【正文】 Verdu. Photoageing of rigid PVCIV Effects of titanium dioxide. Polymer Degradafion and Stabiliry 1998,61：211216[31] Fethi Kamisli, Cem Turan. A study on usability of magnesium oxide with titanium dioxidein PVC door and window profiles. Journal of Materials Processing Technology 2005,159：40–47[32] ，199836洛陽理工學(xué)院畢業(yè)設(shè)計論文外文資料翻譯 A study on usability of magnesium oxide with titanium dioxide in PVC door and window profiles1. IntroductionPolyvinyl chloride is among the most widely used synthetic organic polymer materials. Plasticized polyvinyl chloride positions are widely encountered as, for instance,vinyl sheet goods and as objects formed from chloride is mercially available in a variety of grades, some of which are suitable for preparing rigid,plasticizerfree positions for extrusion .For plastics, prolonged exposure to the sun’s electromagnetic radiation in the ultraviolet (UV) region can lead to photooxdiation and degradation of physical properties, often manifested by color change and embrittlement. Similarly,the UV ponent of ordinary fluorescent lighting can degrade polymers and many of the additives used with them.The effective UV radiation that does reach the earth’s surface extends from about 290–400 nm. This range happens to include the highest energy ponent UV band, and the segment around 300 nm, which is the most distractive to plastics. Some manmade highenergy radiation sources mercury arc lamps, xenon arcs, carbon arcs, and various sunlamps can emit radiation at wave lengths below 290 nm and these can degrade plastics even more severely than natural sun light. Hence, they are often used for accelerated testing of plastics.The energy content of UV radiation in the 290–400 nm can rupture most of the chemical bonds present in polymer structures. Not all the polymers are equally affected by UV radiation, and some have a degree of resistance, otably polymethyl methacrylates and fluorocarbons. Others, that in their pure forms could be expected to be resistant to UV, are degraded because of contaminants present that act as sites for UV energy absorption.Absorption of radiation energy by polymer produces molecular excitations: if the level of absorbed energy is high enough, it can activate a chemical reaction whereby internal bonds (carbon to carbon, carbon to hydrogen, carbon to halogen, etc.) are broken so that polymer degradation results. PVC is damaged by dehydrochlorination (release of hydrogen chloride), autooxidation and echanochemical chain scission. This degradation is caused by the simultaneous sequence of these reactions.Dehydrochlorination, prevailing reaction during processing,leads to increasing discoloration. In the course of the proceeding degradation the physical properties are also changed in the direction of increasing embrittlement. PVC of ideal constitution should be thermally stable, which was concluded from investigations with model substances. Therefore, it has to be assumed that the damage, articularly the dehydrochlorinations, starts from sites of the macromolecule with labile chlorine–carbon bonds. PVC can be degraded by heat and sun lights. The release of hydrogen chloride, which is the indication of PVC degradation in prolonged exposure to the sun’s electromagnetic radiation in the UV region, is occurred according to the following reactions:The color of PVCbased article is changed from yellow to black according to degrees of the degradation. Once the reaction has started, polymers quickly and progressively experience changes in appearance: surface qualities, gloss, chalking, color, electrical properties, tensile strength and elongation。Gay,LAntonPrinet,G在此，我向給予過我支持和幫助的諸位老師和同學(xué)致以誠摯的謝意。在此，我謹向周思凱老師致以誠摯的謝意和敬意。周老師自設(shè)計初，便定期召開會議，詢問設(shè)計進程，并為我們答疑解惑、指點迷津，幫助我們開拓設(shè)計思路。沒有他們諄諄的教導(dǎo)，就沒有我的今天，非常感謝他們教會我很多的科學(xué)知識，以及為人處世之道。這些問題都需要自己在不斷的實踐過程中去領(lǐng)悟。關(guān)于本次設(shè)計，現(xiàn)從以下幾個方面進行簡要概述：1. 設(shè)計中首先分析了我國窗框異型材的現(xiàn)狀和發(fā)展趨勢，對其中的模具設(shè)計和生產(chǎn)有了初步了解。⑤冷卻水孔的中心距為14～16mm。大平面反向圓弧R=420～500制品壁厚。①，～。根據(jù)生產(chǎn)經(jīng)驗總結(jié)：一般來說，擠出速度越快，型腔橫截面平面應(yīng)越凸翹，相應(yīng)外形尺寸要越大；制品壁越厚，型腔的橫截面應(yīng)越凸翹，相應(yīng)外形尺寸要越大，反之亦然；定型模越長，其型腔的橫截面平面越平坦，尺寸越小，反之亦然；冷卻定型水箱無真空負壓時，則定型模型腔尺寸應(yīng)大，橫截面平面越凸翹，反之亦然。 3. 定型模上型板冷卻速率應(yīng)大于下型板。2. 水路應(yīng)盡量靠近定型模型腔，水孔孔壁與型腔距離大于5mm，上下定型板的水孔的中心距應(yīng)大于14mm。1． 根據(jù)型胚所含熱量的分布來布置水路。吸附力要布置均勻，定型模上下兩半真空溝槽要對齊，并要各自相通，但在分型面處盡量與大氣相通。由于進入第一節(jié)定型模時，擠出的型胚仍是粘流態(tài)，易被吸入真空溝槽中，故第一段定型模的前面1～，間距為25～30mm，間距為30～40mm。2. 真空槽設(shè)計算出的數(shù)值需驗證，可按下式驗證：牽引力/真空吸附面積型材的拉伸強度，其結(jié)果必須小于型材的拉伸強度(≥)，否則要調(diào)整真空吸附面積和牽引力。式中：G——型材每米的重量Kg/m1. 真空吸附面積：S=④真空槽(孔)和冷卻水道加工工藝性好。②冷卻水孔分布均勻。v——牽引速度， m/s （按最大值考慮。t——型材最大壁厚，mm L = 40vt2其中： 據(jù)文獻介紹經(jīng)驗公式：制品的壁越厚，形狀越復(fù)雜，要求定型模越長。目前，塑料門窗異型材擠出成型幾乎全部采用真空外定型技術(shù)。所以在定型模中要同時完成冷卻和定型兩個工藝過程，也就同時并列存在著冷卻和定型兩個作業(yè)系統(tǒng)。（2）聯(lián)接螺釘強度的校核 對于將型芯與分流支架板相連接的螺釘，雖然其所承受的僅僅是熔體沿型芯壁流動的黏性剪切力，但由于型芯截面面積一般較窄小，又多內(nèi)筋流道，無法布置大螺釘，所以常常需要進行強度校核。許用應(yīng)力的值得選取可參考有關(guān)的機械工程手冊。另外分流筋的布置還經(jīng)常受到模頭結(jié)構(gòu)空間的限制，很難獲得合理的力學(xué)平衡。 模頭的強度校核擠出機頭設(shè)計中有兩部分的強度是需要校核的。型芯對分流支架板的連接以及型芯鑲件對于型芯的連接，由于截面面積窄小，又多內(nèi)筋流道，對此，考慮多布置小一點的螺釘，重復(fù)安排定位銷釘，以保證整個結(jié)合面密合無縫。模板的鏈接普遍采用圓柱頭內(nèi)六角螺釘，按承受軸向靜載荷的預(yù)緊鏈接要求選用螺釘。由于這種模式，所以保證兩模板之間密合無縫，沒有熔料擠出，對于擠出模頭的品質(zhì)非常重要，否則會因為有熔料的殘留和進一步的降解，干擾正常擠出，并加快模頭的損壞。目前，模頭平直段長度設(shè)計更常采取的做法是將其標(biāo)準(zhǔn)化，由設(shè)計者根據(jù)以往的經(jīng)驗類比選用。尤其對于降低熱敏性的PVCU模塑料的降解風(fēng)險十分有利。本設(shè)計中h=，所以L取值為81mm。因為，聚合物分子松弛雖然是一個較長的過程，而真正對擠出成型過程有影響的一般只是在最初階段。這主要是因為平直流道中的純剪切作用可使聚合物熔體分子松弛，減少前級流道，主要是收縮段流道，分流和變截面等情況產(chǎn)生的粘彈性效應(yīng)的影響。本設(shè)計采用橫向分快法，將整個模腔流道截成幾段，一遍精整工具從每段的兩端觸及流道內(nèi)部加工。 成型段流道設(shè)計模腔成型段流道分為多塊模板來加工，這是因為異型材復(fù)雜結(jié)構(gòu)所形成的細小流道，只有分塊才能進行精整加工，才方便模具調(diào)試時的修正。讓這里不出現(xiàn)流動的死區(qū)和掛料現(xiàn)象是最重要的。根據(jù)分流支架流道在口模圖形上外擴3~5mm，收縮流道長度約10~15mm，所以這里收縮板的厚度設(shè)計為20mm。除了拐角外，是都能夠保證各流動路徑上的壓力損耗相等的。模腔中的外壁流道基本上是型材主體的口模圖形形狀，而分流支架流道只是該型材主體口模圖形基礎(chǔ)上，等距離外擴形成的。模腔流道的設(shè)計就是要在保證各流動路徑上的壓力降相等的前提下，將入口的分流支架流道的截面形狀，改變成出口截面的口模圖形形狀。在分流支架流道之后，是在型芯的外表面與收縮板，預(yù)成型板和口模板的內(nèi)腔表面之間形成的流道，稱為模腔。外壁流道形成于模頭的分流筋和型芯零件的外部。由于內(nèi)部功能塊設(shè)計非常復(fù)雜，常采用經(jīng)驗數(shù)據(jù)，本設(shè)計不做考慮。分流錐的椎的角度在本設(shè)計中設(shè)計成50176。要保證分流錐的迎流面不會出現(xiàn)流動的“死區(qū)”，也不應(yīng)有尖角掛料。如果需要在型芯上設(shè)置內(nèi)筋內(nèi)流道，則要將型芯截出一段作為型芯鑲塊，分別加工，但是型芯的總高度不變。 型芯和分流錐外形設(shè)計型芯和分流錐底部外形與分流支架流道的內(nèi)側(cè)邊界是一致的，都是根據(jù)口模圖形的內(nèi)側(cè)邊界設(shè)計的，其中要去掉準(zhǔn)備作型芯吊錐處理的個別型芯塊和螺釘孔功能塊流道的部分。這樣固定型芯的螺栓和固定型芯鑲塊的分別在型芯的兩端，不會出現(xiàn)位置干涉，所以能夠進行內(nèi)筋內(nèi)流道的設(shè)置。若將型芯設(shè)計成一個整體，那么分割各型芯塊的內(nèi)筋就只能夠采用