Fast seal

Last crawled date: 1 year, 10 months ago

Here is my seal proposal for sealing and locking mechanism. I propose a locking mechanism with a sliding lock fixed by a wedge. It is wery fast you only need to put two sliding bars in the brick, put the brick in th cavity and pump out the air from the cavity to squezze the seal. After this you fix the lock by inserting the wedge in the cavity.

Main problems:

• Long rectangular cavity form – difficult to seal, possible deformation
• Plastic material – relatively high deformation compared to metal.
• Changing loads directions.


Solutions.

• Locking mechanism with even load distribution along the cavity
• Choice of plastic material with high elasticity modulus
• Choice of seal to work with changing load directions

For locking mechanism I choosed a sliding lock between brick and cavity, wixed by a wedge.

For seal I took a Parker four-corner spliced gasket made from Nitril(N7021, Durometer 60) with hollow-o profile B015 and friction fit installation.

Pressure difference of 3 bar is applied to the cavity surface of 17564mm2.
Total force acting on the brick: 17564x10-6x3x105=5269N
The seal preload of 20 pound/inch applied on the 42.3 inches of the seal length give us additional 1226N. Total load on the brick - cavity connection will be 6495N.

When cavity is under vacuum a force of 1756N will be applied on the connection. Because the required seal preload force is of 1226N, pumping air from cavity will be enough to squeze te seal.

The seal diameter is of 3.52mm with maximum compression of 28%, that give us 0.99mm, and the minimum compression will be 20% to allow for 0.3 mm seal displacement because of tolerances set and cavity + block deformations once under loads.

The choice for cavity material was dictated by maximum rigidity to get minimum cavity deformation once under load. My choice is :

DuPont Performance Polymers Rynite® 540SUV BK544 Polyethylene Terephthalate (PET)
40% glass filled with Tensile Modulus 13.5 GPa, Tensile Strength 162 MPa. I got no data for this material yield strength but no reinforced DuPont PET Polymers have tensile strength up to 90 MPa.



FEA calculations(see screenshots) show that with maximum applied load the cavity deformation in in Z direction will be 35 microns(i consider only distance between seal gland bottom and point of contact between brick and cavity).We have 2.5 safety factor for equivalent stress.

Rough estimate of FEA results was made for tensile strength and directional deformation(in my estimate i didn't took into acount flexural stress).

For Tensile strength:

I took a cavity cross section 10mm wide. It give 130 N of total load in point of contact for cross section. We have 2 point of contact per crossection. Therefore for 1 point of contact: 130N/2 = 65N

Crossection minimum width is of 1.76mm. And crossection area is of 1.76mm x 10mm = 17.6x10-6 mm2.
Tensile stress in Z direction is therefore 3.7 MPa. It is of the same order for equivalent stress regions where no flexural stress is present(See picture Equivalent stress and Normal stress).

z Axis deformation rough estimate with no taking into acount flexural deformation was 3microns between point of contact and seal gland.This is close to FEA deformation regions with litle flexural stress.