INDO – GERMAN MODIFICATIONS
RDSO has approved 13 modifications (7 are on brake gear, 4 on bogie and 2 on buffers) to be carried out as per Indo-German project to increase the POH periodicity and life of the components.
The reasons behind the modifications and intended benefits are given below.
Modification done on Brake gear pins and Bushes:
- In earlier design Acetal bushes were used in the brake rigging. Since these bushes were cracking and wearing at faster rate, results in frequent replacement of Acetal bushes during maintenance and POH.
- Hence to prevent frequent replacement of bushes, the brake gear bushes are replaced with Nylon 66 material. To increase the life of the bushes further, the brake gear pins are finished with N-5 ground finish and coated with Chromium to the thickness of 25 microns. The purpose of coating the pins with Chromium is that it is very good wear resistant material.
- After the above modifications on the bushes and pins, the pins practically show no wear during POH and therefore can be reused.
Modification on brake shoe and shoe key:
It is seen that the uneven wear of the brake blocks is due to the faulty design of the brake shoe key and brake head. The brake shoe key is functioning well as long as it is inserted from the top.
For design reasons, the key cannot be inserted from the top in the ICF bogies, as there is insufficient space. If the key is inserted from below, then on application of brakes it will slide downwards and loosen the binding (The slack between the key and shoe increases.)
The present brake shoe head permits the brake blocks to move up and down along the force of friction on the wheel tread due to the large clearance present between end stoppers on brake block and brake head ribs. Due to the free movement the brake block crushes the base plates and ends of ribs during brake application.
So to overcome the above problems on Key and the brake head, they have been suitably modified to have a snug fitting between the brake head and the brake block. The modified design arrests the movements of brake blocks to the minimum. It ensures square striking of brake block surface on wheel tread during brake application.
For design reasons, the key cannot be inserted from the top in the ICF bogies, as there is insufficient space. If the key is inserted from below, then on application of brakes it will slide downwards and loosen the binding (The slack between the key and shoe increases.)
The present brake shoe head permits the brake blocks to move up and down along the force of friction on the wheel tread due to the large clearance present between end stoppers on brake block and brake head ribs. Due to the free movement the brake block crushes the base plates and ends of ribs during brake application.
So to overcome the above problems on Key and the brake head, they have been suitably modified to have a snug fitting between the brake head and the brake block. The modified design arrests the movements of brake blocks to the minimum. It ensures square striking of brake block surface on wheel tread during brake application.
Modification on brake beam safety bracket: Brake beam safety straps provided previously ensures only marginal security. It often breaks while supporting the brake beam in case the hanger pin breaks. Hence to prevent dropping of brake beam on run in case if the brake gear pin fails, a new design of Safety wire rope is introduced in place of the safety strap.
Modification on brake hanger:
When the wheel diameter is maximum, the centre line of brake block coincides with the centreline of wheel. In this condition, the brake block gives lateral and radial force along the centre line of wheel during brake application.
- But when the wheel diameter reduces, the buffer height also reduces. To bring back the buffer height to normal a packing piece is given between the Dashpot and the Axle box.
- Generally whenever the wheel diameter reduces to 839 mm, a 38 mm packing is given between the dash pot and the Axle box, thereby raising the brake block by 38 mm from the centre of the wheel. In this condition, the brake block force is not along the centre line of the wheel but on the upper half of the wheel during brake application and there is a tendency for the brake block to mount over the wheel due to the dragging of brake block by the wheel in the direction of wheel movement.
- To prevent the mounting of brake blocks over the wheels whenever lesser diameter wheels are used, the length of the brake hanger is increased from 205 mm to 235 mm in order to make the centre of brake block to coincide with wheel centre.
Modifications done on the Z-lever hanger pin:
- The flat size of the hexagonal portion of the lever hanger pin was 46 mm, which is smaller than that of the bush used for the Z shaped lever. This resulted in the bushes getting damaged due to the rubbing action against of the hexagonal portion of the lever pin No.3.
- To prevent the damages to the lever bushes and also working out of bushes, the flat to flat of the hexagonal portion is increased from 46 mm to 55 mm.
Modification done for articulation arrangement:
- In ICF coaches it was found that the spindle rod of SAB often broke due to bending of spindle while negotiating a curve. The play for the SAB is only in the vertical plane and not in the horizontal plane. Secondly sufficient support is also not provided leading to high oscillations on bad tracks. To overcome the above said defect, an articulation bracket is provided only for vacuum braked stocks, which facilitates the SAB to move laterally along with the bogie whenever it is negotiating a curve.
Modification done on Equalising stay:
- The 13 tonne bogies stay pins were often found in bent condition and have to be removed only by gas cutting, but there was no problems noticed in the 16 tonne bogies. It was also observed during POH that about 80% of stay rod pins of 13 tonnes bogies are received in bent and 40% have to be removed by gas cut.
- The reason is that the diameter of the pin used for 13 tons bogie is only 24 mm when compared to 31 mm diameter pin used in 16 tons bogies.
- To prevent frequent replacement, the equalizing stays have been standardized with 16 tons capacity for all the newly manufactured coaches.
Modification on Axle box crown bolt:
- During POH, it was found that the axle box housing bolt arrangement has to be replaced due to damages and also during maintenance difficulties were experienced to maintain a constant crown clearance between the bogie frame and the axle box due to working out of bolts. This is mainly due to hitting of the bolts on the run.
- To overcome the above problem, a rubber stopper is provide with the bolt to dampen the shock, to enable to adjust the clearance under the operating condition in case of wheel wear and fatigue of springs. It also enables for the easy replacement of the rubber pads without lifting the coach.
Modification done in the axle guide arrangement:
- Often the guide cap in the axle guide assembly is found dropped. The normal practice is to weld a strip with a bolt 94 and tighten the guide bush at the bottom with a nut. During run, this also drops down due to the vertical and lateral oscillation. The dropping of guide cap results in damages to the threaded portion at the bottom of the guide, since it comes in contact with the dashpot directly.
- To overcome the above problems, the guide cap is completely eliminated by carrying out two modifications on the guide. The purpose of providing the guide cap is to allow the oil from dashpot into the guide with restrictions and also to secure the guide bush in position.
- To allow the oil from dash pot into the axle guide a 5 mm plate with perforated holes is welded with the axle guide at the bottom from inside.
- A circlip is used to secure the guide bush in position.
Modification done on the headstock:
- In the earlier design the vertical pitch hole distance on the headstock for fitment of buffer was only 120 mm. As the resisting area was reduced due to the lesser pitch hole distance, the headstock were getting crack. 95
- To prevent cracking of headstock, the vertical pitch hole distance for buffers on the headstock is increased from 120 mm to 170 mm
Modification on Buffer rubber pads:
- In the earlier design, 14 pads of 20 tonne-inch capacities were being used with a dividing plate interposed between them. But it was found that mixing of old and new pads lead to damage to the pads, as seating was not uniform and also leads to headstock failures. To avoid this, modified rubber pads of 40 tonne-inch capacities (1030 kg-m) of 32 mm thickness are recommended. This leads to reduction in the maintenance required for the buffer in open line.
- The modified rubber pads have increased contact area between the pads, to prevent damages to the rubber pads.
Dimensional check report for the bogie frame:
Modification done on the brake beam of Air braked stock:
- It was found that the designed tolerance was not being maintained in the bogies during manufacturing and to avoid failure of axle guides at the joint, a dimensional check list is separately formed for non-AC, AC and power cars.
Modification done on the brake beam of Air braked stock:
- Often it was found that the brake beam was failing near the central stiffener because of corrosion due to water accumulation. Also there was no provision for hanging the brake beam with a safety wire rope from bogie headstock. To avoid this, now stiffeners of 3.15mm and drain holes are provided. As there was no proper testing procedure for accepting the brake beams, a testing procedure also is suggested.
Testing of Brake Beam:
Apply a tensile load of 12 tonnes between the brake shoe ends and the floating lever end. On 12 tonnes load, an elastic deformation of 3mm is permitted. On removal of load, the truss beam should come back to its normal position. However a permanent deformation of not more than 0.5 mm is permitted.
LATEST MODIFICATION ON COACHES
- Change in securing arrangement of anchor link, similar to that of Fiat Bogie.
- Use of Hopper type Shutters in place of banjo type frosted Shutters in toilets. Provision of ventilator with Arc shape fins with LAV for proper circulation of Air.
- Provision of Resetting Handle with wire rope on end panel for the resetting of ACP from ground itself and APD for Guard van valve and its handle. Increase of vent hole dia in PEAV from 4 to 8 mm.
- Reduced width of brake shoe head by 5 mm from inside.
- Crash worthiness of the coaches is increased by making following modification;
- Mirrors are rounded at the edges, berths are rounded in the corners, side seat backrest holding arrangement is shifted to the inner side, sunk in type mirror shelf, modified berth chain, etc.
