Rotating Machinery Baseplate Grouting

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Why is Machine Baseplate Grouting So Important?

Grouting underneath a machine baseplate is a long established engineering practice to assure machine mounting points are level and that machine loads are properly transferred and distributed down through the baseplate to the concrete foundations. Wayne Bissett from OneSteel recently made a comment that he now often sees machine baseplates bolted down to concrete with no grouting being applied. The people managing these installations are often not aware of the full consequences of poor setup of machine baseplates.

The most widely used application for baseplate grouting is for building column bases, where grouting is strongly specified in standards and is considered best practice. Grouting of column baseplates is all about achieving load transfer under high loading situations such as in extreme wind conditions. Rotating equipment baseplate to foundation connections are an even more arduous application. As well as the need to handle high loading conditions they also need to withstand the effects of machine vibrations. All rotating machines vibrate to varying degrees. Without adequate grouting the vibration forces will start to wears the concrete where it contacts the baseplate causing looseness and increased vibration.

Many years ago a condition monitoring engineer that I regularly talked to complained about a large screw compressor that had vibration problems in the machine support baseplate. As I had solved a few machine base looseness problems I went to check it out myself. The one thing that stood out to me at the time was the compressor support framework had been just bolted down to the concrete floor without any grouting. As the problem of machine and baseplate ‘soft foot’ was not widely understood in those days (1980’s), all my standard rules for tracking down looseness and support problems did not work for this machine. At the time I could not understand what was causing the higher vibrations. All the machines I dealt with in the power station where I worked were properly grouted with well designed baseplates.

Soft foot is most commonly seen in equipment like electric motors that have four individual feet. Shimming under the four feet has to be determined very accurately to ensure the motor frame is not twisted. Twisting of a motor frame causes the motor bearings to be misaligned causing bearing loading and also additional tension in the motor frame encourages resonance vibrations (like tensioning a guitar string). These effects can cause significantly increased machine vibrations and reduced machine life. Machine baseplates are usually specifically designed to be grouted and if not carried out, can easily cause increased resonant vibrations. It is easy to see why the application of baseplate grouting would significantly increase support stiffness, reduces stress points and discourage vibrations.

Rotating equipment baseplate and foundations good practice requires:

• High mass and high rigidity foundations and baseplates designed for long life
• The foundation isolated from other vibrating structures
• Machine feet support surfaces on baseplate machined flat (Weld attached rolled plate not acceptable)
• All machine feet support surfaces set level to within 0.05mm/300mm length (Set by jacking screws or shims at all of the baseplate to foundation Anchor Bolt locations before grouting)
• Grout to be a moisture-free material and resistant to cracking and moisture entry
• Grouting to be void free and achieve adhesive attachment between the baseplate and concrete foundation
• Source (Noyes – OneSteel 2010)

Poor installation practices can easily produce the triple whammy of misalignment vibrations, soft foot vibrations and all amplified by an inadequately supported baseplate. So if you have new machines being installed at your plant, please ensure baseplate grouting is a part of the installation specification. Also if you have machines that are vibrating, it is always important not to ignore how well they are being supported.

Article by Peter Todd Industrial Maintenance Roundtable NSW Facilitator

Technical support for article provided by Rick Noyes - Maintenance Standards Engineer - OneSteel