Spring Washer

BTW: I use to think that spring washers are historically placed - without any actual advantage- for fasteners >3/4"

However the junker's test as well as one of the FEM papers is on a bolt M10 (ie 3/8")

The spring washer is to allow some movement at the bolted joint. It use should not be to hold something completely fast. It is not a locking device for the bolt. If a spring washer is to be used for flexibility other alternatives need to be used to make sure the bolt does not come loose.

Spring washers are also used in other applications such as clevis pins. To keep the pin from shifting specially in application where C or E type clips are used on linkage. Quick shifting of the pin against the clip may force it off.

It depends on the application, the screw thread profile, the materials, the type of vibration, etc.

For most applications spring washers work perfectly fine, for others such as fittings subjected to high mechanical vibration or where, say, the material being fixed varies in thickness, then there are other more suitable fixing methods (eg- double bolts, pins, Nylock nuts, locking adhesive, etc).

The spring washer is not a magic silver bullet for every application and we engineers know it (that is why there are so many locking alternatives on the market). Which one is best, again it depends on the application.

Now the question is - what is the use of spring washer at all?

(In it's most broad terms) from my experience for most electrical and many mechanical nut and bolt or nut and screw connections the humble spring washer is suitable and works well (that is why we use it).

There are spring-washers and there are lockwashers. Each is designed to perform a different function. Unfortunately most people I know call lockwashers as springwashers. So there is a certain semantic confusion. So what are we talking about. Some pictures would surely help.

Google the "Nord-lock fastener". It is a shake-proof washer extensively used on permament way fastenings in northern Europe.

Went through most of the links given and few more too in the mean time .

The basic doubt that arrived was due to (I am in manufacturing section).

The equipments that were made as a legacy of the generation D - were using spring washers (usually split helical) for the only reason I can make out is for locking purpose. Of course no one know (this was a part of transfer of technology documentation from our collaborator). And with them the spring washers are still a common feature.

However in our in-house developments as well in a few other products the locking is exclusively by loctites (lower temperature) and wire lock-inserts (higher).

There was a theory that in a few components (like turbines) you can not afford to have the loose part (washer) with a possibility of slipping from the assembler's hand. So the other means were employed.

Subsequently started doing own _research study on this and that was the source of the information above (in OP).

Few literatures and books still mention the locking feature of spring washers (including the great Wiki), but they can be always not exactly correct can they be? .

In fact I am trying to convince my designers to save the few $s by eliminating the useless. This was just to confirm the fact before taking the drastic step.

I think spring washers aka lock, were invented way back as a means of making fast a bolt or nut. It wasn't perfect, but that was all that was available until other means became available, like nylock, deformed thread, safety wire and anaerobic thread lockers. The spring washer just continued to exist. In fact, spring(lock) washers are perfectly suitable for many applications such as with fasteners that remain in a static condition (no vibration or motion), but then again, if there is no motion there is no need for a washer at all. I can see where a spring washer could AID in fastener loosening where there is relative motion between the fastener and parts.

Spring(lock) washers are reusable whereas the nylock, and others are not.

I take issue with two things you say.

1. Spring washers and lock washers are totally different animals.

2. I do not believe that the function of safety wire is to secure a threaded device, but rather to visually indicate that the threaded device is no longer torqued properly. (Has become loose enough to break the wire.)

Cheers.

I've used safety wired nuts in many transmissions. I have to differ with you in that in most those application to do visual inspection. You have the transmission disassembled so far it would be in poor judgement just to do a visual inspection and not torgue them let alone not replace the wire.

I will agree that it's not there totally to secure the fastener. Its there to keep them if the did come loose from damaging something else. In the case of the transmission the nut get caught in the gears.

Sorry, you have pointed out how much personal context matters. I concede that when used through a threaded stud the function may well be retention of the nut, even if the nut begins to loosen. This would make perfect sense in situations where visual inspection is not easily accomplished. I'd use a cotter pin.

In my youth, I built cranes. We used 1"/8Threads Per Inch x 3" long hex head bolts, drilled for safety wire. The wire we used was mild steel tie wire. .035"dia. The wire was daisy chained through all 18 bolts that attached the swivel head to the frame, as Ron has suggested, not to keep the bolt tight, but to assure wire breakage at the first sign of head movement. It is a bit of an art to tie 18 bolts together with a single length of wire and keep maximum tension on the wire.

The wire was not strong enough to impede a bolt from loosening in any way. It was there as a visual indicator, to negate the need for periodic torque checking.

1. I realize they are different, but they are usually referred to interchangably in term only. Lock washer has become a generic term.

2. There is a correct procedure for using safety wire. After going through the bolt head, the wire is wound counter to the rotation of the bolt (CCW for a CW bolt). I think I got that right. Anyway, the idea is for the wire to be under tension if the bolt has the tendency to loosen. This is always done on fasteners located in an air stream path to a gas turbine intake. If the wire has been applied correctly, there is no reason for the fastener to loosen.

Spring(lock) washers are reusable whereas the nylock, and others are not.

We use wire lock inserts in casings as well as nuts with these inserts. These are re-usable (unlike nylocks)

Chemical retainers (anaerobics) are not reusable but who cares. Put a few drops in next application.

But still the original question remains - assuming the limited usability of the common helical spring washers- why does one see the abundance of its usage?

I've used spring washers on linkage joints (where I would need rotational freedom between the joints) but I didn't want over tight connections, yet I didn't want stuff rattling around. Inherent in that is the use of castellated nuts and holes in the bolts to retain the nut with a clevis or cotter pin.

Hooker

I think you are talking about Belleville springs. If so, the history behind the Belleville spring is as follows. Mr Belleville invented the springs for Napoleon. The prior practise for cannonball cannons was to place powder into the cannon, then the ball, and upon firing the cannon, the canon would recoil across the full with of the deck of the boat.

With the Belleville springs, you could place a significant extra amount of powder in the canon, and shoot the ball twice as far as the canons wirhout the recoil type springs. Thus the Napolean ships could sink his enemy's ship before it came into range to sink Napolean's ship. This was instrumentsl for Napolean to win batles on the sea

Belleville springs have many, many uses today. Catepillar uses them in their clutch assembly, nuclear power plants use them to keep the packing in their valves tight,

Wooden roller coasters use them on the bolts connecting wooden pillars which keep the bolts tight and keep the stucture from falling. There are only a few Belleville spring manufacturers in the USA anf some in Germany and I believe there is still one in Sweden. The washers are cone shaped and made out of high carbon steel, so that if they are flattened, they will retain their shape when loosened. If used in the wrong process, they in deed could present problems, and if not properly heat treated, they will not work as designed

PEbobimm

Reference: Key Belleville Company, Leechburg, PA