It is found that in majority of the cases Machines Testing technicians are seldom part of design or selection process for the testing rig as a whole or test rig elements, though he may be using the system. He is a person who is responsible for testing of rotary machines and many a times he encounters testing problems and yet he is to arrive at conclusive results. As much as feasible, it is important that he is part of design / selection of the testing rig system as whole. If not, at least he must be aware of the functions of each testing rig element to correctly analyze the problems he may encounter during testing.
In the context of testing rig design for rotary machines the system would necessarily include;
(a)A drive machine
(b)A driven machine
(c)A coupling device
(d)A bedplate or base plate or base frame, and
(e)A concrete mass foundation and isolation thereof
For designing of test rig and foundation thereof machine data / details for all the five above are necessary. The complete knowledge of excitation forces, associated frequencies and load transfer mechanism from the machine to the foundation is a must for correct evaluation of dynamic response. A close interaction between the bedplate suppliers, foundation designers and rotary machine supplier as well as appreciation of each other’s limitations, therefore, is essential.
To understand the testing rig system as whole it is desirable to note and understand the following.
1.Though the supplier for all the three machines may be a single agency, invariably manufacturer would be different for each machine.
2.Each machine according to its footprint has its own base frame and bolting arrangement with the foundation.
3.Each machine is balanced independently as a separate unit.
4.Each machine rotor will have its own critical speed.
5.When these machines are coupled together and supplied or installed as a set, the data for individual machine may not fully hold good for the coupled machines. It may need appropriate correction / modification. At times, these machines may be mounted on a common base frame instead of their individual base frame and that will reflect as a change in the mass and Center of Gravity location.
6.The equipment or system drawings and data sheets supplied by the machine manufacturer do provide a host of information about the machine and out of these, only the information required for the bed-plate and foundation design needs to be selected. In certain cases, some data may have to be processed for design purposes. Thus for a properly selected bedplate, designed foundation, careful determination of those design machine parameters that influence the response of test rig system as whole becomes essential.
The available machine data, therefore, needs to be suitably converted and translated in to design machine parameters for use in selection of bedplate and machine foundation design.
It is general practice in the industry to pay more attention only to those machines that do not perform well. More often than not, for every malfunction one keeps on trying modifications in the rotary machine like better balancing, replacing bearings etc. till satisfactory results are achieved. It is worth noting that when malfunction occurs the cause may not be the machine alone but it could be the base plate or foundation too. In certain cases the desired results could be achieved by correcting the source, which may be other than the rotary machine.