Advantages: rich level, deep and detailed drawing. Disadvantage: The picture is easy to reflect light and gray. The hardness mark of pencil lead is usually “H” for hard pencil, “B” for soft pencil, “HB” for soft and moderate pencil, and “F” for pencil with hardness between HB and H.
Pencil is a kind of pen used for writing and drawing. It has a history of more than 400 years. Among them, pencils for drawing can be divided into three stages of development: graphite, wooden penholder and capped pencil. In addition, its color has red-white, black-white, yellow-black stripes.
The hardness mark of pencil lead is usually “H” for hard pencil, “B” for soft pencil, “HB” for soft and moderate pencil, and “F” for pencil with hardness between HB and H. Arrangement (from soft to hard) 9B, 8B, 7B, 6B, 5B, 4B, 3B, 2B, B, HB, F, H, 2H, 3H, 4H, 5H, 6H, 7H, 8H, 9H, 10H and other hardness grades. The larger the number in front of H, the harder the lead core, the lighter the color. The bigger the number in front of B, the softer the lead core, the darker the color. The classification of pencil rods is based on the weight of graphite in the pen core.
The lead core is made of graphite and clay in a certain proportion. After mixing by kneading machine and three rollers machine, the lead core with a certain size (such as HB~3H lead core diameter 1.80~2.10mm) is extruded by core pressing machine. The lead core is dried by heating (50~150 C) and roasted at high temperature (800~1100 C), so that it has a certain mechanical strength and hardness. Finally, it is made by oil immersion treatment. The processing of color lead core is similar to that of graphite lead core, but it does not need sintering.