Mechanical components of the rotary machines testing rigs are principally (a) Cast Iron Bed-Plate or Base Plate or Test Bench (b) Vibration Isolation or Dampening and (c) Concrete mass foundation underneath Bed-Plate or Base Plate.
(A) CAST IRON BEDPLATE OR BASE PLATE:
Cast Iron Bed-Plate or Base Plate is vital element in testing rigs for rotary machines. Hence, it is fundamental to select the right kind of Bed-Plate that is the foundation for quality of rotary machines. Gray cast iron is most preferred material of construction for Bed-Plate or Base Plates since they have excellent vibration dampening characteristics over other metals. Cast Iron Bed-Plate are designed such that their natural frequencies are very low.
Cast Iron Bed-Plate or base plates are available in different sizes, load carrying capacities and configurations. They can also be tailor manufactured to meet specific requirements. They can also be assembled together to create large surface areas as per the requirement. Such assembled Bed-Plates are leveled, aligned and interconnected with each other to obtain flat and plane surface area.
The basic features on Bed-Plate or Base Plate are selected based on their application as part of a testing rig. Following technical details are essentially to be provided by the User / Buyer that helps manufacturer / supplier to suggest the appropriate Bed-Plate
(1)Rotary machines are to be tested in horizontal position or in vertical position or both. E.g. foot mounted and / or flange mounted electric motors
(2)Power rating of testing machines. E.g. H.P. / kW / Torque etc.
(3)Normal operating speed range
(4)Critical speed range
(5)Maximum permissible vibration amplitudes on machines under tests
(6)Maximum anticipated total loads, both static and dynamic
(7)Testing equipment dimensions
(8)Testing equipment mounting arrangement
(9)Center of Gravity locations in the testing equipment in X, Y and Z directions
(10)Equipment foundation edge distance requirements
(11)General arrangement drawing showing plans and elevations for testing equipment
(12)Testing equipment foundation outline drawing, plans and elevations
Bed-Plates or base plates can be of two distinct features. They may be either anchored on to concrete mass foundation or they may be permanently grouted on to the concrete mass foundation or stable, non-flexural rigid concrete shop-floors having requisite load carrying capacity.
We recommend anchored type Bed-Plates since they can be removed for shifting to different locations when required or when re-leveling and re-conditioning is necessitated during their use over a period of time. Here we may say that Bed-Plate anchoring and leveling elements are important elements of any Bed-Plate or base plate for testing rigs. Permanently grouted Bed-Plate or base plates can not be removed from their foundation nor is re-leveling nor reconditioning possible. Permanently grouted Bed-Plate / Base Plates or test benches are economical then anchored type Bed-Plates or base plates.
(B) VIBRATION ISOLATION & DAMPENING:
For electrical machines having rigid rotors IS0–1940/1 recommends balance quality grade (vibration amplitudes) represented as “Gr” (e.g. G0.4, G1, G2.5, G6.3, G16, G40 etc.) where the letter “G” is used as notation for Grade and “r” is the number (in mm/sec) that represents product of eccentricity in mm and rotation speed “ω” in rad/sec.
The compatible vibration isolation elements could be interfaced between Bed-Plate and concrete foundation and / or between concrete foundation and soil around concrete foundation. The vibration isolation can be of two types viz; (a) passive vibration isolation or (b) active vibration isolation.