A Study On Gluing Methods And Technology Of Wheat Straw Particleboard

A series of researches have been engaged in gluing method and technology of wheat straw particleboard. And many results and conclusions have been obtained.1. After describing and analyzing the current development of wheat straw particleboard at home and aboard and advantages in domestic particleboard industry, some technical difficulties in its gluing step of production have been pointed out, which says over-gluing is the vital as well as urgent technical problem. At the same time, researches on theoryanalysis and assessed method about the influential factors in resin spray contributes that resin spray can be assessed by three parameters—the average resin droplet diameter,atomizationangle and the resin droplet distribution.2. After the researches on air-atomizing gluing, including the atomizing characteristic tests on three types of nozzles, which are external mixed two-fluid nozzle,internal mixedtwo-fluid nozzle and mixed triple-fluid nozzle, following conclusions havebeen drawn.(1) The average resin droplet diameter of internal mixed two-fluid nozzle increases with growing of liquid pressure and enlarging of the diameter of liquid, gas outlet, and mixed outlet but decreases with the increasing of the ratio of gas pressure to liquid pressure.The average resin droplet diameters has a wide range , from 20 to 110μm, which is greatlyinfluenced by liquid pressure, then liquid-gas pressure and then diameterof liquid outlet. While atomization angle will becomes lower if liquid pressure,air outletdiameter and mixed outlet diameter increases, but becomes higher if the diameter of liquid outlet, liquid pressureand the pressure ratio of liquid to gas increases. However, it has a narrow range just between 33 degree to 41 degree, and the parameters of controls and structural have the similar but not obvious effects on it. The resin droplet distribution of this nozzle is between 1.2 and 1.8. All in all, the External mixed two-fluidnozzle has its resin droplets in comparatively small diameter, with comparatively atomizing angle, little coefficient of resin distribution, good atomizing effect, little consumption of energy, and well-distributed.(2) The feature of the average droplet diameter of external mixed two-fluid nozzle is basically similar to that of external mixed two-fold nozzle, which means that its averagediameter also has a large fluctuated size between 30 and 120μm, and is influenced in turnby gas pressure, the ratio of gas to liquid pressure and the diameter of liquid outlet. The atomization angle changes similarly as that of external mixed two-fluid nozzle does and the former has a narrow range between 31 degree and 38 degree. This nozzle has its droplet well-distributed, because its distribution coefficients are no more than 1.4. In total, Internal mixed two-fluid nozzle has comparatively large diameter atomizing droplet with a small angle degree, large coefficient in distribution. Ithas an ordinary atomizing effect but relatively high energy consumption.(3) The average resin droplet diameter made by mixed triple-fluid nozzle increases as liquid pressure, the diameter of outlet of liquid, gas and mixed one increase, but decreases as the ratio of twice gas pressure to twice liquid pressure increases, which changes from 15μm to 130μm. This wide range is mainly influenced by the diameter of liquid outlet, once liquid pressure and the ratio of twice liquid pressure to gas pressure in the decreasingorder. The atomization angle decreases when liquid pressure, gas outletdiameter and mixeddiameter increase, but decreases when liquid outlet diameter, gas pressure and the ratio ofgas to liquid pressure increase. The range of atomizing angle is wide, between 30 degree and 45 degree, which is influenced by the parameters of controls and structural similarly but not obviously. The droplet distribution is ordinary with the coefficient of this nozzlefrom 1 to 1.5. Totally speaking, the atomizing effect of Mixed triple-fluid nozzle is betweenthe two above but the energy consumption is the highest of those three types.3. After carrying more researches on the gluing method which uses high pressure and airless, and atomizing characteristic tests on airless nozzle and airless with air-aidednozzle, brief conclusions are as follows: As for airless spray type, it can spray resin intodroplets with the diameter of 70～110μm, whose size can be increased to 20～110μm by adding air-aided. Meanwhile the average droplets diameter will decrease with increasing liquid pressure but will increase because of enlarging the diameter of liquid outlet. Furthermore, in the same liquid pressure, if it can be atomized by air-aided again, the diameter of dropletwill be smaller. Therefore an excellent effect will be achieved.4. After doing researches on the centrifugal atomizing method and atomizing characteristic tests on electric-centrifugal atomizing nozzles, the results are as follows: The average resin droplets ordinarily ranging from 50μm to 120μm, becomes smaller as the increasing of the centrifugal speed, while becomes larger as the increasing of liquid pressure, which has a narrow diameter from 70μm to 100μm. However, the centrifugal speed contributes more. As for the diameter of nozzle's atomizing circle, which ranges widely from 1,200mm to 1,700mm, can be increased by increasing the liquid pressure or the centrifugal speed.5. After researches on the method of resin spray all above, four groups with different average diameters of droplets are classified and relations between major technological parameters like resin content, the average diameter of droplets and the physical functionof strawboard are analyzed. They all show that using different resin content will makes a big difference to the bending strength, elastic modulus, internal bond strength and determinationof thickness swelling rate of water absorption of strawboard, especially to internal bond strength. Therefore, after satisfying national standards, choosing the best average diameter and optimizing gluing technology can decrease the amount of glueusingin particleboardproduction as well as the cost of it.6. Based on the analysis in theory and researches on tests, an experimental system and a set of particular instruments that uses the glue consisting of isocyanate for strawboardgluing are finally exploited. And the result shows that the MDI gluing system and the setof particular instruments are well fitted for strawboard gluing technology, as the sample has meet national standards.