ICF Bogie

Bogie frame

The frame of the ICF bogie is a fabricated structure made up of mild steel. Main sub-assemblies of bogie frame viz. side frames, transoms, headstocks, longitudinal forms the skeleton of the bogie frame. The sub assemblies are fabricated from flanges, webs, channels and Ribs by welding process. Various types of brackets are welded to the frame for the purpose of primary and secondary suspension arrangement, alternator suspension arrangement and brake rigging arrangement. Various brackets viz. brake hanger brackets, brake lever hanger brackets, brake cylinder fixing brackets, anchor link brackets, bolster spring suspension brackets, alternator suspension brackets, belt tensioning bracket/s, axle box guides, suspension straps are welded on the bogie frames. It involves 40 meters (app.) of welding in a single conventional bogie frame. Based on load carrying capacity per axle, the conventional bogie frames are grouped into two types. They are 13 ton bogie frame and 16 ton bogie frame. 13 ton bogie frames are being used in the bogies of all non-AC mainline coaches and 16 ton bogie frames are being used in bogies of all AC coaches, power cars and diesel multiple unit trailer coaches.

EMU Motor Coach type bogie frames, a different design of bogie frame is being used in all coaches of Electric Multiple Units (EMU) and all self-propelled coaches (motor coaches

Bogie bolster

A bogie bolster is the central section of the bogie that carries the entire weight of a coach's under frame. The bogie pivots around it using the center pivot pin. It couples to the bogie frame at each end using the secondary suspension system (typically coil springs and spring plank).

Center pivot pin

A center pivot pin is bolted to the body bolster. The center pivot pin runs down vertically through the center of the bogie bolster through the center pivot. It allows for rotation of the bogie when the coach is moving on the curves. A silent block, which is cylindrical metal rubber bonded structure, is placed in the central hole of the bogie bolster through which the center pivot pin passes. It provides the cushioning effect.

Wheel set assembly

Wheel arrangement is of Bo-Bo type as per the UIC classification. The wheel set assembly consists of two pairs of wheels and axle. The wheels may be cast wheels or forged wheels. The wheels are manufactured at Rail Wheel Factory, Chapra, Bihar or at Rail Wheel Factory of Indian Railways bases at Yelahanka near Banglore in the state of Karnataka. At times, imported wheels are also used. These wheels and axles are machined in the various railway workshops in the wheels shops and pressed together.

Roller bearing assembly

Roller bearings are used on the ICF bogies. These bearings are press fitted on the axle journal by heating the bearings at a temperature of 80 to 100 °C in an induction furnace. Before fitting the roller bearing, an axle collar is press fitted. The collar ensures that the bearing does not move towards the center of the axle. After pressing the collar, a rear cover for the axle box is fitted. The rear cover has two main grooves. In one of the grooves, a nitrile rubber sealing ring is placed. The sealing ring ensures that the grease in the axle box housing does not seep out during the running of the wheels. A woolen felt ring is placed in another groove. After the rear cover, a retaining ring is placed. The retaining ring is made of steel and is a press fit. The retaining ring ensures that the rear cover assembly is secured tightly between the axle collar and the retaining ring and stays at one place. The roller bearing is pressed after the retraining ring. Earlier, the collar and the bearings were heated in an oil bath. But now the practices has been discontinued and an induction furnace is used to heat them before fitting on the axle. The axle box housing, which is a steel casting, is then placed on the axle. The bearing is housed in the axle box housing. Axle box grease is filled in the axle box housing. Each axle box housing is filled with approximately 2.5 kg. of grease. The front cover for the axle box is placed on a housing which closes the axle box. The front cover is bolted by using torque wrench.

Brake beam assembly

ICF bogie uses two types of brake beams. 13 ton and 16 ton. Both of the brake beams are fabricated structures. The brake beam is made from steel pipes and welded at the ends. The brake beam has a typical isosceles triangle shape. The two ends of the brake beam have a provision for fixing a brake head. The brake head in turn receives the brake block. The material of the brake block is non-asbestos and non-metallic in nature.it is a safety item.

Brake head

Two types of brake heads are used. ICF brake head and the IGP brake head. A brake head is a fabricated structure made up of steel plates welded together.

Brake blocks

Brake blocks are also of two types. ICF brake head uses the "L" type brake block and the "K" type brake block is used on the IGP type brake head. "L" & "K" types are so called since the shape of the brake blocks resembles the corresponding English alphabet letter. The third end of the brake beam has a bracket for connecting the "Z" & the floating lever. These levers are connected to the main frame of the bogie with the help of steel brackets. These brackets are welded to the bogie frame. L Type are low friction Composite Brake Block and K Type are high friction Composite Brake Block.

Brake levers

Various type of levers are used on the ICF Bogie . The typical levers being the "Z" lever, floating lever and the connecting lever. Theses levers are used to connect the brake beam with the piston of the brake cylinder. The location of the brake cylinders decides whether the bogie shall be a BMBC Bogie or a non BMBC Bogie. Conventional bogies are those ICF bogies in which the brake cylinder is mounted on the body of the coach and not placed on the bogie frame itself.

Brake cylinder

In an ICF BMBC Bogie, the brake cylinder is mounted on the bogie frame itself. Traditionally, the ICF Bogies were conventional type i.e. the brake cylinder was mounted on the body of the coach. However, in the later modification, the new bogies are being manufactured with the BMBC designs only. Even the old type bogies are being converted into BMBC Bogies. The BMBC bogie has many advantages over the conventional ICF bogie. The foremost being that, since the brake cylinder is mounted on the bogie frame itself and is nearer to the brake beam, the brake application time is reduced. Moreover, a small brake cylinder is adequate for braking purpose. This also reduces the overall weight of the ICF bogie apart from the advantage of quick brake application.

Primary suspension

The primary suspension in an ICF Bogie is through a dashpot arrangement. The dashpot arrangement consists of a cylinder (lower spring seat) and the piston (axle box guide). Axle box springs are placed on the lower spring seat placed on the axle box wing of the axle box housing assembly. A rubber or a Hytrel washer is placed below the lower spring seat for cushioning effect. The axle box guide is welded to the bogie frame. The axle box guide acts as a piston. A homopolymer acetyle washer is placed on the lower end of the axle box guide. The end portion of the axle box guide is covered with a guide cap, which has holes in it. A sealing ring is placed near the washer and performs the function of a piston ring. The axle box guide moves in the lower spring seat filled with dashpot oil. This arrangement provides the dampening effect during the running of the coach.

Dashpot arrangement

The dashpot arrangement is mainly a cylinder piston arrangement used on the primary suspension of Indian Railway coaches of ICF design. The lower spring seat acts as a cylinder and the axle box guide acts as a piston.

The dashpot guide arrangement has the following main components:

Lower Spring Seat Lower Rubber Washer Compensating Ring. Guide Bush Helical Spring Dust Shield. Circlip. Dust Shield Spring. Protective Tube Upper Rubber Washer. Axle Box Guide Screw with sealing washer The axle box guide (piston) is welded to the bottom flange of the bogie side frame. Similarly, the lower Spring seat (cylinder) is placed on the axle box housing wings forms a complete dashpot guide arrangement of the ICF design coaches.

Axle box guides traditionally had a guide cap with 9 holes of 5mm diameter each; however, in the latest design, the guide cap is made an integral part of the guide. Approximately 1.5 liters of dashpot oil is required per guide arrangement.

Air vent screws are fitted on the dashpot for topping of oil so that the minimum oil level is maintained at 40mm.

Traditionally, rubber washers have been used at the seating arrangement of the primary springs of the axle box housing in the ICF design passenger coaches on the Indian Railways. The rubber washer is used directly on the axle box seating area. the lower spring seat sits on the washers. The lower spring seat is a tubular structure and 3/4 section is partitioned by using a circular ring which is welded at the 3/4 section. On the top of spring seat, a polymer ring called NFTC ring sits. The primary spring sits on the NFTC ring. The lower spring seat plays the role of a cylinder in the dashpot arrangement and is filled with oil. In the dashpot arrangement, the top portion is called the axle box guide. The axle box guide is welded to the bogie frame. The axle box guide works as a piston in the Lower spring seat filled with oil. This helps in damping the vibrations caused during running train operation.

The axle box guide, which is welded to the bogie frame has a polymer washer (homopolymer acetal guide) bush fixed at the head. A polymer packing ring and a guide ring is attached with the Acetal guide bush. These two components act as piston rings for the axle box guide. In order to ensure that the packing ring and the guide ring retain their respective place, a dashpot spring is fixed which applies continuous pressure on the piston ring.

The bottom of the axle box guide has a guide cap with perforations so that during the downward movement of the axle guide in the lower spring seat, the oil in the dashpot rushes in the axle box guide. This provides the dampening of vibration in a running coach.

The guide cap is fixed with the help of a steel circlip. However in the new design of Axle box guide, the guide cap is welded with the guide assembly and hence the need of a guide cap has been eliminated. The complete guide and lower spring arrangement is covered with a dashpot cover also known as protective tube. The protective tube has a circular ring over it called the dust shield which prevents the ingress of the dust in the cylinder piston arrangement of the dashpot.

Spring seating

As described above, the rubber washers sit directly on the axle box spring sitting area. Earlier,wooden washers were used. However, with the development of technology, rubber washers replaced wooden washers. Presently, RDSO, Lucknow which is a Research, Design & Standardization organization for the Indian Railways developed a new design for washers made from a polymer commonly known as HYTREL. Hytrel polymer is a product of M/s DuPont .

The reason for replacement of the rubber washers with the hytrel washers was that the rubber washers were not lasting for the full Periodic overhaul cycle of the Railway Coaches which was one year. The washers also had to be replaced in the coaching maintenance depots leading to lifting and lowering of coaches.

Introduction of Hytrel washers was considered a breakthrough in the ICF dashpot design. However, the mass scale replacement of the rubber washers by Hytrel washers without adequate trials lead to massive failure of the axle Box housing.

The hardness of the washers as per the specified limits was to be 63+- 5 Shore D hardness. Another parameters was the load deflection characteristics of the washers.

A study was carried out on a major workshop on Indian Railways and it was found that the washers were having a hardness more than the specified limits. Moreover, the load deflection characteristic of the washers were also not found to be in line with the desired specification.

Within 6 months of provision of Hytrel washers on all the main line coaches, the failure of Axle box housing increased. The reason was the axle box wing cracks. Hence on examination of the failed axle boxes, it was noticed that the Hytrel washers were forming a deep groove of 4 to 8mm on the seating area of the axle box spring seating. They washers were also increasing the diameter of the spring seating due to continuous hitting of the raised section of the sitting area.

The coaches come to the workshop once in a year. During examination of these coaches, it was noticed that the Hytrel washers have not only damaged the axle box housing but also the lower spring seat as well as the Protective tube.

To prevent such damage, RDSO, Lucknow issued a guideline asking the Railways to provide a delrin liner below the Hytrel washers. However, it was indicated that these liners are to be provided only on new coaches and in coaches in which new wheels are fitted.

A look at the drawing of the dashpot arrangement will suggest that this problem is universal for all the coaches, whether a new coach or an old coach. Moreover, the provision of the liners below the Hytrel washers will not stop the damage to the lower spring seat and the protective tube.

Problem of oil spillage

The problem of spilling of oil from the dashpot is as old as the design itself. Numerous design changes have been implemented in the last many years however, the problem of oil spillage is still a challenge.

The cylinder piston arrangement of the dashpot, i.e. the Lower Spring seat and the axle box guide is not fully sealed due to the limitation of the design and practical applicability. Its design provides that when a vertical vibration occurs during the movement of the railway coach, the axle box guide moves down. The downward movement of the Axle box guide puts pressure on the oil in the lower spring seat. The oil rushes up. However, since there are holes in the guide cap, the oil passes through these holes into the hollow body of the axle box guide. This helps in dampening the vertical vibrations. The axle box guide displaces the oil in the lower spring seat and pushes it upwards. Since, only part quantity of oil is able to move up in the hollow portion of the axle box guide, the balance displaced oil moves up.

As per correct maintenance practice, it is to be ensured that the hole in the guide are in alignment with corresponding holes in the guide bush. However, this is practically difficult to maintain in the shop floor of bogie shop.

As the top portion of the lower spring seat is not sealed and only covered with the help of a protective tube also called the dashpot cover, the rising oil has a tendency to shoot above the top rim of the lower spring seat and spill out.

Oil spillage can be prevented by the following actions:

a. Change the dashpot design from the cylinder piston arrangement to hydraulic shock absorbers.

b. Increase the hole diameter from 5mm in the guide cap to more than the existing diameter. However, it must be ensured that the increased diameter of the holes of the guide cap does not lead to less dampening effect.

c. Provide a conical arrangement above the rim of the lower spring seat up to half the height of the dashpot cover. However, the clearances of the protective tube and the outer dia of the proposed conical section at the top of the lower spring seat needs to be taken care of

d. Modify the dust shield ring by incorporating a rubber component in it in such a manner that it also acts as an oil seal

e. Ensure that the hole in the guide are in alignment with corresponding holes in the guide bush

Some of these proposed modifications have already been tried out on the Indian Railways, however, the trials have not yielded a consistent positive feedback.

Buffer Height adjustment

The wheel diameter(tread) reduces due to brake application as the brake blocks rub against the wheel tread. Over a period of time, the wheel diameter reduces up to 819 mm. 819mm is the condemnation diameter for the wheels. This diameter is also not sacrosanct and is changed depending upon the supply position of the wheels. The maximum variation in the wheels on the same axle is permitted up to 0.5 mm, between two wheels of the same bogie up to 5 mm and among the four wheel sets of the same coach up to 13 mm. The diameter of a new wheel is 915 mm. Hence maximum wheel tread wear allowed is (915 mm - 819mm) = 96 mm. In order to adjust for the difference in the wheel tread, a packing is placed under the flange of the lower spring seat. This packing ring is generally made up of NFTC(Natural Fiber Thermosetting COMPOSITE) or UHMWPE (Ultra-high molecular weight polyethylene) material. The thickness of the NFTC packing ring is equal to 50% of the difference between the dia of a new wheel and the wheel in question.

Traditionally, 13mm, 26mm, 38mm, 48 mm packing rings are used. They correspond to wheel diameter of 899-864, 862-840, 839-820 and 819 mm. The correct buffer height is obtained by measuring the height of the bolster top surface from the rail level. In case the buffer height is still not obtained even after placement of the packing ring, then compensation rings are to be inserted below the axle box spring ensuring that the bogie frame height is within 686 + - 5 mm.

Secondary suspension

The secondary suspension arrangement of the ICF bogies is through bolster springs. The bogie bolster is not bolted or welded anywhere to the bogie frame. It is attached to the bogie frame through the anchor link. The anchor link is a tubular structure with cylindrical housing on both the ends. The cylindrical housings have silent blocks placed in them. The anchor link is fixed to the bogie bolster and the bogie frame with the help of steel brackets welded to the bogie bolster and the bogie frame. Both the ends of the anchor link act as a hinge and allow movement of the bogie bolster when the coach is moving on a curved track.

Lower spring beam

The bolster springs are supported on a lower spring beam. The lower spring beam is a fabricated structure made of steel plates. It is trapezoidal in shape with small steel tubes on each end. The location of the bolster spring seating is marked by two circular grooves in the center. A rubber washer is placed at the grooved section. The bolster spring sits on the rubber washer. The lower spring beam is also a free-floating structure. It is not bolted or welded either to the bogie frame or the bogie bolster. It is attached to the bogie frame on the outside with the help of a steel hanger. They are traditionally called the BSS Hangers (Bogie Secondary Suspension Hangers). A BSS pin is placed in the tubular section in the end portion of the lower spring beam. A hanger block is placed below the BSS pin. The BSS hanger in turn supports the hanger. This arrangement is done on all the four corners of the lower spring beam. The top end of the hanger also has a similar arrangement. However, instead of the BSS pin, steel brackets are welded on the lower side of the bogie frame of which the BSS hanger hangs with the help of hanger block. This arrangement is same for all the four top corners of the hangers. Hence, the lower spring beam also become a floating member hinged to the bogie frame with the help of hangers on the top and the bottom. This allows for the longitudinal movement of the lower spring beam.

Equalizing stay rod

The inner section of the lower spring beam is connected to the bogie bolster with the help of an equalizing stay rod. It is a double Y-shaped member fabricated using steel tubes and sheets. The equalizing stay rod is also hinged on both the ends with the lower spring beam as well as the bogie bolster with the help of brackets welded to the bogie bolster. They are connected through a pin making it a hinged arrangement.