How to treat the surface of self-locking tuning screw after machining?
Below, I will directly give you a complete plan for surface treatment of self-locking tuning screws (common for automobiles/radio frequency/precision equipment) after machining, from pre-treatment → core coating (anti-loosening+wear resistance+rust prevention) → material corresponding process → inspection → drawing writing, all of which are versions that can be made directly by the factory, and can be used directly without nonsense.
First, the core requirements of self-locking tuning screws (determine the process)
Self-locking tuning screw = precise thread+frequent adjustment+locking+wear resistance+low friction+rust prevention+dimensional stability.
Thread accuracy: 6g/6H in general and 5g in precision.
Key points: the coating must be thin and uniform, without jamming and affecting the self-locking stroke.
Common materials: carbon steel, 410/304 stainless steel, brass and aluminum.
Second, the standard pretreatment (all materials are common and must be done)
After machining → deburring → degreasing → cleaning → drying.
Deburring: thread mouth, notch and sharp edge of head.
Roll grinding/vibration grinding for 10–30 min, no burr, no curling, and complete tooth shape.
Sharp edge: 0.1× 45 ~ 0.3× 45 (not too large, which will affect self-locking).
Degreasing and degreasing (must be clean, otherwise the coating will fall off)
Ultrasonic degreasing+water washing+pure water rinsing
Requirements: the membrane is broken by water for ≥30s, and there is no oil, fingerprints and cutting fluid residue.
Drying: 100-120℃ for 15-30min, without watermark and residue.
Three, carbon steel self-locking tuning screw (the most commonly used) surface treatment scheme
Scheme a: nylon patch/precoat-the first choice!
Function: self-locking, anti-loosening, wear-resisting, low friction, and does not affect the size.
Coating position: 1 ~ 2 teeth in the middle diameter area of thread (single-sided tape or double-sided)
Coating material: high temperature resistant nylon (≥130℃)
Thickness: 5–15μ m (strictly controlled, too thick to lock, too thin to lock)
Color: blue/red/yellow (optional)
Process: pretreatment → spot coating/roller coating → curing (120–140℃, 20–40 min).
Application: automotive electronics, gearboxes, RF cavities, precision instruments.
Advantages: no elastic sheet, no glue, repeated adjustment for more than 50 times without failure.
Scheme B: Manganese phosphating+immersion antirust oil-low cost, wear resistance and good lubrication.
Film thickness: 3–8 μ m
Function: Wear-resistant, anti-jamming, self-lubricating, slightly rust-proof.
Salt spray: 24–48h
Application: internal adjustment, dry environment, frequent spinning
Note: It must be soaked in oil (rust prevention+lubrication) and cannot be used in high humidity/outdoors.
Scheme C: Nickel plating (bright nickel/semi-bright nickel)+optional nylon coating.
Coating: 3–8 μ m nickel
Function: rust-proof, conductive, good appearance, wear-resistant.
Salt spray: 48–96h
Suitable for: radio frequency, communication, tuning screws that need conduction.
Optional: nylon locking coating after nickel, anti-corrosion and self-locking double insurance.
Scheme d: hard chromium plating (super wear resistance, frequent fine adjustment)
Coating: 3–6 μ m hard chromium.
Hardness: HV 800–1000
Application: high-frequency fine adjustment, precision instruments, and extremely high wear resistance requirements.
note:
Before plating, thread polishing Ra≤0.4μm m.
After plating, * * dehydrogenate (200℃, 2h)** prevent hydrogen embrittlement.
Strictly control the thickness to avoid tooth deformation.
Four, stainless steel (304/410) self-locking tuning screw
First choice: passivation+nylon locking coating
Passivation: Passivate with nitric acid for 15–30 min to improve the corrosion resistance of stainless steel.
Nylon coating: same as carbon steel, 5–15μ m.
Advantages: no hydrogen embrittlement, no rust, no looseness, and can be adjusted repeatedly.
Secondary selection: electrolytic polishing+anti-loose coating
After polishing, Ra is less than or equal to 0.8 μ m, and the thread is smooth and not stuck.
V. Brass/copper alloy tuning screws (commonly used in RF/HF)
Pretreatment: degreasing → weak pickling → pure water cleaning → drying.
Surface treatment:
Tin plating (3–5 μ m): solderable, conductive and anti-oxidation.
Nickel plating (2–5 μ m): wear-resistant and oxidation-resistant.
Thin gold (0.05–0.1μ m): high-frequency conductivity and corrosion resistance (high-end RF).
Self-locking: thread local pressure point (metal self-locking) or thin nylon coating (3-8μm)
Six, automobile recommended combination (direct copy)
1) Automotive electronics/gearbox tuning screw (carbon steel)
Pretreatment+manganese phosphating (3–5 μ m)+nylon locking coating (8–12 μ m, blue)+oil immersion.
Salt spray ≥48h, reliable locking, and can be adjusted repeatedly.
2) RF/new energy electronic control tuning screw (carbon steel/stainless steel)
Stainless steel: passivation+nylon coating (5–10μ m) Carbon steel: nickel plating (3–5μ m)+nylon coating (5–10μ m).
Conductive, rust-proof, anti-loosening and wear-resistant.
Seven, quality inspection points (factory QC will check)
Appearance: uniform coating, no leakage, no bubbles, no peeling and no damage to threads.
Coating thickness: 5–15μ m (nylon) and 3–8μ m (phosphating/nickel).
Anti-loosening performance: according to ISO 16047, it will not loosen after 50 vibration tests.
Spinning property: the gauge is on and off, and the screw-in is smooth and free from sticking.
Salt spray: carbon steel phosphating ≥24h, nickel plating ≥48h, stainless steel passivation ≥96h.
Eight, drawing technical requirements (direct copy)
Surface treatment:
Carbon steel: 3-5μ m manganese phosphating+8-12μm local nylon locking coating on thread (blue), impregnated with antirust oil.
Stainless steel: Nitric acid passivation+local nylon locking coating 5-10μm for thread.
Chamfering without sharp edges is 0.1× 45 ~ 0.3× 45, with deburring and no oil stain.
After coating, the thread stop gauge is qualified, and the thread can be screwed smoothly without sticking.
Nine, avoid pit key (many factories do wrong)
Do not use thick zinc plating/dacromet: the coating is too thick (> 20μm), and the thread is stuck and self-locking is invalid.
High-strength carbon steel (grade 10.9) should not be directly electroplated: hydrogen embrittlement risk, priority should be given to phosphating+nylon.
Don't fully cover the nylon coating: only apply 1-2 tooth diameters, and full coverage will lock up.
Nylon coating must be resistant to high temperature ≥120℃, otherwise the automobile will soften and fall off under working conditions.
