Briefs on CASNUB Bogies
CASNUB bogie consists of two cast iron frames, floating bolster, mild steel spring plank, nested springs, and friction snubbers. Bolster is supported on the side frames through two nested of springs. Two cast iron steel frames are connected by spring planks. Frictional snubber acts as a frictional damper, which dampens the oscillations. Frictional snubbers provide damping action proportional to load.
CASNUB bogie suspension system is two tier suspension system. The bogie suspension is at the bolster level only. If consists of two cast steel side frames, connected by riveted mild steel spring planks. Suspension system is secondary suspension system. Load transfer from bolster to side frames through spring in secondary system and then to axels (wheel set) through axle bearings, elastomer pads and adopter. In secondary suspension system consists of nested helical springs, friction snubbers and bolster. As there is no primary suspension system, the spring plank is subjected to bending and torsion during the wheels trying to adjust, for negotiating track twist. The steel-floating bolster is supported on the side frame through two nests of springs which contains friction snubbers to control oscillations. Friction snubbers are not designed for vertical loading.
In CASNUB bogie load transmission from wagon takes place through central pivot. Tractive and braking forces are transferred through central pivot pin. While bogie negotiating curve free rotation is achieved by side bearers.
The CASNUB bogie assembly consists of the following components: Wheel set with Cartridge Bearing, Adapter, retainer bolt & side frame key assembly, Side frames with friction plates, Bolster with wear liners, Spring plank, fit bolts & rivets, Load bearing springs and snubber springs, Friction shoe wedges, Centre pivot arrangement comprising of Centre pivot top, Centre pivot Bottom, Centre pivot pin, Centre pivot retainer & locking arrangement, Side Bearers, Elastomeric Pad, Bogie Brake Gear & Brake Beam.
Function of each component of CASNUB bogie
Wheel set with Cartridge Bearing - The initial batch of CASNUB bogie was fitted with cylindrical roller bearing axle box and matching wheel set. However standard AAR taper cartridge bearings have been subsequently standardised for these bogies.
Central Pivot & Pivot Pin - Load from wagon is transported to bolster through central pivot which is provided at the center of bolster. Wagon when negotiating a curve and turnouts bogie rotates about central pivot. Central pivot provides relative rotation of bogie frame in the horizontal plane of wagon which avoids development of flange forces causing persistent angular run. Braking and tractive forces are transferred to bogie through pivot pin.
Side Bearer - The two bogie side bearers are fitted at a distance of 1940 mm and 970mm from the center of the bogie. The bogie side bearer is welded along its length of top plate on the bolster 12 mm thick. At the location of side bearer, the bolster plate has been strengthened from below. Different types of side bearers used in CASNUB bogie are - Roller type bearer housed in cast iron steel housing riveted on the bogie bolster, Constant contact type rubber pads & Helical spring side bearer. The main funtion of side bearer - Oscillations are developed due to unevenness of the track as a consequence of this bolster also oscillates. During oscillations load is eccentric. And this eccentric load is taken by side bearers. Bogie while negotiating curve rotates about pivot pin, therefore side bearers provides smooth rotation bogie in horizontal plane.
Floating Bolster - Cast iron floating bolster, nested springs, spring plank and friction forms the secondary suspension system. Load transmission takes place from the wagon to side frames through bolster. Bolster forms the bogie suspension system.
Axle Box - Axle box consists of cartridge bearings. Axle bearings are provided for free ration of axles.
Brake Rig & Brake Shoe - Brake rig and brake shoes ensures application of brakes equally on two wheels of axle. Brake rigs ensures application of brakig force without eccentricity.
Spring Plank, Fit Bolts & Rivets - Two cast iron frames are held in square position by spring plank plates, fit bolts and rivets. Bears the main helical springs. It transfers the loads from bolster to side cast iron frame. Provides rigidity to bogie frame. Spring plank plates are rigidly fixed to side frames by fit bolts and rivets. Two side frames of a bogie are held in correct position by means of spring plank plate.
Friction Shoe Wedges & Snubber Springs - Friction shoe wedges and snubbers springs are damping mechanism in the CASNUB bogie. The damping mechanism in the CASNUB bogie is the frictional damping mechanism (In coaching stock damping mechanism is hydraulic damper). The oscillations are developed (spring, mass and excitation force)in the wagon when it moves on the track, due to unevenness in the track geometry. These oscillations are to be dampened otherwise resonance will occur as a consequence of this high amplitude of oscillations. In CASNUB bogie friction shoe wedges and snubber springs forms the damping mechanism which acts a damper.
Central Buffering Gear - Buffing gear preforms the function of absorbing buffing impacts. Buffing forces are those forces which are developed due to application of brakes.
Main Springs in Suspension System - CASNUB bogies are fitted with two groups of long travel helical spring nests. These springs are provided to transfer the load from the bolster to side frame. Bogie during movement of the track may have to pass through track irregularities causing more impact load. Moreover rocker action of bogie due to twist in the track is avoided by providing springs.
Types of CASNUB bogies in use in IR
CASNUB-22 W, CASNUB-22 W (Retrofitted), CASNUB-22 W (M), CASNUB-22 NL, CASNUB-NLM, CASNUB-22 NLB & CASNUB-22 HS.
This bogie is of 'Wide Jaw' category. The adapter is not provided with elastomeric pad (EM Pad) where the later versions are provided with EM pad.
The shape of the bolster at the bottom is straight and centre pivot, known as IRS type, is fitted with the bolster. A simple straight pin is used to connect bolster with the body of the wagon through centre pivot.
The side bearer is of 'clearance type'. A pair of rollers is used with each bogie maintaining a nominal clearance with the body. Load is transferred to bolster only through centre pivot but not through side bearer while in motion on straight track. Side bearer share vertical load only during motion on curved track.
The brake beam used in this version is known as 'pocket type' or 'sliding type'. The brake head is integral part of the brake beam and slides in the pocket provided in the side frame.
Two types of 22 W - Integral type centre pivot & Non integral type centre pivot.
CASNUB-22 W (M)
This falls under wide jaw category same as 22 W version. The major difference in the side frame as compared to 22 W is provision of negative camber (sag at the middle of the side frame) to take care of maintaining same buffer height while using EM pad. EM pad has been introduced along with the adapter to reduce incidence of higher wheel wear as experienced with the 22 W version.
The bolster used with this bogie is same as that of 22 W version. The only difference is that 'Spherical Type' centre pivot is fitted with this bolster. Pin with castle nut and split pin is used to connect the bolster with the body of the wagon through the centre pivot.
The side bearer used with this version is metal bonded EM pad maintaining constant contact with the body. This improves the stability of the wagon as compared 22 W version.
Hanger type Brake beam assembled with separate brake head through spring loaded brake shoe adjuster is used with this version. This has the advantage in replacing brake beam without running out of the wheel set. But this design has suffered set back due problem of drooping of brake beam and grazing of brake components. This design is discontinued in the later versions of the bogie.
CASNUB-22 W (Retrofitted)
This is basically 22 W version incorporated with some of the better design aspect of 22 W (M).
The main differences with 22W are - Use of elastomeric pad with the adapter & Use of constant contact metal bonded elastomeric pad in side bearer housing.
To accommodate elastomeric pad and to maintain buffer height, the height of the adapter has been reduced. However, it is not possible to use higher diameter wheel set to maintain the buffer height. Wheel below the diameter of 956 mm is to be used with this version.
'Narrow Jaw' category. The side frame is modified to accommodate elastomeric pad similar to 22 W (M) version and pocket to accommodate sliding type brake beam hanger similar to 22W version. The side bearer, centre pivot, bolster are similar to 22W(M) version.
Centre pivot pin is locked by shackle lock unlike castle nut used in 22 W (M) version.
The adapter used with this version is of smaller size to suit to narrow jaw opening of the side frame.
This version is similar to 22 NL version, except for bolster. The shape of the bolster is 'Fish Belly' at the centre to reduce the weight of bogie. However only a marginal weight reduction compared to NL type has been possible.
Similar to NLB version in relation to dimensions of the components.
The only difference is change in material of the side frame and bolster. The equivalent carbon % of side frame and bolster in NL/NLB is 0.85%. This has resulted in reduction of weight of the bogie compared to NL version.
The weight of the NLM version bogie is 5.125 ton where as the weight of NL version is 5.5 ton.
The CASNUB-22 HS bogie has been developed for high- speed operation with maximum permitted speed up to 100 Kmph. The side frame, elastomeric pad, centre pivot, centre pivot lock, adapter are similar to NLB version.
The bolster is mostly same as NLB type except for outer gib opening and higher diameter spigot for the spring seat. The outer gib opening has been increased to 241 mm from 234 mm as in case of NLB type.
The side bearer used with this version is spring loaded constant contact type.
The spring nest in the secondary suspension used with this version is different to that of other version. The spring combination in different version of the bogies are given below:
Type of Bogies
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