I. Lock Nut Types by Application Scenario
1. K-type Axial Lock Nut
Core Features: Designed for axial force, fixing the parts by axial pressure of threaded vice, preventing axial tampering.
Typical application: axial positioning of screws and bearings (e.g. Z-axis drive of CNC lathes), to be used with thrust washers to ensure uniform distribution of axial preload to avoid axial displacement of screws during operation.
2. R-type radial lock nut
Technical advantage: radial holding force design, through the circumferential direction of the friction fixed elements, to prevent radial offset during rotation.
Scenario Adaptation: The connection between pulley and shaft (e.g. crane wire rope pulley) needs to be used in conjunction with keyway to ensure stable radial torque transmission and avoid pulley idling.
3. F-type tooth web lock nut
Anti-loosening principle: the tooth web adopts serrated bite structure, and the tooth surfaces are embedded with each other when vibration occurs, so the anti-loosening performance is upgraded by 50% compared with that of ordinary nuts.
Case: Engine cylinder head bolting, under 100-200Hz high-frequency vibration, it can still keep the preload decay ≤10%, which is better than the 30% decay rate of ordinary nuts.
4. RN Square Lock Nut
Structural advantages: square profile increases the contact area of the wrench, the torque carrying capacity is 40% higher than the hexagonal nut, and it is easy to synchronize the operation of multiple wrenches.
Application Scenario: When large equipment base is fixed (such as mining crusher) and hydraulic torque wrench is needed to apply 300-500N・m torque, square structure can avoid slippage.
Accurate matching of specifications and dimensions
must be strictly consistent with the bolts: metric threads need to confirm the diameter (M8-M64) and pitch (e.g., M12×1.5 fine threads), and imperial threads need to match the UNC/UNF standard (e.g., 1/2"-13UNC), and the error needs to be detected by the through and stop gauges (the through gauges are passed, but the stop gauges are not passed).
Error case: A construction machinery mistakenly used M20×2.5 nuts with M20×2 bolts, resulting in insufficient thread engagement length and slippage under impact load, and then replaced the nut with the same pitch to solve the problem.
Thickness and OD selection logic
Thin nuts (thickness ≤0.8D): suitable for hydraulic valve manifolds and other space-compact scenarios, but the load-bearing capacity is reduced by 20%, and the safety coefficient needs to be increased from 1.5 to 2.0;
Thickened nuts (thickness ≥1.5D): 42CrMo material can withstand 200% overload, such as the flange connection of pressure vessels, and it is necessary to choose nuts with OD ≥1.5D to ensure that the tensile strength of the bolts matches. Matching.
Material properties and working conditions adaptable standards
| Material | Carbon content | tensile strength | Typical areas of application | Cost comparison |
| 45# steel | 0.42%-0.50% | ≥600MPa | General machine tools, agricultural machinery (e.g. harvester chains) | Basics |
| 42CrMo | 0.38%-0.45% | ≥1080MPa | Wind turbine towers, automobile engine crankshafts | Premium (cost + 200%) |
Example of special working condition adaption:
Low temperature environment (-40 ℃): 42CrMo steel by low temperature tempering treatment, impact work ≥ 60J, applicable to the Arctic scientific research equipment;
Wear-resistant demand: 45 # steel nut surface quenching to HRC55, threaded bottom wear resistance increased by 3 times, applicable to textile machinery frequent start-stop scenarios.
The technical realization path of locking performance
Combination strategy of anti-loosening methods
F-type toothed nut: independent anti-loosening, without additional parts, applicable to the maintenance of inconvenient scenarios (such as high-altitude wind turbine towers);
K-type nut + cotter pin: mechanical locking double protection, applicable to mining vibrating screen and other extreme conditions, to prevent the nut from spinning loose.
Points for setting locking torque
Influencing factors:
Difference in type: R-type radial nut torque is 20% higher than K-type axial nut (e.g. M16 specification, K-type is recommended to be 80-100N・m, and R-type needs to be 100-120N・m);
Influence of material: The upper limit of torque of 45# steel nut is 60% of that of 42CrMo (e.g. M20 specification, 45# steel is ≤200N・m, and 42CrMo can be 340N・m). operation specification: use digital torque wrench (accuracy ±3%), according to the diagonal order of 2-3 times tightening, the first 50% torque pre-tightening, and finally reach the standard value.
Five. Balance strategy of cost and reliability
Full-cycle costing model
Ordinary scenarios (annual maintenance ≤ 2 times): 45# steel nut (M12 about 1.2 yuan / a) + anti-loosening glue, the comprehensive cost is 60% lower than 42CrMo program;
Critical scenarios (failure loss ≥ 10,000 yuan): 42CrMo nut (M12 about 8 yuan / a), although the initial cost is high, but the wind power equipment can reduce 90% of the failure of bolt loosening, annual maintenance, and the annual cost of 50% torque preload. Although the initial cost is high, it can reduce 90% of bolt loosening failures in wind power equipment, and the annual maintenance cost can be reduced by 5000 RMB.
Cost-effective selection case
Agricultural machinery: 45# steel knurled nut (anti-loosening grade Class 8), to meet the vibration requirements of field operations, the individual cost is lower than that of 42CrMo by 7 yuan, and the procurement cost of the whole machine is reduced by 30%.
Automobile engine: 42CrMo Dacromet-coated nuts must be used (salt spray resistance of 1,000h), although the individual cost is increased by 15 yuan, the engine overhaul cycle has been extended from 2 years to 5 years. to 5 years.
Sixth, the industry selection of practical points
wind power industry
Demand: tower high-frequency vibration (amplitude ± 2mm) + difficult maintenance at high altitude
Program: 42CrMo flange serrated nut (M36 specifications), with hydraulic tensioner installation (torque of 315-340N.m), the measured loosening rate decreased from 15% to 0.5%.
Food Machinery
Requirements: High hygiene requirements + exposure to acid and alkali cleaners
Solution: 304 stainless steel F-type serrated nut (electrolytic polishing treatment, Ra≤0.8μm), FDA approved, no rust on the surface after corrosion test with cleaners.
Semiconductor equipment
Requirements: clean room (ISO class 5) + non-magnetic
Solution: Titanium RN square nut (permeability μ≤1.001), with PEEK anti-tightening washer, dust particle test <0.5μm particles accounted for ≤0.1%.
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