bearing-housing

name	bearing-housing
description	Bearing housing design — fit selection (H7/k6 etc.), material, wall thickness, oil passages, labyrinth seals, split vs. solid housing, thermal expansion, mounting/dismounting, ISO 286 fits.
metadata	{"priority":7,"promptSignals":{"phrases":["bearing housing","bearing housing design","bearing fit selection","H7 k6 bearing fit","bearing housing material","bearing mounting fit"],"minScore":3}}

Bearing Housing Design — Complete Skill

Fit Selection (ISO 286)

Inner Ring Fits (Shaft)

General rule: rotating inner ring → interference fit (to prevent creep) Non-rotating inner ring: transition or clearance fit

Standard recommended fits (radial ball bearings):

Load magnitude	Shaft fit (rotating inner)	Result
Light (P < 0.07 C)	js6, k6	Transition/slight interference
Normal (0.07–0.15 C)	k6, m6	Interference
Heavy (> 0.15 C)	n6, p6	Heavy interference
Shock	p6, r6	Heavy interference

For hollow or light shafts: reduce fit by one class (k6 → js6)

Outer Ring Fits (Housing)

Rotating outer ring (wheel bearing, rotating housing): interference fit Stationary outer ring (most applications): loose fit to allow thermal expansion

Load condition	Housing fit
Light, stationary outer	H7 (clearance or transition)
Normal, stationary outer	J7 or JS7 (transition)
Heavy axial; need location	K7 (interference)
Rotating outer ring	M7, N7 (interference)

H7 with k6 shaft + H7 housing (most common industrial): Shaft fit: +10 to +35 μm interference (k6) Housing: +0 to +25 μm clearance or near-zero (H7)

Housing Material

Cast iron (GG25): most common; good damping; machining ease; T_max 250°C Steel (EN-GJS-500): stronger than cast iron; for heavy loads; complex shapes possible Aluminum alloy (LM25): lightweight applications; T_max 150°C; CTE = 23×10⁻⁶ /°C (vs. steel 11.7×10⁻⁶) Ductile iron (SG iron): cast + ductile; good for shock load applications

CTE mismatch (steel bearing in Al housing): Δ_thermal = (α_Al - α_steel) × D × ΔT = (23 - 11.7)×10⁻⁶ × 150 × 50 = 0.085 mm at ΔT = 50°C → Al housing expands more → bearing outer ring may lose fit → design for interference at max ΔT

Wall Thickness

Minimum housing wall (for bearing load transmission): t_wall ≥ 1.0 × D_bearing_bore (minimum for cast iron) t_wall ≥ 0.5 × D_bearing_bore (for steel housing) Typical: t = 10–40 mm depending on bearing size and load

Flange thickness (for end caps): t_flange ≥ 0.3 × D_bore; minimum 8 mm for fastener integrity

Housing bore tolerance: Machined to IT7 grade tolerance; bore roundness ≤ 50% of bearing clearance tolerance Surface roughness: Ra ≤ 1.6 μm (for H7 fit); Ra ≤ 0.8 μm for precision

Oil Passages and Lubrication

Oil inlet positioning: Inlet: gravity-fed oil from above (12 o'clock) or pressure-fed from side Grooves: circumferential groove in housing bore (width = 30% of bearing width; depth = 3–5 mm) Oil distribution groove must NOT extend into load zone (bottom of bearing in vertical shaft or side for horizontal)

Oil level (oil bath): Grease-filled: housing 1/3 to 1/2 full (overgreasing → overheating) Oil bath: oil level at center of lowest rolling element (avoid excessive churning)

Drain plug: positioned at lowest point; M16 or M20 standard; dipstick or sight glass for level check

Oil-flow housing (circulating system): Flow inlet at top; drain at bottom; calculate required flow: Q_oil = P_bearing × 10 / (c_p_oil × ρ × ΔT) [L/min; P_bearing = heat generation [kW]; ΔT = oil ΔT [°C]]

Sealing

Grease housing with labyrinth (no contact): Gap: 0.15–0.3 mm; 2–3 labyrinth chambers; fill chambers with grease Excludes contamination; no wear; no friction

Lip seal (radial): Contact-type; polyacrylic or NBR; seals shaft to housing Maximum surface speed: 4–8 m/s (NBR); 10–15 m/s (PTFE) T range: -40°C to +120°C (NBR); up to +200°C (silicone)

V-ring (axisymmetric seal): Non-contact on shaft; contact on face; effective for contamination exclusion Maximum speed: 12 m/s

Split vs. Solid Housing

Split housing (pillow block, two-piece): Split at horizontal centreline; allows assembly without pulling shaft Used for: shafts that cannot be unmounted axially; large shaft diameters Disadvantage: alignment critical; split surface must be flat (Ra < 1.6 μm); less stiff than solid

Solid housing (flanged or cartridge): Maximum rigidity; accurate bore; preferred for precision applications Requires axial shaft assembly

Plummer block (SNL series, SKF/FAG standard): Cast iron split housing; standard for industrial duty; matched to bearing adapter sleeve

Mounting and Dismounting

Mounting interference fits: For small bearings (bore < 80 mm): arbor press or hand tools Medium (80–240 mm): hydraulic press or heating (oil bath to 80–100°C; max 120°C for standard steel) Large (> 240 mm): hydraulic nut + oil injection (SKF Oil Injection Method)

Oil injection method: Pressurized oil (200–300 MPa) injected into mating surface gap → reduces friction → slides fit Enables mounting without exceeding 120°C limit

Dismounting: Bearing puller (hook under ring); never hammer directly on bearing Hydraulic nut for adapter sleeves: presses bearing off taper sleeve

Standards

Standard	Scope
ISO 286	Limits and fits (H7, k6, etc.)
ISO 492	Tolerances for rolling bearings
ISO 15	Fitted dimensions for bearings
SKF, FAG, NSK General Catalogue	Detailed fit and housing recommendations

Output

Provide: shaft fit designation (e.g., k6) with interference range [μm], housing fit designation (e.g., H7) with clearance range [μm], housing material (cast iron/steel/aluminum), wall thickness [mm], bore surface roughness Ra [μm], oil passage and groove geometry, seal type and speed rating [m/s], CTE compensation if housing and shaft materials differ, mounting method (press/heating/oil injection), and applicable standard (ISO 286, ISO 492).