Air Scrubber for 3D Printers
The Prusa i3 MK2S is a great printer especially for the hobbyist or light industrial desktop user. That having been said it is a raw printer without a lot of accessories that would make it a great printer. The is the first in a series of accessories that I designed for the i3. The others are:
This accessory is intended to remove VOC and Ultra Fine particles from the enclosure housing the printer.
3D Printers produce VOC and Ultra Fine particles as a unwanted byproduct of melting and extruding plastics. See recent study by Illinois Institute of Technology and The University of Texas at Austin among others: http://pubs.acs.org/doi/full/10.1021/acs.est.5b04983
Additionally some filaments emit a noxious odor when heated to high temperatures.
Originally the plan was to exhaust 100% of the filtered air either inside the enclosure (moisture elimination & heat retention) or outside the enclosure if internal ambient temperature was not a concern. The exhaust configuration could be changed prior to each print. After several experiments it was determined that a portion of the filtered air (about 40%) should be recirculated and the remainder ported outside the enclosure. By porting a portion of the filtered air outside the enclosure, the pressure inside the enclose is lower compared to ambient. This insures that no unfiltered air escapes from the enclosure during printing. The current Nozzle design accomplishes this. Included is a Restrictor plate to change the mix to 50/50% should the 40/60% cause the enclosure temperature to drop too much when printing ABS or other filament types that require a high stabilized temperature.
The design includes a Extended Grate that can be used to divide the chamber into two sections, one for silica (drying) and one for activated carbon pellets (VOC filtering). In practice it was found that the Activated Carbon Pellets provided adequate anhydrous characteristics and silica was not needed. Should your experience vary, simply insert the Expanded Grate at an appropriate location in the chamber. Fill the section closest to the Fan with Activated Carbon Pellets and the other with Silica. This insures all the air is filtered for VOCs.
This assembly is based on a design by RJ_Make that incorporates a HEPA filter originally designed for iRobot sweepers and a chamber which contains Activated Carbon Pellets. This remix differs from the one by RJ_Make:
- Screws replace rubber bands to hold the various parts together,
- Part count reduced by combining several parts into one,
- Fan exit Nozzle has two outputs - One for overboard and one to recirculate filtered air within the enclosure,
- Adds Exhaust Tube from Nozzle to Enclosure Grommet,
- Includes Enclosure Grommet and optional Restrictor,
- Specification for Fan and optional Speed Controller.
7/12/2017 Update: Removed file "Chamber Top" as it is no longer needed.
- Restore chamber Baffle,
- Modify Chamber to capture the Baffle below filter flange in order to create space between Filter and Baffle,
- Modify Filter to Motor and Expanded Grate by eliminating top several rows of holes to force more air to pass through activated carbon pile,
- Support for alternative Fans.
Added Strengthened Mount courtesy of beikeland.
PLA or ABS may be used to print the various parts. ABS or PETG should be used If ambient temperature will exceed 55°C.
The Tg (Glass Transition Temperature) for Materials:
- PLA = 60°C
- PTEG = 80°C
- ABS = 105°C
The main body consists of two parts:
- Carbon Chamber
- Chamber to Fan Adapter
These two parts are joined together using epoxy, super glue, or hot glue. Care should be taken to properly align both parts so that the HEPA filter can be easily inserted into the top of the resulting assembly. The assembly could have been printed as one part but that would have resulted in excessive support material on the grate at the top of the chamber.
Prepare Nozzle & Chamber to Fan Captive Nuts
These parts contain nut wells suitable for retaining lock nuts the M3x14 screws use to hold these parts to the fan. The nuts must be inserted into the parts before the fan is attached to each in turn. The best method to do this is to temporarily insert a screw of suitable length into the fan side of the part (without the fan installed) and to start the nut on the screw. The Nut can then be properly seated by tightening the screw or by gently taping the nut with a nail set approximately the same size as the nut. Once the nut is seated, remove the screw.
Prepare Fan for Installation
A High Static Pressure Fan is required to force air through the Carbon pellets at an acceptable flow rate. The Fan used (See BOM) was chosen for its form factor (60x60x38mm), CFM flow rate, and cost. This fan was originally used in a Dell computer and is a 4 wire system. The fan is delivered with a connector that would normally plug into the Dell motherboard. Remove this connector. Wire the RED and BLACK wires to the Male Connector as shown below. Note the Red Wire is on the left when observed from the pins side of the connector. Cap and stow the Green & Yellow wires. They are not used in this installation.
This motor is extremely polarity sensitive. Reversing the Fan motor will destroy the unit!
Install Fan & Exhaust Tube
Install Fan into the mating parts using 4 screws in each assembly. The Fan and Nozzle can be rotated into any of 4 positions. Rotate the Fan so that the power wire is positioned as required for your installation. Likewise rotate the Nozzle so that the recirculating air port does not blow air on the print bed but is otherwise unobstructed.
Install the Exhaust Tube to the Nozzle. This is an interference fix. Make sure that no extruded plastic is obstructing the Exhaust Tube opening or the Nozzle flange. The Exhaust Tube should be able to rotate once installed but should not be so loose that it falls off the Nozzle. See completed assembly below.
HEPA Filter Assembly
Optional Fan Speed Control
The Fan can be operated at 100% rated speed by simply plugging the connector into a 12Vdc power supply. However there are often times a slower fan speed is desirable. For these cases a Speed Controller can be used to throttle down the Fan speed and therefore the filtered air volume.
Originally it was thought that the speed control potentiometer would be best located away from the speed control board and that the control board incorporated into the filter body. This proved impractical and the control board and potentiometer are now housed in a separate box with the output wired to the Fan through a mating connector to the one installed on the Fan in the steps above. Files necessary to print the Control Box top and bottom are included in the files section.
An alternate speed control is available with the potentiometer incorporated on the control board. The alternate part is listed below in the BOM. This would require a modification to the included Control Box since the size required is somewhat less and the potentiometer and control board are positioned differently.
Control Board wiring is identical for either version of the control board. See below.
The control board polarities are critical. Reversing the polarities can damage the Control Board and Fan. For this installation the input voltage must be 12VDC.
Speed Control Board Wiring
The mount below is designed to be screwed on to a vertical surface.
Filter Wall Mount
Installation in Prusa i3 MK2S Enclosure
The picture below shows the HEPA Filter mounted in the Prusa i3 MK2S enclosure. Note the positioning of the Mount, Exhaust Tube, and power wire. Not visible is the Nozzle recirculating vent which is pointed down. Also note the Fan to Speed Controller connector that is just visible under the top i3 Support bar.
A Baffle has been introduced that will be installed below the HEPA filter flange in the Chamber. This permits airflow from the entire filter length while forcing all of the flow through more of the activated carbon pile.
The Chamber has been modified to add a flange beneath the filter flange offset by the thickness of the Baffle. The flange extends from the Fan Grate aft 50mm. This allows the Baffle to be installed and removed without use of adhesives.
- Several rows of holes have been removed from the Chamber to Fan and Extended Grate to keep airflow from byassing the activated carbon pile.
Install the Baffle by inserting it into the aft portion of the Chamber and sliding the Baffle forward between the two flanges in the Chamber. The Baffle can be sealed with the Chamber using tape, RTV, hot glue, etc as desired,
Fill the Chamber with activated carbon pellets flush with the aft end of the Baffle while holding the assembly Fan end down.
- Position Extended Grate forward to capture the carbon pile. The Baffle has two flanges incorporated at the aft bottom side that will capture the Extended Grate at the upper flat edge.
Additional Supported Fans
Two additional fans have been added to the BOM to provide for varying levels of noise and airflow:
Fan Part Number RPM CFM Noise Length
Noctura NF-A6x25 FLX 3000 17 19Dba 25mm
Sunon PMD1206PMB3-A 6000 42 47Dba 38mm
San Ace 9G0612G101 11,800 65 58Dba 38mm
The Noctura fan is virtually silent but the airflow is not sufficient to purge the Enclosure in real time. After printing PLA for an hour, one additional hour was required to remove all noticeable odor from the Enclosure. The airflow does appear to be sufficient to create a slight vacuum in the Enclosure therefore trapping the nono-particles within the Enclosure. Temperature rise withing the Enclosure was modest, rising only 5°C to 35°C with a bed temperature of 60°C. Care should be exercised in not opening the Enclosure door for a period of time in order to allow all the nono particles that can be removed to be removed.
The Sanon fan is sufficient for most applications. The noise level is only noticeable when the printer is not running. The Prusa i3 MK2S Hot End cooling fan drowns out the sound of the Sanon fan during printing operations.
Finally the San Ace fan should be used where maximum airflow is required to lower the Enclosure temperature.
Bill of Materials