發(fā)布時(shí)間：2018-03-05 14:16

  本文選題：HDPE管　切入點(diǎn)：熱熔焊接　出處：《西南石油大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：高密度聚乙烯管(HDPE管)具有適度的剛度、良好的柔性、可靠的連接性能和優(yōu)良的輸送性能,因此比其他塑料管材更適用于做燃?xì)夤�。隨著西氣東輸、城市管網(wǎng)建設(shè)等工程項(xiàng)目的進(jìn)行,聚乙烯燃?xì)夤茉趪?guó)內(nèi)的使用呈快速增長(zhǎng)的趨勢(shì)。燃?xì)廨斔陀酶呙芏染垡蚁┕芤ＷC絕對(duì)的安全可靠,質(zhì)量的控制必須非常嚴(yán)格,而其焊接接頭性能的可靠性對(duì)安全施工及應(yīng)用有著重要的影響。因此本文開展了高密度聚乙烯管熱熔焊接數(shù)值模擬研究,這對(duì)獲得高密度聚乙烯管材焊接接頭性能、改進(jìn)焊接工藝、提高管材的應(yīng)用安全等均十分有益。論文的研究?jī)?nèi)容如下:(1)針對(duì)熱熔焊接工藝特點(diǎn),并參考CJJ63-2008《聚乙烯燃?xì)夤艿拦こ碳夹g(shù)規(guī)程》,通過(guò)ANSYS間接耦合的方法建立高密度聚乙烯管熱熔焊接三維有限元模型。模型中考慮了固液相變潛熱、管件與空氣的對(duì)流換熱以及粘彈性材料的溫度相關(guān)性等問(wèn)題,并將焊接過(guò)程分為加熱階段、切換階段和冷卻階段,其中加熱階段對(duì)比解析解、冷卻階段對(duì)比試驗(yàn),驗(yàn)證了有限元仿真溫度場(chǎng)結(jié)果的準(zhǔn)確性,進(jìn)而研究了焊接過(guò)程應(yīng)力場(chǎng)的分布,本模型能夠較為準(zhǔn)確地模擬出焊接過(guò)程中溫度場(chǎng)及應(yīng)力場(chǎng)的分布。(2)建立了加熱階段的溫度場(chǎng)解析模型,其實(shí)質(zhì)是對(duì)移動(dòng)邊界傳熱問(wèn)題(Nuemann解)的研究,求解建立的數(shù)學(xué)模型,得到液固兩相溫度的分布、沿軸向溫度關(guān)于時(shí)間和位置的分布規(guī)律、加熱時(shí)間與熔融層厚度的關(guān)系。(3)分析了焊接加熱時(shí)間、切換時(shí)間、加熱板溫度等工藝參數(shù)對(duì)溫度場(chǎng)分布及熔融層厚度的影響。熔融層厚度會(huì)隨著加熱板溫度和加熱時(shí)間的增加而增加。要想獲得相同的熔融層厚度,加熱板溫度越高,所需要的時(shí)間越短。切換階段,焊件失去熱源并與空氣發(fā)生對(duì)流換熱,熱量流失嚴(yán)重,因此切換時(shí)間越短越好。(4)溫度場(chǎng)的分析結(jié)果顯示:加熱過(guò)程中由于材料導(dǎo)熱性能較差,溫度由焊接端面向非焊接端面擴(kuò)散較慢,熔融層厚度約為3mm-4mm。冷卻過(guò)程中熔融層厚度逐漸變薄,內(nèi)外表面冷卻速度不同,易使融合面局部產(chǎn)生大量微小縮孔、粘結(jié)強(qiáng)度不夠,焊接接頭品質(zhì)下降。建議在熱熔焊接冷卻階段采取措施使管道內(nèi)外表面降溫速率一致,這對(duì)焊接接頭的品質(zhì)有著重要的影響。(5)應(yīng)力場(chǎng)的分析結(jié)果顯示:加熱過(guò)程中焊接端面受熱膨脹,其膨脹趨勢(shì)受到附近較冷區(qū)域的限制,形成熱壓縮,產(chǎn)生壓應(yīng)力。瞬時(shí)應(yīng)力最大值出現(xiàn)在管道內(nèi)表面距離加熱端5mm-10mm處。由于材料粘彈性的特點(diǎn),在冷卻過(guò)程中,管材邊冷卻邊松弛,最終內(nèi)應(yīng)力松弛完畢,不存在殘余應(yīng)力。分析結(jié)果對(duì)實(shí)際焊接過(guò)程有著重要的指導(dǎo)意義,給焊接工藝人員在制定焊接工藝參數(shù)提供參考依據(jù)。
[Abstract]:HDPE pipe with moderate stiffness, good flexibility, reliable connection performance and excellent transportation performance, so it is more suitable than other plastic pipe to make gas pipe. With the development of urban pipe network construction and other engineering projects, the use of polyethylene gas pipe in China is increasing rapidly. In order to ensure absolute safety and reliability, the quality control of high density polyethylene pipe for gas transmission must be very strict. The reliability of the welded joints has an important effect on the safety construction and application. Therefore, the numerical simulation of the hot melt welding of HDPE pipes is carried out in this paper, which can be used to obtain the welding properties of HDPE pipes. It is very beneficial to improve the welding process and improve the safety of pipe application. The research contents of this paper are as follows: (1) aiming at the characteristics of the hot melt welding process, With reference to CJJ63-2008, the three-dimensional finite element model of heat fusion welding of high density polyethylene pipe is established by ANSYS indirect coupling method. The latent heat of solid-liquid phase transition is considered in the model. The convection heat transfer between pipe fittings and air and the temperature dependence of viscoelastic materials are discussed. The welding process is divided into three stages: heating phase, switching stage and cooling stage, in which the analytical solution is compared in the heating stage and the contrast test is made in the cooling stage. The accuracy of temperature field simulation by finite element method is verified, and the distribution of stress field in welding process is studied. This model can accurately simulate the distribution of temperature field and stress field in welding process. The analytical model of temperature field in heating stage is established. The essence of this model is to study the heat transfer problem of moving boundary and to solve the mathematical model. The distribution of liquid-solid two-phase temperature, the distribution of temperature along axial direction about time and position, and the relationship between heating time and melting layer thickness are obtained. The welding heating time and switching time are analyzed. The influence of process parameters such as heating plate temperature on temperature field distribution and melting layer thickness. The thickness of melting layer increases with the increase of heating plate temperature and heating time. The shorter the time is, the shorter the time is. In the switching stage, the welding piece loses heat source and convection heat transfer with air, so the shorter the switching time is, the better the temperature field is. The results show that the thermal conductivity of the material is poor during the heating process. The temperature diffuses slowly from the welding end face to the non-welded end face, and the thickness of the melt layer is about 3mm-4mm. during the cooling process, the thickness of the melt layer gradually becomes thinner, and the cooling rate of the inner and outer surfaces is different, so it is easy to produce a large number of tiny shrinkage holes in the fusion surface, and the bond strength is not enough. The quality of welded joint is decreased. It is suggested that measures should be taken during the cooling stage of hot melt welding to keep the cooling rate of the inner and outer surfaces of the pipeline consistent. This has an important effect on the quality of welded joints. The results of stress field analysis show that the welding end face is heated to expand during heating, and its expansion trend is limited by the colder region nearby, resulting in thermal compression. The maximum instantaneous stress occurs between 5 mm and 10 mm from the inner surface of the pipe to the heating end. Due to the viscoelastic characteristics of the material, during the cooling process, the cooling edge of the pipe is relaxed and the internal stress is relaxed. There is no residual stress. The analysis results have important guiding significance for the actual welding process, and provide reference for welding technologists in the formulation of welding process parameters.
【學(xué)位授予單位】：西南石油大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TE973.3

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