共查询到18条相似文献,搜索用时 187 毫秒
1.
2.
利用一定质量的聚合物熔体在密封容器内其PVT状态变量符合理想气体PVT状态方程的特点,通过自行设计加工的基于PVT原理的实验装置,得到了基于物理定义的聚合物熔体密度和熔体体积弹性模量的数学表达式,验证了聚合物熔体密度和熔体体积弹性模量在理论上存在的一致性变化的特性;在此基础上由聚合物熔体密度、熔体体积弹性模量和超声波传播声速三者之间相互关系,可以推导出超声波声速与聚合物熔体密度存在单值性的数学表达式,并通过实验验证了聚合物熔体密度与超声波声速存在一一对应性。为超声波技术应用于聚合物熔体密度的在线测量提供理论基础和实验数据。 相似文献
3.
周雅文;何亚东;信春玲;闫宝瑞;李庆春 《中国塑料》2010,24(6):91-96
设计了一套用于在线测量注射成型过程中塑化熔体沿轴向及径向温度分布的温差测量系统,对四根不同结构类型的注射螺杆进行实验分析,研究了通过测量塑化熔体温度均匀性进而评价注射螺杆塑化性能的方法。结果表明,使用某一根螺杆加工PS时,在相同的操作条件下,当塑化熔体的轴向平均温差小于0.45 ℃,径向平均温差小于2 ℃时,此时获得制品的重量重复精度能够达到0.035 %,冲击强度大于10.0 kJ/m2,熔体压力波动小于0.7 MPa,表明此螺杆在温度均匀性方面能够满足PS精密制品的注塑成型要求。 相似文献
4.
5.
提出了成型中聚合物熔体温度和密度的超声在线测量方法,并与其他方法对比验证了超声在线测量方法的正确性。设计并制造了底部不封口的流变模具,搭建了超声信号与温度、压力信号采集平台,采集超声信号后进行分析计算,得到聚合物熔体内超声速度变化曲线,结合压力、温度信号,对注射成型中熔体信息进行计算分析。结果表明,超声速度信号可无损定性反映熔体在型腔内的演化过程;借助于压力信号可迭代计算熔体温度演变曲线,与红外光纤温度传感器测量结果相比误差小于6%,实现了对聚合物熔体温度的有损定量分析;对超声信号在时/频域内分别计算分析,得到声阻抗与声速的变化曲线,进而计算得到熔体密度的演变曲线,与压力-体积-温度(PVT)方法计算得到的结果十分吻合,均方差仅0.040 3 g/cm3,实现了对聚合物熔体密度的无损定量测量。超声测量技术可实现注射成型中聚合物熔体信息的在线测量,在实际生产过程中具有广阔的应用前景。 相似文献
6.
7.
基于统计过程控制和误差分析理论,对注射成型过程的注射质量重复精度的在线测量方法进行了研究,分析样本容量和统计误差算法对注射质量重复精度的在线测量精度的影响,并对结果进行分析比较。分别取样本容量为5、10、15,进行3组实验,对采样周期点依次递推更新,进行在线测试,保证测试方法的实时性和精确性。通过改装设计的实验设备对测试方法和计算方法进行了验证,确定了最佳样本容量为10,最佳算法为标准差算法。结果表明,基于超声波熔体密度在线测量的注射质量重复精度测量方法可以对注射制品质量精度进行有效评价,测试精度达到0.50 %~1.50 %,验证了测量方法的可行性。 相似文献
8.
将聚丙烯与1%的滑石粉混合造粒,使用N2作为物理发泡剂,通过自行搭建的非连续超临界N2注气系统,研究发泡注塑工艺过程中注射行程、注射速度、螺杆转速、熔体温度对制品表面质量、减重和泡孔结构的影响。结果表明:注射行程引起的熔体填充量变化是影响制品减重的首要因素,随着填充量的增加,减重下降明显;高压力降速率能够得到均匀泡孔分布且泡孔密度较高的制品;螺杆转速导致停留时间改变对制品表面质量影响较大;熔体温度影响到发泡剂在聚合物熔体中的溶解,螺杆转速130~150 r/min、熔体温度200℃时,能够得到减重、制品表面质量和泡孔结构俱佳的制品。 相似文献
9.
10.
分级注射能够提高聚合物熔体前沿的流动稳定性,改善制品的成型质量。利用Moldflow为CAE平台,通过模拟喷嘴压力曲线的特性与模腔结构的关系,识别出模腔的分级注射点;结合分级注射点对应的注射量与螺杆注射位置的对应关系,导出一个简化的分级注射参数求解模型,并依据熔体成型束缚条件对方案的可行性进行校核,结果表明该方法切实可行。 相似文献
11.
《Polymer-Plastics Technology and Engineering》2013,52(5):819-832
Injection molded parts are driven down in size and weight especially for portable electronic applications. While gains are achieved via cost reduction and increased portability, thinner parts encounter more difficulty in molding due to the frozen layer problem. To increase moldability in thin wall molding, a rapid thermal response (RTR) mold was investigated. The RTR mold is capable of rapidly raising the surface temperature to the polymer melt temperature prior to the injection stage and then rapidly cooling to the ejection temperature. The resulting filling process is done inside a hot mold cavity and formation of frozen layer is prohibited. Concepts of scalable filling and low-speed filling are discussed in the article to address the benefit of this molding method. Simulation results showed that significant reduction in injection pressure and speed can be achieved in RTR molding. In contrast to the filling behavior in conventional molding, the injection pressure in RTR molding decreases as the injection speed decreases, and therefore, extremely thin parts can be molded at lower injection speeds. Filling lengths of both RTR and conventionally molded polycarbonate samples, with two levels of thickness, under two levels of injection speed were experimentally studied. The experimental results demonstrated the advantage of the new molding method. 相似文献
12.
13.
This study investigates the effects that dynamic melt manipulation based injection molding has on the locally induced molecular orientation and tensile strength of injection molded polystyrene. Melt manipulation refers to a process where the polymer melt is manipulated during molding beyond the extent normally encountered in conventional injection molding. The specific melt manipulation process investigated in this article is vibration assisted injection molding, where a conventional injection molding machine is augmented by oscillating the injection screw (in the axial direction) during the injection and packing phases of the molding cycle. The localized final molecular orientation and morphology that results dictates the resultant product response, and typically improved mechanical properties are observed. Specimens with molecular orientation distributed more uniformly along the gage length typically exhibited higher tensile strength than samples with a gradient of orientation along the gage length. Smaller test specimens machined along the gage length of larger molded specimens showed dramatic tensile strength increase in the regions of higher melt manipulation, further supporting the promise of this novel processing methodology. POLYM. ENG. SCI., 47:1912–1919, 2007. © 2007 Society of Plastics Engineers 相似文献
14.
The wall slip of linear polymer melts under ultrasonic vibration is investigated by correcting the slip mechanism, and melt flow behaviors in ultrasonic‐assisted micro‐injection molding (UμIM) method are discussed. Based on the effect mechanism of ultrasonic vibration on the melt, theoretical models of the critical shear stresses for the onset of weak and strong wall slip during UμIM are established, and the change in rheological properties due to the onset of wall slip under ultrasonic vibration is experimental investigated by a built measurement system. The results show that the onset of weak and strong wall slip of the melt in micro cavity are promoted by ultrasonic vibration, which agree with the built theoretical models, and the melt filling capability in micro cavity is enhanced by reducing apparent viscosity and releasing shear stress of the polymer melt, which improves the molding quality of micro polymer parts via UμIM method. POLYM. ENG. SCI., 59:E7–E13, 2019. © 2018 Society of Plastics Engineers 相似文献
15.
Specimens of two engineerig plastics i.e., poly(ether imide), PEI, and poly(2,6-dimethyl- 1,4-phenylene ether), PPE, were injection molded employing a 40t Van Dorn injection molding machine and industrial practices. The mold and melt temperatures and the injection speed were varied in a limited range which furnished acceptable samples. The density, birefringence, residual stress distributions, flexure and tensile properties, and crack development of the injection molded specimens were studied. Vacuum compression molded samples were also prepared to investigate the role played by the cooling rate in shaping microstructural distributions. The results revealed significant differences in the development of microstructure of the molded specimens of the two resins, which was related to rheology and molding conditions on one hand and to development of cracks and ultimate properties on the other hand. 相似文献
16.
Injection molded optical plastic parts require accurate replication of micro‐scale features. The effects of melt viscosity and molding conditions on replication of microscopic v‐groove features in injection molded parts were examined for PC with different molecular weight. The micro‐scale feature size was a continuous v‐groove with 20 μm in depth and 50 μm in width. For injection molding conditions, melt temperature, mold temperature, injection velocity and holding pressure were varied in three levels. As the result, the mold temperature had significantly affected replication for all polymers with different molecular weight. Additionally, the molding conditions that lower melt viscosity led to improved replication. In the case of polymer with high molecular weight, the viscosity decreased with increasing melt temperature. It has been found that high replication of micro‐scale features could be achieved by higher mold temperature and higher melt temperature even with high viscosity PC. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers 相似文献
17.
This paper reports the study of microcellular injection molding of low-density polyethylene- (LDPE) based composites. The effects of adding nanoclays and polymer additives in LDPE as well as rheological property of materials on the cell morphology, mechanical properties and surface properties of microcellular injection molded LDPE based composites are presented. For the microcellular injection molding process, when 3 wt% of nanoclays are added into LDPE-based polymers, the cell morphology can be significantly improved due to the nucleating effects resulting from the broad interface areas between polymer and nanoclays. Also, the addition of low melt flow LDPE into high melt flow LDPE could achieve smaller and denser bubbles in the polymer matrix than neat high melt flow LDPE. 相似文献
18.
Injection molding of semicrystalline plastics was simulated with the proposed stress‐induced crystallization model. A pseudo‐concentration method was used to track the melt front advancement. Stress relaxation was considered using the WFL model. Simulations were carried out under different processing conditions to investigate the effect of processing parameters on the crystallinity of the final part. The simulation results reproduced most of the experimental results in the literature. Comparison is made between the slow‐crystallizing polymer (PET) and fast‐crystallizing polymer (PP) to demonstrate the effect of stress on the crystallization kinetics during the injection molding process for materials with different crystallization properties. The results show that for fast‐crystallizing plastics, stress has little effect on the final crystallinity in the injection molded parts. 相似文献