Advanced Materials Research Vols. 189-193

Abstract: This paper analyzed continuous extrusion cladding process through 3D FE simulation in the non-steady state. The model is used to predict the metal flow characteristics during the entire process. According to the metal flow characteristic, continuous extrusion cladding process is classified into feeding, welding, filling and forming stages. The modeling results predict temperature, stress, strain rate and velocity fields. When the metal flows through the die bearing, the velocity distribution is non-uniformity, because of the non-symmetrical structure and the difference in temperature of the upper and bottom portion of the die cavity. And FEM results also show that the velocity distribution is sensitive to the change in mandrel radius. Increasing the mandrel radius can relatively improve the metal flow velocity in the upper cavity and decrease the velocity in the bottom cavity. There is an optimum mandrel radius value that makes metal flow most uniform. These also provide the theoretical basis for optimizing the technology and the die design.

Abstract: An understanding of flow behavior of polymer melts through a slit die is extremely important for optimizing die design. In this paper numerical simulations have been undertaken for the flow of linear low-density polyethylene through Coat-hanger sheet dies. A new finite element method is proposed to simulate the flow in slit channel using Wagner constitutive model. This is one kind of finite element semi-analytical method by which the velocity distributions in thickness direction is approach by Fourier series. Numerical results of volumetric flow and pressure in coat-hanger dies are given to compare to the three-dimensional simulation using the finite element method. It appears that numerical solutions are as accurate as the complete 3D calculations and the computing time can be saved.

Abstract: The effect of wall conditions on the co-rotating parallel twin-screw extrusion of rigid polyvinyl chloride (RPVC) is studied. The relationship between the shear stress at the screw wall and the slip velocity of the flowing melt obeys Navier’s linear law. At zero pressure difference between the entrance and exit of the melting section of twin-screw extruder, the volumetric flow rate and 3D isothermal flow fields of RPVC are calculated under different wall slip conditions in the metering section of the twin-screw extruder by using the evolution technique in POLYFLOW. The results show that when the slip coefficient is smaller than 10⁴Pa*s/m , the volumetric flow rate of the melt is constant, corresponding to the full slip condition. When the slip coefficient is larger than 10⁴Pa*s/m , with the slip coefficient decreasing, the volumetric flow rate and viscosity increase, but the gradients of velocity, pressure, and shear rate decrease. The residual stress of the product is thus reduced. Therefore, increasing wall slip is good for the stability of polymer extrusion and the product quality. The dispersive and the distributive mixing of the twin-screw extruder under full slip and no slip conditions are also studied. Results show that the mixing performance under no-slip condition is better than under full-slip condition, but slip at the wall is good for the extrusion of heat-sensitive materials.

Abstract: Aiming at 5/12 full-automatic numerical control (NC) bending hoop machine, the paper analyzed the elastic-plastic bending deformation with the knowledge of elastic-plastic bending principle, theoretically mechanics and spring-back, and deduced the relationship of bending moment and curvature ratio, and built the mathematical model between bending hoop turntable’s rotation angle and stirrups angle considering the spring-back deformation. Then the different spring-back angles under two types of stirrups diameter, Φ=8 mm and Φ=10 mm, are measured. The mathematical model of turntable’s rotation angle and stirrup’s angle for 5/12 automatic NC bending hoop machine is modified according to the analysis of bending test data.

Abstract: In this paper, a reasonable 3D FE model for power spinning of ellipsoidal heads with variable thickness has been established under ABAQUS/Explicit and validated. Then the variation of stress, strain and wall thickness during the process are obtained. Furthermore, the influence of the springback on stress, strain and wall thickness are gained with ABAQUS/Standard. The results show the following: (1) In the beginning, large stress, large strain and the thinning zone of wall thickness localize at the small contact zone below the roller; Then the zone extends into a ring and moves towards the position behind the roller; In the end, the ring transfers to the contact zone below the roller again and becomes uneven. The thinning zone is gradually impelled along the generatrix direction, and wall thickness is getting smaller and smaller. (2) The distribution of stress becomes more even after the springback, while the springback has little effect on the distribution of strain and wall thickness.

Abstract: Directing an important kind of joints of the machine tool—roller linear guide, the force analysis of the contact deformation zone of it was presented. In this study, a new structure calculation model was applied to calculate the deformation of the contact area of the roller linear guide, and the contact zone deformation model was built. The abrasion for roller diameter at the middle and both ends was obtained by running test at last. The research results can provide reference to corresponding roller design and service life evaluation.

Abstract: A new type pre-oxidization furnace used for producing PAN-based carbon fiber has been developed. Practical operations showed that the furnace possesses characteristics of reasoanable design, higher temperature controlling precision and high hot efficiency. It is an ideal pre-oxidization furnace.

Abstract: It is usually a time-consuming process to set up three-dimensinal(3D) model of mechanical components with complex surface. In order to solve the problem, this paper adopts consumer cameras and the technique of digital close range photogrammetry ( DCRP ) to establish 3D model, and export the data to 3D mechanical design software (SolidWorks) for further simulation and reconstruction. This method has been proved very effective in practise.

Abstract: Based on the method of polychromatic speckle autocorrelation measuring surface roughness, this paper discussed the influence of the combination of different wavelengths on speckle patterns and speckle elongation ratio when rough surface and polychromatic speckle patterns were simulated. The results show that the smaller the difference of wavelengths combination is, the further peak of the speckle elongation ratio is from the speckle field centre, for the same surface roughness. And the wider area of speckle elongation effects extends. Therefore, influence of combination of wavelengths on measurement precision should be taken into consideration during measuring process.

Abstract: The bearing load is very large when the hydraulic pressure derrick suspends cargo. The hydraulic pressure derrick is a very important component which transfers cargo load to hull. The method of optimization theory based on dual method was transplanted to optimize the hydraulic pressure derrick structure and the optimizing model of the hydraulic pressure derrick was established. The hydraulic pressure derrick structure was optimized under four load cases. The numerical results show that the structure strength and stability of hydraulic pressure derrick are fit.