滾輪注塑模具設(shè)計(jì)【一模四腔】【槽輪】【滑輪】【輪子】【說明書+CAD+PROE】
滾輪注塑模具設(shè)計(jì)【一模四腔】【槽輪】【滑輪】【輪子】【說明書+CAD+PROE】,一模四腔,槽輪,滑輪,輪子,說明書+CAD+PROE,滾輪注塑模具設(shè)計(jì)【一模四腔】【槽輪】【滑輪】【輪子】【說明書+CAD+PROE】,滾輪,注塑,模具設(shè)計(jì),說明書,仿單,cad,proe
摘 要
塑料是一種可塑性的合成高分子材料,具有重量輕且堅(jiān)固,耐化學(xué)腐蝕, 電絕緣性好,價(jià)格便宜,可塑性好等特點(diǎn),廣泛應(yīng)用于電腦、手機(jī)、汽車、電機(jī)、 電器、家電和通訊產(chǎn)品制造中。 注塑成形是成形塑件的主要方法之一, 是指使用注塑機(jī)將熱塑性塑料熔體在 高壓下注入到模具內(nèi)經(jīng)冷卻固化獲得產(chǎn)品的方法。注塑的優(yōu)點(diǎn)是生產(chǎn)速度快,效 率高,操作可自動化,能成型形狀復(fù)雜的零件,特別適合大量生產(chǎn)。 本次課程設(shè)計(jì)的產(chǎn)品為電源按鍵,具有重量輕,強(qiáng)度高,耐腐蝕,易清潔等 特點(diǎn),為大批量生產(chǎn)產(chǎn)品。本次設(shè)計(jì)在針對產(chǎn)品進(jìn)行工藝性分析后,確定模具分 型面、 型腔數(shù)目、 澆口形式、 位置大??; 其中最重要的是確定型芯和型腔的結(jié)構(gòu), 以及它們的定位和緊固方式。此外還進(jìn)行了脫模機(jī)構(gòu)的設(shè)計(jì),合模導(dǎo)向機(jī)構(gòu)的設(shè) 計(jì),冷卻系統(tǒng)的設(shè)計(jì)等。最后繪制完整的模具裝配總圖和主要的模具零件圖及編 制成型零部件的制造加工工藝過程卡片。實(shí)踐證明:該模具結(jié)構(gòu)合理、可靠,并 能保證產(chǎn)品質(zhì)量,對此類注塑產(chǎn)品的模具設(shè)計(jì)有參考價(jià)值。
關(guān)鍵詞:塑料 , 注塑成形 , 模具設(shè)計(jì)
Abstract
Plastic is a synthetic polymer material , with the characteristics of plasticity, light weight, sturdiness, electrical insulation, and which is resistance to chemical corrosion and cheap. It is widely used in computers, mobile phones, cars, motors, electrical, home appliances and communication products manufacturing. Injection molding is one of the main methods of forming plastic parts, it refers to the use of plastic injection machine to inject the thermoplastic melts into the mold under high pressure , after cooled to obtain the products . It has the advantage of fast production speed , high production efficiency , and automated operations , it can form the shape of complex parts, particularly suitable for mass production. The production of graduation project is power button , which has a light weight , high strength , corrosion resistance and easy cleaning features for mass production . After analysis the process of the product , the mold parting line , cavity number , gate form , gate location can be determined , one of the most important is to identify core and cavity structures , as well as their positioning and fastening methods. In addition, it also carries out the design of stripping agencies , mold-oriented organizations and the cooling system .At last, draw a complete mold assembly drawing , major parts diagram , and draw up cards of parts manufacturing and processing process . It is proved that the mold structure is reasonable , reliable and can guarantee product quality , and is valuable for the injection mold design of such products .
Key Words: Plastic , Injection molding , Mold design
I
1.1 引言
隨著塑料工業(yè)的飛速發(fā)展和通用塑料與工程塑料在強(qiáng)度和精度等方面的不斷提高,塑料制品的應(yīng)用范圍也在不斷地?cái)U(kuò)大,如:家用電器、儀器儀表、建筑器材、汽車工業(yè)、日用五金等眾多領(lǐng)域,塑料制品所占的比例正迅速增加,由于在工業(yè)產(chǎn)品中,一個(gè)設(shè)計(jì)合理的塑料件往往能代替多個(gè)傳統(tǒng)金屬結(jié)構(gòu)件,加上利用工程塑料特有的性質(zhì),可以一次成型非常復(fù)雜的形狀,并且還能設(shè)計(jì)成卡裝結(jié)構(gòu),成倍地減少整個(gè)產(chǎn)品中的各種緊固件,大大地降低了金屬材料消耗量和加工及裝配件工時(shí),因此,近年來工業(yè)產(chǎn)品塑料化的趨勢不斷上升。
模具是利用其特定形狀去成型具有一定形狀和尺寸的制品的工具。 在各種材 料加工工業(yè)中廣泛地使用著各種模具,例如金屬鑄造成型使用的砂型或壓注模具、金屬壓力加工使用的鍛壓模具、冷壓模具及成型陶瓷、玻璃等制品使用的各 種模具。塑料模具是指用于成型塑料制件的模具,它是型腔模的一種類型。 模具是工業(yè)生產(chǎn)中的重要工藝裝備。 模具工業(yè)是國民經(jīng)各部門發(fā)展的重要基礎(chǔ)之一。模具設(shè)計(jì)水平的高低、加工設(shè)備的好壞、制造力量的強(qiáng)弱,模具質(zhì)量的優(yōu)劣,直接影響著許多新產(chǎn)品的開發(fā)和老產(chǎn)品的更新?lián)Q代,影響著產(chǎn)品質(zhì)量和經(jīng)濟(jì)效益的提高。 對塑料模具的全面要求是: ①尺寸精度、外觀、物理性能等各方面均能滿足使用要求的優(yōu)質(zhì)制品。 ②高效率、自動化、操作簡便。 ③結(jié)構(gòu)合理、制造容易、成本低廉。 ④盡量減少開模、合模和取制件過程中的手工勞動。為此常采用自動開合模 及自動頂出機(jī)構(gòu)。 ⑤合理的加工工藝、高效的設(shè)備、先進(jìn)的模具。
1.2 塑料模具在國民經(jīng)濟(jì)中的作用
塑料模具(簡稱塑模)的現(xiàn)代設(shè)計(jì)與制造和現(xiàn)代塑料工業(yè)的發(fā)展有極密切的 關(guān)系。 塑模是現(xiàn)代塑料工業(yè)中的重要工藝裝備。 塑模工業(yè)是國民經(jīng)濟(jì)的基礎(chǔ)工業(yè)。 用塑模生產(chǎn)成形零件的主要優(yōu)點(diǎn)是制造簡單、材料利用率高、生產(chǎn)效率高、產(chǎn)品的尺寸規(guī)格一致,特別是對大批量生產(chǎn)的機(jī)電產(chǎn)品,更能獲得價(jià)廉物美的經(jīng)濟(jì)效果。塑模也是成型塑料制品的主要工具, 它的結(jié)構(gòu)和加工精度對塑件的質(zhì)量和生 產(chǎn)效率等有直接的關(guān)系。因而世界各國對塑模的現(xiàn)代設(shè)計(jì)與制造技術(shù)都極為關(guān)注。近年來國外對塑模的熱澆道、溫度控制系統(tǒng)、應(yīng)用數(shù)控機(jī)床加工及減少熱處 理變形等方面都作了許多探索,并取得了一定的成果。 塑模廣泛應(yīng)用于成型塑料制品,它利用塑料在高溫下所具有的流動性或可塑性, 將其成型為具有一定形狀和尺寸, 并通過化學(xué)或物理變化,定型為塑料制品。在塑料加工工業(yè)中,普遍使用有以下幾種塑模:(1)壓縮成型的塑料模具。 (2)壓入成型的塑料模具。 (3)擠出成型的塑料模具。 (4)注射(塑)成型的塑料模具。 此外,還有發(fā)泡成型塑模,真空成型塑模、吹塑成型塑模、玻璃纖維增強(qiáng)塑 料成型塑模等等, 但這些塑模的設(shè)計(jì)是建立在以上所述常用的集中塑模設(shè)計(jì)基礎(chǔ) 上,且比較簡單。隨著塑模成型方法的不斷出現(xiàn),必然將還會產(chǎn)生各種新型塑料 的新型成型模具。 近年來我國塑料工業(yè)生產(chǎn)的發(fā)展速度很快, 塑料的應(yīng)用正普及到國民經(jīng)濟(jì)領(lǐng) 域的各個(gè)部門。采用塑模加工的塑件也很多,如各種管材、板材、異型材、復(fù)合 管材、發(fā)泡型材及棒材等,都廣泛用于紡織品、醫(yī)藥品、化學(xué)物品、機(jī)密儀器、 日用品及機(jī)械行業(yè)中的齒輪、 軸承等機(jī)械零件, 在汽車、 飛機(jī)、 造船業(yè)中的儀表、 車門、內(nèi)襯等,化學(xué)工業(yè)中的貯槽、貯罐、填料等,電子及電信工業(yè)中的電線、 電纜絕緣層及防護(hù)套等也得到廣泛的應(yīng)用, 特別是在建筑工業(yè)中塑料的應(yīng)用更為 廣泛, “以塑代木,以塑代金屬”為人類鉆尋求解決替代有限的木材和貴重金屬 材料開辟了新途徑。 當(dāng)前在我國塑料戰(zhàn)線上出現(xiàn)了許多新的塑膜結(jié)構(gòu)和新的塑模 的加工方法,為我國塑料模具的設(shè)計(jì)與制造走向現(xiàn)代化提供了有利條件。據(jù)資料 介紹, 國外一些工業(yè)比較先進(jìn)的國家在塑模的設(shè)計(jì)與制造方面, 已經(jīng)采用 CAD/CAM 系統(tǒng),這對提高塑料制品質(zhì)量,縮短塑模制造周期,降低塑件成產(chǎn)成本方面取得 較好經(jīng)濟(jì)效益。
1.3 塑料成型模具發(fā)展趨勢
近年來,塑料成型加工機(jī)械和成型模具增長十分迅速,高效率、自動化、大 型、微型、精密、長壽命的模具在整個(gè)模具產(chǎn)量中所占的比重越來越大。 (1) 加深理論研究 隨著對塑料成型加工原理的研究越來越深入, 模具設(shè)計(jì)已由經(jīng)驗(yàn)設(shè)計(jì)階段逐步向 理論計(jì)算設(shè)計(jì)方面發(fā)展。 這些理論為塑料模具的計(jì)算機(jī)輔助設(shè)計(jì)和輔助工程奠定 了基礎(chǔ)。 (2) 高效率、自動化 如多層多型腔注射模結(jié)構(gòu)、各種自動脫出產(chǎn)品和流道凝料的脫模機(jī)構(gòu)、自動分型 抽芯機(jī)構(gòu)、熱流道澆注系統(tǒng)注射模具以及高效冷卻結(jié)構(gòu)。高效自動化的模具與高 速自動化的成型設(shè)備相配合對提高生產(chǎn)效率、提高產(chǎn)品質(zhì)量,降低生產(chǎn)成本起了 很大作用。 (3) 大型、超小型及高精度 隨著塑料應(yīng)用領(lǐng)域日益擴(kuò)大,在建筑、機(jī)械、汽車、儀器、家用電器等采用了許 多大型、精密和高壽命的塑料制品,如汽車殼體、洗衣機(jī)桶、傳動齒輪、軸承等。 大型模具設(shè)計(jì)要求作詳細(xì)準(zhǔn)確的理論計(jì)算,由于模具自重大,物料流程長,型腔 易變形,因此在結(jié)構(gòu)設(shè)計(jì)上需作更為周密的考慮。高精度模具要求配合精度和運(yùn) 動精度都很高,耐磨損,模溫控制精確,在高壓下成型,收縮變形小。 (4) 革新模具制造工藝 塑料模具制造中最困難的部分是型腔,特別是異形復(fù)雜型腔的加工,若采用各種 坐標(biāo)機(jī)床、仿形機(jī)床、光控機(jī)床、數(shù)控機(jī)床等來代替?zhèn)鹘y(tǒng)的機(jī)械加工方法,這樣 不僅縮短制模周期、提高模具精度,而且還降低了勞動強(qiáng)度和生產(chǎn)成本。采用精 密鑄造、冷擠壓、電加工等新工藝技術(shù)給模具型腔加工帶來了巨大方便 (5) 模具計(jì)算機(jī)輔助設(shè)計(jì)(CAD)、輔助工程(CAE) CAD 軟件的主要功能是幾何造型技術(shù), 它將制品圖形立體地精確地顯示在屏幕上, 完成制件設(shè)計(jì)的繪圖工作,對制品或模具進(jìn)行力學(xué)分析。 CAE 軟件中流動軟件可以模擬熔體在模內(nèi)的流動過程,冷卻分析軟件可模擬熔體 的凝固過程和在模內(nèi)的溫度變化,預(yù)測可能出現(xiàn)的問題,如制品缺陷、翹曲、變 形、內(nèi)應(yīng)力等,使計(jì)算結(jié)果優(yōu)化。 (6) 標(biāo)準(zhǔn)化
模具標(biāo)準(zhǔn)化包括塑料注射模零件標(biāo)準(zhǔn)、塑料注射模零件技術(shù)條件、塑料注射模模 架標(biāo)準(zhǔn)、塑料注塑模技術(shù)條件等,其中零件標(biāo)準(zhǔn)包括導(dǎo)柱、導(dǎo)套、推桿、模板等。 模具標(biāo)準(zhǔn)化為塑料模具設(shè)計(jì)和制造都帶來極大的方便,由于標(biāo)準(zhǔn)件可以直接購 買,因此模具設(shè)計(jì)制造者只需精心設(shè)計(jì)和加工型腔,這樣使塑料模具設(shè)計(jì)和制造 周期大為縮短,成本降低,質(zhì)量得到保證。目前發(fā)達(dá)國家標(biāo)準(zhǔn)化程度達(dá)到 30%以 上,我國標(biāo)準(zhǔn)化程度不高,還需大力推廣,充實(shí)完善。
目 錄
1、工藝性分析………………………………………………………(1)
2、確定型腔數(shù)目…………………………………………………… (1)
3、型腔、型芯工作部位尺寸的確定………………………………(1)
4、澆注系統(tǒng)的設(shè)計(jì)………………………………………………… (3)
5、選用模架………………………………………………………… (4)
6、校核注射機(jī) ………………………………………………………(5)
7、推出結(jié)構(gòu)設(shè)計(jì) ……………………………………………………(5)
8、冷卻系統(tǒng)的設(shè)計(jì) …………………………………………………(6)
9、排氣系統(tǒng)的設(shè)計(jì) …………………………………………………(6)
10、總 結(jié) ……………………………………………………………(9)
11、參考文獻(xiàn) ………………………………………………………(10)
如圖所示塑件,材料為ABS,收縮率0.3%~0.8%。生產(chǎn)批量15萬件。
1、工藝性分析
1)該塑件尺寸較適中,一般精度等級,但因形狀復(fù)雜,采用一模四腔。
2)為了方便加工和熱處理,型腔與型芯部分采用拼鑲結(jié)構(gòu)。
2、確定型腔數(shù)目
根據(jù)塑件的生產(chǎn)批量及尺寸要求采用一模2腔。
按照塑件所示尺寸,近似計(jì)算:
塑件體積Vs≈2.7688cm3
查表6-1塑料ABS的密度為 1.02~1.05g/cm3 (注塑級密度為1.05g/cm3)
單件塑件重量:ms=2.128*1.05g=2.9526≈3g
3、型腔、型芯工作部位尺寸的確定
查表6-4ABS塑料的收縮率是0.3%-0.8%。
平均收縮率:S=(0.3%+0.8%)/2=0.6%
型腔工作部位尺寸:
型腔徑向尺寸:L?m+δ0=〔(1+ S )×Ls -X△〕+δ0
型腔深度尺寸:H?m+δ0=〔(1+ S )×Hs -X△〕+δ0
型芯徑向尺寸:lm-δ0=〔(1+ S )×ls -X△〕-δ0
型芯高度尺寸:hm-δ0=〔(1+ S )×hs -X△〕-δ0
中心距尺寸: Cm±δz/2=(1+S)Cs±δz/2
式中 Ls—塑件外型徑向基本尺寸的最大尺寸(mm)
ls —塑件內(nèi)型徑向基本尺寸的最小尺寸(mm)
Hs—塑件外型高度基本尺寸的最大尺寸(mm)
hs—塑件內(nèi)型高度基本尺寸的最小尺寸(mm)
Cs—塑件中心距深度基本尺寸的平均尺寸(mm)
修正系數(shù),取0.5~0.75
塑件公差(mm)
δz—模具制造公差,?。?/3~1/4)△
各工件部位尺寸計(jì)算結(jié)果如圖所示
通常,制品中1mm和小于1mm并帶有大于0.05mm公差的部位以及2mm和小于2mm并帶有大于0.1mm公差的部件不需要進(jìn)行收縮率計(jì)算。
4、澆注系統(tǒng)的設(shè)計(jì)
(1)確定分型面的位置。
(2)確定澆口形式及位置。為了提高生產(chǎn)效率,便于去除澆口凝料采用中心澆口尺寸與位置如圖所示。
塑件在澆口處的壁厚為1.5mm,澆口直徑可以根據(jù)課本:《塑料成型工藝及模具設(shè)計(jì)》P73,取d=2mm
(3)型腔位置的排布。該件采用一模一腔的結(jié)構(gòu)形式,那么澆注系統(tǒng)的設(shè)計(jì)應(yīng)直接采用從主流道到型腔流道的形狀及尺寸相同的設(shè)計(jì),即平行式布置的形式。
(4)初步設(shè)計(jì)主流道及分流道形狀和尺寸。主流道設(shè)計(jì)成圓錐形,其錐角為2°~6°。
分流道截面設(shè)計(jì)成圓形截面,加工較容易,且熱量損失與壓力損失均不大,為常用模式。圓形截面分流道的直徑可根據(jù)塑料的流動性等因素來確定,該塑料為ABS塑料,流動性好,所以選用圓形截面。根據(jù)《塑料成型工藝及模具設(shè)計(jì)》分流道的直徑d可?。病秏m,澆口長度L=1mm.
5、選用模架
(1)型腔強(qiáng)度和剛度的計(jì)算。為了方便加工和熱處腔鑲件可分為兩部分,如圖可看出,型腔為整體式。因此,型腔的強(qiáng)度和剛度按型腔為組合式進(jìn)行計(jì)算。由于型腔壁厚計(jì)算比較麻煩,也可參考經(jīng)驗(yàn)推薦數(shù)據(jù)。
查本書表6-16型腔壁厚S1=8mm,模套壁厚S2=18mm
(2)初選注塑機(jī)
1)注塑量:該塑件制件單件重:ms≈3g
澆注系統(tǒng)重量的計(jì)算可根據(jù)塑件尺寸計(jì)算的澆注系統(tǒng)的體積。
Vj≈0.5107cm3
粗略計(jì)算澆注系統(tǒng)重量 mj≈Vj×p=0.5107×1.05g≈0.53g
總體積 V塑件=(2.769+0.5017)cm3=3.2771 cm3
總重量 M=3.2771×1.05g≈3.434 g
聚苯乙烯的密度為1.054g/ cm3,ABS塑料密度為1.02~1.05g/cm3。
滿足注射量 V機(jī)≥V塑件/0.80
式中 V機(jī)-額定注射量(cm3);
V塑件-塑件與澆注系統(tǒng)凝料體積和(cm3)。
V塑件/0.80=3.277/0.80 cm3=4.096 cm3
或滿足注射量 M機(jī)≥M塑件p/(p1×0.8)
式中 M機(jī)-額定注射量(g);
M塑件-塑件與澆注系統(tǒng)凝料的重量和(g);
p1-聚苯乙烯的密度(g/cm3);
p2-塑件采用塑料的密度(g/cm3)
M塑件p2/ p1×0.8 =0.53×1.05/1.054×0.8 g =0.66g
2)注射壓力: ρ注≥ρ成型
查表知ABS塑料成型時(shí)的注射壓力ρ成型=70~90MPa
3)鎖模力
P鎖模力≥pF
式中p-塑料成型時(shí)型腔壓力,ABS塑料的型腔壓力p=30MPa;
F——澆注系統(tǒng)和塑件在分型面上的投影面積和()
各型腔及澆注系統(tǒng)及各型腔在分型面上的投影面積
F=(3.14×162+3.14×112+3.14×152)=1890.28()
pF=30X1890.28=56708.4N=56.7KN
根據(jù)以上分析、計(jì)算,查表知初選注射機(jī)型號為
注射機(jī)有關(guān)技術(shù)參數(shù)如下
最大合模行程S 160mm
模具最大厚度 180mm
模具最小厚度 60mm
噴嘴圓弧半徑 12mm
噴嘴孔直徑 2mm
動、定模板尺寸 250mm×280mm
拉桿空間 235mm
3)選標(biāo)準(zhǔn)模架 根據(jù)以上分析,計(jì)算以及型腔尺寸及位置尺寸可確定模架的結(jié)構(gòu)形式和規(guī)格,查表可選用 :
定模板厚度:A=50mm
動模板厚度:B=50mm
墊塊厚: C=60mm
模具厚度: H模=40+A+B+C=201mm
模具外形尺寸:180mm×300mm×201mm
6. 校核注射機(jī)
1) 注射量、鎖模力、注射壓力、模具厚度的校核
2) 開模行程的校核 注射機(jī)的最大開模行程S
S≥2h件 +h 澆+﹙5~10﹚
S=2×11+30+8=60mm
式中h件_塑料制品高度﹙mm﹚
h澆_澆注系統(tǒng)高度﹙mm﹚
3)模具在注射機(jī)上的安裝 從標(biāo)準(zhǔn)模架外形尺寸看小于注射機(jī)拉桿空間,并采用壓板固定模具,所以所選注射機(jī)規(guī)格滿足要求
7. 推出結(jié)構(gòu)設(shè)計(jì)
1)推件力的計(jì)算
Ft=Ap(μcosα-sinα)
A——塑料包絡(luò)型芯的面積()
p——塑件對型芯單位面積上的包緊力,
α——脫模斜度
q——大氣壓力0.09MPa
μ——塑件對鋼的摩擦系數(shù)μ,約為0.1–0.3;
A1——制件垂直于脫模方向的的投影面積()
A≈(78.5+207.24+392.5)()=678.24()
Ft=678.24x1.2x(0.3cos40`-sn40`)/=2346.85N 2)確定頂出方式及頂桿位置
根據(jù)制品結(jié)構(gòu)特點(diǎn),確定斜滑塊側(cè)向抽芯機(jī)構(gòu),四個(gè)普通圓頂桿分布在滑塊上。
8. 冷卻系統(tǒng)的設(shè)計(jì)
如圖
由于制品平均壁厚為2mm,制品尺寸又較小,確定水孔直徑為8mm。
由于冷卻水道的位置、結(jié)構(gòu)形式、孔徑、表面狀態(tài)、水的流速、模具材料等很多因素都會影響模具的熱量向冷卻水傳遞,精確計(jì)算比較困難。實(shí)際生產(chǎn)中,通常都是根據(jù)模具的結(jié)構(gòu)確定冷卻水路,通過調(diào)節(jié)水溫、水速來滿足要求。
采用滑塊上及定模板上開水道的形式。
9. 排氣系統(tǒng)的設(shè)計(jì)
由于制品尺寸較小,利用分型面及其它零件的結(jié)合面的配合間隙排氣即可。
10.頂出機(jī)構(gòu)如圖
11. 按要求繪制裝配圖。
總結(jié)與展望
一、總結(jié)
通過本次課程設(shè)計(jì)我學(xué)到了許多知識,我的畢業(yè)設(shè)計(jì)題目是帶輪注塑模具設(shè)計(jì)。此次設(shè)計(jì)要綜合運(yùn)用到我大學(xué)三年里所學(xué)到的理論知識和專業(yè)知識,并為即將踏入社會的我奠定了堅(jiān)實(shí)的基礎(chǔ)。以下是我對這次的畢業(yè)設(shè)計(jì)的一些體會和心得:
這次課程設(shè)計(jì)是一個(gè)理論與實(shí)踐相結(jié)合的過程,這次設(shè)計(jì)教會了我發(fā)現(xiàn)問題時(shí)如何去解決它。解決問題的方法有很多,但是哪一個(gè)更合理這就要通過自己的計(jì)算了。通過這次畢業(yè)設(shè)計(jì),我還發(fā)現(xiàn)了自己的許多不足之處,比如想問題總是過于簡單化,考慮不全面,愛鉆死胡同,想到一個(gè)方案也不管是否合理就埋頭苦算,到最后還是要改。在今后的工作過程中我會做到揚(yáng)長避短。
設(shè)計(jì)時(shí),經(jīng)過不斷的到校圖書館認(rèn)真地查找和借閱相關(guān)的參考資料,不但提高了個(gè)人查閱資料的能力,還擴(kuò)闊了我的知識視野。本模具采用autoCAD、pro/e設(shè)計(jì),在畢業(yè)設(shè)計(jì)其間對軟件的理解與熟練程度得到了很好的提升。
二、今后研究方向
在設(shè)計(jì)的過程中,也出現(xiàn)了一些客觀不足的問題,沒有實(shí)踐條件,不能根據(jù)實(shí)際的情況來作合適、客觀地修改,加上我自己的實(shí)踐經(jīng)驗(yàn)又不多,這樣做出來的設(shè)計(jì),難免有不足之處,希望楊老師能夠體諒。
參考文獻(xiàn)
[1] [塑料模具設(shè)計(jì)手冊]編寫組,模具手冊之二[塑料模具設(shè)計(jì)手冊](第2版)[M],北京:機(jī)械工業(yè)出版社,2001.2
[2] 陳萬林等,[實(shí)用塑料注射模設(shè)計(jì)與制造] [M],北京:機(jī)械工業(yè)出版社,2000
[3] 黨根茂,駱志斌,李集仁,[模具設(shè)計(jì)與制造] [M],陜西:西安電子科技大學(xué)出版社,1995.12
[4] 付宏生,劉京華,[注塑制品與注塑模具設(shè)計(jì)] [M],北京:化學(xué)工業(yè)出版社,2003.7
[5] 模具實(shí)用技術(shù)編委會,[塑料模具設(shè)計(jì)制造與應(yīng)用實(shí)例] [M],第一版,北京:機(jī)械工業(yè)出版社,2002.7
[6] 許發(fā)樾,[實(shí)用模具設(shè)計(jì)與制造手冊] [S],北京:機(jī)械工業(yè)出版社,2000.10
[7] [塑料模具設(shè)計(jì)手冊]編委會,陜西科技大學(xué)計(jì)算機(jī)與信息工程學(xué)院開發(fā),塑料模設(shè)計(jì)手冊(軟件版)V1.0,機(jī)械工業(yè)出版社,2004.6
[8] 朱龍根,[簡明機(jī)械零件設(shè)計(jì)手冊] [S],北京:機(jī)械工業(yè)出版社,1997.11
[9] 華南理工大學(xué) 黃毅宏,上海交通大學(xué) 李明輝,[模具制造工藝] [M],北京:機(jī)械工業(yè)出版社,1999.6
[10] 夏巨諶,李志剛,[中國模具設(shè)計(jì)大典 數(shù)據(jù)庫(電子版) ],中國機(jī)械工程學(xué)中國模具設(shè)計(jì)大典組委會2003.9
[11] 張祥杰,黃圣杰,[Pro/Engineer Wildfire模具設(shè)計(jì)][M],中國鐵道出版社,2004.6
[12] 黨根茂,[模具設(shè)計(jì)與制造][M],西安電子科技大學(xué)出版社,1995年
[13] 張建宇,張南,劉志民,[氣壓瓶蓋注射模具設(shè)計(jì)(電子版)][J]
[14] 賈潤禮,程志遠(yuǎn),[實(shí)用注塑模設(shè)計(jì)手冊][M],中國輕工業(yè)出版社,2000.4
[15] 朱冬梅,胥北讕,[畫法幾何及機(jī)械制圖][M],高等教育出版社,2000.4
15
致 謝
本論文是在導(dǎo)師XXX的悉心指導(dǎo)下完成的,經(jīng)過幾個(gè)月的忙碌和工作,本次畢業(yè)設(shè)計(jì)已經(jīng)接近尾聲,作為一個(gè)大學(xué)生的畢業(yè)設(shè)計(jì),由于經(jīng)驗(yàn)的匱乏,難免有許多考慮不周的地方,如果沒有指導(dǎo)老師的督促指導(dǎo),以及一起工作學(xué)習(xí)的同學(xué)、朋友們的支持,想要完成這個(gè)設(shè)計(jì)是難以想象的。
在這里,首先要感謝的是我的指導(dǎo)老師X老師。X老師雖然工作繁忙,但是每周都抽出時(shí)間來親自指導(dǎo)和檢查督促我們做畢業(yè)設(shè)計(jì),在我做畢業(yè)設(shè)計(jì)的每個(gè)階段,從開題報(bào)告到查閱資料,從設(shè)計(jì)草案的確定、修改,到中期檢查,再到后期詳細(xì)設(shè)計(jì),裝備草圖等等整個(gè)過程中X老師都給予我悉心的指導(dǎo)。除了敬佩老師的專業(yè)水平、嚴(yán)謹(jǐn)?shù)闹螌W(xué)態(tài)度以外,老師科學(xué)研究的精神是永遠(yuǎn)值得我學(xué)習(xí)的榜樣,并會一直積極影響我今后的工作和學(xué)習(xí)。
其次我要感謝我的父母和與我一起做畢業(yè)設(shè)計(jì)的同學(xué)們。父母給了我強(qiáng)大的精神動力,同學(xué)們在本次設(shè)計(jì)中勤奮工作克服許多困難來完成此次設(shè)計(jì),并分擔(dān)了許多工作。如果沒有他們的支持和努力,此次設(shè)計(jì)的過程將變得非常困難。
我還要感謝的是學(xué)校圖書館的開放,讓我們有足夠的資料可以參考、查閱。還要感謝四年以來所有的老師,為我打下了機(jī)械專業(yè)知識的基礎(chǔ);同時(shí)感謝所有的同學(xué)們,正因?yàn)橛辛四銈兊闹С郑敬萎厴I(yè)設(shè)計(jì)才會順利完成。
通過畢業(yè)設(shè)計(jì),使我對塑料注射模具這門課程進(jìn)一步加深了理解。對于各方面知識之間的相互聯(lián)系有了實(shí)際的體會。同時(shí)也深深感到自己初步掌握的知識與實(shí)際需要還有相當(dāng)?shù)木嚯x,還需進(jìn)一步的學(xué)習(xí)和實(shí)踐。
本設(shè)計(jì)由于時(shí)間緊和對知識掌握的程度有限,在設(shè)計(jì)上不很周詳,許多應(yīng)該考慮的因素可能沒有體現(xiàn)出來。在設(shè)計(jì)過程中,我得到了老師的精心指導(dǎo)和各方面的幫助,才得以順利進(jìn)行,在這里再次表達(dá)我的謝意。
附錄
外文資料
TEMPERATURE CONTROL
P. H. J. Ingham
Marketing Manager ,Eurotherm Ltd,Worthing,Sussex,UK
SUMMARY
Commercial 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 INTRODUTION
The 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 PROCESS
2.1 Machine Zoning
From 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 Location
Considering 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 Overshoot
The 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 Temperature
The 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 Control
The 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 system’s 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議的討論,這次會議為模制產(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
2·1 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,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3~4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。
2·2 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龋皇切颓坏臏囟?,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。
2·3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)境變糟,因?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
3·1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:主動的和被動的類型。
主動類的是熱電偶,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。
3·2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)啟動時(shí)間過短將可能是對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。
3·3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??偟囊痪湓拋碚f,對于比例帶到安放點(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將減小到振幅為零。
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