Testing the idlers in the shop should imply that the bearings were replaces, cleaned & packed, etc. At this stage, a good procedure that is consistently done with discipline (no short cuts) should be enough. You shouldn't need to bench test the idler unless balancing is required.

In my opinion it is important to create a process for diagnostic purposes in- site. A stethoscope is a good first first check for conveyor systems were it is easy to reach the idlers.

For those systems not so practical to reach, thermography is a good method.

Antonio Reis

Vitrom Mfg Consultants

www.vitrom.com ■

In South Africa thermography was successfully applied at Richards Bay to analyse idler bearing failure on the move. A thermographic image was recorded onto video whilst driving alongside the conveyor 9throughputs of 11,000tph at 6,5m/s).

There has been some work done on the use of vibration analysis and a machine was developed (called the BAMBINO and developed and marketed in Australia) for on site use. I am not sure whether this system has been successfull.

In the workshop there is a South African company that analysis bearings removed from idler rollers and recertifies them as either fit for use or bad. (The bearings having been removed from the idler roll.)Their system utilises vibration analysis (Bearing Acceptance Testing - contact Farid Hafez at acsrod@icon.co.za).

Gabriel Lodewyks has also been involved in this field and his paper presented at BELTCON 12 may be of interest to you. ■

View this website for a good foundation on acoustic monitoring of bearings: http://www.sdt-canada.com/PDFs/avmlfp.pdf

The Channar 20 km overland (Australia 1989) was designed with idler bearing monitoring. The procedure was as follows:

1. puchase an off-the-shelf noise measurement system that was sensitive to bearing race emissions that could compare trends in changes to the noise state. Railroad bearing montoring, on-the-fly, had already been perfected.

2. develop a monitor that could record idler bearing noise and thermal gradients and perform a post measurement analysis from the field survey recordings

3. develop an acoustic parabolic lens to amplify the noise of each idler roller such that the lens could be mounted on the back of a pickup truck and record the conditions many feet from the target

4. develop a position monitor to track the location of each idler noise recording (pre GPS) such as a stringer postion indicator

5. tune the instruments to increase their vibration sensitivity to the specific bearings in use (series 6308)

This project was developed for Hamersley Iron 14 years ago. Its use was field tested shortly after commissioning. To my knowledge it never gained favor and was abandoned.

Lawrence Nordell

Conveyor Dynamics, Inc.

website: www.conveyor-dynamics.com ■

Exhausting the point:

From my previous posting, SDT North America measures acoustic waves that are generated from roller and race friction that are dependent on lubricant viscosity and fine metal paricle interferaces.

Also SKF has a contact vibration (accelerometer) MicroVibe instrument that can do a good job in the shop.

http://www.skfcm.com/

Lawrence Nordell ■