Degauss Services

The MPS Gaussbusters

On-Call Demagnetizing Services - Worldwide Coverage

WHAT IS DEGAUSSING? Since magnetism is invisible, some say that degaussing (the removal of residual magnetism) is black magic. Others refer to it as an art. Regardless of how you describe it, degaussing or demagnetizing needs to be done systematically and thoroughly in order for it to be effective in preventing damaging shaft currents.

WHAT SIGNS SHOULD YOU RECOGNIZE? The most common signs of shaft current damage (sometimes referred to as electromagnetic discharge) are frosting, pitting or spark tracks on bearings, collars, journals and even shafts. This type of damage is often passed off as mechanical wear, and the typical solution is to incur the cost and replace the damaged parts. If these parts are instead repaired and sent for machining, more residual magnetism may be introduced, causing more severe damage visible only at the next shutdown. In some machines with shaft current problems, the loss of material can be so severe that there is radial or axial movement of the shaft. Proximity probes may register high peaks caused by the presence of high magnetic fields, which can be incorrectly identified as electrical runout or as vibration harmonics. One machine vendor, after trying typical solutions, such as replacing oil, balancing, adding probes with monitoring, finally described the machine as having "mysterious mechanical damage." During MPS's 15 years of investigating shaft currents, no two machines have shown identical symptoms and signs. If a machine has continued problems of varying nature, shaft currents may be a factor. Shaft currents should only be ruled out after a thorough magnetic survey, and shaft voltage and current analysis have been completed.

WHEN SHOULD YOU SURVEY MAGNETICALLY AND DEGAUSS? When necessary,and especially at scheduled or forced shutdowns, check for residual magnetism with a reliable instrument like the MPS Gaussometer. On average, most machines need to be surveyed and degaussed every 2 to 3 years. It is most effective when a machine is disassembled and piece parts are accessible. Always take precautions to prevent the build up of magnetism. For example, avoid welding directly onto a machine or any parts, as demagnetizing is needed afterwards. Parts subjected to magnetic particle inspection will have been highly magnetized and should be degaussed before installation. Require that all subcontractors degauss by adding this to all specifications and contracts. Generally, magnetic field levels which are 2 gauss or below will suffice for most rotating machinery parts and applications. Corners, edges and other uniquely shaped parts may display slightly higher residual magnetism values, so specifying a gauss level somewhat higher is acceptable for these areas.

WHY USE MPS INSTEAD OF A SERVICE OR REPAIR SHOP? If degaussing is done incorrectly, more problems can be generated than are solved. Traditional demagnetizing methods using surface AC demagnetizers or yokes will only affect a small area or surface spot, but underneath more magnetism may be left behind than was removed. This is often the case, and is not realized until after a machine is put back into operation and magnetic fields start to interact. That's when magnetic fields strengthen and currents can be generated. Often, subsequent damage won't be seen until the next machine shutdown. Therefore, if the removal of residual magnetism is skipped, or improperly done, the likeliness of problems will increase. We call ourselves 'experts' because MPS engineers specialize in shaft currents and focus on thorough and lasting, not temporary, solutions.

WHAT WILL THE MPS GAUSSBUSTERS DO ON SITE? MPS engineers will first conduct a magnetic survey. This entails measuring for gauss on the target machine with the MPS Gaussometer and charting the results. In doing this, MPS engineers are able to identify the strength, locations and polarity patterns of the magnetic fields. Areas that have the highest unacceptable levels of residual magnetism will be focused on first. The cable, capable of up to 15,000 ampere turns, is wrapped around the target area. If the part is small or thin, demagnetizing may first be done using the MPS Auto Degauss AC mode to remove the surface magnetism. Then, to reach the magnetism found in parts ½ inch or thicker, the MPS Auto Degauss's automatic full wave DC "downcycling" mode is selected. The polarity of the magnetism is checked and aligned to provide the proper starting polarity in the automatic DC "downcycling" mode. When the start button is pressed, the Auto Degauss downcycles through 15 steps, changing polarity and adjusting each power setting to a calculated percentage of the prior setting. This will slowly reduce magnetism that was in the part by predictably and repeatedly reducing the overall magnetic field with each step. Areas with exceptionally high or stubborn levels of residual magnetism may require repositioning of the cables, possibly with an opposite starting polarity, or different magnetizing field strength. This is the step that has been humorously referred to as magic or as art, but this is when the MPS GaussBuster's experience is most beneficial and visible. If an incorrect setting is made, an inexperienced operator may inject more ill-positioned magnetism than was removed, resulting in more problems than at the onset. Once all gauss levels are within acceptable ranges, MPS engineers consult with the customer to recommend ways to control and reduce the residual magnetism. Recommendations will be made, if needed, for the installation of shaft riding brushes and shaft current condition monitoring products, such as the MPS VCM-C or VCM-E. All MPS degauss consulting work is normally followed up with a thorough report that details all findings and recommendations.

WANT TO LEARN MORE? Ask MPS for the List of Articles on the subject of shaft currents and residual magnetism, or Contact MPS and ask for an available engineer to answer your questions. List of Articles on the subject of shaft currents and residual magnetism, or Contact MPS and ask for an available engineer to answer your questions.