Charcoal Air Filter Housings

With this project we had a client come to us with respiratory issues and had a very strict requirement for clean air.  These are two projects rolled into one, one of which we had something to improve, a premium OEM passenger vehicle pleated paper filter which is charcoal impregnated.  And the other we had to create from scratch, creating a charcoal filter basket to fit an existing housing that would be secured to the top of a motor home.

Housing number one was fairly straightforward, measuring the existing filter, mocking it up in CAD and then creating a sheet metal part that will be a slide in replacement.  The one thing to note (that the pictures don’t show) is that with a slide in metal box, there would be a concern about vibration noise, so we made the part smaller and lined two of the edges (like the OEM filter) with black felt.

Here are the 18ga 304 stainless steel pieces cut on the CNC table, lightly orbital sanded to give a consistent finish and self-clinching fasteners CLS-440 (otherwise known as PEM’s) installed.  Note you can lightly see the plate marked bend bend lines for the piece on the right.  It makes bending material so much easier and faster!  It beats having to create a flat pattern drawing and dimensioning all the bend locations, then using a pair of calipers and scribing those locations onto the part.  It’s all done during the CNC process.  Also due to the small size of hardware (#4-40) and the tolerance on the hole needed for a self-clinching fastener, all the holes were centermarked with the plate marker and easily drilled out to the correct size.  The piece of the left had the holes drilled and countersunk to allow the countersunk undercut screws to fit flush and ensure no binding when it is installed.

The OEM piece and the custom piece (still need holes drilled in the cover).  Onto the next one!

There are a few projects sitting on the table, what to take notice of is the three round pieces and the long flat piece on the right.  The flat piece is slip rolled and is used to attach two of the rings (the top two rings) together.  Then the ring on the bottom will get secured with #4-40 screws.  Note the use of slots on the bottom ring, the cover, this allowed the perimeter to be cut in one shot, allow for some adjustment while screwing the hardware in.  This will also eliminating a post drilling operation, which saves time and the customer money.

Here’s the welding time lapse video of the welding process. Just a quick 30 second snippet!

And here’s the fabrication completed and test fitted part on the housing for the motor home.  Just making sure everything fits and nothing was overlooked prior to prepping the part for powder coat.

The parts are now blasted and have silicone plugs installed to prevent powder from building up in the threads.

It worked out perfectly having two sacrificial #4-40 screws to allow the entire piece to hang horizontally during powder application and when it goes into the oven.  Note: MIG welding wire makes great disposable hanger material.

Here are the final products.  Brushed 18ga stainless steel and 14ga steel powder coated with super durable wet white powder.  Both using #4-40 stainless steel screws and self-clinching fasteners.  The client will cuts out a cotton filter which is reinforced with wire mesh that will go on the bottom of the filter cartridge, the filter is filled with high quality charcoal and then another cotton filter is placed on top.  The cover is secured and the cartridge is put in the air stream and ready to be put to use!

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