HEPA Filter for 3D Printer

2 reviews

jmillerfo

@jmillerfo_84104

Air Scrubber for 3D Printers The Prusa i3 MK2S is a great printer especially for the hobbyist or light industrial…

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2034

updated January 27, 2023

Description

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Air Scrubber for 3D Printers

ThePrusa 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 thei3. The others are:

Enclosure

https://www.thingiverse.com/thing:2396990

Spool Holder

https://www.thingiverse.com/thing:2398480

OctoPrint Print Server

https://www.thingiverse.com/thing:2401423

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 currentNozzle design accomplishes this. Included is aRestrictor 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 aExtended 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 theActivated Carbon Pellets provided adequate anhydrous characteristics and silica was not needed. Should your experience vary, simply insert theExpanded Grate at an appropriate location in the chamber. Fill the section closest to theFan withActivated 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 containsActivated 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 exitNozzle has two outputs - One for overboard and one to recirculate filtered air within the enclosure,
AddsExhaust Tube fromNozzle toEnclosure Grommet,
IncludesEnclosure Grommet and optionalRestrictor,
Specification forFan and optionalSpeed Controller.

7/12/2017 Update: Removed file "Chamber Top" as it is no longer needed.

1/7/2018 Update:

Restore chamberBaffle,
ModifyChamber to capture theBaffle below filter flange in order to create space between Filter andBaffle,
ModifyFilter to Motor andExpanded Grate by eliminating top several rows of holes to force more air to pass through activated carbon pile,
Support for alternativeFans.

3/5/2019 Update:

Added Strengthened Mount courtesy of beikeland.

Print Settings

Printer:

Prusa i3 MK2S

Rafts:

Supports:

Yes

Resolution:

0.20

Infill:

20%

Notes:

PLA or ABS may be used to print the various parts.ABS orPETG should be used If ambient temperature willexceed 55°C.

The Tg (Glass Transition Temperature) for Materials:

PLA = 60°C
PTEG = 80°C
ABS = 105°C

How I Designed This

Main Body

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

AHigh 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.

CAUTION

This motor is extremely polarity sensitive. Reversing the Fan motor willdestroy the unit!

Install Fan & Exhaust Tube

Install Fan into the mating parts using 4 screws in each assembly. TheFan andNozzle can be rotated into any of 4 positions. Rotate theFan so that the power wire is positioned as required for your installation. Likewise rotate theNozzle so that the recirculating air port does not blow air on the print bed but is otherwise unobstructed.

Install theExhaust Tube to theNozzle. This is an interference fix. Make sure that no extruded plastic is obstructing theExhaust Tube opening or theNozzle flange. TheExhaust Tube should be able to rotate once installed but should not be so loose that it falls off theNozzle. 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 theFan through a mating connector to the one installed on theFan in the steps above. Files necessary to print theControl 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 includedControl 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.

Caution

The control board polarities are critical. Reversing the polarities can damage theControl Board andFan. For this installation the input voltagemust be 12VDC.

Speed Control Board Wiring

Filter Mount

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 theMount,Exhaust Tube, and power wire. Not visible is theNozzle recirculating vent which is pointed down. Also note theFan toSpeed Controller connector that is just visible under the top i3 Support bar.

1/7/2018 Update

ABaffle has been introduced that will be installed below theHEPA filter flange in theChamber. This permits airflow from the entire filter length while forcing all of the flow through more of the activated carbon pile.
TheChamber has been modified to add a flange beneath the filter flange offset by the thickness of theBaffle. The flange extends from theFan Grate aft 50mm. This allows theBaffle to be installed and removed without use of adhesives.
Several rows of holes have been removed from theChamber to Fan andExtended Grate to keep airflow from byassing the activated carbon pile.

Assembly Instructions

Install theBaffle by inserting it into the aft portion of theChamber and sliding theBaffle forward between the two flanges in theChamber. TheBaffle can be sealed with theChamber using tape, RTV, hot glue, etc as desired,
Fill theChamber with activated carbon pellets flush with the aft end of theBaffle while holding the assemblyFan end down.
PositionExtended Grate forward to capture the carbon pile. TheBaffle has two flanges incorporated at the aft bottom side that will capture theExtended 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 theEnclosure in real time. After printing PLA for an hour, one additional hour was required to remove all noticeable odor from theEnclosure. The airflow does appear to be sufficient to create a slight vacuum in theEnclosure therefore trapping the nono-particles within theEnclosure. Temperature rise withing theEnclosure was modest, rising only 5°C to 35°C with a bed temperature of 60°C. Care should be exercised in not opening theEnclosure 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 theEnclosure temperature.