塑料成型工藝基礎知識(一)

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所屬分類:塑料文章

yi、juhewudewulizhuangtai

juhewuanjiejingxingnengkefenchenglianglei,yileiweiyoujiejingqingxiang,lingyileiwujiejingqingxiang。youjiejingqingxiangdejuhewu,zaiyibanqingkuangxia,yebushiyigebaifenzhibaidejingti,ershiyigejiejingquhewujiejingqugongcundetixi。wulunshibunengjiejingdejuhewu,huanshikeyijiejingermeiyoujiejingdejuhewu,huoshiyijingjiejingjuhewuzhongdefeijiejingbufendoucunzaizhusizhongbutongdewulijijutai,jisangefeijingtai(bolitai、gaodantaihenianliutai)yuyigejingtai。duiyufeijingtaijuhewueryan,zaiyidingdewailizuoyongxia,juhewudesanzhongwulizhuangtaizaibutongdewendufanweineichuxian。dangwendujiaodi(huochangwen)shi,fenziyufenzizhijiandezuoyonglijiaoda,chushaoshulianjieyoumouxieziyouwai,changlianfenzideyundongjibenshangbeidongjie,zhenggejuhewujuyouyidingdegangxingheyingdu,danbufacui,cishichengxianweibolitai;dangwendushangsheng,reyundongnengliangbuduanzengjia,juhewudetijipengzhang,dadaomouyichengduhou,suiranzhenggedafenzilianshangbunengyidong,danfenzizhongdelianduandouyouzugoudehuodongkongjian,nengfashengweiyi,yinerfenzidexingzhuangkeyifashenglazhihuojuanqudengbianhua,dantamenzaifenzijiegoushangdezongpailieyiranbubian,zheshichengxianchurouruanerfuyoudanxingdegaodantai;ruowendujixushangsheng,zhidaozhenggedafenziliandounengyidong,jikaishisuxingliudong,chengweinianliutai。getaidetezheng,zhuyaoyouxingtainengli (shenchanglvhuoyasuolv) biaoxianchulai。rutu 1-1 suoshi。

塑料成型工藝基礎知識(一)

圖 1-1 在恒壓下熱塑性塑料三態圖

1—feijiejingxingsuliao;2—jiejingxingsuliao

congtu1-1kezhi:

tg biaoshicailiaocongbolitaizhuanhuaweigaodantaidewendu,chengzuobolihuawendu;

tf biaoshicailiaoconggaodantaizhuanbianweinianliutaidewendu,chengzuonianliuwendu;

當溫度升高到Td時,聚合物開始分解,此時的溫度稱作分解溫度;當溫度低于Tx時,在很小的外力作用下,大分子鏈發生斷裂,這一溫度稱作脆化溫度。在脆化溫度下,聚合物處于脆態,材料失去使用價值。聚合物的三態變化是可逆的:當溫度降至Tf時,聚合物將從黏流態轉變為高彈態;當溫度降低到常溫時,塑料將變為玻璃態。在塑料的成型中所以能獲得所要求制品的幾何形狀和尺寸精度,正是利用了聚合物在不同溫度下的三態變化的特性。

Tg~Tf為高彈態。它有兩個特點:(1)在較小外力作用下可產生很大的形變,初始時變形隨溫度的提高而增大,到一定限度后變為恒定,外力解除后能夠恢復原來形狀,這種形變稱為高彈形變;(2)高彈形變不是瞬時發生的, 而是隨時間逐漸發展的。也就是說,高彈變形不像普彈變形 ( 如鋼絲彈簧) 那樣,在外力解除后能立即恢復原狀,而是要延遲一些時間。Tf~Td為黏流態。塑料成型加工就是在這個溫度范圍內進行。 溫度范圍愈寬,成型加工就愈容易,塑料也愈不容易分解。Tf~Td的范圍愈窄,成型加工困難愈大。根據塑料隨受熱溫度的不同而存在著上述三種狀態的這一性質,如果需要把塑料加工成制品,就要求采用與之相適應的各種加工方法。例如,玻璃態塑料可用車、銑、鉆、鋸、刨等機械加工方法;高彈態塑料可用熱沖壓、彎曲、真空成型等二次加工方法;黏流態塑料可用擠出成型、注射成型、壓延成型等加工方法。嚴格地說,聚合物三態轉變的溫度不是完全固定的。聚合物三態的轉變除了與溫度有關外, 還和應力作用的時間和作用力施加的速度等因素有關。因此,嚴格的溫度轉變點Tg、Tf和Td是不存在的,只有從一種變形占優勢轉變為另一變形占優勢的溫度范圍。

tongshi,suizhutongxijuhewufenziliangdezengjia,congbolitaixiangnianliutaideguoduquyuyixianggaowenfanwei。ciwai,zaijuyougangxingfenzidejuhewuzhonggaodantaidewendufanweijiaozhai。

congtu1-1zhonghuankezhidao,feijiejingxingjuhewuhejiejingxingjuhewudesantaibianhuayoumingxiandebutong,qianzheyoumingxiandesantaibianhua,erjiejingxingjuhewudegaodantaiquebumingxian,dangwendugaoyuronghuawendushibianhenkuaidironghuaerchuyunianliu4tai。lingwai,jiejingxingjuhewuzaidiyuronghuawenduxia,tadexingbianlianghenxiao。yejiushishuo,nairexingnengfangmianbifeijiejingxingjuhewuyousuogaijin。liru,yibanjuhefangfazhidedefeijiejingxingjubenyixidetg = 80℃ ,erdingxiangjuhefazhide dejiejingxingjubenyixideronghuawendudadao230~240℃,shiyongfanweikuandeduo。youcikejian,feijiejingxingsuliaozhinengzaicuihuawenduhebolihuawenduzhijianyingyong,erjiejingxingsuliaokezaicuihuawenduzhironghuawenduzhijianyingyong。

er、juhewurongtideliubianxing

shangmianjianyaoditandaolefeijingtaijuhewuzaibutongwenduxiadesanzhongwulizhuangtai、chengxingjiagongdewendufanweiyijiruhexuanyongxiangyingdechengxingfangfa,danshi,jinjinxiaodezheyidianshibugoude。womenzhidao,suliaochengxingjiagongzhipin,wangwangdoushitongguonianliutailaishixiande,yinweizaizhezhongzhuangtaixiadejuhewubujinyiyuliudong,erqieyiyubianxing,zhegeitadeshusonghezaoxingdailaihendadefangbian。weilelejiesuliaodeliubianxingneng,renmenjinxingleshenruxizhideyanjiugongzuo,qudeleyidingdechengguo。 suoweideliubianxueshitongguoyingli、yingbianheshijianlaiyanjiuwuliaodeliudonghebianxingxingnengdeyimenxueke。zaisuliaochengxingjiagongzhong,yinyongliubianxuedechengguoduigongyi、shebeihemojudengfangmianjunyouzhidaoyiyi。

(yi)feiniudunliudong

在塑料成型中,并不限定用黏流態的聚合物(聚合物熔體),也可以采用聚合物分散體(糊狀物或溶液),它們都屬于液體范疇。液體的流動形式有層流和湍流兩種,長期實踐證明,聚合物熔體和分散體在成型過程中的流動絕大多數都屬于層流。液體的流動和變形都是在受有應力的情況下得到實現的。主要應力有剪切、拉伸和壓縮三種應力,其中剪切應力對塑料成型最為重要,按照液體的流 動行為,可以把液體分為牛頓液體和非牛頓液體兩類,而在流體中非牛頓流動極為常見,屬于這類流體的液體常有三種:賓哈液體、假塑性液體和膨脹性液體。塑料成型工藝基礎知識(一)

tu1-2 duishuzuobiaotu

1—pengzhangxingcailiao;2—niuduncailiao ;3—jiasuxingcailiao

rutu1-2suoshi,xielvxiaoyu1shiweijiasuxingcailiao;xielvdayu1shiweipengzhangxingcailiao;xielvdengyu1 shi,liudongquxiancheng45dujiaojiushiniuduncailiao。yishangfeiniudunliutixingweidezhishufangchengbiaodashishiliubianxuezhongdeyigezhongyaoneirong,bingzaigongchengshangdedaoguangfandeyingyong。

(er) yingxiangjuhewuliudongdeyinsu

從上面的分析可以得出結論:黏度是衡量聚合物流動性的尺度,它決定著成型加工的難易程度。黏度較低時,不僅操作較方便,而且產率可提高,同時功率還可降低。所以在成型加工中總是希望在不損害制品質量的前提下設法使聚合物的黏度降低一些。在成型加工中,對聚合物黏度影響最大的是剪切應力、剪切速率、溫度和壓力等。

1、jianqiesulvduijuhewuniandudeyingxiang

有關剪切速率(剪切應力)對聚合物黏度的影響前面已作過介紹,這里須強調的是,剪切應力或剪切速率的增大使聚合物的表觀黏度下降,從而使流動性能大為提高。這類塑料稱為對剪切速率敏感性的聚合物,在擠出成型時主要是通過改變螺桿的轉速的辦法來改變它們的流動性,像聚甲醛、聚乙烯等塑料就屬于這一類。相反,有的聚合物黏度對剪切速率不敏感,加大剪切速率并不能有效增加流動性,而對溫度是敏感的,如果擠出時溫度不夠就盲目增大螺桿的轉速,就會造成螺桿斷裂和機器損壞的事故。像尼龍、有機玻璃、聚碳酸酯等都屬于這類塑料。

2、wenduduijuhewuniandudeyingxiang

suizhuwendudeshenggao,lianduandehuodongnengliyaozengqiang,fenzijiandexianghuzuoyongliyaojianruo,suoyijuhewudeliudongxingyaozengda,biaoguanniandujianxiao,congtu1-3zhongkandehenqingchu。lingyifangmian,butongjuhewudebiaoguannianduduiwendudeyilaiguanxibingbuyiyang。zaitu1-3zhong,duiyujutansuanzhi、cusuanxianweisu、jujiajibingxisuanjiazhi,wendushenggaoyue50℃,biaoguanniandukeyijiangdiyigeshuliangji,yejiushishuozhezhongjuhewudeliudongxingduiwendudeminganxingjigao,zaijiagongchengxingshizhiyaoshaoshaogaibianyixiawendu,jiukedadadizengjiatadeliudongxing。yibanlaishuo,juhewufenziliangangduhefenzilianjiandeyinliyuedashi,zetadebiaoguannianduduiwendudeminganxingjiuyueda。erduiyujuyixi、jujiaquan,qingkuangjiuhenbuyiyang,jibianshiwendushenggao100℃,biaoguannianduyejiangbuleyigeshuliangji。zheleijuhewuduiwenduminganxinghendi,rujinpingzengjiawendulaizengjiaqiliudongxing,wenduzengfuduxingjieyuliangzhezhijian。

塑料成型工藝基礎知識(一)

tu 1-3jizhongsuliaorongrongnianduyuwendudeguanxi

1—jutansuanzhi (4 mpa ) ;2—juyixi ( 4m pa ) ;3—jujiaquan;

4— jujiajibingxisuanjiazhi;5—cusuanxianweisu,( 4mpa );6—nilong( 1m pa )

 

3、yaliduijuhewuniandudeyingxiang

youyunianduyilaiyufenzijiandezuoyongli,dangyetishouyashi,fenzijiandejulisuoxiao,yinci,yetideniandusuizhizenggao。difenziyetiqiyasuoxingdouhenyouxian,danduiyugaofenzirongtiqueburan,juhewurongtichengxingjiagongdeyalidouhengao。liru,jichuchengxingshideyaliyibanzai10~50mpa;zhushechengxingshideyaligaoda30~300mpa,yincitamendeyasuoxingshikeguande。youshiyandezhi,juhewurongtizaishouyouyalishi,qiniandudinghuiyousuozenggao,mouxieqingkuangxiabiaoguanniandunengzengjiayigeshuliangji。youshihuichuxiantongyijuhewuzaitongchangdeyalixiakeyichengxing,dandangyalizengdashi,tajiubuyichengxinghuoshengchanlvxiajiang,shenzhisuliaobiandexianggutibandibunengliudong,dangranbukenengchengxing。huanyinggaizhichu,zaitongyiyalixiadetongyizhongjuhewurongti,ruguozaichengxingshisuoyongdeshebeidaxiaobutong,qiliudongxingweiyeyouchabie,zheshiyinweijinguansuoshouyalixiangtong,suoshoujianqieyingliyirankeyibutong。yaliduijuhewufensantiniandudeyingxiangyujuhewurongtijibenxiangtong,danshiyouyufensantizhongyouyibufenshidifenziwu,suoyiyingxiangchengdujiubijiaoxiao。zaizhefensantizaichengxingshishouyabugao,yincihenshaokaolvzhezhongyingxiang。

4、fenziliangduijuhewuniandudeyingxiang

聚合物的流動是高分子鏈和高分子鏈之間發生相對位移的結果,所以分子量的大小對聚合物的流動性有著極為明顯的影響。隨著分子量的增大,流動性就減小。這是由于分子量越大,相對位移運動越不容易進行。從成型的角度來看,在不影響制品基本性能的前提下,適當降低分子量是很有必要的。因為分子量過高,成型加工溫度就越高,這對生產是不利的。另外,不同用途和不同的加工方法,對分子量的大小也有不同的要求。例如,擠出硬質PVC薄壁異型材,采用分子量較低、平均聚合度為730~870的SG6型樹脂;而擠出軟質PVC異型材選用分子量較高的、平均聚合度為1100~1240的SG3型樹脂為宜。一般來說注射成型加工要求聚合物的分子量比較低,擠出成型加工要求聚合物分子量較高。

5、suliaozhujiduijuhewuniandudeyingxiang

weilegaishanjiagongtexingheshiyongxingneng,youxiejuhewuzaichengxingjiagongshitianjiashaoliangdesuliaozhuji。liru,jiaruzengsujinengshijuhewufenzijianzuoyonglijianruo,youliyulianduandeyundong,bolihuawendujiangdi,liudongxingzengjia,youliyuchengxingjiagong。duiyuneixienianliuwenduhefenjiewendushifenjiejindejuhewu,zaichengxingjiagongshi,bixujiaruyidingliangdewendingji,qiduinianduyeyouyidingyingxiang,gezhongwendingjideyingxiangchengdubuyiyang。weilejiangdisuliaochengben,gaishanguangwendingxing、jueyuanxingdengxingneng,zaibuyingxiangzhipinzhiliangdeqingkuangxiatianjiayidingliangdetianliao,zhejiuhuijiangdijuhewudeliudongxingneng。

6、juhewudeniandusuishijiandebianhua

dangsuoshijiadejianqieyinglibubianshi,juhewuzaihengwenxiadebiaoguannianduhuisuizhusuoshiyinglidechixushijianerzhujianshangshenghuoxiajiang,bingdadaoyidingzhihoujixingtingzhi。duizheyiliudongxingweidejilijieshi,youyulilunjieyanjiubugou,shangbunengzuochudingliangxingdefenxi。jiaruobushouyinglidezuoyong,juhewurongrongguochengwanchengyihou,liubianxingbuyingsuishijianerbianhua。danshishijishanghenduojuhewurongtisuishijianjianjianbianhua,qizhongjuhewurongtiyourefenjieeryinqiniandusuishijianzhujianxiajiangdeqingkuangjiaoduo。zaishijicaozuozhong,yifangmianyingxuanzejiaogaofenziliangjuhewuyitigaozhipindezonghewuxing;lingyifangmianyingkaolvzuigaoniandujixian,gaoyuzhegejixianchengxingjiukunnan。weilejiangdiniandu,yingxuanzenianliuwenduderefenjiebunengjinxingdaoduisuodezhipinzhiliangfashengyingxiangdechengdu。

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