The Falling Sand Abrasion Tester - Model 820 is a popular
apparatus used to measure the resistance to abrasion of paint,
lacquers and other organic coatings. Abrasion results from
abrasive particles falling through a guide tube and impinging the
test specimen, until the substrate becomes
visible.
Description
Based on a design described in ASTM D 968 and other
internationally recognized test standards, the Falling Sand
Abrasion Tester consists of an 8" diameter sand reservoir which
includes a 60° taper funnel. Standardized abrasive particles
placed in the reservoir are released to a guide tube by an
abrasive flow gate key. The guide is a 36" straight, smooth-bore
tube which contains the abrasive particles as they fall.
Specimens are fixed under the guide tube at a 45° angle in a
receptacle that includes an opening at the bottom allowing the
abrasive particles to be collected in a container. A sturdy base
and support system hold the apparatus in a vertical
position.
Abradants
Although a variety of abrasive particles have been used, silica
sand and various grades of silicon carbide continue to be most
popular. To ensure reproducible results, the abrasives must be
graded to a particular sieve size.
Note: Silica sand is typically characterized by its roundness of
grains and produces a slower rate of abrasion on organic
coatings.
It has been noted that for 3 mil dry film thickness, many of the
older coatings would require 20 to 200 liters of silica sand to
achieve a failure. Today's more durable coatings may require up
to 600+ liters of sand to wear-through. For an extremely durable
coating, the Taber Rotary Abraser is preferred as the Falling
Sand method tends to be laborious and time consuming with the
handling of large quantities of abrasive.