3. GRUPO 1: RASGOS DE DESCRIPCIÓN FÍSICA
3.1 Información morfológica
3.1.1 Categoría gramatical
A turnout consists of four sections: Points, Crossing, Checkrails and Closure Rails.
Figure 110 – The parts of a turnout
C6-1 Points
A set of points is a fully assembled pair of switches and stockrail units with chairs, switch stops, rail brace plates and the required rodding attached to correctly operate the switches.
Points may be interlocked (that is connected by rodding to points machines and operated remotely as part of the signalling system), or non-interlocked in which case they are operated manually by levers placed next to the points.
Figure 111 - Points Closure Rails Points
Crossing
Check Rail Check Rail
Rail Brace
Bearers
Switches Plates Stockrails Heel block
Studs/switch stops
Signal Interlocking
C6-1.1 Switch
A standard switch consists of a section of rail or rail steel that has been set and machined to a design shape, then drilled to detail to accommodate gauge rod brackets and heel blocks.
When it is set against the stockrail, it directs the wheel flanges and causes the change of direction of traffic.
C6-1.1.1 Left or right hand switches
Due to the machined shape of the switches, they are classified as being either right or left hand. To identify switches, you must stand at the points looking back towards the “V”
crossing. The switch on the right is the right hand switch; the switch on the left is the left hand switch. (See Figure 112).
Figure 112 – Hand of a switch
C6-1.1.2 Switch types
Switches are produced in various sizes and types. They may be either:
• Conventional
• Undercut, OR
• Asymmetric
1. Conventional switch
Conventional switches are machined from rails and tapered down from a full rail at the heel, to a thin point that fits closely against the stock rail. They are only in use with 47kg and 53kg rail and are not used when turnouts are renewed.
In conventional switches:
o There is no machining on the stockrail.
o The switch rail is machined and vertically set to override the foot of the stockrail.
Right hand switch Left hand switch
V Crossing
Points
Conventional switches may be:
Standard
Standard switches:
o have a narrow machined point of 3mm, o have a straight stockrail.
Figure 113 - Standard Conventional switch Heavy Duty
Heavy Duty switches:
o have a machined point 19mm thick, o have a joggled stockrail,
o are used in 53kg turnouts ONLY,
o are only used where the points are in the facing direction and are subject to heavy wear.
Joggle
Housed
If heavy duty switches and joggled stockrails are used on both rails, a switch
“housing” is provided on one of the switches.
The housing is a specially machined component with a hardened checking face.
It acts as a checkrail to control the position of the wheels when they pass the joggle and switch points.
Figure 115 - Heavy duty switches with housed points 2. Undercut Switches
Switches for use with 50kg and 60kg rail have the stockrail undercut by machining to allow the switch to move partially under the head of the stockrail.
The foot of both the switch and stockrail sit at the same level.
Figure 116 – Undercut switch 3. Asymmetric switch
Switches used with 60kg tangential designs are called asymmetric. They are not machined from rail. They have a thick web and are shallower than conventional and undercut switches.
Asymmetric switches ride on a raised slide table.
Housing
Joggle Heavy duty switch
The switch rail material is forged at the heel to form the shape of the rail section so that it can be welded to the closure rail. A section is cut out from the rail foot at the heel to reduce the force required to operate the points.
It is easier to maintain adequate heel flangeway opening for a given toe opening compared with conventional and undercut switches because the asymmetric section is far stiffer then the standard section in horizontal bending.
The asymmetric shape is more stable under the wheel load.
Figure 117 - Asymmetric switch tip and rollers
C6-1.1.3 Heeled Switches
Heeled switches are switches that pivot from a gapped joint between the switch rail and the adjoining closure rail.
The heel block and fishplate at this joint are designed to allow the movement. The switch length is the total length of the switch rail.
C6-1.1.4 Flexible Switches
Flexible switches are machined from longer rails and fixed towards the end of this rail with blocks to the adjacent stockrail.
A section of the switch rail foot is removed close to the securing (heel) blocks and the switch is designed to flex over its length.
C6-1.2 Stockrails
The rail against which the switch fits is known as the stock rail. It provides support for the closed switch and become the running rail when the switch is open.
In a turnout there are two stock rails. These are identified as being left or right handed in the same way as switches and turnouts are identified.
Stockrails can be either standard full rail sections (for use with conventional switches) or machine undercut (for use with undercut and asymmetric switches).
They are curved, set and/or joggled and drilled during manufacture to suit the chairs and switch stops.
The stockrail on the turnout side of the turnout is bent or ‘set’ in front of the switch to allow the gauge lines of the standard switch.
C6-1.2.1 Front of stockrail
The distance from the point of the switch to the nearest end of the stockrail is called the
“front” of the turnout.
C6-1.2.2 Joggled Stockrail
To compensate for the extra thickness in the nose of a heavy duty switch, the stockrail is
“joggled” by approx 20mm. The setting of the joggle allows for the correct alignment of the switch and also prevents the wheel flange striking the nose of the switch.
C6-1.2.3 Housing
If heavy duty switches and joggled stockrails are used on both rails, a switch “housing” is provided as the gauge will be approx 20mm wide.
The housing is made from manganese steel rail. It acts as a checkrail to control the position of the wheels when they pass the joggle and switch points. The provision of the housing enables the joggled stockrail and heavy duty switches to be used on almost any type of layout.
C6-1.3 Heel block
Heel Blocks are cast wedges that fit in the fishing surfaces of the rail at the rear end between the stockrail and switch.
In heeled switches, the heel block and associated fishplates and bolts are designed to allow a movement of the switch blade at this point similar to a hinge. The heel blocks allow enough movement in the ‘heel Joint’ to allow the switches to be reversed from side to side. (See Figure 119).
In flexible switches there are two heel blocks attached to the end of the switch and the adjacent stockrail and closure rail. They are fabricated blocks that rigidly fix the switch rail to the adjacent rail in the correct geometric position. (See Figure 120).
It ensures that longitudinal thermal expansion and contraction of the switchblade is confined to the unrestrained portion of the switchblade that lies ahead of the anti-creep device.
Figure 119 - Heel block for heeled switches
Figure 120 - Heel block for flexible switches
C6-1.3.1 Heel centre
The heel centre is the distance between centre of the stockrail and the centre of the switch. The heel centre is located at a defined distance from the nose of the switch. At the heel centre the distance between the centre of the switch and the centre of the stockrail is always 159mm.
The heel centre is measured from the gauge face of the switch to the gauge face of the stockrail.
C6-1.4 Anti-creep device
In some tangential turnout designs there are NO heel blocks. The switch stops and the fastening systems hold the stockrail and the switch in the correct position.
In these designs an anti-creep device is fitted between each switchblade and its matching stockrail near the heel end of the switch rail. This is designed to prevent differential
Heel centres
longitudinal movement of the switchblades relative to their stockrails caused through rail creep.
Figure 121 – Anti-creep device
C6-1.5 Cant reducing plates
Cant reducing plates are used on the approaches at either end of the turnout. They provide a gradual reduction of rail inclination from 1:20 on the open track to the flat track plates used through turnouts.
Figure 122 - Cant reducing plates
C6-1.6 Chairs
A chair is a flat plate that is attached with a bolt through the web of the stockrail. Chairs are used to support the points assembly on the bearers. The type of chair is identified by lettering on the end of the plate eg. SR, A, B, C, D.
With undercut switch designs used with 60kg and 50kg switches, the plates are flat under the switch/stockrail.
Asymmetric switches use a different type of fastening and support system. They do not use chairs or rail brace plates.
With the 53kg and 47kg switch designs using standard or heavy duty switches, the plates under the first 3 bearers from the point of the switch have a raised table to support the switch.
1. SR Chairs
Stockrail or S/R chairs are used on the two bearers immediately in front of the switches. Their purpose is to provide additional support for the stockrail.
Figure 123 - “SR” chair 2. A, B, C and D chairs
When a switch is manufactured, it is bent upwards, or vertically set, to allow more steel to be retained in the foot of the switch while still allowing it to close up correctly.
This vertical set equals 9 mm at the point of the switch. Correspondingly, the chair that is placed on the timber immediately under the point of the switch is provided with a 9 mm raised table upon which the switch slides. This chair is called the ‘A’ chair.
Figure 124 - A, B, and C chairs under a standard switch
The next chair back is called the ‘B’ chair. The ‘B’ chair has a table 6 mm tall.
‘C’ chairs are next with a 3mm table.
‘D’ chairs follow and are used as far back as the heel block. ‘D’ chairs have no raised table. The base is flat.
Figure 125 - “D” chair
C6-1.7 Rail brace plates
Rail brace plates are used under the switch assembly. A cast rail brace is attached to the switch assembly and then bolted to the stockrail.
The rail brace contacts the underside of the head and the top of the foot of the stockrail. It is used for stockrail support and to maintain the gauge.
They may be used in place of “A” and “B” chairs or in places “A”, “B”, “C” and “D” chairs on some newer turnouts.
The plates are identified by a number stamped on the end of the plate.
Figure 126 - Rail brace and plate
C6-1.8 Split plates
Split plates are another type of fastening system used to hold the rails in place.
Figure 127 - Double shouldered flat plates and split plates
C6-1.9 Switch plates and fastenings in tangential turnouts
Each turnout manufacture has there own design of plates and fastenings for switches and stockrails. They support the stock rail resiliently without interfering with switch rail movement or maintainability.
TKL Rail uses the “Schwihag System” of inner stockrail bracing clips and special elevated side tables.
PRE uses the PVT Clip – inner stock rail fastening.
VAE uses their own patented switch fastening system
Figure 128 - Asymmetric switch sitting on raised plates
C6-1.10 Switch stops (switch studs)
Switch stops are made from castings, rolled angle section or extended bolts. They are bolted to the web of the stockrail through the chairs or rail brace plates. When the switch is in the closed position, they make contact with its web, providing support for the switch as it is subjected to the thrust of wheel flanges.
When replacing switch stops, make sure you use the correct size. The stops get longer towards the heel.
• If the stops are too long, they will not allow the switch to close.
• If the stops are too short, they will not support the switch.
Figure 129 – Switch stops
C6-1.11 Switch rollers
Special rollers, which are either built into the bed plates or clamped to the stockrail and sit under the switch, are sometimes used to assist flexible switches in opening and closing.
Figure 130 – Switch roller systems from different manufacturers
C6-1.12 In-bearers
Hollow steel turnout bearers that are installed instead of the first two bearers at the switches. Points detection equipment and interlocking can be installed inside the in-bearer. This means that the bays between the bearers are clear of obstructions and can be tamped.
Figure 131 – Steel In-bearers
Figure 132 – Steel In-bearers in track with signalling gear installed
C6-2 Closure rails
The closure rails form the remaining portion of the turnout. These rails are crowed to their correct radius before installation and are fastened on flat double shouldered track plates.
The closure rails on the turnout road must be laid with the correct offset from the mainline to ensure the correct radius from the heel block to the “V” crossing.
C6-3 Crossing
The next section of the turnout is the crossing. It is known as a “V” crossing. Its purpose is to provide a path for the wheel flange to travel across the point where two running rails cross over.
Figure 133 – V Crossing
C6-3.1 Theoretical point and practical point.
Theoretical point
The point where the gauge faces of the running line and the turnout rail would intersect is known as the theoretical point. The theoretical point is the start point for all turnout and crossing dimensions.
It is usually punched marked on the wing rails over the centre bolt. If, however, the punch marks are not visible, you can find the theoretical point of a straight crossing as follows:
1. Stretch a string line along the gauge faces from the front leg to back leg of the crossing. Hold the string 16mm below the running surface.
2. Stretch a second string line along the opposite gauge faces, once again from the front to back leg and hold the string at 16mm below the running surface.
3. Mark the point at which the string lines cross over or intersect. This is the theoretical point of intersection.
Figure 134 – Theoretical and Practical points Practical point
The end or “nose” of the point rail is known as the practical point of the crossing.
The gauge and the checkrail effectiveness are measured from the practical point.
C6-3.2 Crossing rate
The crossing rate is a measure of the angle made by the rail gauge faces at the theoretical point.
The larger the crossing rate, the smaller the angle, the faster the speed through the crossing.
The identifying catalogue number of the crossing is stamped on the top surface of the wing rail end along with the manufacturer’s identification. In newer crossings the information is engraved on a label attached to the web of the crossing showing details of geometry, date of manufacture, material used in the crossing and work order number (See Figure 135).
Figure 135 – Crossing identification label
The catalogue number gives details concerning the rate of the crossing, whether it-has a left or right hand point rail and whether it has the front, back or both legs curved.
Practical Point Theoretical Point of intersection
Crossing rate
Catalogue No.
Manufacture date
Crossing material Rail size
To determine the crossing angle if no identification is available:
1. Locate the theoretical point by stringlining the gauge faces of the crossing.
2. Mark this point.
3. Locate a point where the gauge faces of the point rail and wing rail separate to a distance of exactly 100mm.
4. Accurately measure the distance between this point and the theoretical point.
5. The crossing rate is equal to this measurement, divided by 100.
e.g. The distance from the theoretical point to the point where the gauge faces separate 100mm is equal to 1050 mm.
Therefore, crossing rate = 1050/100 = 10.5.
crossing rate = 1:10.5.
Figure 136 – Crossing rate
C6-3.3 Type of Crossing
There are 2 types of V crossings
• Fixed crossings
• Switchable crossings
C6-3.4 Fixed crossings
These crossings have a wheel flange gap in both rails. Wheel transfer of fixed crossings depend on matching wheel and rail profiles. Fixed crossings are used in conjunction with check (guide) rails to provide lateral guidance in the crossing area.
Fixed crossings may be:
• Fabricated crossings.
• Rail Bound Manganese crossings.
• Compound crossings
• Fully cast crossings
100mm 1 10.5 100mm
1050mm
Theoretical intersection of crossing
Housed rail Point rail
Wing rail Wing rail
C6-3.5 Fabricated crossings
The component parts of the crossing are the wing rails, the point rails and the housed rail.
A fabricated “V” crossing comprises a Vee (made up from the point rail and the housed rail) and 2 wing rails fabricated from sections of rail that have been machined and fitted together with chocks and high tensile fastenings. Certain chocks will be set with epoxy paste.
C6-3.5.1 Hand of fabricated crossings.
All fabricated crossings are also referred to as being either right or left hand. To identify a crossing, stand at the back of the crossing and look toward the practical point.
A right hand crossing is one where the point rail is on the right, a left hand crossing where the point rail is on the left.
A left hand crossing has the point rail on the left hand running rail of the turnout (the rail that connects to the left hand switch).
As a general rule, the point rail should always be laid for the main line or the line carrying the most traffic. This is due to the point rail being more durable than the housed rail.
Figure 137 - Fabricated crossing
C6-3.6 Compound Crossing
A compound crossing is a crossing V point that is manufactured from a single cast nose that is welded to head hardened rails to complete the V. This replaces the point/housed rails in a fabricated crossing.
Compound crossings may be manufactured from manganese steel, chrome vanadium alloys or other materials.
C6-3.6.1 Compound Manganese Crossing
A Compound Manganese crossing is a compound crossing V point that is manufactured from a cast manganese nose which is explosively hardened and flashbutt welded to head hardened rails to complete the V.
Point rail Housed rail
Wing rails Chocks
Left hand crossing
C6-3.6.2 Chrome Vanadium crossing
A Compound Chrome vanadium crossing is a compound crossing V point that is manufactured from a cast chrome vanadium steel nose which is welded to head hardened rails to complete the V.
Figure 138 - Chrome vanadium crossing
C6-3.6.3 Identifying crossings
Compound crossings are identified by the following code on the crossing identification label (See Figure 135).
MN - Compound Manganese (MANG also used in some).
CV - Chrome Vanadium (CHV also used in some).
If there is no plate on the crossing, or the plate is unreadable, the type of material can be established using the following guidelines.
1. If the nose is manufactured from two standard rail sections, machined and fitted together it is a fabricated crossing (normal rail steel).
2. If the nose is manufactured in one piece it will be either Compound Manganese or Chrome Vanadium.
3. If the one piece nose was installed in track before 1999 it will usually be Chrome Vanadium.
4. If the one piece nose was installed in track since 2000 it will usually be Compound Manganese. All current “V” crossing noses are manufactured from Compound Manganese.
5. Chrome Vanadium crossings have the crossing chocks welded to the crossing
5. Chrome Vanadium crossings have the crossing chocks welded to the crossing