Chatter_Detect 101

30th Mar 2021

A simple guide to the Farrat Chatter_Detect system

 

What is Chatter_Detect?

Chatter_Detect is a stand-alone PC-based post-process roll surface inspection system, used for the detection of regular undulations that might grind into the surface of a finish-ground metal roll. These imperfections are caused by vibrations generated during the grinding process.

The hardware is contained in a Chatter_Detect enclosure which is normally mounted on the wheel head of the machine, as shown in Figure 1.

Figure 1 - Chatter_Detect installed on grinding machine
Figure 1 - Chatter_Detect installed on grinding machine

When is it used and why?

Vibration generated by the grinding process may cause undulations to grind into the surface of the metal roll. The degree of which depends on the type of vibration and its frequency relative to the speed of rotation of the roll.

The undulations can be parallel with the roll axis or can lie at an oblique angle to the roll axis.

If they are of sufficient depth, they may appear as “chatter marks”, as shown in Figure 2.

Figure 2 - Example of marked roll, due to chatter vibration
Figure 2 - Example of marked roll, due to chatter vibration

However, most often they are either difficult, or impossible to see by eye, but are significant enough to affect the rolling process. The Chatter_Detect system is designed to detect these invisible marks and to measure their pitch and depth.

How does it work?

The system uses a non-contacting displacement sensor to measure the topography of a finished roll circumference. The test results are displayed as shown in Figure 3 below.

There are two main windows:

Figure 3 – Display of test results
Figure 3 – Display of test results

The upper window shows a graphical plot of the roll surface to provide an exact visual representation of the topography of the roll circumference, “unpeeled” and laid out flat. The undulations in the surface are the chatter marks. This window shows whether the marks are continuous or localised – in the example above they can be seen to be continuous.

The lower window shows a histogram in which the circumference of the roll is split into equal sectors. The depth of any regular marks detected in each sector is represented by the height of the bars (coloured green or red depending on whether the detected marks exceed a user-settable threshold or not). The actual marking pitch is displayed numerically above each bar. The position of the marks around the circumference of the roll relative to the trigger point is also displayed.

What are the benefits?

The Chatter_Detect software is proving successful in helping several Aluminium producers ensure that all ground rolls sent to the mill are free from chatter marks, resulting in almost complete eradication of strip chatter and increased throughput.


 

Testimonials from Farrat Chatter_Detect users:

Andy Wilkes, TSM2 Mill Start Up & Roll Grinding Manager at Bridgnorth Aluminium, UK

“Since our acquisition of the Chatter_Detect system, we have not had a single issue of strip chatter, as the system ensures that all rolls sent to the mill are free from chatter. Because of the success of the system an additional system has recently been acquired by Bridgnorth Aluminium”.

 

Francis RINGLER, General Manager at Rhenaroll, France

”Chatter_Detect and AVAS Monitoring Systems are proving to be very useful on our grinding machine, helping our operators find the best grinding conditions that minimise vibrations and ensure chatter free rolls”.

 


Further development

Recently, at the request of several customers, a vibration monitoring module has been integrated within the Chatter_Detect software (using the same enclosure as above, but with additional hardware including 2 accelerometers and signal conditioning hardware).

This monitors the vibration of the machine during grinding and warns the operator when the levels of vibration exceed a threshold level, turning the green bar graph into red, as illustrated in Figure 4.

The operator normally reacts to this by changing his grinding conditions (feeds and speeds) in a way that the alarm level reduces and turns to green colour.

Several monitoring screens are available, for example on the spectrum screen (Figure 5) it is possible to link each frequency component with a marking pitch, by simply moving the cursor along the frequency axis. This helps in identifying which frequency component is responsible for chatter on the roll, which is invaluable information for the maintenance engineer.

This monitoring option is proving to be very useful for the operators, as explained in the testimonials above.

Most of the systems sold by Farrat in the last couple of years include this option.

Figure 4 – Display of vibration levels during grinding (showing 50 mins of data)
Figure 4 – Display of vibration levels during grinding (showing 50 mins of data)
Figure 5 – Vibration spectrum of Channel 2 showing the vibration and its predicted pitch
Figure 5 – Vibration spectrum of Channel 2 showing the vibration and its predicted pitch

Did you find this Farrat 101 Article useful?

For more information on Chatter_Detect and to explore how Farrat can support manufacturers and machine refurbishers with rapid on-site services, please visit our Vibration & Chatter Control of Machinery page.