A Hegman gauge is the industry standard method of measurement for fineness of grind in the paint and coatings sector. Hegman gauges are used throughout the world to capture key data for quality control and product improvement. The test will allow a user to interpret particle size, by eye, in a dispersion of liquid sample. This sample could be anything from paint, ink, adhesive, resin, battery slurries, beauty products, food products and much more.
TIDAS is a small, automated unit which objectively takes the reading from a Hegman gauge, using intelligent dark field illumination and a customised algorithm to take the measurement. The product was first developed in 1997 in collaboration with a major coatings manufacturer, who sought a more streamlined QC process.
Since then Labman have sold TIDAS units to customers across the globe, who benefit from the consistent and accurate results. We decided to test how much variation there can be from user to user taking manual readings from a Hegman gauge, and explain why it has such an impact when it comes to production.
Milling is exponential
Many products from the coatings industry begin life as a powder or pigment. These raw ingredients are ground down to reach optimum particle size and determining this grinding time is crucial to save unnecessary over-production costs.
This graph shows a typical grind curve. The grind curve is exponential, meaning that as the particles get smaller, the rate of reduction gets slower. In the latter part of processing, even small reductions in grind size can take a very long time to achieve in respect of the process overall.
Finishing processing at the optimum particle size can cut production costs by a huge percentage. TIDAS can be used to determine the exact production time required to achieve the quality standard, but eliminating any over production. This also frees up production facilities to move on to other work.
Measuring the effect of subjectivity
Six human operators were shown a series of seven images (as below) taken by TIDAS of different dispersions on a Hegman gauge. They were asked to provide a rating for each of the seven images.
The graphs shows that due to subjectiveness, the variation from one user to the next for each image was as much as 14µm in some cases.
Whats more, image 2 and image 7 were an exact duplicate of the same image. The results for these two images highlights that the variation not only occurs from operator to operator, but also the difference from the same operator and the same image.
The cost of over-production
It is not usual that a product will be under-ground, as manufacturers tend to err on the side of caution. Due to fineness of grind occurring exponentially, even small reductions in grind size can take a very long time to achieve, and this is when costly, unnecessary production takes place. Not only are manufacturing facilities expensive to run, it holds up production of other work.
By identifying the exact milling time needed to achieve standard quality, this can be hugely cost effective.
TIDAS provides objective, reproducible readings, every time. This provides confidence in streamlined QC and production methods, for companies with sites across the globe.