【正文】 . TYPES OF MOTLONAL TRACES FOR THE LEADING EDGE OF THE CANOPY This is the most monly recognized way of classifying the shield. Based on this criterion, there are three types, lemniscate, caliper, and ellipse. A. Lemniscate. This is the most popular type. The caving shield and the base are jointed by two lemniscate bars which have a total of four hinges .As the hydraulic legs 唐山學(xué)院畢業(yè)設(shè)計(jì) 33 are raised and lowered, the dimentions of the lemniscate bars are selected such that the leaning edge of the canopy moves up and down nearly vertically, thus maintaining a nearly constant unsupported distance between the face line and the leading edge of the canopy. This is a feature that is widely considered most desirable for good roof control. There are clear limits of mining height within which the leading edge of the canopy moves nearly vertically. These limits are strictly controlled by the dimentional and positional arrangements of the canopy, caving shield, lemniscate bars, and the base. Beyond these limits, the edges will move rapidly away from the faceline creating a large unsupported area. B. Caliper. In a caliper shield and the base are connected by a single hinge. When the hydraulic legs are raised, the leading edge of the canopy moves in an are away from the face, thus increasing the unsupported area. This is considered by most users the least desirable feature of the caliper shield. But in practice if the seam thickness varies little, the dimentional and positional arrangement of canopy, caving shield, and the base can be so designed that the distance change of unsupported area will not be significant, on the other hand, when the legs are lowered, it reduces the unsupported area. C. Ellipse. In this type the caving shield and the base are so connected that when the hydraulic legs are moved up and down, the leading edge of the canopy follows an elliptical trace. This type is seldom used. CHOCK SHIELD The chock shield bines the features of chock and the shield .as such it possesses the advantages of both .If all of the four or six legs are installed between the bases, it is called a chock shield. There are regular four or sixleg chock shields in which all legs are vertical and parallel. Others from V or X shapes. Some canopies are a single piece and 唐山學(xué)院畢業(yè)設(shè)計(jì) 34 some are two pieces with a hydraulic ram at the hinge joint. The chock shield has the highest supporting efficiency. They are suitable for hard roof. Roadway supports The setting and advancing of supports at the face is only one aspect of effective strata control. It is also essential to set supports in the roadways so keeping roads safe from the shaft to the coalface. The packs on the side of the roadway and the girders supporting the roof in the roadways and permanent supports. They remain in position until the seam or district is worked out or until they have to be removed to enable the roadway to be repaired. There are various shapes of roadway in use underground, depending on the type of strata encountered and any advantages that can be taken from local conditions. However, the majority of roadways leading to longwall faces are supported by arched girders. These not only support the roof but the sides of the roadway as well. Where there is much co。 4. to advance the AFC。 2. to resist ,or acmodate .Lateral ( horizontal ) movement of the strata。液壓傳動(dòng)》，化學(xué)工業(yè)出版社 [3] 官忠范、李笑、楊敢，《液壓系統(tǒng)設(shè)計(jì) 經(jīng)過(guò)這次畢業(yè)設(shè)計(jì)，我不但學(xué)到了更多的知識(shí)，而且還學(xué)到了老師們那種態(tài)度認(rèn)真 、 作風(fēng)嚴(yán)謹(jǐn)和誨人不倦的優(yōu)良品質(zhì)， 愿 老師們工作順利 。同時(shí)還要感謝我的同學(xué)們，設(shè)計(jì)期間，他們給了我 很大 的幫助，幫助我順利完成了本次設(shè)計(jì) 。 通過(guò) 這次設(shè)計(jì) ，使我對(duì)液壓系統(tǒng)有了更加深入的了解，同時(shí)也發(fā)現(xiàn)我對(duì)液壓系統(tǒng)掌握的遠(yuǎn)遠(yuǎn)不夠，這促使我以后還要更加努力地學(xué)習(xí)來(lái)不斷完善自己。 在這次設(shè)計(jì)中，主要是運(yùn)用各類手冊(cè)、產(chǎn)品樣本來(lái)完成設(shè)計(jì)。 設(shè)計(jì)之初收集了很多關(guān)于 軋機(jī) 方面的資料，對(duì)其各個(gè)部件之間的相對(duì)位置以及液壓系統(tǒng)所控制的相對(duì)應(yīng)的部分做了分析，明確了設(shè)計(jì)目標(biāo) ， 這臺(tái)軋機(jī) 的運(yùn)動(dòng)過(guò)程為快進(jìn) —工進(jìn) —快退， 它的加工方式為 同時(shí)對(duì) 6 條或 6 條以上線材進(jìn)行軋制 。綜合檢查的方法主要是分解檢查，要重點(diǎn)排除一年內(nèi)可能產(chǎn)生的故障因素。 (三 ) 綜合檢查 唐山學(xué)院畢業(yè)設(shè)計(jì) 28 綜合檢查每年一次。剛開(kāi)始清洗時(shí)，因雜質(zhì)較多，可采用 80 目 過(guò) 濾網(wǎng)，清洗后期改用 150 目以上的 過(guò) 濾網(wǎng)； 清洗時(shí)間一般為（ 4860）小時(shí)，要根據(jù)系統(tǒng)的復(fù)雜程度、過(guò)濾精度要求和污染程度等因素決定； 為了防止外界濕氣引起銹蝕，清洗結(jié)束時(shí)，液壓泵還要連續(xù)運(yùn)轉(zhuǎn)，直到溫度恢復(fù)正常為止； 清洗后 要將回路內(nèi)的清洗油排除干凈。清洗油液的溫度為（ 5080） ℃ 時(shí)，系統(tǒng)內(nèi)的橡膠渣是容易除掉的； 清洗過(guò)程中，可用非金屬錘棒敲擊油管，可連續(xù)地敲擊，也可不連續(xù)地敲擊，以利清除管路內(nèi)的附著物； 液壓泵間歇運(yùn)轉(zhuǎn)有利于提高清洗效果，間歇時(shí)間一般為 1030min。 清洗時(shí)注意事項(xiàng)： 一般液壓系統(tǒng)清洗時(shí)，多采用工作用的液壓油或試車油。全系統(tǒng)清洗是指對(duì)液壓裝置的整個(gè)回路進(jìn)行清洗，在清洗前應(yīng)將系統(tǒng)恢復(fù)到實(shí)際運(yùn)轉(zhuǎn)狀態(tài)。 液壓系統(tǒng)清洗、使用與維護(hù) 清洗液壓系統(tǒng) 液壓系統(tǒng)在 制造 、試驗(yàn)、使用和儲(chǔ)存中都會(huì)受到污染，而清洗是清除污染，使液壓油、液壓元件和管道等保持清潔的重要手段。因?yàn)?軋機(jī) 液壓執(zhí)行機(jī)構(gòu)不止這些部分，因此留出其余的部分的油路入口和出口。 繪制裝配圖 將以上內(nèi)容綜合起來(lái)，繪制 軋機(jī) 液壓系統(tǒng)如下圖所示： 唐山學(xué)院畢業(yè)設(shè)計(jì) 26 圖 液壓站裝配圖 泵的入口處設(shè)置減震喉，出口處使用軟管，可以有效降低震動(dòng)對(duì)控制元件的影響， 泵站部分的原理結(jié)構(gòu)比較簡(jiǎn)單，因此直接使用管道 連接，在這里采用焊接式管接頭，焊接式管接頭的特點(diǎn)是連接牢固、密封可靠、耐高壓，但焊接工作量大。由于同一系列、規(guī)格的疊加閥的油口和連接螺栓孔的大小、位置和數(shù)量與相匹配的板式換向閥相同，所以，只要把同一規(guī)格的疊加閥按一定順序疊加起來(lái)，再將板式換向閥直接安裝于這些疊加閥上面，即可組成各種回路。 根據(jù)執(zhí)行機(jī)構(gòu)的回路特點(diǎn)，選用疊加閥式集成，疊加閥式集成是在塊式集成基礎(chǔ)上發(fā)展起來(lái)的，液壓控制元件間的連接不需要另外的連接塊，而是以特殊設(shè)計(jì)的疊加閥的閥體作為連接體，通過(guò)螺栓將液壓閥等元件直接疊積并固定在底層的基塊上。 無(wú)管集成：無(wú)管集 成是將液壓控制元件固定在某中專用或者通用的輔助連接件上，輔助連接件內(nèi)開(kāi)有一系列通油孔道，液壓控制元件之間的油路聯(lián)系通過(guò)這些通油孔道來(lái)實(shí)現(xiàn)。顯然，集成方式合理與否，對(duì)液壓系統(tǒng)的工作性能及使用維護(hù)有著很大影響。在液壓站設(shè)計(jì)中的大部分工作量集中在液壓控制裝置的集成設(shè)計(jì)中。查參考文獻(xiàn) [2]，選用 20 號(hào)機(jī)油。 2)環(huán)境溫度高，宜選用高粘度液壓油；環(huán)境溫度低，宜選用低粘度液壓油。在確定液壓油粘度時(shí)，應(yīng)著重考慮下列因素；工作壓力的高低、工作環(huán)境溫度的高低、工作部件運(yùn)動(dòng)速度的大小和液壓泵對(duì)液壓油 粘 度的要求。 液壓設(shè)備出現(xiàn)的故障，有些是由于液壓油選擇不當(dāng)所引起的?？諝鉃V清器能防止出現(xiàn)這種情況。 空氣濾清器 空氣濾清器是對(duì)空氣進(jìn)行凈化的裝置，它由殼體和濾芯組成，濾芯布置在殼體內(nèi)。按濾芯材料和結(jié)構(gòu)形式的不同，過(guò)濾器可分為網(wǎng)式、線隙式、紙 質(zhì) 式、燒結(jié)式 、片式 過(guò)濾器及磁性過(guò)濾器