A Hegman gauge, sometimes referred to as a grind gauge, grind gage, or grindometer, is an instrument which indicates the fineness of grind or the presence of coarse particles and agglomeration in a dispersion.[1] It is commonly used to determine how finely ground the particles of pigment (or other solid) dispersed in a sample of paint (or other liquid) are. This is important because many types of solid materials must be ground into finer particles in order to be dispersed in liquids.[2] The resulting properties of the dispersion vary based on the size of individual particles and the degree which they are dispersed.

The Hegman gauge consists of a steel block with a series of very small parallel grooves machined into it. The grooves decrease in depth from one end of the block to the other, according to a scale stamped next to them. A typical Hegman gauge is 170mm by 65mm by 15mm, with a channel of grooves running lengthwise, 12.5mm across and narrowing uniformly in depth from 100 μm to zero and used to determine particle size.[3]

Use with paintEdit

A Hegman gauge is used by puddling a sample of paint at the deep end of the gauge and drawing the paint down with a flat edge along the grooves. The paint fills the grooves, and the location where a regular, significant "pepperyness" in the appearance of the coating appears, marks the coarsest-ground dispersed particles.[3] This is the point where oversized particles start to appear in high density and determines the rating for that material.[4] The reading is taken from the scale marked next to the grooves, in dimensionless "Hegman units" (or National Standard units; NS) and/or mils or micrometres.[5] Hegman units are defined in terms of an inverted size scale as shown below:[6]

Hegman Units Mils Microns
0 4.0 101.6
1 3.5 88.9
2 3.0 76.2
3 2.5 63.5
4 2 50.8
5 1.5 38.1
6 1 25.4
7 0.5 12.7
8 0 0

A lesser-used scale, North (or PCU), is also occasionally employed in the paint industry. Like the Hegman scale, this is also inverted compared to the value in microns:

Microns North units
0 100
10 90
20 80
30 70
40 60
50 50
60 40
70 30
80 20
90 10
100 0

Determining the fineness of a paint's grind is important, because too coarse a grind may reduce the paint's color uniformity, gloss, and opacity.[7] The Hegman gauge is widely used for this purpose because it requires minimal skill and only a few seconds' work.[3]

Other usesEdit

Grind gauges are used in a variety of fields, including; food, pharmaceutical, plastic and many others. In all of these fields, grind gauges are utilized to produce, store, and apply dispersion products.

SizesEdit

Hegman gauges are commonly available in the following ranges: 0 to 100 micrometres, 0 to 50 micrometres, 0 to 25 micrometres, 0 to 15 micrometres, and 0 to 10 micrometres.

ReferencesEdit

  1. ^ Koeler, Paint and Coating Testing Manual, p. 743, ISBN 0-8031-2060-5
  2. ^ http://www.astm.org/Standards/D1210.htm
  3. ^ a b c Robert B. McKay, Technological Applications of Dispersions, p. 43 (citing ASTM D1210-79 (1988)). Marcel Dekker, Inc., 1994.
  4. ^ http://www.astm.org/Standards/D1316.htm
  5. ^ Eric Kissa, Dispersions: Characterization, Testing, and Measurement, p. 243. Marcel Dekker, Inc., 1999.
  6. ^ D. Doubleday and A. Barkman, "Reading the Hegman Grind Gauge" Paint, Oil and Chemical Review June 22, 113 1950 pp 34-39, http://www.gardco.com/pages/dispersion/fg/Hegman%20Article.pdf
  7. ^ Peter A. Ciullo, Industrial Minerals and Their Uses: A Handbook and Formulary, pp. 155–56. Noyes Publication 1996.

BibliographyEdit

  • Koleske. Paint and coating testing manual : fourteenth edition of the Gardner-Sward handbook (14th ed.). ASTM. ISBN 0-8031-2060-5.