switch rail
Analysis of Major Defects and Causes in Turnout Operation
After several years of operation, turnouts begin to exhibit various defects, mainly including:
Switch rail issues: uplift, creeping, damage, poor fit (insufficient contact);
Stock rail issues: poor frame alignment, damage;
Frog (crossing) issues: abnormal wear, guard rail damage, separation of assembled frogs;
Component issues: non-standard or failed parts.
Based on investigations, the causes are summarized as follows:
1. Typical Defects of Switch Rails
In continuously welded rail (CWR) turnouts, common defects in switch rails include: uplift of the switch rail, creeping of the switch rail, fracture of the slide plates, jamming of the limiters, poor contact between the switch rail and stock rail, damage to the switch rail, insufficient lowering value etc. These issues adversely affect the normal operation of turnouts.
Switch Rail Uplift
Defect Characteristics:
Excessive gap between the base of the switch rail head and the slide plate.
Wear marks on the anti-creep rib of the switch rail.
No clearance between the anti-creep rib of the switch rail and the lower jaw of the stock rail when closed (as shown in Figure 1).
Figure 1
Causes:
Track geometry issues: Poor vertical alignment or unsupported sections (e.g., voids or hanging sleepers) in the switch area.
Pad-related problems:
Displacement, uneven thickness, crushing, or damage of rail pads under the switch rail.
Uneven thickness of large rubber pads beneath slide plates, leading to irregular rail surface.
Uneven load distribution:
Non-uniform force on slide plates in the middle/rear sections of the switch rail.
Excessively high individual slide plates.
Handling damage:
Deformation due to improper storage, transportation, or loading/unloading.
This kind of problem appears more in 1/9 turnouts, and the 1/12 turnouts (main line turnouts) that have not been cleaned for many years will also have this kind of disease.
Consequences: In severe cases, it may lead to switch rail jamming (stuck turnout operation).
Remedial Measures:
Full-section tamping of the first few sleepers beneath the switch rail head, with synchronized tamping at the heel end.
Replacement/installation of damaged or missing rail pads, and adjustment of overly rigid slide plates.
Replacement of deformed switch rails.
Ballast cleaning and screening of the turnout area.
Switch Rail Creeping
Defect Characteristics:
Misalignment between the two switch rail tips exceeds 20mm.
Displacement of CWR (Continuously Welded Rail) turnouts exceeds 20mm in monitoring records (see Figure 2).
Figure 2
Causes: turnouts seamless locking rail temperature is not standard, turnouts in the presence of non-standard rail. This kind of problem mostly appears in seamless turnouts, especially when there is a non-standard joint in seamless turnouts or when the curved strand is not seamless according to the standard.
Disease consequences: after crawling, the rutting machine rod is not smooth, there is a different force, and in serious cases, it can cause the turnout jamming.
Remedy: seamless turnout stress dissipation, replacement of non-standard rails in the turnout.
Fracture of Slide Plates
Defect Characteristics:
Weld failure, cracking, excessive wear, or lateral tilting of slide plates.
Most frequently occurs on the curved stock rail side (see Figure 3).
Figure 3
Root Causes:
Asymmetric Load Distribution:
The straight (tangent) track direction typically handles higher train speeds and traffic density compared to the curved track.
The straight switch rail is in a free-expansion state at one end, transferring all longitudinal forces to the slide plates, leading to unidirectional fatigue damage.
Maintenance Challenges:
The switch area is congested with equipment (e.g., switch machines), limiting workspace for proper tamping.
Uneven settlement or voids (e.g., hanging sleepers) worsen contact loss between the switch rail and slide plates, accelerating wear.
Consequences:
Severe cases may cause switch rail jamming, disrupting operations.
Corrective Measures:
Strengthen the rutting part of the pounding, eliminate the empty hanging, and replace the sliding bed plate with welded, broken or worn out over the limit. In the process of remediation, it is much easier to replace the sliding bed plate of SC330 turnout without pins than that of 4249 turnout.
Limiter jamming
Disease Characteristics: Limiter stuck, top iron away from the seam, the middle and rear of the tip rail side bend, gauge small, as shown in Figure 4.
Figure 4
Causes: turnout seamless locking rail temperature is not standard, the basic rail is pulled in winter, the limiter T-block top ∏ steel castings in front, summer pressure limiter T-block top ∏ steel castings in the back; turnout track strip crawling, seamless before the string of rails; curved strand is not seamless at the same time, straight and curved strand crawling is not consistent. This kind of problem mainly appears in the curved strand locking length is insufficient within the seamless turnout.
Disease consequences: the tip of the rail is not dense, rebound, conversion resistance, and in serious cases, even pull off the limiter caused by the fork jamming.
Remediation:
First, when the rail temperature is suitable for stress or creeping over the standard fork for stress dissipation and re-locking;
Second, in emergency solutions can be frozen with the tip of the splints into ordinary splints to dissipate the stress (the temperature is suitable for timely dissipation and recovery);
Third, according to the fork design plan to replace the fork within the non-standard rail bar, the whole of the creeping tip rail, the basic rail, re-locking;
Fourth, the paving of seamless fork to fork sidings and Fourth, when laying seamless turnouts, the locking length of the turnout sidings and crossings should not be shorter than 75m, and not shorter than 50m in case of difficulties; if the sidings are less than 50m away from the neighboring turnouts, the locking of the neighboring turnouts should be strengthened.
Poor Contact Between Switch Rail and Stock Rail
Defect Characteristics:
Visible gap between the switch rail and stock rail (as shown in Figure 5).
Figure 5
Root Causes:
Incorrect sleeper positioning in the switch area, leading to poor track geometry.
Foreign objects lodged between the switch rail and stock rail.
Excessive hardness or improper length of backstay blocks.
Incorrect switch rail opening displacement.
Consequences:
Severe cases may result in signal failure or switch rail jamming, disrupting train operations.
Corrective Measures:
Restore proper track geometry by adjusting sleeper positions and framework dimensions.
Remove any foreign objects between the switch rail and stock rail.
Adjust or replace backstay blocks to ensure proper contact pressure.
Calibrate switch rail opening displacement to meet design specifications.
Switch Rail Damage
Defect Characteristics:
Spike rail cracks, falling blocks, side grinding, as shown in Figure 6 and Figure 7.
Causes: Tip rail is often cracked first, and then drop block, drop block generally occurs in the top width of the tip rail 20mm and the following parts, non-stressed surface force, resulting in tip rail injury drop block. Tip rail side grinding occurs in small size turnout curved tip rail, mainly curve radius is small and no super high, train sideways driving crushing tip rail caused; abnormal side grinding may be due to rail direction is bad, tip rail side bend, tip rail fat edge and false close paste, rutting part of the frame size negative deviation, etc. Causes.
Disease consequence: the injury of the pointed rail can be divided into light injury and serious injury, and in serious cases, it can cause the pointed rail to break and the train to derail.
Remedial Measures for Switch Rail Damage
(1) Timely carry out turnout repair rational grinding. Grinding focus on the tip of the rail non-fat edge and basic rail fat edge grinding, on the tip of the rail, basic rail fish scale grinding, on the tip of the rail to reduce the value of insufficient timely grinding.
(2) Replacement of the tip rail when the basic rail of the existing pendant grinding to be synchronized with the replacement.
(3) Adjust the gauge and frame size so that the basic rail of the tip rail is close, and set the direction of the rutting department.
(4) Side grinding greater than 8mm and damage continues to develop the rim of the wheel may climb on the tip rail should be replaced immediately.
(5) set the right direction of the turnout, the overall correction of the gauge and gauge change rate.
(6) The turnout and the line before and after the unit remediation, restoration of the turnout plane, to ensure that the geometric dimensions do not exceed the standard.
(7) Replace the long top iron, so that its gap does not exceed 0.5mm, to avoid the sharp rail side bend.
(8) Correct the turnout frame size, and before and after the slope.
Bolt Hole Cracks at Switch Rail Heel
Defect Characteristics:
Bolt holes radiate cracks in all directions, as shown in Figure 8.
Figure 8
Root Causes:
Poor Joint Maintenance:
Rail surface irregularities: Height deviations, low joints, voids under rails, excessive joint gaps.
Improper stress-free temperature (SFT): Over-tensioning in CWR sections.
Material Defects:
Inclusions/non-metallic impurities or internal fatigue cracks in rail steel.
Surface flaws causing stress concentration.
Consequences: Progressive cracking may lead to complete rail fracture, risking derailment.
Remedial Measures:
Strengthen the maintenance of rail joints, promptly deal with defects such as inclusions, core damage, and external impact damage, and replace rails in a timely manner if cracks are found.
Insufficient Lowering Value of Switch Rail
Defect Characteristics:
Switch rail height exceeds stock rail at cross-sections ≤20mm from the tip (see Figure 9).
Non-load-bearing zones of recessed switch rails are subjected to wheel contact.
Figure 9
Root Causes:
Asymmetric Rail Wear:
Replacement of switch rail without renewing stock rail, leading to:
Vertical wear of stock rail → Loss of recessed fit.
Faster wear on straight stock rails (high traffic) vs. curved switch rails (low traffic).
Support Degradation:
Damaged/missing rail pads under stock rail → Uneven rail height.
Disease Consequences: In serious cases, it can cause the train wheel edge to climb up the sharp rail and then disconnect.
Preventive Measures:
Paired Rail Renewal: Always replace switch rail + stock rail as a set.
Wear Monitoring: Monthly ultrasonic profiling of recessed contact zones.
