挤塑机机头几何形状因子的初步探讨

本文在考虑到现代电线电缆的高速挤出和线芯的拖曳作用影响挤出量时 ,对机头几何形状因子 A、B与线芯直径、模孔尺寸的定量关系进行了探讨 ,并讨论了影响挤出量的因素     

黄/绿色橡皮线挤出机头的设计

<正> 我们设计了两种黄/绿色橡皮线挤出机头,即模口分色机头和环式分式机头。从实际使用情况看,采用环式分色机头的效果较好。本文简要介绍分色机头的结构设计。 1.双色挤出机头的胶料流动原理 (1)模口分色机头:辅色进胶孔通常为圆形胶道,如图1所示。Q_1为主机挤出量,Q_2为辅机挤出量,R为辅色胶道半径,L为辅色进胶孔深度。     

最近共挤出技术的发展

<正> 所谓共挤出技术就是同时多层挤出成形,即利用多台挤出机,使从各台挤出机来的呈塑性流动的材料在同一成形机头的组合模内或模子出口处迭加成多层制品的技术。共挤出技术在电线电缆上除用于色标外,还用于通信电缆和电力电缆中,把物性不同的材料同时多层挤出,如近几年交联聚乙烯电力电缆的双层和三层共挤出成形技术得到广泛应用;通信电缆泡沫聚乙烯绝缘线的双层共挤出成形也由于其物性提高和材料及能源节约而被普遍采用。     

用齿轮泵改善挤塑机的挤出性能

因受进料侧流速和出料侧背压的影响,单螺杆挤塑机的挤出效率很低。而正排量齿轮泵能定量泵送物料,只要改变其转速就可以调节输出量和挤出压力。将齿轮泵安装在挤塑机和机头之间,挤出机就不需产生此模芯区节流阻力更高的背压,只要具有连续塑化、混炼、计量泵送物料的机能即可,此时挤出机的效率就大为提高。分析了齿轮泵-挤出机联合机组的优缺点及其适用场合。     

挤塑机的简易耐用模芯

<正> 在各种聚氯乙烯绝缘电线用挤出模芯中,尤以小规格单根导电线芯的挤出模芯最容易损坏。为延长模芯的使用寿命,湖南冷水滩市电线厂因地制宜地用硬质合金拉丝模作为模芯的出口定径段,与钢材配合焊接成挤压式模芯。自1982年起试用于φ45型挤塑机上,数年来效果甚佳,模芯一直完整无损。与45号钢加工的模芯相比,其使用寿命延长了近百倍。这种模芯的特点是:制作简单,经济耐用,尤其适用于电线电缆中小企业。模芯的制作方法 1.选用外径小、内孔合适的硬质合金拉     

线芯速度对挤塑机挤出量和挤包质量的影响

线缆行业中挤塑机的挤出理论均采用塑料加工行业的挤出理论 ,完全没有考虑内包线芯的拖曳作用对挤出量的影响 ,在高速挤出机上将会带来较大的误差。本文仅对高速挤出机 (带机头 )生产能力和综合工作点作出一些理论分析     

固定对偏模具的改进

我厂连续硫化机原来是用螺钉法校模。这种方法对工艺要求高,如果校模速度缓慢,经常会使机头胶僵热,造成拆模次数频繁,处理不善,机头法兰还会炸裂,严重地影响了连续硫化机的生产连续性。这样,生产上不去,废品还一大堆。面对着这种情况,大家一致认为,必须对机头和校模方法给予改进。于是我们学习西安电线厂的经验,使用固定对心法。开始,导线偏心还严重,后来我们对机头结构、橡皮性能又作了研究,发现橡皮的流动性差,均压情况不理想。我们把橡皮塑性从0.32提高到0.4左右,均压环的孔从12个增扩到16个,从而使偏心情况有所好转,但又出现忽而偏这角,忽而又偏那角的现象,对此,我们分析是:原来的模芯锥角太大(即锥角钝,约80°),橡皮流到均压孔处在模芯与模套间形成回     

8字形自承式市话电缆挤塑护套模具的设计

为提高自承式市话电缆的质量,设计了模芯体与摸芯座及穿线管与摸芯体采用锥面配合、模套与模套座采用过渡配合的挤塑护套组合模具,以及相应的辅助工装。这种模具能保证挤出料流压力均匀,护套厚度一致、平整密实;使用时有一定的互换性,拆装、水平对中方便,不易损坏。所设计的辅助工装,能保证缆芯和吊索在放线时处于同一水平位置,且使两者保持所要求的距离。     

耐高温带状电缆

带状电缆,一类是以聚氯乙烯绝缘排线等为代表的普通带状电缆;另一类是以氟塑料绝缘高温排线等为代表的耐高温带状电缆。介绍了带状电缆的基本种类、性能参数,以及目前的研发生产状况。依据挤管式(改进型)一次挤出成型技术研制YDFR系列高温带状电缆的成功经验,着重介绍了YDFR系列高温带状电缆的基本性能,挤出机机头及模芯、模套的设计,生产工艺控制,以及高温带状电缆的相关技术要点。     

螺杆挤出式毛细管测量聚合物熔体剪切粘度谱

为了准确表征聚合物熔体在挤出加工中,受到螺杆强剪切作用时的流变行为.依据流变学理论,研究了利用螺杆挤出式毛细管测量聚合物熔体剪切粘度的装置和数据处理方法.测试装置由单螺杆干挤出机和可更换模芯的毛细管模具构成.在数据处理中,利用不同长径比的毛细管模芯测得的原始数据,结合三次样条函数方法,完成了Bagley和Rabinow...     

A study of electric stress enhancement. Part 1. Implication in power cable design

The increase in electric stress due to a surface protrusion at the interface between a semiconductive shield and a polymer insulation layer in power cables can lead to localized electron injection into the polymer insulation and result in undesired material degradation. This paper reports the analyses of electric stress enhancement of surface protrusions in several commonly encountered medium- and high-voltage power cable configurations. First, a brief review of the electric stress enhancement theories is presented. Then evaluations using these theories for various power cable configurations are made, and it is shown that theories considering a hyperboloidal protrusion will exhibit more realistic stress enhancement results than the cases based on a spheroidal protrusion. Further examination reveals that, besides the sharpness of a protrusion, thickness of the insulation medium also plays a governing role in the stress enhancement at the interfaces between different dielectric media. Contrary to the conventional wisdom, it is a surprise to observe that a thicker insulation can actually cause higher stress enhancement at a protrusion tip, under a given applied voltage. Because of this, a flatter surface protrusion at a higher voltage setting, which usually has thicker insulation, can result in earlier degradation than a sharper protrusion at a lower voltage, even though sharper extrusions are expected to have higher stress enhancement. As a result, thicker insulation may not always be advantageous in the power cable design for higher voltage applications.     

Aging diagnosis of insulation systems by PD measurements.Extraction of partial discharge features in electrical treeing

The charge height values associated with PD measured during electrical tree inception and growth are processed according to the Weibull distribution. Test arrangements, based on the needle-plane electrode system, consider specimens having either a cavity at the tip or an intimate contact with insulation. It is shown that the Weibull-function parameters have close relation to discharges occurring in cavity and tree channels, and that an indication of inception of electrical trees can be obtained     

空气中电晕放电与绝缘液体中流注放电的测量和分析(英文)

Insulation is one of the most important parts in a high voltage equipment.There are gaseous,liquid and solid insulations which are commonly used.In a high voltage transformer for example the insulating materials are all used.During operation of a high voltage equipment high electric stress may occur.Under extreme condition failure of the insulation may take place.Excessive electric field in air may cause corona discharges while in liquid insulation discharges may take place in the form of streamer.This paper reports experimental results on the corona and streamer discharges in air and silicone oil.The discharges were artificially generated around a needle tip in a needle-plane electrode system with gap length of 4 mm under sinusoidal and triangular voltages.The needle was made of steel with tip radius of 3 μm and curvature angle of 30°.The needle was made by Ogura Jewelry.The discharge pulses were measured using personal-computer based partial discharge(PD)measurement system with sensitivity of better than 0.5 pC.The system is able to measure discharge in time sequential.Phase-resolved analysis of the discharges was done to interpret the physical processes behind the discharges.The experimental results showed that corona discharges took place at negative half cycles.The discharges were concentrated around 270° of phase angle of applied voltage.The discharge magnitude and discharge number of corona clearly dependent on the instantaneous of applied voltage.These were strongly supported by the application of triangular voltage.Streamer discharges occurred at both positive and negative half cycles.The discharges pulses concentrated around the peak of applied voltage at phase angle of 90° and 270°.Experimental results under sinusoidal and triangular voltages revealed that streamer discharge magnitude as well as probability of occurrence was strongly dependent on the instantaneous applied voltage.     

Electric field calculations for needle-plane geometry and space charge in polyethylene

Electric fields in polymeric insulation are calculated with the boundary element method (BEM) in the presence and absence of space charge. A 3-D version of the BEM software is employed to determine the profiles of divergent electric fields produced by metallic and semicon needles embedded in the polymeric insulation. It is shown that the value of the electric field in the insulation decreases rapidly and within 5 /spl mu/m from the tip it is less than 50% of its initial value. The BEM can also provide 3D profiles of the electric field distributions in the presence of space charge.     

用Mason计算针板电极场强大小的适用性分析

在进行XLPE电缆绝缘材料电树枝化试验时,广泛采用针板电极系统,研究了针电极的针尖形状及尖端曲率大小是否满足要求,并采用Mason公式计算针板电极系统最大场强是否适用、是否能正确反映针尖场强实际大小,结果证明试验用针电极尖端形态和尺寸均满足试验设计要求及Mason公式的适用条件,利用Mason计算试验用针板电极最大场强是可行的。     

三元混合式绝缘油与绝缘纸板“液–固”组合体系的沿面闪络特性

油浸式电力变压器中油-纸绝缘体系的"液–固"交界面易发生沿面闪络,导致变压器绝缘失效。为考察新型三元混合式绝缘油对油-纸绝缘体系沿面闪络电压的提升效果,为此以矿物油–纸绝缘为参比,研究了交流电压下三元混合式油–纸绝缘体系的沿面闪络特性,分析了沿面闪络电压、油浸纸板表面损伤、以及沿面闪络后的油中溶解气体特性。结果表明:当针–板电极间距离由5 mm增大至20 mm时,与矿物油–纸绝缘体系相比,三元混合式绝缘油-纸绝缘体系的沿面闪络电压约高10%~20%,主要原因在于三元混合式绝缘油–纸绝缘体系中针电极尖端的电场值较小,且三元混合式绝缘油的击穿性能优于矿物油。经历多次沿面闪络后,三元混合式绝缘油浸渍纸板的表面损伤程度弱于矿物油浸渍纸板,且三元混合式绝缘油中溶解的C2H2及总烃类气体含量低于矿物油。该结果为安全应用三元式混合绝缘油提供了数据支撑。     

高压XLPE电缆击穿的制造因素分析及有效控制

高压电缆尤其是超高压交联聚乙烯(XLPE)电缆在输电运行中一旦被击穿,将对电网造成巨大损害,给国家造成重大损失。同时,企业在生产制造过程中,一旦发生电缆局放值(PC值)超标,甚至耐压测试击穿,给企业造成的经济损失也非常巨大。该文从电击穿理论入手,对高压XLPE电缆的生产制造过程进行了分析研究,找出导致高压击穿及局放值超标的关键要点,如导体毛刺;导体半导电屏蔽带的电导率;模具及流道的磕碰、划伤;材料的洁净和储存;绝缘层中微孔的数量、大小、内应力等。通过对这些容易被忽视,而且又极其重要的生产制造环节进行剖析,并给出控制方法,以达到降低局放值和击穿频率,提高高压XLPE电缆整体品质的目的。     

Development of insulation technology in compact SF6 gas‐filled bushings: Development of compact 800‐kV SF6 gas‐filled bushings

Efforts of designers of gas‐insulated switchgear (GIS) are currently focused on such features as smaller installation area and economical efficiency. Circuit breakers (CB), disconnecting switches (DS), and earthing switches (ES) have been redesigned in more compact configurations. Compactness and light‐weight requirements are applied also to bushings used in GIS. GIS bushings can be divided in three general types: capacitor, gas‐filled, and molded bushings. Requirements of the light weight and the economical efficiency of gas‐filled bushings can be satisfied by improvements in insulation technology. Size reduction can be effectively achieved by moderation of the electric field strength on the outside surface of the hollow insulator in the area of the inner grounded electrode tip. We devised a new inner grounded electrode structure consisting of a cylindrical electrode and a ring electrode supported by column electrodes. This paper describes the effect of reduction of the maximum value of electric field strength on the outside surface of the hollow insulator by a new type of grounded electrode. Then, improvement of insulation performance for electrodes with insulation coating in SF₆ gas is described as the composite insulation technology. Finally, the efficiency of these insulation technologies is described by the basic insulation test results of a prototype compact 800‐kV SF₆ gas‐filled bushing. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(1): 19–27, 2010; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20898     

国产高压XLPE电缆绝缆中允许杂质尺寸的试验研究及方法

电树枝是影响XLPE电缆长期老化性能的重要因素,而确定高压XLPE电缆绝缘层中允许的最大杂质尺寸对于保证其长期老化性能是很重要的。本文利用针电极模拟杂质对从国产220kVXLPE电缆绝缘中所取得的试样进行了相关试验,得到电树枝起始电场强度约为270kV/mm,而杂质尖端最小曲率半径约为10μm。通过计算得到对于220kVXLPE电缆,杂质的最大允许尺寸约为130μm。这一结果与国家标准规定的允许杂质尺寸125μm基本符合,这一试验方法可以用于高压XLPE电缆中允许杂质尺寸的研究。     

500 kV绝缘横担杆塔电气性能分析

随着国家加大超/特高压输电线路的建设力度,对输电线路杆塔的绝缘性能要求也越来越高。结合绝缘杆塔的国内外研究应用现状,提出绝缘杆塔的结构型式;以绝缘横担杆塔为例,参考500 kV单回路酒杯型杆塔,计算了绝缘横担杆塔和普通铁塔的绝缘水平,并在此基础上分析了两者在电气性能上的差异;从减少绝缘子片数和缩短横担长度2个方面分析了其对绝缘杆塔电气性能的影响。研究结果表明：绝缘横担杆塔在工频电压、操作过电压以及雷电过电压下的绝缘裕度都要高于普通杆塔;要实现绝缘杆塔安全性和经济性的统一,可以在减少绝缘子片数的同时适当缩短绝缘横担长度。