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
drive machine
- A
driven machine
- A
coupling device
- A
bedplate or base plate or base frame, and
- 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.
- Though
the supplier for all the three machines may be a single agency,
invariably manufacturer would be different for each machine.
- Each
machine according to its footprint has its own base frame and
bolting arrangement with the foundation.
- Each
machine is balanced independently as a separate unit.
- Each
machine rotor will have its own critical speed.
- 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.
- 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.
Bed-Plates for Rotary Machines Testing Rigs
Re: Bed-Plates for Rotary Machines Testing Rigs
