Marking of flat washers

“Do flat washers need to be marked?” “No?”

“Do they need it?” ……

Today we discuss this issue with you, may be a lot of people in the industry will think “Xiaowan ah, you are a little unprofessional ……”.

As we all know, flat washers as a fastener connection of an important fit, mainly play a role in increasing the contact area, dispersing the role of contact pressure. The vast majority of flat washers used in industrial assembly are unmarked like the one in the picture below.

So what are the cases where flat washers will be marked?

(1) Production plant to avoid mixing materials

Flat washers for the production process of narrow strip stamping molding, production plant in the flat washer surface marking is in order to avoid the production of the same specifications of different materials flat washers, in the production or transit process of material confusion and a means of process control. For example, the “304” in the following figure, that is, on behalf of the flat washer is A2 material. If a manufacturer produces a flat washer of the same specification in 316 material at the same time, then the washer may be marked with “316” or “A4”.

This indication of material identification is common in stainless steel flat washers, the reason is that after the production of stainless steel products are generally only done after cleaning and passivation, from the appearance of bright white, can not intuitively distinguish its material.

The material is clear on the surface of the stainless steel flat washers can effectively avoid the production or assembly process of mixed materials.

(2) standard provisions

Certain product standards specify the requirements of flat washers marked, for example, the standard “EN”, “EN”, “EN”, “EN”, “EN” and “EN”.

For example, the standard “EN 14399-5 (GB / T 32076.5) pre-loaded high-strength bolted structural joints Part 5: flat washers” in the quenched and tempered flat washers should be marked with a concave, as shown below:

For example, the standard “ASTM F436 Hardened Steel Washers” specifies that flat washers subject to this standard should be marked with the “F436” symbol, as shown below:

Flat washers marked or not marked with a standard can be based on?

Looking through the current product standards, standards for flat washers whether to play marking is not clearly defined.

Standard ISO 898-3:2018 (mechanical properties of fasteners – flat washers) The standard is the implementation of the performance requirements for carbon steel, alloy steel material flat washers in 2018, of which chapter 9.2 for the flat washer marking made clear provisions.

Flat washer marking may be at the discretion of the manufacturer or by agreement between supply and demand.

Flat washers shall not be marked with raised letters. Concave marking is usually not recommended because it can change the torque-clamping force relationship of the bolt-nut joint or create stress concentrations that may cause cracking of the washer.

The above two points show that marking of flat washers is not mandatory, and it is up to the supplier to decide or negotiate whether marking is required before ordering. It is not recommended to mark the surface of flat washers with embossed or concave characters.

Austenitic stainless steel flat washer surface concave marking will change the bolt – nut connecting vice torque – clamping force relationship has to be proved, it is certain that, due to the low hardness of austenitic stainless steel, concave marking will not lead to stress concentration in the washer, will not trigger cracking of the washer.