FEATURE BEARINGS, SEALS & GASKETS


BEARINGS: A KEY component in efficient vacuum pump designs


Mark Wakeham, key account manager, and


Mark Pritchard, senior sales and applications engineer, at The Barden Corporation, explore four key trends that are driving the design of


new vacuum pumps and explain why selecting the right bearings for these can help to improve performance and efficiency


S


emiconductors are an integral part of society and demand for these is


rising thanks to the increasing use of consumer electronic devices coupled with the rapidly growing use of AI within industry. Furthermore, today’s requirement for more renewable energy sources, and therefore semiconductors for solar cells, is contributing significantly to the industry’s overall growth. Manufacturing semiconductors requires


an ultra-high vacuum environment lower than 10-7mbar to guarantee there is no risk of contamination – and vacuum pumps are a critical piece of equipment to create the right atmosphere. However, a key component of the pump design is the bearing system.


CHALLENGES There are typically two types of pump: Fore vacuum pumps, which take the pressure from atmosphere down to 10-3 mbar; and then turbomolecular pumps (TMP) which typically operate at ultra high vacuum levels down to 10-9 mbar. In this latter application the bearings are often required to work at high speed. Regardless of the pump type, however, there are some common challenges:


Energy efficiency In a bid to reduce energy consumption and operate as efficiently as possible, pump manufacturers are looking at designing pumps with increased power density, but parasitic losses which take energy from the system need to be taken into consideration. Parasitic losses in a bearing system are mainly down to friction torque generated by the friction between the balls and the raceway, and the lubrication in the bearing. They can be reduced by downsizing the bearing and reducing the number of balls, which also


10 SEPTEMBER 2020 | DESIGN SOLUTIONS


increases the speedability of the bearing, and thus the pump may be able to run faster or more efficiently. But, this poses a challenge because the


loads on the bearing are the same but the ability of the bearing to support those loads is reduced. This can be overcome by looking at alternative materials with improved properties, namely fatigue strength and wear resistance – such as SV30, a martensitic through- hardened, high nitrogen, corrosion-resistant steel.


“Manufacturers


Longevity Reliability is the foundation for a long life and minimal downtime. Using a combination of specialist materials, heat treatments and surface coatings, bearings can be designed that typically run for five years without failures in these harsh environments. Current ‘greased-for-life’ bearing technology can consistently give 30,000+ hour life at high speeds in


Bearing precision plays a big part in pump


efficiency and reliability


excess of 800,000 ndm. Advanced coatings and surface


are under pressure to design and bring their


pumps to market as quickly as possible – and one way to ensure that the process runs


swiftly is to review the length of time taken for bearings to be designed”


treatments can be applied to bearings to combat friction, prevent corrosion and reduce wear; and heat treatment is especially important. At high temperatures retained austenite in a bearing steel negatively affects the dimensional stability of the bearing, causing it to expand, and this can lead to premature failure. Retained austenite in a bearing steel that is not heat treated is approximately 3-4%, but with special heat treatment the level of retained austenite can be reduced to just


0.1%. This delivers better performance


at high temperatures and ultimately a more reliable system with a longer life. Another material that delivers superior


In a bid to reduce energy consumption, pump manufacturers are looking at designing pumps with increased power density


reliable long life performance is ceramic (silicon nitride) balls, thanks to the material’s inherent mechanical properties. Use of ceramic balls in place of steel balls can radically improve bearing performance in several ways. Because ceramic balls are 60% lighter than steel, and because their surface finish is almost perfectly smooth, they exhibit vibration levels two to seven times lower than conventional steel ball bearings. Ceramic hybrid bearings also run at significantly lower operating temperatures, allowing running speeds to increase by as much as 40% to 50%.


/ DESIGNSOLUTIONS


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44