裝配圖導(dǎo)向塊設(shè)計(jì),裝配,導(dǎo)向,設(shè)計(jì) 教學(xué)單位 機(jī)電工程學(xué)院 學(xué)生學(xué)號(hào) 編 號(hào) 英文翻譯 題　　目 并條機(jī) 學(xué)生姓名　 專業(yè)名稱　 機(jī)械設(shè)計(jì)制造及其自動(dòng)化 指導(dǎo)教師　 2015 年 5月 4日 并并條機(jī) 作者：約翰. 恩斯特 單位：赫特福徳大學(xué) 1. 操作裝置 1.1 操作原理 四到八個(gè)粗疏機(jī)或并條機(jī)（見圖5-4）紗條被供給牽伸裝置(3)，一對(duì)給棉羅拉(2)位于每一個(gè)條筒(1)之上以確保進(jìn)料步驟在控制者沒有錯(cuò)誤牽伸時(shí)被執(zhí)行。這對(duì)進(jìn)料輥在一個(gè)粗紗架或工作臺(tái)上進(jìn)行，而且每一個(gè)都積極推動(dòng)。紗條進(jìn)入牽伸裝置離開它，在四到八的牽伸之后，作為一個(gè)經(jīng)紗它缺乏重要的凝聚力。為了避免經(jīng)紗的瓦解，即哪一個(gè)將是其他系統(tǒng)間交接在當(dāng)前的高運(yùn)營速度之下不可避免的，它將紗條快速凝聚在牽伸裝置之后。這個(gè)紗條然后引導(dǎo)管(4)通過一個(gè)通道管(6)裝置進(jìn)入一個(gè)條筒(7)，它必須被放置在這個(gè)條筒里空間最優(yōu)利用的清潔圈里。來使條筒攜帶盡可能多的原料，通過使用軋光或槽輥紗條被壓縮(5)。 圖 5-4 1.2 粗紗架（紗條喂給） 特別的，粗紗架必須是這樣設(shè)計(jì)的 ⊕避免錯(cuò)誤的牽伸； ⊕在發(fā)生紗條斷裂時(shí)機(jī)器停止； ⊕紗條斷裂可以被簡(jiǎn)單、舒適和安全的處理。 為此，它必須提供一個(gè)可旋轉(zhuǎn)的輥或輥副在任一個(gè)條筒上，一個(gè)紗條一個(gè)。一個(gè)引導(dǎo)紗條進(jìn)入牽伸裝置的引導(dǎo)裝置也是必需的，一個(gè)有滾軸的工作臺(tái)或只是一個(gè)滾軸，可以提高必須的指導(dǎo)。在高速操作大牽伸并條機(jī)時(shí)首選滾軸單獨(dú)，當(dāng)運(yùn)輸是被滾動(dòng)方式影響時(shí)摩擦較它依賴滑動(dòng)時(shí)低。橫向進(jìn)給滾軸副也起電接觸軸的作用來監(jiān)視紗條，如果一個(gè)紗條斷裂，這個(gè)金屬軸將接觸。當(dāng)絕緣片不在存在于它們之間時(shí)，機(jī)器停止。 幾乎所有的牽伸機(jī)都有在線紗條喂給，也就是喂給條筒在向機(jī)器運(yùn)動(dòng)的方向上被排列成一長(zhǎng)行。立達(dá)公司提供橫向的進(jìn)給作為一個(gè)選項(xiàng)，這里紗條最初的橫向運(yùn)動(dòng)，在一個(gè)90°角相對(duì)于材料的流動(dòng)方向通過機(jī)器。 在進(jìn)入牽伸裝置之前，它們被轉(zhuǎn)移到物料流動(dòng)方向，對(duì)于一個(gè)工廠有相應(yīng)的機(jī)器布局，在使用空間上，這可以給出經(jīng)濟(jì)上的優(yōu)勢(shì)。 通常的，紗條或許被輸入多達(dá)八條筒每牽伸頭，而且這些條筒或許會(huì)有多達(dá)1000mm的直徑。紗條位置緊密相連是很重要的，但不是在另一個(gè)之上，即當(dāng)它們遇到牽伸裝置時(shí)。 1.3 牽伸裝置 要求 牽伸裝置是并條機(jī)的核心，因此運(yùn)用的部分對(duì)質(zhì)量有最決定性的影響，通常放在牽伸裝置上的要求相當(dāng)?shù)母撸? ⊕簡(jiǎn)單、不復(fù)雜的結(jié)構(gòu)； ⊕平穩(wěn)運(yùn)行的滾軸的堅(jiān)固設(shè)計(jì)（中心）； ⊕一個(gè)操作模式提供一個(gè)高質(zhì)量的產(chǎn)品，甚至在高速運(yùn)行下； ⊕高度的靈活性，也就是，適合所有的紗條，纖維的長(zhǎng)度、纖條的把數(shù)等，在短絨的紡織下這可以被處理； ⊕在牽伸裝置之間對(duì)纖維運(yùn)動(dòng)的最優(yōu)控制； ⊕高精度的操作和調(diào)整； ⊕對(duì)輥的間距和牽伸水平的快速簡(jiǎn)單的適應(yīng)性； ⊕易于維護(hù)和清潔； ⊕最優(yōu)人體工程學(xué)設(shè)計(jì)。 對(duì)于牽伸機(jī)構(gòu)的影響 在所有類型的牽伸裝置，影響牽伸的因素如下 依賴于纖維原料的因素： ⊕大量纖維在須條橫截面； ⊕纖維的有序度(并行處理）； ⊕纖維束的橫截面形狀； ⊕纖維束的緊密度； ⊕纖維之間的附著力取決于表面結(jié)構(gòu)，須條的卷曲，潤滑，壓縮； ⊕纖維長(zhǎng)度； ⊕均勻分布的纖維長(zhǎng)度（主要形式）； ⊕現(xiàn)為樹立的扭轉(zhuǎn)。 1.4 取決于牽伸裝置的影響： ⊕輥軸的直徑； ⊕上羅拉的硬度； ⊕上羅拉施加的壓力； ⊕上羅拉的表面特性； ⊕下羅拉上的槽； ⊕纖維引導(dǎo)設(shè)備的類型和形式，例如壓力棒、銷鍵、皮圈、冷凝器等； ⊕加緊的距離（羅拉設(shè)置）； ⊕牽伸水平； ⊕各種牽伸階段之間的牽伸分布。 1.5 下羅拉 下羅拉由鋼制成，安裝在羅拉支架或在框架中來作為梳針、輥?zhàn)?、滾珠軸承，它們從主傳動(dòng)齒輪積極傳動(dòng)，為了提高它們攜帶纖維的能力，它們形成了以下類型之一的出局槽（見圖5-5） ⊕橫槽； ⊕斜槽（螺旋槽）； ⊕滾花槽。 滾花槽是用于羅拉接收皮圈，來提高皮圈驅(qū)動(dòng)的轉(zhuǎn)換，其他的輥?zhàn)佑休S向的，或者，漸增的、螺旋的槽，后者使其安靜的運(yùn)行，而且與軸向槽相比它更能加緊纖維。在螺旋槽上滾動(dòng)的上羅拉發(fā)生在多種方式上并用更少的沖擊。 下羅拉的直徑可處于20~90mm范圍，但是通常使用的直徑在25~50mm之間，一個(gè)牽伸裝置包括3~6個(gè)這樣的羅拉，在長(zhǎng)的機(jī)器中（總監(jiān)環(huán)錠紡紗機(jī)），下羅拉由用螺釘固定在一起的短的長(zhǎng)度所組成的。 牽伸裝置中羅拉之間的距離通?？烧{(diào)，然后就可適應(yīng)纖維的長(zhǎng)度。 1.6 上羅拉 上羅拉不是主驅(qū)動(dòng)，它們可以是整體輥中的任一（紡紗設(shè)備機(jī)器）或者雙輥（粗紗幀、環(huán)錠紡紗機(jī)器）（見圖5-6）。 滾珠軸承通常只在輥配置中使用，厚圖層成型的輥表面是由合成橡膠組成的，這種涂料的一個(gè)重要特點(diǎn)是它的硬度。軟圖層周圍纖維束在更大程度上比硬的更好的指導(dǎo)纖維。另一方面，它們磨損更快，因此可以更好指導(dǎo)的軟涂層的使用是必要的。也就是很少有纖維可以用高的牽伸水平被移動(dòng)（例如在前面的環(huán)錠紡紗機(jī)器的羅拉），這不是必須的，硬涂層用得更多。 根據(jù)度條款中指定的硬度，以下范圍是有區(qū)別的： 軟 60°~70° 中等 70°~90°硬超過90° 1.7 上羅拉的保養(yǎng)說明 由于在紡紗中涂層的磨損，它們必須得不時(shí)的被重新打磨，這要定期的按照預(yù)定的時(shí)間表去做，使用研磨盤或輥?zhàn)尤コ牧系耐繉?。如果涂層的厚度也減少到定義的最小值，也就是如果它變得太薄而不能在壓力下提供足夠的彈性，然后老的涂層就必須被移除，一個(gè)替代品必須被移到核心。 磨削操作有一個(gè)羅拉表面的粗化效果，即使沒有光學(xué)放大這不是很明顯，在處理敏感纖維時(shí)，粗糙的羅拉表面會(huì)導(dǎo)致拉普光圈的形成。在這種情況下，羅拉涂層可被視為磨削后表面光滑是用了： ⊕應(yīng)用化學(xué)膜例如漆或者另一種平滑介質(zhì)； ⊕酸處理； ⊕用紫外光照（Berkolising，出自Berchtold公司，瑞士）。 1.8上羅拉壓力 要控制纖維，上羅拉必須被迫在高壓下對(duì)下羅拉，這些壓力可以由以下產(chǎn)生： ⊕靜負(fù)載的方式裝載（目前已被淘汰）； ⊕彈性加載（最常用的形式）； ⊕液壓系統(tǒng)（幾乎沒有用過）； ⊕氣動(dòng)加載（立達(dá)公司）； ⊕磁加載（中美合作所的洛威爾公司）。 2. 基礎(chǔ) 早期的并條機(jī)幾乎都是4上4下羅拉牽伸系統(tǒng)，3上4下羅拉系統(tǒng)是早期版本的發(fā)展。之后眾多的新形式出現(xiàn)，在紡織廠所展示的相同品種中沒有機(jī)器像這樣，幾乎只在兩個(gè)牽伸區(qū)進(jìn)行處理。在極端情況下，斷裂牽伸位于1.05~2.5之間，但是通常情況下它們都在1.25~1.8之間，極端總牽伸位于3.5~12之間，但是正常的總牽伸位于4~8之間。 在很多現(xiàn)代的牽伸機(jī)中，牽伸不再是通過交換齒輪來調(diào)整的，而是通過簡(jiǎn)單設(shè)置變速器或步進(jìn)驅(qū)動(dòng)器，調(diào)整步驟可以是連續(xù)的或是離散的。 現(xiàn)代的牽伸機(jī)在它們可以處理的原材料方面更加靈活，而且設(shè)置操作已經(jīng)被簡(jiǎn)化。 3. 上、下羅拉牽伸裝置 這種裝置的特征是中壓滾軸和兩個(gè)下羅拉的約束，這兩個(gè)下羅拉在同一個(gè)支架上進(jìn)行，而且相對(duì)于彼此不可調(diào)。概念可以由主牽伸區(qū)域壓力棒所包含的東西來提高，這種類型的裝置現(xiàn)在主要在梳理室，也在某些程度的牽伸機(jī)上，例如，在Marzoli和Vouk機(jī)器（見圖5-7）。 3.1 上、下有壓力棒羅拉牽伸裝置 這種形式首次被發(fā)展是Platt在1960s而且一直被使用至今。事實(shí)上，壓力棒裝置可能是牽伸機(jī)中使用最廣泛的牽伸裝置形式了。這個(gè)設(shè)計(jì)的發(fā)展起點(diǎn)是實(shí)現(xiàn)牽伸裝置的運(yùn)轉(zhuǎn)更平穩(wěn)，輥?zhàn)痈?，這尤其適用于前輥，不僅僅是由于穩(wěn)定性的影響。對(duì)于一個(gè)給定的圓圈速度，較大的輥?zhàn)涌梢栽谳^低的旋轉(zhuǎn)速度下被操作。 然而，擴(kuò)大輥?zhàn)油瑫r(shí)增加了夾間距，因此，在主牽伸區(qū)，一個(gè)特殊的引導(dǎo)流是必須的，至少對(duì)于短纖維來說，這是一個(gè)導(dǎo)軌或壓力棒，它可以從下邊或上邊開始操作（如普拉的設(shè)計(jì)）。除了普拉的裝置，類似的裝置曾經(jīng)或正在建立的有 Rieter，Schubert & Salzer 和 Toyoda （見圖5-8）。 3.2 上、下有壓力棒羅拉牽伸裝置（Zinser) 嚴(yán)格來說，這也是一個(gè)3羅拉、壓力棒牽伸裝置，但是第4個(gè)羅拉有一些低的加載被添加到輸送輥?zhàn)鳛橐粋€(gè)指導(dǎo)去演示。這指導(dǎo)曲線中的網(wǎng)繞著槽輥直接進(jìn)入輸送中心周，從而促使成條狀。上羅拉有統(tǒng)一的直徑，加大是為了在壓力水平較低時(shí)保持壓力（見圖5-9）。 3.3 上、下羅拉牽伸裝置（Rieter，見圖5-10) 在這個(gè)裝置中，有5個(gè)氣動(dòng)加載壓力輥安裝在兩個(gè)大的（90mm)和兩個(gè)小的（28mm）的不可調(diào)的下羅拉上，壓力輥停放在兩頭。它們的直徑有39mm，盡管這3個(gè)中間輥可能被直徑為28mm的輥取代，這取決于環(huán)境。 實(shí)施牽伸在場(chǎng)B（初始牽伸）和場(chǎng)A（主牽伸），這個(gè)夾間距可以被讀取，也可以通過簡(jiǎn)單的徑向移動(dòng)輥2和4的調(diào)整來適應(yīng)纖維長(zhǎng)度。在主牽伸區(qū)域，一個(gè)壓力棒來確保穩(wěn)定的指引，尤其是對(duì)短的纖維。牽伸裝置排列在一條曲線上，這允許網(wǎng)絡(luò)物質(zhì)流的適當(dāng)指引，這彎曲傾向使得系統(tǒng)容易去服務(wù)。 4. 牽伸裝置的抽吸系統(tǒng) 并條機(jī)的任務(wù)之一就是除塵 ，釋放的塵埃幾乎完全發(fā)生在牽伸裝置，而且這應(yīng)該是全封閉的，所以塵埃不能進(jìn)入到周圍的大氣中。這充滿灰塵的空氣就被吸入提取（如圖5-11所示Schubert & Salzer 機(jī)器 ）。裝置的每一個(gè)輥都有相應(yīng)的清潔裝置，所以飛毛和纖維傾向于堅(jiān)持輥也可以被帶走。 它吸入空氣是通過管道直接進(jìn)入空調(diào)系統(tǒng)的排氣管道，或是過機(jī)器里的過濾器。過濾空氣最好應(yīng)該返回到排氣管道，但也可以吹到房間的空氣中。 5.成卷 紗條放樣 紗條的擺線沉積已被證明是最有利的方法來填充一個(gè)條筒，在這個(gè)過程中，兩個(gè)轉(zhuǎn)移動(dòng)作的沉積點(diǎn)同時(shí)進(jìn)行，旋轉(zhuǎn)板R，引導(dǎo)通過L，吸引紗條遠(yuǎn)離傳送氣缸D ，然后連續(xù)沉積一圈，然而，因?yàn)檗D(zhuǎn)盤C這個(gè)條筒不斷的旋轉(zhuǎn)，它圓的沉積點(diǎn)也是不斷變化的，在條筒里一個(gè)關(guān)于圈的螺旋裝置被生產(chǎn)出來（見圖5-12）。 在許多圈條器中條筒不在轉(zhuǎn)動(dòng)，在這種情況下，這兩個(gè)動(dòng)作都必須從上邊感應(yīng)，這個(gè)板在第二個(gè)大板上高速旋轉(zhuǎn)，第二個(gè)也旋轉(zhuǎn)，但是在較低的速度上。這也導(dǎo)致了圓圈的改變，因此擺線沉積。就一切情況而論，紗條必須被沉積以在條筒的中間從上到下創(chuàng)建一個(gè)中空的空間，確?？臻g使棉層不會(huì)在條筒的中間完全重疊。這可以避免材料形成中央金字塔形，離開條筒半空的部分。中空空間的直徑應(yīng)該是條筒的直徑的四分之一到三分之一（見圖5-13）。 6. 大的和小的紗圈 中空的空間可以用小紗圈（見圖5-15）或者用大紗圈（見圖5-14），小紗圈的直徑即是紗條直徑要小于條筒的半徑。對(duì)于大的紗圈，紗條線圈直徑較大于條筒的半徑。大紗圈通常使用于中小型的條筒，小紗圈通常使用于大的條筒。大約的直徑關(guān)系應(yīng)是： dC/dB = 1．45 或 dC/dB = 2．5 對(duì)于直徑是中型的條筒來說，大的紗圈比小的紗圈好，因?yàn)橄卤P速度可以用于同一的圓周速度（減少力度、噪音和磨損）。而且，條筒的容量在5%~10%以上。然而，對(duì)于大條筒，它會(huì)是更有利的如果板保持盡可能小，這樣少量的就不得不旋轉(zhuǎn)。 - 12 - The Drawfram Author: John Ernst Institution: University of hertfordshire 1. Operating Devices 1.1 Operating Principle Four to eight card or drawframe（see Fig.5-4） slivers are fed to the drafting arrangement (3)．A feed roller pair（2）is located above each can（1）to enable the feed step to be performed in a controlled maner without false drafts．The feed roller pairs are carried in a creel frame or table and each is positively driven．The slivers running into the drafting arrangement leave it，after a draft of 4 to 8，as a web lacking significant cohesion．In order to avoid disintegration of the web，which would other wise be unavoidable at the high operating speeds currently in use，it is condensed into a sliver immediately after the drafting arrangement．This sliver is then guided through a tube（4）via a passage（6）of the tube gear into a can（7），in which it must be laid in clean coils with optimal utilization of the space in the can．To enable the can to take up as much material as possible，the sliver is compressed by passing it through calendering or grooved rollers（5）． Fig．5-4 Modern drawframe． 1.2 Creel（sliver feed） In particular，the creel must be designed so that： ⊕false drafts are avoided； ⊕the machine stops upon occurrence of a sliver break； ⊕sliver breaks can be dealt with easily，comfortably and safely． For this purpose，it is necessary to provide a rotatable roller or roller pair（2）above each can，one for each sliver．A guiding device for leading the slivers into the drafting arrangement is also required．A table with rollers，or simply a line of rollers，can provide the required guidance．Rollers alone are preferred in rapidly operating high-draft drawframes，since friction is lower when transport is effected by means of rolling than when it relies upon sliding．The infeed roller pairs（2）also serve as electrical contact rollers for monitoring the sliver．If a sliver breaks，the metal rollers come into contact when the insulating sliver is no longer present between them，and the machine is stopped． Almost all drawframes have in-line sliver feed，i．e． the feed cans are arranged in a row in the direction of movement into the machine．Rieter offers lateral infeed as an option．Here，the slivers initially move laterally，at an angle of 90°relative to the direction of flow of material through the machine． They are diverted into the material flow direction prior to entering the drafting arrangement．This can give advantages of economy in the use of space for a mill having a corresponding machine layout． Normally，slivers may be fed in from up to eight cans per drawing head，and the cans may have diameters up to 1000㎜（40 inches）．It is important that the slivers lie closely adjacent，but not on top of one other，as they run into the drafting arrangement． 1.3 The drafting arrangement Requirements The drafting arrangement is the heart of the drawframe and thus the part which exerts the most decisive influence on quality．The requirements placed on the drafting arrangement in general are correspondingly high： ⊕simple，uncomplicated construction； ⊕stable design with smooth running of the roller（centricity）； ⊕a mode of operation giving a high-quality product even at high running speeds； ⊕high degree of flexibility，i．e． suitability for all raw materials，fibre lengths，sliver hanks，etc．，that might be processed in the short-staple spinning mill； ⊕optimal control over the movement of the fibres during the drafting operation； ⊕high precision both of operation and adjustment； ⊕rapid and simple adjustability of roller spacings and draft levels； ⊕ease of maintenance and cleaning； ⊕optimal ergonomic design． Influences on the draft In all types of drafting arrangement，the factors that affect the fraft are as follows． Factors dependent upon the fibre material： ⊕mass of fibre in the strand cross-section； ⊕degree of order of the fibres（parallel disposition）； ⊕shape of the cross section of the fiber strand； ⊕compactness of the fibre strand； ⊕adhesion between the fibres dependent upon surface structure， crimp， lubrication， compression of the strand； ⊕fibre length； ⊕evenness of distribution of fibre lengths（staple form）； ⊕twist in the fibre strand． 1.4 Factors dependent upon the drafting arrangement： ⊕diameter of the rollers； ⊕hardness of the top rollers； ⊕pressure exerted by the top rollers； ⊕surface characteristics of the top rollers； ⊕fluting of the bottom rollers； ⊕type and form of fibre guiding devices，such as pressure rods，pin bars，aprons，condenser etc．； ⊕clamping distances（roller settings）； ⊕level of draft； ⊕distribution of draft between the various drafting stages． ． 1.5 Bottom roller Bottom rollers are made of steel and are mounted in roller stands or in the frame by means of needle, roller or ball bearings．They are positively transmission．In order to improve their ability to carry the fibres along，they are formed with flutes of one of the following types（see Fig.5-5）： ⊕axial flutes（a）， ⊕inclined flutes（spiral flutes）（b）， ⊕knurled fluting（c）． knurled fluting is used on rollers receiving aprons，to improve transfer of drive to the aprons．Other rollers have axial or，increasingly，spiral fluting．The latter gives quieter running and more even clamping of the fibres compared with axial fluting．Rolling of the top rollers on spiral flutes takes place in a more even manner and with less jerking． The diameter of the bottom rollers can lie in the range 20 - 90㎜，but normally diameters between 25 and 50㎜ are used．A drafting arrangement includes three to six such rollers．In long machines（i.g. ring spinning machines ）the bottom rollers are made up by screwing together short lengths． Distances between the rollers of the drafting arrangement are usually adjustable and can then be adapted to the fibre lengths． 1.6 Top rollers The top rollers are not positively driven．They can be either one-piece rollers（spinning preparation machines）or twin rollers（roving frames，ring spinning machines）（see Fig.5-6）． Ball bearings are used almost exclusively in the roller mountings．The thick coating forming the roller surface is made of synthetic rubber．An important characteristic of this coating is its hardness．Soft coats surround the fibre strand to a greater extent than harder ones and thus guide the fibres better．In the other hand，they wear out more quickly．A soft coating is therefore used where good guidance is necessary，i.e. where few fibres have to be moved with high draft levels（e.g. at the front rollers of the ring spinning machine）．Where this is not required，harder coatings are mostly used． Hardness is specified in terms of degrees Shore．The following ranges are distinguished： soft 60°- 70°Shore medium 70°- 90°Shore hard above 90°Shore 1.7 Maintenance of the top rollers Since the coatings wear out during spinning，they must be reground from time to time，This is done periodically in accordance with a predetermined schedule，using grinding discs or rollers that remove material from the coating．If the thickness of the coat has been reduced to a defined minimum，i.e. if it has become toothin to provide adequate elasticity under presure，then the old coat must be removed and a replacement must be glued onto the core． The grinding operation has a roughening effect on the roller surface，even if this is not apparent without optical enlargement，in processing of seseitive fibres，rough roller surfaces can lead to formation of laps．In such cases，roller coatings can be treated after grinding to smooth the surface by： ⊕applying a chemical film such as lacquer or another smoothing medium； ⊕acid treatment； ⊕irradiation by UV-light（Berkolising，by the Berchtold company，Switzerland）． 1.8 Top roller pressure To clamp the fibers，the top rollers must be forced at high pressure towards the bottom rollers．This pressure can be generated by： ⊕loading by means of dead weights（now obsolete） ⊕spring weighting（the most usual form） ⊕hydraulic systems（hardly used） ⊕pneumatic weighting（the Rieter company） ⊕magnetic weighting（the Saco Lowell company）． 2. Basics Early drawframes had almost exclusively 4-over-4 roller drafting systems．The 3-over-4 roller system was developed out of this earlier version，and thereafter a multitude of new forms emerged．No other machine in the spinning mill exhibits the same variety of drafting arrange -ments as does this．Processing is carried out almost exclusively in two drafting zones．In extreme cases the break drafts lie between 1.05 and 2.5，but usually they are between 1.25 and 1.8. Extreme total drafts lie between 3.5 and 12，but the normal total draft lies between 4 and 8． In many modern drawframes the draft is no longer adjusted by exchanging gear wheels but by simple setting of variator or stepping drives．The adjustment may be continuous or discrete steps． Modern drawframes are more flexible in terms of the raw material they can process，and setting operations have been simplified． 3. 3-over-4 roller drafting arrangements ． The characteristic feature of this arrangement is engagement of the middle pressure roller with two bottom rollers．The two bottom rollers are carried in a common cradle and are not adjustable relative to each other．The basic concept can be improved by the inclusion of a pressure bar in the main drafting field．This type of arrangement is now found mainly in the combing room，but also still to some extent on drawframes．For example in the Marzoli（Fig.5-7）and Vouk machines． 3.1 3-over-3 roller drafting arrangements with pressure bars This form was first developed by Platt in the 1960s and is still in use today – in fact，the pressure bar arrangement is probably the most widely used form of drafting arrangement for drawframes．The starting point in the development of this design is the realization that the drafting arrangement runs more smoothly the larger its rollers．This applies especially to the front rollers．The effect is due not simply to stability；for a given circumferential speed，larger rollers can be operated at lower speeds of revolution． However，enlarging the rollers simultaneously increases the nip spacings．Accordingly，in the main drafting zone，a special guide system is needed，at least for short fibres；this is the guide rail or pressure bar．It can operate from below or from above（as illustrated in Fig.5-8 for the Platt design）．In addition to the Platt arrangement，similar arrangements have been or are built by Rieter，Schubert & Salzer and Toyoda． Fig.5-10 5-over-4 roller drafting arrangement． 3.2 4-over-3 roller drafting arrangements with pressure bars（Zinser，see Fig.5-9） Strictly speaking，this is also a 3-roller，pressure bar drafting arrangement，but a fourth roller with somewhat lower loading is added to the delivery roller to act as a guide．This leads the web in a curve round the grooved roller directly into the delivery trumpet，thereby facilitating the formation of the sliver．The top rollers are uniform in diameter and are large in order to keep the strain imposed on them low． 3.3 5-over-4 roller drafting arrangements（Rieter，see Fig.5-10） In this arrangement five pneumatically loaded pressure rollers rest on two large（90㎜）and two small（28㎜），non-adjustable bottom rollers．The pressure rollers are suspended from two yokes．They have diameters of 39㎜，although the three middle rollers may be replaced by rollers of 28㎜ diameter depending upon the circumstances． Fig.5-11 Suction clearer for drafting arrangement． Drafting is carried out in Field B (break draft) and in Field A（main draft）．The nip spacings can be read from a scale and can be adjusted to suit the fibre length by simple radial shifting of rollers 2 and 4．In the main drafting field，a pressure bar ensures firm guidance，especially for short fibres．The drafting arrangement is aligned on a curve；this permits proper guidance of the web material flow from the vertical into the horizontal．The curved disposition makes the system easy to service． 4. Suction systems for the drafting arrangement One of the tasks of the drawframe is dust removal．Release of dust occurs almost exclusively in the drafting arrangement and this should be totally enclosed so that dust does not pass into the surrounding atmosphere．The dust-laden air must be extracted by suction（as shown in Fig.5-11 for the Schubert & Salzer machine）．Each roller of the arrangement has an associated cleaning device so that fly and fibres tending to adhere to the rollers can also be carried away． The air drawn away is passed via tubes directly into the exhaust ducts of the air-condition system，or to filters within the machine．The filtered air should preferably be returned to the exhaust ducting，but can also be blown out into the atmosphere of the rooms． 5. Coiling Laying down of sliver Cycloidal deposition of sliver has proved to be the most advantageous method of filling a can．In this process， two shifting movements of the deposition point are carried out simultaneously．The rotating plate R，with its guide passage L，draws the sliver away from the delivery cylinders D and continuously deposits it on a circle．However，since the can is continually rotated by the turntable C，the deposition point of he circle is constantly shifting．A helical arrangement of the circles is produced within the can． In many coilers the cans are no longer rotated．In this case，both movements must be induced from above．The plate rotates at high speed in a second larger plate，which is also rotating but at a lower speed．This also leads to shifting of the circles and hence to cycloidal deposition．In all cases，the sliver must be so deposited that a hollow space is created from top to bottom in the middle of the can．The space is required to ensure that the sliver layers do not overlap completely in the middle of the can．This avoids formation of a central pyramid-shaped column of material，leaving the side portions of the can half empty．The diameter of the hollow space should be about 1/4 – 1/3 of the diameter of the can． 6.Large and small coils The hollow space can be obtained with small coils (Fig.5-15，under-centre -coiling) or with large coils（Fig．5-14，over-centre-coiling）．With small coils the diameter of the sliver coil（dB）is less than the radius of the can（dC）．With large coils，the sliver coil diameter is greater than the can radius．Large coils are generally used in small-to-medium-sized cans and small coils generally in large can．The diameter relations should be approximately dC/dB = 1．45 or dC/dB = 2．5 Large coils are better with small to medium-sized can diameters because lower plate speeds can be used for the same circumferential speed (reduction of force，noise and wear)．Also，the can capacity is 5-10% higher．With large cans，however，it is more advantageous if the plate is kept as small as possible，since then less mass has to be rotated．