塑料成型工藝基礎知識(三)

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所屬分類:加工指南 塑料文章

si、juhewudejiejing

qianmianyijingjieshaoguo,anjiejingxingkehuafenweiyoujiejingqingxianghefeijiejingqingxiangjuhewu。danshi,juyoujiejingqingxiangjuhewujikeyishijingxingdeyekeyishifeijingxingde。tongguoduijiejingshengchengguochengyuzuzhidefenxiyanjiubiaoming,juhewujiejingxingtaishizhedielianjiegou:xianyoufenzizuchenglianshu,youlianshuzhediecheng“dai”;zaiyou“dai”zhongdiechengjingpian;zuihoujingpianyujingpianzhijianduiqichengdadejingti。

weilenongqingjiejingxingjuhewudetexingjiqijiejingjili,jiangyouguanwentifenshuruxia。

(yi)jiejingxingjuhewudezhuyaotexing

  1. 1. 結晶和非結晶的聚合物在物理性能上的差別

juhewujiejingzhihou,qimiduyaozengjia。lirujutansuanzhizaiwanquanjiejingzhihoudexiangduimidushi1. 33,erwanquanmeiyoujiejingshidexiangduimiduwei1. 20。jiejingxingjuhewuyouyumidudezengda,qiemidubujun,dangguangxiantouguoshichanshengzheshexianxiang,jiejingyueduo,zhesheyueyanzhong,guangxianbunengzhijietongguo,suoyitoumingxing、touguangxingjiaocha。feijiejingjuhewu,rujubenyixi、youjiboli、jufengdeng,yinweimidujunyun,dangguangxiantongguoshirutongtongguoshuiyiyangshitoumingde。congwaiguanpanbiejiejinghefeijiejingdejuhewushiguanchajuhewuhoubizhipindetoumingxing,butoumingdehuobantoumingdeshijiejingxingde,toumingdeshifeijiejingxingde。dangranyeyouliwai,rulizijuhewushishujiejingxingde,danquegaodutouming;absshishufeijiejingxingdequebingbutouming。

  1. 結晶型聚合物的物理機械性能

聚合物是否結晶對它的物理機械性能有很大的影響,而且結晶程度不同(所謂結晶度是指在結晶聚合物中晶相部分所占的質量百分比)其物理機械性能有較大的差別,彎曲強度、拉伸強度、硬度、剛度、耐磨性、耐化學腐蝕性及電性能等,結晶型的優于非結晶型的,結晶度高的又優于結晶度低的。反之,結晶度小的聚合物柔軟性和耐折性較好,伸長率高,沖擊強度增大。在成型加工中,往往利用結晶機理,控制成型條件來生產特定性能的制品。

  1. 結晶和非結晶聚合物的溫度-形變曲線的比較

由于結晶聚合物中有非結晶部分,因此在溫度形變曲線上也能反映出玻璃化溫度Tg到熔點Tm之間形變量很小很小;可是進入熔限(從熔融開始至完全熔化)以后,如果分子量不太大,立即成流動狀態(Tm?> Tf );如果分子量比較大就會出現Tm到Tf之間的高彈態,隨著溫度進一步提高到黏流溫度Tf才有可能發生流動(Tm?< Tf)。圖 1-1適用于絕大多數聚合物。從加工角度來看,如果分子量為M1的結晶聚合物其強度已足夠應用的話,就不選用較高分子量M2的聚合物,這樣加工起來方便得多。因為要使分子量為M2的聚合物流動,在熔點以上還要繼續升溫,使加工溫度升高,而且在極高的溫度下出現高彈態,如果不慎將它過冷下來存在于制品中,制品將會產生內應力,出現翹曲、變形、開裂。

塑料成型工藝基礎知識(三)

圖1-1結晶和非結晶塑料的溫度-形變曲線

虛線表示非結晶型塑料;實線表示結晶型塑料;M為分子量,M2 > M1

(er)juhewudejiejingtiaojian

juhewukeyijiejing,danbingbushisuoyoujuhewudounengjiejing,yebingbushizairenheqingkuangxiadoukeyijiejing。jiujingshenmeyangdejuhewukeyijiejingni?fenxijuhewunengfoujiejing,zhuyaoqujueyuqibenshenjiegou。tongguoshijianfenxidezhixialieyinsushiyouliyujiejingde。

  1. 高分子鏈的規整性大,結構愈簡單,就愈容易結晶

xiangjuyixi、juyixichun、jusifuyixideng,tamendefenziliandoubijiaojiandan,bijiaoguizheng,yejiushishuofenzilianchengbijiaozhengqidepailie,zhexiejuhewutongchangdoushijiejingde。yourujulvyixishifeijiejingxingde,keshijupianerlvyixizeshijiejingxingde。zheshiyouyuqianzhedelvyuanzizaizhulianzhong,kongjianpailiezaluanwuzhang,dadajiangdileliandeguizhengxing,erhouzhezhulianshangdelianggelvyuanzizaikongjianfangweiguding,bushizaluanwuzhangde,lianhenguizheng,yiyupaichengyidingdejingge,gurongyijiejing。zaiyibanqingkuangxia,jupianerlvyixichenggaodujiejing,jixieqiangduyegao。

  1. 高分子鏈上取代基的空間位阻小,而且鏈間分子作用力大,有利于結晶

lirujuyixichunnenggouhenhaodijiejing,zheshiyouyuqudaijibijiaoxiao,kongjianweizuxiaoyingbuxianzhu,youliyujiejing。danshijubenyixi、youjibolizebunengjiejing,zheshiyinweiqudaijijiaoda,youyukongjianweizulinjindefenzilianhennankaojin,tongshilianshangdecejibuduicheng,fangailefenzizuchengyidingdejiejingxulie,gubunengjiejing。dangranruguoshidingxiangjubenyixi、dingxiangyoujiboli,youyukongjianpailieguizheng,zezhaoyangkeyijiejing。fenzijianzuoyonglida, shilianyiyujiejinbingzuoguizhengdepailie,yinciyiyujiejing。lirujuduibenerjiasuanyierzhi。

  1. 有利的外界條件促使結晶

溫度的影響:結晶過程是高分子鏈由無規則的排列轉變為有規則排列的過程,這一排列方式的改變,只有在鏈段可以活動的情況下才能完成,而鏈段的運動也只有在聚合物玻璃化溫度Tg以上才發生,所以提供聚合物結晶的溫度一定是高于它的Tg

lengquesududeyingxiang:juhewurongtijisulengquechenggutishi,qilianduanlaibujipailiechengyouxudezhuangtaixingchengjiejingsuoxuyaodeweizhi,cishihuanbaoliuzhuwuxudezhuangtai,zheyangxingchengdejuhewushifeijiejingdejiwudingxingde。lirupingmofajichujuduibenerjiasuanyierchunzhibomoshi,zai50-60℃ deshuixiangzhonghuanmanlengque,cainengdedaojiejingdujiaogaodebomo;youliruchuisujubingxibomo,caiyongjilengfangshilengque,jiukededaojiaogaotoumingdudefeijiejingxingbaozhuangbomo。

lashendeyingxiang:zailashenqingkuangxia,fenzilianhuiyanwailifangxianganyidingguilvzhengqierjinmidipailie,youzhuyugaofenziliandeyouxu。yinci,lashenyeshiyouliyujiejingde。lirubianzhibudebiansijichu,jiucaiyonglelashengongyi,shizhichengweilashenqiangdugao、jiejingxingdebiansi。yishangsuoshudelashenshizhiwailifangxiangyufenzilianpailiefangxiangshiyizhide,youzhuyujiejing,shirongdiantigao;lashenfangxiangyufenzilianchuizhishi,zebuliyujiejing,shirongdianjiangdi。

(san)juhewudejiejingtedian

  1. 晶區與非晶區的共存體系

juhewujiegoudejibendanyuanjuyoushuangzhongxing,takeyizhenggedafenzilianpairujingge,yekeyishilianduanpairujingge,juedaduoshujiejingjuhewudoushiyilianduanzhongpaiduiqichengjingti。ranerlianduanyundongdexingshijiqifuza,tadeyundongyoubunengbushoudafenzichangliandeqianzhi,youyouyujuhewufenzidaiyouzhilianhuoduanjidefuzaxing,yaoxiangqudewanquanjingxingpailiedejingtishifenkunnan。yincijuhewudejiejingshibuwanquande、bujunyunde,budanyoujiejingbufen,erqieyoufeijiejingbufen,shijingquhefeijingqugongcundetixi。

  1. 結晶聚合物熔點是一個溫度范圍(又稱熔限)

difenzijingtironghuayouyidingderongdian。lirubingderongdianwei0℃ ,zaironghuaguochengzhong,suiranwaijiedewendukebi0℃ gaohenduo,danshibingzaironghuazhiqian,tadewendubingbushenggao。zhebiaoming,bingderonghuashizaiyigegudingdewenduxiafashengde。danshijiejingjuhewuderonghuabingbushizaimouyigegudingdewenduxiafashengde,ershibianronghuabianshenggaowendu,congronghuakaishidaoronghuajieshu,wendukeyibianhuayiershidu,shenzhigengduo。zhejiushishuo,jiejingjuhewuderongdianyouyigebijiaokuandefanwei。renmenguidingjingtiquanburonghuashidewendu,chengweirongxiandeshangxian。

jiejingjuhewuderongdianzhisuoyishiyigewendufanwei,qiyuanyinzaiyujiejingjuhewushijingquhefeijingqugongcundetixi,erjiejingbufenhefeijiejingbufendejiegouyouyouhendachayi,suoyitamendejiaojiechubiranyouneiyinglicunzai,shijiejingderonghuabianderongyile,zhejiuyaoshirongdianyousuoxiajiang。jiangdidechengduyuneiyinglidedaxiaoyouguan,neiyingliyueda,rongdianxiajiangdeyuelihai;fanzhi,neiyingliyuexiao,rongdianxiajiangbumingxian。suoyitongyikuaijuhewushangderongdianxiajiangchengduyebuyiyang,yincitaderonghuaxuyaoyigewendufanwei。

qici,huanyujiejingjuhewujiegoulishiyouguan。ruguojiejingwenduyuedi,lengquesuduyuekuai,neimejiejingjiegouyuebuwanshan,cishijuhewuronghuashidewendufanweijiujiaokuan。zheshiyinweidangjuhewuzaibijiaodidewenduxiajiejing,erqielengquesudukuaishi,fenziliandehuodongxingjiaocha,laibujichongfendiaozhengweizhi,shineibuchanshengjiaodadeyingli,erqiefenbubujunyun,yinglidadedifang,shouredeshihouzaijiaodidewenduxiabeipohuai—ronghua,eryinglixiaodedifang,yaozaijiaogaodewenduxiacaihuibeipohuai,suoyixianshichujiaogaoderongxian。fanzhi,ruguozaijiaogaodewenduxiajiejing,erqielengquesudujiaomanshi,liandehuodongxinghao,youliyuliandepailie,suoyineiyinglifenbubujundexianxiangbuneimeyanzhong,gurongdianjiaogao,erqierongxianjiaozhai。zaishijianzhongwangwangcaiyong“tuihuo”defangfajianxiaoneiyingli,shironghuawendufanweisuoxiao,shizhishangrongdianyousuotigao。

  1. 拉伸對結晶的影響

jiejingjiegoushiyigeshifenguizedejiegou,juhewulashenzhihou,keyishifenzilianpingxingdipailieqilai,shitamendeguizexingdaweitigao,weijinyibudejiejingzhunbeilejiaohaodetiaojian。suoyijuhewulashenzhihou,jiejingsulvhuidadatigao。lirudilun(juduibenerjiasuanyierchunzhi),tadejiejingsulvzuikuaidewendushi90℃,danshiruguozai80~100℃duitajinxingqianshen,neimetadejiejingsulvkebiweiqianshenshitigaoyiqianbeizuoyou,qidilunxianweiyoujiaohaodejiejingxing。duiyuyijingjiejingdejuhewu,lashenyenengpohuaijiejing。liruzaijuyixidelashenguochengzhong,weilashenqiandejiejingshimeiyoufangxiangde,yidanshoulalizuoyong,shunlalifangxiangpailiedefenziliandejiejingbuhuibeipohuai,danfenzilianhelalifangxiangchuizhidejiejingjiegoujiuyaobeilalisuopohuai。

(四)結晶型聚合物的成型加工特點

  1. 成型時所需要的熱量大

jiejingxingjuhewujiarezhinianliutaicainengchengxingjiagong,jiangyouguizejinmiduiqidedafenzilianfenli,jilianduanfenli,cishixuyaoyidingnenglianglaipohuailianduanzhongdezuoyongli,shitamenfenlikai,erqiehuanyaoyouyidingnenglianglaishilianduanneixuanzhuan。youyujiejingjuhewufenzilianjianzuoyonglijiaoda,gangxingdabuyineixuanzhuan,yincichengxingshiwaijiebixugonggeijiaodadereliangshijiejingjuhewushixianlianduanfenlidenianliutai。

  1. 體積變化大

任何聚合物體積包括兩部分:一是分子固有的體積,是一個固定值,可以根據化學結構計算出來;一是“空洞”體積,它的大小取決于某一時刻溫度的高低和鏈段運動的狀況。隨著溫度的下降,分子運動能力的減弱,分子間距減小,空洞體積相應減少,當溫度下降到Tg時,鏈段運動停止,分子間距更小,彼此靠近,隨著把空洞趕出的同時而被凍結下來。由此可見,聚合物冷凍時體積的縮小是由于空洞減少而引起的。

duiyujiejingxingjuhewu,congrongrongdaoguhua,lianduancongwuxudaoyouxuerjinmididuiqi,kongjiantijijianshaogengxianzhu。yincichengxinghoudezhipinshousuoda,chicunjingdunanyubaozheng,qiezhipinrongyichansheng“qikong”。juhewuzaiyidingwendu、yalixiachengxinglengquehou,zhipindejihechicunxiaoyumojudejihechicun,cixianxiangjiweishousuo。shousuolvdedaxiaoyujuhewuzhonglei、zhipinxingzhuang、houdu、baoyashijiandengyinsuyouguan,yibanjiejingxingjuhewubifeijiejingxingjuhewudeshousuolvda。yincizaimojushejishi,bixukaolvshousuolv。biao1-1weichangjiansuliaoshousuolv。

biao 1-1?changjiansuliaoshousuolvcankaobiao

塑料成型工藝基礎知識(三)

  1. 冷卻速度對聚合物結晶度的影響

youqishihoubizhipin,lengquesududuijiejingdudeyingxiangzuiweixianzhu,youyubenshenrechuandaodi,yinerlengquesudubuyizhi,biaomianbineibudejiejingdudi,yincibiaomianyuneibujiejingdudechayichujiurongyichanshengyingli,daozhizhipinchanshengliewen、qiaoqu、kailiedengquexian。tongchangduicileizhipinyaojinxingrechulishiqibiaomianyuneibujiejingdudechayijinliangjianxiao。

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