【正文】 ristics will determine how your fluid operates within your system. Fluid property testing is done in accordance with either American Society of Testing and Materials (ASTM) or other recognized standards anizations. 1. Viscosity (ASTM D44597) is the measure of a fluid’s resistance to flow and shear. A fluid of higher viscosity will flow with higher resistance pared to a fluid with a low viscosity. Excessively high viscosity can contribute to high fluid temperature 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. 2. Viscosity Index (ASTM D2270) 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 where temperature extremes are expected. This is particularly important for hydraulic systems that operate outdoors. 3. Oxidation Stability (ASTM D2272 and others) is the fluid’s resistance to heatinduced degradation caused by a chemical reaction with oxygen. Oxidation greatly reduces the life of a fluid, leaving byproducts such as sludge and varnish. Varnish interferes with valve functioning and can restrict flow passageways. 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 metal surfaces to prevent abrasion, scuffing and contact fatigue on ponent surfaces. Ten Steps to Check Optimum Viscosity Range When selecting lubricants ensure that the lubricant performs efficiently 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 fixeddisplacement gear pump that drives a cylinder (Figure 2). Figure 2 1. Collect all relevant data for the pump. This includes collecting all the design limitations and optimum operating characteristics from 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. 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 paring different fluids during operation. Pump normally operates at 92186。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。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。 這種先入先出的系統(tǒng)將減少由于使用混亂和存儲(chǔ)問題造成的液壓油 失效 。這將最大限度地減少交叉污染，確保關(guān)鍵性能得到滿足。因此，從表上可以看出，所舉液壓油的正常工作條件超出了合適范圍，需要更換。 (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)。 (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 畫出線（圖 3中棕色線）。上述黃線倍幾條溫度線分割，這條線所 穿過的區(qū)域是泵中特定潤滑劑的最佳工作溫度（ 69186。 (8) 在表中的粘度軸上找出廠商提供的相應(yīng)潤滑油最佳粘度值之對(duì)應(yīng)點(diǎn)，然后在該點(diǎn)上畫一條水平線與黃色線相交。 (7) 用直線連接這些標(biāo)記點(diǎn)（圖 3 中黃線）。 (6) 在潤滑油溫度為 100 186。C 的線，再根據(jù)潤滑油廠商提供的潤滑油在 40186。這種表較為普遍，一般在大多數(shù)工業(yè)潤滑油的使用指南都附帶此表，當(dāng)然也可以從潤滑油的生產(chǎn)廠商索取。C 時(shí)的粘度值為 。如，在 40 186。C 至 100186。 (3) 研究液壓泵正在使用的順滑油的溫度 —— 粘度特性。一般情況下，泵的正常工作溫度在 92186。 (2) 測(cè)試液壓泵正常工作時(shí)的實(shí)際溫度。通過咨詢廠商，將可以知道泵工作時(shí)潤滑油適宜的粘度范圍。 圖 2 簡單液壓系統(tǒng) (1) 收集液壓泵所有的相關(guān)數(shù)據(jù)。在系統(tǒng)動(dòng)作的過程中，有明確的程序是十分重要的。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。清漆這種沉淀物極有可能卡死閥門，堵塞管道。 (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。 故高粘度指數(shù)的液壓油適用于極端溫度的環(huán)境中。 (2) 粘度指數(shù)（ ASTM D2270）是用來衡量流體粘度隨溫度變化程度的量。過高的粘度可能導(dǎo)致液壓油溫度的升高，無謂的消耗能源。 (1) 粘度（ ASTM D44597）是流體抵抗流動(dòng)和剪切的措施。這些特性對(duì)液壓系統(tǒng)的正常運(yùn)行有很大的影響。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。 (3) 合成液壓油是人造潤滑劑，此類液壓油性能優(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滑性。但當(dāng)使用此類水基液壓油時(shí)其中的幾個(gè)組件的兼容性就必須檢查，包括液壓泵、過濾器、管道、管件及密封材料。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。水基液壓油能起到合適的潤滑作用，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)問題。 (2) 水基液壓油由于其含水量高，故有較強(qiáng)的阻燃性。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 。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。 (1) 目前應(yīng)用最為廣泛的液壓