Morgan Advanced Materials (www.morganadvancedmaterials.com) is a global leader in the production of engineered advanced materials, including ceramics, special brazing alloys, composites and carbon. Key markets for the company’s products include petrochemical, electronics, energy, health-care, industrial, transport and defence.

Morgan’s facility in Coudersport, Pennsylvania, makes carbon-based materials as well asa variety of silicon carbide parts, many in high volumes. Products include mechanical seal faces, as well as axial bearings and radial bearings with diameters ranging from less than 0.9mm to over 500mm.

Components used for mechanical seals require extreme precision in terms of flatness, parallelism and finish. A seal failure in a high-pressure or corrosive application can lead to costly repairs or have substantial environmental or health-and-safety consequences. The focus on continuous improvement in seal face quality at Morgan has led to a 30-year relationship with Engis Corporation (www.engis.com), which has a UK subsidiary in Henley-on-Thames and supplies Morgan with high-precision lapping equipment, application technology and consumables.

Tom Grossman, Morgan’s manufacturing engineering manager, says: “Seals require precision lapping due not only to their material properties but also to their form, fit and function.”

Mike Pisauro, Engis applications manager, says: “When lapping ceramic seals, selection of the lapping plate is critical. It is very important that the appropriate lap plate material be selected for the material being lapped, so that the diamond charging into the plate performs effectively. Engis provides composite plates in copper, iron, tin and ceramic, so that the optimum type can be chosen to suit the material to be lapped.”

Plate selection

An important consideration when selecting plate type is whether or not metals can be tolerated by the parts being lapped, as copper- or iron-based composite plates are typically the workhorses for many lapping processes. “In some cases, customers are concerned about staining or metallic contamination when lapping ceramics,” says Mr Pisauro. “We often recommend the Hyprez HY ceramic lapping plate. Grooving the lapping plate further increases the cut rate of the diamond slurry and creates a channel for the evacuation of abraded material.

“Selecting the right diamond slurry depends on the material removal requirements and the final surface finish of the parts. It is important to consider not only the size of the diamond but also properties such as friability and aspect ratio, as well as uniformity and consistency of the particle size and its distribution within the slurry. With decades of application experience, Engis engineers can select the appropriate slurry and tailor its properties to suit specific needs.”

Engis says that when it comes to developing the lapping process, plate preparation is a key consideration; and when lapping ceramics, it is important to keep the plate slightly damp but not flood it with lubricant, as this can result in the parts ‘hydroplaning’. “The plate conditioning process must also be chosen carefully,” says Mr Pisauro.

“When using ceramic-based lapping plates, they should be conditioned dry, so they produce a powder during the process. Conditioning a wet ceramic lap plate can produce a ‘muddy’ swarf that is difficult to clean and will eventually load the diamond conditioning ring and prevent it from cutting.”

For Morgan, the quality and fit of its ceramic seals is critical. As a general rule, Mr Pisauro recommends slowing the lap plate’s rotational speed toward the end of the process in order to improve the flatness of the seals. Multi-stage processes like this can best be accomplished with machines that offer programmable ‘process recipes’ — such as Engis’s FastLap series of lapping machines.

Joe Boylan, sales and marketing manager for Morgan’s seals and bearings business in North America, says: “The performance bar has continued to rise over the past few years as the application requirements for mechanical seals continue to increase, sometimes to staggering levels. These critical face components are being designed to handle higher pressures, speeds and temperatures.

“Maintaining the integrity of the interface between the seal faces is key. The material technologies we have at Morgan, coupled with the extensive machining expertise of Engis, create the ability to tailor the topography of the seal face to precise levels.”

In conclusion, Engis product manager Alicia Walters says: “No two applications are exactly alike, so it is critical to approach process development from many angles. Engis has the ability to control the machine design, slurries, plate materials and accessories.

"Together with our process development laboratory, we can develop and deliver the optimum lapping process to the end user. The ability to select from a wide range of proven options allows us to quickly achieve the desired results — or develop unique solutions when necessary.”