Hardness Test of Mechanical Pencil Leads

Introduction

The writability of mechanical pencils differs depending on the hardness of the pencil lead. Writing becomes darker as the lead becomes softer and it is possible without breaking the lead as it becomes harder. Therefore, leads are used in different applications depending on their hardness. For example, softer leads are used in sketching and harder leads are used in drafting technical drawings. The leads of mechanical pencils are made by compounding graphite and resin. After extrusion molding, the compound is baked at approximately 1200 °C and then impregnated with an oily material to impart depth of color and lubricity. The symbols B and H mean “black” and “hard,” respectively, and HB means “hard & black,” an intermediate quality between H and B. Accordingly, the order of hardness of mechanical pencil leads is 2H > H > HB>B>2B. Although the symbols B and H are defined by the density drawn on drawing paper by a density measurement machine, there is no scientific definition of pencil lead hardness. Therefore, the following introduces an example of a hardness test of mechanical pencil leads. The hardness of mechanical pencil leads was confirmed by using a SHIMADZU DUH-211 Dynamic Ultra-micro Hardness Tester.

October 24, 2018 GMT