Blow vs Compression vs Extrusion vs Injection Molding Machine

Blow molding – well suited for hollow objects, like bottles

The process follows the basic steps found in glass blowing. A parison (heated plastic mass, generally a tube) is inflated by air. The air pushes the plastic against the mold to form the desired shape. Once cooled, the plastic is ejected.

The blow molding process is designed to manufacture high volume, one-piece hollow objects. If you need to make lots of bottles, this is the process for you. Blow molding creates very uniform, thin walled containers. And, it can do so very economically.
Compression molding – well suited for larger objects like auto parts

The name of this molding method says everything. A heated plastic material is placed in a heated mold and is then compressed into shape. The plastic can be in bulk but often comes in sheets. The heating process, called curing, insures the final part will maintain its integrity. As with other molding methods, once the part has been shaped, it is then removed from the mold. If sheeting plastic material is used, the material is first trimmed in the mold before the part is removed.

This method of molding is very suitable to high-strength compounds like thermosetting resins as well as fiberglass and reinforced plastics. The superior strength properties of the materials used in compression molding make it an invaluable process for the automotive industry.
Extrusion mouldingExtrusion molding – well suited for long hollow formed applications like tubing, pipes and straws

While other forms of molding uses extrusion to get the plastic resins into a mold, this process extrudes the melted plastic directly into a die. The die shape, not a mold, determines the shape of the final product. The extruded “tubing” is cooled and can be cut or rolled for shipment.

Injection molding – well suited for high-quality, high-volume part manufacturing

Injection molding is by far the most versatile of all injection molding techniques. The presses used in this process vary in size and are rated based on pressure or tonnage. Larger machines can injection mold car parts. Smaller machines can produce very precise plastic parts for surgical applications. In addition, there are many types of plastic resins and additives that can be used in the injection molding process, increasing its flexibility for designers and engineers.

The process itself is fairly straightforward; however, there are many enhancements and customization techniques that can be used to produce the desired finish and structure. Injection molds, which are usually made from steel, contain cavities that will form the parts. Melted plastic is injected into the mold, filling the cavities. The mold is cooled, and the parts are ejected by pins. This process is similar to a jello mold which is filled then cooled to create the final product.
The mold making costs in this method are relatively high; however, the cost per part is very economical. Low part cost along with resin and finish options have all contributed to injection molding’s popularity in today’s manufacturing landscape.



Where to Source Plastic Molding Machine

 Automatic molding, a semi-automated form of compression molding, is the process Sunkoo uses for the manufacture of medium-volume to large-volume net molded and near net molded PTFE components. The automatic molding process requires dedicated tooling, typically requires minimal operator intervention and plastic parts can be fabricated relatively rapidly.

With the use of precise tooling and processing, parts manufactured using the automatic molding process can be produced to relatively close tolerances, but not to the accuracy of a fully machined part. Components are economically molded by utilizing a process of automated filling of the die cavity, applying pressure, and part ejection.
The Sunkoo molding department has the capability to produce compression molded PTFE rod and tube stock to meet and exceed your exact specifications and tolerances. Sunkoo has over 1,000 mold sizes to manufacture stock shapes from 1” OD to 26” OD in Virgin PTFE, as well as all industry standard and custom blended materials. One of the benefits of compression molded rod or tube is the relatively low cost of this method. It typically does not require special tooling beyond what Sunkoo already possesses.
With an extensive array of in-house equipment, Sunkoo is your one-stop source to handle all aspects of your compression molding component requirements. Call the specialists at Sunkoo for immediate assistance.

Plastic Machinery Manufacturer

Sunkoo’s enormous strength comes from a wonderful combination of its highly efficient and professional management and a dedicated workforce of qualified and experienced engineers and technicians and marketing personnel, which in turn, leads to world-class manufacturing, testing and R & D , besides meeting requirements of clients’ specifications globally.
We have invested in advanced training to promoted knowledge in the area of technical development, research and production, creating preconditions for innovations. Based on market research and feedback from clients, our R&D department works to engineer products that are innovative and unique for PTFE & UHMWPE machinery.
The objective of our business has been dedicated to plastic extrusion industry with diversified & innovative engineering solutions in the application design & supply of wide range of Injection Molding plastic extruders, recycling units & extrusion ancillaries. we are proud of the leadership position we have earned for our Company.
We constantly aim to accept future challenges in the plastic extrusion technology with emphasis on our manufacturing potential. We have a wide vision for developing special purpose machines extending from light to heavy duty which can easily fulfill the needs of plastic industry and make us a leader.
We have created a wide market for our products with our honesty and integrity. Our clients have complete faith on us and we strive to upkeep the same. With our foresightedness and skills, we have supplied our products to various domestic and overseas markets. We strive to cater to new markets as well as retain our old clients with our expert quality and time bound delivery schedules.

Plastic Extrusion Operator

Extrusion operators, sometimes called extruding and drawing machine operators, control and monitor machines that shape thermoplastic materials. They work in a number of manufacturing industries, including general plastics manufacturing, automobile and automotive parts manufacturing, and aerospace manufacturing.
Preparation Required
While some employers of plastic extrusion operators may hire candidates who don’t have a high school diploma or GED, many employers prefer to hire workers who do. Otherwise, there are no formal educational requirements for this job. However, new hires go through an on-the-job training process that involves starting with basic tasks, such as feeding the machine, under the supervision of experienced operators. As they learn more and more skills, they eventually begin to work independently. It can take a year or more to become highly skilled at operating an extruding machine.
Job Activities
Operating an extrusion machine requires workers to perform several basic tasks. In some cases, they must mix thermoplastic materials in the form of pellets or powder with colored dyes before feeding it into the extrusion machine. Extruding machine operators set the dials and controls on the machine to ensure that the created product is the right size, shape and thickness. Extruding machines are commonly used to produce items and shapes such as hoses, wires or tubes. Once the product is created, extruding machine operators measure and test it to make sure that it conforms to the requested specifications.

Extrusion Methods

By plasticizing, there are dry extrusion and wet extrusion processes and by pressurizing there are continuous and intermittent extrusion processes
Continuous production yields a high efficiency, simple operation for a wide range of applications, such as tubing extrusion, sheet/film extrusion etc.
Profile Extrusion
The Profile Extrusion process, such as drinking straws and medical tubing, is manufactured the same as a regular extrusion process up until the die. Placing a pin or mandrel inside the die extrudes hollow sections, and in most cases positive pressure is applied to the internal cavities through the pin.
Tubing with multiple lumens (holes) must use tooling made for specialty applications. For these applications, the tooling is made by placing more than one pin in the center of the die to produce the number of lumens necessary. In most cases, these pins are supplied with air pressure from different sources. This way, the individual lumen sizes can be adjusted by adjusting the pressure of the individual pins.
Co-Extrusion is the extrusion of multiple layers of material simultaneously. This type of extrusion utilizes two or more extruders to melt and deliver a steady volumetric throughput of different viscous resins to a single die and extrude the resin in the desired form. This process can be used in a variety of extrusion processes (blown film, profile or sheet). The layer thicknesses are controlled by the relative speeds and sizes of the individual extruders delivering the materials.
There are a wide range of reasons why a manufacturer may choose co-extrusion over single layer extrusion. One example is in the vinyl fencing industry, where co-extrusion is used to tailor the layers based on whether they are exposed to the weather or not. Usually a thin layer of compound that contains expensive weather resistant additives are extruded on the outside while the inside has an additive package that is more suited for impact resistance and structural performance.
Extrusion Coating
Extrusion coating is used in a blown or cast film process to coat an additional layer onto an existing roll stock of paper, foil or film. For example, this process can be used to improve the characteristics of paper by coating it with polyethylene to make it more resistant to water. The extruded layer can also be used as an adhesive to bring two other materials together.
Sheet/film Extrusion
For products such as plastic sheet or film, cooling is achieved by pulling material through a set of cooling rolls, usually 3 or 4 in number. Running material too fast creates an undesirable condition called “nerve” which is basically inadequate contact time given to dissipate the heat present in the extruded plastic. In sheet extrusion, these rolls not only deliver the necessary cooling but also determine sheet thickness and surface texture.
Often co-extrusion is used to apply one or more layers on top of a base material to obtain specific properties such as UV-absorption, soft touch or “grip”, matte surface or energy reflection where it is needed.
A common post-extrusion process for plastic sheet stock is thermoforming where the sheet is heated until soft and then formed via a mold into a new shape. Thermoforming can range from line bended pieces to more complex shapes such as computer housings. These more complex forms which often resemble injection molded parts and can be attributed to the various possibilities in thermoforming, such as inserts, undercuts and divided molds.
Plastic sheet and film extrusion onto paper is the basis of the liquid packaging industry. Juice cartons, wine boxes as well as the food packaging industry utilize this process.
Blown film Extrusion
This process is used to manufacture plastic film for products such as shopping bags . Blown film is imilar to any regular extrusion until it reaches the die. The die is an upright cylinder with an annular opening similar to a pipe extrusion die. The molten resin is pulled upwards from the die by a pair of nip rolls high above the die. Changing the speed of these nip rollers will change the gauge or wall thickness of the film. Around the die sits a cooling ring that blows air onto the film tube as it travels past. The airflow cools the film as it travels upwards. In the center of the die is an air outlet trough which compressed air can be forced into the inside of the extruded cylindrical profile, adjusting the bubble volume. The film can then be slit, spooled, printed on or cut into shapes and heat sealed into bags or other items.
Compound Extrusion
Compound extrusion is a process that mixes one or more polymers with additives to create a plastic compound. The feed stock may be pellets, powder and/or liquids, but the product is usually in pellet form and used in other plastic-forming processes such as extrusion and injection molding. Machine size varies from tiny lab machines to the biggest extruders in the industry, running as much as 20 tons per hour, as used by the chemical companies that make base resins. Usually twin-screw extruders are preferred because they offer superior mixing at lower melt temperatures. Most of these have screws and barrels comprised of smaller segments (mixing, conveying, venting and additive feeding) so that the design can be changed to meet the production and product needs. Single-screw extruders can be used for compounding as well, especially with appropriate screw design and static mixers after the screw. Selection of the components to be mixed (viscosities, additive carriers) is as important as the equipment.

Plastic Extrusion vs. Injection Molding

For industrial manufacturers, the methods of injection molding and/or extrusion are specified to make products with different shapes and sizes.

The molten die-casting method is the basis of the injection molding process. The injection-molding unit consists of two elements: the clamping unit, and the injection unit. Unlike extrusion, injection molding forms three-dimensional shapes.
In terms of plastic extrusion, this technology was pioneered by Thomas Hancock in 1820 and Edwin Chafee in 1836 for the processing of rubber. The first thermoplastic extrusion is credited to Paul and Ashley Troester much later, in 1935. This is a method by which molten plastic or varying alternative materials are pushed continuously, driven by feed screws through a two-dimensional die opening. Following this, it passes through a series of templates or blocks where the molten form retains the desired shape as it cools. In the extrusion process, the finished product has a two-dimensional form which is continuous in length. The extrusion method produces linear shapes which can be cut to multiple lengths and / or notched, punched or otherwise fabricated, often continuously in line during the process .
Both extrusion and injection molding have their own advantages. An advantage in using the extrusion process over other methods is its ability to create complex cross-sections. Additionally, both stiff or soft materials can be formed into any shape and the finished materials have a smooth surface finish when compared to other processes. With both the injection molding and extrusion processes, there is minimal waste as the scrap can be recycled again.
  • Injection molding forms three-dimensional shapes.
  • The injection molding process was first established in the 1930s.
  • The thermoplastic extrusion process was fully developed in 1935.
  • Extrusion is a method using molten plastic or many other materials that are pushed through a two-dimensional die opening.
  • In both processes , the scrap can be recycled reducing waste.
  • The injection molding process is based on the molten die-casting method.
  • In the extrusion method, the finished products have a two-dimensional form which are continuous in length and can be cut to multiple lengths and punched or notched.
  • Complex cross sections are created using the extrusion method.
  • In the extrusion process, both stiff or soft materials can be formed into any shape and the finished materials have a smooth surface finish.
  • The extrusion process is ideal for construction materials such as siding , decking, trim or drainage, cosmetic parts such as wall protection, window casements, office furniture or functional components like louvers, brackets, retainers or supports.
  • The injection process is ideal for manufacturing toys, interior automotive components and many other 3 dimensional products.

Plastic Extrusion Basic Information – Supplies & Process & Design

Whether it’s one hundred yards of pipe-tubing or a thousand Crazy Straws, plastic extrusion is in frequent use in today’s plastics industry because it’s readily available and easy to work with. The plastic extrusion process involves melting plastic material, forcing it into a die to shape it into a continuous profile, and then cutting it to length. The process is a good choice for applications that require a final product with a constant cross-section. The low cost and high production rates make it a common manufacturing choice for products such as piping, plastic sheeting, weather stripping, wire insulation and adhesive tape.
Plastic Extrusion Supplies
Prior to beginning the plastic extrusion process, the proper machinery and supplies must be obtained, specifically a plastic extruder machine. This device is a fairly simple machine that facilitates the extrusion process from start to finish. The main components of a plastic extruder include a hopper, barrel, screw drive and screw drive motor.
The second most important component is the raw thermoplastic material intended for extrusion. The majority of extrusion operations rely on resin plastic (small solid beads) to allow for simple loading and quick melting times. Common plastic materials used in the extrusion process include high impact polystyrene (HIPS), PVC, polyethylene, polypropylene, and ABS.
The final component necessary for plastic extrusion is the die. The die serves as the mold for the plastic—in plastic extrusion, dies allow for even flow of the molten plastic. Dies typically must be custom made and may require additional lead time prior to beginning the manufacturing process.
The Basic Process Of Plastic Extrusion
The plastic extrusion process begins with the placement of raw resin into the extruder’s hopper. If the resin lacks additives necessary for the particular application (such as UV inhibitors, anti-oxidants, or colorants), then they are then added to the hopper. Once in place, the resin is typically gravity-fed through the feed throat of the hopper down into the extruder’s barrel. Within the barrel is a long, rotating screw that feeds the resin forward in the barrel towards the die.
As the resin moves along within the barrel, it is subjected to extremely high temperatures until it starts to melt. Depending on the type of thermoplastic, barrel temperatures can range between 400 and 530 degrees Fahrenheit. Most extruder’s have a barrel that gradually increases in heat from the loading end to the feed pipe to enable gradual melting and minimize the possibility of plastic degradation.
Once the molten plastic reaches the end of the barrel, it is forced through a screen pack and fed into the feed pipe that leads to the die. The screen, reinforced by a breaker plate due to high pressures in the barrel, serves to remove contaminants that may be present in the molten plastic. The porosity of the screen, number of screens, and other factors can be manipulated until uniform melting occurs as a result of the right amount of back pressure.
Once in the feed pipe, the molten metal is fed into the die cavity, where it cools and hardens. To expedite the cooling process, the newly formed plastic receives a sealed water bath. In the case of plastic sheeting extrusions, cooling rolls replace the water bath.
Temperature Maintenance
Maintaining the correct temperature level and melting rate of the resin is an important consideration when creating plastic extrusions. Optimal temperature maximizes uniform fluidity of the plastic, and minimizes the possibility for stress and warping of the final product. Variables such as pressure and friction that build up in the barrel of the extruder mean that temperatures are not remaining constant. Heaters must be monitored, lowered, raised, or shutoff as necessary to maintain constant heat within the extruder—cooling fans and cast-in heater jackets can also help maintain proper extrusion temperature.
Importance Of Screw Design
Since the heating rate, feed rate, and other integral extrusion factors are directly dependent on the only moving part in the plastic extruder—the screw—carefully consideration of the size and design of this component is necessary. Calculation of screw diameter and length is based on the melting rate, size of the resin, type of raw plastic, and amount of pressure required maintaining uniformity. For applications where materials are compounded within the barrel of the extruder, a twin-screw design may be used to enable adequate mixing.
Specialty Plastic Extrusion Processes
Many applications call for specialized extrusion processes to obtain adequate results or speed up the production process. Common specialty extrusion processes include:
  • Blown film extrusion: Used to fabricate plastic film products such as grocery and food storage bags The dies in this process feature an upright, cylindrical design that pulls the molten plastic upward as it forms and cools.
  • Coextrusion: Several layers of material are extruded at the same time. Two or more extruders feed different types of plastic into a single extrusion head.
  • Overjacketing: Extrusion is employed to coat an item in protective plastic coating. Exterior wire and cable jacketing is the most common application of overjacketing.
  • Tubing extrusion: Similar to traditional extrusion, except the die includes interior pins or mandrels to facilitate the production of hollow plastic materials.