I. Molding Principles:
Plants contain large amounts of lignin and cellulose. Lignin has no melting point but has a softening point. When the temperature reaches 120-160°C, the hot water-soluble components in lignin begin to dissolve. At 180°C, lignin softens and plasticizes. When pressure is applied at this temperature, the lignin tightly binds with cellulose and mutually bonds with adjacent particles. The briquetting technology utilizes this characteristic of plants to form rods through heating and extrusion.
II. Molding Conditions:
We utilize the softening property of plants to achieve molding, but it must be done under certain conditions.
Due to differences in material types, moisture content, volume, and specific gravity, molding conditions are not fixed, which results in the uncertainty of briquetting technology and complexity of the process. Some technical issues still plague the industry today. Therefore, mastering briquetting technology is equivalent to mastering the entire Mechanized Charcoal production technology.
1. Moisture Content of Raw Materials:
The moisture content of raw materials greatly affects the molding process and product quality. When the moisture content is too high, excessive steam generated during heating cannot be smoothly discharged from the center hole of the rod, causing surface cracking of the rod. In severe cases, it may result in popping or failure to extrude. However, if moisture content is too low, molding also becomes difficult, because trace amounts of moisture promote the softening and plasticizing of lignin.
Effect of raw material moisture content on molding:
Moisture Content 4% 6% 8% 10% 12% 15%
Wood Materials Not Moldable Moldable Moldable Moldable Moldable Not Moldable
Crop Materials Not Moldable Moldable Moldable Moldable Not Moldable Not Moldable
As can be seen from the table, the most suitable moisture content for raw materials is about 10%.
2. Molding Temperature (Theoretical Temperature):
Molding temperature has a significant impact on the rod extrusion speed, density, appearance, and quality. Therefore, appropriate temperature must be adjusted for specific raw materials to ensure rod output quantity and quality. The required temperatures for various raw materials have been introduced previously. It should be noted that if the temperature is too low, it is insufficient to soften the lignin in the raw materials, causing blockage in the extrusion sleeve and difficulty in rod formation. If not careful, the screw may be twisted and broken. If the temperature is too high, the raw materials decompose severely, causing carbonization on the rod surface and making it difficult to form effective pressure, thus failing to mold. Even if molding is possible, the rod density is insufficient. In severe carbonization cases, a carbonized layer forms on the inner wall of the molding sleeve, similarly causing difficulty or failure in rod extrusion.
Generally, pine and hard miscellaneous wood have a relatively wide temperature tolerance, especially larch, which can extrude rods normally at slightly higher or lower temperatures. If 50% larch is mixed with 50% hard miscellaneous wood, the produced rods are very smooth with smooth extrusion, good density, fast speed, and the carbonized charcoal is of the best quality. However, some materials require a narrow temperature range: if the temperature is too low, the material cannot be pushed through; if too high, it fails to mold, or even if molded, cracks appear, density is insufficient, surface carbonization is severe and rough, extrusion is not smooth, smoke is heavy, and the carbonized charcoal is poor in quality with many broken pieces.
3. Heating
Currently, electric heating coils are generally used for heating. Our factory uses heating coils made of stainless steel tubes with high-temperature insulation materials, with a service life four times that of ordinary heating coils.