Self-locking Nut Using Precipitation Hardening Steel
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Solution Overview
Problem
Existing self-locking nuts made of stainless spring steel, such as AISI 302, experience a progressive decay in braking torque when subjected to increased screwing/unscrewing cycles, especially at high temperatures, leading to unreliable performance and necessitating frequent replacement, which increases maintenance costs and material waste.
Innovation Solution
A self-locking nut with a helical spring made of precipitation hardening stainless steel, specifically semi-austenitic PH steel like 17-7 PH (AISI 631), is designed with longitudinal V or U-shaped slots and a stabilisation treatment to maintain high braking torque values consistently across a large number of cycles at both ambient and elevated temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the helical spring is made of stainless spring steel such as AISI 302 steel, then the braking torque is very high at the first unscrewing, but the braking torque decays progressively with increasing number of screwing/unscrewing cycles
Solution Approach 1:
The patent changes the material parameters of the helical spring by using precipitation hardening stainless steel with specific chemical composition (17-7 PH type steel with 17-19% Cr, 6.5-8% Ni, 0.4-0.7% Co, 0.35-0.65% Mn, 0.03-0.06% Mo, 0.03-0.06% Ti, and C ≤ 0.08%) and specific mechanical properties (tensile strength ≥ 1400 N/mm², elongation ≥ 10%). This material parameter change enables the spring to maintain high braking torque consistently over many screwing/unscrewing cycles, resolving the contradiction between initial braking torque and duration of action.
2Temperature
If the nut is used at high temperatures, then the operating temperature range is extended, but the braking torque performance decays more rapidly
Solution Approach 1:
The patent employs precipitation hardening stainless steel (17-7 PH type) as a composite material system that combines the beneficial properties of stainless steel (corrosion resistance, high temperature stability) with precipitation hardening mechanisms. The specific alloy composition and heat treatment create a microstructure that maintains mechanical properties at high temperatures, enabling the nut to operate reliably from -50°C to 400°C without rapid braking torque decay.
3Reliability
If the nut is replaced frequently to maintain performance, then the braking torque reliability is maintained, but the maintenance costs and material waste increase
Solution Approach 1:
The patent applies preliminary action by pre-hardening the helical spring through precipitation hardening treatment before the nut is put into service. This preliminary heat treatment creates a stable microstructure that resists degradation during subsequent screwing/unscrewing cycles, allowing the nut to maintain reliable braking torque performance for at least 30 cycles without replacement, thereby reducing material waste and maintenance costs.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The nut achieves approximately twice the unscrewing braking torque of existing nuts and maintains consistent performance for at least 30 screwing/unscrewing cycles, reducing the need for frequent replacement and associated costs, while operating effectively from -50°C to 400°C.
Implementation Method 1
a helical spring arranged to compress the segments and made of precipitation hardening stainless steel
Implementation Method 2
made of precipitation hardening stainless steel, specifically semi-austenitic PH steel like 17-7 PH (AISI 631)
Data Source
AI summary
The invention relates to a self-locking nut (1) having an upper threaded collar (3) provided with longitudinal slots (7), being V or U shaped, also with sharp edge, defining in the collar a plurality of circular arc segments (9) compressed by an external helical spring (5), and in which the collar slots have such a width as not to allow the mutual contact of the circular arc segments (9) compressed by the spring. The spring of the self-locking nut is made of precipitation hardening stainless steel whereby it shows high constancy of braking torque features even for repeated screwing/unscrewing cycles. The invention also relates to a method for manufacturing the nut.