Sealing force

In seals which are not pressure-energized, sealing force is provided by the residual stress in the compressed seal, so that stress relaxation becomes an important factor. Even for more common simations using pressure-energized seals, residual stress is required at initial start-up—or after a... 

To put in context the above-mentioned complexities, let us consider two real-life scenarios where, ideally, we wish to quantify the drop in sealing force ... 

The initial sealing force, item 4, should be roughly known from initial design studies, but it may be subject to considerable uncertainty and must be based on an assumption of the worst combination of seal-housing tolerance variables. The residual sealing force may be estimated if there is knowledge of the stress-relaxation rate of the elastomer, using... 

The unfortunate conclusion must therefore be that, although calculated predictions of sealing force retention may have some value in some situations, where a temperature drop is concerned, only experience, or experimental testing, is likely to provide anything near the correct answer. 

A 200 g sample, prepared by addition of substrate to mixed acid, followed by quenching into water, filtration and washing, decomposed vigorously at a late stage of drying in a vacuum oven, which was pressurised and the seal forced open. This behaviour might have been due to inadequate washing and residual sulfuric acid. 

Control measures shall include good alignment, properly sized gaskets, appropriate spacing, uniform sealing force, and avoidance of threaded fittings. 

The measurement of decay of sealing force with time is a most important design consideration and, although this has been long appreciated, the widespread use of such tests was inhibited by the inherent instrumental... 

The reactor wells are pre-loaded with catalyst (diluted with silicon carbide if desired) and inserted into the module. Two graphite seals are used per well, one to pressure seal each vial and one to prevent bypass flow around the vial. A single central bolt in tension supplies the sealing force onto these seals (Fig. 3.12b). 

Notice that if we use Eq. (6.4.11) for A and Eq. (6.4.10) for pi Sg we recover the same Thiele modulus Eq. (6.4.9) for the straight tube. The geometry of the situation for a slab is identical with that for a single pore, and both give the same expression for the effectiveness factor. The assumption that the edges are sealed forces the problem into a one-dimensional form by making it possible to take the concentration constant over any plane parallel to the face. The graph of j versus h is shown as the left-hand curve in Fig. 6.7. 

The West Company offers two pieces of equipment to check rubber-vial type closure systems, i.e. the Seal Force Tester, which quantifies residual compressive forces, and the Seal Force Monitor, which checks the forces applied during the capping and sealing operation. 

Keller, R.G. Control of factors relating torque to sealing force for C.T. closures, Packaging Technol., April 1982. 

Container/closure seal integrity has been reviewed by the Parenteral Drug Association (1983) and the Parenteral Society (1992). Variation in the overall height of the combined vial and closure will result in different closure-seal forces being applied at the crimping head. Quality control tests are proposed such as the dye intrusion challenge, liquid loss or bacterial... 

Whereas many sealing force measurements are made at normal ambient temperature and the decay measured is primarily physical, when stress relaxation is used to measure aging resistance the conditions arc deliberately cho.scn to make the chemical elTccts dominant. 

The types of stress relaxation test standardized (for rubbers) split into the two intended purposes. Seals are commonly stressed in compression or in a complex mode of stressing that compression can represent. Hence, sealing force tests arc usually made in compression. The bulk of such test pieces slows oxidative aging and also the uptake of any fluid. but swelling and aging effects do have to be considered in long-term applications. 

Perfluoroelastomers provide the elastomeric properties of fluoroelastomers and the chemical resistance of PTFE. These compounds are true rubbers. Compared with other elastomeric compounds, they are more resistant to swelling and embrittlement and retain their elastomeric properties over the long term. In difficult environments, there are no other elastomers that can outperform the FPMs. These s)mthetic rubbers provide the sealing force of a true elastomer and the chemical inertness and thermal stability of polytetra-fluoroethylene. 

Sealing force for gaskets Hydraulic 14 tie-rods 6 tie-rods 32 compression screw jacks 27 tie-rods/ electrolyzer rack... 

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