Torque required to tighten the cap for leak proof

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SUMMARY

The required torque to tighten a polypropylene cap with a 32mm diameter and an EPDM rubber seal for leak-proof performance is estimated to be between 20Nm and 65Nm, depending on the calculation method used. The user calculated a 40% compression of the seal to handle a water pressure of approximately 600N. The discrepancy in torque values arises from different approaches to account for friction, with one method yielding 20Nm based on direct compression force and another using a lead screw torque formula yielding 65Nm. Accurate calculations require consideration of frictional forces and the specific equations for thread engagement and seal compression.

PREREQUISITES
  • Understanding of torque calculations and their applications
  • Familiarity with EPDM rubber seal properties and compression
  • Knowledge of frictional forces in threaded engagements
  • Basic principles of mechanical engineering related to fasteners
NEXT STEPS
  • Research the equations for calculating torque in threaded fasteners
  • Study the properties and behavior of EPDM rubber seals under compression
  • Explore lead screw torque calculation methods and their applications
  • Investigate the impact of friction on torque requirements in mechanical assemblies
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Mechanical engineers, product designers, and anyone involved in the design and assembly of leak-proof containers or fasteners requiring precise torque specifications.

Acchu
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Hello Anyone,
Could you help me in finding the torque req. for a cap to leak proof?
My cap (polyproplene) which dia. was 32mm and its detail specs are,
thread major dia.- 28.5mm, min. dia. - 26mm, pitch - 3mm, thread angle-45deg
which has a EPDM rubber seal placed inside (outer dia 26.5mm & inner dia-18.5mm with thick 1.5mm)

I want to know.. what should be the torque required to tighten the cap, so that It will be leak proof? or in other way what is the % of seal compression req. for leak proof? to handle the water pressure of ~600N in a plastic container.
 
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Acchu said:
Hello Anyone,
Could you help me in finding the torque req. for a cap to leak proof?
My cap (polyproplene) which dia. was 32mm and its detail specs are,
thread major dia.- 28.5mm, min. dia. - 26mm, pitch - 3mm, thread angle-45deg
which has a EPDM rubber seal placed inside (outer dia 26.5mm & inner dia-18.5mm with thick 1.5mm)

I want to know.. what should be the torque required to tighten the cap, so that It will be leak proof? or in other way what is the % of seal compression req. for leak proof? to handle the water pressure of ~600N in a plastic container.

What approach should I consider? Shall I go with lead screw torque calc.? or any other
 
You should calculate how much you want to compress the interior rubber seal, this should give you an estimate of force, and from there you can estimate the torque needed to achieve the desired compression force on the seal.
 
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Mech_Engineer said:
You should calculate how much you want to compress the interior rubber seal, this should give you an estimate of force, and from there you can estimate the torque needed to achieve the desired compression force on the seal.
Thanks for your suggestion. As per the water pressure, I suppose to compress the seal by 40% based on this if I directly estimate the torque I'll get ~20Nm. If I use torque formula of lead screw concept, I'll get ~65Nm. So got confused. Guide me which way I need to go
 
The discrepancy in torque may have to do with friction, are you taking friction into account when calculating the required screw torque?
 
Mech_Engineer said:
The discrepancy in torque may have to do with friction, are you taking friction into account when calculating the required screw torque?
Yeah. I consider frictional force of thread engagement too while doing torque and got the result of ~20Nm. Hope in lead screw torque Calc. approach also friction parameter will be considered right?
 
Acchu said:
Yeah. I consider frictional force of thread engagement too while doing torque and got the result of ~20Nm. Hope in lead screw torque Calc. approach also friction parameter will be considered right?

What equations are you using for each calculation?
 
Mech_Engineer said:
What equations are you using for each calculation?
For thread engagement force :
Frictional force, Ff = m g (sin α + μ cos α)

For comp. of seal :
E = Stress / Strain
Stress = E*Strain
Force/Area = E*Strain
Force = E*Strain*Area

Resultant force = Frictional force + Comp. force

And the Compressive torque, Tc = K x Force x d (where k=Coeff. Friction of seal & d=PCD of seal)
Here I got 20Nm

2nd approach of lead screw torque formula:
Torque = F*Dm/2*(L+u*PI*DM)/(PI*Dm-u*L)
I got 60Nm.