Bolt förbelastningskontroll och enhetlighetsförsäkring
- Hur bestämmer jag det rimliga utbudet av BOLT -förbelastning?
Bestämma enligt bultstyrkan betyg . förbelastningen av 8 . 8 betygsbultar är 60% - 70% av deras utbytesstyrka (som ungefär 200 - 230 Kn för m24 -bultar), som inte bara säkerställer tillräcklig kläm connected parts, the bolt preload for connecting rails and fishplates must generate sufficient friction on the contact surface to prevent relative sliding. When the friction coefficient is 0.3, the preload must be>=180kN (60kg/m rail). Refer to industry standards. TB/T 3395.2 Standard föreskriver att spårbultens förbelastningsavvikelse måste vara mindre än eller lika med ± 5%, vilket måste följas strikt under installationen, och både vanliga järnvägar och järnvägar med hög hastighet måste uppfylla detta krav. Med tanke på miljöfaktorer kan förbelastningen i lågtemperaturområden ökas med 5% - 10% för att kompensera för lågtemperaturkrympning av material och minskas med 3% - 5% i höga temperaturområden för att undvika bultens lossning.
- Vilka problem kan ojämna förbelastning orsaka?
Unbalanced rail stress. If the preload deviation exceeds 10%, one side of the rail will bear greater pressure, and the local stress concentration factor will reach 1.5 - 2.0, which is easy to produce fatigue cracks. This risk is higher in heavy - haul railways. Different bolt loosening rates. Bolts with small preload may loosen by 20% - 30% within 3 months under vibration load, leading to rail displacement at that part, requiring frequent retightening and increasing maintenance costs. Uneven deformation of connected parts. Fishplates or pressing plates may bend, affecting the fit with rails, reducing the contact area by 10% - 15%, and accelerating component wear. This problem will appear in ordinary railways in 1 - 2 years. Increased vibration when trains pass. Uneven preload causes track stiffness fluctuation, vibration acceleration increases by 20% - 30%, passenger comfort decreases, and noise increases by 5 - 10 db .
- Hur kontrollerar jag enhetligheten i Bolt -förbelastningen?
Install by torque coefficient method. Ensure preload by controlling torque (such as 300 - 350N·m for 8.8 grade M24 bolts). Calibrate the torque wrench before installation, with accuracy within ±3%, and test the torque coefficient for each batch of bolts. For high - speed railways and heavy - haul railways, use hydraulic stretchers for installation to directly control the bolt elongation (elongation deviation<=±0.05mm). The preload uniformity can reach ±2%, which is much better than the torque method. Tighten bolts in a symmetrical Beställning . Första pre - Dra åt diagonala bultar (50% vridmoment), dra sedan åt andra bultar till det angivna vridmomentet i sin tur för att undvika förlust orsakad av deformering av anslutna delar .. bultar. De med förbelastningsavvikelse som överstiger ± 5% måste justeras för att säkerställa total enhetlighet.
- Vilka faktorer påverkar enhetligheten i bultförbelastningen?
Differences in thread accuracy between bolts and nuts. Threads with low accuracy (such as grade 8g) will cause large fluctuation of tightening torque, and the preload deviation may exceed 15%. It is necessary to select bolts and nuts with matching accuracy (such as grade 6g bolts with grade 6H nuts). Uneven lubrication. Uneven application of grease on the thread surface will cause the friction coefficient to change by ±0.05, increasing the preload deviation by 10% - 15%. During installation, ensure uniform lubrication and the same amount of grease applied to each bolt. Surface flatness of connected parts. Uneven surface of rails or fishplates will cause concentrated stress points and uneven preload loss. Before installation, the contact surface must be ground, with flatness deviation<=0.1mm/m. Differences in operator operation. Uneven force during manual tightening will cause preload avvikelse upp till 20%. Automatiska åtdragningsverktyg (såsom elektriska vridmomentnycklar) måste användas för att minska påverkan av mänskliga faktorer.
- Vilka är skillnaderna i förbelastningskrav för bultar i olika delar?
The preload requirement for turnout bolts is the highest, 10% - 15% higher than that of ordinary lines, and the uniformity deviation must be<=±3%. Because turnouts are weak links of the track with complex stress, it is necessary to ensure that each bolt is stressed consistently. The preload of outer bolts in curve sections is 5% - 10% higher than that of inner bolts to resist the outward lateral force of rails. The preload of outer bolts in curves with 600m radius must be>=220kN (8.8 grade M24), and that of inner bolts>=200kN. The preload of fishplate bolts at rail joints must be uniform, with deviation<=±4% to avoid steps at joints. Ordinary railways and high - speed railways must strictly control this to ensure smooth train passage. The preload of sleeper bolts is relatively low (such as 100 - 150kN), but the uniformity requirement is high (±3%) to prevent sleeper cracks due to Ojämn stress, som är mer känslig för betongsvängare.