The spunbonded nonwoven fabrics are drawn by means of air drafting. With the different drafting mechanisms applied, the specific drafting method also varies from machine to model. In the spunbonding system, the commonly used drafting methods mainly include wide slit suction type (negative pressure) drafting, wide slit positive pressure drawing, and round tube type drawing.
1. Wide slit suction type (negative pressure) drafting
Wide slit suction type (negative pressure) drafting is characterized by closed-type spinning drafting channels, air-laid, positive-pressure drafting airflow and cooling airflow combined into one, and combined with the suction wind of the synthetic mesh machine The negative pressure generated by the device accelerates the gas flow and achieves drafting of the fibers. Since the basic shape of the drafting passage is a tapered shape which is large and small, the airflow in the passage is accelerated to realize the drafting of the fiber.
The wide slit suction drafting process is currently the most widely used process in the world.
Second, wide slit positive pressure drafting
The wide slit positive pressure drafting adopts an open spinning drafting passage, the air flow (some models adopt a static yarn splitter), the integral type independent drafter, and the positive pressure airflow as the drafting power The spinning channel is fully open. The cooling airflow has substantially no drafting function, and generally uses compressed air (the pressure is generally within 1 MPa) to achieve the drawing of the fiber.
According to the actual operation situation, the wide slit positive pressure drafter has higher drafting speed and better material adaptability, but due to the high outlet air velocity of the drafting device, it increases the difficulty of controlling the uniformity of the laying. .
Third, round tube drafting
The circular tube drafting process is often referred to as “tube drafting”, which adopts an open spinning drafting channel, mechanical (such as pendulum type) dividing wire, forming a net, and using a large number of independent round tubes (tube diameter is about 8). ～16mm, length up to several meters) drafting device, using positive pressure airflow as the drafting power. After the draft airflow (compressed air) enters the annular space of the drafter, it is sprayed downward from the flow guiding cavity into the drafting pipe and ejected from the lower portion. The high velocity airflow creates a negative pressure at the inlet of the tow and draws the tow and ambient air into the tube, and the tow is accelerated by the airflow in the channel and is drawn. In the tubular drafting system, the drawing speed of the fiber can reach 3000 to 5000 m/min, so it can be applied to both the PP spinning system and the PET spinning system requiring a higher drawing speed.
The drafting method of the round pipe can achieve a higher drafting speed, the wire speed can reach 5000-7000 m/min, the drafting effect is ideal, and the drafting of the fiber is also sufficient, which is currently used for the production of polyester nonwoven fabrics in China. The main process.