Spring washers are one of the most common mechanical devices, used to secure threaded fasteners against self-loosening. The way a spring washer works is that it increases the preload by increasing the contact area, compared to the bolt with no locking device used at all. This will slightly improve the number of cycles it will take for the bolt to loosen, but it will not permanently prevent it. The main reason is that the spring washer doesn’t solve the issue of the gap, free space remaining between the threads of the nut and the bolt. Incredibly enough, there is only about 15% efficient metal to metal contact between the threads. Everything else is empty space that enables plenty of side to side movement for the bolt, which is the main reason for its eventual loosening. On top, being metal itself, a spring washer can cause damage to contact faces and can corrode in place.
Now, when instead of a spring washer you use a few drops of Loctite 243 (or any other Loctite grade that fits the bill – you can find more information on selecting the right product here), the liquid threadlocker completely fills all gaps between threads and prevents any movement of the bolt within the nut. Secured that way, it will be completely vibration proof and stay in place forever – if that’s what you want. If not, the assembly can be easily dismantled with hand tools, for repairs, regular maintenance, any other reason. Although, you will notice that the assembly opens at roughly 25% more torque than tightening torque. Additionally, liquid threadlocker will seal the threads from humidity penetration and in that way prevent corrosion.
One bottle of 50 ml will suffice for about 850 pcs of M10 bolts. And the good news is, whatever the size of your bolts, you don’t need to keep a different Loctite threadlocker on stock for it, as you would have to do with different sizes of spring washers.
Spring washers are not the only mechanical locking solution for the threaded assemblies. There are others, and most of them equally inefficient, but I’ll go into that in some of the following articles.