五寸軟盤蓋注射模具設(shè)計(jì)【一模兩腔】【側(cè)抽芯】【說明書+CAD】
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工 裝 工 藝 過 程 卡材料名稱牌 號(hào)45鋼簽 名日期擬 制生產(chǎn)編號(hào)0001工裝圖號(hào)01工裝名稱型腔下料規(guī)格審 核零件圖號(hào)A3零件名稱型腔數(shù) 量1每件毛坯數(shù)1批 準(zhǔn)車間工序工 序 內(nèi) 容操作者日期是用設(shè)備及工具單件定額合格數(shù)量返修數(shù)量檢驗(yàn)員檢驗(yàn)日期鍛造備料 將毛坯加工成平行六面體 265x235x45mm退火熱處理 退火刨床刨平面刨平面平面留余量是1 mmB635銑床銑平面銑各個(gè)平面留磨削余量0.6 mm,側(cè)面留余量0.4 mm留臺(tái)階X60W磨床磨平面磨各個(gè)平面,留磨削余量0.3 mm,側(cè)面保持垂直。M7120A劃線鉗工劃出對(duì)稱中心,各個(gè)孔的定位。銑床銑型腔粗加工型腔X60W切割線切割切割出型腔拼塊孔。銑床銑型腔精加工型腔X60W退火熱處理磨床磨平面精加工平面檢驗(yàn)工 序 許 可 登 記 處簽 名日期總頁數(shù)日期工序數(shù)量疵 病 特 征允 許 理 由技 術(shù)檢 驗(yàn)車 間2003.6.10頁次1工 裝 工 藝 過 程 卡材料名稱牌 號(hào)45鋼簽 名日期擬 制生產(chǎn)編號(hào)0001工裝圖號(hào)01工裝名稱型芯下料規(guī)格審 核零件圖號(hào)A3零件名稱型腔數(shù) 量1每件毛坯數(shù)1批 準(zhǔn)車間工序工 序 內(nèi) 容操作者日期是用設(shè)備及工具單件定額合格數(shù)量返修數(shù)量檢驗(yàn)員檢驗(yàn)日期鍛造備料 將毛坯加工成平行六面體 165x235x57mm退火熱處理 退火刨床刨平面刨平面平面留余量是1 mmB635銑床銑平面銑各個(gè)平面留磨削余量0.6 mm,側(cè)面留余量0.4 mm留臺(tái)階。X60W劃線鉗工劃出對(duì)稱中心,各個(gè)孔的定位。銑床銑平面銑平面留型芯小凸臺(tái)。磨床磨平面磨各個(gè)平面,留磨削余量0.3 mm,側(cè)面保持垂直。M7120A銑床銑型腔粗加工型腔X60W切割線切割切割出型腔拼塊孔。銑床銑型腔精加工型腔X60W退火熱處理磨床磨平面精加工平面檢驗(yàn)工 序 許 可 登 記 處簽 名日期總頁數(shù)日期工序數(shù)量疵 病 特 征允 許 理 由技 術(shù)檢 驗(yàn)車 間2003.6.10頁次1目 錄摘要 2一:塑件的工藝特性分析.3二:模具結(jié)構(gòu)設(shè)計(jì).61. 型腔數(shù)量以及排列方式.6 2. 分型面的選擇63. 注射機(jī)的選定.84.主流道的設(shè)計(jì) 95.分流道的設(shè)計(jì).10三. 成型零件的設(shè)計(jì)與計(jì)算.121. 成型零件的設(shè)計(jì).122.模具型腔側(cè)壁和底版厚度的計(jì)算.17四.合模導(dǎo)向機(jī)構(gòu)的設(shè)計(jì).19五. 推出機(jī)構(gòu)的設(shè)計(jì).23六. 側(cè)向分型與抽芯機(jī)構(gòu)的設(shè)計(jì).24七.連接件的選用.25八. 模具的裝配.26九.答謝語.26五寸軟盤蓋注射模具設(shè)計(jì)XXXXXXXXXXXXX學(xué)校 摘要: 在綜合分析塑件結(jié)構(gòu),使用要求。成型質(zhì)量和模具制造成本的基礎(chǔ)上,介紹結(jié)構(gòu)簡單,形狀規(guī)則的塑件成型。采用側(cè)向分型抽芯機(jī)構(gòu),使塑件能一次成型。設(shè)計(jì)了相應(yīng)的的側(cè)向分型抽芯的注射模。并介紹了模具的工作過程。關(guān)鍵詞:注射模 抽芯機(jī)構(gòu)。AbstractBased on the comprehensive analysis on the plastic parts strcture service require-ment, moulding quality and mouding quality and mould manu facturing cost. Acorresponding injection mould of internal side core pulling was designed.By adopting the mulit-direction and multi-combination core-pulling .acorresponding injection mould of interal side core pulling was designed,the working process of the mould was in-troduced.Key words:injection mould ,medialcoe pulling.一塑件件的工藝特性分析 1 該塑件為五寸軟盤蓋配件,它要與另外部件匹配使 用。要使側(cè)面的兩個(gè)小圓柱定位到另外一個(gè)部見上,所以從 塑件的使用性能上分析,必須具備有一定的綜合機(jī)械性能 包括,良好的機(jī)械強(qiáng)度,一定的彈性和耐油性,耐水性,耐 磨性,化學(xué)穩(wěn)定性和電氣性能。符合以上性能的有多種塑料 材料,從材料的來源以及材料的成本和調(diào)配顏色來看,ABS 比較適。ABS是目前世界上應(yīng)用最廣泛的材料,它來源廣,成本底,符合該塑件成型的特性。因此制作該塑件選用ABS塑料。表一:ABS的主要技術(shù)指標(biāo)密度比溶吸水率收縮率熱變形溫度1.02-1.050.8-0.980.2%-0.4%130-1600.3%-0.8%83-103.抗拉強(qiáng)度拉伸彈性模量彎曲強(qiáng)度沖擊強(qiáng)度體積50Mpa1.8X10780Mpa11HB9.7HB6.9X10表二;ABS的注射工藝參數(shù) 注射機(jī)類型螺桿轉(zhuǎn)數(shù)噴嘴形式噴嘴溫度 螺桿式50-70直通式180-190。 料筒的溫度模具溫度注射壓力保壓力 190-200 200-220 170-19050-7060-90Mpa30-60 Mpa 注射時(shí)間保壓時(shí)間冷卻時(shí)間成型周期 3-5 S15-30 S10-30 S30-70 ABS五毒,無味,呈微黃色,成型的塑料件有較好的光澤。密度為1.02-1.05g/cm3。ABS有極好的抗沖擊強(qiáng)度,且在低溫下也不迅速下降。有良好的機(jī)械強(qiáng)度和一定的耐磨性,耐寒性,耐油性,耐水性,化學(xué)穩(wěn)定性和電氣性能。ABS有一定的硬度和尺寸穩(wěn)定性,易于成型加工。經(jīng)過調(diào)色可配成任何顏色。其缺點(diǎn)是耐熱性不高,連續(xù)工作溫度為70度左右,熱變形溫度約為90度左右。耐氣候差,在紫外線作用下易變硬發(fā)脆。其成型特點(diǎn):ABS在升溫時(shí)黏度增高,所以成型壓力較高,塑料上的脫模斜度悄大,ABS易吸水,成型前加工要進(jìn)行干燥處理;易產(chǎn)生熔接痕,模具設(shè)計(jì)時(shí)應(yīng)注意盡量減小澆注系統(tǒng)對(duì)料流的阻力;在正常的成型條件下,壁厚,溶料溫度及收縮率影響極小。ABS成型收縮率,拉伸模量,泊松比與剛的摩擦因素。表三;塑料名稱成型收縮率/%拉伸模量E/X103Mpa泊松比U與剛的摩擦系數(shù)fPE1.5-3.50.212-0.980.490.23-0.5PP0.4-3.01.6-6.20.430.49-0.51PS0.2-0.81.4-8.90.380.45-0.75ABS0.1-0.71.91-1.980.380.20-0.252產(chǎn)品工藝性與結(jié)構(gòu)分析。1).尺寸的精度。塑件的尺寸公差推薦值參考模具設(shè)計(jì)與制造手冊(cè)表二的精度等級(jí)參考表2-18:表四:材料高精度一般精度低精度ABS345該塑件由于不接納其它裝配尺寸,其精度不必太高。故選用一般精度IT4,其公差參考教材塑料成型工藝與模具設(shè)計(jì)。2)粗糙度:作為儀表外殼,外觀良好就得了,光澤度不必太高,塑 件表面的粗糙度要比模具型芯低。塑件模具表面的粗糙度可取Ra=0.8.模具型芯的表面粗糙度取Ra=0.3.3). 斜度: 脫模斜度取決與塑件的形狀,壁厚及塑料的收縮率,一般取30,1。30。本塑件由于型腔深度很小,兩側(cè)也采用抽芯。但由于考慮到塑件跟其它部件配合使用,要使塑件配合好所以要塑件兩側(cè)角度,所以要使塑件強(qiáng)行脫模的方式。而且往里偏有個(gè)小角度;本塑件與另外部件配合使用,要有一定的彈性才能使塑件能放進(jìn)指定的位置,塑件要有足夠的強(qiáng)度和剛度,才能經(jīng)受推件桿的推力而不使塑件變形,該產(chǎn)品壁厚均勻:本產(chǎn)品取2mm.表五;塑料種類制件流程最小壁厚一般制件壁厚大型制件壁厚塑料 ABS0.751.75-2.62.4-3.23.塑件工藝分析:本塑件外形中等,形狀簡單,尺寸精度不算高,壁厚均為2 mm材料是ABS收縮率取0.05%,凈重約25G,塑件外形長150mm,寬64mm,局部高24 mm.由于塑件中有些地方通空和凹槽,為了減小加工難度,降低制作成本,所以采用凸模,凹模鑲塊加入。因塑件長邊兩端是圓柱小凸臺(tái)伸出,所以要采用斜導(dǎo)柱側(cè)向分型機(jī)構(gòu)才能.使塑件出模。二. 模具結(jié)構(gòu)設(shè)計(jì)1:型腔數(shù)目及排列方式:1)型腔數(shù)目的確定: 由于該塑件要進(jìn)行長期大批量生產(chǎn),為了提高生產(chǎn)效率,降低塑件的生產(chǎn)成本,且該塑件制件尺寸也比較對(duì)稱,塑件的質(zhì)量控制要求的尺寸精度,性能和表面粗糙度較低,采用一模兩腔生產(chǎn)模具。可保證塑件的最佳生產(chǎn)經(jīng)濟(jì)性,又達(dá)到制件最佳的技術(shù)經(jīng)濟(jì)性。2)型腔的布局: 型腔的排布與澆注系統(tǒng)布置密切相關(guān),因此型腔的排布應(yīng)使每個(gè)型腔都能從總壓力中均等地分得所須的足夠壓力,以保證塑料熔體同時(shí)均勻充滿每個(gè)型腔,使各型腔的塑件內(nèi)在質(zhì)量均一穩(wěn)定,所以型腔設(shè)計(jì)為:2:分型面的設(shè)計(jì): 分型面是決定模具結(jié)構(gòu)形式的重要應(yīng)素,它與模具的整 體結(jié)構(gòu)和模具的制造工藝有密切的關(guān)系,并且直接影響 到塑料熔體的流動(dòng)充填特性及塑件的脫模,因此,分型面的選擇是注塑模具設(shè)計(jì)中的一個(gè)關(guān)鍵。 選擇分型面時(shí)一般應(yīng)尊循以下幾項(xiàng)基本原則:1. 分型面應(yīng)選在塑件外形最大輪廓處;2. 確定有利的留模方式,便于塑件順利脫模;3. 保證塑件的精度要求;4. 滿足塑件外觀質(zhì)量的要求;5. 便于模具的加工與制造;6. 對(duì)成型面積的影響;7. 排氣的效果的考慮;8. 對(duì)側(cè)向抽芯的影響。注射模一般有的有一個(gè)分型面,有的有兩個(gè)分型面。分型面的形狀有平直分型面,傾斜分型面,階梯分型面,曲面分型面,復(fù)合分型面。在這里考慮到塑件分型面選在塑件外形最大輪廓處,要保證有利的留模方式,要便于塑件順利脫模,保證塑件的精度要求,便于模具加工,采用單個(gè)平直分型面。如圖;3.注射機(jī)的選定;以鎖模力為技術(shù)參數(shù),必須大于模具在開模方向的投影面積上的總注射力。P=P x KC x KS1式中 P-型腔內(nèi)注射壓力, MpaPB-基本壓力,MpaKc-材料系數(shù),ABS材料取KC=1.15KS-塑料復(fù)雜系數(shù),KS=1-1.5。PB與塑件平均壁厚T1,進(jìn)澆口流程長度L的流程比L/T有關(guān),本塑件T=2mm,在這里采用側(cè)澆口,估算L=400mm,故L/T=200,所以PB=32MPa,由于該塑件簡單,取KS=1,則:P=32 x 1.15 x 1=36.8 MPa鎖模力為;F=1.5 xP x A x 0.1式中;F-所需的鎖模力,KN。P-型腔內(nèi)注射壓力。A-塑件投影面積,A=150 x 6.5=97.6F=1.5 x 36.8 x 97.5 x 0.1=538.2 KN所以選用臥式S/Z 100/60。 型號(hào)國產(chǎn)注射機(jī),其主要技術(shù)參數(shù)參考注射模設(shè)計(jì)。4 主流道的設(shè)計(jì) 主流道的設(shè)計(jì)參考教材塑料成型工藝與模具設(shè)計(jì)P114表5-2主流的部分尺寸: ()SR 符號(hào) 名稱 尺 寸h d主流道小端直徑 注射機(jī)噴嘴直徑+1 SR主流道球面直徑 噴嘴球面半徑+1 L h 球面配合高度 35 主流道錐角2060 L主流道長度 盡量60DD主流道大端直徑 d+2Ltg(/2) 查模具設(shè)計(jì)與制造簡明手冊(cè)P386表2-40常用熱塑性塑料注射機(jī)型號(hào)和主要技術(shù)規(guī)格s/z 100/60:噴嘴球半徑=12;主流道小端直徑=4。則主流道小端直徑d=4+1=5; 球面配合高度h取4; 主流道錐角取30;主流道球面直徑SR=12+8=20; L和D還待定。因?yàn)槎0搴穸群蛣?dòng)模底板總長為60,所以澆口套L=56mm.經(jīng)計(jì)算D=5+3=8mm.5. 分流道設(shè)計(jì)(1)分流道的長度和斷面尺寸:分流道的斷面尺寸根據(jù)塑件的成型體積,塑件的壁厚,塑件形狀,所用塑料的工藝性能,注射速率和分流道的長度等因素確定。該塑件壁厚為2mm小于3mm,質(zhì)量為25g,所以:D=0.2654W4L式中:W-流經(jīng)分流道的塑料量(g)L-分流道的長度 (mm)D-分流道的直徑 (mm)參考部分塑料常用分流道斷面尺寸推薦范圍,ABS材料的D=4.8-9.5 mm。這里取D=6 mm。為了便于加工分流道的斷面做成圓形,分流道長度L取50 mm;分流道的布置如圖:(2).澆口的設(shè)計(jì)。因?yàn)樵撍芗怯脙砂迨蕉嘈颓荒?,所以采用?cè)澆口,就是澆口開設(shè)在分型面上,從塑件側(cè)面進(jìn)料,其形狀簡單加工方便。側(cè)澆口的形式: 參考塑料成型工藝與模具設(shè)計(jì)P118表5-4側(cè)澆口形式的推薦尺寸:l=0.72.0;b=1.55.0;t=0.52.0。再參考塑料成型工藝與模具設(shè)計(jì)P122式5-7側(cè)澆口的尺寸計(jì)算的經(jīng)驗(yàn)公式:b=【(0.60.9)A1/2】 30;t=b。式中 b-測澆口的寬度();A-塑件的外側(cè)表面積(2);t-測澆口的厚度()。先計(jì)算A值:A=20060=120002故 b=【(0.60.9)A1/2】30;=【(0.60.9)109】30=2.183.27()再對(duì)照上面給定的推薦值b取2.5;t取1.0;l取1.0。三 成型零件的設(shè)計(jì)與計(jì)算 成型零件決定塑件的幾何行狀和尺寸。成型零件工作時(shí),直接與塑料接觸,承受塑料熔體的高壓、料流的沖刷,脫模時(shí)與塑料間還發(fā)生摩擦。因此,成型零件要求有正確幾何形狀,較高的尺寸精度和較低的表面粗糙度,此外,成型零件還要求結(jié)構(gòu)合理,有較高強(qiáng)度、剛度及較好的耐磨性能。1.成型零件的設(shè)計(jì)為了提高零件的加工效率,裝拆方便,保證兩個(gè)型腔形狀,尺寸一致,采用組合式凹模中的整體嵌入式凹模結(jié)構(gòu)。在凹模與定模板間的配合用。影響成型零件的尺寸因素有:1).塑件的收縮率,其值為s=(Smax-Smin )Ls;式中 s-塑料收縮率波動(dòng)所引起的塑件尺寸誤差;Smax-塑料的最大收縮率;Smin-塑料的最小收縮率;Ls -塑件的基本尺寸。2).模具成型零件的制造誤差;參考塑料成型工藝與模具設(shè)計(jì)P所列出的經(jīng)驗(yàn)值,成型零件的制造公差約占塑件總公差的-,或取IT7-IT8級(jí)作為模具制造公差。模具成型零件制造公差用z表示。這里取z=0.05收縮率的波動(dòng)引起塑件尺寸誤差隨塑件的尺寸增大而增大。在計(jì)算成型零件時(shí),所用到的收縮率均用平均收縮率來表示= 100%式中 -塑件的平均收縮率;Smax-塑料的最大收縮率;Smin-塑料的最小收縮率。為了方便計(jì)算成型零件的公差,在此前必須先把塑件的尺寸及公差標(biāo)上。 第一類尺寸:型腔尺寸的計(jì)算:計(jì)算公式參考教材P151式(5-18):(LM)z =(1+ )LS-(0.50.75)z式中 -表示塑料的平均收縮率;(=0.55%)LS-表示塑件的基本尺寸;-表示塑件尺寸的公差;Z-取/3。當(dāng)制件的尺寸較大、精度級(jí)別較底時(shí)式中取0.75,當(dāng)精度級(jí)別較高時(shí)式中取0.5。本塑件為殼體配件其精度要求不高,故在本設(shè)計(jì)中取0.75。 150尺寸的計(jì)算:查教材P66表3-8該尺寸的公差為=0.62。利用公式(LM)z =(1+ )LS-0.75z=(1+0.55%)150-0.750.62005=150.360.05mm 64尺寸的計(jì)算:查教材P66表3-8該尺寸的公差為=0.32。利用公式(LM)z =(1+ )LS-0.75z=(1+0.55%)64-0.750.320.05=64.112.05 mm 4尺寸的計(jì)算:查教材P66表3-8該尺寸的公差為=0.14。利用公式(LM)z =(1+ )LS-0.7 5z=(1+0.55%)4-0.750.14 0.05=4.06 0.05mm28尺寸的計(jì)算:查教材P66表3-8該尺寸的公差為=0.24。利用公式(LM)z =(1+ )LS-0.75z=(1+0.55%)28-0. 750.240.05=27.980.05 mm 32尺寸的計(jì)算:查教材P66表3-8該尺寸的公差為=0.26利用公式(LM)z =(1+ )LS-0.75z=(1+0.55%)32-0.750.260.05=31.980.05mm R10尺寸的計(jì)算:查教材P66表3-8該尺寸的公差為=0.18。利用公式(LM)z =(1+ )LS-0.75z=(1+0.55%)10-0.750.180.05=10.190.05 mm 50尺寸的計(jì)算:查教材P66表3-8該尺寸的公差為=0.32。利用公式(LM)z =(1+ )LS-0.75z=(1+0.55%)50-0.750.50.05=50.030.05mm. 8尺寸的計(jì)算:查教材P66表3-8該尺寸的公差為=0.16。利用公式(LM)z =(1+ )LS-0.75z=(1+0.55%)8-0.750.50.05=7.920.05mm . R5mm尺寸的計(jì)算:查教材P66表3-8該尺寸的公差為=0.14。利用公式(LM)z =(1+ )RS-0.75z=(1+0.55%)5-0.750.140.05=4.920.05mm第二類型腔深度的計(jì)算:計(jì)算公式參考教材P151式(5-20)(HM)z =(1+ )HS-z式中 HM-表示型腔的深度;-表示塑料的平均收縮率;HS-表示塑件凸出的高度;-修正系數(shù),=1/21/3,精度要求低時(shí)取小值,反之取大值。在此取1/3。-表示塑件的基本尺寸;Z=1/3。(1)基本尺寸為4的計(jì)算:查教材P66表3-18該尺寸的公差為=0.14。利用公式 (HM)z =(1+ )HS+0.5z=(1+0.55%)4-0.50.140.09=4.090.09 mm(2)基本尺寸為2的計(jì)算:查教材P66表3-18該尺寸的公差為=0.12。利用公式 (HM)z =(1+ )HS+0.5z=(1+0.55%)2-0.50.120.06=2.070.06第三類型芯尺寸的計(jì)算:(1)尺寸為4的計(jì)算:查教材P66表3-18該尺寸的公差為=0.14。利用公式 (HM)z =(1+ )HS+z=(1+0.55%)4-0.50.140.04=3.980.04(2)型芯高度尺寸為22的計(jì)算:查教材P66表3-18該尺寸的公差為=0.22。利用公式(LM)z =(1+ )LS+0.5z=(1+0.55%)22+0.50.220.05=22.230.05mm(3)尺寸為16的計(jì)算:查教材P66表3-18該尺寸的公差為=0.20。利用公式(LM)z =(1+ )LS+0.75z=(1+0.55%)16+0.750.200.05=16.240.05mm(4)尺寸為26的計(jì)算:查教材P66表3-18該尺寸的公差為=0.24。利用公式(LM)z =(1+ )LS+0.5z=(1+0.55%)26+0.750.240.05=26.320.05mm(4)尺寸為14的計(jì)算:查教材P66表3-18該尺寸的公差為=0.18。利用公式(LM)z =(1+ )LS+0.75z=(1+0.55%)14+0.750.180.05=14.20.05mm第四類中心距離的尺寸計(jì)算中心距離尺寸的計(jì)算公式參考教材P151式5-22:(CM)Z/2=(1+) CSZ/2式中 -表示塑料的平均收縮率;(=0.55%)CS-表示塑件的基本尺寸;-表示塑件尺寸的公差;Z-取/3。44尺寸的計(jì)算:查教材P66表3-8該尺寸的公差為= 0.28。利用公式 (CM)Z/2=(1+) CSZ/2=(1+0.55%)440.025=44.240.025 mm2. 模具型腔側(cè)壁和底版厚度的計(jì)算塑料模具型腔在成型過程中受到熔體的高壓作用,應(yīng)具有足夠的強(qiáng)度和剛度,如果型腔側(cè)壁和底版厚度過小,可能因硬度不夠而產(chǎn)生塑性變形甚至破壞;也可能因剛度不足產(chǎn)生翹曲變形導(dǎo)致溢料和出現(xiàn)飛邊,降低塑件尺寸精度和順利脫模。因此,應(yīng)通過強(qiáng)度和剛度計(jì)算來確定型腔壁厚。1)矩形型腔的結(jié)構(gòu)尺寸計(jì)算在本模具設(shè)計(jì)中采用了整體矩形型腔,整體矩形型腔的結(jié)構(gòu)簡圖如下:因本模具的型腔大體上似矩形,并且其l40-5025-3050-6030-3560-7035- 42由于采用一模兩腔的設(shè)計(jì),澆流道和澆口總長度為50+2=52mm.因?yàn)橛玫叫钡怪颓缓穸热?0mm.所以型腔的外形尺寸:250 X 220 X 40mm.型芯的外形尺寸的確定:由于有側(cè)向分型。所以型芯的一邊直接取150mm.另一邊,52+2 x 64+35 x 2=250mm.H取50mm.3模架的選用 根據(jù)型芯,型腔的尺寸和用到側(cè)向分型有導(dǎo)滑槽.因此選用的模架外形尺寸為: B355 X 400的模架.根據(jù)模架選用的支撐板的厚度取30mm,推件板,推件固定板取15mm.四.合模導(dǎo)向機(jī)構(gòu)的設(shè)計(jì) 導(dǎo)向機(jī)構(gòu)的保證動(dòng)摸或上下模合模時(shí)正確定位和導(dǎo)向的零件。合模導(dǎo)向機(jī)構(gòu)主要有導(dǎo)柱導(dǎo)向和錐面定位兩種形式。在這里我采用導(dǎo)柱導(dǎo)向的形式。1:導(dǎo)向機(jī)構(gòu)的作用:1)定位作用 模具閉合后,保證定模或上下模的位置的正確,保證型腔形狀和尺寸的精度;導(dǎo)向機(jī)構(gòu)在模具裝配過程中也起定位作用,便于裝配和調(diào)整。2)導(dǎo)向作用 合模時(shí),首先是導(dǎo)向零件接觸,引導(dǎo)動(dòng)定模上下模準(zhǔn)確閉合,避免型心先進(jìn)入型腔造成成型零件的損壞。3)承受一定的側(cè)向壓力 承受塑料溶體在充型過程中產(chǎn)生單向側(cè)壓力和動(dòng)模板(因是雙分型面)自身的重力。2:導(dǎo)柱導(dǎo)向機(jī)構(gòu)(一)導(dǎo)柱1、導(dǎo)柱的結(jié)構(gòu)采用如圖所示: 2、導(dǎo)柱結(jié)構(gòu)和技術(shù)要求:(1)長度 導(dǎo)柱導(dǎo)向部分長度=50+40+30+812=130mm. 直徑 由于模架355 x 400型。選用比較大,.參考塑料注射 模中小型模架標(biāo)準(zhǔn)的尺寸組合。選用:導(dǎo)柱d32 x 130 x40.實(shí)用注塑模設(shè)計(jì)手冊(cè)。(2)形狀 導(dǎo)柱前端做倒角。(3)材料 導(dǎo)柱應(yīng)具有硬而耐磨的表面,堅(jiān)韌而不易折斷的內(nèi)心,因此采用T10A鋼經(jīng)淬火熱處理,硬度應(yīng)達(dá)到5055RC。導(dǎo)柱固定部分表面粗糙度為Ra0.8。導(dǎo)向部分為Ra0.4。(4)數(shù)量布置 導(dǎo)柱均勻分布在模具四周如下圖所示:(5)配合精度 導(dǎo)柱固定端與模板之間采用H7/m6的過度配合;導(dǎo)柱的導(dǎo)向部分采用H7/f7的間隙配合。(二)、導(dǎo)套1 、導(dǎo)套的結(jié)構(gòu)形式 導(dǎo)套的典型結(jié)構(gòu)如圖所示:此類型導(dǎo)套為直導(dǎo)套,結(jié)構(gòu)簡單,加工方便,適用于簡單模具或?qū)缀竺鏇]有墊板的場合:2、導(dǎo)套結(jié)構(gòu)和技術(shù)要求1)形狀 為使導(dǎo)柱順利進(jìn)入導(dǎo)套,在導(dǎo)套的前端倒圓角。導(dǎo)柱孔最好做成通孔,以利于排出孔內(nèi)空氣及殘?jiān)鼜U料。如模板較厚,導(dǎo)柱孔必須作成盲孔時(shí),可在盲孔的側(cè)面打一小孔排氣。2)材料 導(dǎo)套用與導(dǎo)柱相同的材料或銅合金等耐磨材料制造,其硬度一搬應(yīng)低與導(dǎo)柱硬度,以減輕磨損,防止導(dǎo)柱和導(dǎo)套拉毛。導(dǎo)套固定部分和導(dǎo)滑部分的表面粗糙度百一般為 Ra0.8。因此選用:導(dǎo)套d=32 x 40( I ).的導(dǎo)套。GB 4619.3-84,材料 T8A。固定形式和配合精度 采用H7/r6配合鑲?cè)肽0?。參考?shí)用注塑模設(shè)計(jì)手冊(cè):五.推出機(jī)構(gòu)的設(shè)計(jì)一、推出機(jī)構(gòu)的設(shè)計(jì)原則1 推出機(jī)構(gòu)應(yīng)盡量設(shè)置在動(dòng)模一側(cè),2 保證塑件不因推出而變形損壞,3 機(jī)構(gòu)簡單動(dòng)作可靠,4 良好的塑件外觀,5 合模時(shí)的正確復(fù)位 .二 、脫模力的計(jì)算注射成型后,塑件在模具內(nèi)冷卻定型,由于體積的收宿,對(duì)型心產(chǎn)生包緊力,塑件要從模腔中脫出,就必須克服因包緊力而產(chǎn)生的摩擦阻力。對(duì)于不帶通孔的殼體類塑件,脫模時(shí)還要克服大氣壓力。一般而論,塑料制件剛開始脫模時(shí),所需克服的阻力最大,即所需的脫模力最大,根據(jù)力平衡原理,列出平衡方程式:F=Ap(cosa-sina)式中:-塑料對(duì)鋼的摩檫系數(shù),約為 0.1-0.3A-塑件包容型芯的面積,P-塑件對(duì)型芯的單位面積上的包緊力,這里取P=3 X 10 7pa三簡單推出機(jī)構(gòu)1、為了推出機(jī)構(gòu)更簡單、更靈活和省料,決定采用推桿推出機(jī)構(gòu)。設(shè)計(jì)推桿的位置應(yīng)從以下幾方面考慮:(1)、推桿應(yīng)設(shè)在脫模阻力大的地方。(2)、推桿應(yīng)均勻布置。(3)、推桿應(yīng)設(shè)在塑件強(qiáng)度較大處。其布置圖如下圖所示:2、推桿的直徑為8,尾部采用臺(tái)肩的形式,臺(tái)肩的直徑D與推桿的直徑約差46mm的簡單結(jié)構(gòu)。采用GB1298-86。參考實(shí)用注射塑設(shè)計(jì)手冊(cè)。3、推桿的材料采用T8A碳素鋼,熱處理要求HRC50,工作端配合部分表面粗糙度Ra0.8。六.側(cè)向分型和抽芯機(jī)構(gòu)的設(shè)計(jì) 由于本塑件側(cè)面有凸臺(tái),所以安裝側(cè)向分型機(jī)構(gòu),側(cè)向分型 與抽芯一般可分為機(jī)動(dòng),液壓或氣動(dòng)以及手動(dòng)形。這里采用機(jī)動(dòng)向分型機(jī)構(gòu)。其結(jié)構(gòu):1斜倒柱的設(shè)計(jì):斜導(dǎo)柱與其固定的模板之間采用過度配合H7/m6。為了運(yùn)動(dòng)的靈活,滑塊上斜導(dǎo)孔與斜導(dǎo)柱之間可以采用較輕松的間隙配合H11/b11,或在兩者之間保留0.51mm的間隙。 斜導(dǎo)柱的材料多為T8、T10等碳素工具鋼,也可以用20鋼滲碳處理。由于斜導(dǎo)柱經(jīng)常與滑塊磨擦,熱處理硬度HRC55,表面粗糙度 0.8m。抽芯距:S=2+3=5傾斜角度的確定:根據(jù)公式:sina=s/Ltga=s/HH=40.S=5所以 a=12斜倒柱L=404181mm.d=12mm.2 側(cè)滑塊的設(shè)計(jì):側(cè)滑塊的高度不能大于滑塊的滑動(dòng)部分長度,根據(jù)型芯板的厚度,這里側(cè)滑塊的高度取 25+15=40。所以滑塊的滑動(dòng)L要大于40,取L=60mm,其寬度要大于型腔的寬度64,這里去S=70mm,所以側(cè)滑塊的外型尺寸為70x60x40mm.。采用45號(hào)鋼加工。導(dǎo)滑槽采用的是T形的形式其配合用H8/f8的間隙配合。其零件圖見圖紙零件圖。七.連接件的選用1). 銷釘?shù)倪x用:由于連接的各種板料比較大所以銷釘選用35號(hào)鋼,熱處理硬度28-38HRC銷 GB/T 117 16 x 50 :參考圓柱銷系列.2). 螺釘?shù)倪x擇:(1). 定模緊固螺銓的選用; 定模底板的厚度和定模板的總長為60mm.所以選用的螺銓型號(hào)為: GB/T 5782 M20 X 40 .(2). 動(dòng)模緊固螺銓的選用: 動(dòng)模底板,墊塊,動(dòng)模支撐板和動(dòng)模板的總長度為185mm.所以選用螺銓的型號(hào)為:GB/T 5782 M X 140.(3) 連接滑塊螺釘?shù)倪x用: 根據(jù)所有連接的定位塊和倒滑槽的長度這里選用: GB/T 5782 M12 X 60.八. 模具的裝配1模的裝配: 將定模板平放在平臺(tái)上,先將型腔放進(jìn)去,再把四根斜倒柱,四個(gè)鍥緊塊和八個(gè)型腔拼塊敲入指定的位置,把上模板放上去,對(duì)準(zhǔn)好倒套孔和澆口套孔,把倒套和澆口套敲進(jìn)去,訂上銷釘,最后將澆口套螺釘,定模螺釘旋上緊固,完成定模裝配。2 動(dòng)模的裝配: 把動(dòng)模板倒放在平臺(tái)上,先將四個(gè)側(cè)滑塊放進(jìn)倒滑槽,把定位塊擰好,裝上彈簧螺釘將滑塊固定好,在型芯放進(jìn)去,再放入型芯拼塊和四個(gè)倒柱。放上動(dòng)模板,對(duì)準(zhǔn)好各種孔位后放上推桿定位板后把拉料桿,推件桿放到其位置,再將墊塊對(duì)準(zhǔn)各種孔位放上去,再將下模板放上把螺釘旋上即可,最后把動(dòng)模翻過來,把定模倒套對(duì)準(zhǔn)倒柱放進(jìn)去。整套模具裝配完成。然后檢驗(yàn),試模.九 答謝語在本設(shè)計(jì)的時(shí)間里,得到了機(jī)械工程系老師的大力支持和指點(diǎn),在收集資料和編寫過程中,也得到了機(jī)械工程系資料室和學(xué)校圖書室的支持和幫助,在此一并表示衷心的感謝。主要參考文獻(xiàn)1 屈華昌主編 塑料成型工藝與模具設(shè)計(jì)北京:機(jī)械工業(yè)出版社19962 李云程主編 模具制造工藝學(xué) 北京: 機(jī)械工業(yè)出版社 20013 周開勤主編 機(jī)械零件手冊(cè) 北京:高等教育出版社 20014 范有發(fā)主編 沖壓與塑料成型設(shè)備 北京:機(jī)械工業(yè)出版20015 許德珠主編 機(jī)械工程材料 北京:高等教育出版社1991附錄外文資料TEMPERATURE CONTROL P. H. J. Ingham Marketing Manager ,Eurotherm Ltd,Worthing,Sussex,UK SUMMARYCommercial plastic materials are organically based and are therefore heatsensitive .Accurate temperature control of melt processes such as injection moulding is therefore necessary if problems caused by thermal degradation are to be avoided.The injection moulding process is considered form a temperature controlriewpoint and some of the control methods or techniques are described.since it should not be forgotten that good temperature control can lend to materials and energy savings. 1 INTRODUTIONThe injection moulding process is concerned with the efficient conversion of plastics raw material into moulded product of acceptable standards.Some of ths parameters which determine acceptability are weight,dimensions,colour and stenght,all of which can be affected by the conditions under which the material is processed.Having established by the conditions for thwese parameters so as to deermine acceptability,limits can be set for the conditions under which the material is processed.One of the most important parameters contributing to the correct operation of an injection moulding machine is temperature.All plastics materials can be correctly processed only within a certain range of temperatures which varies from materialFor some mateials and mould types the band isvery small and for others it can be quite wide.Any attempt to define the limits within which the product is acceptable determines the need for some form of control.There are a number of types of control which,if applied correctly,can lead to adequate performance.Significant material and energy savings can be achieved by correctly pplying the right type of control equipment.The reliability of the system and the degree of operator supervision required also depend very largely on the balance struck between initial cost and performance.It is the purpose of this chapter to examine the injection moulding machine from a temperature control viewpoint and to outline some of the control methods can be used ,together with advantages and disadvantages. 2 THE PROCESS2.1 Machine ZoningFrom a control viewpoint,an injection moulding machine consists of a number of zones (each equipped with a means of measauring the temperature) and a controller,which compares the measured value of the set-point and controls the heat input to the zone in such a way as to remove any different between the heat input to the zone in such a way as to remove any difference between the tow. Yu dividing the machine into a number of zones the different temperature requirements of different zones and their different heat input needs can most easily be met (Fig.1).For this purpose a typical small machine may have three or four barrel zones and a nozzle one. The zones nearest to the material feed hopper are where the plastic is melted and thus require fairly large heat inputs. However, in the zones hearest to the nozzle, the heat produced, by the rise in pressure needed to force the plastic into the mould, means that relatively little additional heat input is requied when the machine is running. Indeed, if the machine cycle very short, with some materials it may be that more heat is generated than required to maintain the temperature, which will then rise uncontrollably mless some form of additional cooling is applied.2.2 Thermocpuple LocationConsidering again the barrel zones:these consist of a metal arrel with wall thickness sufficient to withstand the high pressures produced during the mjection cycle. The most common form of heating is electrical and is ipplied using band heaters strapped around the barrel (Fig.2). A controller of any kind can only control the temperature at the point of measurement. Ideally this will be as deep into the barrel wall as possible, since it is the temperature of the plastic which is required and not that of the barrel. Plastic is a poor thermal conductor and depending on whether the net heat dow is into or out of the plastic, a thermocouple deep into the barrel wall will register a temperature above or below the actual temperature. If the measuring element is shallow or on the barrel surface, the difference between the measured and actual melt temperatures can be very large. For any given conditions of operation there will be a more or less fixed difference between the melt and measured temperatures and acceptable produce may be produced. If ,however, the conditions, e.g. machine speed or ambient temperature, change, this may give rise to a melt temperature which does not result in the production of acceptable product. It is therefore important to place the thermocouple as close to the melt as possible , i.e. deep the barrel.2.3 Temperature OvershootThe resultant system of an electrical band heater strapped around a thick walled barrel with a deep thermocouple is typical of most plastics processing machinery and present a number of control problems. Not only must stable control be achieved during normal running of the machine but acceptable start-up performance must also be achieved. The machine must be brought to its normal operating temperature as quickly as possible and preferably with no overshoot. (Overshoot is said to occur if the temperature is rising or falling at such a rate as it reaches set-point that it does not stop there but continues past by some amount before returning towards set-point again; see Fig.4.) The basic cause of temperature overshoot in the system is multiple heattransfer lags, i.e. where the heat generated electrically first raises the temperature of the heater thermal mass and is then conducted from the second thermal mass to a third and so on, until the heat reaches the point of measurement which, as stated already, is as near as possible to the point in the process to be controlled. In the simplest cast of multiple heat transfer only two thermal masses would be significantly involved, namely those of the heater and the load. If the thermal mass of each is about the same, this tends to represent about the worst case for overshoots (and hence controllability). Poor heat transfer from heater to load worsens the situation, since the heater temperature (during start-up, for example)can then become very much higher than the load temperature; when the power to the heater is cut off the final temperature reached (ignoring heat losses and assuming equal thermal masses for heater and load) will be the mean of their respective temperatures at the instant when the power is cut off. Thus ,the overshoot in load temperature increases as the heat transfer becomes worse.A particularly bad case of overshoot (and controllability) occurs where heat is transferred through a considerable thickness of heat-conducting material. This is exactly the situation which is presented by an injection machine barrel with deep set thermocouple. This sort of heat transfer represents in effect an infinite order multiple heat transfer: several minutes can elapse between switch-on of power and a significant change in thermocouple temperature. In fact the response has almost the appearance of a delay (i.e. transport lag ) although there is really a considerable difference between this heart-transfer lag and a true delay. During the time of the heart-transfer lag, heat is being fed into the barrel, so that even if the source of heat were switched off at the instant the deep thermocouple began to respond, the thermocouple temperature would continue to rise as the heat energy already fed in distributed itself evenly throughout the thickness of the barrel wall.A large part of the total lag can in practice be caused by the heart-transfer lag which occurs with a resistance heater. From the heater element thermal mass, via electrical insulation, to the outer surface of the barrel. For the lag through the barrel wall(or for any similar from the heat transfer) doubling the heart-transfer distance results in four times the lag. Iron, from which most injection machines are made, is a rather poor material for heat transfer: for example similar lag are obtained in aluminium and iron when the distance in aluminium is five times greater. 3. METHODS OF CONTROLLING TEMPERATURE 3.1 Measuring the TemperatureThe first item in the control system to consider is the measuring element, of which there are tow basic electrical types: active and passive.The active type are thermocouples. There are formed by the junction of tow dissimilar metals and give an output voltage proportional to the difference in temperature between the thermocouple and the point of measurement (Fig.3). The fact that the millivolt output of the thermocouple in relation to temperatures is non-linear and that it depends on a stable reference temperature for comparison purposes are factors , Which must be taken into account in the controller. Thermocouples are very robust mechanically. (This is an obvious advantage in the environment of the moulding shop.) They also exhibit good repeatability from example to example of the same type. The two most common types used in plastic processing are both base metal thermocouples and these are nickel chrome/nickel aluminium (Type K) and iron/jconstantan (Type J). The passive types rely on having a resistance which varies with temperature in a known manner and thus, when fed from a constant current upon temperature. Such elements do not require a reference temperature to be generated by the controller. The commonest are the platinum resistance thermometer (which occupies a larer volume than a thermocouple and is more fragile)and the thermistor(which operates on the same principle and has the same disadvantages). The thermocouple is by far the most common measuring elcment used in practice. The siting of the thermocouple will depend upon the degree of control required, as will the choice of controller.3.2 ON/OFF ControlThe simplest form of controller provides ON/OFF control of load power. The measured temperature is compared with the set-point and if it is too low, power is applied to the load; if it is too high the power is switched off. In practice there will be a small amount of hysteresis in the controller (mainly so that spurious noise signals on the thermocouple and effects due to mains regulation should not result in rapid ON/OFF chattering of the load power control relay). If the thermocouple and heater are in very close proximity, i.e. there is no appreciable lag, the temperature will cycle with an amplitude somewhat in excess of the controller hysteresis and with the natural period of the system. There will inevitably be some overshoot on start-up because full power will be applied to the load until the set and actual temperatures become equal and any stored energy in the heater will continue to be transferred to the load even after switch-off. It can be seen that if the thermocouple is deep in the barrel (thus measuring the melt temperature more closely) the system lags will be considerably increased and the temperature cycling will be of a longer period and will become much larger. Similar comments apply to the start-up overshoot. Thus ,in the least demanding circumstances, an ON/OFF controller with a shallow thermocouple may give acceptable results. However, with the large heaters required to give short start-up overshoot will probably be unacceptable for all but the least demanding situations and will be worse if account is taken of correct siting of the thermocouple. The natural period of the system results from a combination of heater power and location, sensor location, and the thermal mass of the system.3.3 Proportional Control (P only)If we take an ON/OFF controller and force the switching of the output within the controller itself (with variable mark: space ratio)at a rate which is higher than the natural period, then we have proportional control. As the measured temperature approaches the set temperature, the relay will switch off(for a short time) the power supplied to the load. This point, at which just less than full power is applied to the load, is the lower edge of the proportional band. As the actual temperature approaches the set temperature more closely, less and les power is applied to the load until, when the two become equal, the power input is zero. It is general for the proportional band to be downscale of the set-point, i.e. at set-point the power fed to the load is zer. The proportional band is usually defined as a percentage of the controller set-point scale span. Since the power applied to the load is proportional to the error or difference between actual and measured temperature (a so-called error-actuated system),it follows that if any power is required to maintain the temperature there must be some error in the system. This error is known as offset or droop (Fig.5). Since, on start-up, the load power will first be switched off at a temperature below the set-point, the resultant overshoot will be reduced. With a sufficiently large proportional band and sufficiently rapid cycling of the output power (compared to the systems natural frequency) the oscillations in temperature will cease eventually. However, this does not necessarily mean that there will be no sart-up overshoot in temperature, but only that the subsequent oscillation will decay to zero amplitude. 英文翻譯 注塑模的溫度調(diào)節(jié)系統(tǒng) 商用塑料是最常用的,但它是熱敏感性材料。如果說因熱引起的問題是可以避免的,那么象注塑模中熔化過程中精確的溫度控制就是有必要的。 從溫度控制的觀點(diǎn)和一些控制方法和技術(shù)的角度來考慮(這些方法和技術(shù)因不應(yīng)忘記而被敘述),好的溫度控制能節(jié)約和熱能。 一、介紹 注射模過程曾引起一次會(huì)議的討論,這次會(huì)議為模制產(chǎn)品的塑料原材料制定了可行性標(biāo)準(zhǔn)。一些可行性參數(shù)是重量,尺寸,顏色和強(qiáng)度。所有這些參數(shù)都受材料制造環(huán)境的影響。為了決定其可行性,為這些參數(shù)已經(jīng)建立了相應(yīng)的公差。對(duì)注射機(jī)的正確操作起作用的眾多參數(shù)中,最重要的一個(gè)參數(shù)是溫度,所有的塑料產(chǎn)品的制造都只有在特定的溫度范圍內(nèi)。這個(gè)特定的溫度范圍因材料而異。一些材料的這個(gè)溫度范圍相當(dāng)寬,而另一些材料的這個(gè)范圍卻相當(dāng)窄。 為使產(chǎn)品在允許溫度限制范圍內(nèi),需要某些形式的溫度控制。如果應(yīng)用正確,這里有大量的類型能導(dǎo)致正確控制形式的操作。通過正確的應(yīng)用控制設(shè)備。能節(jié)省貴重的塑料和能量。系統(tǒng)的現(xiàn)實(shí)性和操作者監(jiān)管要求的程度,也很大程度上依賴于最新消耗,運(yùn)輸消耗,工作費(fèi)用三者之間的平衡。 這章的目的是從溫度控制的角度來檢查注射模具和列舉一些常用的溫控方法以及其優(yōu)點(diǎn)。 二、 過程21 模具的分類 從控制的角度來說,一個(gè)注射模具由許多分區(qū)和一個(gè)控制部分組成(每一個(gè)分區(qū)有一種測量溫度的方法),控制器比較兩者之間的不同測量價(jià)值和控制兩者之間的不同,而用某種方法輸入到這個(gè)分區(qū)的熱移走。通過劃分模具的分區(qū),能使這些分區(qū)更容易認(rèn)識(shí),不同的分區(qū),要求有不同的溫度和不同的熱輸入(如圖1)為了達(dá)到這個(gè)目的,一個(gè)典型的小模具就可以有34個(gè)桶型區(qū)和噴管區(qū)。這些離主流道襯套最近的區(qū)域是塑料要求熔化的地方。因此要求有相當(dāng)大的熱量進(jìn)給。然而,在離主流道襯套最遠(yuǎn)的澆口處,通過增加注射壓力,使塑料和澆口之間產(chǎn)生摩擦熱。這意味著,當(dāng)模具在工作時(shí)只需要相當(dāng)小的熱量輸入。如果機(jī)器的循環(huán)周期非常短。某些材料在制造過程中比被要求的熱量產(chǎn)生更多的熱量,為了保持溫度,就需要采用某些形式的冷卻方式應(yīng)用。22 熱電偶的安裝 再考慮這些桶型區(qū):一個(gè)型腔應(yīng)具有足夠的壁厚。用以承受足夠的壓力。最平常的加工方法是電加熱和使用一個(gè)帶狀的加熱片貼在型腔周圍(如圖2),在任何類型的一個(gè)控制器都只能控制一個(gè)點(diǎn)的測量溫度的測試,而且盡可能貼近型腔。因?yàn)槲覀冃枰氖撬芰系臏囟?,而不是型腔的溫度,塑料是熱的不良?dǎo)體。依靠純熱進(jìn)去塑料,如果熱電偶安放在型腔的表面或非常淺,那么測量值和實(shí)際值之間將會(huì)有非常大的差異。 任何給出的操作環(huán)境都或多或少的存在實(shí)際值和測量值之間的差異。然而如果環(huán)境變化,如模具的運(yùn)動(dòng)速度和周圍的環(huán)境溫度變化,這都可以影響到工件的熔化溫度。因此,熱電偶的安裝位置要盡可能的靠近型腔的內(nèi)壁。23溫度過調(diào)量 一個(gè)具有一個(gè)熱電偶的加熱片貼在一個(gè)深孔型腔的壁上。它的合模系統(tǒng)是最典型的塑料加工機(jī)械,而且存在著大量的控制問題,不僅在正常的模具工作期間必須完成穩(wěn)定的控制,而且可行的合理的初始操作也必須完成機(jī)械可以在不用調(diào)節(jié)時(shí)盡可能完美而迅速地使它達(dá)到正常的操作溫度(如果溫度上升或下降,以某一頻率。就是說它經(jīng)過那點(diǎn),但不停留在那點(diǎn),而是在它返回那點(diǎn)時(shí)繼續(xù)通過一定數(shù)量的點(diǎn)。在這種情況下,過量調(diào)節(jié)就出現(xiàn)了。如圖4) 在系統(tǒng)中引起過量調(diào)節(jié)的基本原因是,多個(gè)熱傳導(dǎo)滯后等產(chǎn)生的殘余熱量。首先,引起受熱物體的溫度上升,然后,傳遞給第二個(gè)受熱物體,同時(shí)使第二個(gè)物體溫度上升,然后從第二個(gè)受熱物體傳遞給第三個(gè)受熱物體。以次類推直到熱在傳遞過程中達(dá)到控制溫度的點(diǎn)附近。 舉一個(gè)最簡單的多個(gè)熱傳遞的例子,如果兩個(gè)受熱體,如果每個(gè)受熱體都是一樣的,那將是過調(diào)量中最糟的。一種情況,沖加熱到裝入的差的熱傳遞使環(huán)境變?cè)悖驗(yàn)榧訜釡囟龋ㄈ缭陂_始時(shí)的溫度)。將使最終裝入溫度遠(yuǎn)高于其本身。當(dāng)加熱電源切斷時(shí),最終溫度就達(dá)到了。(忽略溫度損失和假設(shè)加熱熱量和吸收熱量相等)。這將意味著最終電源切斷時(shí),最終各方面的溫度。因此,過調(diào)量作為過調(diào)量作為熱傳遞在裝入溫度上升時(shí)變地更糟。 在特別糟的過調(diào)量(可控制)的情況出現(xiàn)在熱傳遞通過熱導(dǎo)體材料的深處,這是實(shí)際的環(huán)境。這個(gè)環(huán)境是一個(gè)具有深的安裝電熱偶的注射模具環(huán)境。這套熱傳遞系統(tǒng)抽繪一個(gè)無限次續(xù)的多熱傳遞系統(tǒng)的影響。在打開電源和在熱電偶中的一次重要轉(zhuǎn)變之間需要幾分鐘的時(shí)間。實(shí)際上,這反映的是一種延時(shí)的表現(xiàn)(如傳導(dǎo)滯后),雖然熱傳導(dǎo)滯后和真正的延時(shí)之間存在著差異,在熱傳導(dǎo)滯后和真正的延時(shí)之間存在著差異,在熱傳導(dǎo)滯后的時(shí)間中,熱進(jìn)給到型腔,以至于熱源被切斷的瞬時(shí)深的熱電偶開始反應(yīng),當(dāng)熱能已經(jīng)進(jìn)給通過整個(gè)型腔壁后來完全地分配本身。 總的滯后的大部分,可以是由于發(fā)生在熱阻傳導(dǎo)體的熱傳導(dǎo)滯后引起,熱阻傳導(dǎo)體從熱的基本發(fā)熱體,經(jīng)過電隔離在型腔外表,因?yàn)闇笸ㄟ^型腔壁(或任何一個(gè)類似的熱傳導(dǎo))兩倍的熱傳導(dǎo)距離而產(chǎn)生了四倍的滯后。大多數(shù)注射模具制造用的鋼材對(duì)熱傳導(dǎo)是相當(dāng)差的材料。舉一個(gè)簡單的例子:當(dāng)在鋁中的距離比在鐵中大五倍時(shí)。在鐵和鋁中能得到相同的熱滯后。 三、 溫度控制的方法31溫度的測量 在控制系統(tǒng)中,首先要考慮的一條是測量的元素,它有兩種基本的電子測量類型:主動(dòng)的和被動(dòng)的類型。 主動(dòng)類的是熱電偶,它由兩種不同金屬片和一個(gè)外部電壓組成。這個(gè)外部電壓與熱電偶和測量點(diǎn)之間的不同溫度相稱(如圖3);熱電偶的毫伏輸出電壓與溫度不成線性關(guān)系,它依賴一個(gè)作為比較目的的穩(wěn)定的參考溫度,這一事實(shí)都是在控制器里必須考慮的因素,熱電偶具有相當(dāng)強(qiáng)的機(jī)動(dòng)性(這在模具工廠的環(huán)境中是相當(dāng)有利的)。這些因素也表現(xiàn)好的重復(fù)性。從例子到相同的類型的例子,兩個(gè)最常用在塑料加工過程的例子都是金屬熱電偶的基本組合材料,它們是鎳鉻/鎳鋁合金(類型K)和鋼/銅合金(類型J)。 無源類熱電偶,存在一種阻力,這種阻力使溫度不同于眾所周知的那種方式。因此,當(dāng)在恒流電源的作用下,這種阻力將產(chǎn)生電壓,這個(gè)電壓依賴于所通過的材料的溫度。最常用的是鉑阻熱電偶(這種熱電偶比以前講的普通熱電偶具有更大的容量,并且更容易碎。)和熱敏電阻(它是用同樣的原理進(jìn)行工作具有同樣多的不利條件)。熱電偶是在實(shí)踐中被大量使用的最常用的測量工具。熱電偶的定線將依賴于要求控制的度數(shù)和所選的溫度控制器。32控制器的開關(guān) 控制器的最簡單的形式提供負(fù)載電源開關(guān)的控制,測得的溫度與安裝點(diǎn)比較,假如溫度太低,負(fù)載電源將參與工作,假如溫度太高,負(fù)載電源見被切斷,在實(shí)際中,在控制器中有一些磁滯現(xiàn)象。如果熱電偶和加熱器非常接近,那么這就不存在滯后,溫度將以某種振動(dòng)進(jìn)行循環(huán)。這個(gè)振幅是由控制起的滯后和系統(tǒng)的自然周期引起,因?yàn)槿β实碾娫丛谝蟮臏囟群蛯?shí)際溫度相等之前一直提供負(fù)載,所以在開始時(shí)有一定的過調(diào)量是不可避免的。很明顯,如果熱電偶在型腔壁的深層(因此測量的熔化溫度更接近)。系統(tǒng)的滯后增大,溫度的循環(huán)周期將變長,振幅將變大,也同樣在開始時(shí)有一個(gè)過調(diào)量。 因此,一個(gè)具有線的熱電偶開/關(guān)控制器可以得出所接受到的結(jié)果,這是起碼的要求。然而具有大的熱電偶的開/關(guān)控制器要求有一個(gè)更短的啟動(dòng)時(shí)間。如果計(jì)算考慮了這個(gè)熱電偶的正確安放位置,那么這個(gè)啟動(dòng)時(shí)間過短將可能是對(duì)于所有控制器來說是不接受和更糟的。除這起碼的要求。 這套系統(tǒng)的自然時(shí)期來源于一個(gè)熱電偶能量與位置的聯(lián)合作用,傳感器的位置和系統(tǒng)的熱量集中區(qū)域三個(gè)因素。33比例的控制(僅僅是P的控制) 如果我們使用一個(gè)開/關(guān)控制器,并且迫使輸出量轉(zhuǎn)換。在控制器內(nèi)部本身有一個(gè)頻率,這個(gè)頻率高于自然時(shí)期的,然后我們將要進(jìn)行一個(gè)比例的控制問題。當(dāng)測量的溫度接近安放點(diǎn)的溫度時(shí),繼電器將在短時(shí)間內(nèi)切斷提供負(fù)載電源,在比最大電源電壓少一些的這個(gè)點(diǎn)是比例帶的最低邊緣,當(dāng)實(shí)際溫度接近安放點(diǎn)的溫度時(shí),越來越少的電源電壓進(jìn)給量,直到兩者完全相同時(shí),電源輸入量將變成零。總的一句話來說,對(duì)于比例帶到安放點(diǎn)呈降低的比例趨勢。例如在安放點(diǎn)的電量進(jìn)給為零。 比例帶的定義就是一個(gè)控制器安放點(diǎn)的范圍段的一個(gè)百分率。因?yàn)殡娫簇?fù)載的誤差是成比例的,或是實(shí)際溫度與測量溫度之間存在著差異(一個(gè)所謂的誤差一個(gè)實(shí)際系統(tǒng)),這產(chǎn)生的后果將是假如任何電源要求保持溫度,這將使在系統(tǒng)中產(chǎn)生某些錯(cuò)誤,這個(gè)誤差就是眾所周知的偏差和下降(如圖5)。然而在開始上升階段,在溫度還低于安放點(diǎn)時(shí),負(fù)載電源將被關(guān)掉,短期內(nèi)的結(jié)果將降低,用一個(gè)足夠大的比例帶和足夠快的外部輸出電壓的循環(huán)(與系統(tǒng)本身的自然頻率相比)溫度的波動(dòng)將最終停止。然而,這并不意味著這里沒有上升的過調(diào)量,而僅僅只是意味著在此以后的波動(dòng)將減小到振幅為零。
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