Dust is contained in the cylindrical holder (A) into which it is tightly packed. It has been found that any dust which is clean and dry with most particles below 10 micrometers diameter, can be packed in this way, and will form a stable cake; yet when the dust is scraped off the surface, it can be readily dispersed. Dust is scraped into a groove in the surface of a scraper head (K). Along this groove a stream of air is passed so the dust is carried down the inner tube (J). At (L) it is passed through the jet which breaks up any remaining aggregates.

Scraping is carried out by rotating the dust holder (A) round the threaded spindle (F) through the intermediary of the gears (C), (E) and (D), which act as a differential gear and cause the holder to travel very slowly down the threaded spindle (F). In this way an extremely thin layer of dust is scraped off at each revolution of the holder (0.007") or 0.18mm. A variable speed motor provides adequate power for driving the mechanism over a speed range of about 1000:1.

The large dust chamber has an internal diameter of 1.5 inches (38mm). When very low concentrations are required the small chamber can be fitted, thereby reducing the internal diameter to 0.530 inches. The small chamber and scraper head are supplied with the mechanism.

The unit is normally supplied for use with 120V, 60Hz/230V, 50Hz. Voltage is automatically selected via an internal sensor.

Capacity

With the dust packed to within 8mm (0.31 in.) of the container face, the working capacity is 40.80cc (2.48 cubic inches). With the small chamber fitted and using the small scraper head the working capacity is 5.0cc (0.30 cubic inches)

Inlet pressure and flow

With an inlet pressure of 5 PSIG or 10 PSIG the flow rate from the outlet is 12 to 15 liters per minute respectively, using a standard jet with an orifice of 0.052 inches diameter. High pressures of a least 16 PSIG are recommended for complete deaggregation. At this pressure flow, rate is approximately 25 LPM.

Speed

The differential gearing is such that the dust container will move down 0.007 inches (0.18mm) for each revolution that it makes (digitally displayed).

Volume of dust dispersed

From the information given, the volume of dust dispersed can readily be calculated. For example, with the large dust container and speed of 0.1 rpm, rotations will be made in one hour. This will give a downward displacement of 1.08mm and given the 38mm diameter of the scraper head the volume dispersed is 1.22cc.

For further information see paper by inventor Dr. B.M. Wright published in the Journal of Scientific Instruments, Vol. 27, No. 1, page 12, 1950 and Review of Scientific Instruments, Vol. 34, Sept. 1963, pages 1023-5. A more recent reference is contained in the book entitled Generation of Aerosols and Facilities for Exposure Experiments, Ed. by Klaus Willeke, Ann Arbor Science Publishers, Ann Arbor, Michigan (1980).

Specifications

Electronic Module