overhead crane rails wheels electrical system

Overhead Crane Rails, Wheels & Electrical System

1. Crane Rails

Crane rails are running tracks assembled by steel rails. They guide cranes along predefined routes and transfer wheel loads to the foundation.

A complete rail set normally consists of two steel rails. During crane operation, rails shall have no lateral or longitudinal displacement and shall be adjustable. All metal fasteners for rails shall be free of cracks, loosening and corrosion. Cracked components must be replaced immediately; other defects shall be rectified in time.

1.1 Installation Tolerances for Crane Rails on Concrete Structures

  • Rail center‑line position deviation: ±5 mm
  • Rail top‑surface elevation deviation: ±5 mm
  • Center‑to‑center distance between two rails:
    • When crane span ≤ 10 m: deviation ±5 mm
    • When crane span ＞ 10 m: deviation \(\boldsymbol{\pm[5+0.25(S‑10)]\ mm}\) (S = crane span in mm)
  • Relative elevation deviation of two parallel rails at the same cross‑section of workshop: ≤ 10 mm

1.2 Installation Tolerances for Crane Rails on Steel‑beam Structures

  • Deviation of crane‑beam centre‑line against design axis: ≤ 5 mm
  • Rail centre‑line offset: ≤ 1/2 of crane‑beam web thickness
  • Centre‑to‑centre distance deviation between two rails: ≤ 3 mm
  • Elevation difference of two rails at the same cross‑section:
    • At crane‑beam supports: ≤ 10 mm
    • At other positions of crane beam: ≤ 15 mm
  • Lateral offset & height difference between adjacent rail ends: ≤ 1 mm

2. Crane Wheels

Crane wheels support crane self‑weight and payload, enabling cranes to travel back and forth along rails.

According to flange shape, wheels are classified into double‑flange wheels, single‑flange wheels and flangeless wheels.

Tread profiles include cylindrical, conical and crown‑shaped.

2.1 Wheel Scrap Criteria

Wheels operating on rails shall be scrapped if any of the following conditions occurs:

  1. Surface cracks or other defects affecting service performance.
  2. Flange thickness worn down to 50 % of original thickness.
  3. Flange bending deformation reaches 20 % of original thickness.
  4. Tread thickness worn down to 15 % of original thickness.
  5. Roundness out‑of‑tolerance:
    • Travel speed below 50 m/min: roundness ≥ 1 mm
    • Travel speed above 50 m/min: roundness ≥ 0.1 mm

2.2 Rail Gnawing: Features & Causes

Features of rail gnawing

  1. Bright polished marks on rail side; burrs appear in severe cases.
  2. Bright spots on inner wheel flange and rail top surface.
  3. Obvious gap variation between wheel flange and rail within short travel distance.
  4. Crane body drifts or twists especially during start‑up and braking.

Main causes of rail gnawing

Excessive installation deviation of rails; inconsistent speed / unsynchronized start‑up of separately‑driven motors; inconsistent driving‑wheel diameters; poor wheel installation accuracy; deformation of metal structures.

3. Crane Electrical System

3.1 Power Distribution Requirements

  1. Main power switch: Each crane shall be fitted with a main power disconnection switch. Acceptable types: disconnector, isolator combined with switching device, circuit‑breaker with isolating function. They shall comply with GB/T 5226.32‑2017 clauses 5.3.2 and 5.3.3.
  2. Main circuit‑breaker: Installed in main power circuit. It shall feature magnetic trip function. Rated current shall exceed crane rated operating current; magnetic trip setting shall exceed maximum operating current. Its breaking capacity shall handle short‑circuit current occurring on the crane.
  3. Main power circuit shall preferably be equipped with contactors capable of breaking power circuits.
  4. Emergency‑stop devices:
    • One or more emergency‑stop switches operable from control stations shall be provided. In emergency conditions, they shall stop all motion drives. Partial‑stop exceptions are permitted for certain hazardous drives, e.g. ground‑operated gantry cranes may only stop crab/travel motion via ground‑mounted E‑stop.
    • Emergency‑stop shall consider load‑dropping risk circuits such as electromagnetic chucks and pneumatic holding devices.
    • Emergency‑stop push‑buttons shall be red and non‑auto‑reset.

3.2 Electrical Protection Requirements

3.2.1 Motor Protection

Motors shall adopt one or more of the following protection options according to motor type and control mode:

  1. Instantaneous or inverse‑time over‑current protection; instantaneous trip setting ≈ 1.25 × maximum motor starting current.
  2. Thermal sensing elements embedded inside motors.
  3. Thermal overload protection.

3.2.2 Circuit Protection

All circuits shall be protected against over‑current caused by short‑circuit or earth fault. Instantaneous protective devices shall break circuits upon short‑circuit / earth fault. For small‑cross‑section long control / auxiliary circuits where earth‑fault current cannot trigger instantaneous trip, add thermal trip to prevent insulation burnout.

3.2.3 Phase‑loss & phase‑reversal protection

Phase‑loss and phase‑reversal protection shall be fitted when phase abnormality may create hazards.

3.2.4 Zero‑position protection

Every motion mechanism shall have zero‑position protection. After shutdown caused by fault or power loss, mechanisms shall not restart automatically upon power restoration. Manual reset of controller to zero position is required before restart.

3.2.5 Undervoltage protection

After power supply interruption, safety‑related loads and equipment that shall not auto‑start shall remain de‑energized to prevent unintended restart after power recovery.

3.2.6 Stator abnormal power‑loss protection for hoisting mechanism

Hoist motor shall be equipped with stator abnormal power‑loss protection. If motor runaway occurs due to fault of speed governor or forward/reverse contactors, brakes shall apply immediately.

3.2.7 Overspeed protection

Overspeed switches shall be installed for hoisting mechanisms and unbalanced luffing mechanisms where overspeed creates risks. Typical setting range: 1.25‑1.4 × rated lowering speed, subject to control‑system performance.

3.2.8 Lighting & Signals

  1. Lighting and signal circuits shall be independent, fed from upstream side of main circuit‑breaker / main isolating switch. Lighting & signals shall remain energized after main switch is switched off. Short‑circuit protection shall be fitted for main branch and sub‑branches.
  2. Illumination for operator cabin and electrical room: minimum 30 lx. Supplementary lighting may be arranged below crane girders for working areas.
  3. Fixed‑type lighting voltage ≤ 220 V; portable hand‑held lighting voltage ≤ 36 V.
  4. For outdoor cranes with overall height ＞ 30 m: install red obstruction lights at ends if no higher surrounding structures exist, risk of collision exists, or crane obstructs air/water traffic. Obstruction lights shall not be cut off when crane stops working.
  5. Indication for main‑power ON/OFF status; fault and alarm signals as required. Critical indicators shall be visible and audible for operators and relevant personnel.

3.3 Crane Safety Monitoring & Management System

This system is part of crane electrical control system, not an independent product. It monitors crane operation and records key operating parameters and safety status.

Display requirements:

  1. Display information shall be clearly readable under various environmental conditions, without glare or obstruction of operator’s view.
  2. Real‑time display of crane operating status via graphics, images, charts and texts. Simplified Chinese characters shall be supported.
  3. Acoustic‑optical alarm devices shall deliver clear warning signals for crane operators and personnel within hazard zones.