Looking for hardware grade 5 socket head screws

[dalegoldston]

I am having difficulty locating someone that sells grade 5 ASTM-A449 socket head screws. I need 3/4-10 x 1.75 long. Any help would be appreciated. I am needing something in the 130 ksi range.

Thanks
Dale

Thanks
Dale

 

[drawoh]

dalegoldston,

Socket head cap screws usually are supposed to be high strength, unless they are stainless. Do you need approximately 130ksi, or at least 130ksi?

Why such a specific alloy? Do you have inspection and certification issues?

--
JHG

 

[dalegoldston]

I have a unit that is armor I am bolting down for a vibration test. I have now grade 8 bolts holding it down. One of those lost a thread during diss-assembly and damaged my product. I am hoping that by using a bolt that is softer that I can prevent any damage to my product if a screw decides to break. So the 130 ksi is just a step down from the bolts I am using now. Suggestions are welcome for sure.

Thanks
Dale

 

[Screwman1]

When you say "lost a thread", what do you mean? Where and when did the failure occur? The answer to that will tell us a lot about what the solution should be. In general; if it was a fatigue failure, you need to tighten the bolts tighter- a 3/4-10 SHC should be targeting around 38,000# of clamp per bolt and torque (estimated) of around 480 ft. lb. to get them up around 75% of yield.

 

[dalegoldston]

They are being torqued at 120 ft lbs ea on a quantity of 12. Hard to tell when the failure happened, it is just noticed when removing the bolts to remove the unit. The screw seizes then the fight is on to get it out. This has happened 4 times in the process of testing 20 units.

Thanks
Dale

 

[hydtools]

If a grade 8 socket head capscrew siezes I would suspect the female thread failed, not the capscrew.

Ted

 

[SwinnyGG]

a grade 8 socket head capscrew siezes I would suspect the female thread failed, not the capscrew.

I agree with this.

Also, this statement:

I am needing something in the 130 ksi range.

rules out Grade 5 fasteners.....

Damage to fastener threads could be caused by number of things.

Before changing the material, I'd take at look at

1) fastener length. If the fasteners are too short, you won't have enough thread engagement. This increases the load on each thread and if you only have a couple threads engaged, you can ruin fasteners- grade 8 or not. You want 2x bolt diameter of thread engagement length, at minimum, to fully develop the strength of whatever fastener you are using.

2) Installation torque. 120ft-lbs is extremely low for a 3/4" fastener. You're not generating very much preload- and if the fasteners are 3/4, I have to assume the product is designed to be mounted with a high level of preload.

In short, buy fasteners that are the correct length and torque them correctly before you go chasing a problem that's harder to solve.

 

[EdStainless]

Your bolts are loose.
My cheat sheet shows 375ft-lb min.
With loose bolts rattling around no wonder you got thread damage.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[Tmoose]

Imperial/inch series SHCS are mighty hard to find.

Metric ones are more like coelecanths and less like unicorns.

But the comments by others about tightening are well heeded.

 

[Tmoose]

Is the torque being monitored on the non-damaged bolts during dis-assembly ?

 

[DAVIDSTECKER]

If I understand this right you are drilling and tapping some sort of Armor plate?
Most material from what I've seen for armor plate typically work hardens, the Hadfield Manganese we use definitely does.
It sort of sounds like to me that you are getting some sort of galling.
It is very common with the stainless steel nuts and bolts and even screw shackle threads.
You can hand thread the parts together and they just lock up when you try to take them apart.
My guys in the shop have presented me with many examples of this over the years.
We use silver anti-seize to prevent that from happening.

 

[dalegoldston]

Thanks for all the replies/suggestions.
-the torque we are using is based on what is used in the field for mounting the assembly. It is 155 ft lbs, not 110.
-limited to requirements given by our customer.
-we know the fastener is the correct length but it is only 1.75" long.
-we may look at a coating to help with the galling, which is probably what is happening.

Thanks
Dale

 

[Tmoose]

"-we know the fastener is the correct length but it is only 1.75" long."

The thread engagement is what counts. Is that the same as in service?

============.=========.==========
A449-04b Specification for Hex Cap Screws, Bolts, and Studs, Steel, Heat Treated, 120/105/90 ksi Minimum Tensile Strength, General Use

I don't think ASTM A449 covers SHCS. Is the product retained by Hex head cap screws or Socket Head cap screws in service ?
I'd bet a nickel there is a detailed procedure for installation including torque and fastener lubrication requirements.

 

[Screwman1]

The 175 is way to low for for a 3/4" SHC- it is not adequate to resist the in-service loading. You need to get that torque increased to get the parts to stay tight and live.

Dick

 

[SwinnyGG]

The other thing to remember is that hardness values for bolt materials are quoted as CORE hardness- the largest percentage of the cross section will be at the nominal hardness, but the surface, which experiences the fastest cooling, will always be harder than the core.

In other words, the surface of a grade 5 bolt is not that much softer than the surface of a grade 8 bolt- so just dropping to grade 5 likely won't solve your problem, as the galling mechanics won't change very much.