外文翻譯----有關(guān)帶式輸送機(jī)的驅(qū)動(dòng)裝置設(shè)計(jì)的一些研究

1、<p><b>　　機(jī)電工程學(xué)院</b></p><p>　　畢業(yè)設(shè)計(jì)外文資料翻譯</p><p>　　設(shè)計(jì)題目: </p><p>　　譯文題目: 有關(guān)帶式輸送機(jī)的驅(qū)動(dòng)裝置設(shè)計(jì)的一些研究

2、 </p><p>　　學(xué)生姓名： 劉延濤 </p><p>　　學(xué) 號(hào)： 20054740218 </p><p>　　專業(yè)班級(jí)： 車輛工程0502 </p>

3、<p>　　指導(dǎo)教師： 徐 蕓 </p><p>　　正文：外文資料譯文 附 件：外文資料原文 </p><p>　　出自: The South African Institute of Materials Handling </p><p>　　有關(guān)帶式輸送機(jī)驅(qū)動(dòng)裝置設(shè)計(jì)的一些研究</p&g

4、t;<p>　　J.H. Rall 理工學(xué)碩士, </p><p>　　漢森變速器（控股）有限公司董事</p><p>　　P. Staples 理工學(xué)碩士, </p><p>　　輸送機(jī)知識(shí)與信息科技（控股）有限公司（CKIT）董事、總經(jīng)理 </p><p><b>　　摘要：</b></p&g

5、t;<p>　　這是是一篇關(guān)于探討運(yùn)送大量顆粒物質(zhì)的動(dòng)力和平板橡膠輸送帶之間的驅(qū)動(dòng)裝置的綜述。它關(guān)注的是大批量的物料輸送，而不是像喂料或計(jì)量輸送帶，大傾角式輸送機(jī)等特殊情況。它主要研究電機(jī)聯(lián)軸器和驅(qū)動(dòng)滾筒之間的減速器，帶速，軸承壽命，使用因數(shù)，制動(dòng)器和逆止器等。 </p><p><b>　　概述</b></p><p>　　The ever in

6、creasing rate of consumption of earth's raw materials has brought with it a need for faster movement of these materials from the point of extraction to the point of process or usage and transporting these materials t

7、hrough the process plant and disposing of the waste in the shortest possible time. 地球原材料的消耗越來越多，那就需要很快地將這些材料從一個(gè)地方轉(zhuǎn)移到使用它的地 方，而且要通過一定的工藝來運(yùn)輸這些物料并且要在最短的時(shí)間內(nèi)處置廢物。許多物料輸送的方法是從輪手推車送到自卸卡車或接送的車輛上，或是依靠一定的空氣流在空氣導(dǎo)管中進(jìn)行散料輸送。這種輸送方式中，

8、在限制成本的前提下，在可靠的長距離的物料輸送中帶式輸送機(jī)發(fā)揮了非常重要的作用。 </p><p>　　Each method of material conveying has its advantages and disadvantages. One of the problems with belt conveyors is that soft friable material can be degraded

9、, particularly in loading and unloading. 每一種物料輸送都有其優(yōu)點(diǎn)和缺點(diǎn)。帶式輸送機(jī)的問題之一是，輸送帶柔軟易降解，特別是在裝貨和卸貨的時(shí)候。如果維持整體尺寸是很重要的話，那么照目前的技術(shù)來說這在復(fù)雜的輸送系統(tǒng)中是很困難。 </p><p>　　Conveyor systems have become larger and more complex and drive

10、 systems have also been going through a process of evolution and will continue to do so. 輸送系統(tǒng)已變得越來越大，越來越復(fù)雜，驅(qū)動(dòng)系統(tǒng)也已經(jīng)歷一個(gè)演進(jìn)過程而且會(huì)繼續(xù)演進(jìn)下去。</p><p>　　Bigger belts require more power and has brought the need for l

11、arger individual drives as well as multiple drives such as 4 drives of 1000 kW each on one belt. 大帶要求很大的驅(qū)動(dòng)力。不僅需要更大的獨(dú)立驅(qū)動(dòng)裝置，同時(shí)也需要多驅(qū)動(dòng)裝置比如一個(gè)帶需要4個(gè)各1000KW功率的驅(qū)動(dòng)器。完整驅(qū)動(dòng)裝置中軸的安裝是另一個(gè)變化，它要求更緊湊重量更輕的驅(qū)動(dòng)裝置。這往往傾向于在輸送帶和硬齒面齒輪旁邊配置一個(gè)直角驅(qū)動(dòng)器來

12、減小驅(qū)動(dòng)器的尺寸和質(zhì)量。</p><p>　　2. 傳動(dòng)比與帶速 </p><p>　　Depending on the quantity, size, distance and characteristics of the material to be conveyed, the absorbed power, width, tensile requirements and top co

13、ver thickness of the belt will be decided. 根據(jù)待輸送物料的數(shù)量，規(guī)模，輸送距離和其特點(diǎn)的不同決定了帶的吸收功率，寬度，拉伸要求和厚度等。 </p><p>　　Large volume conveyor belts run in the range of 2 to 6 metre/second and the allowable bend radius of t

14、he belt determines pulley diameters which for large belts is of the order of 0,8 to 1,5 m giving pulley speeds between 50 and 125 rpm. 大部分的傳送帶帶速范圍在2～6m/s，并且由帶允許的彎曲半徑?jīng)Q定了托輥的直徑。大型傳送帶的托輥直徑在0.8～1.5m之間，托輥速度在50～125rpm之間。 <

15、;/p><p>　　Assuming that 4 pole motors are used, this gives a reduction ratio required between 12:1 and 30:1. 假設(shè)使用4極電機(jī)，這能提供12:1～30:1之間需要的減速比 。 </p><p>　　Most modern gear manufacturers do not use

16、a higher ratio per stage than 5:1, which means that speed reducers will be either 2 or 3 stage reduction. 大部分的齒輪制造商不會(huì)采用過高的傳動(dòng)比，每級(jí)傳動(dòng)比不超過5:1，這意味著將會(huì)是2～3級(jí)減速。（除小功率的蝸桿減速器或是扭矩臂和V帶驅(qū)動(dòng)器可能會(huì)使用）。 </p><p>　　There is a m

17、isconception that one can reduce the cost of the gearspeed reducer by using a 6 or 8 pole motor, but even an 8 pole motor on the higher speeds would require a reduction above 6:1 and a 2 stage unit would still be require

18、d. 有一種誤解以為減速器使用6或8極電機(jī)可以降低成本，但即使是8極電極能有更高的速度，且每級(jí)減速比超過6:1，這樣仍然需要2級(jí)傳動(dòng)。大部分變速器的成本與低速軸的扭矩有關(guān)系。因此，只要確定了這一點(diǎn)，除了使用了4極電機(jī)以外使用其他任何電機(jī)相比之下都是沒有任何經(jīng)濟(jì)優(yōu)勢(shì)可言的。 The motor manufacturers, because of size and volume, generally supply 4 pole mot

19、ors at the lowest price, and as a rule therefore</p><p>　　Where ball and roller bearings are used in the electric motors some manufacturers prefer 6 pole or even 8 pole speeds for motors over 1000 kW. 電動(dòng)機(jī)

20、使用球軸承和滾子軸承的一些制造商喜歡6極甚至8極的轉(zhuǎn)速，能給電機(jī)提供超過1000千瓦的功率。 </p><p>　　3.1 選擇單個(gè)或多個(gè)驅(qū)動(dòng)器 </p><p>　　Having calculated the power required to drive the belt and having considered the belt tension and angle of cont

21、act, a decision can be taken on whether the belt should be fitted with single or multiple drive. 在計(jì)算出驅(qū)動(dòng)皮帶所需功率和皮帶張力和包角之后就可決定就帶是否應(yīng)裝有一個(gè)或多個(gè)驅(qū)動(dòng)器。 </p><p>　　This decision is often influenced by other equipment

22、installed in a plant and multiples of other smaller drives are often used. 這一決定往往受安裝在工廠的數(shù)倍于經(jīng)常使用的小驅(qū)動(dòng)器等設(shè)備的影響。 Drive size may also be determined by the nearest standard motor available. 驅(qū)動(dòng)器的大小也可能由最近可用的標(biāo)準(zhǔn)電動(dòng)機(jī)決定。如果一個(gè)驅(qū)動(dòng)器離主要?jiǎng)?/p>

23、力源有相當(dāng)?shù)木嚯x，那么就要用一根長的電纜來連接電機(jī)和驅(qū)動(dòng)器。這樣一來，在選擇我們使用的電機(jī)的數(shù)量和尺寸時(shí)電纜尺寸和變壓器的成本就可能發(fā)揮一個(gè)很重要的作用。隨著電機(jī)的啟動(dòng)，電動(dòng)機(jī)的峰值電流可能是6相滿載電流。一個(gè)電機(jī)或一組電機(jī)的運(yùn)行電流與最后一個(gè)電機(jī)啟動(dòng)時(shí)的啟動(dòng)電流之間的聯(lián)系對(duì)驅(qū)動(dòng)器的選擇會(huì)有很強(qiáng)的影響。 </p><p>　　3.2 低速軸的連接</p><p>　　Drive from

24、 the reducer to the belt pulley shaft is either by "flexible" coupling from a drive pack mounted on a foundation next to the structure or by shaft mounted drive unit hanging on the pulley shaft. 從減速器到皮帶輪軸的傳

25、動(dòng)一種是通過與安裝在構(gòu)架旁邊的基礎(chǔ)部件上的驅(qū)動(dòng)裝置的“彈性”耦合來實(shí)現(xiàn)，一種是通過掛在帶輪軸上的驅(qū)動(dòng)裝置的軸來實(shí)現(xiàn)。驅(qū)動(dòng)裝置可以安裝空心軸，通過摩擦鎖合原理來驅(qū)動(dòng)或是安裝實(shí)心軸用一個(gè)剛性聯(lián)軸器將其與輸送機(jī)軸連接起來以實(shí)現(xiàn)驅(qū)動(dòng)。附件中給出了一些典型的附屬裝置草圖。（見附錄A ）。 </p><p>　　4.1 起動(dòng)方法﹑驅(qū)動(dòng)器的大小和保護(hù)裝置的選擇 </p><p>　　During st

26、art up of conveyor belts, a considerable mass is usually involved which requires acceleration, and to reduce the length of time that the motor draws starting current, a "slip coupling" is fitted between the dri

27、ve motor and speed reducer. Alternatively, slip ring motors are used to achieve a quick but gentle start up with control of the peak current. 在啟動(dòng)傳送帶時(shí)，通常涉及到一個(gè)需要加速的相當(dāng)大的質(zhì)量。為了縮短電機(jī)達(dá)到啟動(dòng)電流的時(shí)間，需要在減速器和驅(qū)動(dòng)電機(jī)之間安裝一個(gè)“滑動(dòng)聯(lián)軸器”。另外，滑環(huán)電

28、動(dòng)機(jī)的使用，實(shí)現(xiàn)了通過控制電機(jī)的峰值電流以實(shí)現(xiàn)快速且柔性啟動(dòng)。功率10kW以下的小帶直接在線器啟動(dòng)采用直接耦合是很正常的，</p><p>　　There is a multitude of slip couplings on the market for use with DOL start motors, but for larger belts the majority in use are liquid

29、type couplings, either straight traction or traction with delayed fill or controllable fill (scoop type). A fluid coupling will always "slip" a small amount and will help multiple drives to share load, provided

30、 the coupling "fill" has been carefully adjusted. 市場(chǎng)上有很多種與D.O.L.啟動(dòng)機(jī)配套使用的滑動(dòng)聯(lián)軸器，但對(duì)于較大的輸送帶來說多數(shù)使用液體耦合器，無論是連續(xù)牽引或是延遲填補(bǔ)牽引或是可控填補(bǔ)填補(bǔ)牽引（杓子式）。流力耦合器總是會(huì)做少量的“滑動(dòng)”以幫助多個(gè)</p><p>　　4.2 電動(dòng)機(jī)起動(dòng)（D.O.L.與液力偶合器）</p>

31、;<p>　　On multiple drives accepted practice is to start the motor on the secondary drive first and say 3-5 seconds later one of the primary drive motors and then the next primary motor say 5-10 seconds later.

32、多個(gè)驅(qū)動(dòng)器啟動(dòng)的一般做法是先啟動(dòng)次級(jí)驅(qū)動(dòng)器電機(jī)3～5秒鐘后在啟動(dòng)另一個(gè)主級(jí)電機(jī)，持續(xù)5～10秒鐘后啟動(dòng)下一個(gè)主級(jí)電機(jī)。 </p><p>　　In practice, however, the observed starting procedures and delay times vary a great deal. 然而，在實(shí)踐中觀察到啟動(dòng)開始后和理想狀態(tài)有一個(gè)時(shí)間延遲。一個(gè)非常常見的現(xiàn)象是觀察到次級(jí)驅(qū)

33、動(dòng)電機(jī)由于保守耦合的選擇，啟動(dòng)電流有所下降，但很快又開始上升，由于延遲填補(bǔ)耦合增加了它的滑動(dòng)力矩，而帶依然平穩(wěn)。如果主級(jí)驅(qū)動(dòng)器是在耦合扭矩大幅度增加之前的正確時(shí)間啟動(dòng)的，帶就會(huì)在過低電流狀態(tài)下帶速增加。聯(lián)軸器的相對(duì)滑移影響到它的扭矩和電機(jī)電流，而且很快帶就可以啟動(dòng)了，峰值電流很快也將下降。 </p><p>　　In the case of scoop controlled fluid couplings all

34、 motors are started in quick succession and then all couplings filled slowly. 在杓子式液力偶合器中所有電機(jī)都很快成功的啟動(dòng)然后所有聯(lián)軸器開始緩慢填補(bǔ)?；h(huán)電動(dòng)機(jī)也采用類似的的方式啟動(dòng)。這兩種方法無疑對(duì)皮帶，皮帶輪是有利的方式。 </p><p>　　采用杓子式液力偶合器或滑環(huán)電機(jī)有可能使較小型電機(jī)的使用更安全和開關(guān)裝置維修成本的節(jié)

35、省。 </p><p>　　4.3 其他驅(qū)動(dòng)器方法 </p><p>　　Where a variable conveying rate is required, DC drives can be used as well as squirrel cage motors with frequency control. 如果要求輸送率變化的，那么直流驅(qū)動(dòng)器可以當(dāng)作鼠籠電動(dòng)機(jī)來實(shí)現(xiàn)變頻

36、控制。另一種方法是用水文靜態(tài)驅(qū)動(dòng)器，但大功率驅(qū)動(dòng)器的運(yùn)行和維護(hù)費(fèi)用上很可能會(huì)高于采用SC電機(jī)液力偶合驅(qū)動(dòng)器和或滑環(huán)電動(dòng)機(jī)。 </p><p><b>　　4.4 帶保護(hù)</b></p><p>　　Belt protection against overload and stalling is commonly done by a centrifugal switc

37、h driven by a roller on the underside of the belt. 帶保護(hù)是為了防止超載和失控。其做法通常是通過皮帶下方的托輥驅(qū)動(dòng)的離心開關(guān)來實(shí)現(xiàn)的。然而，這并不是現(xiàn)在使用的非常靈敏和最尖端的方法。 </p><p>　　One method consists of fitting a pulse generator to the drive gearbox low sp

38、eed shaft and similar pulse generator to a roller driven by the belt. 一種恰當(dāng)?shù)姆椒ㄊ窃隍?qū)動(dòng)變速箱低速軸上安裝一個(gè)脈沖發(fā)生器，皮帶驅(qū)動(dòng)的托輥上裝上類似的脈沖發(fā)生器。監(jiān)測(cè)器能不斷的檢測(cè)脈沖頻率，如果輸送帶跑偏的話它就會(huì)給出警報(bào)或直接使帶停下來。通過使用監(jiān)測(cè)器來控制滑環(huán)電動(dòng)機(jī)的啟動(dòng)能將帶的跑偏滑動(dòng)控制在最低限度內(nèi)。監(jiān)測(cè)器可控制轉(zhuǎn)子電阻繼而控制起動(dòng)轉(zhuǎn)矩。 </p

39、><p>　　5. 5. 帶式輸送機(jī)制動(dòng) </p><p>　　5.1 正向制動(dòng) </p><p>　　As a general rule, friction will reduce the normal forward speed of the belt and load and bring it to rest in a relatively short time

40、. 一般說來，摩擦?xí)档推дＧ斑M(jìn)的速度并增加負(fù)載使其在相對(duì)較短的時(shí)間內(nèi)停止。停車時(shí)間的長短主要取決于卸料結(jié)束條件。如果一個(gè)帶給另一個(gè)帶送料是，平穩(wěn)的條件，轉(zhuǎn)載倉的大小和帶的布局可能會(huì)需要一個(gè)制動(dòng)帶的其他方法而不是靠正常的摩擦。 </p><p>　　On a downhill section of a conveyor discharging onto a level or uphill belt i

41、s generally the place where braking is required. If one belt runs on longer than the rest of a system of conveyors, bunkers or transfer chutes can be overloaded and may even be a hazard, but this is generally a very rare

42、 condition. 一般來說向下卸料或是向上輸送的帶都需要制動(dòng)。如果一個(gè)輸送帶輸送部分比輸送機(jī)其它部分長很多的話，輸送斜槽就可會(huì)超載甚至可能是遭到破壞，但這種情況很少出現(xiàn)。 </p><p>　　Considering a conveyor layout as per sketch (see appendix B) fitted with a brake on the gearbox high spee

43、d shaft, it can be seen that when stopped under load the inertia of the load would tend to pick up the gravity tensioner and release the tension in the belt between drive and head pulley and may even go slack by the time

44、 the load comes to rest. 先初步根據(jù)輸送帶的布局（見附錄B ）在變速箱高速軸上裝制動(dòng)器，可以看到，當(dāng)又載荷的情況下停止的時(shí)候載荷的慣性往往會(huì)依靠重力拉緊和釋放驅(qū)動(dòng)器和前部帶輪之間帶的張緊力，甚至帶還可能會(huì)松弛。反轉(zhuǎn)時(shí)驅(qū)動(dòng)器因制動(dòng)器作用而不動(dòng)，但負(fù)載會(huì)在重力的作用下使帶加速。而當(dāng)驅(qū)動(dòng)器和頭部滾筒張緊時(shí)，就會(huì)使因負(fù)載而加速</p><p>　　A brake fitted on a do

45、wnhill belt drive would again release tension between drive and head pulley and pick up the take up, but this would tend to release tension on the driving (or stopping) pulleys and allow the belt to slip. 安裝在卸料帶的制動(dòng)器將再

46、次釋放驅(qū)動(dòng)器和頭部滾筒之間的張緊力，但這往往會(huì)釋放正在運(yùn)行（或停止）的帶輪的張力，并使得帶有滑動(dòng)。這對(duì)皮帶和帶輪有害，而且也是很危險(xiǎn)的。制動(dòng)帶正確的方法像是這樣的：在帶尾部滾筒或反轉(zhuǎn)時(shí)的其它滾筒上采取行動(dòng)。 </p><p>　　Another application where brakes are sometimes used is on belts running through a mobile stac

47、ker, to reduce the risk of the belt snagging; should the stacker be moved while the belt is stationary. 另一個(gè)制動(dòng)器有時(shí)會(huì)用到的方法有時(shí)用一個(gè)移動(dòng)堆垛機(jī)來制動(dòng)皮帶，以減少帶的刮傷；帶固定的時(shí)候堆垛機(jī)應(yīng)能夠移動(dòng)。但在尾部滾筒上仍然要裝一個(gè)制動(dòng)器，在驅(qū)動(dòng)器或輸送機(jī)頭部安裝一個(gè)鉗制器。 </p><p><

48、;b>　　附件 ：</b></p><p>　　FROM : The South African Institute of Materials Handling </p><p>　　BELT CONVEYOR DRIVES - A CONSIDERATION OFSOME DESIGN ASPECTS</p><p>　　J.H. Rall P

49、r.Eng., BSc Eng., MSAIME Hansen Transmissions(Pty) ltdP. Staples Pr.Eng BSc, MSAIMEManaging Director Conveyor Knowledge and InformationTechnology (Pty)Ltd (CKIT)</p><p><b>　　Summary:</b></

50、p><p>　　This is a short review of part of the link between the electric power grid and flat rubber covered belts used for transporting large volumes of granular material. It is concerned with high volume materi

51、al conveying and not with special cases such as feed or metering conveyors, steep inclined conveyors etc. It considers mainly the speed reducer between motor coupling and drive pulley, ratings, bearing life, service fact

52、ors, stopping and anti-runback devices</p><p><b>　　General</b></p><p>　　The ever increasing rate of consumption of earth's raw materials has brought with it a need for faster mov

53、ement of these material from the point of extraction to the point of process or usage and transporting these materials through the process plant and disposing of the waste in the shortest possible time. Many methods of m

54、aterial handling are employed from wheel barrows to dump trucks or shuttle cars, to pneumatic ducts carrying pulverised particles in an air stream. In this line of movement, </p><p>　　Each method of material

55、 conveying has its advantages and disadvantages. One of the problems with belt conveyors is that soft friable material can be degraded, particularly in loading and unloading. If the maintenance of lump size is important,

56、 this can present difficulties on a complicated conveyor system.</p><p>　　Conveyor systems have become larger and more complex and drive systems have also been going through a process of evolution and will c

57、ontinue to do so.</p><p>　　Bigger belts require more power and has brought the need for larger individual drives as well as multiple drives such as 4 drives of 1000 kW each on one belt. Shaft mounting of the

58、 complete drive unit is another change which has brought with it the requirement for more compact and lighter drive units. This tends to favor a right angle drive configuration with the motor next to the belt and hardene

59、d gears to reduce the dimensions and mass of the drive.</p><p>　　2. Drive Ratio and Belt speeds</p><p>　　Depending on the quantity, size, distance and characteristics of the material to be conv

60、eyed, the absorbed power, width, tensile requirements and top cover thickness of the belt will be decided.</p><p>　　Large volume conveyor belts run in the range of 2 to 6 metre/second and the allowable bend

61、radius of the belt determines pulley diameters which for large belts is of the order of 0,8 to 1,5 m giving pulley speeds between 50 and 125 rpm.</p><p>　　Assuming that 4 pole motors are used, this gives a r

62、eduction ratio required between 12:1 and 30:1.</p><p>　　Most modern gear manufacturers do not use a higher ratio per stage than 5:1, which means that speed reducers will be either 2 or 3 stage reduction. (Ex

63、cept for small powers where worm reducers, or torque arms and V belt drives may be used).</p><p>　　There is a misconception that one can reduce the cost of the gear-speed reducer by using a 6 or 8 pole motor

64、, but even an 8 pole motor on the higher speeds would require a reduction above 6:1and a 2 stage unit would still be required. The bulk of the cost of a gearbox is related to the low speed shaft torque and therefore havi

65、ng determined this, there is generally no economic advantage at all in using anything but a 4 pole motor. The motor manufacturers, because of size and volume, generally sup</p><p>　　Where ball and roller bea

66、rings are used in the electric motors some manufacturers prefer 6 pole or even 8 pole speeds for motors over 1000 kW.</p><p>　　3.1. Choice of Single or Multiple Drive</p><p>　　Having calculated

67、 the power required to drive the belt and having considered the belt tension and angle of contact, a decision can be taken on whether the belt should be fitted with single or multiple drive.</p><p>　　This de

68、cision is often influenced by other equipment installed in a plant and multiples of other smaller drives are often used. Drive size may also be determined by the nearest standard motor available. Where a drive point is s

69、ituated some considerable distance from the main power source, a long cable may be involved to supply electric power to the drive. In this case, the cable size and cost of transformers may play an important part in the s

70、election of number and size of motors used. With dire</p><p>　　3.2. Method of Low Speed Shaft Connections</p><p>　　Drive from the reducer to the belt pulley shaft is either by "flexible&qu

71、ot; coupling from a drive pack mounted on a foundation next to the structure or by shaft mounted drive unit hanging on the pulley shaft. When shaft mounted, the drive unit can be either hollow shaft, driving through a fr

72、iction locking element or solid shaft attached by a rigid coupling to the conveyor shaft. Some typical attachments are shown in the sketches. (See appendix A).</p><p>　　4.1. Choice of Starting method, drive

73、 size and Protection</p><p>　　During start up of conveyor belts, a considerable mass is usually involved which requires acceleration, and to reduce the length of time that the motor draws starting current, a

74、 "slip coupling" is fitted between the drive motor and speed reducer. Alternatively,slip ring motors are used to achieve a quick but gentle start up with control of the peak current. On small belts below 10kW d

75、irect on line starting directly coupled is quite normal and on belts, say below 100 kW D.O.L. starting with "slip</p><p>　　There is a multitude of slip couplings on the market for use with D.O.L. start

76、motors, but for larger belts the majority in use are liquid type couplings, either straight traction or traction with delayed fill or controllable fill (scoop type). A fluid coupling will always "slip" a small

77、amount and will help multiple drives to share load, provided the coupling "fill" has been carefully adjusted. As a rule, each coupling has a slightly different characteristic and if adjusted to share load corre

78、c</p><p>　　4.2. Motor Starting: (D.O.L. with fluid coupling)</p><p>　　On multiple drives accepted practice is to start the motor on the secondary drive first and say 3-5 seconds later one of th

79、e primary drive motors and then the next primary motor say 5-10 seconds later.</p><p>　　In practice, however, the observed starting procedures and delay times vary a great deal. A very common sight is to see

80、 the secondary drive motor running and due to conservative coupling selection, the starting current drops somewhat, but starts rising quickly again due to the delayed fill coupling increasing it's slip torque, while

81、the belt remains stationary. If a primary drive is started at the correct time before the coupling torque has increased too far, the belt is brought into motion much</p><p>　　In the case of scoop controlled

82、fluid couplings all motors are started in quick succession and then all couplings filled slowly. A similar procedure is followed with slip ring motors and these two methods are undoubtedly the kindest to the belt, pulley

83、 and lagging etc.</p><p>　　The choice of scoop type fluid couplings or slip ring motors is likely to lead to the use of smaller motors with safety and possible savings on switch gear maintenance. </p>

84、<p>　　4.3. Other Drive Methods</p><p>　　Where a variable conveying rate is required, D.C. drives can be used as well as squirrel cage motors with frequency control. Another method is by hydro-static d

85、rive; again ideal for variable speed, but overall running and maintenance costs on big powers are likely to be higher than a fluid coupling drive, with S.C. motor or slip ring motor.</p><p>　　4.4. Belt Prot

86、ection</p><p>　　Belt protection against overload and stalling is commonly done by a centrifugal switch driven by a roller on the underside of the belt. This, however, is not very sensitive and more sophistic

87、ated methods are now used.</p><p>　　One method consists of fitting a pulse generator to the drive gearbox low speed shaft and similar pulse generator to a roller driven by the belt. A monitoring unit compare

88、s the pulse frequencies continuously and if they go outside set limits, an alarm is given or the belt stopped. On start up, belt slip can be kept to a minimum by using the monitoring unit to control the start up on slipr

89、ing motors. The monitoring unit can control the rotor resistance and so the starting torque. Alternatively, t</p><p>　　5. Stopping a Belt Conveyor </p><p>　　5.1. Forward stopping</p>&l

90、t;p>　　As a general rule, friction will reduce the normal forward speed of the belt and load and bring it to rest in a relatively short time. The allowable time for stopping depends mainly on the discharge end conditio

91、ns. Where one belt feeds onto another, tripping conditions, transfer bunker size and belt layout may indicate a need for a belt to be slowed down by other methods than normal friction.</p><p>　　On a downhill

92、 section of a conveyor discharging onto a level or uphill belt is generally the place where braking is required. If one belt runs on longer than the rest of a system of conveyors, bunkers or transfer chutes can be overlo

93、aded and may even be a hazard, but this is generally a very rare condition.</p><p>　　Considering a conveyor layout as per sketch (see appendix B) fitted with a brake on the gearbox high speed shaft, it can b

94、e seen that when stopped under load the inertia of the load would tend to pick up the gravity tensioner and release the tension in the belt between drive and head pulley and may even go slack by the time the load comes t

95、o rest. The load assisted by the gravity take up would then accelerate the belt in the return direction while the drives are stationery with brakes on. When t</p><p>　　A brake fitted on a downhill belt drive

96、 would again release tension between drive and head pulley and pick up the take up, but this would tend to release tension on the driving (or stopping) pulleys and allow the belt to slip. This can damage the belt and pul

97、ley lagging and can also be dangerous. The proper method of stopping a belt like this is on the tail pulley or other pulley on the return belt after it leaves the take up.</p><p>　　Another application where

98、brakes are sometimes used is on belts running through a mobile stacker, to reduce the risk of the belt snagging; should the stacker be moved while the belt is stationary. Here again a brake would be fitted to the tail pu