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      • Effect of Process Parameters on Porosity in Aluminum Lost Foam Process

        Porosity is a main defect in aluminum alloy castings, which is also thought to be severe in aluminum alloy castings produced by lost foam process due to the pyrolysis of the polystyrene foam pattern during pouring. Fundamental experiments were carried out to evaluate the effect of process parameters such as the melt treatment, the cooling rate and the density of expanded polystyrene (EPS) foam on porosity in A356.2 bar casting. The effect of melt treatment including degassing and refining was investigated. The effect of cooling rate was also evaluated by changing the mold packing material such as the silica sand, the zircon sand and the steel shots. Gas entrapment due to the turbulent metal flow during mold filling in conventional molding process results in porosity. Mold filling sequence in lost foam process is different from that in conventional molding process. The effect of molten metal flow was estimated by comparing the density of the casting by conventional sodium silicate molding with that by lost foam process. Density measurement was conducted to analyze the extent of porosity in the casting. Source of the porosity in lost foam process can be divided into two factors, i.e. turbulence in molten metal flow and entraining residue or gas from the pattern during pouring....

        2020-11-10 09:33:08瀏覽:28 LostfoamprocessmoldpackingmaterialEPSporositymelttreatment

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      • 熱塑性聚烯烴(TPO)防水卷材專用料的研制

        以聚合型TPO樹脂為基礎原料,通過添加阻燃劑、光屏蔽劑、潤滑劑和其它助劑等制備TPO防水卷材專用料.結果表明,當TPO樹脂總用量為70%時,改性料的性能和經濟成本達到較好的平衡.通過改變配方中rPO-AHPO-B添加比例,進一步調節產品的加工性能、力學性能和焊接施工性能.測試結果表明,TPO-B的加入可提高改性料的加工性能、片材的韌性和焊接性能,但強度會隨其用量的增加而降低,當其用量過高時,焊接過程中容易出現變形和出油現象.TPO樹脂中TPO-B用量控制在20%~30%時,產品具有最佳綜合性能.對于北方寒冷地區推薦選用TPO-B用量為30%的柔軟配方,對于南方高溫地區推薦選用TPO-B用量為20%的高強度配方....

        2020-08-11 22:29:03瀏覽:34 熱塑性聚烯烴防水卷材熔體流動速率接縫剝離強度thermoplasticPolyolefinwaterproofingsheetmeltflow

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      • 熔融縮聚合成聚乳酸-聚乙二醇共聚物及其性能研究

        采用羧基封端乳酸預聚物與聚乙二醇熔融縮聚合成了聚乳酸-聚乙二醇共聚物,并用GPC、FTIR、1H-NMR等方法表征了預聚物與共聚物,結果表明,預聚物的羧基封端率高于95%,預聚物的相對分子質量可由投料比(物質的量比)控制.熱分析結果表明,共聚物中聚乳酸鏈段呈無規分布,而聚乙二醇鏈段能夠形成結晶微區.力學性能測試結果表明,共聚物的斷裂伸長率達371%,有望在聚乳酸韌性改性方面得到應用....

        2020-07-10 14:39:05瀏覽:43 聚乳酸生物可降解聚乙二醇熔融縮聚poly(L-lacticacid)biodegradablepoly(ethyleneglycol)melt

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      • 聚乙二醇改性聚乳酸的合成與性能表征

        以外消旋乳酸(D,L-LA)和不同數均分子量(M_n)的聚乙二醇(PEG)為原料,通過熔融縮聚法,合成了系列聚乳酸聚乙二醇(PLEG).最佳工藝條件為:以(Sn(Oct)_2)為催化劑,m(Sn(Oct)_2)為0.8%,n(PEG):n(D,L-LA)=1:600,聚合溫度170℃,壓力0.096MPa條件下,反應8h.用特性粘度測試、FT-IR、XRD、接觸角等對其進行表征,實驗結果表明系列PLEG中PLEG-800接觸角為63°,表明其親水性能最好;PEG-800和乳酸共聚合成的PLEG的粘均分子量最大,可達48997,與PDLLA相比,結晶度有較大提高,親水性得到改善....

        2020-07-10 14:39:05瀏覽:32 聚乳酸熔融縮聚聚乳酸-聚乙二醇親水性表征polylacticacidmeltpolycondensation

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