Designs and variants

The various bushing types, its designs and variants are described in the following:

Solid bronze bushings

SKF Solid bronze bushings are available in metric sizes as straight (fig. 1) or flanged (fig. 2) bushings. This robust bushing material is suitable for a wide range of applications. These bushings are applicable for oscillating movements in both radial and axial directions or for applications where rotating speeds are low.
Solid bronze bushings can be lubricated with oil or grease, whereas the lubricant not only improves the sliding properties, but also reduces wear and prevents corrosion. Those bushings with a bore diameter d > 14 mm have an an axial lubrication groove in its sliding surface and are indicated by the designation suffix G1.
All surfaces of a solid bronze bushing are machined.

Sintered bronze bushings

SKF sintered bronze bushings are available in metric sizes as straight (fig. 3) or flanged (fig. 4) bushings. These self-lubricating and maintenance-free bushings consist of a porous bronze matrix impregnated with a lubricant. The oil impregnation enables very high sliding velocity and makes these bushings suitable for rotating applications.
SKF does not recommend machining or grinding of the sliding surface of a porous sintered bushing due to the risk of closing the bushing pores.

Wrapped bronze bushings

SKF wrapped bronze bushings are available in metric sizes as straight (fig. 5) or flanged (fig. 6) bushings. They are wrapped from strips and calibrated. These bushings are an excellent solution for dirty environments where high levels of contamination make relubrication necessary. They are resistant to shock loads and vibrations at slow speeds.
The diamond-shaped lubrication pockets in the sliding surface (fig. 7) need to be filled initially with grease. A good quality lubricant reduces friction and wear by separating a bronze bushing from its shaft. To protect the bushing and lubricant in highly contaminated environments, SKF recommends using seals.

PTFE composite bushings

SKF PTFE composite bushings are available as straight bushings (fig. 8) in metric and inch sizes, as flanged bushings (fig. 9) in metric sizes. These bushings are self-lubricating as well as maintenance-free and due to their low friction provide a long service life. Despite of their compact design, they can accommodate heavy radial loads and are suitable for relatively slow rotational or oscillating movements. They also have good dimensional stability and thermal conductivity.

PTFE composite bushings consist of a sheet steel backing on which a 0,2 to 0,4 mm thick porous layer of tin/bronze is sintered (fig. 10). Furthermore, by a rolling process the pores of the sintered layer are filled with a mixture of PTFE (polytetrafluoroethylene) and molybdenum disulphide additives. This additional 5 to 50 μm thick running-in layer provides an optimum combination of the mechanical properties of the sintered tin/bronze and the good sliding and lubricating properties of the PTFE mixture.

Running-in period
During a short running-in period, minute amounts of the PTFE material from the running-in layer are transferred to the counter surfaces. After this transfer has taken place, the characteristics low friction and wear properties of these bushings are reached.

POM composite bushings

SKF POM composite bushings are available as straight bushings (fig. 11) in metric and inch sizes. Pockets in the sliding surface make these bushings suitable for applications that require minimal maintenance under difficult operating conditions, for example in contaminated environments where lubricant cannot be supplied continuously or frequently. Therefore, the grease reservoirs should be filled prior to installation. Despite of their compact design, POM composite bushings can accommodate heavy radial loads and are less sensitive to misalignment. They are suitable for slow rotational or oscillating as well as linear movements.

POM composite bushings consists of a sheet steel backing on which a 0,2 to 0,4 mm thick layer of tin/bronze is sintered. The principal characteristic of these bushings is their relatively thick (approximately 0,25 to 0,45 mm) covering layer of acetal resin (POM – polyoxymethylene) with additives. This covering layer has pockets to retain grease and is firmly attached to the sintered tin/bronze layer (fig. 12).
The thickness of the covering layer makes these bushings less sensitive to misalignment and the edge loading associated with that misalignment.

PTFE polyamide bushings

SKF PTFE polyamide bushings are available in metric sizes as straight (fig. 13) or flanged (fig. 14) bushings. These cost-effective, self-lubricating and maintenance-free bushings are designed for dry operations. However, a lubricant can improve the performance. Despite of their thin-walled design, PTFE polyamide bushings are wear-resistant and can accommodate moderate loads. Their compact design provides good heat dissipation and, therefore, relatively high sliding velocities.

Filament wound bushings

SKF filament wound bushings are available as straight bushings (fig. 15) in metric sizes. They have excellent dry sliding characteristics and the low friction sliding surface does not require additional lubricant. However, a lubricant can protect against contaminants and has no negative effect. These bushings are developed to accommodate heavy loads, vibrations and provide maintenance-free operation even under those extreme conditions and in corrosive environments.
However, filament wound bushings have only a limited capacity to accommodate solid particles embedded into the filament wound material. Therefore, SKF recommends protecting the sliding surface against the ingress of contaminants (Design of bushing arrangements) when the bushing is to be used in highly contaminated environments.
SKF filament wound bushings, which are often dimensionally interchangeable with solid bronze or steel bushings, can be machined using normal methods on all surfaces, except for the sliding surface. To facilitate mounting, the bushing may be split lengthwise into two halves by using a diamond coated grinding wheel. Sufficient cooling fluid should be applied as well to avoid excessive temperatures, as they can destroy the bushing.

SKF filament wound bushings are manufactured by a winding technique from a self-lubricating composite. The unique sliding surface layer consists of high-strength polyester and PTFE (polytetrafluoroethylene). The backing consists of wound high-strength tensioned glass fibres. Both layers are manufactured by winding endless strands in a criss-cross pattern (fig. 16) and are embedded in an epoxy resin matrix so that they are firmly attached to each other.

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