Radial shaft seals

For SKF's 35 × 52 × 7 HMSA10 RG, the cited metric h11 shaft fit gives 34.840–35.000 mm and the H8 housing bore gives 52.000–52.046 mm. The 35 mm identifies the shaft counterface. The example also requires at least 7.3 mm housing depth under the metal-inserted guidance. Verify finish, shaft motion, lubricant, speed and pressure separately. SKF, pp. 81, 83–84, tables 6 and 10.

Function and interfaces

The outside diameter seals against the housing. The lip runs on the shaft, with a garter spring in some designs. An auxiliary lip can exclude contaminants. SKF, Industrial shaft seals, pp. 63, 70.

SKF shows the spring side facing retained oil. Contaminant exclusion can use an outward-facing lip, and opposing seals can serve both tasks. An outward lip can let excess grease escape during replenishment. SKF, pp. 20–23.

This article concerns industrial radial lip seals. Axial V-rings and metal face seals appear as alternatives in SKF's arrangement examples but have different contact geometry; their operating data do not transfer to radial lip seals. SKF, pp. 21–23.

Construction and material variants

Metal-cased and rubber-covered outside diameters are different constructions. SKF's HMS5 and HMSA10 designs have a metal insert and a beaded rubber outside diameter. Both have a spring-loaded primary lip; HMSA10 adds a non-contacting auxiliary lip. Other designs use contacting auxiliary lips, which add friction and heat. “Double lip” alone consequently does not identify contact behavior or permissible speed. SKF, pp. 63, 70, 106.

SKF's material codes distinguish polymer families from particular compounds. Its table identifies R and RG as nitrile rubber (NBR); RG is the optimized nitrile compound used for HMS5/HMSA10. The V variant uses fluoro rubber and, for these families, a stainless steel garter spring. PTFE is another sealing-lip material with separate counterface requirements. These codes do not establish a universal compound formulation, hardness, spring alloy grade, or interchangeability between manufacturers. SKF, pp. 31–32, 81, 106.

The catalog describes NBR resistance to mineral oils and mineral-oil-based greases, among other media, and describes RG as having favorable compatibility with synthetic oils. That description is not a compatibility guarantee for every base oil, additive package, solvent, concentration, or temperature. Lip material, fluid identity, and thermal conditions remain coupled. SKF, pp. 32, 35, 106.

Speed, heat, pressure, and shaft motion

Rotational speed in revolutions per minute and circumferential speed in metres per second describe different quantities. The latter depends on shaft diameter. Friction, speed, fluid viscosity, and heat transfer influence temperature at the sealing edge, so bulk lubricant temperature alone does not establish lip temperature. Inadequate lubricant film and excess heat can accelerate damage. SKF, pp. 25, 35, 80.

For the HMS5/HMSA10 oil- or grease-lubricated family, the December 2021 catalog states an operating temperature range of −40 to +100 °C, short-term exposure to +120 °C, circumferential speed up to 14 m/s, and pressure up to 0.05 MPa. The catalog explicitly says these individual maxima must not occur together. They are not a rectangular operating envelope or an approved duty point for every size. SKF's general grease guidance also halves the permissible circumferential speed calculated for oil lubrication. SKF, pp. 20, 107.

Differential pressure increases lip loading, contact area, friction, and temperature; speed guidance for unpressurized service then ceases to apply. Pressure can also push the seal out of its bore, which explains the catalog's low-pressure-side shoulder or retaining-ring arrangement. Pressure-profile seals are separate designs with separate limits. SKF, p. 79.

Coaxiality error is the offset between shaft and housing-bore centerlines. Dynamic runout is rotating shaft eccentricity that the lip must follow. Greater speed can prevent the lip from tracking that motion, interrupting the lubricant film and permitting leakage. Seal section, material, and temperature affect allowable runout; diameter tolerance is not a substitute for either alignment or runout control. The catalog's curves are guidance, rather than numerical acceptance limits derived here for a particular assembly. SKF, pp. 70–73.

Shaft counterface and housing bore

The counterface is a functional sealing surface, not merely a shaft of the correct nominal diameter. SKF distinguishes diameter tolerance, roundness, surface roughness, directional machining lead, hardness, and the axial track swept by the lip. Its general elastomer guidance gives at least 30 HRC surface hardness, increasing to 45 HRC where handling or installation damage is a concern; it also describes limited low-speed, well-lubricated, contaminant-free exceptions. The higher PTFE values in the same paragraph concern a different lip material. SKF, pp. 80–81.

Roughness values retain their parameter and source column. For example, SKF's table 5 ISO column gives shaft Ra = 0.2–0.5 µm and Rz = 1.2–3 µm, while its DIN column gives Ra = 0.2–0.8 µm and Rz = 1–5 µm. These columns are not interchangeable. SKF explains that an excessively smooth surface can impair lubricant supply, while excessive roughness increases wear. Plunge grinding minimizes directional lead; scratches, burrs, and rust remain separate defects even when a roughness reading falls within range. These are catalog recommendations, not a reproduction of the full standards. SKF, pp. 80–81, table 5.

The housing has its own requirements. SKF's general metric guidance uses an H8 bore, a burr-free 15–30° entry chamfer, and a shoulder fillet limited by bore size. For metal-cased or metal-inserted seals, bore depth is at least 0.3 mm greater than nominal seal width. Table 9's ISO column gives housing Ra = 1.6–3.2 µm and Rz = 6.3–12.5 µm; its footnotes qualify metal-cased seals and sealing compounds. Shaft finish values do not describe the housing interface. SKF, pp. 83–84, tables 9–10.

Worked example: SKF 35 × 52 × 7 HMSA10 RG

The catalog's 35 × 52 × 7 size row and designation key identify a nominal 35 mm shaft, 52 mm housing bore, and 7 mm seal width. HMSA10 selects the auxiliary-lip construction and RG selects the nitrile compound. The 35 mm dimension is the intended shaft diameter, not the free diameter of the flexible lip. SKF, pp. 106, 110–111.

The following are derived dimensional examples using that nominal size and the catalog's general metric tables. They do not establish actual manufactured dimensions or an approved assembly.

Source: SKF, pp. 81, 83–84, tables 6 and 10.

For an assumed speed of 1,500 r/min and nominal diameter d = 0.035 m, circumferential speed follows from circumference per revolution:

v = π d n / 60
  = π × 0.035 m × 1,500 min⁻¹ / 60 s·min⁻¹
  = 2.749 m/s (rounded)

This is geometric arithmetic, not a selected operating speed. A value below the family's individual speed maximum does not establish acceptable pressure, lubrication, temperature, runout, or service life. SKF, pp. 25, 107.

Two catalog qualifications matter for this example. Table 2's generic elastomer outside-diameter tolerances explicitly exclude beaded outside diameters, so they cannot supply HMSA10 free outside diameter or press-fit interference. Also, the product table's housing cross-reference points to pp. 85–86, whose headings concern HRS and HS/SS seals. The dimensional example above uses the general metal-reinforced housing guidance on pp. 83–84, rather than importing those other families' geometry. SKF, pp. 67, 83–86, 106, 110.

Assembly effects and coverage limits

Entry geometry and installation damage affect subsequent sealing. SKF describes rounded or chamfered shaft entries, protective sleeves across threads and grooves, initial lubrication with the retained lubricant, and press tooling that applies load near the seal outside diameter. Its grease-between-lips provision concerns contacting auxiliary lips; HMSA10's auxiliary lip is non-contacting. Engineering synthesis: a seal's nominal size, compound code, and undamaged appearance cannot alone establish the condition of its running edge after assembly. SKF, pp. 82, 87–88, 106.

The numerical examples use SKF publication 18729 EN/1, December 2021. They describe that manufacturer's catalog context, not all radial shaft seals or current-lot certification. The full ISO/DIN standards, actual compound formulation, free lip diameter, beaded outside-diameter tolerance, application-specific fluid compatibility, and physical qualification are outside this coverage. The catalog's pumping comparison uses a 60 mm shaft and SAE 30 oil; its relative-life chart supplies no operating-hour life for the 35 mm example. Customer operating conditions, actual lip temperature, pressure transients, contamination, shaft motion, and acceptable leakage remain application-specific. SKF, pp. 106–107 and publication imprint.

Related reference

Production planning references explains how component identity relates to an assembly definition.