如何计算单位载荷，滑动速度

单位载荷和滑动速度意味着什么？

What is meant by Specific Load and Sliding Speed?

位载荷，也称支承压力，是由在轴承使用寿命期间施加到轴承上的力而定的。它是施加在轴承材料的力和接触面积的函数。单位负载的SI（国际标准）单位是（N / mm2），也称为（MPa）。

滑动速度，也称为速度（U），是轴承表面和配合表面（轴，推力面或衬套滑动面）之间的相对滑动速度。滑动速度的SI单位是（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).

为什么单位载荷和滑动速度很重要？

Why are Specific Load (MPa) and Sliding Speed (U) important?

这些因素MPa 和 U用于确定轴承设计以及依据各种应用要求选择的轴承材料是否合适。例如，通过先选择轴承材料，设计人员可以指定适当的轴承尺寸以满足应用要求。或者，在确定轴承尺寸后，设计者可以选择满足各种应用要求的轴承材料。

干摩擦轴承设计的重要因素是载荷（MPa）和滑动速度的乘积，即U系数。在干摩擦轴承设计中，U系数与摩擦系数共同决定了由热摩擦产生的热量，产生的热量与轴承材料的耐热能力有关。

在润滑应用中，滑动轴承在轴和滑动轴承表面之间形成流体动力润滑膜的能力取决于单位载荷（MPa）和滑动速度（U）之间的关系、润滑剂的动力粘度（centiPoise）和轴承的长径比（B / D）。这些因素之间的关系是：其中7.5值是基于ISO单位的比例因子。

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.

如何计算单位载荷?

How to calculate specific load?

为确定在最坏情况下轴承抗永久变形的能力，必须首先确定最大作用力Fmax。为了确定对耐用轴承设计至关重要的最大力，必须考虑：预期的设计载荷；基于其他类似设计的载荷记录；测量的载荷，动力源信息例如扭矩与速度；冲击负荷。最大单位载荷用于确定轴承材料是否具有足够的承载能力来支撑最大载荷。

在确定某些GGB产品的轴承寿命时，使用平均或加权平均轴承载荷F确定轴承材料是否能够提供足够的寿命（在考虑滑动速度的情况下）。当载荷数据限定为最大值和最小值时，将计算平均轴承载荷。如果最小/最大载荷之间的载荷范围相对较小（小于25％），则只需取两个值的平均值即可。如果载荷范围相对较大，则取差值的2/3，并将其添加到最小载荷以得到“保守”平均值。如果载荷与时间的关系记录可用，假设速度稳定，则可以使用加权平均值：

其中tn 和Fn分别是每次/载荷增量和St的次数和负载。

当速度变化时，将转数n1, n2 ... nn 和 Sn替换为时间增量t1, t2 ... tn 和 St

既然已经确定了最大和平均力，则很容易计算出单位载荷：

对于滑动轴承，投影面积A = Di´B，基于滑动轴承的内径Di乘以轴承长度B：

对于止推垫圈，A = 0.25 ´ p ´ (Do2 – Di2), 其中Do和Di分别是垫圈的外径和内径。

对于法兰轴承垫圈表面，A = 0.04 ´ p ´ (Do2 – Di2), 其中Do是法兰外径，而Di是法兰轴承内径。

对于直线导轨，A = L´W，其中L =轴承材料长度； W =轴承材料的宽度。

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.

如何计算滑动速度

How to calculate Sliding Speed

滑移速度U（也称为速率）通常并不难确定，尤其是在由电动机或发动机驱动的应用中。速度会在轴承/配合表面界面处产生热量，随着时间的流逝，热量会影响轴承性能。速度越大，产生的热量越大。相对运动非常缓慢或偶尔，可能不会产生足够的热量来降低轴承材料的性能。

速度U（以米/秒为单位）是根据基本应用类型计算得出的：

连续旋转：

对于滑动轴承，Di =滑动轴承内径，单位：mm，N =轴速度，单位：rpm：

对于止推垫圈，Do =垫圈外径，单位：mm，Di =垫圈内径，单位：mm； N =转速，单位：rpm：

摆动运动：

对于滑动轴承， Di =内径，单位：mm，Nosc =轴摆动速度，cpm：

对于止推垫圈，Do =垫圈外径，单位：mm，Di =垫圈内径，单位：mm；Nosc=振荡速度，单位：rpm：

直线运动：

对于滑动轴承和直线导轨，Ls =线性行程长度，单位：mm，c =循环速率，单位：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: