三、挤出机：

生产板材和片材的挤出机在结构上与其他挤出制品所用挤出机没有大的区别，

可以是单螺杆挤出机，也可以是双螺杆挤出机。

（1)单螺杆挤出机 用于挤出板材或片材的单螺杆挤出机的螺杆直径一般为

65~200mm,长径比L/D≥20.需要在挤出机螺杆头部设置过滤板或过滤网，过滤

板的孔径和孔数、过滤网的目数和层数，应根据塑料的品种及制品厚度来决定。

非排气式单螺杆挤出机适用于HDPE、LDPE、PP、PVC等热塑性塑料的挤出成型。

排气式单螺杆挤出机适用于PS、PMMA、PC等热塑性塑料的挤出成型。

（2)双螺杆挤出机

用于挤出板（片）材的双螺杆挤出机分为平行双螺杆和

锥形双螺杆两种。平行双螺杆挤出机的螺杆直径为80~140mm,长径比L/D≤21,

锥形双螺杆挤出机的小端直径为35~80mm.双螺杆挤出机适用于PVC板与片的挤出成型。                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 

 三辊压光机的温度和速度

1.三辊压光机的温度

三辊压光机的温度直接影响板、片材的表面粗糙度和平整度。从机头挤出的

板材温度较高，为使板材缓慢，防止板材产生内应力而翘曲。三辊压光机的

三个辊筒要加热，并且辊筒温度应高到足以使熔融料和辊筒表面完全紧贴，使板

片表面上光或轧花。但温度又不能过高，温度过高会使板、片材难以脱辊，表面

产生横向条纹，甚至将其拉坏。温度过低，板材不能贴紧辊筒表面，板材表面易

产生光泽。一般控制中辊温度，上辊温度稍低，约比中辊低10℃

右，下辊的温度，约比中辊低20℃.如生产硬质PVC板材时，三个辊筒的温

度依次为70~80℃、80~90℃、60~70℃.

具体温度根据塑料品种及板（片）厚度决定。生产PVC、ABS板（片）时

辊筒温度不超过100℃,生产PP板（片）时，有时要超过100℃.

2.三辊压光机的速度

三辊压光机的线速度挤出量相适应，如对压光较厚的板坯，三辊压光

机的线速度应比挤出线速度略快10~25,将板材少量牵伸，以防止板、片材

下垂变形或厚度不均匀。对于压光薄片就不一样，三辊压光机的线速度则比压光

厚的板坯要快得多。若三辊速度太慢，板、片材表面会出现皱褶；若三辊速度太

快，过分拉伸会降低板、片材的强度和厚度。

4.2.4 板材厚度与模唇间隙及三辊间距的关系

1.板片厚度与模唇间隙

成型板、片材时，模唇间隙一般等于或稍小于板材或片材的厚度，物料挤出

后膨胀，通过牵引达到板材或片材所要求的厚度。板材厚度及均匀度除可调整口

模温度进行控制外，还可调整口模阻力块，以改变口模宽度方向各处阻力的大小

从而改变流量及板材厚度。通常板材厚度需微调时，可通过调节模唇间隙来实现，

厚度调节幅度较大时，应当调节阻力调节块。为了获得厚度均匀的板材，可将模

唇间隙调节成中间较小，两边较大的形式。

机头模唇流道长度与板材厚度有关，一般取板材厚度的20~30倍。

2. 板材厚度与三辊间隙

三辊间隙一般等于或稍大于板材厚度，板与片通过进一步收缩至院谢

度。三辊间隙沿板材幅宽方向应调节一致。

聚乙烯、聚内烯板材与其他塑料板材有些不同，三辊间隙处留有一定量的存料，

因为聚烯板材挤出时为熔融状态，当机头出料不均时，就会出现缺料、大块斑等现象。但存料也不能太多，因聚烯熔体易结皮，使板材表面出见“排骨”状的条纹，影响制品质量