CBC Coupler
1. Brief Description :

    CBC (Centre buffer coupler)is a device for connecting one rolling stock with another in a train formation. It is centrally located at both ends of the rolling stock. It allows the vehicles to move independently to accommodate track curvature and elevation change while remaining connected (coupled) together.

    With CBC, the centre buffer coupler combines the draft and buffing gear in one. It is able to transmit both the tensile and the compressive forces.Indian Railways uses AAR type centre buffer couplers. The draft capacity of the AAR coupler depends on the strength of knuckle, which is the weakest link in the assembly.

    With CBC, coupling action between wagons is automatic. Shank/ Draw bar is cast together with the coupler head. Tail end of the draw bar is connected to draft gear through a central pin. Draft gear fits into the draft gear pocket of coach/ wagon and absorbs energy both in buffing and draw modes, with a designed limit of stroke in each mode. Absorption of energy (impact) is achieved through the rubber pads provided in the draft gear.

    The maximum permissible free slack in the draft gear is 25 mm, beyond this it shall be removed and reclaimed or condemned. The knuckle type centre buffer coupler has been adopted for BOX, BOXN and other new design of wagons. The working strength of CBC coupler is 120 tonnes.

    CBC also has a transition version called "Transition Coupler" which incorporates a screw coupling and a pair of side buffers to permit attachment with wagons fitted with screw coupling.

2. Advantages :

    • Automatic Coupling type. Less time is required for coupling.

    • Safe for shunting of staff.

    • Uncoupling is easy and less efforts are required.

    • Feature to prevent de-coupling in the event of derailment/accidents.

    Fig.: 1
    Fig.: 2
    Fig.: 3
3. Main Components of CBC :

    • Coupler body : Coupler head,Coupler shank, Coupler tail,Coupler guard arm,Coupler lock chamber, Coupler shank wear plate.

    • Knucle: Knuckle nose,Knuckles lock face,Knuckle front face,Knuckle thrower / Kicker, Knuckle pin.

    • Support device and wear plate.

    • CBC operating handle.

    • Yoke Pine

    • Draft Gear.

    Fig.4: H-Type CBC Couplers used in LHB Coaches
4. Defects in CBC :

    • Knuckle pin bent, broken or of wrong size.

    • CBC striker casting cracked more than 25 mm at any location, CBC yoke pin support plate missing or its bracket broken.

    • CBC shank cracked or bent out of alignment, CBC shank wear plate or housing worn by 10 mm Shank wear plate missing where originally fitted.

    • CBC look lift assembly so defective that the coupler cannot be coupled/uncoupled.

    • Knuckle pin APD deficient.

    • Overdue ROH/POH by more than one year.

    • Any wagon loaded more than CC or permitted excess.

5. Safety Implication while failure :

    (a) One of the failures of the coupler system having safety implication is train parting. Prescribed precautions are to be taken at the time of coupling of CBC and it is to be ensured that the lock lift levers of both the couplers are completely dropped. Items to be observed in the event of train parting are locking status of knuckles of both the couplers, whether knuckles were found locked or open, position of lock lift lever of CBC in which knuckle was found open, whether it was fully or partially dropped, and whether manual uncoupling rod was locked.

    (b) Buffer defects have significant effect on derailment proneness. The effect, basically, is due to eccentricity of buffing forces caused by such defects.

    (c) The eccentricity in buffing forces can be in:

      (i) Vertical direction, in which case Q values are affected.

      (ii) Horizontal direction, when Y values are affected.

      (iii) Inclined direction, when both Y and Q values are affected.

      Video on H-Type Coupler