Galling is a form of wear which is caused by adhesion between sliding surfaces. Common causes of gailing are High loads, poor lubrication and when similar metals are comes in contact. It affects the threads of Stainless steel 304 bolts and nuts.
Torque and galling of Stainless steel fasteners
| Type | Condition | Load (lbs) | Surface treatment | Initial hardness | Time for galling to occur (Seconds) |
|---|---|---|---|---|---|
| 303 | Annealed | (only preload) | None | 85 Rb | 3 |
| 303 | Annealed | 750 | Tufftrided* | 85 Rb | 25 |
| 303MA | Annealed | 300 | None | 88 Rb | 2 |
| 303MA | Annealed | 1350 | Tufftrided* | 88 Rb | 58 |
| 317 | Annealed | 500 | None | 85 Rb | 7 |
| 317 | Annealed | 750 | Tufftrided* | 85 Rb | 27 |
| 347 | Annealed | 600 | None | 89 Rb | 8 |
| 347 | Annealed | 500 | Tufftrided* | 89 Rb | 22 |
| 416 | Heat Treated | 400 | None | 43 Rc | 12 |
| 416 | Heat Treated | 1000 | Tufftrided* | 43 Rc | 37 |
| 440A | Annealed | 650 | None | 96 Rb | 15 |
| 440A | Annealed | 1000 | Tufftrided* | 96 Rb | 47 |
| 440C | Heat Treated | 800 | None | 59 Rc | 17 |
| 440C | Heat Treated | 1100 | Tufftrided* | 59 Rc | 41 |
Prevention of galling in SS Fasteners
There are several ways by which gailing can be prevented:
1) Lubrication of solid molybdenum disulphide particles prevent metallic contact of fasteners and minimises abrading.
2) Solid film of lubricants which contains copper, silver or aluminium particles can also be used. These lubricants decreases coefficient of friction.
3) PTFE sealing tape can also offer protection from galling, these are widely used in larged threaded components like pipes and valves.
4) Coatings such as Polyseal, Xylan or wax may also prevent galling on Stainless steel 304 fasteners.
Which factors trigger galling?
Exposed surfaces, Small particle or debris stuck between metal surface, fast movement of material under high pressure or similar metals contact are most common triggers of gailling in Stainless steel fasteners.
Why stainless steels bolts are prone to seizing?
Below are some of the main reason for seizing of ss bolts:
High friction events
Clean, oxide-free contact
Work hardening & ductility
Will slower installation of SS Nuts really help?
Yes, Heat and frication are primary reason why gailling happens. Therefore slower installation will reduce the chance of seizing.