Causes of Nylon Casing Damage and Failure
Aug 05, 2025| Causes of Nylon Casing Damage and Failure：
(I) Causes of Nylon Casing Blockage: Failure to properly protect the nylon casing holes during the production, transportation, pre-laying, and routine maintenance of concrete turnout sleepers can lead to blockage.
Specifically, the following key causes exist:
1. Improper operation: During the turning or installation of sleepers, improperly inserting tools such as crowbars into the nylon casing to pry it can directly damage the casing. 󠄐󠄹󠅀󠄪󠄢󠄡󠄨󠄞󠄡󠄞󠄧󠄦󠄞󠄡󠄤󠄢󠄬󠅒󠅢󠄟󠄮󠄐󠅅󠄹󠄴󠄪󠄡󠄬󠅒󠅢󠄟󠄮󠄾󠅑󠅝󠅕 󠄪󠄡󠄣󠄢󠄧󠄩󠄡󠄩󠄧󠄩󠄧󠄩󠄬󠅒󠅢󠄟󠄮󠇘󠆭󠆘󠇙󠆝󠅵󠇗󠆭󠆁󠄐󠇗󠅹󠅸󠇖󠆍󠅳󠇖󠅹󠅰󠇖󠆌󠅹󠄬󠅒󠅢󠄟󠄮
2 Problems with the internal thread of the casing: During laying, if the internal thread of the nylon casing is damaged or difficult to tighten, using hard operations such as hammering may cause further damage to the thread, thereby increasing the risk of blockage. 󠄐󠄹󠅀󠄪󠄢󠄡󠄨󠄞󠄡󠄞󠄧󠄦󠄞󠄡󠄤󠄢󠄬󠅒󠅢󠄟󠄮󠄐󠅅󠄹󠄴󠄪󠄡󠄬󠅒󠅢󠄟󠄮󠄾󠅑󠅝󠅕󠄪󠄡󠄣 󠄢󠄧󠄩󠄡󠄩󠄧󠄩󠄧󠄩󠄬󠅒󠅢󠄟󠄮󠇘󠆭󠆘󠇙󠆝󠅵󠇗󠆭󠆁󠄐󠇗󠅹󠅸󠇖󠆍󠅳󠇖󠅹󠅰󠇖󠆌󠅹󠄬󠅒󠅢󠄟󠄮
3 Entry of foreign matter: During the operation, if hard debris such as metal blocks and ballast accidentally fall into the nylon casing and these debris are difficult to remove by conventional means, they will form a blockage in the casing and hinder the normal screwing of the T-bolt. 󠄐󠄹󠅀󠄪󠄢󠄡󠄨󠄞󠄡󠄞󠄧󠄦󠄞󠄡󠄤󠄢󠄬󠅒󠅢󠄟󠄮󠄐󠅅󠄹󠄴󠄪󠄡󠄬󠅒󠅢󠄟󠄮󠄾󠅑󠅝󠅕󠄪󠄡󠄣󠄢󠄧󠄩 (II) Analysis of Nylon Casing Adhesion: During the initial rollout of concrete turnout sleepers, due to insufficient understanding of the material properties of nylon casing and its susceptibility to grease and deterioration, the industry had not yet established clear regulations requiring the use of specialized grease for nylon casing lubrication. Therefore, during turnout pre-laying and routine maintenance, engineering units commonly applied "butter" as a lubricant and anti-corrosion measure. However, after several years of use, adhesion between the nylon sleeve and the T-bolt was discovered. An in-depth investigation determined that this was primarily due to a chemical reaction between certain components in the "butter" and the nylon material, causing the nylon sleeve to deteriorate and adhere tightly to the T-bolt.
Analysis of Causes of Nylon Sleeve Debonding:
1. Base Elasticity and Tamping Issues. Inconsistent base elasticity and inadequate tamping are key causes of nylon sleeve debonding. When the turnout sleeper hanger plate passes a train, the bolt and nylon sleeve threads vibrate repeatedly, causing wear and tear that can exacerbate sleeve thread damage. This vibration is further exacerbated by dynamic train loads, especially when the iron plate experiences "ship-bend" deformation. The pull-out force exerted by the T-bolt on the nylon sleeve is extremely strong. Under long-term, repeated application, the nylon sleeve is prone to debonding and failure.
2. Design Flaws: In the early days of concrete turnout tie applications, the nylon sleeves and T-bolts had design flaws in their thread forms. The threads were trapezoidal. When subjected to longitudinal forces, this type of thread was prone to uneven force distribution due to the clearance between the nylon sleeve and the T-bolt threads. When there was a tendency to pull out, the upper threads were subjected to greater force, which could lead to progressive damage to each thread from top to bottom, ultimately causing overall thread stripping.
Analysis of Causes of Nylon Sleeve Breakage
1. Contamination: During turnout pre-laying or routine maintenance, improper protection of the oiled nylon sleeve bores can allow hard debris such as sand, metal shavings, or fine gravel to inadvertently fall into the sleeve bores. When the T-bolts were screwed in, these impurities generated strong compressive forces within the nylon sleeve, damaging the material and causing cracking and failure. 2. Installation Clearance Issues: If the gap between the nylon sleeve and the concrete tie is too large, the sleeve may be subjected to uneven stress during the T-bolt installation process. This stress may cause cracks or fractures in the sleeve at weak points.
3. Design Flaws: If the nylon sleeve wall is designed to be excessively thick, it may lack toughness. Toughness is the ability of a material to absorb energy and deform without immediately breaking when subjected to impact or compression. Materials with insufficient toughness are more prone to brittle fracture when subjected to stress. Furthermore, if the nylon sleeve design does not allow for sufficient elastic expansion and deformation, it may not be able to effectively release stress through deformation when subjected to external forces, increasing the risk of failure due to cracking.
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