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鋼絞線(xiàn)帶式輸送機(jī)的發(fā)展
托馬森 （英）
總經(jīng)理
摘 要：早期帶式輸送機(jī)的發(fā)展被認(rèn)為是與鋼絞線(xiàn)帶式系統(tǒng)相同的需求而發(fā)展起來(lái)的，其本質(zhì)就是各種設(shè)計(jì)原理與槽形帶式輸送機(jī)突出部分的優(yōu)缺點(diǎn)進(jìn)行比較，而這一部分的發(fā)展恰恰表明，在傳送系統(tǒng)中最可能也最有用的發(fā)展，就是對(duì)其外形輪廓的改進(jìn)。
鋼絞線(xiàn)帶式輸送機(jī)發(fā)展
在1795年時(shí)，最初的帶式輸送機(jī)不便于操作，而且僅涉及一些簡(jiǎn)單的外形，直到1850年后，隨著世界范圍內(nèi)的谷物貨量大量增加，促使傳送帶技術(shù)有了較大的改進(jìn)。
第一種形式的傳送機(jī)是在一個(gè)槽形及其內(nèi)運(yùn)行的水平傳送帶，其工作原理是引進(jìn)導(dǎo)輪系統(tǒng)用滾動(dòng)摩擦來(lái)替代滑動(dòng)摩擦，以便減少傳送中的摩擦損失。隨著需求的不斷增長(zhǎng)以及大量的集中裝卸貨物的需要，使得在這一時(shí)期最普遍的貨物帶式輸送機(jī)。草型帶式輸送機(jī)以及鋼絞線(xiàn)帶式輸送機(jī)都獲得較大發(fā)展。
在1860年后期，大量使用帶有錐形或蝶形滾動(dòng)導(dǎo)輪的槽形帶式傳送機(jī)，直到1890年才過(guò)時(shí)被淘汰。1865年傾向于將直線(xiàn)集中器或跨輪引入到傳送機(jī)發(fā)明設(shè)計(jì)中，這使得托馬斯.羅賓在1896年獲得該產(chǎn)品的專(zhuān)利權(quán)，被認(rèn)為是歷史上第一臺(tái)槽形帶式輸送機(jī)。從那時(shí)起，許多重大改進(jìn)在跨輪傳送帶和操作結(jié)構(gòu)等一些細(xì)節(jié)方面。但在1900年早期，所有的槽形帶式輸送機(jī)都具有相同的外型，在外型上并沒(méi)有改進(jìn)。
同最初的機(jī)器相比，鋼絞線(xiàn)帶式輸送機(jī)真正意義上獲得較大成功的發(fā)展是在1952年，而在1859年，最早期的設(shè)計(jì)形式之一。
圖中包括兩條平行無(wú)較差的皮帶制成膠質(zhì)的傳送帶，被按一定距離貼附在彎曲的金屬表面上，使得這種帆布式槽形帶式輸送機(jī)正常運(yùn)行，也有許多相似的輸送帶類(lèi)型，但它們承受從動(dòng)帶被剛性的貼附在主動(dòng)帶上，主動(dòng)帶并不能完全與草圖設(shè)計(jì)吻合，或者是潤(rùn)滑劑承受重壓，最終從主動(dòng)帶脫落等。
鋼絞線(xiàn)傳動(dòng)帶系統(tǒng)成功地克服了這些缺點(diǎn)，并且這一技術(shù)被大范圍的用在傳送機(jī)長(zhǎng)距離的應(yīng)用中?，F(xiàn)在一種單臂長(zhǎng)54米的螺紋槽系統(tǒng)已經(jīng)被考慮在設(shè)計(jì)中。
鋼絞線(xiàn)傳送帶系統(tǒng)設(shè)計(jì)原理的基本不同在于采用一種圓形的金屬線(xiàn)形式的主動(dòng)帶，而不是傳統(tǒng)的將從動(dòng)帶附著在主動(dòng)帶上。第一步改變致力于克服通過(guò)三角皮帶輪式運(yùn)行中的水平傳送帶被鋼絞線(xiàn)替代所產(chǎn)生的困難。第二步改變是著眼于鋼絞線(xiàn)傳送帶系統(tǒng)本身可以進(jìn)行操作，這與早期設(shè)計(jì)的目標(biāo)恰恰相反。主動(dòng)帶主要依附于從動(dòng)帶上，這些鋼絞線(xiàn)被放置在傳送帶表面壓制好的滑軌上，它或許是緊依靠摩擦力是鋼絞線(xiàn)傳送帶在主動(dòng)帶上向后滑行，然而同所有帶式輸送機(jī)依靠摩擦力在傳送帶上運(yùn)載貨物相比，鋼絞線(xiàn)時(shí)僅需滿(mǎn)足在傳送帶和主動(dòng)鋼絞線(xiàn)間的摩擦力應(yīng)大于在傳送帶和貨物之間的摩擦力，這應(yīng)使得傳送帶制動(dòng)器僅僅牢固在主動(dòng)鋼絞線(xiàn)上。
鋼絞線(xiàn)帶式輸送機(jī)也可用于特殊形式的表面，在斜面?zhèn)魉蜋C(jī)整體系統(tǒng)中等級(jí)是21，一些特殊形式的可達(dá)28，在傳動(dòng)鋼絞線(xiàn)上不存在打滑脫落的現(xiàn)象。
鋼絞線(xiàn)帶式輸送機(jī)伴隨著發(fā)動(dòng)機(jī)進(jìn)一步發(fā)展而發(fā)展的，當(dāng)發(fā)動(dòng)機(jī)功率達(dá)到300千瓦時(shí)（被認(rèn)為是最杰出的設(shè)計(jì)）；由此而開(kāi)始建造長(zhǎng)達(dá)3000米，功率8000千瓦的傳送機(jī)。
鋼絞線(xiàn)傳送給與槽形傳送機(jī)除在工作方式上不同，其它一些末端的輸出單元是相似的，也聯(lián)合從動(dòng)帶與主動(dòng)帶，一個(gè)典型的例子是上部的卸貨裝置。明顯地，除傳動(dòng)單元終端設(shè)備之外的其他設(shè)備要比傳統(tǒng)的槽形帶式輸送機(jī)復(fù)雜得多，并且占據(jù)更多的空間，特別是在考慮張力等作用下更是如此，這并不是真正意義上的傳動(dòng)裝置，而是僅對(duì)其功率額定值進(jìn)行比較，當(dāng)它滿(mǎn)負(fù)載時(shí)，需能控制運(yùn)處的鋼絞線(xiàn)傳送機(jī)正常工作。
傳動(dòng)鋼絞線(xiàn)的張力模數(shù)保持在相對(duì)低的水平是為了獲得較低的初始扭矩，并且當(dāng)每個(gè)傳動(dòng)鋼絞線(xiàn)拉緊時(shí)，張力系統(tǒng)需要占據(jù)較大的空間，并且更復(fù)雜。
后期的鋼絞線(xiàn)帶式輸送機(jī)設(shè)計(jì)理念與傳統(tǒng)的非常相似的，在傳送機(jī)中也存在摩擦，并且垂直找平裝置是一系列的懸垂鏈，但如果應(yīng)用于不同的領(lǐng)域，應(yīng)考慮各種不同的性能，且考慮降低傳送機(jī)的摩擦損失，可以通過(guò)減少動(dòng)件的數(shù)量和重量，這種損失正常值為30%，而額定的摩擦損失取決于工作中的傳送帶與貨物之間的損失，而采用滑輪裝置可大大減少這種損失，理論上測(cè)量能答曰降低10%的損失，做一基本比較，這一事實(shí)很令人吃驚。關(guān)于摩擦損失已經(jīng)證實(shí)往往很難克服，并且所有的觀測(cè)數(shù)據(jù)和設(shè)計(jì)標(biāo)準(zhǔn)，顯示出不同的測(cè)試結(jié)果，另外摩擦損失取決于各種因素，此外，輸送機(jī)摩擦將隨著安裝和維護(hù)的溫度，壽命和標(biāo)準(zhǔn)變化。在一些大型設(shè)備安裝中，比較部分摩擦值至少在一個(gè)基本設(shè)計(jì)中能看到如下不同之處：
傳統(tǒng)型
鋼絞線(xiàn)型
回轉(zhuǎn)件數(shù)量
100
76
可動(dòng)件數(shù)量
100
64
摩擦損失
100
67
鋼絞線(xiàn)帶式輸送機(jī)的垂直找平系統(tǒng)與槽形機(jī)設(shè)計(jì)和計(jì)算原理是相同的，必須進(jìn)行反復(fù)測(cè)試確保懸垂鏈脫落這樣的事情不會(huì)發(fā)生。鋼絞線(xiàn)傳送帶被定義為橫向堅(jiān)固縱向輕柔的帶式輸送機(jī)，而從動(dòng)帶依附于兩條平行主動(dòng)帶的側(cè)翼或邊緣部分。減速齒輪箱和活動(dòng)單元來(lái)對(duì)主動(dòng)鋼絞線(xiàn)進(jìn)行控制，以及對(duì)不同鋼絞線(xiàn)拉伸張力的差別超界調(diào)整。此外，每一根主動(dòng)鋼絞線(xiàn)在工作中允許承受不同的拉伸力。
鋼絞線(xiàn)傳送帶獨(dú)特的特點(diǎn)是體現(xiàn)在傳送帶上，最初是一種加強(qiáng)橡膠傳送帶，被鑄造在以450毫米為間隔的彈簧搭接片上，這些搭接片伸出起搭架輪之外，如圖二所示，并且機(jī)械的附著在金屬制動(dòng)器上，橡膠傳送帶與主動(dòng)鋼絞線(xiàn)相連，這可以被一種鑄造結(jié)構(gòu)所代替，一些較小的交叉搭接片以間隔100毫米的距離完全鑄造在傳動(dòng)帶和制動(dòng)器上，以便使主動(dòng)鋼絞線(xiàn)僅僅固定在傳動(dòng)帶邊緣。最近，已經(jīng)對(duì)此作進(jìn)一步改進(jìn)，如圖四，當(dāng)貨物在其上移動(dòng)時(shí)，制動(dòng)器僅僅控制主動(dòng)鋼絞線(xiàn)，這也使得當(dāng)發(fā)生超重時(shí)，增加傳送帶的穩(wěn)定性。另外可以采用更好的交叉搭接片。
長(zhǎng)期集中使用傳送機(jī)，最終得更換傳送帶，這是很正常的，或者是由于表面的摩擦損失造成的,或許是機(jī)械性的損壞，但主要取決各個(gè)部分的壽命，例如影響橡膠、化合物壽命的因素有熱障、光照和氧化等，因此必須發(fā)展特種橡膠化合物來(lái)增加其壽命。
主動(dòng)鋼絞線(xiàn)的特點(diǎn)使它可以近似的被那些金屬線(xiàn)大小、抗疲勞性和內(nèi)部的潤(rùn)滑性符合鋼絞性設(shè)計(jì)特點(diǎn)的金屬線(xiàn)所代替。有一些敘對(duì)變電鍍，同向順捻每一根細(xì)金屬線(xiàn)或金屬繩，通常這些金屬性能應(yīng)達(dá)到直徑60毫米，并且斷面負(fù)荷達(dá)到260噸，隨著鋼絞線(xiàn)帶式系統(tǒng)的張力的增加應(yīng)特別注意盡量減少金屬線(xiàn)接頭的數(shù)量，當(dāng)主動(dòng)鋼絞線(xiàn)承重100噸時(shí)，每一部分都是如此。
順著傳送帶每間隔5到10米有一個(gè)直徑大約300毫米的三角皮帶輪，顯然這些皮帶輪應(yīng)具有堅(jiān)固的齒輪結(jié)構(gòu)，但實(shí)際上這些皮帶輪被設(shè)計(jì)為表面可替換的橡膠值得滑輪，這些滑輪成對(duì)出現(xiàn)在交接臂上，傳送帶本身能平衡每一個(gè)滑輪上的負(fù)載，在所有的傳動(dòng)機(jī)設(shè)計(jì)中都應(yīng)基本的考慮避免鋼絞線(xiàn)脫軌情況發(fā)生，應(yīng)謹(jǐn)慎的設(shè)計(jì)懸垂鏈，眾所周知，懸垂鏈本身就能避免滑落，在設(shè)計(jì)中，鋼絞線(xiàn)帶式系統(tǒng)應(yīng)用同樣，但是若有效的防止滑落發(fā)生卻極有可能增加負(fù)載條件和限制初始扭矩。
鋼絞線(xiàn)帶式輸送機(jī)在設(shè)計(jì)最主要不同在于將從動(dòng)傳送帶于主動(dòng)鋼絞線(xiàn)分開(kāi)較好的設(shè)計(jì)方案，應(yīng)將它們和在一起，而分開(kāi)它們是方便于在設(shè)計(jì)上給與更多的靈活性，并且能夠引起傳統(tǒng)帶式輸送機(jī)沒(méi)有涉及的理念，且能更廣泛的應(yīng)用在許多領(lǐng)域，傳送帶可以是直得，也可以是彎曲的，如圖八所示，它可以允許達(dá)到320°的角度仍保持主動(dòng)帶的基本特征，但得結(jié)合兩個(gè)環(huán)形從動(dòng)帶，這一特征的30﹪ 被用于鋼絞線(xiàn)傳動(dòng)帶的安裝調(diào)試。其他的設(shè)計(jì)原理廣泛應(yīng)用于前面提到的，當(dāng)住主動(dòng)系統(tǒng)里傳送帶較足時(shí)的操作，這一獨(dú)特的特征，使得主動(dòng)單元也可以同某些電子設(shè)備相連，但得將其防止在無(wú)塵干凈的環(huán)境中，這種靈活性也使得從動(dòng)裝置可以放置在傳送機(jī)的任一點(diǎn)，也可以將貨物直接通過(guò)主動(dòng)鋼絞線(xiàn)傳遞，鋼絞線(xiàn)帶式輸送機(jī)的其他部分（拉力系統(tǒng)）涉及的獨(dú)特性，毫無(wú)疑問(wèn)，它將比槽形帶式輸送機(jī)更復(fù)雜占據(jù)更多的空間。
存在許多原因但其最根本原因在于每一條主動(dòng)鋼絞線(xiàn)和從動(dòng)帶常須承擔(dān)設(shè)備的拉力牽引。從動(dòng)帶上的拉力微不足道的，它必須滿(mǎn)足主動(dòng)帶上的張力作用，尤其是在一個(gè)長(zhǎng)的平面輸送機(jī)，拉里幾乎都由主動(dòng)單元承受這種傳送機(jī)，在初始指令期間主動(dòng)鋼絞線(xiàn)的拉伸運(yùn)動(dòng)可以替代，在整臺(tái)傳送機(jī)開(kāi)動(dòng)前，這種效應(yīng)被儲(chǔ)存在從動(dòng)帶拉力系統(tǒng)中，當(dāng)然當(dāng)傳送機(jī)停止運(yùn)行時(shí)，將被釋放。在一個(gè)長(zhǎng)達(dá)15000米的傳送機(jī)可以被拉伸80米，同槽形帶式輸送機(jī)相比，鋼絞線(xiàn)傳送機(jī)占據(jù)如此大的空間最主要時(shí)期必須滿(mǎn)足主動(dòng)鋼絞線(xiàn)和長(zhǎng)期拉伸和相對(duì)高的彈性拉伸作用。固定的拉伸范圍大約是1﹪，在它首次運(yùn)行幾百小時(shí)后，這已被制造商消除在制造階段，但傳統(tǒng)做法還是在鋼絞線(xiàn)接頭處留有足夠的空間，以便于引入額外的鋼絞線(xiàn)時(shí)的需要模數(shù)的選擇可以控制彈力，減少?gòu)椓?，減少所占空間，同時(shí)有效的彈性可以保證獲得較低的終止扭矩。
從鍛件方面的信息可以看出鋼絞線(xiàn)帶式系統(tǒng)同槽形帶式系統(tǒng)有許多方面完全相同，但也存在一些不同之處。大多數(shù)的傳送機(jī)是較短的且低功率的，毫無(wú)疑問(wèn)，槽形帶式輸送機(jī)帶動(dòng)許多傳送機(jī)的發(fā)展，然而在一些長(zhǎng)距離或者起吊升起來(lái)運(yùn)輸貨物的領(lǐng)域，細(xì)膠線(xiàn)帶式輸送機(jī)展示其特殊優(yōu)點(diǎn)，且其獨(dú)特的設(shè)計(jì)時(shí)它來(lái)這些領(lǐng)域成為唯一選擇。
若想準(zhǔn)確的定義出鋼絞線(xiàn)傳送帶的應(yīng)用領(lǐng)域是有些困難的，幾乎三分之一被應(yīng)用于沒(méi)有太大的競(jìng)爭(zhēng)的領(lǐng)域，每一種情況下，它們被選擇是由于某一些方面的特征，基本上鋼絞線(xiàn)傳送帶一般不適合那些短的普通傳送機(jī)應(yīng)用的領(lǐng)域，這主要取決于終端設(shè)備的大小，另外終端設(shè)備的花費(fèi)包括傳送機(jī)的每一部分，在鋼絞線(xiàn)傳送系統(tǒng)的中，一般不給予考慮動(dòng)力需求的花費(fèi)，在摘要中，當(dāng)前的鋼絞線(xiàn)傳送帶的競(jìng)爭(zhēng)領(lǐng)域似乎是：
供率低于750千瓦的斜面輸送機(jī)，或者是長(zhǎng)度少于3000米的水平輸送機(jī)，并不是鋼絞線(xiàn)傳送帶的競(jìng)爭(zhēng)的主要領(lǐng)域。
當(dāng)這些參量進(jìn)一步提高時(shí)，鋼絞線(xiàn)帶式輸送機(jī)選擇的首要產(chǎn)品成為更有競(jìng)爭(zhēng)力。
在水平輸送機(jī)中，摩擦損失的能量是相當(dāng)大的，這邊增加了鋼絞線(xiàn)傳送帶的運(yùn)行費(fèi)用，此外在其他方面并沒(méi)有什么本質(zhì)區(qū)別。
在鋼絞線(xiàn)帶式系統(tǒng)中較有意義的發(fā)展是對(duì)當(dāng)前鍛件的改進(jìn)，未來(lái)幾年這應(yīng)是首要的花費(fèi)，在運(yùn)行費(fèi)用方面，這包括對(duì)主動(dòng)鋼絞線(xiàn)的每一根金屬線(xiàn)的股線(xiàn)都要加強(qiáng)，最初的試驗(yàn)結(jié)果展示其抗老化、 其壽命是傳統(tǒng)金屬繩的3倍，鋼絞線(xiàn)帶式系統(tǒng)最近的發(fā)展表明，其完全可以同長(zhǎng)距離的繩索運(yùn)輸相競(jìng)爭(zhēng)。雖然現(xiàn)在還沒(méi)有被考慮，當(dāng)前在澳大利亞西部的Worsley Alumina Ptr:Ltd公司正在建造一個(gè)有兩個(gè)螺紋槽系統(tǒng)，長(zhǎng)達(dá)52000米鋼絞線(xiàn)帶式輸送機(jī)系統(tǒng)。
Worsley Alumina Ptr:Ltd位于西澳大利亞——附近，設(shè)備的整體部分由量太鋼絞線(xiàn)帶式輸送機(jī)串聯(lián)組成，并且經(jīng)由陸路運(yùn)輸將呂土巖從礦山運(yùn)到精制廠(chǎng)。
在涼臺(tái)傳送機(jī)交叉處，貨物表皮左旋50°，通過(guò)花道進(jìn)入第二個(gè)傳送機(jī)，在兩臺(tái)輸送機(jī)間，主動(dòng)傳送機(jī)的角度和張力單元系統(tǒng)都應(yīng)相互協(xié)調(diào)、適應(yīng)。傳送機(jī)必須標(biāo)準(zhǔn)化且?guī)缀醺鞑考慵苫Q。
長(zhǎng)度 31000米 21000米
標(biāo)高 72米 14米
貨物 鋁土巖
密度 1520kb/m3
額定功率2040m.t.p.h
年產(chǎn)量（噸） 9.06×106
帶寬 900毫米
運(yùn)行速度 6.35m/s
主動(dòng)帶 57千米（直徑）
間距 4.75米
功率 5300kw 3600kw
如果條件許可，鋼絞線(xiàn)傳送機(jī)將能獲得進(jìn)一步發(fā)展，可以將傳送帶的長(zhǎng)度擴(kuò)展到更長(zhǎng)。
作者非常感謝得到Worsley Alumna Pty.Ltd公司的幫助和相關(guān)的資料。
本文涉及：
1．傳送帶輸送機(jī)的標(biāo)高——來(lái)自Hetzel and Albright John Wiley & sons
2．帶式輸送機(jī)的抗阻力數(shù)據(jù)——來(lái)自H.P.Lachman .
附錄B
DEVELOPMENT OF THE CABLE BELT CONVEYOR
lan Main Thomson BSc (Eng.)
Managing Director
Cable Belt Ltd
Summary
The early development of belt Conveying is discussed showing how the Cable belt system developed from the same requirements. The various design concepts are compared with those of the troughed belt conveyor highlighting the areas of advantage and disadvantage.
The areas of conveying where the Cable Belt system is most useful and the likely developments are outlined. These and other developments have led to many major conveyor installations including a 2 flight 52 km system being constructed to the Cable Belt design.
Development of the Cable Belt Conveyor
The origin of the belt conveyor is not easy to clearly identify but there are references to simple forms as early as 1795. However it was not until the dramatic increase in the world trading of grain after 1850 that major improvements were made1.
The first form of conveyor was a flat belt running in a trough which was quickly improved by the introduction of straight idlers to replace sliding friction by rolling friction. The need to increase the capacity and centralise the material load led to the appearance at the same time of both of the most common forms of heavy duty belt conveyors, the troughed belt conveyor and the Cable Belt conveyor.
In the late 1860's the use in troughed belt conveyors of straight rollers with conical or dished ends was obsolete until the early 1890's. The introduction in 1865 of inclined straight 'concentrator' idlers led to the conveyor in the Thomas Robins Jnr. patent of 1896, which is regarded as the first troughed belt conveyor. Since that date whilst there have been many important improvements in the detail of the idler, belt and drive construction, the basic concept of the troughed belt conveyor is the same as outlined in the work completed in the early 1900's.
The Cable Belt conveyor principle whilst of earlier origin was not developed in a truly successful form until 1952.
One of the earliest forms was that developed in 1859 and shown in the sketch fig. 1. This consisted of two parallel endless leather or rubber belts to which were attached at intervals curved meta1 spreaders supporting a canvas trough. There were many other similar conveyors but they all suffered from the same basic defect that the carrying belt was rigidly attached to the driving belts. This led to the disadvantages that the drive belts do not stretch alike and that the spreader bars are stressed and eventually break free from the drive belts.
The Cable Belt system successfully overcame these defects and since its introduction has generally been accepted in the conveyor field for Long distance applications. A substantial proportion of the single flight conveyors over 5 km long that have been installed are now of the Cable Belt design.
The fundamental design differences made in the Cable Belt system were to use a round drive belt in the form of a wire rope, and not to attach the carrying belt to the drive belts. The first of these changes was aimed at getting over the difficulty of training to run in parallel a pair of flat belts by substituting positively located round cables running in grooved pulleys.
The second change was the point that allowed the Cable Belt system to operate successfully in contrast to the other earlier attempts. The carrying belt merely rests on the drive cables, these cables sitting within shoes which are moulded on the be1t surfaces. It may seem that depending on friction alone the Cable Belt is liable to have the belt slip backwards on the drive cables. However as all belt conveyors depend on friction between the belt and the material carried to allow them to operate at all, the only requirement is that the friction between the belt and the drive cables should be greater than between the belt and the material. This was achieved by shaping the belt shoes to grip the drive cables.
It has been possible using Cable Belt belting with specially formed surfaces to run on slope conveyor systems where the overall grade is 21° and with particular sections of 28°, without experiencing slipping of the belt on the drive cables.
Whilst the Cable Belt conveyor was developed at a time when the powers available of up to 300 kW were regarded as outstanding the basic concept is still retained even when now, single conveyors of 30000 metre length and 8000 kW power are being built.
The terminal units are similar to those in a conventional troughed conveyor except that they also serve to separate and rejoin the carrying belt and drive cables. A typical example of a head discharge unit is shown in fig. 6.
Obviously the terminals other than the drive unit are more complex than in a conventional troughed conveyor and take up more space particularly in the case of the tensioning arrangements. This is not true of the drive as for a comparable power rating it is compact and has the advantage that it can be located remote from the Cable Belt conveyor belt line.
As the modulus of elasticity of the drive cables is kept relatively low in order to allow the use of very low starting torques and each drive cable is tensioned, the tension system does require substantial take-up space and is more complex as is illustrated in fig. 7.
The concepts behind the design of the Cable Belt conveyor are very similar to a conventional conveyor in that there is conveyor friction and the vertical alignment is a series of catenaries but of course the factors used vary considerably because of the different characteristics.
The conveyor friction losses are considerably reduced principally because of the significantly lower number and weight of moving parts in a comparable system.
This reduction is normally in the order of 30%. In addition the friction losses due to the working of belt and material as they pass over the idlers are significantly less. it has been determined empirically that there is in the order of a 10% reduction in the friction losses.
The establishing of the facts, even on a comparative basis, with regard to conveyor friction has proved difficult as all the data is empirical and the various design standards can show markedly different results. In addition conveyor friction will vary with temperature, age and standards of installation and maintenance. However in a recent major installation it has been possible to compare the friction values, at least on a design basis and as can be seen below these bear out the differences.
Conventional
Cable Belt
Number of Rotating Parts
100
76
Weight of Moving Parts
100
64
Friction Losses
100
67
In determining the vertical alignment of the Cable Belt system whilst the formulae and calculation are the same, great care must be exercised as it is not possible to allow 'lift off' in catenaries to occur.
The Cable Belt is best defined as a belt conveyor with a laterally rigid but longitudinally flexible carrying belt which is supported at or near its edges on two parallel endless looms of drive cable, these cables in turn being supported at intervals by grooved pul1eys. The integral reduction gear and drive unit drives both drive cab1es and incorporates a differential to equalise tensions in the cables. In addition each of the drive cable circuits is separately tensioned to allow for the differential stretch of these during operation.
The unique feature of the Cable Belt system is the belt. Originally this was a fabric reinforced rubber belt which had moulded into it spring steel straps at 450 mm intervals. These straps protruded beyond the edges of the bell as illustrated in fig. 2, and had mechanically attached to them a metal shoe with rubber Lining where it gripped the drive cable. This was superseded by a one piece moulded construction shown in fig. 3 where smaller cross section straps at intervals of 100 mm were moulded entirely within the belt and the shoes to grip the drive cables were continuous mouldings along the edge of the belt.
Recently a further change was made, illustrated in fig. 4 whereby the shoes which grip the drive cable on the material carrying run have been moved inwards. This increases the stability of the belt when subjected to overloading and in addition allows the use of smaller cross section straps.
It is normal that on a typical long centre conveyor the eventual replacement of the belt is not for reasons of abrasion of the surface or mechanical damage, but due to the various ageing processes that affect rubber compounds such as heat, sunlight, and ozone. As a result it has been necessary to develop special synthetic rubber compounds that are inherently resistant to ageing.
The specification of the drive cables whilst similar superficially to a normal wire rope are specially made to a Cable Belt specification with design criteria laid down for individual wire size, fatigue life and internal lubrication. They are of galvanised construction, Lang's Lay with either a fibre or wire rope core. Currently they are used in sizes up to 60 mm diameter and breaking loads of 260 tonnes. As this is the tension reinforcing member of the Cable Belt system great attention is paid to reducing the number of splices and drive cables of up to 100 tonnes weight for each section have been used.
Along the line of the conveyor it is supported at intervals of between 5 and 10 metres by grooved pulleys approximately 300 mm in diameter. Previously these pulleys were of a hardened steel construction but the current design is for a pulley with a replacement rubber lined tread. These pulleys are mounted in pairs on articulated arms which allow the conveyor to self align and equalise the loads on each pulley as can be seen in fig. 5.
Whilst this condition is normally avoided in all conveyor design, it is essential, to prevent derailment of the drive cables, to design catenaries correctly and conservatively.
As is well known the normal catenary formulae are approximations which allow a factor of safety against 'lift off'. In designing the Cable Belt system the same formulae and factors are used, but effectively the protection against 'lift off' is increased by determining worst possible loading conditions and limiting the starting torques. This situation is helped in that the conveyor friction is such and modulus of the drive cables is selected to ensure that there is virtually no additional breakaway torque required even to start a long flat overland Cable Belt system.
The major difference in designing a Cable Belt conveyor lies in the separation of the carrying belt and the drive cables. Whilst good design practice requires that they should be kept together, the ability to separate them does give considerable flexibility in design and allows the introduction of concepts unknown in the conventional belt conveyor. The most widely used of these is in the many circumstances where a straight line route or one incorporating curves is not feasible, and the unit known as an angle station is employed. As can be seen from fig. 9 this allows any angle up to 320° to be accommodated and still retain the feature of a single drive but incorporate two separate carrying belt circuits. This feature is used in about 30% of the Cable Belt installations. The other concept that is widely used is as mentioned earlier, the ability to place the drive unit remote from the belt line. This feature, which is unique, allows the drive unit and its associated electrical equipment to be located in a position with easy access for maintenance but away from the dust and dirt associated with a conveyor discharge or return belt line. This flexibility also allows the drive unit to be placed at any point in the conveyor, including if necessary on the material carrying run of the drive cables.
The other part of the Cable Belt design that is unique is the tensioning system and there is no doubt that this is more complex and takes greater space than would be required in a troughed belt conveyor. There are several reasons for this but the principal reason is the necessity to provide equipment to separately tension each drive cable and the carrying belt. Whilst the tension in the carrying belt is nominal it is still necessary to cater for the drive cable tension movement, particularly in long flat conveyors which, of necessity, are tensioned at or near the drive unit. In such conveyors the tension movement of the drive cables is substantial during the start sequence. Before the whole conveyor is moving the effect is that it is necessary to 'store' in the carrying belt tension system a length of belt equivalent to the elastic stretch of the drive cables. This of course is released when the conveyor stops. In a typical 15000 metre long conveyor this stretch can be up to 80 metres.
The main reason for taking up a greater space than a troughed belt conveyor is the necessity to cater for both the permanent stretch and the relatively high elastic stretch of the drive cables. The permanent stretch of about 1% which occurs in the first few hundred hours of running could be eliminated during manufacture but it conveniently provides the necessary space for splicing of the cable as well as generating extra cable which can be used when resplicing is necessary The choice of the modulus that governs the elastic stretch is a compromise between minimising the stretch to reduce the space requirements and having sufficient stretch to ensure very low 'breakaway' torques.
As can be seen from the foregoing information the Cable Belt system while fulfilling the same role in many ways is quite different from the troughed belt conveyor. As most conveyors are of short length and low horsepower there is no doubt that the troughed belt conveyor is the correct solution for many conveyor applications. However in those areas of long lengths or high lifts the Cable Belt system often shows decisive advantages and in those cases where its unique design concepts can be used it may be the only choice.
To define the precise applications which a Cable Belt system is suitable for is difficult, as nearly one third of the systems installed are in applications in which they were not the most competitive solution. In each case they were chosen for one of the unusual features that the system offers. As a general rule the Cable Belt in its current form is not technically suitable for short centre conveyors mainly due to the size of the terminals. In addition to the cost of the terminal equipment the main cost component of any belt conveyor, the belt, in the Cable Belt system has a constant cost irrespective of the power requirements. This 1oads the capital cost on low power conveyors but reduces it on high power conveyors in comparison with a troughed belt conveyor.
In summary the current competitive situation of the Cable Belt system appears to be :-
·In slope conveyors of less than 750 kW or level conveyors of less than 3000 metre length the Cable Be1t is not the most competitive solution. Above these parameters the Cable Belt becomes increasingly competitive