Thermoforming triangular troughs

This analysis for thermoforming triangular troughs focuses on the manufacturing process speed and follows the method of Kershner and Giacomin for thermoforming cones. We distinguish between what happens before and after (free versus constrained forming) the melt touches the prismatic mold. Neither free nor constrained forming yields analytical solutions for the required forming time. Our analysis is restricted to the fabrication of triangular troughs from nearly Newtonian melts, the second simplest relevant problem in commercial thermoforming. The simplest relevant problem, thermoforming cones, yielded analytical solutions for the forming time. Whenever we thermoform straight edges into rigid packaging, the problem of a melt stretching into a triangular trough arises. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

In-mold shrinkage and stress prediction in injection molding

In-mold shrinkage may occur for product parts that solidify under low holding pressure and are not restricted by ribs or flanges. It not only affects the final product dimensions but in addition may have a large effect on the residual stress distribution. A simple elastic model is used to study the effect of in-mold shrinkage on final product dimensions and residual stress distributions. Friction between polymer surface and mold wall as well as deformation of the mold cavity are taken into account. The model uses local values for temperature, pressure, and crystallization, which belong to the standard output of most simulation codes.     

Thermoforming of ordered polypropylenes

Uniaxial molecular ordering of polyolefin billets by a process of roll-drawing produces clear, transparent sheets having greatly increased strength and modulus in the draw direction whereas the strength and modulus in the transverse direction remain essentially unaltered. Such sheets may be laminated together by means of ultrasonic welding, electromagnetic induction heating or simple pressure lamination using adhesive tie layers to produce multiply laminates with controlled biaxial properties. These self-reinforced laminates have mechanical properties which compare favorably with advanced aramid or carbon fiber composites. Conventional thermoforming techniques may be employed to convert these highly ordered sheets into shaped products having potential commercial value. In these investigations examples are presented to illustrate the methods of laminating and thermoforming of ordered polypropylene sheets. Examples are also presented to demonstrate the feasibility of pressure forming of ordered polypropylene laminates into more complex three-dimensional shapes without loss of their mechanical properties. The techniques described in this paper may be applied to other crystalline polymers to create a new spectrum of self-reinforced plastics capable of approaching the limits of performance.     

PET片材热成型技术

介绍目前我国PET片材热成型加工技术中成型设备、加工原理、模具制作、加工工艺，为PET片材加工业的发展及开发应用提供参考。     

Modeling for prediction of restrained shrinkage effect in concrete repair

A general model of autogenous shrinkage caused by chemical reaction (chemical shrinkage) is developed by means of Arrhenius' law and a degree of chemical reaction. Models of tensile creep and relaxation modulus are built based on a viscoelastic, three-element model. Tests of free shrinkage and tensile creep were carried out to determine some coefficients in the models. Two-dimensional FEM analysis based on the models and other constitutions can predict the development of tensile strength and cracking. Three groups of patch-repaired beams were designed for analysis and testing. The prediction from the analysis shows agreement with the test results. The cracking mechanism after repair is discussed.     

Statistical linear regression analysis of prediction models for creep and shrinkage

Several models for the prediction of creep and shrinkage of concrete are compared statistically with test data available in the literature. The models are algebraically transformed into a linearized form and statistical regression is then carried out. Although the BP model performs distinctly better than the ACI and CEB-FIP Models, the scatter is large for all models, due to the difficulty in predicting material parameter values without any tests of the given concrete.     

Assessment and prediction of drying shrinkage cracking in bonded mortar overlays

Restrained drying shrinkage cracking was investigated on composite beams consisting of substrate concrete and bonded mortar overlays, and compared to the performance of the same mortars when subjected to the ring test. Stress development and cracking in the composite specimens were analytically modeled and predicted based on the measurement of relevant time-dependent material properties such as drying shrinkage, elastic modulus, tensile relaxation and tensile strength. Overlay cracking in the composite beams could be very well predicted with the analytical model. The ring test provided a useful qualitative comparison of the cracking performance of the mortars. The duration of curing was found to only have a minor influence on crack development. This was ascribed to the fact that prolonged curing has a beneficial effect on tensile strength at the onset of stress development, but is in the same time not beneficial to the values of tensile relaxation and elastic modulus.     

电冰箱内胆热成型工艺研究

概述了电冰箱内胆的主要成型工艺,探讨了控制内胆壁厚分布的主要影响因素和技巧,并总结了内胆生产过程中常见的质量缺陷及解决方法。     

Thermoforming of liquid crystalline polymer sheets

Liquid crystalline polymer (LCP) extruded sheets were further processed by the conventional thermoforming method. The available processing temperature range was defined through the structural, thermal, and elevated temperature mechanical characterization of the extruded sheet. This temperature range was found for LCP to be quite narrow, in the proximity of the crystal-mesophase transition. The structural changes imposed on the LCP sheet during forming and its thermal stability were investigated using wide angle X-ray diffraction, mainly for the determination of the chain orientation distribution, DSC, and dynamic mechanical analysis. Thermoforming onto a symmetrical male mold was found to enhance the orientation in the extrusion machine direction and even change the preferred orientation in the extrusion transverse direction to orientation along the thermoforming direction. Annealing at the thermoforming temperature range results in a more ordered and thermally stable structure accompanied by just a slight orientation loss.     

Thermoforming of reinforced thermoplastic stiffened structure

For thermoforming of continuous fabric reinforced thermoplastics, fabric shearing is the dominant deformation mode. The maximum shearing angle depends on the textile architecture and it is expressed as a locking angle, i. e., the smallest possible angle between warp and weft yarns. Wrinkling and buckling occur when the locking angle is exceeded or when too high compression stresses are introduced in the fabric during forming. To avoid these undesired effects membrane stresses must be introduced into the fabric, e.g., by using blankholders. In the first part of this paper a new pneumatic clamping device will demonstrate the advantages of easy handling and flexible force variation. The second part deals with a technology to form and join continuous fiber reinforced fabrics in one step: Tailored Blank Technology. This method reduces the manufacturing steps and offers the advantage to produce parts with different thicknesses or to add profiles and inserts to the main sheet. First results about the temperature windows will be discussed for glass fiber reinforced polypropylene.     

热成型过程中的冷却过程分析

建立了热成型冷却过程分析所用的物理模型和数学模型,并给出了速算图。