Primary Design Considerations.

All porous products, whatever the material of construction, have specific properties and limitations which must be taken into account in design and manufacturing processes. Proper attention to these characteristics will help control costs in manufacturing, while at the same time, produce the best combination of properties and performance.

In order to select the best media for any application, you should be able to provide Mott with the following information:

Primary application considerations

• Desired particle retention
• Process temperature
• Pressure drop
• System pressure
• Flow rate
• Corrosive effects, if any
• Operating fluid – type, density, viscosity

Primary media considerations

In some cases, you may already know what type of Mott media is the best choice for your application. Standard products are designated by shape and media grade, but other characteristics may be altered to “fine tune” product performance:

• Pore size
• Pore size distribution
• Number of pores per unit area

Manufacturing/assembly considerations

OEMs who wish to alter the shape or configurations of Mott products need to be aware of procedural limitations and guidelines to avoid compromising permeability. Listed here are basic considerations.

• Forming – Mott porous metal media has significant ductility, which allows cold forming within certain limits. For example, Mott standard 316L stainless steel, 1/16"- thick sheets can be roll formed into cylindrical filter cartridges with an outside diameter as small as 1 1/4". Smaller diameter tubes may be formed by using thinner sheets.
• Machining – Conventional machining will close surface pores, making the machined surface impermeable. It is possible, however, to keep surface pores open with electrical discharge machining (EDM).
      If conventional machining is to be applied, Mott recommends using only water-soluble oils as lubricants. The machined components may subsequently be reactivated with a proprietary technique developed by Mott, performed at the factory. Customer-machined media may be returned to have this technique applied. As a value-added supplier, Mott provides these machining services. Ask our sales professionals for more information.
• Brazing – Brazing porous metal is extremely difficult. The porous metal tends to act as a wick, so when molten braze is applied, it is soaked up into the pores, filling them and destroying porosity. To avoid this effect, Mott has developed a special brazing technique which will be performed upon request.
• Welding – Mott sintered porous metal can be readily welded – to themselves, and to solid metal parts – as long as certain procedures are followed. Approximately 50% of porous metal consists of voids which tend to collapse under the heat of the welding arc. When this happens, additional metal must be added during the welding process to compensate for volume. This can be accomplished with a filler rod, or can be provided in the weld preparation of the mating solid component.
      Achieving optimal welds requires proper joint design. Our in-house weld shop has the experience and expertise to get the job done right. Contact us directly for more information on our services.

Cleaning considerations

Mott porous metal media can be cleaned for continuous reuse through a variety of techniques. Which method is best depends on the application – how the media is used, and what types of gases, liquids and particles are present. The following table shows some of the more common cleaning techniques.

Descriptions of other cleaning methods, and more detailed information, may be obtained by contacting Mott Specialty Porous Sales, or downloading the following PDF (48.8 K) document: Cleaning of Porous Metal Products.