Gear heat treatment for toughening up your teeth

Gears, particularly load-carrying power transmission gears, play a vital role in every field of industry, from aerospace, agriculture and automotive, to winching and wind generation. Each gear wheel's performance characteristics, with regard to its load carrying capacity, operating environment, applied stresses and design life, are determined by the microstructure and grade of ferrous-alloy typically employed, the type of gear and its mechanical specification, the actual gear cutting process and the choice of heat treatment method to achieve the required physical properties.

According to experts, heat treatment is a core competency that represents around 30% of typical gear manufacturing overheads, so selecting the right heating and quenching process is vitally important for durability, reliability, cost control and the avoidance of over-engineering. Keighley Laboratories of West Yorkshire, which offers advanced analysis, testing and heat treatment of metals on a single site, provides a range of case hardening, induction hardening, Tufftride ferritic nitrocarburising and other processes for high performance gears and believe it can assist customers by engineering out cost and engineering in performance.

"Ideally, we like to be involved as early as possible in the gear design process, because our metallurgical experts can advise on the optimum material, our heat treatment professionals can identify how to achieve the correct hardness profile, at the right price, and our practical experience of heat treating hundreds of thousands of gears and gear teeth means we can often foresee technical issues down the line and avoid them," says Heat Treatment Commercial Manager, Michael Emmott.

"We pride ourselves on keeping gear wheel distortion to a minimum and processing materials according to their metallurgy and technical requirements, giving the correct strength characteristics for the identified torque transmission," he continues. "Keighley Labs offers different types of jigging to cope with different gear geometries and assist with distortion control, as well as various quenching techniques like press quenching for cooling thin or complex parts and molten salt baths for processes such as austempering and martempering, which keep distortion to an absolute minimum. A variety of gear shapes and sizes demands not only flexibility in the heat treatment process, but also in the quenching, and that's what we can offer."

Case hardening generally and carburising and carbonitriding in particular are the most commonly used techniques for high performance gears, producing a softer, tougher core to avoid tooth breakage, while achieving a hard wear-resistant case to prevent pitting. It lends itself to both high and low volume requirements and a wide variety of gear shapes and sizes, up to around 1 metre in diameter and 2 tonnes in weight at the Keighley Labs facility. Case depths between 0.1mm and 5mm are achievable, with PLCs and oxygen probes enabling temperatures and cycle times to be accurately controlled. Test pieces are also highly representative of processed batches, thanks to excellent repeatability.

For larger gears up to 3.5 metres in diameter and 4 tonnes in weight, or where deeper hardening to 10mm is required, Keighley Labs offers induction hardening, which uses high, medium or low frequency alternating current to heat the surface of a gear tooth. Both spin hardening and tooth-by-tooth or contour induction hardening methods are available, with the tooth-by-tooth techniques especially suitable for larger gear wheels. Spin hardening is usually a rapid process, often completed in a matter of minutes, whereas tooth-by-tooth, also known as progressive or zone hardening, is more time consuming, although both methods ensure low distortion.

For relatively fragile gear geometries, Tufftride ferritic nitrocarburising is a further option. A comparatively low temperature, low distortion salt bath process, it produces a thin, iron nitride compound layer that is particularly resistant to wear and prized for its excellent sliding and running properties, ideal for gear wheels. Other specialist heat treatment techniques are available, as well as pre- and post- hardening processes such as annealing, normalising, stress relieving and tempering.

Internationally certificated for all heat treatment processes, with the options of metallurgical inspection by its UKAS accredited in-house testing service, Keighley Laboratories has experience of processing gears of all types and all sizes from several millimetres to several metres, although most fall in the mid-range sizes for mainstream power transmission applications. It can handle volume contracts and special one-offs for a single gear set, although there is naturally a premium for the smallest jobs, since setting up times for a one-off are much the same as for a batch.

"A customer once said, half-joking I assume, surely you just throw my small job into the furnace with lots of other stuff," says Michael. "But we always endeavour to supply a gear wheel that's fit for purpose, which means that heat treating a left hand and a right hand helical gear, for example, demands as much individual attention as a batch of monster gear wheels destined for crushing plant on the other side of the world. In either case, if the teeth start dropping off, that would be a catastrophe and that's exactly what we're paid to avoid."

For further information, e-mail: memmott@keighleylabs.co.uk  Refer to page 161

Axial angular contact rolling bearings
with integrated electromechanical brake

A new, ultra compact, lightweight bearing solution with integrated electromechanical brake has been developed for ceiling mounts in medical operating theatres. The same bearing unit can also be used in examination tables, mammography devices, X-ray cameras, surgical microscopes and stair lifts.

The Schaeffler Group's new ZAXB bearing unit incorporates an AXS angular contact roller bearing that supports high axial loads and tilting moments. This ensures that the numerous medical devices, computers and monitors can be moved to their optimal ergonomic positions smoothly and reliably. The integral electromechanical brake ensures secure location, once the desired position has been found.

Compared to conventional bearing systems with separate brake, the ZAXB is much lighter and more compact. At the same time, the unit is a closed system, which means there is less exposure to aggressive cleaning chemicals that could damage the materials used.
 
Ceiling mounts in operating theatres have to support a growing number of increasingly heavy devices, whilst also enabling quiet, vibration-free positioning. Classic mechanical components play a "supporting" role in this context. The bearings must exhibit high static load safety and tilting rigidity in the smallest-possible installation space. At the same time, their inside diameter should be relatively large to allow the supply lines and cables to pass through easily.

The new unit with integrated brake comprises an outer ring with fixing thread, an inner ring with coil and pressure springs, an adjusting nut with fixing thread, an anchor plate with axial movement facility and a lining plate that is connected to the outer ring. There are also two double direction axial angular contact roller bearings in an 'O' arrangement. As a result of this 'O' arrangement and the contact angle of 60 degrees, the bearing unit provides high load-carrying capacity and exhibits significant radial stiffness. The bearing rings and adjusting nut are precision-turned parts made from high-strength steel, while the axial roller and cage assemblies and axial bearing washers are manufactured using non-machining methods.
 
The integrated brake prevents the bearing unit from rotating when the current is turned off, as the anchor plate is pressed against the brake lining by springs. Therefore, the ceiling mount is safely fixed. When current is supplied, an electromagnet pulls the anchor plate against the springs and releases the brake lining so that the unit can rotate and be brought smoothly into another position.
 
The Schaeffler Group's Industrial Division supplies INA and FAG-branded rolling bearings and plain bearing solutions, as well as linear and direct drive technology to around 60 different industrial sectors via the Group's market-driven global organisational structure and application engineering. The product portfolio includes more than 225,000 products, their sizes ranging from miniature bearings with diameters of just a few millimetres (used for example in dental drills), to large-sized bearings with outside diameters of several metres, required for example in wind turbines.

For further information, e-mail: info.uk@schaeffler .com or view website: www.schaeffler.co.uk   Refer to page 31

New improved online condition
monitoring system for industrial machinery

The Schaeffler Group's maintenance management and condition monitoring division, Schaeffler Industrial Aftermarket Services offer an improved version of its FAG DTECT X1 online condition monitoring system. The new system is more compact than its predecessor and offers increased functionality and flexibility.

The new individual modules - the monitoring unit and the multiplexer - are now integrated in a single, compact unit that offers a high degree of flexibility for end users. The new FAG DTECT X1 s is suitable for a wide range of industrial vibration monitoring applications.

Unlike its predecessor, the new system combines all control modules into a single compact housing, which measures just 260 x 150 x 90mm, enabling easy installation in control cabinets. The integrated multiplexer enables the recording of signals from up to eight different sensors.

The FAG DTECT X1 s can save up to 16 separate monitoring tasks and execute these automatically. The system is protected to IP67 and can therefore be installed in harsh environments, in ambient temperatures from -20 deg C to + 70 deg C.

The system monitors vibration conditions, which if left undetected, can cause costly unplanned shutdowns of plant and machinery. These conditions include damage to bearings and gears, as well as shaft misalignments. If a specified threshold value or alarm limit is exceeded, the system triggers an alarm. The vibration monitoring data can be analysed directly on site at the central control station or this data can be retrieved via a TCP/IP communications link and analysed by either the end user or by Schaeffler Industrial Aftermarket Services. This means that operators can make changes to system parameters remotely from anywhere in the world.

The FAG DTECT X1 s is designed for use in a wide range of industrial environments, including the monitoring of rotating components and machines such as bearings, gearboxes, compressors, fans, pumps, rolling stands, paper mills and drives.

All commonly used acceleration, speed and displacement sensors can be connected to the FAG DTECT X1 s system, enabling process parameters such as speed, temperature, torque and pressure to be monitored.

For further information, e-mail: info.uk@schaeffler .com or view website: www.schaeffler.co.uk   Refer to next page