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D1210-05 – Standard Test Method Technical Guide
📐 Apparatus Design and Gage Configurations
The Hegman-type gage specified in ASTM D1210-05 (Reapproved 2022) is a precisely manufactured block designed to assess the degree of dispersion in pigment-vehicle systems. The apparatus is constructed from hardened steel, stainless steel, or chrome-plated steel, measuring approximately 170 mm in length and 15 mm in thickness. The top surface is ground smooth and planar, featuring a machined path 127 mm in calibrated length.
The path depth tapers uniformly from about 100 µm (4 mils) at 10 mm from one end to zero depth at the other. Preferred calibrations on the graduated scale are Hegman units and micrometers. The standard covers three distinct path width configurations:
| 🟦 Configuration | 📏 Path Width | 📐 Block Width |
|---|---|---|
| Two Parallel Paths | 12.5 mm (0.5 in) each | 65 mm (2.5 in) |
| Single Wide Path | 50 mm (2 in) | 90 mm (3.5 in) |
| Single Standard Path | 25 mm (1 in) | 65 mm (2.5 in) |
In addition to the tapered gage, a stepped gage configuration is specified for cleanliness (texture) rating. This gage features two delimited sections, each of 6.5 cm² area, with two distinct depths designed for particle counting.
⚙️ Test Methodology and Procedures
Tapered Gage Method: The product is spread by a scraper along the tapered path. As the scraper moves from the deep end toward the shallow end, the gap forces particle agglomerates to the surface. A direct reading is taken from the graduated scale at the exact point where particles or agglomerates form a definite pattern (typically 5 to 10 distinct scratches or specks across the width).
Stepped Gage Method (Cleanliness Rating): The product is drawn across a stepped gage containing two wells of different depths. A visual count is made of the particles deposited in the two delimited areas, allowing for a quantitative cleanliness or texture rating.
📌 Technical Note: When using the single path gage, it is possible to assess both fineness and cleanliness. For printing inks and paste-like systems, refer specifically to Test Method D1316 (NPIRI Grindometer), which governs that distinct application.
📊 Result Interpretation and Significance
This test method is essential during pigment milling. The operator can judge if pigment agglomerates have been sufficiently broken up so as not to interfere with smoothness of the finished coating film. The standard provides two distinct data outputs:
| 🎯 Property Measured | 📐 Methodology | ⚡ Interpretation |
|---|---|---|
| Fineness of Dispersion | Tapered Gage Draw-Down | Reading where particles form a definite pattern. Higher Hegman units indicate finer grind. |
| Cleanliness / Texture Rating | Stepped Gage Particle Count | Count of inclusions in standardized 6.5 cm² areas at two depth levels. |
⚠️ Regulatory and Safety Note: The values stated in SI units (micrometers) are regarded as the standard. This standard does not purport to address all safety concerns; users must establish appropriate health, safety, and environmental practices and determine regulatory applicability prior to use.
❓ Frequently Asked Questions
🔍 What is the primary purpose of the Hegman-type gage?
It is used to measure the degree of dispersion (fineness of grind) of pigment in a pigment-vehicle system, such as liquid coatings and intermediates, ensuring agglomerates are small enough for a smooth finished film.
💡 What calibration units are used on the gage scale?
The preferred calibrations on the graduated scale are Hegman units and micrometers (µm). The path depth typically tapers from 100 µm (0 Hegman) down to 0 µm at the shallow end.
⚡ What is the difference between the tapered and stepped gage methods?
The tapered gage provides a continuous direct reading of fineness from a wedged path. The stepped gage contains discrete wells of two specific depths for counting particles, which provides a cleanliness or texture rating.
📌 Can this test method be used for printing inks?
While ASTM D1210 covers general pigment-vehicle systems, the specific standard for printing inks is ASTM D1316, Test Method for Fineness of Grind of Printing Inks By the NPIRI Grindometer.