Dust can be an invasive contaminant that can cause overheating and other failures of electronics and other types of equipment. “Settling dust” test standards from various industries are published to help manufacturers prove their product can handle a dusty environment by being well-sealed, or unaffected by such contaminants.
A settling dust test has dust blown upwards in a chamber where the sample is placed, then the blower is turned off so that the dust has time to settle on the sample. Some test standards also refer to this type of test as “vertical dust flow”.
There are some test standards that call for ‘blowing dust’ or sand, such as Mil-Std 810. This type of test is designed to simulate outdoor environments, and is a distinctly different test than settling dust. A blowing dust test requires a small wind tunnel and metered flow of particles, making for an expensive and complicated system.
A settling dust test chamber is simpler. Dust material is placed in a collector, or trough, at the bottom of the chamber, where air nozzles periodically agitate the material, causing a cloud in the chamber. After the agitation, the dust cloud is allowed to settle onto the test sample, which sits above the collector.
Homemade set-ups for doing these tests are not uncommon, but if not built right, can be very messy. Some test labs dedicate a separate room for this type of chamber, just to keep down on the risk of dust spreading.
The sample is rotated by hand periodically, allowing the dust to settle on all sides. Glove-ports and a window are desirable so the operator can handle the sample without repeatedly opening the chamber, which can make a mess.
Tests for electrical enclosures may require that a light vacuum pressure, or under-pressure, be applied to the enclosure during the test. The vacuum makes the ingress of dust more likely if the sample’s seal is not sufficient.
Dust tests are often specified for use with “Arizona road dust”. Incredibly, this dust is standardized and four grades are available. There are also tests which require talcum powder, concrete powder, or various fibers as the contaminant.
Industry standards with settling dust tests:
SAE J575 (Rev. NOV2006), Section 4.5
ISO 20653 (2006-08-15), Section 8.3.1
DIN 40050, Part 9, IP Codes 5K and 6K, vertical dust flow
IEC EN 60529 (IEC 529), IP-5 and IP-6, vertical dust flow, with under-pressure
IEC EN 60068-2-68 (IEC 68-2-68), LA2, vertical dust flow