西门子S7—200 PLC在钛管材感应退火炉控制系统中的应用

采用中频感应加热炉对钛管材进行退火热处理,是稀有金属加工领域一项常用技术和工艺。本文针对钛管材加热用中频感应退火炉的设备特点和工艺要求,介绍了以西门子S7—200系列PLC为核心的退火炉控制系统,论述了其硬件系统构成和应用软件设计。     

Heat Conveyance Mechanism and Applications

The application of heat conveyance is presented under the assumption of low velocity and viscosity, and the factors affecting heat transfer are analyzed. Methods for reducing the flow resistance and increasing the efficiency of integrated heat transfer are presented after the characteristics of the vertical flow field are analyzed. The distributing rules of liquid flowing in the tube and heat transfer are obtained by numerical simulation, which shows that a full tube has the highest integrated heat transfer coefficient when the twisted‐tape insert is ca. 500–600 mm. The analyses indicate that the length of the twisted‐tape insert leads to a wide range of performance, i.e., a higher heat transfer coefficient can be obtained or the floating resistance can be lowered according to the actual working conditions. A higher level of integrated heat transfer coefficient is still maintained under such conditions. The above analyses indicate that the application of heat conveyance could guide the design of new enhanced heat transfer structures.     

多口径钢管涡流探伤系统的研究与设计

该文针对实际生产过程中,钢管口径种类多的情况,研究设计了一种新型涡流探伤系统。该系统实现了自动化控制,操作安全可靠,生产效率高。适合Φ73～Φ340 mm口径钢管探伤工艺,具有广阔的推广应用前景。     

管子管束的内置旋转式超声波定量检测技术

在管子管束的在役检验和检修中,通常采用的电磁方法对缺陷及壁厚减薄不能进行精确定量。介绍了内置旋转式管子及管束超声波检测技术,可对管子内部缺陷及内外壁减薄进行全面检测。定量精度与普通超声波检测一致,满足检测及检修的要求,提高了热交换器管子及管束检测的准确性和可靠性。     

Parametric finite element study of slotted end connections to circular hollow sections

The influence that the shear lag phenomenon may have on the strength of tubular connections has been addressed in design provisions with variable efficiency factors that affect the tube net area. However, an experimental program carried out on gusset plate connections to the ends of circular hollow section (CHS) members has indicated that these provisions may be overly conservative. As part of the experimental program, a total of eight specimens was tested under quasi-static tension and compression loading considering three connection types frequently used in practice. Moreover, results of a parametric analysis undertaken based on finite element models of these connections (where the responses were verified with the test results) showed considerable differences between the calculated connection strength and the predicted capacity by design provisions. In the finite element analysis, a nonlinear time step analysis was performed considering nonlinear material properties and 8-noded solid elements were used throughout the modeling. The gradual propagation of cracks in the material was emulated by definition of a maximum equivalent strain as the failure criterion with the activation of a “death feature” of the elements. The influence of parameters such as: the weld length (L_w), a proposal to use the eccentricity reduced by half the flange-plate thickness and the tube diameter-to-thickness (D/t) ratio have been studied. The analysis results have shown that a gradual transition between several failure modes takes place as the weld length increases. Also, the likelihood of developing the full efficiency of the tube net cross-sectional area, if a minimum ratio of L_w/w=1.0 is used, is illustrated.     

二辊式矫直机辊型及换辊方法的改进

在旧矫直机上将单向双曲线辊型改成双向圆弧辊型后,不仅保证了矫直精度,便利整体换辊,还降低了噪音。     

Static and fatigue design of CHS-to-RHS welded connections using a branch conversion method

This paper evaluates the hypothesis that welded hollow section connections, which have circular hollow section (CHS) branch (or bracing or web) members welded to a rectangular hollow section (RHS) chord member, may be converted into “equivalent” connections whereby the circular branch member is replaced by a square branch member. Although this notion has existed for the static design of such connections, its implementation into design recommendations or specifications has never been checked against existing test data. This is performed herein, using a database of gapped and overlapped CHS-to-RHS N-connection tests undertaken by others, and the suitability of this procedure is examined for both existing and proposed new static design recommendations for RHS welded connections. For fatigue design, no design guidance exists for CHS-to-RHS welded connections. Thus, a database of welded CHS-to-RHS T-connection fatigue tests, undertaken by both the authors and others, under branch axial loading or branch in-plane bending, is used to evaluate the replacement of the circular branch with an equivalent square branch, in the context of contemporary fatigue design procedures. It is shown that, for the connection types examined, this substitution of a circular branch member by an equivalent square branch member is a valid operation, with an adequate level of safety, for both the static and fatigue design of such connections. This indicates that existing design rules for planar RHS-to-RHS welded connections can likely suffice for the unusual case of CHS-to-RHS welded connections.     

Fatigue Behavior of Concrete-Filled Fiber-Reinforced Polymer Tubes

To date, research on concrete-filled fiber-reinforced polymer (FRP) tubes (CFFT) has focused on the effect of static loads, simulated seismic loads, and long-term sustained loads. Dynamic fatigue behavior of CFFTs, on the other hand, has received little or no attention. This paper reports on an experimental study to evaluate damage accumulation, stiffness degradation, fatigue life, and residual bending strength of CFFT beams. A total of eight CFFT beams with four different types of FRP tube were tested under four point bending. Test parameters included reinforcement index, fiber architecture, load range, and end restraints. Fatigue performance of CFFT beams is clearly governed by characteristics of the FRP tube and its three phases of damage growth: matrix cracking, matrix delamination, and fiber rupture. Lower reinforcement index increases stiffness degradation and damage growth, and shortens fatigue life. End restraints, e.g., embedment of FRP tube in adjacent members, promote composite action, arrest slippage of concrete core, and enhance fatigue life of CFFT beams. It is suggested that a maximum load level of 25% of the static capacity be imposed for fatigue design of CFFTs. With proper design, CFFTs may withstand repeated traffic loading necessary for bridge girders.     

On the evaluation of design parameters effects on the heat transfer efficiency of energy piles

In this paper a methodology for comparative evaluation of design alternatives of cast-in-place energy piles (EPs) is presented. The methodology proposes the comparison to be based on the difference between the temperature of fluid in the pipes and the temperature at the axis of the pile, under a constant heat injection rate in a homogeneous infinite concrete - ground solid, for a period that the thermal influence between all the pipes has been developed, while the conductive heat transfer along the pile is not significant. It is proved that the temperature at the axis of an EP does not depend on the number of the pipes, thus behaving as a reference temperature at a given time for an EP of a given diameter. The difference between the mean fluid temperature in the pipes and the temperature at the axis of the pile is analysed in four components. It is proved that only one of these components depends on time, and it is common in all EPs of the same diameter, the other three depending on the basic design parameters of the EPs, i.e. the number of pipes, the type and dimensions of pipes and the heat/flow characteristics in the pipes. EPs with different design parameters can be compared, the comparison based on the, easily calculated, constant in time temperature difference between the fluid and the axis of the pile.