外文翻譯--液壓系統(tǒng)與液壓油的選擇

1、<p><b>　　中文3960字</b></p><p>　　附件1：外文資料翻譯譯文</p><p>　　液壓系統(tǒng)與液壓油的選擇</p><p>　　液壓機(jī)直到工業(yè)革命時(shí)期才由英國(guó)機(jī)械師約瑟夫·布拉瑪根據(jù)帕斯卡定律制造出來(lái)。1795年，他申請(qǐng)并獲得了液壓機(jī)的相關(guān)專(zhuān)利，從此布拉瑪液壓機(jī)聲名鵲起。布拉瑪通過(guò)計(jì)算發(fā)現(xiàn)如果在一個(gè)

2、小面積面上施加一個(gè)不大的力，那么，它將在相對(duì)較大的面上產(chǎn)生一個(gè)較大的力，而唯一影響機(jī)器發(fā)揮這種力的因素是這個(gè)面上所施加力的大小。</p><p>　　1 什么是液壓系統(tǒng)？</p><p>　　從集成鋼的小型組裝流程和造紙廠的應(yīng)用可以發(fā)現(xiàn)，液壓系統(tǒng)在今天已經(jīng)有了非常廣泛的應(yīng)用。液壓幫助操作員完成許多重要工作(抬沉重的負(fù)荷、轉(zhuǎn)向軸、孔鉆進(jìn)精度等)，同時(shí)有效降低了機(jī)械聯(lián)動(dòng)的成本，這一切都?xì)w功于

3、帕斯卡定律，帕斯卡定律表述如下：</p><p>　　“由于液體的流動(dòng)性，封閉容器中的靜止流體的某一部分發(fā)生的壓強(qiáng)變化，將毫無(wú)損失地傳遞至流體的各個(gè)部分和容器壁（圖1）?！?lt;/p><p><b>　　圖1 帕斯卡定律</b></p><p>　　由布拉馬對(duì)帕斯卡定律的應(yīng)用可知，如果在一個(gè)10平方英寸的面上作用100磅的力，那么整個(gè)容器內(nèi)的每

4、平方英寸上將產(chǎn)生100磅的力。也就是說(shuō)，這種力能在100平方英寸的面上產(chǎn)生1000磅的力。</p><p>　　液壓系統(tǒng)是對(duì)帕斯卡定律的合理運(yùn)用，它通過(guò)液壓油在兩點(diǎn)間傳遞能量。液壓油幾乎是不可壓縮的，所以它能輕松地在瞬間傳遞力量。</p><p>　　2 液壓系統(tǒng)的組成</p><p>　　液壓系統(tǒng)的主要組成部分是液壓缸，液壓泵，閥和執(zhí)行機(jī)構(gòu)（馬達(dá)，油缸等）。&l

5、t;/p><p><b>　　2.1 液壓油箱</b></p><p>　　液壓油箱的作用是存儲(chǔ)壓油，傳遞出系統(tǒng)熱量，回收排出的污染物質(zhì)和促進(jìn)系統(tǒng)中游離液體或氣體的釋放。</p><p><b>　　2.2 液壓泵</b></p><p>　　液壓泵通過(guò)作為傳輸媒介的液壓油的運(yùn)動(dòng)，將機(jī)械能轉(zhuǎn)化為液壓

6、能。液壓泵有齒輪泵，葉片泵，柱塞泵幾種類(lèi)型。這些不同類(lèi)型的泵都有特定的應(yīng)用，如曲軸柱塞泵或變量葉片泵。所有泵的工作原理都是相同的，利用液體體積對(duì)抗負(fù)載或壓力。</p><p><b>　　2.2 液壓閥</b></p><p>　　液壓閥主要是由錐閥芯或圓柱閥芯構(gòu)成，它用于系統(tǒng)的啟動(dòng)，停止和引導(dǎo)流體流動(dòng)。液壓閥可以通過(guò)氣動(dòng)、液壓、電氣、人工或機(jī)械等方式驅(qū)動(dòng)。<

7、/p><p><b>　　2.3 執(zhí)行機(jī)構(gòu)</b></p><p>　　液壓執(zhí)行機(jī)構(gòu)是帕斯卡定律的終端，它的目的是將液壓能轉(zhuǎn)變回機(jī)械能。這可以通過(guò)液壓缸轉(zhuǎn)換為直線(xiàn)運(yùn)動(dòng)，或用液壓馬達(dá)將其轉(zhuǎn)化為旋轉(zhuǎn)運(yùn)動(dòng)。和液壓泵一樣，液壓缸和液壓馬達(dá)也因特定的應(yīng)用而設(shè)計(jì)成不同的類(lèi)型。</p><p>　　3 液壓系統(tǒng)潤(rùn)滑的重點(diǎn)組件</p><p

8、>　　考慮到維修成本和任務(wù)的重要程度，液壓系統(tǒng)的各組成元件中，泵和閥門(mén)是關(guān)鍵組成部分。從潤(rùn)滑的角度看，泵的幾個(gè)部件必須單獨(dú)進(jìn)行維護(hù)，其中包括：</p><p><b>　　3.1 葉片泵</b></p><p>　　不同廠家生產(chǎn)的泵存在一定差異，但它們均以類(lèi)似的設(shè)計(jì)原則工作既將轉(zhuǎn)子連接到驅(qū)動(dòng)軸上后裝入定子，同時(shí)使其與軸保持偏心。葉片則插入到轉(zhuǎn)子上，并能沿定子內(nèi)

9、表面運(yùn)動(dòng)。</p><p>　　通常情況下葉片和定子內(nèi)壁總是有接觸的，因此會(huì)產(chǎn)生大量的磨損。這將導(dǎo)致葉片從槽中脫落。葉片泵花費(fèi)巨大代價(jià)提供穩(wěn)定的流動(dòng)。在工作溫度工作時(shí)，正常的粘度為14至160cSt。葉片泵一般不適用于液壓油質(zhì)量難以保證的高壓系統(tǒng)，同時(shí)抗磨添加劑的優(yōu)劣對(duì)泵有著巨大影響。</p><p><b>　　3.2 柱塞泵</b></p><

10、;p>　　和所有的液壓泵相同，柱塞泵也被設(shè)計(jì)為定量泵和變量泵兩種。柱塞式液壓泵用途廣泛且造型復(fù)雜，能應(yīng)對(duì)各種類(lèi)型系統(tǒng)的用途及要求。柱塞泵效率高，工作壓力高達(dá)6000萬(wàn)磅，而它卻只產(chǎn)生很小的噪音。同時(shí)柱塞式液壓泵的抗磨損設(shè)計(jì)往往優(yōu)于其余泵的設(shè)計(jì)。柱塞式液壓泵正常工作的運(yùn)動(dòng)粘度值為10到160cSt。</p><p><b>　　3.3 齒輪泵</b></p><p&

11、gt;　　齒輪液壓泵從結(jié)構(gòu)上分有兩種形式，內(nèi)嚙合式液壓泵和外嚙合式液壓泵。兩者都有各自的子類(lèi)型，但它們都是通過(guò)兩個(gè)嚙合齒輪間流體的流動(dòng)發(fā)展而來(lái)?？傮w上來(lái)說(shuō)，齒輪泵的效率低于葉片泵和柱塞泵，齒輪泵的優(yōu)點(diǎn)在于它有更強(qiáng)的抗污能力。</p><p>　　(1) 內(nèi)嚙合式齒輪液壓泵所能產(chǎn)生的壓力高達(dá)3000至3500帕斯卡。這一類(lèi)的液壓泵因?yàn)檎扯鹊牟煌軕?yīng)對(duì)很廣的粘度范圍，最大運(yùn)動(dòng)粘度值為2200cSt，而其此類(lèi)液壓泵的噪

12、音極低。即便是內(nèi)嚙合式液壓泵的液壓油保持在很低的粘度，它的工作效率也很高。</p><p>　　(2) 外嚙合式齒輪液壓泵可處理的壓力范圍在3000至3500磅之間。這些泵一般應(yīng)用于廉價(jià)，中壓，中批量生產(chǎn)，定排量的系統(tǒng)中。在這一系列中泵的運(yùn)動(dòng)粘度值范圍有限，一般不到300cSt。</p><p><b>　　4 液壓油</b></p><p>

13、;　　現(xiàn)如今，液壓油在液壓系統(tǒng)中扮演了很多重要角色。它的主要功能是在系統(tǒng)間傳遞能量以保證系統(tǒng)動(dòng)作順利完成。同時(shí)，液壓油還擔(dān)負(fù)著潤(rùn)滑、散熱、防污的重任。在選擇液壓油時(shí)因考慮粘度、密封相容性、存儲(chǔ)和添加劑的封裝。目前市面常售的液壓油主要為石油基液壓油、礦物液壓油和合成液壓油。</p><p>　　(1) 目前應(yīng)用最為廣泛的液壓油是由石油或礦物質(zhì)為基礎(chǔ)制成。礦物液壓油的性能主要取決于添加劑的使用，原油的質(zhì)量及其提煉的過(guò)

14、程。添加劑對(duì)石油基液壓油的主要性能特點(diǎn)起主導(dǎo)作用。常用的液壓油添加劑主要包括防銹添加劑、抗氧化(R&O)添加劑、防腐蝕劑、反乳化劑、抗磨（AW）添加劑、極壓(EP)添加劑、粘度指數(shù)增強(qiáng)劑和泡沫抑制劑?？傮w上來(lái)說(shuō)，礦物液壓油的性?xún)r(jià)比很高，是非常好的選擇。</p><p>　　(2) 水基液壓油由于其含水量高，故有較強(qiáng)的阻燃性。常見(jiàn)的類(lèi)型有水包油乳化液、水型油乳液和水乙二醇混合物。水基液壓油能起到合適的潤(rùn)滑作

15、用，但是由于水基液壓油的特點(diǎn)，需要隨時(shí)監(jiān)控以防出現(xiàn)問(wèn)題。水基液壓油往往用于要有耐火特性的情況下，此時(shí)液壓系統(tǒng)會(huì)處在高溫的環(huán)境中。溫度升高將導(dǎo)致液壓油內(nèi)的水分加速蒸發(fā)，從而導(dǎo)致液壓油粘度的增加。有時(shí)凝結(jié)的蒸餾水進(jìn)入液壓系統(tǒng)中，可能使液壓油重新平衡。但當(dāng)使用此類(lèi)水基液壓油時(shí)其中的幾個(gè)組件的兼容性就必須檢查，包括液壓泵、過(guò)濾器、管道、管件及密封材料。水基液壓油的價(jià)格比常規(guī)的石油基液壓油高，而且它還有一些其它缺點(diǎn)（例如，較低的耐磨性），因此在使

16、用時(shí)需權(quán)衡利弊。</p><p>　　(3) 合成液壓油是人造潤(rùn)滑劑，此類(lèi)液壓油性能優(yōu)秀，即使是在高溫高壓的液壓系統(tǒng)中也能保持極好的潤(rùn)滑性。一般，合成液壓油具有阻燃（磷酸酯）、低摩擦、自動(dòng)清污（有機(jī)酯與增強(qiáng)酯合成的碳?xì)浠衔铮┖蜔岱€(wěn)定性。同時(shí)合成液壓油的缺點(diǎn)也很明顯，它們比傳統(tǒng)液壓油更貴，需要特殊處理，甚至有些液壓油可能略有毒性，而且它們常常不能與密封材料共存。</p><p><b

17、>　　5 流體性質(zhì)</b></p><p>　　在選擇液壓油時(shí)，需考慮以下幾個(gè)特點(diǎn)：粘度、粘度指數(shù)、抗氧化性和耐磨性。這些特性對(duì)液壓系統(tǒng)的正常運(yùn)行有很大的影響。流體性質(zhì)的測(cè)試工作可在美國(guó)試驗(yàn)與材料協(xié)會(huì)（ASTM）或其他任何公認(rèn)的標(biāo)準(zhǔn)組織進(jìn)行。</p><p>　　(1) 粘度（ASTM D445-97）是流體抵抗流動(dòng)和剪切的措施。與低粘度的液壓油相比，高粘度的液壓油在流

18、動(dòng)時(shí)會(huì)受到更大的阻力。過(guò)高的粘度可能導(dǎo)致液壓油溫度的升高，無(wú)謂的消耗能源。粘度過(guò)高或過(guò)低都會(huì)損壞液壓系統(tǒng)，所以液壓油的選用是個(gè)關(guān)鍵因素。</p><p>　　(2) 粘度指數(shù)（ASTM D2270）是用來(lái)衡量流體粘度隨溫度變化程度的量。通常在相同條件下，液壓油的粘度指數(shù)越高，它所能保持其粘度不變的溫度范圍越大。故高粘度指數(shù)的液壓油適用于極端溫度的環(huán)境中。這對(duì)于在室外作業(yè)的液壓系統(tǒng)來(lái)說(shuō)尤為重要。</p>

19、<p>　　(3) 抗氧化性（ASTM D2272及其它）是指液壓油抵抗由溫度引起的氧化而使液壓油降解的能力。氧化時(shí)液壓油的壽命大大降低，而且會(huì)產(chǎn)生諸如污泥和清漆之類(lèi)的副產(chǎn)品。清漆這種沉淀物極有可能卡死閥門(mén)，堵塞管道。</p><p>　　(4) 耐磨性（ASTM D2266及其它）是潤(rùn)滑油減少邊界接觸摩擦磨損率的能力。這會(huì)使液壓油在金屬表面形成一層保護(hù)膜以防止元件表面的磨損、劃傷和接觸疲勞。<

20、;/p><p>　　6 檢查最佳粘度范圍的十個(gè)步驟</p><p>　　在選擇潤(rùn)滑油時(shí)，應(yīng)確保潤(rùn)滑油能在液壓泵和液壓馬達(dá)中有效運(yùn)作。在系統(tǒng)動(dòng)作的過(guò)程中，有明確的程序是十分重要的。假設(shè)有一個(gè)由一定量齒輪泵驅(qū)動(dòng)液壓缸的簡(jiǎn)單液壓系統(tǒng)（圖2）。</p><p>　　圖2 簡(jiǎn)單液壓系統(tǒng)</p><p>　　(1) 收集液壓泵所有的相關(guān)數(shù)據(jù)。這其中包括泵

21、在設(shè)計(jì)中的局限性和其出廠時(shí)所規(guī)定的最佳工作條件。通過(guò)咨詢(xún)廠商，將可以知道泵工作時(shí)潤(rùn)滑油適宜的粘度范圍。如，液壓泵所需潤(rùn)滑油的粘度需在13cSt到54cSt之間，而最佳粘度為23cSt。</p><p>　　(2) 測(cè)試液壓泵正常工作時(shí)的實(shí)際溫度。這個(gè)步驟極其重要，因?yàn)橐簤罕霉ぷ鲿r(shí)，使用任何潤(rùn)滑油，實(shí)際溫度都是必不可少的參考條件。一般情況下，泵的正常工作溫度在92ºC左右。</p><

22、p>　　(3) 研究液壓泵正在使用的順滑油的溫度——粘度特性。這里推薦使用國(guó)際標(biāo)準(zhǔn)化組織粘度評(píng)級(jí)系統(tǒng)（適用于40ºC 至 100ºC）。如，在40 ºC時(shí)的粘度值為32cSt，100 ºC時(shí)的粘度值為5.1cSt。</p><p>　　(4) 一張ASTM D341的標(biāo)準(zhǔn)石油產(chǎn)品粘度-溫度表是必不可少的。這種表較為普遍，一般在大多數(shù)工業(yè)潤(rùn)滑油的使用指南都附帶此表，當(dāng)然

23、也可以從潤(rùn)滑油的生產(chǎn)廠商索取。</p><p>　　(5) 結(jié)合第三步研究潤(rùn)滑油粘度特性所得到的結(jié)論，首先在圖表的溫度軸（x軸）上找出溫度所對(duì)應(yīng)的線(xiàn)如40 ºC的線(xiàn)，再根據(jù)潤(rùn)滑油廠商提供的潤(rùn)滑油在40ºC時(shí)的粘度在圖上找出對(duì)應(yīng)的粘度線(xiàn)，然后標(biāo)記兩條直線(xiàn)的交點(diǎn)（圖3中紅線(xiàn)）。</p><p>　　(6) 在潤(rùn)滑油溫度為100 ºC時(shí)，重復(fù)第五步，并標(biāo)記點(diǎn)（圖3中

24、深綠色線(xiàn)）。</p><p>　　(7) 用直線(xiàn)連接這些標(biāo)記點(diǎn)（圖3中黃線(xiàn)）。這條線(xiàn)表示了在一系列溫度時(shí)，潤(rùn)滑油的粘度。</p><p>　　(8) 在表中的粘度軸上找出廠商提供的相應(yīng)潤(rùn)滑油最佳粘度值之對(duì)應(yīng)點(diǎn)，然后在該點(diǎn)上畫(huà)一條水平線(xiàn)與黃色線(xiàn)相交。接著從此交點(diǎn)引一條垂直線(xiàn)（圖3中綠線(xiàn)）至表底部。上述黃線(xiàn)倍幾條溫度線(xiàn)分割，這條線(xiàn)所穿過(guò)的區(qū)域是泵中特定潤(rùn)滑劑的最佳工作溫度（69ºC）

25、。</p><p>　　(9) 當(dāng)粘度分別為泵所需粘度的最大值和最小值時(shí)，重復(fù)步驟8畫(huà)出線(xiàn)（圖3中棕色線(xiàn)）。介于最高溫度和最低溫度間的區(qū)域是為泵選擇理想潤(rùn)滑油的根據(jù)既算選潤(rùn)滑油的溫度范圍必須在這個(gè)區(qū)域內(nèi)。</p><p>　　(10) 在圖表上找出步驟2所述測(cè)出溫度所對(duì)應(yīng)的值，如果這一值落在最高溫度和最低溫度所形成的區(qū)域之間，則表明該液壓油適合這個(gè)系統(tǒng)。否則，就要更換液壓油。因此，從表上可

26、以看出，所舉液壓油的正常工作條件超出了合適范圍，需要更換。</p><p>　　圖3 粘度-溫度表</p><p>　　此外，請(qǐng)遵守以下液壓油的管理原則:</p><p>　　(1) 標(biāo)記所有的輸入液壓油和液壓油箱。這將最大限度地減少交叉污染，確保關(guān)鍵性能得到滿(mǎn)足。</p><p>　　(2) 在液壓油的存儲(chǔ)設(shè)備中采用先入先出的方式。這種先

27、入先出的系統(tǒng)將減少由于使用混亂和存儲(chǔ)問(wèn)題造成的液壓油失效。 </p><p>　　液壓系統(tǒng)是以流體為基礎(chǔ)的相對(duì)復(fù)雜的系統(tǒng)，它能輕松地將能量轉(zhuǎn)變?yōu)橛杏玫膭?dòng)作。但是只有根據(jù)系統(tǒng)要求選擇了合適的液壓油，液壓系統(tǒng)才能正常工作。在選擇液壓油時(shí)，要合理考慮到液壓油的粘度。當(dāng)然需要考慮的重要參量還有很多，包括粘度指數(shù)、耐磨性和抗氧化性等。</p><p><b>　　附件2：外文原文</

28、b></p><p>　　Hydraulic Systems and Fluid Selection</p><p>　　It wasn’t until the beginning of the industrial revolution when a British mechanic named Joseph Bramah applied the principle of Pasc

29、al’s law in the development of the first hydraulic press. In 1795, he patented his hydraulic press, known as the Bramah press. Bramah figured that if a small force on a small area would create a proportionally larger for

30、ce on a larger area, the only limit to the force that a machine can exert is the area to which the pressure is applied. </p><p>　　What is a Hydraulic System?Hydraulic systems can be found today in a wide va

31、riety of applications, from small assembly processes to integrated steel and paper mill applications. Hydraulics enable the operator to accomplish significant work (lifting heavy loads, turning a shaft, drilling precisio

32、n holes, etc.) with a minimum investment in mechanical linkage through the application of Pascal’s law, which states:</p><p>　　“Pressure applied to a confined fluid at any point is transmitted undiminished t

33、hroughout the fluid in all directions and acts upon every part of the confining vessel at right angles to its interior surfaces and equally upon equal areas (Figure 1).” </p><p>　　By applying Pascal’s law an

34、d Brahma’s application of it, it is evident that an input force of 100 pounds on 10 square inches will develop a pressure of 10 pounds per square inch throughout the confined vessel. This pressure will support a 1000-pou

35、nd weight if the area of the weight is 100 square inches.</p><p>　　The principle of Pascal’s law is realized in a hydraulic system by the hydraulic fluid that is used to transmit the energy from one point to

36、 another. Because hydraulic fluid is nearly incompressible, it is able to transmit power instantaneously. </p><p>　　Hydraulic System ComponentsThe major components that make up a hydraulic system are the re

37、servoir, pump, valve(s) and actuator(s) (motor, cylinder, etc.). </p><p>　　ReservoirThe purpose of the hydraulic reservoir is to hold a volume of fluid, transfer heat from the system, allow solid contaminan

38、ts to settle and facilitate the release of air and moisture from the fluid.</p><p>　　PumpThe hydraulic pump transmits mechanical energy into hydraulic energy. This is done by the movement of fluid which is

39、the transmission medium. There are several types of hydraulic pumps including gear, vane and piston. All of these pumps have different subtypes intended for specific applications such as a bent-axis piston pump or a vari

40、able displacement vane pump. All hydraulic pumps work on the same principle, which is to displace fluid volume against a resistant load or pressure. </p><p>　　ValvesHydraulic valves are used in a system to

41、start stop and direct fluid flow. Hydraulic valves are made up of poppet’s or spools and can be actuated by means of pneumatic, hydraulic, electrical, manual or mechanical means. </p><p>　　ActuatorsHydrauli

42、c actuators are the end result of Pascal’s law. This is where the hydraulic energy is converted back to mechanical energy. This can be done through use of a hydraulic cylinder which converts hydraulic energy into linear

43、motion and work, or a hydraulic motor which converts hydraulic energy into rotary motion and work. As with hydraulic pumps, hydraulic cylinders and hydraulic motors have several different subtypes, each intended for spec

44、ific design applications.</p><p>　　Key Lubricated Hydraulic ComponentsThere are several components in a hydraulic system, that due to cost of repair or criticality of mission, are considered vital component

45、s. Pumps and valves are considered key components. Several different configurations for pumps must be treated individually from a lubrication perspective, including:</p><p>　　Vane PumpsThere are many variat

46、ions of vane pumps available between manufacturers. They all work on similar design principles. A slotted rotor is coupled to the drive shaft and turns inside of a cam ring that is offset or eccentric to the drive shaft.

47、 Vanes are inserted into the rotor slots and follow the inner surface of the cam ring as the rotor turns. </p><p>　　The vanes and the inner surface of the cam rings are always in contact and are subject to h

48、igh amounts of wear. As the two surfaces wear, the vanes come further out of their slot. Vane pumps deliver a steady flow at a high cost. Vane pumps operate at a normal viscosity range between 14 and 160 cSt at operating

49、 temperature. Vane pumps may not be suitable in critical high-pressure hydraulic systems where contamination and fluid quality are difficult to control. The performance of the fluid’s antiw</p><p>　　Piston P

50、umpsAs with all hydraulic pumps, piston pumps are available in fixed and variable displacement designs. Piston pumps are generally the most versatile and rugged pump type and offer a range of options for any type of sys

51、tem. Piston pumps can operate at pressures beyond 6000 psi, are highly efficient and produce comparatively little noise. Many designs of piston pumps also tend to resist wear better than other pump types. Piston pumps op

52、erate at a normal fluid viscosity range of 10 to 160</p><p>　　Gear PumpsThere are two common types of gear pumps, internal and external. Each type has a variety of subtypes, but all of them develop flow by

53、carrying fluid between the teeth of a meshing gear set. While generally less efficient than vane and piston pumps, gear pumps are often more tolerant of fluid contamination. </p><p>　　1. Internal gear pumps

54、produce pressures up to 3000 to 3500 psi. These types of pumps offer a wide viscosity range up to 2200 cSt, depending on flow rate and are generally quiet. Internal gear pumps also have a high efficiency even at low flui

55、d viscosity.</p><p>　　2. External gear pumps are common and can handle pressures up to 3000 to 3500 psi. These gear pumps offer an inexpensive, mid-pressure, mid-volume, fixed displacement delivery to a syst

56、em. Viscosity ranges for these types of pumps are limited to less than 300 cSt.</p><p>　　Hydraulic FluidsToday’s hydraulic fluids serve multiple purposes. The major function of a hydraulic fluid is to provi

57、de energy transmission through the system which enables work and motion to be accomplished. Hydraulic fluids are also responsible for lubrication, heat transfer and contamination control. When selecting a lubricant, cons

58、ider the viscosity, seal compatibility, base stock and the additive package. Three common varieties of hydraulic fluids found on the market today are petroleum-ba</p><p>　　1. Petroleum-based or mineral-based

59、 fluids are the most widely used fluids today. The properties of a mineral-based fluid depend on the additives used, the quality of the original crude oil and the refining process. Additives in a mineral-based fluid offe

60、r a range of specific performance characteristics. Common hydraulic fluid additives include rust and oxidation inhibitors (R&O), anticorrosion agents, demulsifies, antiwar (AW) and extreme pressure (EP) agents, VI im

61、provers and defoamants. Miner</p><p>　　2. Water-based fluids are used for fire-resistance due to their high-water content. They are available as oil-in-water emulsions, water-in-oil (invert) emulsions and wa

62、ter glycol blends. Water-based fluids can provide suitable lubrication characteristics but need to be monitored closely to avoid problems. Because water-based fluids are used in applications when fire resistance is neede

63、d, these systems and the atmosphere around the systems can be hot. Elevated temperatures cause the water in the </p><p>　　3. Synthetic fluids are man-made lubricants and many offer excellent lubrication char

64、acteristics in high-pressure and high- temperature systems. Some of the advantages of synthetic fluids may include fire-resistance (phosphate esters), lower friction, natural detergency (organic esters and ester-enhanced

65、 synthesized hydrocarbon fluids) and thermal stability. The disadvantage to these types of fluids is that they are usually more expensive than conventional fluids, they may be slightly toxic and </p><p>　　Fl

66、uid PropertiesWhen choosing a hydraulic fluid, consider the following characteristics: viscosity, viscosity index, oxidation stability and wear resistance. These characteristics will determine how your fluid operates wi

67、thin your system. Fluid property testing is done in accordance with either American Society of Testing and Materials (ASTM) or other recognized standards organizations.</p><p>　　1. Viscosity (ASTM D445-97) i

68、s the measure of a fluid’s resistance to flow and shear. A fluid of higher viscosity will flow with higher resistance compared to a fluid with a low viscosity. Excessively high viscosity can contribute to high fluid temp

69、erature and greater energy consumption. Viscosity that is too high or too low can damage a system, and consequently, is the key factor when considering a hydraulic fluid.</p><p>　　2. Viscosity Index (ASTM D2

70、270) is how the viscosity of a fluid changes with a change in temperature. A high VI fluid will maintain its viscosity over a broader temperature range than a low VI fluid of the same weight. High VI fluids are used wher

71、e temperature extremes are expected. This is particularly important for hydraulic systems that operate outdoors.</p><p>　　3. Oxidation Stability (ASTM D2272 and others) is the fluid’s resistance to heat-indu

72、ced degradation caused by a chemical reaction with oxygen. Oxidation greatly reduces the life of a fluid, leaving by-products such as sludge and varnish. Varnish interferes with valve functioning and can restrict flow pa

73、ssageways.</p><p>　　4. Wear Resistance (ASTM D2266 and others) is the lubricant’s ability to reduce the wear rate in frictional boundary contacts. This is achieved when the fluid forms a protective film on m

74、etal surfaces to prevent abrasion, scuffing and contact fatigue on component surfaces.</p><p>　　Ten Steps to Check Optimum Viscosity RangeWhen selecting lubricants ensure that the lubricant performs efficie

75、ntly at the operating parameters of the system pump or motor. It is useful to have a defined procedure to follow through the process. Consider a simple system with a fixed-displacement gear pump that drives a cylinder (F

76、igure 2). </p><p><b>　　Figure 2</b></p><p>　　1. Collect all relevant data for the pump. This includes collecting all the design limitations and optimum operating characteristics from

77、 the manufacturer. What you are looking for is the optimum operating viscosity range for the pump in question. Minimum viscosity is 13 cSt, maximum viscosity is 54 cSt, and optimum viscosity is 23 cSt.</p><p&g

78、t;　　2. Check the actual operating temperature conditions of the pump during normal operation. This step is extremely important because it gives a reference point for comparing different fluids during operation. Pump norm

79、ally operates at 92ºC.</p><p>　　3. Collect the temperature-viscosity characteristics of the lubricant in use. The ISO viscosity rating system (cSt at 40ºC and 100ºC) is recommended. Viscosity

80、is 32 cSt at 40ºC and 5.1 cSt at 100ºC.</p><p>　　4. Obtain an ASTM D341 standard viscosity-temperature chart for liquid petroleum products. This chart is quite common and can be found in most indus

81、trial lubricant product guides or from lubricant suppliers.</p><p>　　5. Using the viscosity characteristics of the lubricant found in Step 3, start at the temperature axis (x-axis) of the chart and scroll al

82、ong until you find the 40 ºC line. At the 40ºC line, track upward until you find the line corresponding to the viscosity of your lubricant at 40ºC as published by your lubricant manufacturer. When you find

83、 the corresponding line, make a small mark at the intersection of the two lines (red lines, Figure 3).</p><p>　　6. Repeat Step 5 for the lubricant properties at 100ºC and mark the intersection point (da

84、rk blue line, Figure 3).</p><p>　　7. Connect the marks by drawing a line through them with a straight edge (yellow line, Figure 3). This line represents the lubricant’s viscosity at a range of temperatures.&

85、lt;/p><p>　　8. Using the manufacturer’s data for the pump’s optimum operating viscosity, find the value on the vertical viscosity axis of the chart. Draw a horizontal line across the page until it hits the yell

86、ow viscosity vs. temperature line of the lubricant. Now draw a vertical line (green line, Figure 3) to the bottom of the chart from the yellow viscosity vs. temperature line where it is intersected by the horizontal opti

87、mum viscosity line. Where this line crosses, the temperature axis is the optimum o</p><p>　　9. Repeat Step 8 for maximum continuous and minimum continuous viscosities of the pump (brown lines, Figure 3). The

88、 area between the minimum and maximum temperatures is the minimum and maximum allowable operating temperature of the pump for the selected lubricant product.</p><p>　　10. Find the normal operating temperatur

89、e of the pump on the chart using the heat gun scan done in Step 2. If the value is within the minimum and maximum temperatures as outlined on the chart, the fluid is suitable for use in the system. If it is not, you must

90、 change the fluid to a higher or lower viscosity grade accordingly. As shown in the chart, the normal operating conditions of the pump are out of the suitable range (brown area, Figure 3) for our particular lubricant and

91、 will have to be cha</p><p><b>　　Figure 3</b></p><p>　　Also, observe the following hydraulic fluid management practices.</p><p>　　Implement a procedure for labeling all

92、incoming lubricants and tagging all reservoirs. This will minimize cross-contamination and assure that critical performance requirements are met.</p><p>　　Use a First-In-First-Out (FIFO) method in your lubri

93、cant storage facility. A properly executed FIFO system reduces confusion and storage-induced lubricant failure.</p><p>　　Hydraulic systems are complicated fluid-based systems for transferring energy and conv

94、erting that energy into useful work. Successful hydraulic operations require the careful selection of hydraulic fluids that meet the system demands. Viscosity selection is central to a correct fluid selection. There are