Blown films, sometimes referred to as tubular films, are manufactured by extruding molten resin vertically through a circular die. Introducing air through the center of the die creates a bubble. The air drives the bubble upward, and slowly cools the material. Nip rollers flatten the material into a tube that can be reeled for creating bags and pouches, or slit and then reeled as a flat sheet of film. Blown films are pre-stretched by virtue of their manufacturing process.
Cast films are made by extruding melted resin horizontally through a flat die to create a sheet of material that is pinned to a highly polished chilled roller by means of an air curtain or vacuum box. Additional chill rollers quickly cool the film prior to trimming and rolling. Cast films are minimally pre-stretched allowing for improved depth of drawing for thermoforming operations. Typically, cast films have an even distribution of polyolefins due to increased gauge consistency due to the manufacturing process.
What Is An Extruder, And Does Our Company Need One?
To understand what an extruder is, we must first know what the process of extrusion is. Extrusion is when a material, usually pellets, dry powder, rubber, plastic, metal bar stock or even food is heated and pushed through a die. A die is essentially a mold that shapes the material as it is forced through the small opening to the other side. It’s one of the most common ways to produce sheets and strips of stock metal, plastic and rubber shapes.Production of cast film is a continuous process where a thermoplastic material is extruded from a slot die onto a chill roll, quenched, and wound.
The resulting film has machine direction orientation compared to a somewhat limited bidirectional orientation achieved in blown film processing. Cast film extrusion, because of the high speed and output, can be limited to dedicated applications such as lamination web, printed packaging film, and a growing market- stretch wrap.Design Features
The film blowing machine is mainly composed of an extruder, a die head, a die head, a cooling device, a foam stabilizer, a herringbone plate, a traction roller, a winding device and the like.
ExtruderMulti-wall paper bags are used to transport and store dry flowable bulk materials. The paper shipping sack originated over a century ago. Today billions of units are produced and filled each year. Variations of the industrial paper bag include the pasted valve bag, pinch bottom open mouth bag, self opening satchel bag, and the sewn open mouth bag.
There are two basic types of paper bag: Open Mouth and Valve. An open mouth bag is a tube of paper plies with the bottom end sealed. The bag is filled through the open mouth and then closed by stitching, adhesive, or tape. Valve bags have both ends closed (pasted) and are filled through a valve.