【作者】 戴元坎；

【导师】 周持兴； 俞炜；

【作者基本信息】 上海交通大学 ， 材料学， 2008， 博士

【摘要】 汽车橡胶密封条由EPDM橡胶复合材料通过挤出加工成型。由于橡胶材料的挤出胀大特性,挤出体与挤出口型形状不一致,所以挤出口模设计需要根据所需产品断面修正。目前在生产中口模的设计主要是通过“试差法”不断调试修正来完成,效率低、成本高。如果能够通过计算机模拟橡胶挤出流动状态、预测挤出产品形状并优化设计口模结构,则可以大量节约产品调试成本和时间,这将对汽车橡胶密封件产业的发展具有重要意义。当前在橡胶产品挤出加工计算机模拟领域,公开发表的文献不多,而且多局限于简单形状产品流动状态的局部分析。即使在我公司所接触的世界知名汽车密封条企业,利用计算机模拟方法设计挤出口模也是一大难点,还未完全应用于生产中,出于保密原因,更是没有相关公开文献发表。本文就是在没有多少前人经验可借鉴的背景之下,结合企业需求开展研究。即应用POLYFLOW软件对EPDM橡胶密封条的挤出成型及口模设计进行分析,建立从材料流变性能测试、流变模型选择到挤出过程模拟分析和口型流道设计的方法,通过实际挤出验证,指导生产中口模设计与工艺优化。采用RH7-2双筒毛细管流变仪和Gemini200平板旋转流变仪测试研究了EPDM混炼胶的流变性能。实验表明,在小振幅的动态剪切流场下,EPDM材料的储能模量远大于其损耗模量,说明材料以弹性响应为主,表现为类固体行为。在稳态流动条件下,材料弹性很弱,可以忽略。采用Bird-Carreau粘性模型可很好拟合EPDM60橡胶熔体的稳态剪切流场中得到的流变曲线。通过不同结构橡胶密封条的挤出模拟详细地分析了壁面滑移、牵引速度、流量对挤出状态的影响。分析结果表明:壁面滑移对挤出状态影响很大,口模内壁表面越光洁,就越容易发生壁面滑移;牵引速度越大,挤出断面越小;流量越大,挤出断面越大。若要挤出得到相同大小的断面,流量和牵引速度的调整符合正比的线性关系,这点对实际生产调试具有重要指导意义。虽然PTT粘弹性模型比Bird-Carreau纯粘性模型更符合实际,但弹性引起的变化所占比例较小,所以在实际应用中,针对复杂的计算模型,由于计算方法、软硬件、时间与成本的限制,采用粘性模型更有实际意义。综合上述研究结果,一方面结合流量平衡原理及正向模拟分析,提出了一套可以定量计算口模流道大小、形状及深度的设计方法。另一方面,根据速度重分布原则,结合正向模拟和逆向模拟,提出了一套可以定量计算挤出口模口型形状和大小的设计方法。上述设计方法在实际操作中应用都很方便。此外,通过分析,发现变截面流道结构比单一截面流道结构好,挤出口模的压力小、能耗少。将上述模拟方法用于解决企业的实际问题,取得了重要成果。如在小机头优化设计过程中,得到了速度、压力和流量更为平衡的流道结构;在解决机头焦烧问题过程中,找到了焦烧产生的位置和原因,提出了新的套筒结构;运用逆向设计方法设计的某头道密封条口模成功用于生产中;又如通过流量平衡准则,重新设计了一种新式结构的挤出机头,解决了机头焦烧、压力大、温度分布不均、挤出效率不高等问题,并应用在申雅公司的六号生产线上。这些研究成果说明本课题的研究已经达到了生产应用的阶段,在国内汽车密封条行业开创了在橡胶挤出加工领域应用计算机模拟的新方向。本论文的主要创新点归纳如下:结合CAE模拟技术,提出了一套进行汽车橡胶密封条挤出口模结构设计的数字化分析计算方法,结合CAD/CAM技术,形成了完整的口模结构设计/分析/加工的3C技术平台(CAD/CAE/CAM)。具体内容表现在以下5个方面:1材料模型分析:通过纯粘性模型和粘弹性模型的分析结果和实验验证比较,认为EPDM混炼胶在稳态剪切流场中主要表现为高粘性、低粘弹性。从而为EPDM橡胶的挤出分析应用纯粘性模型提供依据,避免了应用粘弹性模型而带来的大量问题。2工艺分析:通过模拟结构复杂的橡胶密封条的挤出流动状态,详细分析并得到了壁面滑移、流量及挤出牵引速度和断面挤出胀大的关系,对橡胶密封条实际挤出过程中工艺参数的调试具有现实指导意义。3流道设计:通过流量平衡原理和正向分析,提出了口模挤出流道形状、大小和深度的定量设计计算方法。4口型设计:根据速度重分布原则,结合逆向分析、正向分析和口型膨胀分析,提出了一套进行EPDM橡胶密封条挤出口型逆向设计的方法。5实际应用:1)解决机头焦烧问题:分析容易引起胶料焦烧的区域,优化机头结构,从而解决了申雅淮安分公司的橡胶密封条挤出生产线的机头焦烧问题。2)新型机头设计(专利申请准备中):分析熔体的流动状态,优化设计了一种新型的机头结构,在申雅上海公司的6号线上得到了应用,效果反映很好。该新型结构公司正准备申请专利。更多还原

【Abstract】 Auto sealing strip of rubber is produced through extrusion process with composite of EPDM rubber mixture. Extrudate swelling is widely represented in rubber extrusion, which induces deformations in the extruded profile, and requires die corrections to obtain the target product. Until recently, die designing for rubber extrusion has been largely dominated by empirical know-how and repeated trials to improve on the initial designs. But it often leads to non repetitive moulds and results, even high cost and time consuming. If the rubber extrusion and profile forecast and die optimization can be simulated with computer, then trial cost and time consuming can be saved much, and product quality can be improved too, which has important significance to promote the development of industry of Auto rubber sealing . Until present, the opening publications in the field of computer simulation of rubber sealing extrusion were not much, and most of them were limited to the local analysis of melt flowing of simple profile. Even in the world famous companies of Auto sealing systems, to design the extrusion die by simulation are also a big difficulty, which has a far distance to be used practically.In the base of above background, in this project, the extrusion processing and die design of sealing strip of EPDM were studied with Polyflow simulation. A whole analysis method was set up including rubber rheological properties testing, rheological model studying, extrusion simulation, extrusion die designing, and test verification with real rubber profile.The rheological properties of EPDM composites were tested with RH7-2 Capillary Rheometer and Gemini200 Flat-plate Rotational Rheometer. The test results showed that the storing modulus of EPDM composites was far bigger than their loss modulus in dynamical shear flowing field of small vibration amplitude, elasticity is the main response. In the steady flowing, the elasticity of EPDM composite was very weak and can be omitted. The Bird-Carreau viscosity model met the rheological properties in the steady flowing of EPDM composites very well.From the extrusion simulation of several rubber sealing strips, the influence of wall slip, traction velocity and flux to extruding status were analyzed detailedly. The results showed wall slip had big influence to extrudate. Bigger traction velocity induced smaller extrudate, and bigger flux induced bigger extrudate. For the purpose of getting the same extrudate, the adjust of flux and traction velocity accorded with the direct linear relation. Although the simulation result with PTT visco-elastical model was more accordant with the reality than the result with Bidr-Carreau viscosity model, but the elasticity was still weakly. In real application, for the complex profile, because of the limitation of calculational methds, software and hardware, time and cost, it is more reality to use viscosity model for simulation.Synthesizing the above studies, on the one hand, uniting with flux balance principle and direct extrusion simulation, a new way of designing die structure was set up. On the other hand, a new way of inverse designing the extrusion die shape was set up according to the velocity rearrange principle. Moreover, it was found that the adaptive flow channel with variational cross section was better than the straight flow channel with single cross section, because the extrusion pressure of the former was smaller and then saving energy consuming.Important achievements were acquired after the application of the above studies to solve problems in the real production. For example, from solving the vulcanization of EPDM composite inside the extrusion head, the place of vulcanization was found, and then a new flow channel structure was designed. Through the flux balance principle, a new extrusion head was designed to solve the problems of vulcanization, high extrusion pressure, uneven temperature distribution and low efficiency, which was used successfully in the extrusion line-6 of Shanghai Saic-Metzeler Sealing Systems Corporation(4S company). These applications showed that the studying of this project has reached the real application, and start a new phases of CAE simulation applied in rubber extrusion field in domestic rubber seal industry.The innovations of the present research work are listed as follows:With CAE simulation technology, a set of digital designing way of extrusion die of auto rubber seal was brought forward, then uniting CAD/CAM technology, the integrated 3C(CAD/CAE/CAM) system of designing, simulation and manufacturing of extrusion die was set up. The detailed innovations are the follow 5 sides.1 Analysis of rheological model of EPDM compositesFrom the comparison of the simulation results of viscosity model and visco-elasticity model with test result, it is shown that EPDM composites has high viscosity and low elasticity in the steady shear flowing field. Which supplyed the proof of using viscosity model in the EPDM composite extrusion simulation, and avoided problems of using visco-elasticity model.2 Process analysisThrough the simulation of extruding flowing of complex rubber seal, the relationship of wall slip, flux, traction velocity and extrudate swelling was gained, which was useful to instruct the debugging of the extrusion process. 3 Design of flow channel of extrusion dieWith flux balance principle and direct simulation, a new way of designing quantificationally the flow channels’s size, shape and depth was set up.4 Design of extrusion die lipWith velocity rearrange principle, direct simulation, inverse simulation and die lip expansion, a new way of designing quantificationally the extrusion die lip of rubber seal was set up.5 Application.1) Solving the vulcanization inside the extrusion head:Through analyzing the vulcanization area inside the extrusion head, the extrusion head used in 4S company(Huai an Subsidiary) was optimized to solve the vulcanization problem.2) Design of new extrusion head:Through the flux balance principle, a new extrusion head was designed and used in the extrusion line-6 of Shanghai Saic-Metzeler Sealing Systems Corporation(4S company) and acquired good results更多还原