Ball Bearing Selection Guide: Sizes, Life Time and Lubrication

Ball Bearing Selection Guide: Sizes, Life Time and Lubrication - Bearing is standard parts that we often encounter in most of the moving tool both manual tools and electrical tools. What is bearing? Bearing is the machine parts that supporting the rotating shaft or moving straight shaft. Bearing able to keep a straight shaft rotation or movement can take place in a smooth, safe and long lifespan. Bearings should be sturdy enough to allow the shaft as well as other machine parts work well. If the bearing isn’t functioning properly, then the achievements of the entire system will decrease or can’t work properly.

Many types of bearings used in industrial machinery including ball bearing, roller bearings, thrust bearings, needle bearings, spherical bearings, tapered bearings etc. Each type of bearing has advantages and disadvantages in accordance with their respective functions. In this post I will explain about the ball bearing mainly on the topic of how to choose a ball bearing based on sizes, life time and lubrication.

Before getting into the topic of ball bearing selection guide, we must be known what it is ball bearing? Ball Bearings are a type of rolling-element bearing that uses balls to maintain the separation between the moving parts of the bearing. The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. Ball bearing construction consists of outer ring, inner ring, steel ball, cage and shield as in the image below.

An advantages of ball bearing is at a very low friction. Lubrication was also very simple, just with grease, even on ball bearings with shield no longer need lubrication. But in general, ball bearings are more suitable for small loads. Bearing speed is also limited by centrifugal force that occurs in the steel ball.

How to choose a good ball bearing based on sizes, life time and lubrication, the following explanation:

Selection of the ball bearing sizes

Ball bearing sizes selected from a catalog of standard bearings. Although different brands of bearings, but usually bearing the same code as standard. The ball bearing code refers to the size of the inner ring diameter, outer ring diameter, and width. In general, the inner ring diameter is taken as a benchmark, then the outer ring diameter and width adjust to various alternative sizes.

The ball bearing code consists of basic and supplementary numbers as below:

Note:

Type, bearing types, as 6 = Deep Groove Ball Bearing
Series, outer ring diameter, as 0 = Extra Light, 2 = Light, 3 = Medium, 4 = Heavy etc. (see Table of Code Deep Groove Ball Bearings)
Bore, inner ring diameter, as 00 = 10 mm, 01 = 12 mm, 02 = 15 mm, 03 = 17 mm and 04 to 96 is bore sizes x 5 mm, for example if bore is 05 so the inner ring diameter is 05 x 5 mm = 25 mm.
Sealing, bearing seal or shield, as RSR = Standard Rubber Seal, HSR = Hycar Seal, VSR = Viton Seal, ZR = Metal Shield, 2ZR = 2 Metal Shield etc.
Radial Clearance, radial clearance class, as CN = Normal Clearance, C1 = Clearance Class 1 etc
Precision Class, as PN = Normal Precision Class, P1= Precision Class 1 etc.

Table of ball bearing sizes for type of the deep groove ball bearing is below:

Deep Groove Ball Bearing Sizes
Code	Dimensions (mm)			Code	Dimensions (mm)			Code	Dimensions (mm)
Code	d	D	B	Code	d	D	B	Code	d	D	B
6000	10	26	8	6200	10	30	9	6300	10	35	11
6001	12	28	8	6201	12	32	10	6301	12	37	12
6002	15	32	9	6202	15	35	11	6302	15	42	13
6003	17	35	10	6203	17	40	12	6303	17	47	14
6004	20	42	12	6204	20	47	14	6304	20	52	15
6005	25	47	12	6205	25	52	15	6305	25	62	17
6006	30	55	13	6206	30	62	16	6306	30	72	19
6007	35	62	14	6207	35	72	17	6307	35	80	21
6008	40	68	15	6208	40	80	18	6308	40	90	23
6009	45	75	16	6209	45	85	19	6309	45	100	25
6010	50	80	16	6210	50	90	20	6310	50	110	27
6011	55	90	18	6211	55	100	21	6311	55	120	29
6012	60	95	18	6212	60	110	22	6312	60	130	31
6013	65	100	18	6213	65	120	23	6313	65	140	33
6014	70	110	20	6214	70	125	24	6314	70	150	35
6015	75	115	20	6215	75	130	25	6315	75	160	37
6016	80	125	22	6216	80	140	26	6316	80	170	39
6017	85	130	22	6217	85	150	28	6317	85	180	41
6018	90	140	24	6218	90	160	30	6318	90	190	43
6019	95	145	24	6219	95	170	32	6319	95	200	45
6020	100	150	24	6220	100	180	34	6320	100	215	47
Note : d = Inner Ring Diameter, D = Outer Ring Diameter, B = Bearing Width

Determine of the ball bearing life time

Ball bearing life time is the ability to hold the load bearing acting on it both radial force and axial force. The greater ability to withstand load bearing, it will be the longer life of the bearing. Therefore, when we choose a ball bearing sizes, we have to consider the bearing life through:

(1) Determine the equivalent load on bearing

Equivalent load is a load that causes deformation when there is contact between the steel balls with a ring at the maximum stress. Equivalent load can be calculated using the formula:

Note:

P = Equivalent load (kg)

X = Radial force factor

F_r = Radial force (kg)

Y = Axial force factor

F_a = Axial Force (kg)

(2) Determine the bearing capacity

Bearing capacity is the limit strength or ability of ball bearing in the receiving load. Based on data from the ball bearing code for the selected of ball bearing sizes, bearing capacity can be determined by the following formula:

Note:

C = Bearing capacity (kg)

i = Total row per bearing

a = Contact angle (o)

Z = Total steel ball per row

D_a = Steel ball diameter (mm)

f_c = Bearing factor based on type, precision class and material

After knowing the equivalent load and bearing capacity, we can determine the bearing life time, as the ball bearing strength parameters. Ball bearing life time can be calculated using the formula:

Note:

L_h = Bearing life time (hour)

f_h = Bearing life factor

where the bearing life factor can be calculated by the formula:

Note:

f_h = Bearing life factor

fn = Bearing speed factor

C = Bearing capacity (kg)

P = Equivalent load (kg)

where bearing speed factor is calculated by the formula:

Note:

fn = Bearing speed factor

n = Bearing speed (rpm)

Lubrication of ball bearing

Once we choose a ball bearing size by considering the ball bearing life time, the next step is to perform maintenance on bearings so that the bearing life time is maintained. One form of treatment is to lubricate the bearings.

Lubrication of ball bearing aimed to (1) reduce friction and wear between the steel ball and cage, (2) carry out the heat that occurs, (3) to prevent corrosion and (4) avoid the entry of dust. There are two ways lubrication with grease lubrication and oil lubrication.

Grease lubrication is preferred because the sealing is simpler and all the grease of good quality can provide longevity. Common way of greasing is to fill the inside of the bearings with grease as possible.

Lubrication oil is a useful way of high speed or high temperature of bearing. The most popular is the bags lubrication. In the process of this lubrication, the oil must be loaded until the middle of the steel ball lowest. Oil temperature must be maintained through the cooling pipes or water circulation.

Ball bearing calculation formulas above is taken from the handbook of Design of Machine Elements by Sularso & Kiyokatsu Suga and Mechanical Engineering Design by Shigley & Mitchel

That is a description about Ball Bearing Selection Guide: Sizes, Life Time and Lubrication. If you find misconceptions in the ball bearing formula, please provide the correction in the comment box.