Friday, March 30, 2018

LONG WELDED RAIL - Definitions

Long Welded Rail (LWR) (ACS No. 8 of 2002) is a welded rail, the central part  of which does not undergo any longitudinal movement due to temperature variations. A length greater than 250metre on Broad Gauge (BG) and 500 metre on Metre Gauge (MG) will normally function as LWR. The maximum length of LWR under Indian conditions shall normally be restricted to one block.

Continuous Welded Rail (CWR) is a LWR which would continue through station yards including points and crossing.

Short welded rail (SWR) is a welded rail, which contracts and expands throughout its length.

Notes: Normally the length of SWR is 3 x 13 metre for BG and 3 x 12 metre for MG. Provisions for laying and maintenance of SWR are contained

Breathing Length is that length at each end of LWR/CWR, which is subjected to expansion/contraction on account: of temperature variations. Usual breathing lengths in BC and MG for different types of track structures and for different temperature zones.

Switch Expansion, Joint (SEJ) is an expansion joint installed at each end of LWR/CWR to permit expansion/contraction of the adjoining breathing lengths due to temperature variations.

Buffer Rails are, a set of rails provided in lieu of SEJ at the ends of LWR/CWR to allow expansion / contraction of adjoining breathing lengths due to temperature variations. These will be laid with prior approval of Chief Engineer at locations where provision of SEJ is not permitted. Buffer rails may also be temporarily laid to facilitate maintenance/renewal operations

Rail Temperature is the temperature of the rail at site as recorded by an approved type of rail thermometer. This is different from ambient temperature, which is the temperature of air in shade at the same place.

Note: Tacks on Indian Railways have been divided into four rail temperature zones as shown in the "Map of India showing Rail Temperature zone"

Mean Rail Temperatures (tm) for a section is the average of the maximum and minimum rail temperatures recorded for the section.

Destressing is the operation undertaken with or without rail tenser to secure stressfree conditions in the LWR/CWR at the desired/specified rail temperature.

Installation Temperatures (ti) is the average rail temperature during the process of fastening the rails to the sleepers at the time of installation of the LWR/CWR.

Destressing Temperature (td) is the average rail temperature during the period of
fastening the rails to the sleepers after Destressing LWR without the use of rail
tenser. If rail tenser is used, td for all practical purposes is equal to as defined. Range of td or to shall be within the limits of rail temperature shown below:

Prevailing Rail Temperature (tp) is the rail temperature prevailing at the time when any operation connected with Destressing is carried out.

Stress-free Temperature (t0) is the rail temperature at which the rail is free of thermal stress. When tensors are utilised for the Destressing operation the work has to be carried out at tp which shall be lower than stress free temperature. The
extension to be applied by the tensor shall be calculated from the following formula: -

Expansion = La (t0 - tp)
Where 'L' is the length of segment of the rail to which the extension is applied and a is the coefficient of linear expansion of rail steel.

Rail Tensor is a hydraulic or mechanical device used for stretching the rail

Anchor Length (la) is the length of track required to resist the pull exerted on rails by the rail tensor at temperature tp .For practical purposes, this may be taken as equal to 2.5 metre per degree Celsius of (to - tp) for MG.

Hot Weather Patrol is the patrol carried out when the rail temperature exceeds td + 200C.For concret sleeper track with sleeper.

Cold Weather Patrol is the patrol carried out during cold months of the year in specified sections as per instructions of Chief Engineer.

Consolidation of track is the process of building up ballast resistance to the tendency of movement of sleeper either initially before laying LWR or making up subsequent loss of resistance by anyone of the following

i). For track structures consisting of sleepers other than concrete sleepers -
a) Passage of at least 3,00,000 gross tonnes of traffic on BG or at least 1,00,000 gross tonnes of traffic on MG when compaction of ballast is done using hand operated compactors / consolidators or rammers.

b) Passage of at least 50,000 gross tonnes of traffic on BG or at least 20,000 gross tonnes of traffic on MG or a period of two days, whichever is later, when compaction is done by means of mechanised shoulder and crib compactor.

ii) For the track structure consisting of concrete sleepers, passage of at least 50,000 gross tonnes of traffic on BG or at least 20,000 gross tonnes of traffic on MG or a period of two days whichever is later.

iii) At least one round of stabilisation by Dynamic Track Stabiliser (DTS).

iv) For newly laid LWR/CWR. at least three rounds of packing, last two of which
should be with on-track tamping machines.

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