Bead fusion in polystyrene foams

A quantitative technique has been developed to measure the extent of fusion between expanded beads in molded polystyrene foams. Experiments were conducted with ASTM D638 tensile test specimens that were molded under conditions to produce various levels of bead fusion in the foam. The tensile properties of the foam for various levels of bead fusion were measured according to ASTM D638 standards. The fracture surfaces of the tensile specimens were analysed by quantitative image analysis techniques to measure the degree of bead fusion in the sample. This technique was then used on a commercial pattern to map the variations in bead fusion at numerous locations in the molded part. The results indicate that there is a good correlation between the tensile properties and the measured bead fusion. Significant variations in bead fusion may be present in a single molded part.     

Formulation and Compaction of Nonfracturing Deformable Coated Beads

Abstract

There has been considerable interest in making tablets from spheronized bead rather than through encapsulation. It is obvious that the forces present during compaction may break a coating intended to control drug release. This effect may be moderated by cushioning agents incorporated into the bead formulation or situation between the beads. Our work describes the latter method.     

On crack propagation in the welded polyolefin pipes with and without the presence of weld beads

The main aim of the paper is to study the influence of both material inhomogeneity and weld bead geometry on crack propagation in welded polyolefin pipes. Axially and circumferentially oriented cracks are studied and the stress intensity factors are compared considering different positions of the cracks. Two cases of the welded pipe system are compared, one considering the optimal weld bead geometry and the other one considering the geometry after removing the weld bead once the welding process is finished. In both cases the inhomogeneous distribution of material properties inside the welded region is considered. The results show that the weld might have a negative effect on the lifetime especially when the weld bead is removed. Though the weld bead increases the stress concentration near the notches due to which a circumferential crack may appear the resulting lifetime is still comparable to that of an axial crack propagating in a homogeneous pipe.     

OPTIMIZATION OF WELD BEAD DIMENSIONS IN GTAW OF ALUMINUM-MAGNESIUM ALLOY

The Gas Tungsten Arc Welding (GTAW) process is frequently used in welding of aluminum alloys, because of its possible heat input control. This control can be utilized through a good selection of the process variables, which in turn results in optimizing the bead dimensions. The object of this investigation was to study the effect of TIG process parameters on weld bead dimensions. Suitable combinations of tungsten electrode parameters and process variables can lead to optimum GTAW bead dimensions. With alternative current (AC) polarity, a weld bead may be formed between two 3-mm thick pieces of 5005 aluminum-magnesium alloy sheets. The effect of electrode diameter, vertex angle, and the welding current and speed on the bead dimensions were investigated. Results revealed that the rate of increase of bead width with current increase is greater than that produced by decreasing travel speed, and means that the bead width can be controlled more efficiently by welding current rather than by welding speed. For example, bead width can be reduced by half by increasing the welding travel speed three times, whereas it can be doubled when the current has is doubled. In contrast, bead depth is found to be more sensitive to welding speed rather than to the welding current. One of the important results of the present investigation was that the average heat-affected zone width decreased as the welding current and/or speed increased. On the other hand, it was found that the influences of electrode diameter and apex angle on the bead width were similar to their effects on the arc size. The bead width was found to decrease with an increase in the electrode diameter to a certain extent, and increase slightly with an increase of the apex angle.     

Experimental investigation on the effects of process parameters of GMAW and transient thermal analysis of AISI321 steel

Gas metal arc welding (GMAW) develops an arc by controlling the metal from the wire rod and the input process parameters. The deposited metal forms a weld bead and themechanical properties depend upon the quality of the weld bead. Proper control of the process parameters which affect the bead geometry, the microstructures of the weldments and the mechanical properties like hardness, is necessary. This experimental study aims at developing mathematical models for bead height (HB), bead width (WB) and bead penetration (PB) and investigating the effects of four process parameters
viz: welding voltage, welding speed, wire feed rate and gas flow rate on bead geometry, hardness and microstructure of AISI321 steel with 10 mm thickness. The transient thermal analysis shows temperature and residual stress distributions at different conduction and convection conditions.     

基于 CMT 电弧增材的焊缝成形尺寸规律研究

目的研究焊接参数对焊缝成形尺寸的影响规律。方法基于冷金属过渡技术,采用正交试验方法得到在不同参数组合下焊缝熔宽、余高和第2层增高,通过多元线性回归拟合,建立了焊缝熔宽、余高和第2层增高与焊接参数之间的回归模型。结果影响焊缝熔宽和余高的主要焊接参数是焊接速度,影响焊缝第2层增高的主要焊接参数是送丝速度,而层间温度的变化对熔宽会有显著影响,但是对余高和第2层增高的影响不大,而且焊缝第2层的增高与余高在数值上存在较大的差异,对比预测值和试验值验证了回归模型的准确性。结论通过改变焊接速度可以引起熔宽和余高的显著变化,层间温度对余高和第2层增高不会造成很大影响。     

红珠实验软件的设计与开发

红珠实验是一个重要的质量管理学实验，本文在分析红实验软件的目标和需求基础上，对软件实验系统进行了设计，并原原实验加了人机工程学的反应时测试验。用Delphiclient/ServersSuite开发实现了单机版的实验系统。     

Influence of EPS bead fusion on pattern degradation and casting formation in the lost foam process

The effects of bead fusion in the pattern on foam degradation and on casting formation have been studied. Injection molded ASTM D638 tensile specimens have been used to develop a microscopic technique to quantify the extent of bead fusion in the pattern. The tensile properties of the polymer have been correlated with the measured degree of bead fusion. A variety of experiments have been conducted to highlight the effects of fusion on foam degradation. The flow behavior of a molten aluminum alloy has been studied in patterns with various levels of fusion. The results indicate that the degree of fusion has a significant effect on bead collapse and viscous residue formation in the polymer. The mold fill times generally increase with increasing bead fusion in the pattern. The temperature at the metal front drops more rapidly as the bead fusion increases.     

Effect of the friction coefficient in the discrete element method simulation on media motion in a wet bead mill

In order to provide information on different sample materials to be ground by a bead mill under wet conditions, we have investigated the effect of the friction coefficient in the discrete element method (DEM) simulation on bead motion in the mill. This is also a joint attempt of simulation and experimental works — the former employs the DEM to simulate the bead motion in the mill and the latter is based on the observation of the bead motion in the same mill by a video recorder. Two kinds of sample, gibbsite and limestone, were used for the milling and they were suspended in water at solid concentrations from 2.5 to 10.0 wt%. The bead velocity simulated at different friction coefficients in the DEM was compared with the experimental data and the coefficient classified into two: one is the coefficient between bead and bead, μ_i, and the other between bead and wall, μ_w. The proper μ_i and μ_w are 0.2 and 0.25 for gibbsite and 0.2 and 0.3 for limestone according to the joint work, irrespective of milling conditions.     

空心玻璃微珠含量比对涂料隔热性能的影响

主要研究了自主研制的空心玻璃微珠涂料的隔热性能。通过隔热模型试验，考察了空心玻璃微珠涂料的隔热性能，对比了空心玻璃微珠含量比对涂料隔热性能的影响，并对其隔热机理和含量比的影响原因进行了探讨。指出空心玻璃微珠涂料是一种具有良好隔热性能的涂料，能产生明显的隔热效果，但过高的空心玻璃微珠含量比将对隔热性能产生劣化影响。     

中空玻璃微珠粒度分布分形特征及其与空隙率关系的研究

为研究中空玻璃微珠粒度分布分形特征与空隙率的关系,测量了6种中空玻璃微珠的粒度累积分布,用统计学概念与分形理论分别考察了中空玻璃微珠的粒度分布法则及其分形特征。结果表明:中空玻璃微珠粒度累积频率与相应的上限粒径的对数值有良好的线形关系,粒度符合对数正态分布法则;各中空玻璃微珠的粒度累积频率与粒径与最大粒径比值的双对数值呈线形关系,相关系数在0.95～0.98之间,强的相关表明各中空玻璃微珠的粒度分布的分形结构是客观的;随着中空玻璃微珠粒度分布分形维的增加,其空隙率减少。     

590 MPa级高强钢双面双弧立焊焊缝组织性能

为研究590 MPa级高强钢双面双弧工艺得到的焊接接头组织与性能的关系,采用钨极氩弧焊(TIG)与熔化极气体保护焊(MAG)方法获得成型良好的焊接接头,经过拉伸、冲击、弯曲试验及光学显微镜、扫描电镜、EBSD分析,对590 MPa级高强钢双面双弧立焊打底焊与盖面焊焊接接头的组织及性能进行了研究.结果表明:打底焊缝组织主要为贝氏体,盖面焊缝组织以贝氏体与针状铁素体为主;打底焊缝经历过一次热循环后组织得到一定程度的细化;打底焊缝硬度值与盖面焊缝相近,盖面焊缝热影响区最高硬度值高于打底焊缝热影响区最高硬度;2 mm坡口间隙性能较5 mm坡口间隙有较大提高,2 mm坡口间隙断口以韧窝断裂为主,5 mm坡口间隙断口以解理断裂为主.     

镀银磁性PMMA微球的制备

采用化学镀法制得了表面包覆银层的导电磁性聚甲基丙烯酸甲酯(PMMA)微球。对粗糙度不同的微球进行镀银,研究了银在微球上的沉积机理。表面改性使磁性PMMA微球功能化,具有和银强烈结合的能力,从而得到包覆均匀的导电磁性微球。研究了硝酸银和磁性微球的含量对包覆效果及导电性能的影响,并通过SEM和EDS对镀银磁性微球的表面形貌及组成进行了分析。     

A novel technology to manufacture biodegradable polylactide bead foam products

Bead foaming technology with double crystal melting peak structure has been recognized as a promising method to produce high-performance low-density foams with complex geometries. Polylactide (PLA) bead foaming has been of the great interest of researchers due to its origin from renewal resources and biodegradability. However, due to the PLA’s low melt strength and slow crystallization kinetics, the attempts have been limited to the manufacturing methods used for expanded polystyrene (EPS). In this study, we developed microcellular PLA bead foams with double crystal melting peak structure in a large content using a lab-scale autoclave system followed by molding of the beads. PLA bead foams were produced with expansion ratios and average cell sizes ranging from 6 to 31-fold and 6 to 50 μm, respectively. The high-melting point crystals generated during gas-saturation significantly affected the expansion ratio and cell density of the PLA bead foams by enhancing the PLA’s melt strength and promoting cell nucleation around the crystals. The tensile properties of the molded EPLA bead foams showed that EPLA bead foams with double crystal melting peak can be a promising substitute not only for EPS but also for expanded polypropylene (EPP) bead foams.     

Effects of reinforcement filler and temperature on the stability of β-crystal in glass bead filled polypropylene

The effects of crystallization temperature (T_c), glass bead content and its size on the formation of β-crystal and structural stability of originally formed β-crystal in glass bead filled polypropylene (PP) were examined. The differential scanning calorimetry (DSC) measurements indicated that the amount of β-phase in PP crystals was a function of the crystallization temperature and glass bead content. For a constant crystallization temperature, it was observed that the amount of β-crystal initially increased with increase in glass bead content up to 30 wt.%, and then decreased slightly with further increase in the filler content. From the DSC data, a disorder parameter (S) was derived to define the structural stability of originally formed β-crystals. The structural stability of originally formed β-crystals was enhanced with increase in either the crystallization temperature or the glass bead content. Also, the influence of glass bead size (4–66 μm) on the formation and stability of β-crystals in PP/glass bead blends was studied. Large glass bead particles suppressed the formation and decreased the stability of β-crystals.     

EPS bead fusion effects on fold defect formation in lost foam casting of aluminum alloys

The effects of bead fusion in the polymer pattern on fold defect formation in castings produced by the lost foam process have been investigated. Castings of aluminum alloy 319.1 were produced with commercial patterns that were molded with varying levels of bead fusion. Each casting was broken into over 40 pieces to identify the fold defect on the fracture surface. The results indicate that castings produced with patterns with high bead fusion exhibit a greater number and a larger area of folds than parts obtained by using foams with low bead fusion.     

The effect of glass bead content on the mechanical properties of acrylonitrile/styrene/acrylate copolymer

The influence of glass bead content and the loading rate on the mechanical properties of polyacrylonitrile/styrene acrylate (ASA) copolymer was investigated. For this copolymer, tensile yield strength and work to fracture were significantly reduced as the bead content was increased. Tensile yield strength decreased linearly with increasing glass bead content according to the Leinder equation. It was found that the variation of tensile yield strength with log (loading rate) follows that of Eyring's equation for yielding. The presence of the weldline reduced the tensile yield strength of both unfilled and filled materials. Flexural modulus and flexural strength also varied in a predictable fashion with glass bead concentration. The increase in modulus with glass bead content followed Kerner's equation.Crack growth resistance values of the unfilled ASA and its composites were measured at three loading rates using the generalized locus method. It was found that the resistance to steady crack propagation,J _R, was a sensitive function of glass bead content and loading rate. Within the range of these experiments,J _R decreased with increasing glass bead content and loading rate.     

玻璃微珠改性聚丙烯的熔融、结晶与形态

采用玻璃微珠改性聚丙烯并对复合材料的熔融、结晶行为与形态结构进行了研究.结果表明,玻璃微珠一定程度上起到了异相成核作用,有利于PP的结晶,提高了结晶速率.与单螺杆挤出复合材料相比,双螺杆挤出复合材料的塑化效果较好,玻璃微珠与基体的粘接情况也较好.冲击断面呈现典型的脆性断裂特征,玻璃微珠大量蓄积在冲击断面.而拉伸破坏断面表现出显著的塑性变形,形成大量带状或纤维状形变区域,材料最终的拉伸性能则取决于玻璃微珠与基体粘接和脱粘的综合效果.     

Investigation the parameters for torsion ductility of bead wire

Torsion testing is used to determine the quality of steel wire used for beads in pneumatic tires. However, strain aging (dynamic and static) caused by interstitial carbon and nitrogen atoms bound to mobile dislocations increases yield strength and decreases bead formability. Processing parameters of bead wire, such as line speed, lead bath temperature and wire diameter, were investigated, and theoretical calculations were made to estimate the effect of these parameters on strain aging. Nitrogen concentration was measured in bead wire samples with varying numbers of twists to failure during torsion testing. Surface morphologies of twisted bead wires were examined by scanning electron microscopy. Experimental data showed that torsional properties of bead wire were a function of stress relief temperature on and theoretical calculations showed that line speed and temperature have to be optimized for optimum torsion ductility.     

Predicting of bead undercut defects in high-speed gas metal arc welding (GMAW)

In the gas metal arc welding (GMAW) process, when the welding speed reaches a certain threshold, there will be an onset of weld bead undercut defects which limit the further increase of the welding speed. Establishing a mathematical model for high-speed GMAW to predict the tendency of bead undercuts is of great significance to prevent such defects. Under the action of various forces, the transferred metal from filler wire to the weld pool, and the geometry and dimension of the pool itself decide if the bead undercut occurs or not. The previous model simplified the pool shape too much. In this paper, based on the actual weld pool geometry and dimension calculated from a numerical model, a hydrostatic model for liquid metal surface is used to study the onset of bead undercut defects in the high-speed welding process and the effects of different welding parameters on the bead undercut tendency.