纺纱学第6章.ppt

第六章 并条 Both card sliver and combed sliver must go through drawing to receive further blending and alignment. The draw frame corrects for weight variation and fiber misalignment. Drawing is the term applied to the operation involving the doubling and drafting of slivers. Doubling is the combination of several slivers that are then attenuated by a draft equal in number to the slivers combined, thereby resulting in one sliver of a similar count. Drafting is the process of attenuating the count of a material using a combination of pairs of rollers. OBJECTIVES OF DRAWING Straighten the fibers and make them parallel to the central axis of the sliver; Improve short-term, mid-term, and especially long-term evenness in the sliver; Improve consistency of the product delivered to spinning for lower yarn variation; Produce the proper weight sliver for the following process. PROCESS OF A DRAWFRAME A drawing frame uses a series of rollers arranged in pairs and rotating at different speeds, to draw out, or draft, sliver. At the drawing frame, several card slivers (usually six to eight) are combined to further blend the fibers. The slivers are pulled from the back of the machine through a series of pairs of rollers. The back pair of rollers is rotating at a lower speed than the pair at the front of the frame. Because the sliver is being taken up at a faster speed than it is being delivered, the sliver becomes thinner as it is drafted. The main parts of a draw frame are the creel, drafting system, sliver condensing section, coiler, and suction system. A GILLBOX 牵伸DRAFTING 牵伸的基本原理 一、牵伸的实质： 将须条抽长拉细，即使须条内各纤维沿轴向（长度方向）产生相互间的位移，从而使纤维排列在更长的长度上，使须条截面减细。 二、实现牵伸的条件 1、有两个积极握持的钳口（加压） 2、两钳口之间有一定的距离（隔距） 3、两钳口要有相对运动，输出钳口的表面速度大于喂入钳口的表面速度（速度差）。 三、牵伸倍数：须条被牵伸的程度 机械牵伸值：E=V2/V1 V2 —前罗拉表面速度 V1 —后罗拉表面速度 实际牵伸值： 牵伸效率：实际牵伸值与机械牵伸值之比。 η取决于滑溜、纤维损失、加捻等。 牵伸配合率：牵伸效率的倒数，用于棉纺。 四、总牵伸和部分牵伸：当牵伸机构有两对以上的钳口时，称为多区牵伸机构。总牵伸等于各部分牵伸的连乘积： 五、牵伸区中纤维分类 1、被控制纤维和浮游纤维： 受前罗拉或后罗拉控制，并以该罗拉表面速度运动的纤维，称