Plastic extrusions are plastic shapes produced by forcing molten plastic through a die. Plastic extrusion is a continuous process that produces long plastic profiles; plastic strips, plastic channels, plastic trim and other basic plastic shapes are all produced by plastic extruders. Plastic extrusions play an important roll across industry, commerce and in consumer markets.
Automotive manufacturers employ extruded plastics as engine components and as decorative and functional trim on auto exteriors. PVC extrusions, particularly PVC tubes, are used extensively in plumbing systems and in wastewater treatment operations. Chemical processing operations also make use of extruded plastic tubing, and because different plastics feature different qualities of reactivity when exposed to chemicals, plastic materials are chosen for their applications based on such qualities. Acrylic extrusions, for example, are characterized by their optical clarity and durability. They are, for these reasons, often well suited to use as tubing in chemical processing, because their contents can be easily visible when inspected by workers. Some unique applications call for an extrusion that features the qualities of more than one material. In these cases, coextrusion can be used to mix two plastics together, allowing for the qualities of two plastic materials to be present in one product.
The term polymer extrusion is sometimes used interchangeably with plastic extrusion. This is not incorrect, though it is not the most precise way to describe the process. Technically, a polymer is a large molecule made up of many similar monomers, which are small molecules. Biopolymers like proteins and nucleic acids are essential for life. These are not the kinds of polymers to which the words "polymer extrusion" refer. When the words "polymer" and "extrusion" are paired together, they refer only to plastics and elastomers (natural rubber is an example of an elastomer). In the case of plastic extrusion, a very long list of plastic materials is at the disposal of companies that provide plastic fabrication services. High density polyethylene (HDPE), low density polyethylene (LDPE), PETG, PVC, butyrate, vinyl, polypropylene, and polystyrene are just a few of the most commonly extruded thermoplastics. A thermoplastic is a plastic material that, when exposed to sufficient heat, becomes plasticized. A plasticized thermoplastic can be shaped into useful products and retain the shape once cooled. Thermoplastics are highly valued for this quality, and they are also valued because they can be recycled at the end of their lifespans and reshaped by the same process.
The plastic extrusion process is very standardized, and there are few deviations between extrusion operations in terms of the basic principles of extrusion. Operating temperatures and output speeds may vary depending on the properties of the plastic material, but plastic extrusion processes resemble each other very closely aside from these differences. The extrusion process begins with a collection of raw plastic materials in a hopper suspended above a conveyance channel. When a panel at the bottom of the hopper is removed or retracts, gravity directs the plastic into the channel. Inside the channel is a long shearing screw that forces the plastic down the channel as it turns. The friction caused by the turning of the screw causes the plastic to become molten. Some extruders feature supplementing electrical heating elements to aid in the melting of the plastic. By the time the plastic reaches the end of the channel, it is ready to be shaped. At the end of the channel is a die, which is a specially-designed tool used to form raw materials into usable products. In the case of plastic extrusion, a die is a metal plate cut with a hole through which the plastic is forced.
When the molten plastic reaches the die, it is forced through, taking its shape as a result. The plastic emerges on the other side of the die as newly extruded plastic material. The plastic is quickly cooled, which causes it to harden and keep its shape. The extrusion can then be cut and prepared for shipment or sent for additional processing like labeling, painting, anti-static treating or other surface treatment. The shape of an extrusion die determines the shape of the extrusion. Every die is different; they are specially designed to accommodate individual processes. The simplest possible die designs are nothing more than simple shapes. A circle-shaped die would produce a plastic rod, while a square-shaped die would produce a continuous plastic square. Extrusions like pipes require dies fitted with special pins that allow hollow places to form. Textured plastic sheets like floor mats can also sometimes be produced by extruders. Plastic sheet dies would be flat with grooves to create the texture. The coextrusion process, in which two or more plastic materials are combined in a single extrusion, features one die connected to a forked conveyance channel into which the different materials are directed and mixed together. The number of possible extruded plastic shapes is limited only by the imaginations of their designers.
Plastic Extrusions - Creative Extrusion & Technologies, Inc.
Plastic Extrusions Manufacturers - Creative Extrusion & Technologies, Inc.
Plastic Extrusions Manufacturers - Polytec Plastics, Inc.
Plastic Extrusions Manufacturers - SFR Industries Inc.
Plastic Extrusions - SFR Industries Inc.
Plastic Extrusions - Preferred Plastics, Inc.
Have you ever wondered how commonly used plastic products, such as pipe/tubing, weather stripping, fencing, deck railings, window frames, plastic films and sheeting, thermoplastic coatings, and wire insulation, are manufactured? These products, commonly called extruded plastics, are the result of plastic extrusion, a low cost, low-tech production method. Plastic extrusions are considered a subsidiary of injection molded plastics, which are manufactured using another plastic molding technology, albeit a more complex process than plastic extrusions.
Plastic extrusion is similar to plastic injection technology. It is a high-volume plastic manufacturing process where raw plastic materials, which are in the form of pellets, powders, granules, or flakes, are fed into the barrel of the extruder. Heat generated from rotating screws inside the barrel and heaters arranged along barrel liquefies the material. The liquid polymer is then forced into a die to shape it into a continuous profile. Once the output cools and hardens, it is cut to desired length.
Due to a number of benefits, plastic extrusion is used to produce numerous extruded plastics-PVC channels, plastic channels, plastic strip, and plastic profiles to name only a few. Below, we will list several benefits of the plastic extrusion process.
High speed, high-volume and low-cost production: Plastic extrusion is a highly efficient and inexpensive process compared with other molding methods. It offers low wastage since the molding process utilizes thermoplastic, which repeatedly undergoes melting and hardening, enabling the manufacturer to reuse the plastic that is left after trimming or cutting the extruded products. Plastic is easy to melt, which results in a quicker production run and low energy intake. Extrusion machines can run continuously which cuts the chances of inventory shortage. Moreover, cheap feedstock, reduced tooling costs, and low disposal expenditure mean this is the ultimate low-cost production method.
Flexibility: Plastic extrusion molding offers flexibility when the product is required to have a consistent cross sectional profile. Additionally, the machine can produce complex shapes with differing thickness, hardness, size, color, and texture; the only catch is the cross section needs to remain the same throughout. Flexibility also comes in another form-manufacturers can easily tweak the process to produce plastic sheets or make products that mix plastic attributes.
Allows post-extrusion alteration: Plastic takes time to cool down; it remains hot after it is removed from the extruder. This makes it easy for manufacturers to implement changes to the plastic after the completion of the extrusion process, using a variety of tools like rollers, shoes and dies.
Coextrusion: Compared with other molding methods, plastic extrusion can accommodate coextrusion. Plastic extrusion generally refers to single layer extrusion; as the name suggests, coextrusion involves using two or more extruders. Plastic is pumped from two (or more) extruders to a single die. The main benefit of this is that different types of plastic and compound with different thickness can be fed into the system at different speeds. This is done to achieve products that meet a wide range of functional requirements, from UV treatment to polymers that glows in the dark.
Plastic extrusion is an exceptionally versatile process, which allows plastics to be made of intricate shapes and different thickness, hardness, size, color, and texture.
Given the various types of extruded plastics available, evidently, it is not possible to make all those profiles and related variations with one method. However, if examined closely, mainly a single extrusion process, with number of tweaks, is employed for manufacturing of different types of extruded plastics. Here in this blog, we are discussing those tweaks in methods.
Method for extruding standard profiles
In the simplest and most common process, to make profile extrusion, resin is passed through a barrel, which melts the plastics. Then the molten plastic is molded by different set of dies, based on the requirement. For instance, to make hollow sections a mandrel is placed within the die. Similarly, for multi lumen tubes, a couple of pins are tooled in to the die, and as the molten plastic moves through the pins, it extrudes two holes in the product. Sometimes, positive pressure is also applied to supplant the whole process to adjust the size of the lumen with pressure.
Extrusion with multiple extruders
When multiples layers of plastic needs to be extruded, a process called, co-extrusion is employed. In this manufacturing method, multiple, however, typically, two extruders are used for melting different types of the resin and delivering material for extrusion at steady rate and volume. The materials delivered by the extruders are passed through a single die to give a desired shape and form. The process is specifically used when blown film and sheets are to be fabricated. With this method, a single product is made from two types of resin in layers, one layer provides the structural integrity, and the other layer, which usually is thinner, adds protection against weathering effects on the polymer.
Extrusion for Making Plastic Shopping Bags
The method used for making shopping bags and plastic films is known as blown film extrusion. The method is similar to standard plastic extrusion but it employs a different type of die, which is the shape of cylinder having annular opening. As the molten material leaves the barrel of an extruder, a couple of rolls pulls the material to change the gauge of the molten resin, and the die tooled with an air outlet blows air into the cylindrical profile to give it the final shape. At the end, a cooling mechanism, typically, cooling ring is affixed to cool the film. To regulate the thickness of a product, the rate of revolution of the rolls is changed according the needs of the product.
Extrusion for making Kernels
Some machines make plastic pellets by extruding different types of resin together. The machines follow the same procedure as that of standard extrusion, however, the finished products are not profiles or tubes but beads, which act as a raw material for manufacturing processes.
Extrusion with 3D Printers
With the development of modern 3D printers, plastic can be extruded into elaborate shapes and structures. 3D printing is a new addition to the extrusion process, giving fabricators opportunity to fabricate any shape imaginable. Instead of a molten resin, in this process, a filament is utilized as a feedstock.
Manufacturing thin gauge sheets has its own set of challenges that play critical factors in the extrusion process, including mechanical and physical properties, raw materials, working conditions, roll construction, and drooping. Many manufacturers experience these problems, which influences quality and downtime.
Therefore, we are discussing the origin of common problems and their solutions in extruded plastics process.
For ideal extruded plastics, you need to maintain stable head pressure, have consistent temperature at heating zones, and create uniform melt flow. Most of the problems originate from these three factors. Therefore, when thin gauge is involved, uniform melt homogeneity and melt pressure should be achieved. In the following, we are discussing other factors that influence the extruded plastics process.
Variations in Concentration of Raw materials
The factor that surpasses other elements in regulating the quality of the product is the raw materials. From homogeneity of the molten resin to the finish of the product, all quality is directly determined by the raw material. For thin gauge extrusion, process conditions need to be stable, without any major pressure surges, also known as pressure oscillations. Change in the pressure affects the uniformity of the molten resin. In a standard settings, pressure oscillations of ±50 psig are considered acceptable, however, anything above that influences production. To achieve stable process conditions, variation in concentration of raw materials in terms of virgin and regrind blends should be avoided.
The lack of melt bank uniformity can cause many variations in the product, ranging from spotty finish to irregular polishing patterns. To check the presence of dull spots on the finished product, regulating the chrome-roll temperature is essential. The temperature should be kept high to discourage freezing of the bank. The other way is to shorten the distance between the die-lip exit and the primary nipping rolls- the ideal distance is 4 to 8 inches. However, there are factors that limit the distance between the die lip and primary rollers, such as area covered by the die, the die deckles, and appendages. To avoid this problem, the die should be tooled with contours to reduce the cross section area.
Design of Rolls
When production of thin gauge is involved, rolls should have capacity to manage high roll loads. For this purpose, special rollers known as spherical tapered rollers are considered suitable. However, when spherical tapered rollers are installed in an extruder, additional equipment, such as bearing journals and roll shafts, also need to be designed appropriately in the extruder.
The common problem that all fabricators face is deflection of the roll. To rectify this problem, three solutions are available. The first involves a crowned roll, which has a pre-ground camber. This technique, however, limits the range of the production because the dimension and geometry of the camber remain fixed. The second method involves counter-bending rolls, however, just like the first method, the technique limits the production window. The last solution involves roll skewing. The roll skewing method, unlike the first two solutions, is highly versatile and removes deflection in a wide range of operations.
There have been various positive signs for the growing economy. Plastic solutions are among the materials that are used in a large spectrum of industries and applications. When the demands for these products increase it is an indicator that other industries may also have increasing demands. Plastic solutions are more widely accepted as a viable and trustworthy component compared to their counterparts such as metal or wood. There are numerous benefits when utilizing plastic products. Plastic extrusion products have been proven as a vital material for the medical and clean room industries. These industries require sterility and the surface of plastic items are ideal for maintaining high levels of cleanliness. The uniform molecule structure is also a significant advantage. The medical industry, for example, benefits from this structure because many medical applications require tubing and through the plastic extrusion process manufacturers can achieved the desired specifications of those applications.
To meet the higher demands many manufacturers have been upgrading facilities in recent months which allows for faster and larger volumes of plastic extrusions but also more accuracy when cutting the plastic items. Sophisticated products are equipped with more intricate parts so manufacturers must have the capabilities to adhere to exact specifications even down to the smallest measurements. These newer processes have very interesting attributes and even though the products are being manufactured at a faster pace the integrity of the structures are not being compromised. Manufacturers will work with customers to create affordable solutions that adhere to sterility and dimension requirements.
Plastic Extrusion Terms
- The resistivity of molten plastic material to forward flow.
- The part of the plastic extruders encasing the screw or plunger.
- The sleeve forming the inner surface of the plastic extrusions barrel.
- The plastic extrusions process of pressing or smoothing material between rollers.
- Sometimes referred to as sidings it is extruded PVC-U boards that are used as outdoor weather-resistant fade panels.
- Any plastic material prepared for subsequent manufacturing processes, specifically plastic extrusions, molding or calendering.
- The transition section of a screw channel in which a reduction in the screw channel volume occurs.
- A tank typically containing water through which plastic extrusions are constantly passed for cooling.
- The technique of cross-linking a plastics material.
- The section of two-stage plastic extruders in which an increase in screw channel volume occurs.
- The component on plastics extruders affixed to the plastic extruder's head through which the melt is pushed to form the desired profile.
- In moulds, the main support for the punch or mould cavity.
- A free flowing blend of compound or resin and other ingredients as prepared for an additional manufacturing operation specifically for plastic extrusions or molding.
- The product or result of the plastic extrusions process. An extrudate is a product or material forced through a shaping orifice as a continuous body.
- The minimal inner diameter of the plastic extruders barrel
- A coating technique in which molten plastic feeds directly from plastic extruder dies into a nip-roll assembly combined with the substrate.
- Also called a caterpillar, it is an apparatus used for the continous removal of extrudate from the die.
- The unique process of aging a thermoplastic or thermoset product and examining the percentage of retained physical and chemical properties after exposure to heat for a prolonged period of time.
- Any plastic extrusions material heated to a plastic condition.
- A term that refers to the strength of molten plastic.
- The element of tubing tie that shapes the outer surface of a tube.
- Resins or mixtures of resins with compounding additives in the shape of similar-sized tablets and granules that have been extruded or chopped into short segments to prepare them for molding or extrusion operations.
- A barrel with a temperature control, wherein a plunger pushes material in a melted state to the die.
- Any of several physically similar polymerized synthetics or chemically altered natural resins, such as thermoplastic materials (polyvinyl, polystyrene, polyethylene) or thermosetting materials (epoxies, polyesters, silicones used with fillers, stabilizers, pigments).
- A helically grooved rotating element inside the barrel of screw plastic extruders. The main purpose of a screw is to melt and feed raw material from the feeder to the die, but it also homogenizes, compresses and pressurizes the material.
- A machine comprised of a barrel with a temperature control. It houses one or more rotating screws, which pass plastic materials from the feed aperture and move them in the form of melt under pressure through a die.
- An apparatus for reeling extruded plastics material.
- A term that refers to the family of materials that can be melted only once during the original processing and cannot be reprocessed after the original part is made.
- Any material, such as polyethylene, Santoprene and ABS, that can be remelted and reprocessed without considerable loss of properties or scrap loss.
- An apparatus at the discharge stage of the screw for finishing homogenizing and blending of the melt.
- An extruded PVC-U channel used to contain and protect pipes or cables.
- A procedure utilizing a sizing die with a vacuum applied to the outer surface of the extrudate.
- A generic term for PVC, it is one of various compounds of ethylene that are polymerized to form resins and plastics (e.g. polyvinyl or polyethylene plastics).