Quaternary Crushers Oil Tanks and Conveyor Idlers

Hennie Matthee Diagnostic Engineering Thermographer, Sishen, Kumba Iron Ore Ltd., South Africa

ABSTRACT

Infrared imaging is an excellent tool that is widely used for locating electrical problems. Too often we neglect the mechanical applications. Companies today are under tremendous pressure to reduce costs while maintaining production. As thermographers, we understand the value of IR systems for surveying electrical problems. However, we must realize it is also important to focus just as eagerly on mechanical systems. All plants literally contain thousands of low-speed bearings that are virtually impossible to inspect cost-effectively using vibration monitoring. Conveyor systems like idlers, however, are quite easy to inspect with thermography. Idlers that fail have a direct influence on production. The inspection technique is simply to compare similar bearings while the system is under load. IR is an effective tool in condition monitoring programs because this highly visual technology communicates information clearly and effectively. The source of thermal anomalies can be identified and repaired prior to equipment failure. This leads to a better predictive maintenance program and overall maintenance and operational savings costs. The benefits are significant. In potentially flammable environments, there may be a reduction in fire hazards. Certainly, there will be more focused and cost-effective maintenance. System-wide, there will probably be a reduction in the power required to drive the machine.

We as thermographers must remember that our surveys must include all factors of operation systems for us to be effective. This paper will demonstrate the need for this attention by using IR systems for Root Cause Failure Analysis to eliminate costly maintenance issues.

TEMPERATURE SENSOR COMPARISON

Routine inspection was done on crushers with the infrared camera. The main objective of this IR inspection was to determine the accuracy of the Pt 100 (a common platinum resistance thermometer) by comparing counter shaft and oil temperature readings with the LCD display and to report any anomalies.

Figure 1. Thermogram of PT 100 at oil tank. AR 01 : Max Figure 2. Thermogram of crusher counter shaft. Temperature 51.9 0C AR 01: Max Temperature 46.4 0C

Figures 1 and 2 illustrate a study comparing the readings from the PT100 sensors and infrared thermography. As you can see from the figures, the placement of the sensors is crucial in order to report the correct temperature; thermography can aid in locating the best area.

CASE STUDY - QUATERNARY CRUSHERS OIL TANKS

It is second nature to a thermographer to be curious, consequently looking at all possible effects of heat flow effects. For this reason I looked at the oil reservoirs. To my surprise the thermal image indicated temperature differences at the bottom of some of the oil reservoirs. The question this raised, as always, was: “What do the images tell us?” Thanks to the thermal patterns the root cause problem could be determined. By using IR the maintenance personnel improved the design of the reservoirs and the availability of the crushers and reduced maintenance costs by extending oil life.

Figure 3. Thermogram indicates residue at bottom on oil Figure 4. Thermogram indicates residue at bottom on oil reservoir F752-G3100. reservoir F756-G3200

Figure 5. Thermogram on test project of new oil filter Figure 6. Thermogram on test project F755on F752-G3200 system indicates no residue G3200 indicates residue at bottom of oil tank.

To clarify the abnormalities indicated by the thermogram, oil samples were taken from the bottom of the all the reservoirs were temperature differences were indicated in the infrared images. The lowest suction point of the reservoir is located 100mm from the bottom of the reservoir. To insure that bottom samplings were taken the following sampling method was used.

Filter Focus (a company specializing in protecting the integrity of oil by filtering oil to below 1 micron, removing water in solution down to 20 ppm, removing free sulphur and saving on current maintenance and repair costs) made use of a one-way valve mounted at the end of a 20 mm PVC electrical pipe to take bottom oil samples. (See figures 7 and 8).

Figures 7 and 8. Photos of one way valve plunger mounted on a PVC electrical pipe.

The pipe was immersed into the oil. When the PVC pipe was at the base of the reservoir the plunger of the valve opened the valve and the oil flowed to the inside of the pipe due to the oil level gravity. The pipe was removed from the reservoir and the oil was drained into the sampling bottle. The oil samples were dispatched to Sishen mine Oil Lab to be analyzed. The Oil reports of the reservoirs confirmed the build up at the bottom of the tanks. The build up indicated high Iron (Fe), Copper (Cu), Lead (Pb), Silica (Si) and Water (H2O)

The oil analysis results were as follows:

Unit Fe Cr H2O Si Pb PQ
755-3200 13321.0 3328.0 969.0 2103.0 16050.0 6784.00
756-3100 5882.0 1602.0 713.2 190.0 6150.0 4288.00
752-3200 258.0 442.0 1.0 6.0 268.0 120.00
756-3200 10459.0 1635.0 798.5 2095.0 5424.0 5749.00

Table 1. Oil analysis results

Figures 9 and 10. Photos: Oil sample of F755 – G3200.

The oil analysis report indicated that the oil was very contaminated and that the lab instruments filters were blocked in the analyzing process. What the IR image actually revealed was the residue and build up at the bottom of the tank. Positioning the suction point higher and not at the bottom of the tank would protect the oil pump from sucking in water and sludge. This sludge could not be effectively removed by the filtration system installed at the reservoir, as there was no drain point to drain all the oil from the tank. Thus, new oil would be contaminated when refilling. These findings were discussed with maintenance personnel to resolve the problem and to establish the best solution. The following solutions were recommended by Diagnostic engineering:

A. Clean the reservoir by hand.

Cleaning by hand can only be executed when major repair work is scheduled for a specific crusher. To do this the oil must be drained and the reservoir must be opened, flushed out, and cleaned by hand. This method will be effective, but very time consuming.

B. Make use of the filtration system.

The existing filtration system can be used. The oil in the reservoir can be stirred, so that the residue at the bottom of the tank can be forced to move. The oil will flow through the filtration system and the filters will then clean the oil to the filter specifications. This will take time and the cost of filters is expensive. Some of the contaminants might pass through the filter causing unnecessary wear.

C. Redesign the oil reservoir

Redesign the oil reservoir so that the sludge can be drained at any time. This design will also drain water from the tank. The design will still protect the pump and filters, and there will be no need to drain all the oil, reducing costs.

D. Install new filter system on all oil reservoirs.

Install the same filter system that is on 752-3200 on all the other reservoirs. The oil reports indicate that this new filter system is working. The IR images indicate that there are fewer residues at the bottom of the tank.

Maintenance personnel decided to redesign the oil reservoir and to install the new oil filter system on all the reservoirs.

CONCLUSION

With regular IR inspections on the oil reservoirs the IR image will indicate the residue at the bottom of the tank and maintenance personnel can be tasked to drain the sludge.

CASE STUDY – CONVEYOR IDLERS

Sishen Mine (Kumba Iron Ore) was asked to do an infrared inspection at SAPO (South African Port Operations) Saldanha since the problems experienced there have a direct impact on the mine. These conditions are unique in Saldanha. The temperature variations, regular rainfall, wind and seawater spray are the main factors contributing to a high rate of corrosion on equipment. The major defects currently experienced on the idlers are the collapse of bearing ends and corrosion. Two companies, due to their competitive price and their willingness to manufacture the rollers according to present specifications of Saldanha, supply the rollers in use. By using thermal inspections the best idler for these conditions could be determined.

Conveyor Belt specifications:

The main inspection was done on all the conveyor drives, substations, conveyor equipment, hydraulic systems and the tippler.

The first inspection indicated that there were major problems on the conveyor idlers. The problem SAPO was experiencing was the misalignment of the conveyor belts and the continuous replacement of idlers. The inspection was to determine the reason for the deterioration of the current rollers, recommendations on how to solve the problem and help with necessary modifications.

Garland rollers are a chain of belt conveyor rollers that replace the conventional steel idler frame and separate rollers. These chains feature loops or hooks at both ends, which are used for hanging them on flanges that run parallel to the conveyor. As garland rollers move freely, they minimize large items impact load on the rollers and the load on the belt is spread over a longer section.

The hotspots detected on the idler bearings were between 27 degree Celsius and 290 degree Celsius at normal load conditions. The amount of problems detected was more than 400 garlands consisting out of five idlers per garland. Most of the problems were detected on the blue idlers with yellow outer seals. It was clear that there was a problem with the idlers. The defects were reported to the Quality Manager at SAPO. The garlands were schedule to be changed at the next maintenance window.

Infrared images of the some of the problems

To monitor the newly installed idlers a follow up inspection was scheduled. On the next IR inspection, the hot spots were still high on the new installed idlers. The Examiners of SAPO informed us that the some of the new idlers failed between 2 - 13 days in operation. One of the idlers was inspected to determine the cause of failure. It was clear that the bearing failed. Probable causes of failure could be excessive belt tension, overloading, improper lubrication, under-designed idlers, misalignment of idler or structure, eccentric or outof-balance idler, or quality of the idler.

One of the new installed idlers

Idler installed on 02-05-2002 Removed on 15-05-2002. Tonnage 747107 tonnes

The controlled IR inspection indicated that the average working temperature of one idler supplier (B) under load was between 8 and 12 degree Celsius. The average working temperature of the other supplier (A) was between 27 and 170 degree Celsius.

48.1°C

133.9°C

AR02

120

40 100

AR01

80 30

60

40 20

20 11.6°C

5.5°C

Figure 23. Thermogram of idler Supplier A and. Supplier

B. Supplier A SP01: 63.0°C, SP02: 48.1°C Supplier B SP03: 16.8°C, SP04: 18.5°C, SP05: 19.8°C, SP06: 24.1°C

One idler per supplier was cut open to see from its design what could be the cause of the temperature differences.

Inside view of idler Bearing end cap

Figure 24. Photo of idler Supplier A. 6203 Bearings; Shaft 30mm

Seal arrangement

Seal

The main differences between the two suppliers were the outer seal, inner seal and the thickness of the bearing cap. Supplier A use a cheap outer seal with no inner seal, supplier B used a labyrinth outer seal and an inner dust seal. Supplier A used a no name brand bearing while supplier B used SKF bearings. The quality manager has addressed this problem and a modification was done on the bearings.

The bearing end caps of supplier A gave no support to the bearing under load conditions. This caused the end cap to deform under load and misalign the bearings. The result of misalignment was overheating and failure of the bearings.

Due to the variations in temperature, the air inside the idler heated up and cooled down, forming water inside the idler. This water entered the bearing causing the bearing to fail because there was no inner seal.

CONCLUSION

Thermography can be used to help choose the best idler and to detect design shortcomings. IR inspections on conveyor equipment helped SAPO Saldanha to determine the best idler supplier under their specific conditions and redesign conveyor equipment to increase production and reduce maintenance costs.

ACKNOWLEDGEMENTS

The author wishes to acknowledge the cooperation of Maintenance and Oil Lab personnel at Sishen Kumba Iron Ore Company for there assistance. We are also grateful for the support of Filter Focus South Africa personnel and H Rohloff (PTY) Ltd. Johannesburg South Africa who provided additional data and information for this paper.

ABOUT THE AUTHOR

Hennie has an ITC Level III Thermographer certification and has been using IR for 8 years. He was appointed at Sishen Mine on the 1 January 1986. He was trained as a Fitter and turner and qualified in August 1990. He achieved the following qualifications: National Higher Diploma N6 Mechanical and National Higher Diploma N6 Electrical at Kathu College. He has experience in the reconditioning of Hydraulic and Electrical equipment. He started at Diagnostic Engineering in 1994. He implemented and developed standards for Balancing at Sishen mine. He was part of the vibration section for 6 years where he was responsible for analyzing and reporting of all vibration readings. He started the Thermal Infrared program in 1999.