Pencil Hardness Gauge / Gage

---

Performs the ASTM D3363 Pencil Hardness Test

---

Assess quantitatively the rigidity or firmness of organic coatings applied to rigid substrates such as metal.

---

The H-501 Pencil Hardness Gage/Gauge is practical for use in the laboratory, on the production line, or in the field to assess quantitatively the rigidity or firmness (elastic modulus) of organic coatings applied to rigid substrates such as metal. Hardness values may define requirements for particular coatings applications or may be used to evaluate state-of-cure or aging of coating.

The Pencil Hardness Gage/Gauge is unique in that it provides a compact single unit for performing this test, rather than a set of easily lost individual pencils. The importance of this advantage is especially apparent when several individuals are working with a single instrument.

Kit Contents

Micro-Metrics H-501 Pencil Hardness Gauge fourteen leads Dressing disk Carrying case

Principle

When two materials of different degrees of hardness of rigidity are forced against each other, one of the materials either yields or crumbles, while the other is unaffected. Thus a scale of relative hardness can be established on the basis of the ability of one material to scratch or deform another. This principle has long been used in the mineralogy field where it is known as the Mohs Hardness Scale (F. Mohs, 1820). Thus, the hardest material, diamond, is arbitrarily given a hardness value of 10, and other materials range downward through, for example, Corundum–9, Quartz–7, Apatite–5, Calcite–3, and Talc–1.

Mechanical drawing pencil leads of available grades cover a range of useful organic coatings. The crumbling mode of failure is also an essential characteristic of the drawing leads, which is necessary for this application.

The Pencil Hardness Gage/Gauge design allows the user to force pencil leads of increasing hardness values against a coated surface in a precisely defined manner until one lead mars the surface. Surface hardness is defined by the hardest pencil grade that fails to mar the painted or coated surface.

The leads supplied with the Micro-Metrics Pencil Hardness Gage/Gauge, listed from softest to hardest, are:

6B, 5B, 4B, 3B, 2B, B, HB, F, H, 2H, 3H, 4H, 5H, 6H

The leads are supplied in a carrying case that identifies each lead (individual leads may come without identification, or the identification mark may be difficult to read). Choosing and installing the eight leads most commonly used will allow the leads most appropriate to the surface(s) being tested to be always at the ready.

Five small circular pieces of 400 grit carburundum paper mounted on a plastic dressing disk are provided to facilitate dressing the lead points while they are in place in the gage.