The hand pallet truck assembly line integrates component preparation, welding, coating, hydraulic system installation, and final testing. Steel plates are cut and bent into forks and frames, followed by robotic welding and powder coating. In clean-room conditions, hydraulic cylinders are assembled with precision seals. The main line mounts the cylinder, steering wheels, handle linkage, and load rollers, followed by oil filling and bleeding. Rigorous testing includes no-load operation, rated load capacity verification, and leak detection to ensure product reliability and performance.
I. Product Structure
1.1 Main Frame System
- Frame: Constructed from high-quality C-channel steel or rectangular steel tubes formed into “H” or “gate” configurations through stamping and welding, supporting the forks and rear wheel bracket
- Forks: A pair of parallel fork arms with wedge-shaped tips for easy pallet entry, surface finished through polishing or plastic coating; standard lengths are 1150mm/1220mm (compatible with Euro/JIS pallets)
- Front Wheel Carrier: Pivot structure connecting the fork tips, equipped with steering bearings allowing 180° horizontal rotation
1.2 Hydraulic Lifting System
- Hydraulic Cylinder: Single-acting plunger-type cylinder, rated pressure 12-16MPa, typical stroke 120mm (standard lifting height)
- Pump Unit: Hand-lever operated dual-plunger pump with release valve (lowering valve), enabling three-stage lifting (fast/slow/precision)
- Oil Reservoir: Steel oil storage chamber integrated into the cylinder outer wall, capacity approximately 0.3-0.5L, using ISO VG32 hydraulic oil
- Seal Assembly: Polyurethane (PU) oil seals + dust wipers, pressure rating 25MPa, operating temperature -20°C to +80°C
1.3 Control Mechanism
- Tiller Handle: Φ25-32mm seamless steel tube with dip-coated or rubber-wrapped surface, integrating hydraulic control lever (three positions: lift/lower/neutral)
- Link Mechanism: Lever system connecting the handle to the pump rocker arm, mechanical advantage ratio approximately 1:12
1.4 Wheel System
- Load Rollers: Polyurethane (PU) twin wheels or nylon single wheels, installed at fork front ends, diameter Φ74/80mm, width Φ50-70mm
- Steering Wheels: Large-diameter rubber/PU wheels (Φ180-200mm), mounted on rear crossbeam with bearing housings and dust covers
II. Assembly Production Process
2.1 Component Pre-processing
| Process | Description | Quality Checkpoints |
|---|---|---|
| Steel Cutting | Laser cutting or shearing machine cutting frame plates and fork blanks | Dimensional tolerance ±0.5mm, deburring R0.5 |
| CNC Bending | Fork forming (R-angle control), oil tank shell bending | Angle tolerance ±0.5°, springback compensation |
| Machining | Cylinder body turning (internal bore honing Ra0.8), piston rod chrome plating (hard chrome layer 15-20μm) | Coaxiality ≤0.05mm, hardness HV≥800 |
2.2 Welding and Coating
Frame Welding Process:
- Fixture Assembly: Using specialized jigs to align forks with crossbeam, ensuring fork outer width 540/685mm (standard pallet compatible)
- CO₂ Gas Shielded Welding: Weld height 5mm, full welding at joints, post-weld inspection (magnetic particle testing)
- Shot Blasting: Steel shot size 0.8-1.2mm, surface roughness Sa2.5 grade, removing oxide scale and weld slag
- Electrostatic Powder Coating:
- Pre-degreasing → Water rinsing → Phosphating (zinc series) → Drying (120°C × 20min)
- Epoxy powder spraying (thickness 60-80μm) → Curing (180°C × 25min)
- Standard colors: RAL 1028 (yellow) or RAL 2004 (orange)
2.3 Hydraulic System Assembly (Clean Room)
Key Procedures:
- Cylinder Cleaning: Kerosene ultrasonic cleaning, internal bore wiped with lint-free cloth, cleanliness level NAS 8
- Seal Installation:
- Guide ring → Y-seal (lip facing pressure side) → O-ring → Dust wiper
- Apply special lubricant (Molykote 111), avoid twisting
- Pump Testing: Manual pressure test, lifting pressure ≤12MPa, pressure drop ≤0.5MPa after 5 minutes holding, no crawling phenomenon
2.4 Final Assembly and Testing
Main Assembly Steps:
- Frame Assembly: Install rear wheel axle and steering wheels, adjust bearing clearance (0.1-0.2mm), fill with lithium-based grease
- Cylinder Installation: Hinge cylinder bottom pin with frame crossbeam; connect piston rod top with fork lifting plate via cotter pin; check lifting plate-to-fork clearance (0.5-1.0mm)
- Control Mechanism Connection: Install tri-link mechanism, adjust handle neutral position; handle operating force controlled within 15-25kgf range
- Hydraulic Piping Connection: Connect high-pressure hoses to cylinder and pump body, using 24° cone seals or O-ring seals, tightening torque per specifications
- Oil Filling and Bleeding: Fill with No. 46 anti-wear hydraulic oil, repeatedly operate handle for lift-lower cycles to purge air bubbles from lines; observe oil level sight glass, maintain level between 1/2 and 2/3
- Load Roller Installation: Press polyurethane twin wheels or nylon wheels into fork front ends, check rotation flexibility
Factory Testing:
- No-load Performance: Lifting height meets specification (typically 120mm), lowering speed controllable (no rapid descent), steering flexible without jamming
- Load Testing: Rated capacity 1.5-3 ton static load test (24 hours without permanent deformation), dynamic travel test without abnormal noise
- Sealing Test: Hydraulic system pressure holding test, pressure drop not exceeding 0.5MPa within 5 minutes, no external leakage
III. Quality Control
- Critical Control Points: Welding strength, cylinder sealing, fork parallelism (≤2mm/m), overall load capacity
- Traceability: Establish quality records documenting batch information of critical components (hydraulic parts, bearings, wheels)
IV. Process Optimization Directions
- Welding Automation: Adopt six-axis robotic arms for frame welding, improving weld consistency and reducing labor costs
- Modular Assembly: Pre-assemble cylinder units with valve blocks and piping, requiring only quick-connect on site, shortening assembly cycle
- Environmental Processes: Promote water-based coatings replacing powder coatings to reduce VOC emissions; adopt low-temperature curing processes for energy saving
Note: Main differences between load capacity levels (2T/2.5T/3T/5T) lie in fork plate thickness (3.0/3.5/4.0/5.0mm) and cylinder bore diameter (Φ40/45/50/60mm), enabling flexible production through quick-change fixture systems.