【正文】 rtically, 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 SHIELDThe 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 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 supportsThe 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 convergence, stilts are attached to the legs of the arches. As the roof in the roadway gradually lowers, the arch is forced down the stilt instead of being damaged.Struts of steel or wood are placed between the flanges of the arches to ensure that each girder is properly spaced from its neighbors and to prevent the arches form buckling.To prevent loose rocks falling in the roadway, the space between the arch and the roof and sides is covered in with lagging。4. to advance the AFC。液壓傳動》，化學工業(yè)出版社[3] 官忠范、李笑、楊敢，《液壓系統(tǒng)設(shè)計同時還要感謝我的同學們，設(shè)計期間，他們給了我很大的幫助，幫助我順利完成了本次設(shè)計。在這次設(shè)計中，主要是運用各類手冊、產(chǎn)品樣本來完成設(shè)計。綜合檢查的方法主要是分解檢查，要重點排除一年內(nèi)可能產(chǎn)生的故障因素。剛開始清洗時，因雜質(zhì)較多，可采用80目過濾網(wǎng)，清洗后期改用150目以上的過濾網(wǎng)；　　清洗時間一般為（4860）小時，要根據(jù)系統(tǒng)的復(fù)雜程度、過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，液壓泵還要連續(xù)運轉(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?！　∏逑磿r注意事項：　　一般液壓系統(tǒng)清洗時，多采用工作用的液壓油或試車油。、使用與維護　　液壓系統(tǒng)在制造、試驗、使用和儲存中都會受到污染，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。將以上內(nèi)容綜合起來，繪制軋機液壓系統(tǒng)如下圖所示：泵的入口處設(shè)置減震喉，出口處使用軟管，可以有效降低震動對控制元件的影響，泵站部分的原理結(jié)構(gòu)比較簡單，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是連接牢固、密封可靠、耐高壓，但焊接工作量大。根據(jù)執(zhí)行機構(gòu)的回路特點，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)計的疊加閥的閥體作為連接體，通過螺栓將液壓閥等元件直接疊積并固定在底層的基塊上。顯然，集成方式合理與否，對液壓系統(tǒng)的工作性能及使用維護有著很大影響。查參考文獻[2]，選用20號機油。在確定液壓油粘度時，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、工作部件運動速度的大小和液壓泵對液壓油粘度的要求?？諝鉃V清器能防止出現(xiàn)這種情況。按濾芯材料和結(jié)構(gòu)形式的不同，過濾器可分為網(wǎng)式、線隙式、紙質(zhì)式、燒結(jié)式、片式過濾器及磁性過濾器等。用過濾器對油液進行過濾是十分重要的。查參考文獻[6]，選擇型凸緣聯(lián)軸器，該型號聯(lián)軸器公稱扭矩為[T]=4000Nm。2) 計算聯(lián)軸器的計算轉(zhuǎn)矩 由于機器起動時的動載荷和運轉(zhuǎn)中可能出現(xiàn)的過載現(xiàn)象，所以應(yīng)當按軸上的最大轉(zhuǎn)矩作為計算轉(zhuǎn)矩Tca，查參考文獻[6]，計算轉(zhuǎn)矩按下式計算；TCa=KAT 式中 T——公稱轉(zhuǎn)矩，單位為N對于高速傳動軸，應(yīng)選用平衡精度高的聯(lián)軸器，例如膜片聯(lián)軸器等，而不宜選用存在偏心的滑塊聯(lián)軸器等。1) 選擇聯(lián)軸器的類型聯(lián)軸器有剛性聯(lián)軸器、撓性聯(lián)釉器兩大類，其中撓性聯(lián)釉器又可以分為無彈性元件的撓性聯(lián)釉器和有彈性元件的撓性聯(lián)釉器兩大類別。但散熱條件不好。為了安裝支撐管道的管夾，在油箱上表面幾處不同的地方焊接上鋼板。油路系統(tǒng)的噪音源，以泵站為首，因此，進行油箱設(shè)計時，從下列幾方面減輕噪音：l 油箱與箱蓋間增加防振橡皮墊：l 用地腳螺栓將油箱牢固固定在基礎(chǔ)上；l 油泵排油口用橡膠軟管與閥類元件相連接；l 回油管接頭振動噪音較大時，改變回油管直徑或增設(shè)一條回油管，使每個油管接頭的通路減少。隔板的位置在油箱的中間，將吸油區(qū)和回油區(qū)分開，隔板的高度，最低為油面的1/2。l 油箱隔板 為了使吸油區(qū)和壓油區(qū)分開，便于回油中雜質(zhì)的沉淀，油箱中設(shè)置了隔板。l 油箱體 油箱體由Q235鋼板焊接而成,取鋼板厚度5~8mm，箱體大者取大值，本油箱板厚度為8mm。這種結(jié)構(gòu)的液壓油箱，近年來被我們廣泛應(yīng)用在工程機械、建筑機械等行走機械上。每套模具的體積大、造價高、利用率低。 液壓系統(tǒng)的熱平衡條件： 機器在長期連續(xù)工作下，應(yīng)該保持系統(tǒng)的熱平衡，其熱平衡式為： H=0， HKA=0， 查參考文獻[1]，P40，取K= KW/℃，將K=，得： ==℃查參考文獻[1]表332所給的允許值為：一般工作機械≤35℃，故系統(tǒng)溫升驗算合格。查參考文獻[5]，P7，取η=，代入公式得： N== 所以，液壓泵輸入功率N=。液壓系統(tǒng)發(fā)熱的主要原因，是由于液壓泵和執(zhí)行元件的功率損失以及溢流閥的溢流損失所造成的，當液壓油溫度升高后，會引起油液粘度下降，從而導(dǎo)致液壓元件性能的變化，壽命降低以及液壓油老化。因此，進行油箱設(shè)計時候，要考慮油箱的容積、油液在油箱中的冷卻、油箱內(nèi)的裝置和防噪音等問題。整體式液壓站是將液壓控制閥組及蓄能器等均安裝在液壓泵站上。例如利用軋機機身或底座作為液壓油箱存放液壓油。2） 分散配置型液壓裝置是將液壓控制系統(tǒng)的液壓泵及其驅(qū)動電動機、執(zhí)行原器件和輔助元件按照機械設(shè)備的布局、工作特性和操