Schaeffler UK was part of the team that successfully completed the replacement of the main trunnion bearings on a BOS (Basic Oxygen Steelmaking) plant at Tata Steel Port Talbot.

By replacing the drive-side trunnion bearings with split rolling bearings, Schaeffler also helped to save the customer five extra days of work. If solid rather than split bearings had been used, the customer would have had to disassemble the bull gear unit (i.e. the main drive unit for the BOS plant vessel).

TATA Steel Port Talbot has two BOS Steel making vessels (V1 & V2) in operation. The original vessel was installed in the late 1960s by UK company Ashmore, Benson, Pease & Co and was subsequently upgraded in 1991/1992 by Mannesmann Demag, including trunnion bearing replacements. Each vessel has a steel making capacity of 330 tonnes. Loss of operation of a BOS vessel would result in significant lost revenue for Tata Steel.

Simon Life, BOS Plant Departmental Engineer at Tata Steel Port Talbot comments: “The bearing replacement work was very successful. The bearings were fitted to a high standard with expertise provided by Schaeffler throughout the installation process. During the bearing changeover, we encountered several problems with components being damaged and jacking issues. However, all problems were discussed with Tata, Schaeffler engineers and Central Engineering support, and between all parties, solutions were generated, action lists compiled and remedies implemented. Without Schaeffler’s expertise, the bearing change would not have run so smoothly.”

In July 2011, Schaeffler UK received a telephone call from an area works engineer at the BOS Plant, advising of a sudden bearing failure on the non-drive side (NDS) of the V2 BOS plant vessel.

The BOS Plant engineers arranged a meeting and a request was made for two engineers from Schaeffler Germany to be on site at Port Talbot soon afterwards. A meeting subsequently took place at Port Talbot to discuss action plans and how to replace the trunnion bearings.

As Dave Wall, Senior Applications Engineer at Schaeffler UK recalls: “A method statement document was drawn up by Schaeffler UK, which specified the sequence and method to replace the bearings and outline the TATA requirements. Included in this document was a detailed tooling list and a step-by-step procedure for the dismounting and mounting of the drive-side (DS) & non drive-side (NDS) bearings.”

“The standard ‘solid’ bearing on the DS was replaced by a special FAG split spherical roller bearing [SSRB], which is the recommended replacement spare, as this reduces the amount of downtime when installing the replacement bearing. The NDS bearing was to be replaced with a similar solid bearing. In addition, various surrounding components also required replacing, once the secondary damage caused by the bearing failure had been identified,” confirmed Wall.

Removal of the Drive Side bearing 

The cutting away of the existing bearing took a total of 36 hours. The distance between the trunnion spacers (bearing seating width) was measured in order to determine the thickness required for two special, TATA designed, split ‘dovetail’ spacers. These were required to ensure that the new split bearing would be correctly secured in place.

The new split SRB inner ring halves with clamping rings, outer ring half and bottom roller cage halves, were fitted without any problems.

Removal of the Non-Drive Side bearing 

The original bearing on the NDS had failed during operation, which had caused the BOS converter to drop down. It was now resting on the bearing housing and the housing covers.

After lifting, parts of the damaged bearings were removed, including cage pieces; outer and inner ring fragments and rolling elements. All the components were sent for forensic examination to TATA Central Engineering Metallurgy & Inspection Dept. The housing back cover, bearing pressure plate and sleeve spacer were found to be seriously damaged. New ones had to be urgently manufactured by Tata Steel’s Central Engineering Shops (CES). The bearing inner ring had disintegrated and the sleeve had to be cut off due to its deformed shape. After removing the damaged bearing, it was also discovered that the trunnion back spacer was in need of repair. Again, machining work was urgently carried out by CES.

Due to the subsequent damage to the bearing housing, Schaeffler expertise was required to manually repair this surface to restore it back to an acceptable condition.

During the dismounting process the NDS Ladder Expansion Bearing Rollers had to be replaced. To facilitate the Ladder Roller replacement and installation of a TATA manufactured solid inner bearing housing cover, the bottom half of the housing had to be moved away from the journal using specially manufactured crossbeams.

Mounting of the new Non-Drive Side bearing 

The new bearing was first pre-mounted to determine the correct sleeve spacer width. The bottom half of the housing was then moved back into position and the crossbeam construction removed.

Mounting of the new bearing was challenging, as the collapse of the original bearing had caused the vessel to move out of alignment.

The lowering of the converter was also a challenge as the vessel had to be moved sideways by 40mm to achieve the correct installation position. Side shifting was initially a problem for the vessel lifting contractor but the problem was successfully overcome.

Final mounting steps for the NDS and DS bearings 

For the DS bearing, the remaining roller cage and outer ring halves were installed. For both bearings, the housing caps were fitted and each bearing was 100 per cent filled with grease, including the surrounding free space.

The housing covers were bolted in position and new seals with their tensioning devices were fitted. After having successfully completed the work in under 2 weeks, Schaeffler engineers were pleased to be leaving behind a very happy customer.

After the bearings were installed, the work didn’t finish there. Schaeffler UK prepared a recommended practical maintenance schedule list and forwarded this to the BOS Engineers, which was well received. In addition, customer “as built” cross-sectional drawings were updated to show the actual parts (with measurements) now in place at V2. Schaeffler UK participated and contributed to the Bearing Failure Review meetings with Tata Steel that followed the bearing replacement for the BOS vessels.

“Since replacing the trunnion bearings, engineers from Schaeffler UK have also supervised two further BOS vessel bearing changes in a very short timeframe of just two months: Converter C at SSI UK / Teesside and Converter 1 at Tata Steel Port Talbot. Schaeffler has now been selected as the preferred supplier of main trunnion bearings for the two BOS plant vessels at Tata Steel Port Talbot,” confirms Dave Wall.

Schaeffler (UK) Ltd,                         

Forge Lane                                                              

Sutton Coldfield                                                        

West Midlands B76 1AP                                          

Tel:   0121 313 5870  Fax:  0121 351 7686
e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.This email address is being protected from spambots. You need JavaScript enabled to view it.       
www.schaeffler.co.uk

By Paul Uher and Ernesto Wiedenbrug, Ph.D.
Everybody who is responsible for maintenance of VFDdriven application knows the feeling… The application was running well, and now it acts up and trips sometimes, and the drive’s trip message isn’t much help. Now what?

This paper discusses such a case, and how being able to see the dynamic interaction of voltage level and frequency changes led to the solution.

Situation:

Paul Uher from SKF Industrial Market in Sweden was called into a major bearing manufacturing plant to offer service for a VFD-driven application that was causing problems.

The drive is a 400V 30hp manufactured by Danfoss, and the load is an eccentric press which creates the rollingelements for bearings. Paul’s customer had explained that the application worked well for about two hours and then it started slowing down, finally coming to a stop, even though no changes were being made on the load-side.

Torque and Speed vs. Time

Frequency and Voltage vs. Time

Figure 1: Torque, speed, frequency and voltage level vs. time during healthy operation.

Action:

This description clarified that the problem had to be in one of two spots: Eitherthere was something wrong with theexternal control signals/programming tothe drive, or the issue was internal, in thedrive control itself. In order to answerthe question as to which of thesealternatives was causing the slow-down,it was necessary to get “eyes” onto whatwas happening. Obtaining a clear pictureof dynamic VFD application problems likethese is only possible by seeing howfrequency variations, voltage levels,torque requirements and motor speedinteract with one another. This is what
the software component VFD4000 delivers for the SKF Dynamic Motor Analyzer - EXP 4000. Fig. 1 shows these four traces for 40s of healthy operation, where fifteen 2s cycles of the eccentric press are followed by a short no-load period.

The application started to slow down after roughly two hours of successful operation. The difference in the healthy signature of Fig 1 is apparent in the frequency and voltage vs. time plot in Fig 2. The traces show that the voltage ramps down towards the end of each stroke of the eccentric press, while the drive tries to maintain a constant frequency until it shuts down for a very brief instance.

Figure 2: Frequency and voltage vs. time during faulty operation.

Volts per Hz:

One control technique internal to VFDs is called “Volts per Hertz” [1]. It means that voltage level gets changed in proportion to the frequency changes for frequencies below nameplate, as shown in Fig 3. In other words, if the motor runs at half nameplate frequency, it should be supplied by half nameplate voltage. A Volts per Hertz control typically doesn’t raise the voltage level above nameplate for frequencies higher than the nameplate frequency of the motor. This type of control has the ability of delivering full torque for the low speed range, and full nameplate power for the speeds above nameplate – at the expense of dropping torque capabilities in the high-speed region.

Even if a drive had a different control strategy than V over f, this rule of thumb will still apply for applications that have relatively small frequency changes as is the case being analyzed here. The voltage and frequency vs. time traces of Fig 2 show that there are times where the expected normal behavior of the drive falls apart: voltage level ramps down while the drive attempts to maintain constant frequency output. This answers the question – the problem is originating internally in the VFD.

Figure 3: Voltage level and torque vs. speed for V/f control.

Correction:

Since now it was clear that the problem somehow originated internally in the drive, and wasn’t caused by the external control signals, the next step was to approach Danfoss application support and ask for help. The VFD manufacturer’s application engineer was able to diagnose the issue by looking at the voltage, torque, speed and frequency plots vs. time of healthy operation and during the slow-down. The problem was that the eccentric press required a very high peak torque to manufacture this particular batch of rolling elements. Over time the motor started heating up, causing the stator resistance to rise – ultimately starving the magnetic flux and the torque-generation capability.

The solution was described in an application note that was emailed by the Danfoss application engineer, explaining which two drive settings needed to be set differently to shift the drive from the default high-efficiency settings towards peak torque settings that this application required [2].

Results and Conclusion:

Changing the two parameters in the VFD setup as suggested by the Danfoss application engineer solved the issue upon first try. The eccentric press has been working reliably ever since.
This case study shows how VFD applications can introduce unique complexities never offered by line-operated motor applications. The voltage level and frequency vs. time traces were key to diagnose the root cause problem being in the drive control. That data, together with the torque vs. time plots were the information that allowed the Danfoss application engineer to diagnose the issue, and realize the simple solution. The “VFD Details” plots of the VFD4000 gave eyes to the maintenance engineer, allowed him to isolate the problem, and gave eyes to the VFD application support to solve the issue.

References:
[1] “Application Guide for AC Adjustable Speed Drive Systems.pdf”, pg. 14, NEMA 2007.
[2] “Instruction Manual – VLT 5000”, Danfoss.

For further information, please visit http://www.whitelegg.com

Lifecycle Cost Analysis: The Key to Asset Sustainability
Non-profit Uses Bigfoot CMMS to Improve Facility Service, Reduce True Total Costs

Reduce, reuse and recycle are the three watch words of environmental sustainability for saving money, energy and natural resources. But what can facility managers do to ensure asset sustainability, which encompasses the cost-efficiency of buying, operating and servicing maintenance and repairs?
In other words, how do you determine which products to purchase, when they should be replaced and how to efficiently service them to maximize your return on investment?

HIGH SPEED, LOW VOLTAGE INSPECTION AT LONDON STANSTED

London Stansted Airport is open for business 24/7 and the reliable and continuous operation of its passenger terminal has to be assured for much more than just day-to-day working.  As London's third busiest airport it also needs to be at the ready for every eventuality, whether the cause is bad weather or a security alert.   Historically, this put the maintenance teams, responsible for the reliability of all low voltage equipment, under huge time pressure.  

At best, engineers had four hours per night in which to conduct predictive maintenance inspections.  By the time they had made the system safe, this window of opportunity reduced even more.  This meant the entire inspection cycle was significantly protracted and no system could be checked under load.  

With the installation of IRISS CAP Series infrared inspection windows, the savings in terms of inspection time and associated costs have been massive. Payback was instant.  But the benefits extend way beyond that.

An initial thermal survey of the fully energised low voltage systems that serve the main terminal block took only five hours, showing just two minor cable faults.  For the first time the airport had a benchmark for trending future performance and the complete assurance that everything is working optimally.

“Quite simply, this was not possible before we installed IRISS CAP Series infrared inspection windows,” confirmed Engineering Compliance Manager, David Potter. “We were able to check individual circuits when they were switched off but busbars continued to be a particular concern.  They contain a huge amount of copper that absorbs a lot of heat over time before they go into fault status.  You can’t see this if the system isn’t live.”

Mission impossible
London Stansted Airport has permission to handle 35 million passengers per year.  Its throughput peaked at 23 million in 2007 but currently around 17.5 million people pass through the terminal building each year.  Night operations largely involve Ryanair and easyJet aircraft returning to the base and also cargo flights.  And although the early hours of the morning provide a relatively quiet period for planned maintenance, passenger processing normally starts around 3.30am by which time all electrical systems must be running.  

David Potter, an engineer with 24 years experience at London Stansted Airport, is responsible for strategic planning and maintenance of electrical distribution on site, both high and low voltage.  But whilst parts of the high voltage network can selectively shutdown without compromising the operation, the low voltage equipment does not have similar capacity.  

“Our high voltage network is owned and managed by UKPNS but maintenance of low voltage equipment is down to our own engineering teams,” he confirmed. “We agree the maintenance schedule with the Airline Operators Committee three months in advance and our Maximo planning system flags up what needs to be inspected each night but in every case it’s a race against time.  Nevertheless, this work is vital.”

Understandably the electrical infrastructure at London Stansted Airport is huge.  Power is brought onto the site at 33kV and transformed down to 11V.  The low voltage network feeds all manner of systems in the main terminal building, typically IT and baggage handling.  So any unexpected interruption in the power supply could have serious consequences.  

The potential cost of failure is also huge.  Service Quality Rebate scheme (SQR) is a system whereby the airport has to pay compensation to its customers, the airlines and handling agents, if it fails to meet an agreed level of expectation.  

Although efficient maintenance had so far prevented serious low voltage system failures, David Potter wanted greater assurance.  He had considered the introduction of infrared windows to complement outsourced thermal imaging surveys and to allow live inspection, but all available products on the market were deemed unsuitable.  

He explained: “A small crystal window may have been fine for small switchgear but the size of our equipment meant that we would end up with so many windows, our substation would look like a submarine. Even if it had been viable from a practical standpoint, the cost would be huge.  And crucially an individual window would be too small to allow the all important inspection of an entire busbar.”

Polymer breakthrough
The ‘Eureka’ moment came when David Potter saw a feature in a trade press magazine on IRISS Custom Application Product (CAP) Series infrared windows made from transmissive polymer.  This fully impact resistant material allows the window to be any size which is perfect for applications involving large switchgear.  

Initially IRISS considered the project in two phases but the surprisingly low cost allowed substations serving the terminal block to be fitted with windows in one fell swoop.  The potential savings in inspection time and the ability to inspect live systems, including the busbars, easily justified the investment.   

“It’s rare to see something completely new that works well and I couldn’t believe this was available from a company in Essex.  The windows are really high quality, very well constructed,” David Potter continued. “I was also impressed by IRISS as a company and I would certainly recommend it to others. Nothing was too much trouble and its engineers were very professional. The specification was approved on 6th November 2012, a comprehensive installation plan was then drawn up by IRISS and the entire job completed by Christmas.”

The IRISS team worked flexibly to complete the job within the time constraints imposed by 24 hour operation.  Having installed an isolation sheet on each cabinet, the thick door panel was removed to the access road where the required hole was cut with a jigsaw and the appropriate IRISS CAP Series window fitted.  
Easy busbar inspection
This work continued until a total of 72 windows had been installed, comprising a combination 6”, 12” and 24” products all available in the standard range.  The largest window is of course ideal for the thermal inspection of busbars and multiple components.

In reality the CAP product can be fully customised to suit the application and benefits to users are manifold.   A window no longer needs to be round, nor is its size restricted; a crystal window by comparison becomes too fragile beyond a 4” diameter. IRISS technology reduces the number of windows required, their installation time and associated costs.

Following the installation of the IRISS CAP Series windows at London Stansted Airport, the impact on inspection time was immediate. IRISS undertook the first thermal imaging survey with the benefit of its infrared windows on 8th January this year.  And it is testimony to the skill of the London Stansted Airport maintenance team that only two minor faults were discovered.  Given the scale of the operation this is a considerable achievement.

“It took just five hours to complete the job in daylight hours.  That also included walking from one substation to the next and coffee breaks!” David Potter confirmed. “Previously it would take us two nights to inspect just one panel.  Now there’s no need for isolations or back feed and our engineers’ safety is completely assured.  A single thermographer with a thermal imaging camera and without PPE can do everything.”

First ever benchmark
The resultant thermal inspection report from IRISS provided a comprehensive snap shot of the health of the entire low voltage network at London Stansted Airport.

David Potter added: “I now have the thermal performance of each system printed out in this report and, for the first time, a benchmark on which to base future thermal inspections.  Previously, it would have taken us a couple of years to inspect the whole complete network and even then we had no idea what was happening under load.”

“All we could say is that everything had been thoroughly inspected.  Now we can see the live circuits and cables and the temperature rise on busbars,” he continued.  “This means we are able to apply trends to every system.  In short, I now know the terminal is truly safe and that’s a big tick against my list.  I’m really sold on this technology.”

visit www.iriss.com

Background
With an annual beer production of 139.2 million hectolitres, Heineken is the third largest brewer in the world.

In the UK Heineken operates four sites; Hereford, Manchester, Tadcaster and Ledbury. Key brands include Fosters, John Smiths, Bulmers, Strongbow, Newcastle Brown, Heineken and Kronenbourg 1664, some of the most iconic drink brands in the marketplace!

As part of a total productive maintenance (TPM) project, Mick Scrimshaw, Heineken UK's training consultant, invited a number of providers to discuss how they could carry out a training needs analysis for 40 technicians. This was to identify where the skills gaps were and also assess competence in key areas; MCP Consulting and Training was selected as the chosen partner.