Step 8: Testing Methods and Sample Materials
This is simply a measurement of the collected gasses at the top of the 3D Printer during an actual print. The part printed is the "Material Certification Object".
Dynamic Error Testing:
This is the test where we determine the "what could possibly go wrong" and duplicate the issue in a controlled area - the column.
The assumption for this test, is a run-away heater resistor or cartridge. Any error that allows the heater block to increase temperature of the material while printing continues.
Gasses are emitted whenever pyrolysis is breached for all materials. Therefore we conducted some intermediate tests to determine the temperature that indicated a breach. When the breach temperature was determined, we moved to the 3D Printer and started to print at 20 degrees below this temperature with the intent of increasing temperature to the point of breach to discover any issues.
We discovered that in most cases contact of the plastics to the overheated nozzle resulted in a boiling type action that repels (adds back pressure) the material. As printing continued (1-3 minutes) , we eventually reached a point where the extruder pressure required was greater than the grip capabilities of the extruder and material slippage ensued. Within a minute, the material was cut through by the extruder teeth and pressure ceased.
At this point we realized we would need to start at a lower temperature and again increase till we meet the pyrolysis value. We then discovered that while we could print slightly longer, as the nozzle approached a pre-breach temperature value, the same effect began and extrusion stopped. The purpose was to determine the amount of material still in the hot-end that could now continue to be exposed to an ever increasing temperature. The amount of material for 2 tests was almost identical at .3grams or about 24mm of 3mm ABS material.
We now have an "amount" of material for our Dynamic testing.
As we were testing 3mm, 2.8mm, 2.1mm and 2.9mm material, testing samples were cut by weight rather than length.
Combined or Cumulative Testing:
The next set of tests were to measure the accumulation of gasses in a small enclosed space. HCN is lighter than air and will accumulate at the highest spot in the room. As it transitions into the room, it is diluted by the total volume of air in the room. Thus, while a reading directly above the exhaust slot may be 1ppm, by the time that small volume dissipates within the room, it is almost zero. As the opening or slot in the the lid during dynamic testing was about 3 square inches, it represented a column of combined gas and air of that same size. Therefore it can be said that a reading of 1ppm was a reading within a 3 inch rectangular column. That column of mixture expands to about 4 feet square as it rises to the ceiling, and therefore, the PPM declines in kind.
The goal of this test is to determine the absolute worst case accumulated HCN emitted by two each failed 3D Printers operating in an small space. The amount of sample material was doubled to equate to two failed units. The results could also be useful for those with printer farms as they typically use 8+ printers in close proximity.
All 3D Printing ABS materials tested are available on-line from a long list of respected vendors here.
NOTE: There was almost no variation in test results from one ABS vendor to the next.
All 3D Printing Nylon materials are available here,.
All non-3D Printing Trimmer and Weed-whacker Line are available at most Home Improvement stores.