Compressor valves are important compressor components. They are found in automotive air conditioning systems and in household refrigerators, for example, i.e., devices that convert heat to cold. Consisting of a hardened steel spring, these valves are subject to very high cyclic loads as they open and close. Small and thin, these valves have a frequency of between 60 strokes (Hz) per minute – fast as a hummingbird’s wings – and 200 Hz in more modern compressors.
“There is a lot going on with compressors these days,” says Stefan Jonsson, Senior Application Specialist at Sandvik Materials Technology, which develops and manufactures advanced stainless steels, special alloys, titanium and other high-performance materials.
“Environmental issues are driving developments in household appliances such as refrigerators and air conditioners with so-called inverters, or step-free compressors. In the industrial segment, refrigerant media like CFCs are disappearing to be replaced by pure carbon dioxide (CO2). In both cases, this results in greatly increased stress impact in terms of cyclical velocity, pressure and temperature, which means that there are growing demands on the blade steel.”
Unlimited cooling demand
The United States consumes more energy for air conditioning than all other countries combined, but growth is rapid in many other places on earth. More than a hundred million American households now have air conditioning and forecasts indicate that there will soon be as many in China. There seems to be an almost insatiable demand for cooling while energy issues are increasingly important. Many countries have introduced legislation and targets to reduce energy consumption in society. One result of this is that refrigerator and air-conditioning compressor manufacturers are purchasing high-performance materials for the new low energy standards.
“In China, a major manufacturer of refrigerator compressors had to redesign its compressors to achieve energy goals. The company was looking for a material with high fatigue strength – combined with high performance – and chose Sandvik Hiflex™ strip steel for its compressor valves,” says Jonsson. “It is estimated that this could help to reduce the country’s electricity consumption by about 25 TWh per year and reduce carbon dioxide emissions by 225 million tons per year providing of course that all households use refrigerators with such high efficiency compressors.”
“Our unique strip steel is tailor-made for these new compressors. A compressor valve made from Sandvik Hiflex™ can last decades, amounting 20 billion or more oscillations during its lifetime. Talk about fatigue resistance!” exclaims Jonsson.
In technical terms, this is often referred to as a new generation of high strength martensitic stainless chromium steel. The steel has up to ten percent improved flexibility and up to 25 percent improved strength against impact fatigue, compared with the best available competitive materials. From an environmental perspective, Sandvik Hiflex™ improves compressor efficiency and reliability. The material thus prolongs the life of the compressor and can also help to reduce noise levels.
“It is interesting that a seemingly quite insignificant component of a compressor – in terms of size and cost – can play such a crucial role in the performance. We now see that about a third of compressor manufacturers choose Sandvik Hiflex™ in their new advanced and energy efficient compressors. In addition, the new steel in the compressor valves for compressors, and thus the entire air-conditioning equipment, can shrink in size,” concludes Jonsson.
This article was published in May 2015