Step 9: Test Procedures
If you are using material listed here, then you can skip the Dynamic testing and move to the 3D Printing Active testing.
If you are testing a completely new and a "known to be untested" material, then we suggest you start with the Dynamic Error testing as more safety is involved.
Setup your test equipment and column as shown in step 5
Open a 1" wide exhaust slot on the plastic lid of the column.
Make sure the sensor element is in the line of hot air flow.
Remember to read the safety Step 2
If you don't have a scale for the material, 3mm ABS is about 24mm 3mm Nylon is about 27-28mm for .3 grams.
The intent is to measure any emissions at and slightly above the temperature you are going to use during printing. We suggest printing temperature plus 30 more degrees "C". This insures you are not on the edge of breaching pyrolysis. In our testing we went way beyond breaching pyrolysis for other evaluations. The system defined here uses a variac to adjust the AC voltage to the heater cartridge. This is an open loop, but still maintained temperature within a few degrees. You can use any temperature control you need to slowly apply the heater voltage. The voltage rise along with temperature is meant to be slow, taking place over about a 30 min span. You can raise the temperature to about 125C quickly, but from there on, take it slow. With our setup we adjusted to 50 volts and allowed the temperature to rise to about 125-130C for a 120 volt Heater Cartridge. From there we stepped voltage up as follows:
60, 70, 75, 80 if needed.
Again, this transition should take about 30 min.
When you reach 30 degrees "below rated temperature, you should start logging every minute any HCN readings including "0" as you transition on up to rated plus 30.
Once at the rated plus 30 mark, let the material set at that temperature for 5 min, again logging HCN readings each minute.
At the end of the 5 minutes, the test is complete. You should average your readings.
Items of note:
1. If your peek reading is less than 4.7ppm, it is considered safe by OSHA and other health organizations. However, from our measurements, a value higher than 0.1ppm on average is unusual.
2. If the smoke detector sounded it's alarm, then the material is definitely unstable. The only material that tripped our smoke detector was trimmer line #2.
3. If the material spits out small puffs of smoke, then it is close to breaching pyrolysis.
4. HCN can "accumulate" at the ceiling of the room. Therefore a constant reading of 4.0ppm to 4.7ppm will accumulate to a higher value at the highest point in the room and this is why we want to watch out for unusual readings.
3D Printing Active
This is a basic monitoring of HCN sensor levels during the middle of a 3D Print. Again, we used the "Material Certification Object".
The printer is configured as shown with the large plastic hood or, in this case an inverted storage box. A hole about 2X the diameter of the sensor is cut on the hood for gasses to escape. The sensor detector module is placed such that gasses escaping will pass by the sensor. All cooling fans are to be turned off.
NOTE: The 2BEIGH3 uses NEMA 23 steppers and temp of these units reached 80C-104C with fans OFF. One unit required a replacement due to the number of tests. You should cool steppers between tests.
You will need to ensure that no room air currents modify the path of the rising heated air.
The printing temperature should be the maximum for most prints. This will vary from printer to printer and in some cases, the material may come with suggested temperature values.
If you use the "Material Certification Object", it has a wide and thin (4 - 8 layer) seat. Temperature should be settled by the time the center square begins printing. This will be the beginning of your measurements for HCN as read from the HCN sensor unit.
Document any readings including "0" every 30 seconds. Watch to make sure no reading exceeds 1ppm. After about 10 minutes of printing, you should have accumulated about 20 readings. This of course is the test of interest to most of us that print.
You should run an "average" of the 20 or so numbers to come up with an average value of HCN emissions. If your peek reading is less than 4.7ppm, it is considered safe by OSHA and other health organizations. However, from all of our measurements, a value higher than 0.1ppm on average is unusual. As mentioned above, HCN can "accumulate" at the ceiling of the room. Therefore a constant reading of 4.0ppm to 4.7ppm will accumulate to a higher value at the highest point in the room and this is why we want to watch out for unusual readings.