Influence of foaming technology on fibre breakage in long fibre-reinforced polypropylene composites parts

It is generally believed that the residual fibre length is one of the most important factors influencing on the mechanical properties of fibre-reinforced polymer matrix composites. In this study, long-glass fibre-reinforced polypropylene (LGFRPP) with initial fibre lengths of 12?mm was prepared and then moulded into parts via conventional injection moulding (CIM) and foamed injection moulding (FIM). The design of experiment (DOE) based on the Taguchi method was first used to determine the optimised processing conditions to increase the residual fibre length of the LGFRPP. The results indicated that foaming conditions have a substantial influence on the residual fibre length of the foamed samples. Based on the DOE, a set of optimised processing condition was selected, and two representative samples of CIM and FIM were carefully investigated using dynamical mechanical analysis, scanning electron microscopy, optical microscopy, etc. The experimental results further showed that the residual fibre length and the mechanical properties of the LGFRPP FIM components were better than those of the CIM components. It was also determined that there is a close relationship between the fibre breakage and the mechanical performance.     

Integrated compounding and injection moulding of short fibre reinforced composites

Abstract

Composites of high density polyethylene (HDPE) and carbon fibre (C fibre) were compounded and moulded into tensile test bars in compounding injection moulding (CIM) equipment that combines a twin-screw extruder and an injection moulding unit. Two HDPE grades exhibiting different rheological behaviours were used as matrices. The mechanical properties of the moulded parts were assessed by both tensile and impact tests. The respective morphologies were characterised by scanning electron microscopy (SEM) and the semicrystalline structures of the matrices investigated by X-ray diffraction. The final fibre length distribution and fibre orientation profiles along the part thickness were also quantified. The composites with lower viscosity exhibit higher stiffness, higher strength and superior impact performance. Both composites exhibit a three layer laminated morphology, featuring two shell zones and a core region. Interfacial interaction is favoured by a lower melt viscosity that enhances the wetting of the fibre surfaces and promotes mechanical interlocking. The composites display a bimodal fibre length distribution that accounts for significant fibre length degradation upon processing. The dimensions of the transversely orientated core differ for the two composites, which is attributed to the dissimilar pseudoplastic behaviour of the two HDPE grades and the different thermal levels of the compounds during injection moulding. Further improvements in mechanical performance are expected through the optimisation of the processing conditions, tailoring of the rheological behaviour of the compound and the use of more adequate mould designs.     

New large-scale production method for C/C-SiC ceramics: Investigating the influence of chopped and nonwoven CF

Carbon fibre reinforced carbon and silicon carbide dual matrix composites are a commercially produced using the liquid silicon infiltration (LSI) process. In comparison to the state of the art LSI process, the first production step—the shaping of the carbon fibre reinforced plastic green body—is realised through thermoset injection moulding. Using this method, the complete process can be automated. Simultaneously, the injection moulding technology allows complex geometries with near net shape in short cycle times of about two to five minutes. Thereby, this large-scale process offers a wide range of shot weights from a few mg up to 100?kg, also in multi-component technology. Also, several manufacturing steps can be omitted. This improves the reproducibility, and working in closed environments improves the employees’ health protection. Further process steps, like pyrolysis and silicon infiltration follow the state of the art. Although, this promising approach significantly shortens the fibres, the defined plastic processing is highly reproducible and generates similar mechanical properties like manual processes, due to the better fibre/matrix interaction in the plastic composite. In addition, continuous fibre preforms can be inserted to fulfil higher requirements.     

Orientation effects during the flow of short-fibre reinforced thermoplastics

A study has been carried out to investigate molecular orientation in injection moulded bars of short glass fibre reinforced polypropylene and polyethylene. For the range of fibre concentrations encountered commercially, the fibres do not appear to have any direct effect on the matrix orientation. As the fibre concentration increases, however, the matrix orientation becomes dominated by the orientation of the fibres. These effects are interpreted in terms of current ideas of the rheology of polymer melts during injection moulding and the crystallization of polymers at fibre surfaces.     

Vegetable fibres in automotive interior components

This paper gives a brief status of the state of the art of the use of plastic/vegetable fibre composite materials for interior car parts and the technologies to realise such parts (injection moulding, low pressure injection moulding, thermoforming, thermocompression and co-injection moulding). The development activity on composite plastic-wood materials to be used in the automotive sector performed by J.C.A. is also presented, in particular the research lines performed on several kinds of vegetable fibres (eucalyptus, jute, flax, kenaf) to be applied on semi-finished products: granules (short vegetable fibre) for injection moulding, and extruded sheets (long and short vegetable fibre) for thermoforming.     

Bastfaserverstärkte,biologisch abbaubare Polyester – Einfluß der Faserverfeinerung durch Dampfdruckaufschluß

A biodegradable copolyester was compounded in a twin-screw extruder with 25 wt.-% hemp fibres and then injection moulded into tensile test bars. Two different types of fibres were used: An exclusively mechanically treated fibre (MEC) and a fibre refined by steam explosion (STE). The mechanical properties of STE fibres are 30% lower than those of MEC fibres, nevertheless the same reinforcing effect was obtained. This is mainly due to the higher aspect ratio of STE and the better fibre distribution in the STE composites. A maximal reinforcement was not achieved, because of a too weak fibre matrix adhesion in combination with an insufficient fibre length caused by fibre damage in the extrusion and injection moulding process.     

Blow moulding of long glass fibre composites

Abstract

Precompounded discrete fibres have long been used as reinforcement in injection moulding particularly with polypropylene and nylon matrixes. Usually the lengths of the fibres in the finished article have been in the range 0·2–1·00 mm and for convenience are labelled short glass fibres. The last 15 years has seen the development of precompounded long glass fibres, having lengths in the finished article of typically an order of magnitude longer than for short glass fibres.

The present paper describes experiments on the blow moulding of long glass fibre reinforced virgin and recycled polymers. The long glass fibre compounds have been made using in house technology, for which the matrix interface conditions are known and can be varied. Bottles of 2 L capacity with integral handles were blown as the primary testpieces for evaluating blowability of these new materials and for investigating the reinforcing structures obtained in the bottle walls. Mechanical properties were evaluated at room temperature before and after recycling and at elevated temperatures up to 100°C, which are particularly relevant to the blow moulding applications envisaged.     

Squeeze film testing of ceramic pastes

Abstract

Equipment is described in which pastes are squeezed out from the region between two parallel circular discs. The force on the upper disc is measured for different fixed approach speeds of the discs. Two disc diameters are used, in conjunction with two ceramic pastes and one model paste. Different surface finishes are used on the discs and the effects of adding glass fibre and alumina fibre to the pastes are examined. Industrial squeezing flows are found in such processes as filtration, pressing, rolling, and injection moulding. A theory for squeezing flow is given which shows that, under certain conditions, a plot of squeezing force against the reciprocal of gap will be a straight line. The conditions are that the shear stress is constant and that the flow is dominated by shear forces. This is shown to occur in many real cases, although the biaxial extension of the bulk material also affects the load. It is shown that, for ceramic pastes, plate velocity has little effect on the force. For all pastes, rougher surfaces increase, and lubrication reduces, the force required to squeeze the paste. Wall slip is shown to occur in some non-lubricated situations. Fibre addition usually increases the stiffness of the pastes, especially for longer, thinner, fibres. In one case, a paste is found to flow more easily when thick, short fibres are used. Rings of coloured paste are used to show that several deformation profiles are possible: bell shaped, triangular, and near parabolic. Tests are shown to be simple to perform and the shear stresses obtained in this geometry found to be higher than those for flow in dies.     

注射成型中的纤维取向

阐述了短纤维增强复合材料在注射成犁中纤维的取向问题。并用MOLDFLOW软件对具体注塑制品的纤维取向进行了模拟．对影响纤维取向的主要工艺参数(速度、压力、温度)进行了必要的分析。     

Evaluation of the moulding process for production of short-fibre-reinforced C/C-SiC composites

For the production of C/C-SiC brake discs via the liquid silicon infiltration method (LSI), the hot pressing process is the state of art technique for the moulding of the CFRP composites. This technique consists of several manual steps which increase production cost. The overall cost can be reduced by implementing injection moulding process.In this paper the influence of the moulding process (hot pressing, injection moulding) on the properties of semi-finished and final products during the production of short-fibre-reinforced C/C-SiC composites by means of the LSI process are examined. The starting polymer is chemically characterised. Carbon-fibre-reinforced plastic (CFRP) composites are fabricated by hot pressing, as well as injection moulding process. The CFRP composites are converted into porous C/C composites by pyrolysis. Liquid silicon is infiltrated to form dense C/C-SiC composites, which are further investigated during the course of this paper. Significant differences in properties of the composites are discussed.     

Study of mouldability in gas-assisted injection moulded fibre-reinforced Nylon parts

Abstract

Investigation of the characteristics of gas penetration in gas-assisted injection moulding (GAIM) of parts plays an important role in the successful application of gas-assisted injection moulding. Although these have been proposed by various investigators, quantitative rules based on well designed experiments on fibre-reinforced plastic materials have not been reported previously. Additions of glass-fibre bring about rather dramatic changes in material viscosity and heat conductivity, etc. In the present paper, spiral tube moulds with uniform diameters of 8 and 10 mm, respectively, and a plate mould of 3 mm thickness with gas channel design of semicircular crosssection were moulded using glass-fibre reinforced Nylon resin. The effects of fibre content, tube diameter, and processing parameters, including gas pressure, delay time, and injection stroke on gas penetration characteristics and mouldability for fibre-reinforced Nylon parts were investigated experimentally. It was found that the coating melt thickness decreases with increasing gas pressure, until the gas pressure reaches a critical value, when the coating melt thickness becomes relatively constant for the spiral tube. Meanwhile, using a longer delay time for gas injection will increase the skin melt thickness. The hollowed core ratio increases with increasing diameter of spiral tube. Alternatively, the hollowed core ratio of GAIM plate and spiral tube parts increases when the content of glass-fibre is increased. However, when the fibre content is over 10 wt-%, it shows less influence on the hollowed core ratio for plate parts. Furthermore, although the area of the moulding window decreases with increasing content of fibre, they all show good mouldability. From these results, one can provide an empirical formula to CAE simulation designers and part/mould designers for GAIM fibre-reinforced Nylon parts to achieve suitable mouldability and accurate CAE simulation.     

Fibre orientation structures and their effect on crack resistance of injection moulded transverse ribbed plate

Abstract

An extensive study of the fibre orientation structures developed in a transverse ribbed plate during injection moulding, and the use of these structures to investigate the effect of local fibre orientation state on crack initiation resistance, is reported. The fibre orientation results for the ribbed plate, measured using large area image analysis system developed at Leeds University, showed that after an initial settling down period, the central core region, where the fibres are aligned perpendicular to the flow direction, decreased in size monotonically, with an associated monotonic increase in the outer shell regions, where the fibres are aligned preferentially along the injection direction. Interestingly, the level of orientation in the two regions remained almost constant: only the proportions of the two regions were found to change with flow length. Across the plate, close to the gate, the central core region was found to have a lens-like shape, while at the other end of the plate the core was thinner and also consistent in thickness across the sample width. The transverse rib was found to cause little disturbance to the fibre orientation of the base plate. The different proportions of the shell and core regions at different locations over the ribbed plate provided an ideal case to test the proposition of Friedrich that the crack resistance of a short fibre reinforced material depends on the number of fibres that are perpendicular to the crack tip. The impact test results gathered in this way confirmed this hypothesis of Friedrich.     

Properties of bio‐based polymer nylon 11 reinforced with short carbon fiber composites

In this work, micro‐composite materials were produced by incorporating 3‐mm long reclaimed short carbon fibers into bio‐based nylon 11 via melt compounding. A systematic fiber length distribution analysis was performed after the masterbatching, compounding and an injection moulding processes using optical microscopy images. It was found that the large majority of the fibers were within the 200–300 μm in length range after the injection moulding process. The mechanical (flexural and tensile), thermo‐mechanical, and creep properties of the injection moulded materials are reported. We found that an enhancement in flexural and Young's modulus of 25% and 14%, respectively, could be attained with 2 wt% carbon fiber loading whilst no significant drawback on the ductility and toughness of the matrix was observed. The creep resistance and recovery of the nylon 11, tested using dynamic mechanical thermal analysis at room temperature and 65°C, was significantly improved by up to 30% and 14%, respectively, after loading with carbon fiber. This work provides an insight into the property improvement of the bio‐based polymer nylon 11 using a small amount of a reclaimed engineered material. POLYM. COMPOS., 36:668–674, 2015. © 2014 Society of Plastics Engineers     

Residual orientation in injection‐moulded plaques of atactic‐polystyrene I: The effect of processing conditions

Injection moulded polymer articles often have residual macromolecular or crystalline orientation which can have a significant impact on the optical and mechanical properties of the moulded article. Small angle neutron scattering (SANS) was used to measure the molecular shape and orientation of deuterated blends of injection moulded polystyrene. For ～1‐mm‐thick mouldings of uniform rectangular cross‐section, the eccentricity in the SANS pattern gave a direct measure of the residual molecular orientation over the length scale ～100–1,500 Å. The residual orientation was found to vary significantly with injection moulding conditions with comparative residual orientation decreasing with decreasing mould fill‐time, and increasing with mould thickness and moulding temperatures. The orientation was found to be a minimum in the centre of the mould and highest near the surface and the average orientation at a particular position in the mould was found to be strongly correlated with the volume of material deposited as a solid skin layer during injection moulding. POLYM. ENG. SCI., 58:1322–1331, 2018. © 2017 Society of Plastics Engineers     

Fire reactions of ceramic and polymer moulding composites

Abstract

Abstract

Low cost ceramic dough moulding compounds/composites (CDMC) are composed of inorganic metal silicates and chopped fibre reinforcements. This paper investigates the fire reactions of these materials under severe thermal and heat conditions. This research is targeted to potential applications in the replacement of glass fibre reinforced polymeric insulation materials such as phenolic composites as engine heat shields which experience high temperature and heat transmission. The materials developed can provide good properties, including heat insulation with high thermal stability for engine drafts, where traditional glass/phenolic composites were used and gave a very short life cycle. This work compares the thermal properties of the glass fibre reinforced phenolic composites and metal silicate composites produced under the same processing conditions. The results show that CDMC possesses significantly better thermal stability and heat resistance in comparison with phenolic moulding composite (phenolic dough moulding composites). The indication was that under the testing condition of heat flux of 75?kW?m^?2 intended for materials used for applications in marine, transport and possibly nuclear waste immobilisation, the integration of the CDMC was kept intact and survived as a high temperature insulation material.     

In process monitoring of polymer batch to batch variation in injection moulding

Abstract

Injection moulding studies are reported, during which in process measurements have been used to monitor batch to batch variation of several production grade polymers. Three materials were studied: a polyamide 6, a polyacetal, and a flexible poly(vinyl chloride), all of which were commercial injection moulding polymers supplied by industrial collaborators. Instrumented high precision electric and servohydraulic moulding machines were used to mould parts in house from a number of different material batches. Moulding conditions were kept constant throughout and several process variables were monitored during injection, including melt pressure, melt temperature, and viscosity index –a specific pressure integral calculated from primary injection. Part weights were measured to provide an indication of part quality. Results showed that in each case, variations between batches produced a measurable effect on part quality. These variations were detected by in process measurements, particularly by viscosity index, which tracked significant changes in part weight. Several ‘problem’batches not identified by the compounder's internal quality checks were detected, and the influence of regrind and a development compound were also clearly identified. No simple relationship between viscosity index and part quality was observed for the limited processing range covered. Overall, the studies show the potential of in process measurements to provide a real time, sensitive indication of process variation.     

高技术陶瓷产品的精密注射成型制备技术的应用与发展

讨论了陶瓷粉末注射成型制备精密陶瓷部件这一新技术及其国内外发展状况。先进陶瓷精密注射成型的科学基础是现代高分子精密注塑理论和现代陶瓷制造技术,它将高分子流变学、陶瓷粉体技术、陶瓷工艺学和金属模具精密制造技术结合在一起。该技术突出的优点有:①可净近成型各种复杂形状的陶瓷零部件,使烧结后的陶瓷产品无需进行机加工或少加工,从而减少昂贵的陶瓷成本;②成型制品具有极高的尺寸精度和表面光洁度;③可实现微成型(Micro Injection Molding),制备μm-mm范围内的微型陶瓷零件;④成型过程机械化和自动化程度高,重复性好,便于规模化低成本生产。该技术已用于陶瓷发动机、通讯产业中光纤连接器插芯(Ferrule)、计算机工业中光盘盒磁盘驱动用陶瓷轴承和生物医学用陶瓷制品等精密陶瓷件的制造。随着微注射成型新技术的发展,微型陶瓷部件将应用于环境要求苛刻、结构复杂的MEMS系统。     

Glass fibre orientation within injection moulded automotive pedal: Simulation and experimental studies

Abstract

Modelling and measurement of the fibre orientation distribution within a reinforced thermoplastic automotive clutch pedal are presented. Products have been manufactured on an injection moulding machine equipped with accurate process monitoring. The fibre orientation distributions at selected points within the pedal were measured using a fully automated, polished section/reflection microscopy image analysis system. Simulation was undertaken using commercial software with a fibre orientation prediction algorithm. The predicted fibre orientation distributions are compared with experimental results in order to assess the accuracy of the software in both thin and thick (～5 mm) sections of the pedal.     

尼龙-11的注射成型技术

介绍了尼龙－１１的注射成型特性，制品与模具的设计、成型设备，成型工艺条件等。     

注射压塑成型工艺

注射压塑成型是在加工压注塑基础上发展的一种先进加工技术,其特点是：可获得较高的流动距熟／壁厚之比,可降低夹昆力和注射压力,加工过程中材料应力较低,有利于模制大型零件。