Bearing & Bushing Glossary
- Sintering
- A powder-metallurgy process in which compacted metal powder is heated below its melting point in a protective atmosphere so the particles bond at their contact points, forming a coherent solid that retains a controlled pore structure.
- Oil-impregnated bearing
- A porous sintered bearing whose interconnected pores have been filled with lubricating oil under vacuum, so the bearing carries its own lubricant reservoir.
- Self-lubricating bearing
- A bearing that supplies its own lubricant during service without external oiling or greasing; in sintered types the oil is released from the porous wall as the bearing warms.
- Interconnected porosity
- A continuous network of open pores through the bearing wall that stores oil and allows it to migrate to the running surface; typically of the order of 20 to 25% by volume in sintered bronze of this type.
- Capillary action
- The surface-tension effect that holds oil within the pores at rest and draws it back into the matrix on cooling, recharging the reservoir after each duty cycle.
- PV value
- The product of bearing pressure (P) and sliding velocity (V); the key design limit for plain self-lubricating bearings because frictional heat rises with PV.
- Bearing pressure (P)
- The load carried divided by the projected bearing area (bore diameter multiplied by bearing length), expressed as a stress on the running surface.
- Sliding velocity (V)
- The linear speed of the shaft surface at the bore, derived from shaft diameter and rotational speed; combined with pressure to give the PV value.
- BP25 sintered bronze
- The general-purpose oil-impregnated sintered bronze grade, tin-bronze based, offering good corrosion resistance and the highest speed capability among the porous grades.
- FP20 sintered iron
- The economical iron-based sintered grade, harder and lower in cost than bronze, suited to slower speeds, higher unit loads and intermittent motion.
- SO16 alloy
- A specialised sintered alloy grade supplied as solid and hollow bearing blanks for machining bespoke bearings, paired with the dedicated impregnation oil METADOP.
- Vacuum impregnation
- The process of evacuating air from a porous bush under vacuum and then admitting oil so that lubricant is forced into the open pores, fully charging the reservoir.
- ISO 2795
- The international standard covering dimensions of sintered bushes, giving the type its interchangeable size envelope.
- DIN 1850
- A German standard specifying dimensions for plain bearing bushes, widely referenced for sintered bush interchangeability.
- Green compact
- The fragile, unsintered part formed by pressing metal powder in a die, held together only by mechanical interlocking before sintering.
- Sizing
- A post-sinter pressing operation that brings the bore and outside diameter to final tolerance and burnishes a smooth running surface; also used after fitting to correct the bore without cutting.
- Ball sizing
- A finishing method in which an oversized ball or pin is pushed through the bore to burnish it to size, preserving surface porosity rather than smearing it closed.
- Bore closure (close-in)
- The reduction in a sintered bush's internal diameter that occurs when it is pressed into an interference housing; allowed for in design so the fitted bore reaches the correct running clearance.
- Press-fit (interference fit)
- The method of retaining a sintered bush by pressing it into a slightly smaller housing bore, holding it by interference without adhesive or fasteners.
- Running clearance
- The small diametral gap between shaft and fitted bore that allows an oil film to form; too little risks seizure, too much spoils the film.
- Running-in (break-in)
- An initial period of reduced-load, reduced-speed operation that beds in the surfaces and establishes a stable self-lubricating oil film.
- Boundary lubrication
- A regime in which surfaces are separated only by a thin adsorbed oil layer rather than a full fluid film; typical of self-lubricating bushes at low speed.
- Hydrodynamic film
- A pressurised fluid film that fully separates shaft and bore at sufficient speed and load, minimising wear.
- Cylindrical bushing
- A plain sleeve bush without a collar, used where axial location is provided elsewhere; offered in BP25 bores from 2 to 125 mm and FP20 from 3 to 100 mm.
- Flanged bushing
- A bush with an integral collar (flange) that locates the bearing axially and carries light thrust; offered in BP25 and FP20 from 3 to 60 mm bore.
- Collar diameter (Ø Coll.)
- The outside diameter of a flanged bush's collar, quoted alongside the flange thickness in the size designation.
- Flange thickness (Ép.)
- The axial thickness of a flanged bush's collar, abbreviated from the French epaisseur, specified per size.
- Bore (Ø Int.)
- The internal diameter of a bush, which becomes the running fit against the shaft after installation and close-in.
- Outside diameter (Ø Ext.)
- The external diameter of a bush, which forms the interference fit with the housing.
- Bearing blank
- A plain sintered cylinder, solid or hollow, supplied for machining into a custom bearing when no standard bush size fits.
- Hollow blank
- A pre-bored sintered blank for machining larger or non-standard bushes; offered with bores from 38 to 85 mm and outside diameters up to 175 mm.
- Solid blank
- A solid sintered cylinder for machining custom bearings; offered in outside diameters from 20 to 145 mm and lengths from 40 to 120 mm.
- Friction plate
- A flat self-lubricating composite plate for planar and linear sliding such as wear pads and slide ways; supplied 375 by 375 mm in thicknesses from 4 to 20 mm.
- Impregnation oil
- The lubricant charged into the porous matrix and used to re-oil bushes after cleaning; matched to the grade, such as TURBO T100 for BP25 and FP20 or METADOP for SO16.
- Food-grade lubricant
- An oil formulated for hygienic areas where incidental product contact is possible, such as the PE1152 grade used to impregnate bushes for food and packaging machinery.
- Surface finish (Ra)
- The arithmetic average roughness of the shaft counterface; a fine ground finish, typically around Ra 0.4 to 0.8 micrometres, promotes a continuous oil film.
- Maintenance-free (dry-running)
- A characteristic of self-lubricating bushes that run without added lubrication over their design life, making them suited to sealed or inaccessible assemblies.
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