This article will take a detailed look at the manufacturing of plastic rods.
We will go in-depth on topics such as:
This chapter will discuss the definition of plastic rods, their function, and the materials used in manufacturing.
A plastic rod is a solid plastic shape made by the process of plastic extrusion or plastic co-extrusion. These have a contrast of plastic tubing and hollow plastic profiles. Plastic rods are found in various industries, including aerospace, electronics, petrochemicals, marine, and transportation.
They are often used as raw materials in these industries in order to be machined into parts for seals, gaskets, corrosion-resistant pieces, bearings, static control, sleeving, insulation, and others.
They are also used in the construction sector and in commercial businesses, all with the aim of serving applications that are related to the structural support of industrial equipment and the displays of point of purchase.
Plastic rods are made by the processes of plastic extrusion or plastic co-extrusion. These processes are described in detail below.
The main process performed in the production of plastic rods is called the plastic extrusion process. In this process of the extrusion of plastics, the raw compound material usually begins in the form of nurdles. These are small beads, often called resin, that are gravity-fed from a top-mounted hopper and then into the barrel of the extruder. Colorants and UV inhibitors in the form of pellets or liquid are placed in as additives, and they can be mixed together with the resin prior to arriving at the hopper.
The plastic extrusion process has much in common with the plastic injection molding process from the point of the extruder technology, but it differs in the sense that it is a continuous process. The process of pultrusion can offer many similar profiles in continuous lengths, usually with reinforcement. This is achieved by pulling the finished product out of a die instead of extruding the polymer melts through the die.
The material then enters through the feed throat, which is an opening near the rear of the barrel, and comes into contact with the screw. This rotating screw commonly rotates at 120rpm, and its job is to force the plastic beads forward into the heated barrel.
The temperature required for extrusion is rarely equal to the set temperature of the barrel due to effects such as viscous heating. In most contained processes, a heating profile is set for the barrel. In this barrel, three or more independent PID-controlled heater zones do the job of gradually increasing the temperature of the barrel from the rear. This rear is where the plastic enters towards the front. This allows the plastic beads to melt gradually as they are pushed through the barrel, and it also helps in lowering the risk of overheating, which may result in the degradation of polymers.
More heat contained in the process is contributed by the intense pressure and friction that takes place inside the barrel. Generally, if an extrusion line is working on certain materials fast enough, the contained heaters can be shut off, and the temperature of the melt can be maintained by the pressure and friction inside the barrel. In a large number of extruders, cooling fans are present to keep the temperature below a set value if too much heat is generated. Cast-in cooling jackets are put into use if the process of forced air cooling is insufficient.
The molten plastic leaves the screw at the front of the barrel and travels through a screen pack headed to remove any containment in the melt. The screens are made stronger by reinforcing them with a breaker plate, which is a thick metal puck drilled through with many holes. The reinforcement is performed since the pressure at this point can exceed 5000 psi or 34MPa. The breaker plate assembly or the screen pack also does the work of creating back pressure in the barrel. This back pressure is needed for the uniform melting and proper mixing of the polymer.
The amount of pressure generated can be tweaked by varying the composition of the screen packs, which involves the number of screens contained, their wire weave size, and other parameters. The rotational memory of the molten plastic is also eliminated by the combination of the screen pack and the breaker plate. This combination also further creates longitudinal memory. Molten plastic enters the die after it passes the breaker plate. This die then gives the final product its profile. It must be designed so that the molten plastic will evenly flow from a cylindrical profile to the profile shape of the product. The act of an uneven flow can result in the production of a product that has unwanted residual stresses at certain points in the profile, which can cause warping upon cooling. A numerous number of shapes can be created but with the restriction of the continuous profiles.
The end product is then cooled, usually by pulling the extrudate through a water bath. Because plastic is a very good thermal insulator, it is difficult to cool down quickly. Plastic conducts its heat away 200 times more slowly than steel. A sealed water bath contained in a tube or extrusion line is acted upon by a carefully controlled vacuum so as to keep the newly formed, molten tube or pipe from collapsing.
In some products, such as plastic sheeting, the process of cooling is achieved by pulling through a set of cooling rolls. For very thin sheeting and films, air cooling can be made very effective as an initial cooling stage as in blown film extrusion. The plastic extruders are also used to reprocess recycled plastic waste and other raw materials after sorting, blending, and cleaning. The material is often extruded into filaments that can be cut up into pellet stock or beads to be used further in processing.
Plastic rods are not actually always made completely from plastic. In some situations, they can be co-extruded with other non-plastic materials like metals. Co-extrusion is thus an altered process of extrusion in which a single product is made from two or more different materials mixed together. For one to be able to achieve this, multiple extruders which are pointed at a single die do the work of melting the polymers which are intended to make the product.
After these become molten, the materials are forced into the die at an even volume and pace. When the materials fill it out in layers, they enter the die at the same time. The goal of co-extrusion is to produce a product that contains properties and qualities that it cannot get from just the use of one polymer.
In order to lower material costs or to strengthen the core of the rod, manufacturers often choose to co-extrude a plastic rod with a different type of plastic or other material. In applications that require little structural strength, the issue of low-cost co-extrusion materials is usually considered.
In areas where better structural support is needed, the component metal is usually used as the material that fills the rod. Aside from the noted qualities, the plastic co-extrusion process also aims to increase resistance in wear and the permeability of oxygen.
There are various designs of extruders available in the market nowadays to carry out the extrusion processes. Depending on the operation mode, these can be subdivided into two types: continuous extruders and discontinuous extruders. The distinction between the two is the part that makes the material move. Continuous extruders contain rotating parts, while discontinuous extruders contain reciprocating parts. Continuous extruders can further be divided into two groups, which are screw extruders and drum or disk extruders.
These are the most common continuous extruders due to their advantages of low cost, toughness, simple design, high performance, and reliability. A standard single screw extruder contains three geometrically varying zones. The contained zones are the feed zone, metering zone, and the compression zone. These zones are formed by constant pitch, but vary the depth of the screw.
The depth of the screw channel experiences a linear decrease from the feed zone towards the metering zone. This action causes the compression phenomena. For the same screw length and diameter, zone length and maximum or minimum channel depths may vary. Hence, different screw profiles are possible. The environments inside the extruder may also depend on factors such as screw profile, screw speed, and set temperature. These factors affect the heat dissipation, local heat conduction, velocity of the profile, and the residence time inside the extruder.
These extruders are classified as continuous extruders, but they do not use screws to convey the material. Disk extruders use disks or drums to facilitate the extrusion process. For this reason, disk extruders are also named screwless extruders. Most versions of disk extruder are operated based on viscous drag transport.
This type of extruder utilizes a rotating drum and barrel to perform the extrusion process. In drum extruders, the polymeric material is fed into the annular space between the barrel and the drum. As the drum rotates, the material is carried along the circumference of the barrel. As one full rotation is yet to be completed, there is a wiper bar that does the function of scrapping the melt from the drum and directs the flow to the exit. This flow is later directed to the extruder die.
Multi ram extruders operate in a continuous manner. Other designs of the extruder have four plunger cylinders. Of these cylinders, two are for plasticizing and the other two are for pumping. The cylinders used for pumping are connected by an intricate shuttle valve.
The plastic formulas used in the extrusion of plastic rods are wide and many. But despite this fact, most of them fall into two groupings, thermosets and thermoplastics. Of these two, thermoplastics are for the majority of plastics. These thermoplastics consist of plastics that can soften and melt when they experience heating or that can be reheated and hardened when cooled.
They can also be heated and remolded again and again. This category includes plastics such as PVC, ABS, polythene, polypropylene, polycarbonate, and polystyrene. Thermosets can also become molten when heated, and they can also harden when cooled, but unlike thermoplastics, thermosets cannot be successfully reheated, reshaped, or re-hardened. Thermosets examples include polyesters, phenolics, epoxies, and silicones. Because of these qualities of thermosets, they lack an advantage over thermoplastics.
Usual manufacturing methods of thermoplastics include injection molding, extrusion, casting, pultrusion, machining, grinding, and the process of welding. Stock shapes like rods, sheets, films, tubes, and pipes are readily available for secondary operations. Raw materials are also provided in materials including plastic resin, powder, gel, and liquid form. Polymeric resins make up the majority of thermoplastics.
Polymeric resins contain long chains of several smaller monomers that are held together by covalent bonds. Additional polymers and condensation polymers are the two types of thermoplastics. Plastics that are found in the additional polymers group are those types of plastics that make covalent bonds without the loss of molecules or even the loss of atoms in the reaction.
Condensation polymers are polymers that always lose a molecule during the bonding process, like water. In these two types of groups, the materials can be broken down into monomers, binders, intermediates, base polymers, elastomers, and materials of rubber, all based on their chemical composition and the formation of the bond. These thermoplastics can also be divided by their specific properties.
Despite using polymerized materials only, the manufacturers can resort to adding powders, fibers, plasticizers, and ceramics. This is done in order to improve or alter the features of a plastic material. They play a significant role in the processing and fabrication of thermoplastics.
Thermoplastics are resins that retain solidity at room temperature, become soft when heated, and eventually become fluid as a result of the process of crystal melting or crossing the glass transition temperature. In the processing of thermoplastics, there is no chemical bonding involved, and thermoplastics can be poured into a mold to cool and solidify in their desired shape. They can also be reheated, recycled, and remolded without affecting the properties of the material.
Such materials are used in processes that include extrusion, thermoforming, and injection molding. These types of plastics often have the ability to resist shrinking and at the same time offer good elasticity and better strength. More benefits include good adherence to metals and a high-quality aesthetic finish. These types of plastics can be recycled, and they can also be reshaped with little impact on the properties of the material. They also employ good electrical insulation and resist chipping, at the same time enhancing their anti-slip properties.
Despite all these pros, they also have some cons, including the fact that they are not good for all applications due to their property of softening when heated. They are also more expensive than thermosetting polymers.
When purchasing thermoplastics, one should consider the fact that these thermoplastics offer a wide range of different crystalline structures and densities. It is also ideal for one to note and understand the properties of a given plastic rod with regard to the final product or the area of application.
In selecting the right thermoplastic for a certain specific application, one should understand that additives, raw materials supply, and the manufacturing process are important influencing factors. For depth considerations, one should look into electrical, physical, mechanical, and optical specifications that, at the same time, include the issue of the melting point, dimensions, and the contained flexibility.
These types of plastics are also called thermosetting resin or thermosetting polymers. They are usually liquid at room temperature, and they are able to harden as they are heated or when a chemical is added to them. Thermoset plastics are typically produced using reaction injection molding (RIM) or a process called resin transfer molding (RTM), and the thermosets form permanent chemical bonds during the curing process.
These chemical bonds which are formed between the monomer chains within the material are called cross-links, and they do the job of holding the contained molecules in place. They also change the nature of the material, thus preventing it from melting and also preventing it from returning to a liquid state. Thermoset plastics are set into a form that is specific once they are heated. But the process of overheating may cause them to degrade without entering a fluid phase.
These thermoset plastics are ideal for use in situations where heat is a factor; examples include electronic housing, electronic appliances, and chemical processing equipment. This is also due to their greater structural integrity and their ability to resist both heat and chemicals found in these thermosets. Thermosets are also able to resist deformation and the effects of impact. Some general thermoset examples include epoxy resins, phenolics, and polyimide. These examples are often used in composites.
Thermosets have some advantages, including: being able to be molded with a different range of tolerances, typically being cheaper compared to components fabricated from metals, having a cheaper setup and tooling cost compared to thermoplastics, and having a higher strength-to-weight ratio. But despite all these pros, they come with some cons, including the inability to be reshaped or remolded and the fact that thermosets cannot be recycled.
Although this is not needed in most cases, some manufacturers choose to further fashion their plastic rods through secondary ways such as drilling, painting, deburring, coating with powder, labeling, industrial finishing, and notching. These plastic rods can be clear or can come in different colors, which also include custom-matched colors.
Manufacturers love the idea of working with extruded plastic rods due to the versatility and the plastic extrusion’s wealth of material choices. Plastic rods are an ideal choice for one looking for inexpensive, quick, and durable products.
Despite the different materials used to extrude or co-extrude plastic rods, all these plastic rods share some of the uncommon properties of materials made from plastic. Some of these properties include low density, the inability to conduct, low porosity, greater structural integrity, resistance to corrosion, resistance to heat, and malleability.
Manufacturers have the ability to produce different plastic rods containing different chemical combinations and also being made from different materials. Due to this, there is room for the creation of plastic rods which have particular properties for specific applications.
This type of plastic rod is made up of acetal, also referred to as polyoxymethylene. This is a high-strength, semi-crystalline, and low friction engineering plastic with low absorption in moisture. This type of plastic rod has excellent wear properties and also excellent abrasion properties in both wet and dry environments. The acetal plastic rod is also easy to machine, and acetal enables an outstanding choice for applications that require tight and complex tolerances.
Acetal plastics are resistant to chemicals that are included in some fuels and solvents. Most of the applications of acetal plastic rods include manifolds, bearings and bushings, food processing and packaging machinery parts, wear pads, wear strips, and pump and valve parts.
This type of plastic rod is made up of acrylic, which is also known as Plexiglas. This type of plastic is strong, stiff, and available in clear and other colors. Its glass-like properties include its clarity, transparency, and brilliance, but it is half the weight and more times the impact resistance of glass.
Some applications of acrylic plastic rods include indoor and outdoor signs, architectural glazing, safety shields, sneeze guards, and POP displays.
This type of plastic rod is made up of polyimide, which is an extremely high temperature- and creep-resistant plastic material mostly used in high heat environments. And in these environments, thermoplastic materials are due to lose their plastic mechanical properties and as a lightweight metal replacement.
Polyimide plastic rods have very long-term performance at cryogenic temperatures and also up to 500 °F (260 °C), thus making them a common choice for use in aerospace and other industrial applications. They are also used in chip test sockets, wafer clamping rings, semiconductors, and material handling machinery, and also they are put to use in valve seats and sealing.
High-density polyethylene is a chemically resistant, strong, durable, lightweight plastic material that is ideal for a variety of applications. High-density polyethylene plastic rods are easy to fabricate and weld using thermoplastic welding equipment, thus making them excellent for use in fabricated water tanks and chemical tanks.
High-density polyethylene plastic rods are also widely used in applications which include the cutting of boards for food preparation, marine constructions, orthotics and prosthetics, water pipe flanges, and outdoor and indoor playground systems.
Nylon rods are made up of nylon, which is a stiff and strong engineering plastic containing outstanding properties in wear and bearing. The nylon plastic rod is usually used to replace metal bearings and brushes, resulting in the elimination of the need for external lubrication, reducing the weight of the part, dampening operating noise, and decreasing the wear on mating parts.
Some other applications of the nylon plastic rod include wear pads, gears, and packaging machinery parts.
Polyetheretherketone rods are also referred to as PEEK plastic rods. They contain high-performance engineering plastic that has outstanding resistance to harsh and aggressive chemicals. It also has a very high mechanical strength and stability in its dimensions. The PEEK plastic rod offers hydrolysis resistance to steam, seawater, and water in general.
The PEEK plastic rod has the ability to maintain certain stiffness at temperatures of a high magnitude, and it is also suitable for continuous use at temperatures as high as 338 °F (170 °C). Some of the applications of the PEEK plastic rod include aerospace parts, seals, medical instrument parts, food processing machinery components, bushings, bearings, and pump and valve components.
Polycarbonate is a transparent, stiff, and strong thermoplastic with outstanding impact resistance even at low temperatures. The polycarbonate plastic rod is easy to machine and contains excellent stability in its dimensionality.
Some of its applications include indoor and outdoor signs, POP displays and graphic holders, skylights, architectural glazing, face shields, semiconductor machinery components, machine guards, and transparent manifolds.
The polypropylene plastic rod is a chemically resistant plastic rod with excellent aesthetic properties at a cost that is low. The polypropylene plastic rod is easy to weld using thermoplastic welding equipment, and it is also often fabricated into water and chemical tanks.
Some of the applications for the polypropylene plastic rod include rigid outer prosthetic sockets and also in lower and upper extremity orthoses.
The polytetrafluoroethylene plastic rod is a soft, low friction fluoropolymer rod that has outstanding resistance to weathering and chemicals. The polytetrafluoroethylene plastic is stable at temperatures of a magnitude of up to 500 °F (260 °C), and it is also used in temperate environments.
Polytetrafluoroethylene plastic also has very many excellent properties in electrical insulation. Some applications of the polytetrafluoroethylene plastic rod include the use in pump parts, manifolds, semiconductors, scientific equipment, seals, and gaskets.
This type of plastic rod, also referred to as PVC plastic rods, is strong and stiff and is of a low-cost plastic material that is easy to fabricate and easy to bond using solvents and adhesives. The polyvinyl chloride plastic rod is also easy to weld using thermoplastic welding equipment. Some applications of the PVC plastic rod include valve and pump housings, cabinets, and welded chemical tanks.
This chapter will discuss the applications and benefits of plastic rods.
Each type of plastic grouping contains different pros and cons. For example, thermoplastics are generally easier to mold and are faster to produce compared to thermosets. Aside from this, thermosets tend to have components of superior strength. And unlike thermoplastics, they are able to retain their strength when they are heated.
For further identification, each plastic material is able to offer different qualities and attributes in relation to how the manufacturer may want it. Taking, for example, PVC, this component has a higher resistance to heat, chemicals, and fire, and it is most popular in the building of exteriors, metal anodizing, sewage treatment, and chemical processing.
Acetal plastic rods contain very low water absorption ability and are resistant to chemicals, but despite this, they are relatively weak and susceptible to heat. Because of these qualities, they are suitable for food processing applications that do not require high heat resistance or strength. The manufacturers that make flexible and scratch-resistant products are likely to use plastics which include HDPE or acrylic. These two types of plastics are valued for the ease with which they can be manipulated.
Plastic rods are found in various industries, including aerospace, electronics, petrochemicals, marine, and transportation. They are often used as raw materials in these industries so as to be machined into parts for seals, gaskets, pieces that are corrosion resistant, bearings, static control, sleeving, insulation, and other contained acts. They are also used in the construction sector and in commercial businesses, all with the aim of serving applications that are related to the structural support of industrial equipment and the displays of point of purchase.
A plastic rod is a solid plastic shape made by the process of plastic extrusion or plastic co-extrusion. Despite the different materials used to extrude or co-extrude plastic rods, all these plastic rods share some of the uncommon properties of materials made from plastic. Some of these properties include their low density, inability to conduct, low porosity, greater structural integrity, resistance to corrosion, resistance to heat, and malleability.
Plastic channels are plastic products that have linear extruded profiles. They have a constant cross-sectional shape across their axis. They are long and narrow structures, and their depth is relatively short. These products serve a variety of functions and uses...
Plastic extrusion, also known as plasticating extrusion, is a continuous high volume manufacturing process in which a thermoplastic material -- in a form of powder, pellets or granulates -- is homogeneously melted and then forced out of the shaping die by means of pressure...
Plastic trim products are extruded linear profiles that can be made to any length. Because of its ability to attach, hold, and seal, plastic trim has many applications. Plastic, HDPE, LDPE, butyrate, PVC, acrylic, and...
Nylon tubing, also known as polyamide tubing, is a type of tubing made from polyamide resin, which has a strong resistance to abrasion. It is used in high-pressure and high-temperature applications...
Plastic fabrication is the process of designing, manufacturing, and assembling a product made out of plastic material or composites that contain plastic. There are numerous plastic fabrication methods known today, considering the wide variety of products made out of plastic...
Plastic materials are objects artificially made from organic compounds called polymers along with other additive components. They possess excellent formability, making them extremely versatile for many different fabrication and manufacturing processes...
Plastic tubing is a form of tubing that is manufactured from a mixture of a polymer with a variety of chemicals to form a material that can be solid or flexible. Since its first use in the 1950‘s, plastic tubing has revolutionized industrial processes and has found a use in a wide variety of applications...
Poly tubing is a highly flexible, lightweight, and durable tubing that is produced from polyethylene, a polymer that is made from the polymerization of ethylene. It is a very versatile form of tubing that has break and crack resistant walls...
PVC is a tough chemically resistant synthetic polymer of vinyl chloride used especially for making pipes, films and electrical insulation. It is made by polymerizing vinyl chloride, and...
Silicone tubing is a very tough elastomer that exhibits high strength, flexibility, and resistance. Silicone tubing can be stretched without tearing and is highly versatile. It cannot be weakened with repeated bending and twisting due to...