Electronically Controlling the System of Preheating Intake Air by Flame for Diesel Engine Cold-Start

In order to improve the cold start performance of heavy duty diesel engine, electronically controlling the preheating of intake air by flame was researched. According to simulation and thermodynamic analysis about the partial working processes of the diesel engine, the amount of heat energy, enough to make the fuel self ignite at the end of compression process at different temperatures of coolant and intake air, was calculated. Several HY20 preheating plugs were used to heat up the intake air. Meanwhile, an electronic control system based on 8 bit micro controller unit (MCS 8031) was designed to automatically control the process of heating intake air. According to the various temperatures of coolant and ambient air, one plug or two plugs can automatically be selected to heat intake air. The demo experiment validated that the total system could operate successfully and achieve the scheduled function.

Oblique Y-groove cracking test of the welding cold cracking susceptibility of domestic X-70 pipeline steel

Gas Transmitting From West to East Project' is significant. It should ensure the welding quality and safety of pipeline. The task is very arduous to guarantee the quality of the project in the condition of long line, complex weather and geology features. In this paper, the welding cold cracking susceptibility of domestic X 70 pipeline steel adopted by the project, which is one of the most interesting questions of welding quality about petrol pipeline, was studied by means of oblique Y groove cracking test. The crack ratio of surface and section was tested under the conditions of different welding materials and preheat temperature .The thickness of plate steel was 14.7 mm and 10.3 mm . The results reveal that X 70 pipeline steel has good crack resistance. The research has important value for the construction of large scale pipeline engineering and the application of domestic X 70 pipeline steel.

Effect of Preheating Temperature on Surface Cracking of High Nitrogen CrMn Austenitic Stainless Steel

18Mn18Cr0.5N steel specimens were preheated at the temperatures from 1100 to 1250°C for 5 min,and then cooled to 950°C and compressed.The cracking behaviors were investigated using optical microscopy and scanning electron microscopy.The results showed that the hot workability of 18Mn18Cr0.5N steel gradually decreased with increasing preheating temperature between 1100 and 1200°C,and quickly deteriorated up to 1250°C.Above 1200°C,delta ferrite particles appeared in 18Mn18Cr0.5N steel,promoted cavity coalescence on grain boundary,and accelerated surface crack formation during the hot working process.

Cold Cracking of Flux Cored Arc Welded Armour Grade High Strength Steel Weldments

In this investigation, an attempt has been made to study the influence of welding consumables on the factors that influence cold cracking of armour grade quenched and tempered （Q＆.T） steel welds. Flux cored arc welding （FCAW） process were used making welds using austenitic stainless steel （ASS） and low hydrogen ferritic steel （LHF） consumables. The diffusible hydrogen levels in the weld metal of the ASS and LHF consumables were determined by mercury method. Residual stresses were evaluated using X-ray stress analyzer and implant test was carried out to study the cold cracking of the welds. Results indicate that ASS welds offer a greater resistance to cold cracking of armour grade Q＆T steel welds.

COLD-WORKING AND HEAT-CRACKING IN Ni-Cu-BASE MONEL ALLOY K-500

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侧线废液储罐封头开裂的原因及处理建议

在奥氏体不锈钢容器的开裂案例中,应力腐蚀开裂占据了相当大的比例。以PBT装置中的四氢呋喃侧线废液储罐为例,针对该不锈钢容器出现裂纹的问题,本文从材质、温度、介质以及焊接等多个角度对其裂纹产生的原因进行了深入分析。研究提出了在封头制造过程中应优先选择含稳态奥氏体不锈钢材料,并且严格控制加工工艺,同时适当采用机械锤击方法来消除残余应力等预防措施,以预防奥氏体不锈钢容器的应力腐蚀开裂。通过这些措施,可以有效提高奥氏体不锈钢容器的耐腐蚀性和可靠性,从而减少应力腐蚀开裂的风险,确保容器的长期稳定运行。

Preparation and performance of a cold gas dynamic sprayed high-aluminum bronze coating

By mixing preheated high-aluminum bronze powders with different amounts of Al_2O_3 powder, a low-pressure cold-sprayed coating was prepared and sprayed onto a Cr12MoV steel substrate. The hardness of the coating and the bonding strength between the coating and the substrate were tested with a HV-1000 microhardness tester and a mechanical universal testing machine. The surface microstructure, cross-section and tensile fracture surface of the coating were observed with a scanning electron microscope(SEM). Correspondingly, the influences of the preheat treatment temperature of the bronze powder and the Al_2O_3 content on the coating performance were investigated. The results indicate that the hardness of bronze powders decreased and the coating deposition rate increased after the preheating treatment of the bronze powder. The Al_2O_3 content in the mixed powders contributed to the deformation of bronze powders during the spraying process. This trend resulted in varied performance of the coating.

Ultrasonic Analysis of Cracking Propagation Morphology in the Fusion Zone of High Strength Steel

Cracking morphology in the fusion zone of HQ130 high strength steel was researched by 'the y-slit test' and 'three-point bend test', ultrasonic test and microscope. HQ130 and QJ63 high strength steel was welded by Ar+CO2 gas shielded arc welding under the condition without preheating. Experimental results indicated that welding cracks were produced in the partially melted zone of the weld root of HQ130 steel side and propagated parallel to the fusion zone. The cracks were developed alternatively between the weld and the partially melted zone, and are not strictly ruptured at W/F (weld metal/fusion zone) boundary surface. Controlling weld heat input (E) about 16 kJ/cm could make the cracking rate lowest and satisfy the performance requirement of welded joint zone.

Analysis of the cause of crack in cold rolling of QSn6.5-0.1 strip

In order to know the cause of cracks in cold rolling of QSn6.5 0.1 copper alloy strip, a lot of experiments and analysis were done. The microstructure changes of QSn6.5 0.1 were investigated by means of metallurgical microscope. The morphology of cracks and surface defects were examined using scanning electron microscope. Macroscopic residual stresses produced in every process during manufacturing in the QSn6.5 0.1 strip were measured by X ray diffraction method and hole drilling method. The results show that the cracks in the QSn6.5 0.1 cold rolling strip were caused due to the derivation of metallurgical defects, such as SnO 2, S, fine looses,the inverse segregation unable to clear up when milling, and the accumulation of all kinds of resi dual stresses. When the accumulation of the residual stress reaches the material′s breaking strength, the cracks will be generated. Several measures to avoid the development of these kinds of cracks were put forward, such as: controlling the casting technology, improving homogenization annealing procedure (680 ℃/7 h) and milling quality(using the second milling when necessary), working out a more reasonable rolling technology to ensure intermediate annealing in time.

Finite Element Method Investigation of the Effect of Cold Expansion Process on Fatigue Crack Growth in 6082 Aluminum Alloy

Cold expansion is an efficient way to improve the fatigue life of an open hole. In this paper, three finite element models have been established to crack growth from an expanded hole is simulated. Expansion and its degree influence are studied using a numerical analysis. Stress intensity factors are determined and used to evaluate the fatigue life. The residual stress field is evaluated using a nonlinear analysis and superposed with the applied stress field in order to estimate fatigue crack growth. Experimental test is conducted under constant loading. The results of this investigation indicate expansion and its degree are a benefit of fatigue life and a good agreement was observed between FEM simulations and experimental results.

Study on mechanism of circumferential cracks in cold-region tunnels

There exists frost damage in cold-region tunnels. The circumferential cracks affect the function of tunnels. Using three-dimensional finite element method, the authors analyzed the mechanism of circumferential cracks in cold-region tunnels It is proved that the internal thermal stress in lining exceeds the tensile strength of concrete, which is the direct cause for circumferential cracks occurring. The laws of thermal stress in lining induced by parameters such as temperature drop, horizontal drag coefficient and length of lining are analyzed. The conclusions are valuable to the design and construction of cold-region tunnels considering the thermal stress.

The mechanism of hot crack formation in Ti-6Al-4V during cold crucible continuous casting

Hot crack is one of common defects in castings, which often results in failure of castings. This work studies the formation of hot crack during cold crucible continuous casting by means of experiments and theoretical analysis. The results show that hot crack occurs on the surface and in the circumference of ingots, where the solidified shell and the solidification front meet each other. The tendency of hot cracking decreases with the increase of withdrawal velocities in some extent. The hot crack is caused mainly by the friction force between the shell and the crucible inner wall, and it takes place when the stress resulting from friction exceeds the tensile strength of the shell. The factors of μ_m, η_t, η_s and η_m, affecting hot cracks are analyzed and verified. In order to decrease the tendency of hot cracks, technical parameters should be optimized by decreasing μ_m, η_t, η_s and η_m.

Potential Cracking in Hydrogen Plant with Light Feedstocks (Part II)

This paper presents the analysis of potential thermal cracking of light feedstocks in the SMR. Two different feedstocks, natural gas and light hydrocarbon (HC) feedstock at two different mixed feed inlet temperatures, are selected to study the HC thermal cracking. Effect of Crossover Piping Volume on feed thermal cracking is also discussed.

Correlation analysis of longitudinal cracks and vertical deformation within asphalt pavement of cold regions

The asphalt pavement longitudinal crack is a common distress in cold regions,resulting from uneven deformation of the subgrade.Analysis of the correlation law between uneven deformation and crack distress is of positive significance for understanding the mechanism of crack initiation,and putting forward treatment measures.In view of the complexity of longitudinal crack inducement and road surface deformation,the grey relational method was used to analyze this relationship.Through long-term monitoring of the vertical deformation data of typical road sections,the vertical deformation law of the pavement surface and its deformation characteristics under the action of temperature field are analyzed.Parameters such as vertical relative deformation,vertical relative deformation rate and vertical differential deformation VDSr were constructed to describe vertical deformation characteristics.Typical distribution characteristics of longitudinal fractures and their length and distribution characteristics are also described.The grey correlation analysis theory was utilized to analyze the relationship between deformation characteristics of sections,cross sections and monitoring points and longitudinal crack characteristics(length and location).The analysis reveals a linear positive correlation or a high correlation between several indicators.This study can provide a deeper understanding of the occurrence and development mechanism of longitudinal cracks in asphalt pavement of cold areas,and give references for the research of road engineering structure,materials and distress prevention.

Micro Crack of Aluminum Sheet During Cold Rolling

The micro crack of aluminum sheet during cold rolling lubricated with emulsions is investigated. Experi-ments show that micro cracks occur after cold rolling process and this is attributed to various parameters, for instance, the thin oxide film formed at the sheet surface. The micro crack spacing thus becomes an important parameter which deserves more concerns. The aspect ratio of these micro cracks is then analyzed theoreti-cally, which takes into consideration of the oxide fracture process. The good agreement between the obser-vations and the theoretical predictions validates the analysis. The approach can shed some new lights on the mechanical process of aluminium sheet during cold rolling.

大型往复式压缩机曲轴深度裂纹焊接修复

某企业一台大型往复式压缩机在检修时发现曲轴产生深度裂纹缺陷。对曲轴最危险截面进行强度校核,对曲轴材料焊接工艺进行抗裂性试验,对焊接方法进行比较与工艺分析,最终采用常温下手工氩弧焊的方法来恢复曲轴原有功能。

冷轧带钢渗氮铁锅开裂剥落原因分析及改进措施

在采用某公司生产的厚度为1 mm的XLQ01冷轧带钢制作铁锅的过程中,经渗氮处理后出现开裂问题,铁锅经碰撞后渗氮层易剥落。本研究采用扫描电子显微镜、直读光谱仪、金相显微镜等检测手段对渗氮铁锅样品的断口微观形貌、化学成分、金相组织及原材料的表面粗糙度、化学成分、金相组织、晶粒度进行分析,结果表明,渗氮铁锅开裂剥落的原因主要有以下两个方面:一方面,渗氮开裂样品中存在粗大的原始组织和穿晶分布的针状氮化物,破坏了基体的连续性,增加了表面层脆性及切口敏感性,在外力作用下导致开裂;另一方面,原材料表面粗糙度大,渗氮温度高,渗氮层疏松,在压应力作用下导致渗氮层开裂剥落。本研究针对渗氮铁锅开裂剥落的原因提出了相应的改进措施,有效避免了渗氮铁锅开裂剥落。

某电机齿轮冷挤压裂纹形成机理研究

针对材料为20Cr的某电机齿轮在冷挤压成形时内齿齿顶面上出现的裂纹缺陷,基于DEFORM-3D对其冷挤压过程进行了模拟,研究了其裂纹形成机理。有限元结果表明,内齿的金属流动速度小于中部及下部外齿的流动速度,内齿齿顶面上齿根处的金属流动速度最小,此处流动最不均匀,易产生应力集中;对齿面的最大主应力及损伤分布进行了分析,得出在内齿齿顶面上,中部及距离下端面1 mm左右的位置应力集中最明显,拉应力较大且大于材料抗拉强度,损伤值也较大且大于临界损伤值,会产生裂纹,与实际情况相符合。通过改变凹模入模角来控制成形缺陷情况,当凹模入模角为23°时,齿根处拉应力下降,损伤值减小,投入生产后次品率从原本的50%降为1%。

孔挤压强化对GH4169孔结构高温疲劳裂纹扩展行为影响研究

为探究孔挤压强化对镍基高温合金GH4169孔结构疲劳裂纹扩展行为的影响规律,针对孔挤压强化后螺栓孔特征模拟件开展残余应力松弛及疲劳裂纹扩展试验。结果表明,经热松弛稳定后,孔边依旧可以保持至少400 MPa的残余压应力水平,且孔壁表面残余应力松弛幅度高于内部;孔挤压强化后疲劳裂纹扩展速率降低一个数量级,随着相对挤压量增加,疲劳裂纹扩展速率降低幅度增大,疲劳裂纹扩展寿命增幅为4~22倍。结合有限元仿真及断口分析,孔挤压强化对疲劳裂纹扩展的影响机制可归结为松弛至稳定后的残余压应力抵消部分外载应力,导致有效应力强度因子范围减小,使得疲劳裂纹扩展速率降低。基于该机制,利用残余应力修正的Walker模型对疲劳裂纹扩展寿命进行预测,误差在1.8倍分散带以内。

超大规格2024铝合金扁锭开裂行为研究

随着航空航天大型结构件尺寸的增大,高强铝合金铸锭的尺寸也要增大,铸锭成型难度也随之增大。通过铸造过程数值模拟研究了铸造速度和刮水器位置对500 mm×2300 mm和600 mm×2500 mm规格2024铝合金扁铸锭温度场及应力场的影响规律。结果表明,铸造速度对液穴深度影响最大,提升铸造速度能够大幅降低铸锭内应力,但是大幅增加了液穴深度,不利于减轻铸锭疏松和热裂;提升刮水器位置可以大幅降低铸锭的应力。提出了降低铸造速度的同时提升刮水器位置的工艺优化方向,该工艺可以制备超大规格2024铝合金扁铸锭。