發(fā)布時(shí)間：2017-12-27 18:22

  本文關(guān)鍵詞：輪胎生產(chǎn)中擠出工藝的實(shí)驗(yàn)研究和教值模擬　出處：《中國科學(xué)技術(shù)大學(xué)》2016年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 輪胎膠料 流變學(xué) 擠出 共擠出 擠出脹大 口模設(shè)計(jì) 有限元方法

【摘要】：擠出是聚合物材料的基本成型工藝之一,子午線輪胎的一些重要半成品部件,例如胎面,便是通過擠出成型的。由于流體彈性的存在,輪胎膠料在離開擠出口模后會(huì)出現(xiàn)明顯的脹大,使得擠出物的截面形狀與口模出口處的截面形狀不同,這樣一來便增加了模具設(shè)計(jì)和工藝控制的難度。擠出工藝分析是輪胎工程界和學(xué)術(shù)界長期關(guān)注的一個(gè)具有挑戰(zhàn)性的應(yīng)用基礎(chǔ)問題,盡管人們對(duì)此已經(jīng)進(jìn)行了長達(dá)幾十年的研究,但至今尚未透徹理解輪胎膠料特殊的流變學(xué)行為,某些復(fù)雜擠出工藝的分析方法也有待完善。在這樣的背景下,本文采用實(shí)驗(yàn)研究和數(shù)值模擬相結(jié)合的方法,開展了一系列的研究工作,試圖針對(duì)輪胎生產(chǎn)中的擠出成型工藝提出一套完整有效的數(shù)值求解策略。利用動(dòng)態(tài)剪切流變儀RPA2000、雙料桶毛細(xì)管流變儀Rosand RH2200和旋轉(zhuǎn)流變儀Physica MCR 301在寬廣的剪切速率(頻率)范圍內(nèi)對(duì)多種典型輪胎膠料進(jìn)行了系統(tǒng)的流變學(xué)測(cè)試,較全面的揭示了膠料的剪切粘度、復(fù)數(shù)粘度、儲(chǔ)能模量和損耗模量等隨剪切速率、振蕩頻率、剪切應(yīng)變和溫度的變化關(guān)系。膠料的粘度會(huì)隨著剪切速率的增加而減小,屬于典型的剪切變稀流體,但在低剪切速率下卻沒有明顯的牛頓粘度平臺(tái)。當(dāng)測(cè)試溫度由80℃上升至100℃時(shí),膠料的粘度會(huì)出現(xiàn)下降,但隨著溫度的進(jìn)一步升高,由溫度變化引起的粘度差異越來越小。顆粒填充會(huì)影響膠料粘彈性行為的線性,硫化體系則不會(huì)。此外,利用Cox-Merz關(guān)系對(duì)穩(wěn)態(tài)和動(dòng)態(tài)粘度數(shù)據(jù)進(jìn)行比較發(fā)現(xiàn),毛細(xì)管流變儀和旋轉(zhuǎn)流變儀測(cè)得的剪切粘度均低于動(dòng)態(tài)剪切流變儀測(cè)得的復(fù)數(shù)粘度。基于流變學(xué)測(cè)試結(jié)果,先后利用Carreau模型和Phan-Thien-Tanner (PTT)模型對(duì)輪胎膠料的流變學(xué)行為進(jìn)行了純粘性和粘彈性表征,并在通過建立毛細(xì)管擠出的有限元模型考察了牛頓流體、剪切變稀流體和粘彈性流體的擠出脹大行為。對(duì)于牛頓流體和剪切變稀流體,輕微的脹大現(xiàn)象來自擠出前后速度場(chǎng)的重新分布,牛頓流體的擠出脹大比為常數(shù),剪切變稀流體的脹大比隨著體積流量的增加逐漸減小。對(duì)于粘彈性流體,擠出脹大現(xiàn)象產(chǎn)生的主要原因是高Weissenberg數(shù)下流體的彈性回復(fù)。粘彈性模型計(jì)算出的擠出脹大現(xiàn)象更為明顯,且脹大比會(huì)隨著體積流量的增加而增加,與實(shí)際相符,說明相比純粘性Carreau模型,粘彈性PTT模型更適合輪胎膠料擠出工藝的數(shù)值模擬。此外,為分析壁面滑移對(duì)毛細(xì)管測(cè)量的影響,建立了毛細(xì)管流變儀的有限元模型。仿真結(jié)果表明,壁面滑移的存在會(huì)使毛細(xì)管流變儀測(cè)得的剪切粘度偏小,從而揭示了實(shí)驗(yàn)中動(dòng)態(tài)和穩(wěn)態(tài)粘度曲線間存在偏差的原因。針對(duì)計(jì)及擠出脹大的共擠出問題的求解,首次提出了一種分步迭代方案,解決了同時(shí)計(jì)算擠出物自由表面和材料交界面變形所存在的困難。結(jié)果顯示,受擠出物脹大和彎曲的影響,擠出物下游的材料交界面形狀與口模出口處的交界面形狀存在明顯差異,表明了計(jì)及擠出脹大段的必要性。利用任意拉格朗日-歐拉(Arbitrary Lagrangian-Eulerian, ALE)方法建立了輪胎胎面單擠出成型和共擠出成型的有限元模型,模擬得到的擠出物截面輪廓和材料交界面形狀均與試驗(yàn)結(jié)果符合良好,只在局部存在一定差異。此外,還利用流體體積(volume of fluid,VOF)方法建立了輪胎胎面單擠出成型的有限元模型,該方法能夠描述胎面擠出的動(dòng)態(tài)過程并計(jì)及傳送帶牽引對(duì)擠出物截面形狀的影響,但對(duì)比ALE方法的計(jì)算結(jié)果發(fā)現(xiàn),在同樣的網(wǎng)格尺度下,VOF方法的計(jì)算精度相對(duì)較差。針對(duì)矩形擠出物建立了口模數(shù)值逆向設(shè)計(jì)的有限元模型,發(fā)現(xiàn)設(shè)計(jì)出口模尺寸會(huì)隨著體積流量的增加而減小,隨著壁面滑移程度的提高而增大。在仿真結(jié)果的基礎(chǔ)上,利用數(shù)控機(jī)床將設(shè)計(jì)出的口模加工成實(shí)物并安裝在擠出機(jī)上進(jìn)行了擠出試驗(yàn),發(fā)現(xiàn)在高體積流量下,擠出物的截面形狀對(duì)擠出速度的變化不敏感。此外,測(cè)試獲得的擠出物輪廓略小于數(shù)值逆向設(shè)計(jì)中的目標(biāo)輪廓。為分析差異產(chǎn)生的原因,建立了正向擠出模型并加大了模具壁面的滑移程度。提高滑移程度后,擠出物的輪廓更加接近測(cè)試結(jié)果,可見在口模的數(shù)值逆向設(shè)計(jì)中,必須選擇合理的滑移模型和參數(shù)才能獲得準(zhǔn)確的模具形狀。最后對(duì)全文工作進(jìn)行了總結(jié),并對(duì)今后的研究工作進(jìn)行了展望。
[Abstract]:Extrusion is one of the basic forming processes of polymer materials. Some important semi-finished parts of radial tire, such as tread, are extruded. Due to the existence of fluid elasticity, the tire rubber will obviously expand after leaving the extrusion die, so that the cross-sectional shape of the extruder is different from the cross-section shape at the outlet of the die, which will increase the difficulty of mold design and process control. The extrusion process analysis is a long-term concern of tire engineering and academia challenging application foundation problems, although people have done research for decades, but has not yet thorough understanding of tire rubber special rheological behavior, some complex extrusion process analysis methods also need to be improved. Under such a background, a series of research work has been carried out by combining experimental research with numerical simulation, aiming at providing a complete and effective numerical solution strategy for extrusion process in tire production. By using dynamic shear rheometer, RPA2000 capillary rheometer Rosand RH2200 and double barrel rotary rheometer Physica MCR 301 in the shear rate (frequency) wide range of various typical tire rubber were systematically rheological tests, comprehensively reveal the glue viscosity, complex viscosity, storage modulus and loss modulus the change of shear rate, oscillation frequency, shear strain and temperature relationship. The viscosity of the rubber decreases with the increase of the shear rate, which belongs to the typical shear thinning fluid. However, there is no obvious Newton viscosity platform at low shear rate. When the test temperature rises from 80 to 100 degrees, the viscosity of the rubber will decrease, but with the further increase of temperature, the viscosity difference caused by temperature will be smaller. The particle filling will affect the linearity of the viscoelastic behavior of the rubber, and the vulcanization system will not. In addition, the relationship between steady state and dynamic viscosity data is compared by using Cox-Merz relationship. It is found that the shear viscosity measured by capillary rheometer and rotational rheometer is lower than that measured by dynamic shear rheometer. The rheological results based on the Carreau model and has Phan-Thien-Tanner (PTT) model of tire rubber rheological behavior of pure viscous and viscoelastic characterization, and the Extrusion Swell Behavior of shear thinning fluid, Newton fluid and viscoelastic fluid was investigated by establishing the finite element model of capillary extrusion. For Newton fluid and shear thinning fluid, the slight swell phenomenon comes from the redistribution of velocity field before and after extrusion, and the expansion ratio of Newton fluid is constant. The dilatancy ratio of shear thinning fluid decreases with the increase of volume flow rate. For viscoelastic fluids, the main cause of the extrusion swell is the elastic recovery of the fluid under high Weissenberg numbers. The extrusion swell phenomenon calculated by viscoelastic model is more obvious, and the expansion ratio will increase with the volume flow rate increasing, which is consistent with the fact. It shows that compared with the pure viscous Carreau model, the viscoelastic PTT model is more suitable for the numerical simulation of tire rubber extrusion process. In addition, in order to analyze the influence of wall slip on capillary measurement, a finite element model of capillary rheometer is established. The simulation results show that the existence of wall slip makes the shear viscosity smaller than that measured by capillary rheometer, which reveals the reason for the deviation between dynamic and steady viscosity curves. For solving the problem of CO extrusion with extrusion swell, a step by step iteration scheme is first proposed to solve the difficulties of simultaneous calculation of the deformation of free surface and material interface. The results show that the shape of the interface between the downstream material and the exit interface of the extrusion die is obviously different from that of the extrudate, which indicates the necessity of considering the extrusion swell section. The use of arbitrary Lagrange Euler (Arbitrary Lagrangian-Eulerian ALE) method to establish the finite element single tire tread extrusion and co extrusion model, simulated extrusion profile and interface shape are in good agreement with the experimental results, there are some differences in local. In addition, the volume of fluid (volume of fluid VOF) method was established for tire tread extrusion finite element model, this method can describe the dynamic process of tread extrusion and traction belt and influence on the extrusion section, but the calculation results of the ALE method found in the same grid the scale and accuracy of the VOF method is relatively poor. A finite element model for the reverse design of the rectangular die is established for the rectangular extrusion. It is found that the size of the design outlet decreases with the increase of volume flow and increases with the increase of the wall slip. On the basis of the simulation results, the dies designed by the NC machine were processed into physical objects and installed on the extruder for extrusion test. It was found that under high volume flow, the cross-sectional shape of the extruders was not sensitive to the change of extrusion speed. In addition, the extrusion profile obtained by the test is slightly smaller than the target contour in the numerical reverse design. In order to analyze the causes of the difference, the forward extrusion model was established and the sliding degree of the die wall was increased. After improving the slip degree, the contour of the extruder is closer to the test result. Therefore, in the numerical reverse design of the die, we must choose a reasonable slip model and parameters to get the accurate die shape. Finally, the full text work is summarized, and the future research work is prospected.
【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：O37

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