Technical ceramics – tough benefits

Efficiency and longevity have become increasingly critical selling points for pumps – so important that manufacturers are looking at every element of the design and manufacturing process to see where improvements can be made. One area that can result in significant operational improvement is the adoption oftechnical ceramic components.The material has been overlooked in the past because of the assumption that high cost outweighs any benefits. Now, as manufacturers struggle to meet tighter environmental and maintenance controls, many are following the lead of companies like Grundfos who are investigating ways to incorporate the material into both existing and new pump designs.

Technical ceramic

Components made from advanced ceramics are hardwearing, long lasting and stable. They are particularly ideal for tough, long-lifespan products like domestic and industrial pumps where they offer considerable advantages over metal components. Circulating heating pumps with ceramic components typically last 15+ years. In short they are the difference between a confident lifetime guarantee and costly failures, problems that impact directly on a company’s reputation and future sales.Technical ceramics can be formulated and fired into a material second only to diamond in its hardness, and yet can still be manufactured in a variety of detailed, complex shapes using manufacturing techniques such as Ceramic Injection Moulding (CIM), dry pressing and extrusion. The components can also be easily joined to metals or other ceramics using metallising and brazing techniques.While several leading pump manufacturers are already confidently using ceramic for bearings and seal rings for submersible, centrifugal and other industrial pumps, and have done for many years, it still remains an exception to the rule despite the evident benefits, as described in the example below.

Case study

In circulator pumps used in central heating systems and domestic service systems, quiet, stable and efficient performance over long operational periods, often up to 5,000 hours a year, is highly desirable.The innovative thinking of world leading pump manufacturer Grundfos led them to realise that the traditional stainless steel-shaft / carbon bearings used in the pump were having a direct impact on both the pump’s longevity and noise. Grundfos investigated how the pump performance could be improved and found that the combination of alumina ceramic shafts and bearings offered superior reliability and increased lifetime of its pumps.Stainless steel-shaft / carbon bearings continue to remain common in pump design and manufacture, but the material combination does not always offer the best abrasive wear resistance to limescale and black iron oxide particles present in heating systems. The gradual wearing of these pump components increases noise levels,reduces pump efficiency and in some cases causes pump seizure.Ceramic shafts / bearings rotating in the water, containing abrasive wear particles, result in almost negligible wear, therefore maintaining tight clearance tolerances and virtually no noise increase over time. So why have not more pump manufacturers chosen ceramic? Here we look at some of the common misconceptions about the material.

Misconceptions

1. Ceramic is expensive. Manufacturing technical ceramics to precise tolerances include numerous processing steps that may result in a higher unit cost than that associated with polymers or more basicmetals. However, the overall price/performance ratio must be considered. The hidden costs of using lower performing materials include shorter product life, more frequent maintenance, an increased failure rate (and returns), reduced performance plus increased wear and noise over time.2. Ceramic is brittle. Are ceramics brittle? This is probably the most common question ceramic engineers get asked and the answer is both yes and no. In particular flexural strength and fracture toughness tend to make most engineers nervous when talking about ceramics – maybe the legacy of broken dinner plates and bathroom tiles. However the new age of high tech ceramic materials achieve high levels of strength. They are at different ends of the spectrum to the ceramics most people are more familiar with in the home. They are comparable to some standard metallic materials and by applying best design practices the concern that they are brittle can be removed.

Minimising tensile stress, avoiding stress raisers, ensuring loads are under compression and calculating accurate stress distribution will prevent failure. The ceramic material is deliberately formulated to achieve the highest level of mechanical and physical strength. Leading ceramics manufacturer Morgan Technical Ceramics produces ceramics with such unique properties that they are used for vehicle and body armour applications. The company’s technology allows them to meet the highest demands of urban warfare ballisticprotection.Ceramic materials are so durable that they also offer surgeons and patients new options for joint replacement surgery. Innovative manufacturing techniques are taking the proven biocompatibility and long-term durability benefits of the material to an increasingly wide range of medical applications.3. Only simple shapes can be mass-produced. Technological and material developments have advanced significantly from the days of ceramic sparkplugs and insulators back in the 1920s. Dry pressing, isostatic pressing, green machining and extrusion are forming technologies that are now commonplace.For components requiring high precision and medium to high volumes Morgan Technical Ceramics in Stourport, for example, offers Ceramic Injection Moulding (CIM). CIM is an innovative forming technique to manufacture a range of components, including those with a high geometric complexity, offering an economic solution for difficult production problems. Excellent batch-to-batch repeatability and process capabilities achieve tolerances of ±25μm without additional diamond grinding. CIM offers a solution when component complexity goes beyond the boundaries of more basic forming technologies such as dry pressing or an alternative to the CNC machining of ceramics when higher volumes are not viable.4. You can’t grind ceramic to tight tolerances due to its extreme hardness. Ceramics are well known forbeing extremely hard (Rockwell Hardness 75-86 R45N), second hardest to diamond. Ceramics can be machined in high volume to micron precision tolerances using state of the art diamond processing and grinding wheel technology. For example on a 09.5mm × 200mm long rod, 0.5μm roundness, 2μm straightness and 5μm OD tolerances can and are being mass produced. 

5. Ceramic shrinks. The only time advanced ceramics shrink is during their manufacture. Ceramic components are fired at high temperatures to remove the binder and subsequently sinter the material to form a fully dense body. During sintering the component shrinks uniformly by as much as 25% while retaining theshape. With good process control close tolerances can be obtained in the as fired part, often making post sintering machining unnecessary.6. Ceramic lacks temperature stability. In very high-speed applications, heat from friction during rolling can cause problems for metal bearings. These problems are reduced by the use of ceramics due to their excellent thermal properties. Alumina can operate at temperatures in excess of 1200°C, depending on the grade selected. Typical coefficient of thermal expansion (CTE) at room temperature is between 6.3 to 8.1 × 10⁻⁶/°C.7. Ceramics are porous. They can be designed to be porous for certain applications such as filters. However ceramic pump components can be sintered to full density with zero open porosity. Typical density of alumina is 3.5 to 3.95 g/cm³ & Zirconia 5.5 to 6.0 g/cm³.Times have changed, and ceramic is becoming increasingly common not just in the pump industry but in every industry – from aerospace to semiconductor, military to medical.As a result of a myriad of environmental and performance-related requirements manufacturers have no choice but to look at the bigger picture and begin investing in the areas that will offer long-term rewards. The key is to find and work in partnership with a materials expert – not just a supplier. A company that can work with you and your teams from concept and feasibility through prototype and development to full production will help minimise the costs associated with change. Once you have found that partner and successfully integrated ceramics into your design, you will never look back.