如何計(jì)算單位載荷，滑動(dòng)速度
單位載荷和滑動(dòng)速度意味著什么？
What is meant by Specific Load and Sliding Speed?
位載荷，也稱支承壓力，是由在軸承使用壽命期間施加到軸承上的力而定的。它是施加在軸承材料的力和接觸面積的函數(shù)。單位負(fù)載的SI（國際標(biāo)準(zhǔn)）單位是（N / mm2），也稱為（MPa）。
滑動(dòng)速度，也稱為速度（U），是軸承表面和配合表面（軸，推力面或襯套滑動(dòng)面）之間的相對滑動(dòng)速度。滑動(dòng)速度的SI單位是（m / s）。
Specific Load, also referred to as bearing pressure, is based on the forces that will be applied to the bearing over its lifetime. It is a function of the force and contact area of the bearing material. The SI (International Standards) units for Specific Load are Newtons per square millimeter (N/mm2), also referred to as Mega Pascal (MPa).
Sliding speed, also referred to as speed (U), is the relative sliding speed between the bearing surface and the mating surface (shaft, thrust face or liner slide surface). The SI units for sliding speed is meters per second (m/s).
為什么單位載荷和滑動(dòng)速度很重要？
Why are Specific Load (MPa) and Sliding Speed (U) important?
這些因素MPa 和 U用于確定軸承設(shè)計(jì)以及依據(jù)各種應(yīng)用要求選擇的軸承材料是否合適。例如，通過先選擇軸承材料，設(shè)計(jì)人員可以指定適當(dāng)?shù)妮S承尺寸以滿足應(yīng)用要求?；蛘撸诖_定軸承尺寸后，設(shè)計(jì)者可以選擇滿足各種應(yīng)用要求的軸承材料。
干摩擦軸承設(shè)計(jì)的重要因素是載荷（MPa）和滑動(dòng)速度的乘積，即U系數(shù)。在干摩擦軸承設(shè)計(jì)中，U系數(shù)與摩擦系數(shù)共同決定了由熱摩擦產(chǎn)生的熱量，產(chǎn)生的熱量與軸承材料的耐熱能力有關(guān)。
在潤滑應(yīng)用中，滑動(dòng)軸承在軸和滑動(dòng)軸承表面之間形成流體動(dòng)力潤滑膜的能力取決于單位載荷（MPa）和滑動(dòng)速度（U）之間的關(guān)系、潤滑劑的動(dòng)力粘度（centiPoise）和軸承的長徑比（B / D）。這些因素之間的關(guān)系是：其中7.5值是基于ISO單位的比例因子。
The factors, MPa and U, are used to determine the suitability of a given bearing design and choice of bearing material to the various application requirements. For example, by first selecting a bearing material, the designer can specify the proper bearing dimensions that will meet the application requirements. Alternatively, by first determining the bearing dimensions the designer may then select a bearing material that will meet the various application requirements.
An important factor in designing for a dry bearing is the product of Specific Load (MPa) and Sliding Speed, known as the U factor. The U factor in combination with the coefficient of friction determines the rate of heat generated by thermal friction for a given dry bearing design which relates the bearing material’s ability to resist heat.
In a lubricated application, the ability of a sleeve bearing to develop a hydrodynamic lubrication film between the shaft and the sleeve bearing surface is determined by the relationship between Specific Load () and Sliding Speed (U), the dynamic viscosity (centiPoise) of the lubricant and the bearing length-to diameter ratio (B/D). The relationship between these factors is: where the 7.5 value is a proportionality factor based on ISO units.
如何計(jì)算單位載荷?
How to calculate specific load?
為確定在最壞情況下軸承抗永久變形的能力，必須首先確定最大作用力Fmax。為了確定對耐用軸承設(shè)計(jì)至關(guān)重要的最大力，必須考慮：預(yù)期的設(shè)計(jì)載荷；基于其他類似設(shè)計(jì)的載荷記錄；測量的載荷，動(dòng)力源信息例如扭矩與速度；沖擊負(fù)荷。最大單位載荷用于確定軸承材料是否具有足夠的承載能力來支撐最大載荷。
在確定某些GGB產(chǎn)品的軸承壽命時(shí)，使用平均或加權(quán)平均軸承載荷F確定軸承材料是否能夠提供足夠的壽命（在考慮滑動(dòng)速度的情況下）。當(dāng)載荷數(shù)據(jù)限定為最大值和最小值時(shí)，將計(jì)算平均軸承載荷。如果最小/最大載荷之間的載荷范圍相對較?。ㄐ∮?5％），則只需取兩個(gè)值的平均值即可。如果載荷范圍相對較大，則取差值的2/3，并將其添加到最小載荷以得到“保守”平均值。如果載荷與時(shí)間的關(guān)系記錄可用，假設(shè)速度穩(wěn)定，則可以使用加權(quán)平均值：
其中tn 和Fn分別是每次/載荷增量和St的次數(shù)和負(fù)載。
當(dāng)速度變化時(shí)，將轉(zhuǎn)數(shù)n1, n2 ... nn 和 Sn替換為時(shí)間增量t1, t2 ... tn 和 St
既然已經(jīng)確定了最大和平均力，則很容易計(jì)算出單位載荷：
對于滑動(dòng)軸承，投影面積A = Di′B，基于滑動(dòng)軸承的內(nèi)徑Di乘以軸承長度B：
對于止推墊圈，A = 0.25 ′ p ′ (Do2 – Di2), 其中Do和Di分別是墊圈的外徑和內(nèi)徑。
對于法蘭軸承墊圈表面，A = 0.04 ′ p ′ (Do2 – Di2), 其中Do是法蘭外徑，而Di是法蘭軸承內(nèi)徑。
對于直線導(dǎo)軌，A = L′W，其中L =軸承材料長度； W =軸承材料的寬度。
To determine the bearings capability of resisting permanent deformation under worst case scenarios we must first determine the maximum applied force, Fmax,. To determine the maximum force, which is critical to a robust bearing design, we must consider: anticipated design loads; load history based on other similar designs; measured loads; power source information like torque versus speed; shock loads. Maximum specific load, p max, is used to determine if the bearing material has sufficient load capacity to support the maximum load.
When determining bearing life for select GGB products, an average or weighted average bearing load, F, is used to determine if the bearing material will provide sufficient life when considering the sliding speed. The average bearing load is calculated when load data is limited to minimum and maximum values. If the load range is relatively small (less than 25%) between the min/max loads, then simply take the average of the two values. If the load range is relatively large then take 2/3 of the difference and add it to the minimum load for a “conservative” average. If a load versus time history is available, assuming a steady speed, then a weighted average is possible:
where tn and Fn are the times and loads respectively for each time/load increment and St.
When the speed varies, substitute the number of revolutions, n1, n2 ... nn and Sn for the time increments t1, t2 ... tn and St.
Now that the maximum and average forces have been determined, the specific load is very easy to calculate:
—— For sleeve bearings the projected area, A = Di ′ B, based on the sleeve bearing inside diameter, Di, multiplied by bearing length, B:
—— For thrust washers, A = 0.25 ′ p ′ (Do2 – Di2), where Do and Di are the washers outside and inside diameters respectively.
—— For flanged bearings thrust surfaces, A = 0.04 ′ p ′ (Do2 – Di2), where Do is the flange outside diameter and Di is the flanged bearing inside diameter.
—— For linear slideways, A = L ′ W, where L = bearing material length; W = bearing material width.
如何計(jì)算滑動(dòng)速度
How to calculate Sliding Speed
滑移速度U（也稱為速率）通常并不難確定，尤其是在由電動(dòng)機(jī)或發(fā)動(dòng)機(jī)驅(qū)動(dòng)的應(yīng)用中。速度會(huì)在軸承/配合表面界面處產(chǎn)生熱量，隨著時(shí)間的流逝，熱量會(huì)影響軸承性能。速度越大，產(chǎn)生的熱量越大。相對運(yùn)動(dòng)非常緩慢或偶爾，可能不會(huì)產(chǎn)生足夠的熱量來降低軸承材料的性能。
速度U（以米/秒為單位）是根據(jù)基本應(yīng)用類型計(jì)算得出的：
連續(xù)旋轉(zhuǎn)：
對于滑動(dòng)軸承，Di =滑動(dòng)軸承內(nèi)徑，單位：mm，N =軸速度，單位：rpm：
對于止推墊圈，Do =墊圈外徑，單位：mm，Di =墊圈內(nèi)徑，單位：mm； N =轉(zhuǎn)速，單位：rpm：
擺動(dòng)運(yùn)動(dòng)：
對于滑動(dòng)軸承， Di =內(nèi)徑，單位：mm，Nosc =軸擺動(dòng)速度，cpm：
對于止推墊圈，Do =墊圈外徑，單位：mm，Di =墊圈內(nèi)徑，單位：mm；Nosc=振蕩速度，單位：rpm：
直線運(yùn)動(dòng)：
對于滑動(dòng)軸承和直線導(dǎo)軌，Ls =線性行程長度，單位：mm，c =循環(huán)速率，單位：cpm：
Sliding Speed, U, also called velocity, is usually not that difficult to determine especially in applications that are driven by motors or engines. Speed generates heat at the bearing/mating surface interface which, over time, will affect bearing performance. The greater the speed, the greater the amount of heat generated. Very slow or very occasional periods of relative motion may not develop sufficient heat to degrade the bearing material’s properties.
Speed, U, in meters per second, is calculated based on the basic type of application:
Continuous rotation:
—— For sleeve bearings, Di = sleeve bearing ID in mm, N = shaft speed, rpm:
—— For thrust washers, Do = washer OD in mm, Di = washer ID in mm, N = speed in rpm:
Oscillating motion:
—— For sleeve bearings, Di = ID in mm, Nosc = shaft oscillating speed, cpm:
—— For thrust washers, Do = OD in mm, Di = ID, Nosc in mm = oscillating speed in cpm:
Linear motion:
—— For sleeve bearings and linear slideways, Ls = linear stroke length in mm, c = cycling rate in cpm:
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