CURTIN UNIVERSITY OF TECHNOLOGY

CURTIN UNIVERSITY OF TECHNOLOGY

SCHOOL OF MECHANICAL ENGINEERING

MECHANICS 234: LABORATORY EXPERIMENTDYNAMIC BLANACE OF A ROTOR1. OBJECTIVE

To achieve dynamic balance of a rotor assembly by attachment of masses in the correct angular and axial position

2. APPARATUSTecquipment Dynamic Balancing Machine. The machine consists of a balanced cylindrical shaft mounted in ball bearings attached to a rigid frame. A set of four blocks in provided. These blocks are of different mass and may be clamped to the rotor in any angular and axial position on the shaft. A protractor scale and linear scale are provided to allow accurate angular and axial positioning of the blocks on the shaft. The frame carrying the rotor will be rigidly attached to the main machine structure by screws (to check for static balance). The rotor frame will also be suspended from the machine structure by a spring system (to check for dynamic balance).

3. PRE-LAB ASSIGNMENT To be completed prior to the lab session in groups.The mr value for each mass has been determined as listed in Table I.Table I

Block No.mr

1

2

3

4

(a) Select:

(i) any two blocks;

(ii) any angle between them;

(iii) two axial positions (length scale), use lengths between 0 to 170mm so that the blocks fit onto the actual laboratory shaft.

(b) Enter the appropriate values in Table II and Table III.Table II

Block No.mrSelected Calculated

1

2

3

4

(c) If the shaft is DYNAMICALLY balanced it will also be STATICALLY balanced. Because, in this particular experiment the mr values of the remaining two blocks are known we can find their required angular positions from a force polygon. Draw the Force Polygon on this sheet and list the calculated values in Table II and Table III.(d) Note: Any plane may be used as a reference plane for l, eg. Zero on the scale.Table III

Block No.mrlmrl

1

2

3

4

The remaining couples (mrl) in Table III can be found by constructing a couple polygon to scale and hence the remaining l values may be found.

NOTE: You must show your completed force and moment polygons and Table II and Table III prior to being given entrance into the laboratory session. In particular the length values must be realistic, that is, the masses must actually fit onto the shaft. The minimum distance between masses must be at least 10mm. Force Polygon

Moment Polygon

4. LABORATOTY WORK

The actual laboratory session will consist of the students, in groups, attaching the four masses to the rotor in the angular and linear positions given by their calculations as tabulated in Table II and III. The rotor will be checked for both static and dynamics balance. Marks will be given for the accuracy and completeness of the prelab work and the successful demonstration of static and dynamic balance of the shaft. Marks will be deducted if the shaft is not balanced on the first demonstration. Student Name:.. Student Number: Laboratory Date:

Dr. Howard, Senior Lecturer