# Sealing with two hard, flat surfaces

• kandelabr
In summary, it is possible to calculate the amount of air leaking through the gap using the Reynold's Equation or a CFD simulation.
kandelabr
Imagine the following scenario:

There is a hollow steel cube. I cut the top facet off so that I get a box with a lid and then polish both cut surfaces so that geometry fits almost perfectly (no gaps are larger than 1/100 of a milimeter or so - or even smaller).
Then I close the box and introduce some pressurized air into it.

I press hard enough on the lid that all geometric faults are eliminated due to elastic properties of steel and also press hard enough to counter the force exerted by pressure.

Is there a way to calculate the amount of air leaking through the "gap" on account of surface roughness? I can specify Ra or Rz values, say Ra 0.2 - or any other value.

Thanks,
kandelabr

Yes, it is possible to calculate the amount of air leaking through the gap. This calculation is based on the Reynold's Equation, which defines the relationship between the pressure drop across a pipe and the flow rate. This equation can be modified for a given surface roughness and applied to the scenario you have described. You can also use a computational fluid dynamics (CFD) simulation to model the air flow in the box and calculate the leakage rate.

## 1. How do I properly seal two hard, flat surfaces?

To properly seal two hard, flat surfaces, you will need to clean the surfaces thoroughly to remove any debris or residue. Then, apply a thin layer of sealant or adhesive evenly to one of the surfaces. Carefully place the other surface on top and apply pressure to ensure a tight seal. Allow the sealant to dry completely before handling the sealed surfaces.

## 2. What type of sealant should I use for sealing two hard, flat surfaces?

The type of sealant you should use for sealing two hard, flat surfaces depends on the materials of the surfaces and the intended use of the sealed surfaces. Some common types of sealants include silicone sealants, epoxy adhesives, and polyurethane sealants. It is best to consult with a hardware store or manufacturer for specific recommendations.

## 3. Can I use a sealant to seal two surfaces that will be exposed to water or moisture?

Yes, there are sealants specifically designed for use in wet or damp environments. These sealants are typically water-resistant or waterproof, and can provide a strong and durable seal for surfaces that will be exposed to water or moisture.

## 4. Is it necessary to use a primer before sealing two hard, flat surfaces?

In some cases, using a primer before sealing two hard, flat surfaces can improve the adhesion and effectiveness of the sealant. This is especially true for surfaces that are porous or have uneven textures. It is best to consult with a professional or follow the instructions on the sealant product for specific recommendations.

## 5. How long does it take for a sealant to dry and create a strong seal?

The drying time for a sealant can vary depending on the type of sealant used, the temperature and humidity levels of the environment, and the thickness of the applied layer. In general, most sealants will dry within 24 hours and will reach full strength within 48-72 hours. However, it is important to follow the manufacturer's instructions for the specific sealant being used.

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