Filter Analysis Describes the History of Wear

Across-bar cooler is one of the main pieces of equipment in cement production. It is used for the transport and cooling of clinker, one of the ingredients of cement. Cement kilns operate with a cross-bar cooler which consists of four grates driven by a hydraulic station.

Any pump failures cause downtime and stop cement production. Therefore, it is important for the pump to operate smoothly on continuous basis.

Hydraulic Circuit

Pilot Pump
The pilot pump provides oil flow to the proportional valve which controls the position of the swash plate. It also controls the oil flow from the main pump (axial piston pump) at 22 liters per minute.

Boost Pump
The boost pump refills the main pump with the same amount of oil removed by the shuttle valve to cool the oil. Oil flow is 50 liters per minute.

Main Pump
The main pump consists of an axial piston pump with variable displacement and variable direction. It provides flow in two directions (174 to 214 liters per minute) and controls the movement of the grates.

Closed-loop Circuit
In a forward direction, the pump suction comes from Port B (low-pressure side). Oil flow from Port A (high-pressure side) flows forward across the grate. When the swash plate position is reversed, the pump suction from Port A (low-pressure side) changes the direction of oil flow. Oil flow from Port B (high-pressure side) moves across the grate in reverse direction.

What Happened
During a routine filter change, the technician noticed a large amount of metal wear debris in the bowl filter. An internal inspection revealed a problem in the boost pump. Because it was a pressure-line filter of the boost pump, the technician collected all metal from the bowl and analyzed it visually using an optical microscope. Wear particles larger than 100 microns were observed (Figure 1), and an emergency warning was issued to change the pump and filter immediately before the failure caused the machine to stop.

Figure 1. Surface striations caused by the severe abrasive wear mechanism before the particle was removed.

Results
The gear pump was replaced. To confirm that the defect actually existed, the pump was opened and visually inspected.

Close-up photos of the housing and gear of the defective pump show severe wear damage (Figure 2).

Figure 2. Gear Housing

Conclusion
Wear particles collected by the oil filter were inspected using a microscope. It was concluded that the filters contained wear particles which characterize the most significant mode of pump wear. The filters remove and store metallic particles generated from the rubbing surfaces. The size and morphology of wear particles collected in the oil filters are larger than those deposited by ferrography.

The history of wear and early failure of the sliding surfaces can be seen by following the striation marks caused by abrasion (Figure 1). The varying colors of wear particle surfaces reveal specific information about the temperature of the sliding surface from which the wear particles were removed.

About Portland Cement

Cement is made by heating limestone with small quantities of other materials (such as clay) to 1,450°C in a kiln. The resulting hard substance, called “clinker”, is then ground with a small amount of gypsum into a powder to make "ordinary Portland cement", the most common type of cement (often referred to as OPC).

Portland cement is a basic ingredient of concrete, mortar and most non-specialty grout. The most common use for Portland cement is in the production of concrete. Concrete is a composite material consisting of aggregate (gravel and sand), cement and water. As a construction material, concrete can be cast in almost any shape desired and, once hardened, can become a structural (load-bearing) element. Portland cement may be gray or white.

Reference
http://en.wikipedia.org/wiki/Cement

Clinker
According to Merriam-Webster, clinker is defined as: 1) a brick that has been burned too much in the kiln, or 2) stony matter fused together, slag.

Reference
www.merriam-webster.com/dictionary

About the Author

Ahmed Safwat Hassan is a preventive and predictive maintenance manager at CEMEX in Egypt. CEMEX is a building materials supplier, providing cement and concrete products to construction projects in various sectors: industrial, commercial, residential and municipal. For more information about CEMEX, visit www.cemex.com.