【摘要】 <正> 近几年来,有的文化用纸的低速造纸机在流浆箱改造时,套用了通常用于车速较高的造纸机的流浆箱的元件(如阶梯扩散器、孔板配上消能棒和导流片,等等),但由于流浆箱和元件设计不够合理,主要参数选择不当,从而导致效果不佳,没有达到降低成纸横幅定量差和改进匀度的目的。国外对低速造纸机流浆箱的研究很少,流浆箱方面的研究工作大都集中在车速较高的造纸机流浆箱。例如瑞典KMW公司在研究KMW气垫流浆箱时对孔板的布浆整流性能进行了更多还原

【Abstract】 During recent years, holey plates with energy evaporation rods and flow guides, or step diffusers have been installed in headboxes of certain slow-speed paper machines in China.They serve as distributing and rectifying element.Field reports on their performances present rather diversified results, mainly due to the lack of better knowledge on the stock flow mechanism in headboxes, as well as on the appropriate assessment of distributing and rectifying elements. Furthermore, groundwood pulps and straw pulps extensively employed in Chinese mills differ very much in nature from chemical wood pulps used in other countries. It is thought that the adoption of holey plates or step diffusers as distributing and rectifying elements in headboxes may be one good approach among others in the redesign and rebuilding of slow-speed machines. Hence, a better understanding of the flow mechanism of groundwood pulps and straw pulps and the performances of open type flat-bottom headboxes equipped with holey plates or step diffusers seems to be essentially necessary. And, if mathematical models of the stock flow in such open type headboxes can be established,it would be very useful for designing such headboxes. In our experiment, the furnishes are: （1）80% Market groundwood pulp （imported）+20% masson’s pine sulfite pulp, produced in Guangzhou Mill, designated by GP/SP. （2）Mixed furnish of bagasse pulp and awn stalk pulp, designated by SB/ASP. Experimental results lead to the following conclusions: 1. D（τ_w）～τ_w curves for stock pipings Assuming steady, parallel flow of stock within the stock pipe and zero flow at the pipe walls, it is established that: D（τ_w）=4Q/πR³=4/τ_w³integral from n=0 to τ_w（f（τ）τ²dτ） that is, D（τ_w） is a function of τ_w alone. Consequently, curves relating D（τ_w） to τ_w can be obtained （refer to Fig. 3 and Fig. 4 in main text of this article） ,curves thus obtained follow a Ostwald pattern or "synthesized rheological" pattern. When the stock flow shear stress at the pipe wall, τ_w, exceeds a certain value, the relationship between D（τ_w） and τ_w approaches linearity. 2. Mathematical models for stock flow in open type flat-bottom headboxes: Dimensionless equation for factors affecting the velocity profile of stock flow in the slice opening is derived through dimensional analysis. Microcomputerization of the equations gives: （1）Distributing and rectifying element: holey plates Refer to the equations （19） , （23） and （25） in the main text of this article. （2）Distributing and rectifying element: step diffusers Refer to the equations （20）, （24） and （26） in the main text of this article. 3. For the scope covered in our experiment, the optimum length of the pond can be expressed as: （1）With holey plate as the distributing and rectifying element: L_opt=8.9063H+0.205……（27） （2）With step diffuser as the distributing and rectifying element: L_opt=1.4582H……（28） 4. Stock flow Reynold’s number R_cap* can be determined by the following equations: f（t_w）=3/4D（τ_w） +1/4D’（τ_w）……（2） μ_ap^*=τ_w/f（τ_w） ……（5） R_cap^*=DUρ/μ_ap^* ……（6） Considering that the state of flow and its related characteristics as well as the geometry of the channel through which stock flows are being taken care of by the Reynold’s number R_cap^*, the above expression is considered to be valid.更多还原