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SNFA Group has specialized in the manufacture of high precision ball and roller bearings since its foundation in 1952. SNFA has continuously invested in the bearing product range technology. In 1968, to meet the rising demand for high quality super precision bearings for the machine tool market, SNFA formed two new manufacturing units in Europe : SOMECAT SpA, near Torino in Italy, and SNFA Bearing Ltd, near Bristol in UK. The latest major and important extension to SNFA's manufacturing resources was completed in 2003. This involved the doubling in size to 6,500 m˛ of their Italian facility, Somecat SpA, located near Turin. |
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With more than 50 years of experience, exclusively within the design and manufacturing of special bearings for advanced technology, in particular for Aerospace and Machine Tool application, SNFA has become the reference point in the world of high quality, advanced technology bearings.
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As the Group's activity expanded, SNFA gradually implemented an organizational structure based on three major product groups with the objective of reaching the highest levels of specialization in :
- Cylindrical and spherical roller and ball bearings for the Aerospace industry
- High precision angular contact ball bearings for machine tool and other special applications
- Special bearings for high performance applications
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Products Special Bearings
SNFA also manufactures special integral race assemblies of different types as per customer specifications :
- Integrated squirrel cage bearings,
- Gear bearings,
- Thin section bearings,
- Specific integrat
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MATERIALS
SNFA constantly develop new material solutions with new raw materials, new heat treatments or thermo-chemical treatments and specific surface treatments like:
Deep nitriding process:
Nitriding is one of the thermo-chemical treatments used by SNFA in order to obtain case hardening. SNFA offers deep nitriding on AMS 6481 steel, which offers high rolling fatigue performance. This steel is used by SNFA for both structural bearings subject to high temperatures and to hard particle contamination. It can also offer improved performance in poor lubrication environments. |
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The deep nitriding cycle performed by SNFA enables us to reach a case depth of 0.6 to 0.8 mm with surface hardness over 65HRc. This operation may also be performed on thin-section rings. The nitrided process offers compressive residual stresses across the total case which is associated to a homogeneous and uniform microstructure. |
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Chromex®40 stainless steel
Based on nitrogen enriched steel , SNFA has developed new heat treatments in order to propose the CHROMEX® 40 steel. This new corrosion resistant steel offers higher performances than AMS 5618 (440C) steel. CHROMEX® 40 steel (corrosion resistant steel) is currently used for aerospace applications. ue to the heat treatment developed by SNFA, CHROMEX® 40 steel can operate at high or low temperature. It offers a minimum hardness of 58 HRc and the structure is always uniform and homogeneous and this gives a good fatigue life.
CHROMEX® 40 steel under salt spray test offers exceptional corrosion resistance. |
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PEEKT 450 CA30 cages
SNFA propose moulded bearing cages in PEEKT 450 CA30 (Poly Ether Ether Ketone). Carbone fibres included in the PEEKT 450 CA30 offer the design improved mechanical properties which are comparable to metallic cages. This property permits some comparisons to metallic cages for many applications. PEEKT 450 CA30 allows a maximum continuous temperature up to 150°C. The very low density also offers a very good dynamic behaviour for the cages.
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PEEKT 450 CA30 offers the following benefits :
- Chemical stability when subjected to lubricants and solvents
- Controlled and repeatable manufacturing process
- Loow coefficient of friction in poor lubrication environments
- A good fatigue which has been tested on our test rigs
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Si3N4Ceramic
Through the evolution of bearing technology SNFA have focused research on new materials. SNFA have designed and manufactured ball and roller bearings that have either all ceramic components or are hybrids with steel races and ceramic rolling elements.
Ceramics offer the following advantages:
- high hardness
- low density (3,2 compared with 7,8 for SAE 52100 or M50 steel)
- long fatigue life
- low coefficient of friction
- excellent resistance to wear
- excellent corrosion resistance
- good resistance to high temperature and thermal shock
- good electrical insulating properties
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SNFA have selected Silicon Nitride (Si3N4) as the most appropriate for all applications. Compared with components in the usual bearing steels, SNFA ceramic components offer:
- LONGER FATIGUE LIFE
- HIGHER ROTATIONAL SPEED
- INCREASED OPERATING TEMPERATURE
- GREATER ABILITY TO OPERATE IN HOSTILE ENVIRONMENTS (corrosive, chemical, reduced lubrication...)
- SIGNIFICANT WEIGHT REDUCTION
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Pyrowear® 675 low pressure carburising steel
Pyrowear® 675 (AMS 5930) is a corrosion resistance steel and the carburising treatment allows us to use it for structural bearings. The chemical composition and the thermo chemical treatment optimised by SNFA offers very good operating capacities. SNFA has developed a specific carburising cycle with low pressure without pre oxidation. This process improves case quality and uniformity. It also offers a surface hardness higher than 62HRc and a case depth from 0.8 to 1.2 mm.
Pyrowear® 675 carburised rings gives compressive residual stresses throughout the total case depth
TSI induction surface treatment
SNFA has developed induction surface treatment on CHROMEX® 40 steel in order to be able to propose stainless steel structural bearings. The ring heat treated with induction quenching offers case hardness higher than 58HRc while the core hardness remains lower than 40 HRc. The steel keeps a good toughness. The exact case depth can be determined by our engineers according to the demands of the specific application.
The case depth heat treated by induction keeps compressive residual stresses and the structure remains uniform and homogeneous. Bearing fatigue life and corrosion resistance of this CHROMEX® 40 steel under salt spray gives better performance than other stainless steel.
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Machining Process
In order to respond to specific needs for non circular bearings, SNFA has developed special grinding CNC machines for elliptical shapes or trilobe shapes.
Due to the high control of our grinding and control process, SNFA obtains a good level of compressive residual stresses in each bearing raceway. The residual stress level is necessary to achieve a good fatigue life for all bearing components.
Grinding and control process are subject to continuous improvement in order to meet specific needs. Innovative solutions have been developed by SNFA in our R&D programmes. SNFA proposes to introduce and to control the residual stress profile on all bearing raceways. The surface roughness can also be developed and controlled with the average surface roughness.
USP® process, elliptical and trilob grinding
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SNFA has always strived to improve the quality of his products and to bring a better solution for specific applications. The homogeneity of residual stress profile can be checked by Barkhausen noise analysis and are estimated by a specific SNFA software. For hybrid bearing applications requiring ceramic balls, SNFA has developed a new non destructive test method (RUSSAW®) to determine surface and sub surface defects.
An automatic roller control system has been developed by SNFA in order to reject non conforming components. This control system inspect both dimension and raw material. New inspection equipment (contact less measurement, surface topography, 3D measurement) are also available in our metrology laboratory.
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- Test rig to analyze the grease lubrication
- Test rig to study the tribological behaviour of angular contact bearings
- Test rig to characterize the tribological behaviour of different materials and coatings
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Design/Engineering
SNFA has been developing many software in order to help bearing design for aerospace and machine-tool bearing applications.
These software are used every day by our design departments.
SECBA (SNFA Consultant for Bearing Application) is an advanced bearing analysis software package developed by the SNFA ® Group. SECBA is to be used in the design of a spindle or shaft to accurately analyse the operation of the bearing whether it is for the simpler static single bearing case or for the complicated dynamic multi bearing system.
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Version 5.0 has been developed to work within the Microsoft Windows ® operating system and has a user interface that is simple to understand and easy to use. It takes full advantage of all the latest SNFA research into bearing analysis.
A simpler version, without the dynamic analysis capability is also available. SECBA includes the SNFA Bearing database exportable in DXF format. SECBA is able to calculate all bearing internal data like:
Stresses - Angles - Movements or loads - Expansions of elements - Lives
In function of:
Speed effects on elements - Movements or loads - Element temperatures and materials - Preloads - Fitting or clearances of ring
SECBA provides also calculation of:
Frequencies and vibrations in function of waviness and local defects - Minimum fittings and max speed before fit loss - Minimum axial load to avoid skidding - Bearing radial and axial rigidities Etc...
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The shaft design is done easily thank to a reactive design. Forces, rigidities, gears and pulleys can be inserted and associated to the different working conditions of the shaft. Temperatures and materials of the parts of the shaft and of the housing can be modified. Bearing assemblies, preloading, fittings, all possible configurations can be created.
SECBA's output is:
- Shaft elastic line picture - Nodes movements - Bearing reactions - Bearing detailed internal data - Bearing lives Output data can be saved in RTF format or exported to MS Word. |
TEST RIGS
SNFA designs his own test rigs in order to meet applications and customers requirements for existing or future projects. This is the reason why SNFA test rigs keeps capacity to offer higher performance and are subject to continuous improvements. SNFA test rigs permit us to evaluate raw material but also different bearing internal geometry (or specific applications). The test rigs are automatic and computerized and permit us to test all the bearing components by changing speeds, loads, lubrication temperatures, etc...
Bearing damages during the test are determined automatically with accelerometer sensors. SNFA has also BBP test rigs which allow us to determine new raw material solutions compared to existing raw material. This type of test is carried out under Hertz pressure until 7 Gpa. High speed test rigs permits us to test different bearing design meeting the bearing specification of the concerned application. The improvement of these high speed test rigs allows us today to reach 2.106 ndm. False brinelling test rigs permit us to test bearing raceways subject to false brinelling between rolling elements and rings. Many other test rigs enable SNFA to answer to customer needs and requirements based on your applications.
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