The New Technique of Veneer Hot-pressing Drying

    木材干燥是木业生产加工中举足轻重的重要环节之一，而单板干燥在胶合板、实木复合地板基材、集装箱地板、人造木（又称科技木）等生产过程中同样是很关键的工序。目前大部分企业采用网带干燥机、辊筒干燥机或者人工晒干的方法进行单板干燥，前两者干燥成本高，费电、费热能，单板易开裂、破损；后者需要大量的场地及人员，而且对干燥

后单板的含水率无法得到控制和保障。

Wood drying is one of the most important approach in wood processing, and it is also the key step in the production of plywood, basic wood of composite solid floorboard, container floorboard, man-made wood (technical wood). At present most companies make use of band dryer, roller dryer or manual dryer. The former two methods cost high, not only wasting electric power and heat energy, but are very likely to cause veneer split and broken. The last one requires large field and involves more staff; besides, the moisture content after drying is hardly controlled and guaranteed.

木材干燥就是要排除木材中的水分。在一般情况下，木材内部的含水率高于外部的含水率，木材加热时，木材外部的温度高于内部温度，含水率梯度迫使水分由内部向外部移动，而温度梯度迫使水分由外部向内部移动，这二个方向相反的水分移动互相对抗，致使离木材表层不远的地方呈现了一个水分移动缓慢区，从而对干燥过程产生阻力。在保证干燥质量的前提下，提高干燥速度是干燥的基本原则，传统的干燥方法只有靠提高干燥温度来解决干燥速度，现在一种新型的热压干燥工艺解决了这一难题。

The purpose of wood drying is to extract water from wood. Generally the moisture content inside wood is higher than that outside on the surface. And during the heating, the external temperature is higher than the internal. Therefore, the movements of water from two opposite directions competes against each other, when the moisture gradient will force moisture to move from the internal out, yet the temperature gradient forces it to move into the veneer. Such competition gives rise to a slow movement area of water just in the vicinity of the surface, which resists and retards the drying process. The fundamental principle of drying is to accelerate the drying speed without sacrificing the drying quality. However, the conventional method can only accelerate the speed by increasing drying temperature. Fortunately, we have now a new hot-pressing drying technique as solution.

我们用经过特殊加工的热压板，以接触传导的方式，直接加热木材单板。由于加热板供热温度高，与被干木材接触紧密，传热量大，木材内部水分移动缓慢区迅速被冲破，温度很快就达到高温，蒸汽压力瞬间提高，促进了木材内部水分向外部的移动。为了能使大量水分在大面积的板间及时排放出来，单板热压干燥的热压板专门设置了大密度的透汽槽，使大量蒸汽迅速通过沟槽排出，达到快速干燥的目的，这一技术对一些不易干燥的硬杂木树种尤其有效。

Particularly processed platens are used to directly heat the veneer through contact conduction. Due to the high temperature, and the close contact large quantity of heat is conducted. Thus instantly broken though is the slow moving area of water inside the wood, whose temperature becomes high, and whose vapor pressure instantly increases. This will accelerate the movement of water from inside to outside. In order to ensure that large amount of water inside a large wood piece can be discharged immediately, large numbers of breathing grooves are made on the platen to facilitate the exhalation. As a result, quick drying can be achieved. This technique is proved effective especially for hardwood and serayah.

由于压力的作用，被干木材的收缩将会大于其正常干缩量，使之密度增加，尺寸稳定性得到提高，起到整平单板的作用。但过高的压力，不仅会带来较大的材积损失，而且会产生表面硬化和开裂。为此单板热压干燥机在整个多层热压板的闭合机构中，设计了同步闭合系统，使每层压板间的闭合间隔相同，上下每层板间对单板的压合力相同，并可通过液压控制系统随意调整压力。

Because of the pressure, the dried wood will experience more shrinkage than normal, with density increased, board size stabilized and veneer leveled and straightened. Yet, excessive pressure will bring about not only more wood volume loss, but surface rigidified or split. To solve such problems, synchronic closure system is devised for the closure set with multiple platens. Then equal closure time between each two platens and equal pressing force onto the veneer can be realized. Moreover, the pressure can be adjusted freely by the hydraulic control system.

木材干燥时，含水率在下降过程中会产生一定量的收缩，且由于树种的不同，收缩量亦不相同。热压干燥过程中，热压板与被干燥单板是压合接触的，如果不及时脱开，将会使单板产生开裂现象。使用同步闭合系统解决了这个问题。热压干燥机用PLC系统设置了单板干燥过程中的呼吸程序，使用时可根据不同的情况确定呼吸频率和呼吸时间，让单板充分收缩及散发水分。

During the drying process, a certain amount of shrinkage will occur along with the decrease of moisture content. Different types of wood will have different shrinkage rate. Thanks to the contact pressing, veneer may split if the platen and veneer cannot separate with each other immediately. The synchronic closure system can solve this problem. This platen dryer deploys the PLC system to control the breathing process of veneer drying. It can adjust breathing frequency and duration according to respective conditions; thus ensure a complete shrinkage and exhalation.

单板热压干燥机与传统的网带、辊筒干燥机相比，具有省电（功率仅11KW）、省热能（热能消耗仅40万大卡），车间占地面积少（仅10平方米），生产效率高（每天可干燥20m³左右）操作维护简单，日常损耗低等优点，该机的普及必将给单板干燥技术带来新的进步。

Veneer hot-pressing dryer, compared with conventional band or roller dryer, is electricity-saving (power at 11 KW), heat-saving (heat consumption at 400,000 Kilocalorie), workshop area-saving (10 M²), and it is also characterized by high production efficiency (daily veneer drying at 20m³), easy-maintenance, and low daily damage. And the popularization of this machine will be a breakthrough to the veneer drying technique.