iv Calculate the equivalent dynamic load from the equation P XF r YF a v Make a

# Iv calculate the equivalent dynamic load from the

• 16

This preview shows page 9 - 13 out of 16 pages.

(iv) Calculate the equivalent dynamic load from the equation. P = XF r + YF a (v) Make a decision about the expected bearing life and express the life L 10 in million revolutions. (vi) Calculate the dynamic load capacity from the equation C = P ( L 10 ) 1/3 (vii) Check whether the selected bearing of series 60 has the required dynamic capacity. If not, select the bearing of the next series and go back to Step (iii) and continue. 3.9 Design for cyclic loads and speed
In certain applications, ball bearings are subjected to cyclic loads and speeds. As an example, consider a ball bearing operating under the following conditions: (i) radial load 2500 N at 700 rpm for 25% of the time, (ii) radial load 5000 N at 900 rpm for 50% of the time, and (iii) radial load 1000 N at 750 rpm for the remaining 25% of the time. Under these circumstances, it is necessary to consider the complete work cycle while finding out the dynamic load capacity of the bearing. The procedure consists of dividing the work cycle into a number of elements, during which the operating conditions of load and speed are constant. Suppose that the work cycle is divided into x elements. Let P 1 , P 2 , …….…... P x be the loads and n 1 , n 2 ,…….. n x be the speeds during these elements. During the first element, the life L 1 corresponding to load P 1 , is given by Let us assume that the first element consists of N 1 revolutions. Therefore, the life consumed by the first element is given by, Similarly, the life consumed by the second element is given by Adding these expressions, the life consumed by the complete work cycle is given by If P e is the equivalent load for the complete work cycle, the life consumed by the work cycle is given by, where, N = N 1 + N 2 + ……. + N x (a) (b)
Equating expressions (a) and (b), The above equation is used for calculating the dynamic load capacity of a bearing. When the load does not vary in steps of constant magnitude, but varies continuously with time, the above equation is modified and written as In case of bearings, where there is a combined radial and axial load, it should be first converted into equivalent dynamic load before the above computations are carried out. Example 3.2 A single-row deep groove ball bearing has a dynamic load capacity of 40500 N and operates on the following work cycle: (i) radial load of 5000 N at 500 rpm for 25% of the time; (ii) radial load of 10000 N at 700 rpm for 50% of the time; and (iii) radial load of 7000 N at 400 rpm for the remaining 25% of the time. Calculate the expected life of the bearing in hours. Solution Given C = 40500 N Step I Equivalent load for complete work cycle Consider the work cycle of one minute duration. The values of load P and revolutions N are tabulated as follows: (3.5) (3.6)
From equation 3.5 Step II Bearing life (L 10h ) According to the load life relationship, 3.10 Bearing with probability of survival other than 90% In the definition of rating life, it is mentioned that the rating life is the life that 90% of a group of identical bearings will complete or exceed before fatigue failure. The reliability R is defined as, Therefore, the reliability of bearings selected from the manufacturer’s catalogue is 0.9 or 90%. In

#### You've reached the end of your free preview.

Want to read all 16 pages?

• Two '10
• DRWEW
• Ball bearing, contact bearings, Rolling Contact Bearing

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern