What is purging in extrusion?
The extrusion process, unlike injection molding, is a continuous process. Purging procedures for thermoplastic extruders must be performed often to avoid issues with product waste, untimely breakdowns and production downtime. High-Temperature Extrusion Procedures. Cleaning Of The Vent Hole.
What is a blown film extrusion?
Blown film is another extrusion processes used to fabricate film products. In this case the extrusion die is shaped as a circle and air pressure is used to further expand the film. After it is expanded to the desired dimensions it is cooled to solidify the polymer. A schematic of the blown film process is shown in Fig.
How can you overcome the defects of blocking and splitting in the extrusion blown film process?
Reduce winding tension. Lessen treatment levels. Inadequate film cooling; reduce cooling roll temperature or reduce line speed. Inadequate levels of anti-block additive; increase anti-block.
What is extrusion packaging?
In the packaging production process, plastic extrusion consists of guiding thermoplastic material under pressure through a die with a hole that is generally complex in shape. The resulting cross-section of the material is the same shape as the hole.
What is purge compound?
A purging compound is a liquid that is run through the hotrunner of a plastic injection molding device to purge the colored reisin. The purpose of this is to get rid of the coloration, so that future runs aren’t colored incorrectly.
What are the advantages of cast film over blown film?
Cast film is minimally pre-stretched compared with blown film giving it improved depth of drawing for thermoforming operations. The cooling process can be used to produce different characteristics in the final product. Cast film can be thinned by winding the film out of the roller faster than it is extruded.
What is the difference between blown and cast 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.
How do you get the wrinkles out of a blown film extrusion?
There are several ways to do this. Use an air ring with an upper-lip conical extension, thereby increasing the diameter of the bubble where the bubble is released from support in the major cooling-air stream. A longer intermediate conical air-ring lip and larger upper lip can accomplish this even more effectively.
How do you prevent a melt fracture?
Melt fracture can be reduced or eliminated by streamlining the die flow channel, reducing shear stress in the land region, using a processing aid, adding die-land heaters, operating above the critical shear stress for melt fracture (known as “super extrusion”), or adding ultrasonic vibration—a little known but highly …
What are the disadvantages of extrusion?
Disadvantages of extrusion
- Variations in size of product.
- Product limitations because of only one type of cross section can be obtained at a time.
- High initial cost setup.
How does extrusion process work?
Plastic extrusion works by melting, processing and re-melting a type of plastic referred to as thermoplastic resins. The resins generally come in a bead or pellet form which allows them to be used in the extrusion machinery.
What is the best way to purge a nylon extruder?
Nylon: Purging nylon from an extruder can be very challenging. One effective method is to use a maleic anhydride (MAH) grafted material. MAH has a high affinity for nylon, thus, grafted materials are often used as a tie layer between nylon and other polymers. • Use a grafted material that has a high percentage of MAH.
What are the disadvantages of purge compounds?
Some purge compounds have low melt strength and are difficult to use in blown film systems and others produce high levels of smoke at high temperatures, which may be an issue with cast film or extrusion coating operations. A purge additive is another component that must, at some point, be removed before production can resume.
What are the different methods of extrusion cleaning?
Let’s take a look at some of the different methods. The first and easiest method of extrusion cleaning is “disco purging.” This is done by ramping the extruder speed (rpm) up and down at a relatively high interval using the normal production material formulation.
What are purge resin additives?
The contaminant could be in the form of gels, a resin from a previous formulation, fiber contaminants, or additives such as talc, calcium carbonate, or a pigment masterbatch. Purge resins can remove contaminants through mechanical means or through the use of chemical agents—those that use both are purge additives.