| 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).
