Latest Flow Dry Technology News
Wednesday 30th December 2015
A gasket can be defined as a layer of material which is placed between two mating surfaces (flanges) to prevent fluids or gases from escaping, or entering a closed system. The fluid (liquid or gas) may be under pressure or in a relative vacuum.
So with a number of variables to consider how do you select the right gasket for your application? Here are a number of key criteria to consider.
How The Finished Quality of the Mating Surfaces Affects Gasket Choice
If the two mating surfaces were perfectly machined then surface A would perfectly match surface B (see diagram above) and there would be little or no requirement for a gasket. The diagram above shows a cross section of a flange joint.
However in the real world these surfaces are often imperfect as shown in the highlighted circle above. The mating faces may be porous, imperfect and uneven and hence gaskets are required. As well as the physical properties such as porousness, and uneveness, other qualities of the flange materials, such as their chemical properties and hardness all have an impact on what type of gasket is needed.
If the two surfaces are likely to be very uneven then a product like the rubber coated steel or aluminum (aluminium) gaskets would be ideal. The rubber coating, although only typically a fraction of a milimeter thick provides enough tolerance to adapt to an uneven surface. Wheras a solid metal gasket would not tolerate unevenness as well.
Of course a composite gasket may cost slightly more, but it may be a lot cheaper than trying to achieve perfectly machined flange faces in the product.
The Temperature Range of the System Affects Gasket Choice
When operating in hot exhaust systems, like the automotive sector then it's important to understand that you may need high temperature gaskets.
For example many standard materials which can be die cut will not tolerate high temperatures. Especially fabric, paper and plastic based gaskets.
The reinforced metal gaskets which have a perforated metal core like 304 stainless which is coated in vermiculite can withstand 1000 degrees Centigrade of temperature.
The Reactivity of the Gasket to the Fluid or Liquid Within the System Affects Gasket Choice
In the above example we mentioned vermiculite coated reinforced gaskets. But vermiculite, while having fantastic temperature range, will not perform so well with fluids. This is because the vermiculite material may wick moisture into it's structure. So for fluid based systems it may be better to use graphite coated metal gaskets which still tolerate high temperatures up to 800 Deg Celcius but which do not react to fluids.
The Reliability and Evenness of the Load Pressure Affects Gasket Choice
Some applications will naturally have poorer distribution of load across the mating surface or may deteriorate with use. Some gaskets, by their forgiving nature may also "relax" over time, reducing their load retention and dropping the torque range of the connecting faces.
If retaining a good torque setting with minimal relaxation is important then perhaps a metal stainlesss gasket is the best option. Although the trade-off is that you will need to have highly machined flange faces for this type of gasket to perform well.
Cost Considerations for Choosing The Right Gasket
Obviously there is a cost variable when choosing gaskets, for example the reinforced low carbon steel coated with graphite is going to cost more than a straight metal gasket, but equally to use straight metal will require more costs in the machining of the flange mating surfaces.
- We've covered a few of the main considerations for choosing gaskets and there are other things to consider such as:
- vibration and movement
- chemical compatibility and resistance
- lifespan of the products
- whether the gasket is a composite part including adsorbent properties too
The good news is you don't need to have all the answers because our experts at Flow Dry Technology are here to help advise you on how to select the best gasket solution for your needs. We've got our own rapid gasket prototyping facility and gasket research and development (R&D) laboratory and with well over 70 years of industry leading gasket manufacturing and know how we're here to support you.
Posted by John Logan at 12:42