Engineering led vibration & noise consultancy

Where the vibration problem involves self-excited chatter instability, or resonant magnification, we carry out modal analysis to identify the deflection modes associated with the offending resonance.

Modal analysis is an experimental technique that is used to identify the mode shape of a structure as it vibrates at resonance. It is an essential process if there is a requirement to understand the resonant behaviour of a structure so that steps can be taken to improve it.

Troubleshooting using Modal Analysis

When troubleshooting problems of vibration, our engineers frequently discover that while a troublesome vibration can be traced to a specific exciter such as a gear mesh or bearing “defect”, there is nothing abnormal about the condition of that exciter. The problem, in these situations, is often caused as a result of resonant amplification of the vibration in which, at certain operating speeds, the “normal” vibrations are magnified by the structural resonances to abnormal levels.

In these situations, simply replacing the gear or the bearing that is the source of the vibration will not provide a solution. Instead, it is essential that modal analysis be carried out in order to identify the mode shapes so that the areas that require stiffening or damping can be readily pinpointed.

On-site Practicalities
We have, over the years, carried out many hundred such modal analyses on structures ranging in size from as small as a boring bar to as large as an overhead gantry crane. We have at our disposal a range of shakers and hammers to excite the structure under test and can often complete the data collection over the course of just a few hours thus keeping down-time to a minimum.

The stiffness of manufacturing machines, especially metal cutting machine tools such as machining centres, lathes and grinding machines, is important because it governs the magnitude of the displacement, or push-off, of the tool as it deflects under the influence of the cutting forces, and this of course affects the accuracy of the finished component.

In order to achieve the required component accuracy, a second pass comprising a lighter finishing cut has to be performed and this has a knock-on effect on cycle time. The accuracy of components produced by metal forming machines such as presses, guillotines, nibblers etc. can be equally undermined by lack of stiffness of the structure of the machine. Surface finish problems such as chatter marks associated with chatter vibration during cutting can also sometimes be attributed to a lack of stiffness of the machine on which the operation is being carried out.

An important part of investigating these problems is the measurement of the load-v-deflection characteristics of the machine so that problems of poor stiffness can be readily identified.

Our engineers, in some applications, go a step further and make use of modal analysis software to produce exaggerated, slow-motion animations of the way in which the structure distorts under load. This enables rapid identification of the exact source of the unwanted flexibility.

Most people would not consider the idea of buying a house without first getting a survey of its condition carried out by an expert. Many machines cost far more than a house, so wouldn’t it make sense to do the same thing when investing in machinery?

Many companies have availed themselves of our machine performance fingerprinting service to provide a “survey” of the performance of a machine that they are considering purchasing, or to compare the performance of several contenders. Our fingerprinting service is especially useful if you are considering having a machine refurbished, upgraded or revamped. As an example, we have carried out before and after refurbishment fingerprints on most of the roll grinding machines installed in the roll shops of a large UK steel producer.

Before Refurbishment

Identifies sources of high vibrations from worn gears, damaged bearings, etc. and pinpoints regions of flexibility caused by slideway wear, for example.
Helps to identify nature of refurbishment work required, and to prioritise activities.

After Refurbishment

Helps guide and optimise the process of re-installation of the machine.
Helps fine-tune the performance of the refurbished machine.
Assesses the effectiveness of the refurbishment work carried out.
Provides a baseline fingerprint against which the performance of the machine can be compared in the future.

If you are considering buying new machinery or having an existing machine upgraded or refurbished contact us first to find out how we can help you minimise the risk associated with your investment by providing you with the maximum possible information upfront about the performance of the machine in question.

Pre and Final Acceptance Tests on new & re-furbished machines (PAT & FAT)

These are extremely useful set of measurement tests that we carry out for the buyer of a grinding machine, when the machine that he bought is still at the manufacturer’s plant (Pre Acceptance Tests). These are specific tests that will be carried out alongside the buyer’s own set of acceptance tests, which will focus on the identification of any abnormal vibrations, in particular those that could have the potential to affect product quality in the form of visible or invisible chatter marks on the surface of the finished roll.

We will use our own Chatter_Detect system to ensure that all rolls produced during the tests are chatter free. Any identified sources of vibrations along with our recommendations will be reported in a detailed report and will be brought to the attention of the manufacturer.

FAT tests are similar in nature and are carried out at the customer’s site. The emphasis on these is to ensure that the transit of the machine and its installation on the new location do not bring about any new potential vibration sources. Again Chatter_Detect will be used to ensure that the produced rolls are chatter free.

Chatter Detect is a post-process inspection system designed to help roll shop personnel to ensure that the surfaces of finish ground rolls are free of chatter marks before dispatching them to the mill.

When rolling steel and aluminium strip, especially those designed for applications that demand high quality surfaces such as automotive, can-stock and litho, it is imperative that rolls are free of grinder chatter or other regular banding marks. The same also applies to textured rolls.

The system is normally installed permanently on a particular machine or can be easily moved from machine to machine, as desired. It incorporates a highly sensitive, non-contact displacement transducer mounted to the wheelhead that is used to measure the topography of a roll surface on completion of grinding.

The system is capable of detecting regular marks with a depth as small as 0.05 µm, these being invisible to the naked eye.

Recently Chatter_Detect has also found application in the aerospace industry where it is used to good effect to check the surfaces of commercial aircraft landing gears sliders, where surface quality is of utmost importance.

One of our greatest strengths lies in the experience we have gained over many years in the analysis of the resonant behaviour of structures.

Detailed modal analyses have been carried out on literally hundreds of structures of all types. Structures we have tested range from as small as a contact lens turning machine to as large as a steel rolling mill. This invaluable experience puts us in a unique position to be able to offer informed guidance in structural design, particularly in the design of new machinery of all types.

We can offer help at most stages in the design process, as shown in the adjacent idealised design process flowchart, but most particularly at the design review and prototype measurement and test stages.

AVAS for Rolling Mills

We offer a range of computer based vibration monitoring systems to help producers of steel and aluminium strip to ensure that their products are free of chatter marks by controlling mill chatter and providing tools to trace the sources of abnormal mill vibrations

• AVAS Mill Module – “front-line”, rapid response system for the detection of strip-marking vibrations. Designed to be an early warning system mainly for the benefit of the mill operator, and other shift personnel, who need to make on-the-spot decisions and take immediate actions.
• AVAS Tracking and Trending Module – “back-room”, detailed analysis system designed to assist the technologist to identify and quantify the contributions of the major vibration sources, or exciters, to strip marking problems.
• AVAS Database Module – provides a central database in which all of the coil and roll vibration histories can be stored together along with the process parameters and which then provides enhanced data analysis facilities using custom queries.

AVAS for Roll Grinders

The AVAS Grinder Module is a rapid response computerised vibration monitoring system that helps Roll Shops to ensure that the rolls that they supply to the rolling mills are free of grinder chatter marks and other unwanted surface defects

A primary function of the system is to warn of the presence of chatter and other abnormal vibrations while grinding. It is particularly applicable to machines that are not always continuously manned as it records a vibration history for the roll and also computes a cumulative Roll Quality Index (RQI) which provides a simple indication of the likelihood of the presence of chatter marks in the surface of the roll. The status of the RQI alarm at the end of the grind helps the operator to judge whether he should pass the roll or whether more finishing passes are needed to get rid of any chatter marks.

AVAS for Levellers

Tension leveller equipment is notorious for its ability to spoil the surface appearance of steel and aluminium strip that has been successfully rolled through the mills with a high quality, unmarked surface. We can supply AVAS vibration monitoring system configured for application to tension levelling and flattening machinery and other post-rolling processing equipment to ensure that chatter and other unwanted vibrations occurring while levelling or flattening the strip are avoided and that the finished product is free of leveller chatter or other regular banding.

Sensors on the leveller roll bearing housings detect the presence of resonant vibrations and the system provides a tool for the operators to select the quietest speed at which to run the line. The system can also help in the diagnosis of the vibration source responsible for the marking problem, in particular whether the source is related to work, intermediate or back rolls.

We also offer a worldwide, rapid-response, on-site service for the troubleshooting strip chatter and other mill vibration problems.

We actively seek to take part in collaborative research both at UK and European levels.

Via their previous existence at AMTRI, our engineers benefit from a long association with a research and development environment and have been directly and indirectly involved in numerous research projects, including those funded by European programmes such as the Framework series and the earlier Brite and Esprit programmes. While at AMTRI, our engineers won funding via the DTI’s SMART programme to develop the post-process roll surface inspection system known as Chatter_Detect. Since its inception Chatter_Detect has now evolved to include in-process vibration monitoring during grinding helping operators find the best grinding conditions that minimise vibrations.

Recent Farrat industrial vibration control research projects include:

• KTP1 – in partnership with the University of Manchester and Innovate UK – 36-month R&D project exploring the detailed characterisation of Farrat’s isolation materials to drive improvements in manufacture and quality control and provide the ability to design new materials that are specifically designed for optimal performance in specific applications. Focus on supporting industrial applications but methods could be used for all applications.
• KTP2 – in partnership with Salford University and Innovate UK – 36-month R&D project exploring methods to predict behaviour and performance of isolated systems.
• IMPACT Project – 12-month R&D project to understand the performance of Farrat Industrial Vibration Control (IVC) solutions in-situ. Includes conducting a series of vibration measurement tests and analysis of key equipment installations using Farrat IVC solutions.
• AVM Performance Characterisation – 12-month R&D project testing and updating the performance of all Farrat Anti-Vibration Materials (AVM), covering load vs deflection, natural frequency and damping.
• HTZ Project – 12-month R&D project to analyse customer value-added processes in key industrial segments, with a view to drive product and service innovation.