Barden Cuts Bearing Costs On Hippag Air Generator

Barden has helped Ultra Electronics Precision Air Systems to reduce bearing costs and assembly times on its high-pressure pure air generator by 40-50 per cent. Ultra produces a range of mini-compressors known as Hippag (High Pressure Pure Air Generators). These are compact, lightweight, electrically powered air compressors that are carried on-board various military platforms. The Hippag airborne compressor provides a continuous source of high-pressure pure air to cool the infrared seekers of an aircraft's defensive missiles, keeping them ready for action.

Hippag also provides a controllable energy source for the pneumatic ejection of aircraft munitions, while meeting the emerging requirement for launching increased quantities of smaller, smart munitions. More than 5,600 Hippags have been delivered for defence applications around the world. Hippag has been developed for the F-35 JSF aircraft and is being supplied for Boeing's Small Diameter Bomb programme, the Eurofighter Typhoon, the US Marine Corps AV-8B Harrier, AH-1W Supercobra, F/A-18 C/D Hornet and the US Navy F/A-18 E/F Super Hornet aircraft.

At the heart of the Hippag system is a bearing assembly based on a swash plate configuration. Supplied by Barden, this super-precision bearing is a customer-designed assembly that comprises a pair of bearings mounted on a cranked shaft with a 15-degree offset between axes. The bearing's main function is to transfer rotary motion into linear motion, enabling the axial motion of the Hippag compressor pistons. The bearing assembly will typically comprise a pair of solid, pre-loaded angular-contact bearings on the swash axis and a second pair of angular-contact bearings for the shaft axis, which are spring preloaded and share a double row inner ring.

The bearings are made from carbon chrome and use standard steel balls, as the Hippag application speeds are relatively low (less than 700rpm). These two bearing sub-assemblies are then mounted onto the offset shaft. Ultra subsequently receives this completed sub-assembly from Barden, which it simply drops into its Hippag housing to mate with the brushless DC motor, which sits on one side of the bearings, with the compressor on the other side. Martin Carpenter, engineering director at Ultra, said Barden's original design was selected because it utilised lower-cost manufacturing methods that used existing tooling and (at the time) a cellular-manufacturing approach that also contributed to a lower-cost bearing solution.

The new bearing assembly integrates directly with the Hippag unit and is smaller and lighter than the original. The original flange-mounted assembly has been replaced with a threaded outside diameter that enables through-grinding. 'The latest design incorporates precision-milled "pots" in the outer ring for the piston rod ends, which reduces the component count. 'Over the years, we've made lots of design iterations, including a low-duty unit in SAE52100 and a special high-duty unit that uses our "Cronidur 30" corrosion-resistant steel with its increased fatigue strength,' said Gary Hughes, application engineering manager for aerospace at Barden.

According to Hughes, there were several engineering challenges to be overcome. For Barden, Hippag is a low-speed high-load application with a short life of less than 500 hours and so the design had to reflect this. Hughes added: 'Through a 360-degree revolution of the Hippag, there's a constantly varying load cycle on the bearings and so we had to develop new methods of modelling this. 'This led to a bearing devolved from the original Ultra design to two bearing pairs and a cranked shaft. 'Investment in new machinery at Barden also enabled us to reintegrate the bearings into the Hippag shaft. 'We were able to eliminate the use of external clamping by incorporating threaded outside diameters on the bearings,' finished Hughes.

Barden Provides Super-Precision Bearings

The Barden Corporation offers custom-designed, super-precision bearings for use in a wide variety of high-performance air handling systems. Certain technologies demand custom-engineered, high-precision bearings rather than standard catalogue bearings. Air handling or air movement systems, for example, often require high-precision bearings, especially if the application is critical or requires a bearing solution that offers long life, high reliability and high speeds.

Other factors that make high-precision custom bearings essential to many applications are high temperatures, high pressures, poor lubrication, low vibration levels or abnormal contamination levels. Air handling systems are commonly found in every industry sector. Examples include axial and radial flow fans, compressors, turbomolecular pumps, dry pumps, emergency magnetic touchdown systems, turbochargers, air conditioning systems and cooling systems used on military aircraft for engine, avionics or infrared weapon systems.

Barden's manufacturing plant in Plymouth has more than 1,700m2 of cleanrooms for contaminant-free assembly and inspection of bearings. The company designs and manufactures super-precision bearings to a minimum of P4/ABEC 7 quality standards. Bearing sizes range from 5mm to 180mm outside diameter. Most bearing solutions are angular contact or deep groove and are available as hybrid (steel races with ceramic balls) depending on the individual application. Barden is capable of manufacturing bearings to a geometric tolerance of P2 or better and envelope dimensions to P4 or better.

Raceway roundness is better than half a micron, with raceway surface finish better than one micro inch Ra. For the aerospace and defence sector, Barden provides bearing solutions for the relatively small fans that are used in electronics cooling systems on aircraft, as well as bearings for the larger, more powerful axial and radial flow fans, which are frequently found in military aircraft start-stop air handling applications. Super-precision angular-contact and deep-groove ball bearings are also used in cooling systems for avionics bays and for military aircraft and helicopter engines.

On military aircraft, Barden bearings are also being used on the latest advanced weapons ejection systems. The bearing solution, which may include special flanges, threads or tapped holes, is custom engineered for the specific application, enabling the customer to quickly fit the bearing assembly into their own pneumatic ejection system. Often, the bearing assembly is so critical to the overall product that none of the system can be assembled without the bearing.

Multiple bearing solutions may need to be engineered to suit the customer's different product variants. The bearing solution may also help to reduce the customer's overall design and assembly costs. Air conditioning systems on aircraft also use super-precision bearings. Bleed valves, which are designed for flow and pressure regulation, take the air from the aircraft engines and move hot or cold air around the aircraft. While this particular application may not require the very high-precision levels offered by Barden, they benefit from material combinations such as Cronidur/ceramic in order to survive arduous operating conditions.

Once the bleed air has been used to control the temperature of the cabin air, it must then be moved around the aircraft. The fan speeds here are moderate but the bearings are critical in ensuring that the fan can deliver the correct mixture of hot or cold air to the required location on the aircraft at the right time. Turbochargers are another important application area for super-precision bearings. Barden is currently producing a high-speed ball bearing cartridge for use in automotive turbochargers.

The bearing itself incorporates two rows of balls built to a controlled end float. The design of the cartridge includes features for delivery of lubricating oil directly to the raceways and also for an oil film around the outside diameter of the bearing, which provides damping from high levels of vibration. The high speed of the turbocharger creates its own challenges and requires a bearing cage that is mechanically strong in order to resist the high ball-to-cage contact loads, but that is suitably compliant to ensure that wear is not a limiting factor.

Another growing air handling application for super-precision bearings is in fuel-cell technologies, where the fuel cell requires a compressor for the hydrogen used in the reaction. Barden engineers bearing solutions for a number of different high-performance pump manufacturers, for use in extreme, hostile environments. By using new materials, special coatings and by adding real value to the customer's own design, Barden can help the customer reduce design costs, minimise component count, reduce assembly time, as well as optimise the overall efficiency and reliability of the air handling system.

In turbomolecular pumps, for example, the most important requirements are long life, reliability and high-speed performance. Used predominantly to create high vacuum conditions for semiconductor, analysis and SEM applications, these bearings typically require a solution that comprises ceramic balls, a special coating, is greased for life and that has a special high-quality raceway finish. Semiconductors, solar panels and flat-panel displays all require a production process that is clean and free of any contaminants that may adversely affect the process.

Working chambers are normally flooded with gas and evacuated using dry vacuum pumps to create a working vacuum. In semiconductor manufacturing, the etching tools need to operate in a vacuum chamber while they etch miniature grids of electronic circuitry onto silicon wafers. This type of operation is so intricate that all contaminants must be removed from the production chamber before work can begin. It is therefore common to see rows of dry vacuum pumps installed under production floors in many semiconductor manufacturing plants.

Another example of where high-precision custom bearings are used for air handling is in emergency touch-down bearings for active magnetic bearings (AMBs). AMBs use actively controlled electromagnetic forces to control the motion of a rotor or other ferromagnetic body, providing a practical method of suspending shafts (both axially and radially) in numerous applications, including compressors, blowers, air conditioning systems, gas expanders (used as venting devices in gas pipelines) and in energy storage systems as emergency back-up power.

However, as most AMBs require continuous power input and an active control system to hold the load stable, if this system fails then high-performance rolling element back-up bearings, such as those produced by Barden, are needed to help control the system and bring it safely to a stop.

Barden Bearings Make Surgical Robots More Accurate

Trevor Morris, product engineering manager at Barden, describes how super-precision bearings help guarantee the accuracy and flexibility of articulated arms used in surgical and industrial robotics. A large selection of measurement and inspection systems, industrial robots and medical equipment now uses flexible arms to provide the degree of movement needed to carry out specific tasks such as handling, assembly, welding, measurement and surgical manoeuvres.

Flexible arms are used by industrial robot laser-welding systems, portable measurement-arms, laser-inspection systems and the latest CO2 laser surgical arms that perform intricate surgery on patients. Many flexible-arm systems have articulated joints that enable the end of the arm to be moved through 360deg, with three-to-six axes of movement. Each of these articulated joints requires one or more bearings of some sort, in many cases super-precision bearings.

Barden is a Plymouth-based manufacturer of super-precision angular contact and deep-groove ball bearings. Morris said: 'Barden has recently engineered a number of bearing solutions for flexible arms. 'One particular project included a flexible CO2 laser arm for performing intricate medical surgery on patients. 'We have also provided bearing solutions for portable measuring and inspection arms, as well as for industrial robot systems.' The surgical laser arm is an excellent example of a system that requires super-precision bearings.

All surgical laser units have a similar basic structure. The flexible arm is connected to a vertical pillar. This in turn is connected to the main body of the system, which contains the controls and display panel, as well as a firing-tube system that contains the CO2 molecules to be lasered. The flexible arm normally needs two or three articulated joints to give it the required freedom of motion. Sets of precision mirrors positioned at each articulated joint and the pillar direct the laser beam in a unidirectional straight line, from the firing tube at the base of the system through to the end of the flexible arm (where the hand-piece is located), which in turn focuses the laser beam onto the patient.

The surgeon requires complete freedom of movement of the hand-piece, which is provided by the articulated joints in the flexible arm. However, this flexibility creates a potential problem for the laser beam, which must travel in a straight line at all times throughout the system, regardless of the movements made by the surgeon. Typical surgical arms are around 2-3m in length, meaning the laser has to maintain its position at all times. The slightest deviation of the laser beam from the centre of the arm will cause operational problems at the hand piece.

A small angular deviation of more than 1mm over a 2-3m length can cause large errors in accuracy. Precision bearings are critical in ensuring that the laser beam maintains its position throughout the length of the system. Morris said: 'Normally we would supply bearings for the base of the pillar for rotational movements, then sets of bearings for each articulated joint in the flexible arm. 'Positional accuracy and controlling axial and radial run out of bearing sets are the key factors when it comes to selecting bearings.' A typical surgical arm will require bearings for articulated joints that guarantee no more than five microns of radial run out. These bearings therefore must be manufactured to at least ABEC 7 standards, sometimes to ABEC 9 (ISO P2).

Morris added: 'Rotational accuracy of the bearings is also important. 'This means providing a smooth running, low friction, low-noise bearing that is lubricated for life. 'For flexible arm joints, the deep-groove ball bearings are fitted with special oil-impregnated seals.' Barden's Flexeal is an oil-impregnated aluminium seal with a fibrous backing. It prevents loss of lubricant from the bearings and prevents the ingress of contaminants, which can lead to increased bearing wear. These seals are fitted to a super-finished recess in the bearing.

Morris said: 'Typically, bearings for articulated, flexible surgical arms are required to operate for at least five years, depending on the application. 'Therefore, if the bearings wear too fast due to poor running surfaces, cleanliness or lubrication, the life of the arm will be affected, which in turn affects the accuracy of the hand-piece. 'The same can be said for other flexible-arm applications such as robotics and portable measurement and inspection arms. 'Super precision bearings are essential components in these types of systems.' Barden designs and manufactures super precision bearings to a minimum of P4/ABEC 7 quality standards. Bearing sizes range from 5-250mm outside diameter. Most bearings manufactured are either angular contact or deep groove types.

Barden can make bearings to a geometric tolerance of P2 or better and envelope dimensions to P4 or better. Raceway roundness is better than half a micron, with raceway surface finish better than one micro-inch Ra.