Bolted joint with gasket
Bolted joint with gasket
(OP)
I have a molded plastic part nut, piece of aluminum stamped part, a gasket, and thread forming screws. This seems to be pretty straigth forward stuff. I need to figure out what clamping force is needed to seal up the joint. This clamping force needed to withstand various vibration effect, etc. I also need to figure out what torque requirement to produce this force and to see if this would also strip out the plastic thread (produced by thread forming screws).
Anyone has a web site or step by step formula, so I can check my calculation.
Thanks
APH
Anyone has a web site or step by step formula, so I can check my calculation.
Thanks
APH





RE: Bolted joint with gasket
A more time effective method might be to tighten the screws up to failure and then take 75% of that as a seating torque and try one of the assemblies in test. You will have to determine the cost benefit ratio for this joint to determine how much time to invest in the joint analysis.
Dick
RE: Bolted joint with gasket
APH
RE: Bolted joint with gasket
Basically you need to develop enough contact force to seat the gasket - used to be 1600psi for a generic "y" value - check the gasket mfrs catalog [Garlock has good info http://www.garlock.net/ ]- O-rings have 0-200psi to seat; & also take the pressure force once it's sealed.
If it's too much force for the plastic part, maybe use Helicoils or Keenserts.
You could get the req'd torque from the good old F=5T/d formula in Shigley.
RE: Bolted joint with gasket
My application is not like vessel design and stuff. This is an electronic component ans has no internal pressure except from vibration and atmoshperic condition. I could still use the "Y" value, but I'm having problem with finding out the parameter that I need to use "Y" value. One of the key value is to determine minimum seating stress for the gasket. this would require me to know the stiffness of the material. I'm having a hard time to find this, unless getting it from experiment which I'm going to do anyway.
APH
RE: Bolted joint with gasket
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Bolted joint with gasket
Basically you're saying an O-ring type gland. Unfortunately, it's pretty late in the game to do this. THe "0.2" constant on your formula. Is that the K factor for zinc finish type on the screw?
APH
RE: Bolted joint with gasket
The use of a self energizing gasket like an O ring will greate a seal while requiring almost no clamp load.
Dick
RE: Bolted joint with gasket
APH
RE: Bolted joint with gasket
O-Rings certainly get around this, even in face seal applications. Since compression carefully controlled, seal is achieved well below the torque requirements that could prematurely strip out the box threading of the flange.
At this stage of the game, redesign and manufacturing is out of the question, I would be looking toward a gasket adhesive which would promote sealing properties at relatively low clamping pressures. There are several on the market which work well on plastic surfaces. The advantage here is that your flanging is plastic, but be sure to look at the adhesive chemical properties since many can compromise the plastic surface.
Good luck with it!
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
RE: Bolted joint with gasket
APH
RE: Bolted joint with gasket
On the stuff I've worked on In general flange thickness/stiffness has been under-estimated.
If the flange is "thin" and the bolts "widely separated" or too far from the main part diameter or structure the the clamping pressure gets real low between the bolts. The joint looks like this, ^|^|^| .
RE: Bolted joint with gasket
APH
RE: Bolted joint with gasket
IN extreme cases 1 plate per bolt can be used.
http://www.cantonracingproducts.com/valve_covers/6...
RE: Bolted joint with gasket
In almost all cases, a hole is preferred to a slot.
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Bolted joint with gasket
APH
RE: Bolted joint with gasket
Could you shed more light on your respond.
Thanks
APH