Crane Buffer Selection: Rubber, Polyurethane, Hydraulic & Spring
Key Points Crane buffers are installed at the end of the travel path to absorb kinetic energy and cushion impacts. ① Four types exist—rubber, polyurethane, hydraulic, and spring—with hydraulic buffers offering the highest energy absorption (800–2500 J/kg); ② Buffer stroke = braking distance × 1.25, and safety distance ≥ buffer stroke + braking distance; ③ Bridge buffers mount at both ends of the end carriages, while trolley buffers mount on both sides of the trolley frame; ④ Kelude Heavy Industry equips cranes with polyurethane buffers as standard (lightweight, corrosion-resistant), with hydraulic buffers available as an option for large-tonnage cranes requiring smooth braking.
Buffer Types and Construction
Buffers are safety protection devices on cranes, installed at the end of travel on both ends of the end carriages or both sides of the trolley frame. When the crane reaches its limit position, the buffer collides with the end stop, absorbing kinetic energy to cushion the impact. ISO 4301 Crane Design Standard requires that the ends of both the bridge and trolley travel mechanisms be fitted with buffers or end stops. Buffer selection must be calculated based on crane mass, travel speed, and buffer stroke. The Crane Safety Protection System Engineering Design standard specifies that safety distance = braking distance × 1.25 + buffer stroke.
| Model | Type | Buffer stroke(mm) | Maximum Absorbed Energy(k J) | Maximum Impactspeed(m/s) | applicable tonnage(t) | reference price(RMB) |
|---|---|---|---|---|---|---|
| JHQ-A3 | Rubber | 30 | 0.5 | 0.5 | ≤5 | 80~150 |
| JHQ-C6 | Rubber | 50 | 1.5 | 0.8 | ≤16 | 120~250 |
| JHQ-B10 | Polyurethane | 80 | 3.0 | 1.0 | ≤32 | 180~400 |
| JHQ-B16 | Polyurethane | 100 | 6.0 | 1.2 | ≤50 | 300~600 |
| YHQ-80 | Hydraulic | 80 | 10 | 1.0 | ≤50 | 600~1500 |
| YHQ-150 | Hydraulic | 150 | 25 | 1.5 | ≤100 | 1200~2500 |
| YHQ-250 | Hydraulic | 250 | 60 | 2.0 | ≥100 | 2000~3500 |
| SHQ-100 | Spring | 60 | 2.0 | 0.8 | ≤20 | 150~400 |
Buffer Energy Calculation Formula
The kinetic energy absorbed by a buffer is calculated as E = ½mv², where m is the total mass of the moving parts (kg) and v is the impact velocity (m/s). When selecting a buffer, the buffer stroke s and braking deceleration a must also be considered:
Ek = ½ × m × v²
Favg = Ek / s (average buffer force)
a = v² / (2s) (impact deceleration, must be ≤ 4 m/s²)
Buffer stroke is selected based on s ≥ v²/(2a), with a safety factor of 1.25: sselected = s × 1.25.
Buffer Selection Example: 32t Overhead Crane
Given: Total crane mass m = 32,000 kg (including trolley), long-travel speed v = 0.5 m/s (30 m/min), buffer stroke must match the rail end stop.
Step 1: Calculate Kinetic Energy
Ek = ½ × 32,000 × 0.5² = 4,000 J = 4.0 kJ
Step 2: Determine Buffer Stroke
Using allowable deceleration a = 2.5 m/s², s = v²/(2a) = 0.25/(5) = 0.05 m = 50 mm
With safety factor 1.25: sselected = 50 × 1.25 = 62.5 mm, round up to standard stroke of 80 mm
Step 3: Verify Energy Absorption
Favg = 4,000 / 0.08 = 50,000 N = 50 kN
From the catalog, polyurethane model JHQ-B10 has a maximum energy absorption of 3.0 kJ < 4.0 kJ — does not meet requirements
Select JHQ-B16 (maximum energy absorption 6.0 kJ, stroke 100 mm) — meets requirements
Recommended Solution: For the 32t overhead crane, use polyurethane buffer model JHQ-B16 (energy 6.0 kJ, stroke 100 mm), with one unit installed at each end of the crane bridge.
Buffer Selection Example: 50t Overhead Crane
Given: Total crane mass m = 55,000 kg (including trolley, using a 1.1 factor), long-travel speed v = 0.67 m/s (40 m/min).
Step 1: Calculate Kinetic Energy
Ek = ½ × 55,000 × 0.67² = 12,345 J ≈ 12.3 kJ
Step 2: Preliminary Selection of Hydraulic Buffer
s = v²/(2a) = 0.449/(2 × 2.5) = 0.09 m = 90 mm, after applying safety factor sselected = 112 mm
From hydraulic buffer specifications: HYD-160 has a stroke of 120 mm, maximum energy absorption of 15 kJ, and maximum impact velocity of 1.5 m/s
Step 3: Verification
Ek = 12.3 kJ < 15 kJ | v = 0.67 m/s < 1.5 m/s | Stroke 120 mm ≥ 112 mm
Recommended Solution: For the 50t overhead crane, use hydraulic buffer model HYD-160, with two units installed on the same side (each absorbing 50% of the kinetic energy ≈ 6.2 kJ, ensuring adequate safety margin). Kelude Heavy Industry equips cranes ≥ 50t with hydraulic buffers as standard, providing an energy redundancy of ≥ 25%.
Buffer Installation and Inspection Standards
Per ISO 4301 Crane Design Standard and JB/T 2300-2011 requirements: the centerline deviation between the buffer and the end stop impact centerline must be ≤ 5 mm; the mounting surface must be perpendicular to the direction of travel; buffers at both ends must be the same model and installed at the same height; hydraulic buffers require air bleeding after installation. Inspection: during no-load testing, the buffer must make smooth contact with the end stop without tilting; under rated load, the buffer must fully absorb the impact energy, and the end stop must not bear impact loads.
Replacement Interval: Rubber buffers — 3 years; polyurethane buffers — 5 years; hydraulic buffer seals — 3 years (complete unit — 5 years). Replace immediately if any of the following conditions are observed: surface cracks on rubber/polyurethane buffers with a depth ≥ 3 mm, permanent compression deformation ≥ 15% of original height, hydraulic buffer oil leakage or reset time exceeding 3 seconds, or loose mounting bolts.
Kelude Heavy Industry offers periodic buffer inspection and replacement services. Polyurethane buffers are standard on cranes ≤ 32t, and hydraulic buffers on cranes ≥ 50t. Every crane ships with a buffer maintenance manual.
Frequently Asked Questions
Q: Should I install one buffer or two?
A: At least one per side. Kelude's standard configuration: one at each end of the crane bridge (both ends along the same rail direction) and one on each side of the trolley. For large-tonnage cranes (≥50 t), two buffers on the same side are recommended to better distribute impact forces.
Q: Which is better — rubber or polyurethane buffers?
A: Polyurethane buffers offer superior overall performance: 2–3 times the elasticity of rubber, better oil and corrosion resistance, no low-temperature brittleness, and a service life of five years (versus three for rubber). They cost roughly 1.5–2 times more than rubber buffers. Kelude ships polyurethane buffers as standard, reserving rubber buffers for light-duty equipment up to 5 t.
Q: Do buffers need periodic replacement?
A: Yes. Rubber buffers should be replaced every three years, polyurethane every five, and hydraulic buffers depending on seal condition — typically a full overhaul every 3–5 years. Kelude specifies the replacement interval for buffers in the crane's factory manual and offers a complete spare parts supply service.
Q: Is a bigger buffer always better?
A: Not necessarily. An oversized buffer consumes excessive stroke, which can shorten the effective travel range of the crane. An undersized buffer, on the other hand, may bottom out against the buffer stop during impact — a hard collision. Kelude matches the buffer's energy rating precisely to the crane's travel speed and mass through careful selection calculation.
This completes our technical guide to the four main crane buffer types — rubber, polyurethane, hydraulic, and spring. Kelude ships polyurethane buffers as standard on cranes up to 32 t and hydraulic buffers on units of 50 t and above, with a full range of spare parts and replacement services available. For buffer selection calculation, contact the Kelude technical team.
