备的结构设计提供借鉴。

Optimization design of wide face water slots for medium-thick slab casting mold

A three-dimensional finite-element model has been established to investigate the thermal behavior of the medium-thick slab copper casting mold with different cooling water slot designs. The mold wall temperatures measured using thermocouples buried in different positions of the mold with the original designed cooling system were analyzed to determine the corresponding heat flux profile. This profile was then used for simulation to predict the temperature distribution and the thermal stress distribution of the molds. The predicted temperatures during operation matched the plant measurements. The results showed that the maximum temperature, about 635 K in the wide hot surface, was found about 60 mm below the meniscus and 226 mm from the center of the mold. For the mold with the type I modified design, there was an insignificant decrease in temperature of about 5 K, and for the mold with the type II modified design, the maximum temperature was decreased by about 15 K and the temperature of the hot surface was distributed more uniformly along the length of the mold. The corresponding maximum thermal stress at the hot surface of the mold was reduced from 408 MPa to 386 MPa with the type II modified design. The results indicated that the modified design II is beneficial to the increase of mold life and the quality of casting slabs.

The optimization of mold fluxes used for casting the peritectic steel of heavy slabs at Baosteel

In order to solve the problem of the high surface longitudinal crack ratio of heavy peritectic steel slabs produced by the No. 3 continuous caster at Baosteel,the physical properties of the original mold flux and the optimized mold flux were compared in a comprehensive way by using analytical measures, such as a slag film heat-flow simulator, a thermowire molten flux crystallization tester and an X-ray diffractometer in the laboratory. The results reveal that one of the major reasons for the cracks is the poor heat transfer ability of the original mold flux. However, the optimized mold flux with a high basicity features a high crystallizing rate,low crystallization temperature and low heat-flow density. Therefore, the optimized mold flux is more suitable for casting peritectic steel by the heavy slab continuous caster. The test results show that the slabs produced by using the optimized mold flux had no surface longitudinal crack in four test casts, while the surface longitudinal crack ratio of the slabs produced by using the original mold flux was 5%. The optimized mold flux can effectively prevent slab surface longitudinal cracks from occurring.

模具真空热处理

热处理是保证模具性能和寿命的关键环节,真空热处理具有无氧化、无脱碳、可脱脂脱气、表面质量好和热处理变形小等优点,广泛应用于模具的热处理。首次修订的标准GB/T 22561—2023真空热处理规定了金属材料在真空状态下热处理设备、工艺过程与工艺规范等要求,有利于指导和规范模具真空热处理生产,提高模具质量,推动我国模具工业高质量发展。

20钢/316L复合管固液复合制坯工艺研究

双金属复合管在石油运输行业中应用前景广阔,结合性能是考察复合管是否合格的重要指标之一。为了能在轧制成形过程中得到高品质的复合管材,在复合管制坯过程中要求实现界面处的冶金复合。以20钢和316L为原材料,基于结合温度及元素扩散情况,采用固液复合方式,并且结合界面的温度模型及通过Pro CAST软件模拟,获得了外模最佳预热温度为1050—1100℃。通过现场试制界面处实现了冶金复合,在最佳温度范围既保证了固态20钢和液态316L之间能达到冶金复合,又能使元素有充分的扩散时间而增强了界面结合强度,同时又可以防止因元素过渡扩散而导致316L腐蚀性能下降。该方法为后续复合管连轧提供了优良的管坯,可实现高品质复合管的现场生产。

一种用于设计电加热滚塑工艺的传热计算方法

首先针对一个空模具以及生产4种不同厚度的氢气瓶内胆的电加热滚塑工艺,通过实验分别测量了模具表面和模内的温度、加热时间和耗电量,并据此计算了在这5种情形下的加热效率和放大系数。然后提出了一种用于设计电加热滚塑工艺的计算方法。即在模具的材料和质量、模内粉料的物性和质量、工艺参数确定后,先计算出有效热能,接着根据放大系数初步估算出在加热阶段电热丝需发出的热能,并由此得出满负荷的加热功率和电热丝的长度。然后利用static bed模型通过FLUENT软件仿真计算出加热时间和电热丝实际需发出的热能。以一个中空立方形的塑料制品的电加热滚塑工艺为例说明了该方法的应用步骤,并研究了满负荷的加热功率和模具材料对加热效率、加热时间和电热丝实际需发出的热能的影响。结果表明,加热效率随氢气瓶内胆厚度的增加而下降,加热时间随着满负荷功率的增大而减少的速率变得越来越慢。采用钢制模具的加热时间比采用铝制模具更长,电热丝也需发出更多的热能。

注塑模具温度智能化控制研究进展

综述了国内外在模具温度控制技术领域的研究进展,从模具冷却系统、加热方式以及控制方式这3个方面进行了介绍,并展望了模具温度控制的未来发展趋势。

注射成形增强半固态AZ91D镁合金的组织及性能

为了研究半固态注射成形技术对AZ91D镁合金显微组织、力学性能以及腐蚀行为的影响,通过对半固态注射成形镁合金进行热处理及电化学腐蚀分析,研究了镁合金成形件在注射成形中与热处理后的组织及性能变化。结果表明,相对于压铸镁合金,半固态注射成形镁合金的组织均匀、力学性能优良、晶粒细小且平均晶粒尺寸为20~30μm,能获得质量良好的显微组织。镁合金的热处理对晶界第二相的数量和分布有较大影响,能作用于材料性能。经时效处理后,镁合金硬度从63.47 HV提高到74.05 HV,抗拉强度从125.56 MPa提高到150.91 MPa,抗拉强度提高了20.2%。在质量分数为3.5%的NaCl溶液的电化学腐蚀中,合金的自腐蚀电位为-959.56 mV,经固溶+时效处理后,自腐蚀电位先升高到-927.55 mV后下降至-988.94 mV,耐腐蚀性能先增高后降低。