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All about Plastic Extrusion and Helpful Tips for Buying Extruder Machinery

Plastic extrusion is a kind of continuous process for high volume manufacturing, where a certain thermoplastic material can be made in the form of pellets, powder, or granulates. Thereafter, they are homogeneously melted and moved into shaping die by applying pressure.

For example, screws are made with the molten plastic flowing into the rotating molds. As your plastic melts, it will pass through the die, where it is going to acquire the shape of the die-hole shape, and will then leave the extruder. This extruded product is known as an extrudate.

A typical plastic extruder will consist of 4 zones:

1. Feed zone

The flight depth is constant in this zone. The flight depth is the distance between the main diameter of the screw at the top of the flight and the minor diameter of the screw at the bottom of the flight.

2. Transition zone/compression zone

In this zone, the flight depth begins to decrease. The thermoplastic substance is crushed and starts to plasticize as a result.

3. Mixing zone

The flight depth remains constant in this zone. A particular mixing device may be used to ensure that the material is completely melted and homogeneously blended.

4. Metering zone

The flight depth in this zone is lower than in the mixing zone, but it remains constant. In this zone, the pressure also forces the melt using the shaping die.

What can be created by using plastic extrusion?

Plastic extrusion is a technique that presses the molten plastic using a die to create tubes and plastic profiles. The procedure is used to make a wide range of goods and component parts for both industrial and home applications.

Thermoplastics will be utilized to force these plastics into shape because they are the best sort of material for melting and cooling to form a rigid shape. Two of the mainly included thermoplastics for plastic extrusion are polypropylene and PVC. Let us discuss here a few different applications for plastic extruder.

1. Tubing

Extrusion of plastic can be used to make a wide variety of pipes and tubes. Tubes can be extruded to transport vast amount of liquid or gases, such as sewerage or water pipes, on one end of the scale.

Tubes with a considerably smaller diameter, on the other hand, can be made for items like medical tubing or straws! Tubing is one of the most common things made by plastic extrusion, and it is also one of the simplest to make because it can be extruded to any length and cut to the desired size.

Extruded tubes can be made not just to a given diameter, but also can be thicker or thinner as needed.

Extruded tubes can be hard or flexible, depending on the type of plastic employed. This means that plastic tubes can be manufactured to remain rigid for use in plumbing and sewage while also becoming more flexible.

Garden hoses, medical tubing, and tubes that transport food, chemicals, or gases in a factory setting will all be made with more flexible plastic extrusions.

2. Profiles

To best suit the required design, cross-section shapes can be extruded in a range of various plastic types. Rain gutters, railing, trims, and seals for windows and doors are examples of profiles, which are forms rather than simple tubes.

Co-extruded elements, such as rubber seals on window trims, can frequently be added to profiles like these. Furthermore, adding another kind of plastic to the expulsion process.

3. Solid extrusions

Extrusions don’t have to be hollow tubes or profiles and they can be solid shapes as well. Plastic planks and decking, as well as a variety of curved bar stock for industrial or automotive usage can be made in this way.

Solid form extrusion is beneficial for making outdoor furniture, such as benches and fences because the plastic is a weatherproof, low-maintenance alternative to wood that lasts far longer.

4. Insulation

Plastic extrusion can also be used to make the insulation that surrounds the electrical cable. This is accomplished by passing a wire through the die and then extruding plastic around it to form an insulating layer.

Other types of cable can also go through this extrusion process to make them waterproof and resistant to corrosion and abrasion, as well as easier to handle.

5. Sheets and film

Extruded sheeting and film can also be used as a protective screen or as part of window glass. Extruded plastic film can also be used to make plastic packaging like blister packs.

Few Different types of plastic extrusion line

There are several designs of extruders that are available in the market today. We will take up a few important ones here and briefly discuss them.

1. Single screw extruders

Single screw extruders are the most prevalent continuous extruders in the polymer extrusion sector because of their numerous advantages, including low cost, simple design, toughness, reliability, and a high performance/cost ratio.

Any standard single screw extruder will have 3 geometrically varying zones:

· Feed zone

· Metering zone

· Transition or compression zone

The consistent pitch of the screw, but variable channel depth creates the three zones. The compression phenomenon is caused by the screw channel’s depth decreasing linearly from the feed zone to the metering zone.

The term «single-stage» refers to screw designs having only one compression portion. For the same screw length and diameter, zone length, as well as maximum and minimum channel depths, may vary. As a result, several screw profiles are feasible.

2. Twin-screw extruders

Generally, twin screw extruder is categorised as continuous multiple screw extruders in general. The name comes from the fact that these extruders contain two Archimedean screws in their design.

There are several classes for twin-screw extruders since there are more design characteristics that may be adjusted in twin-screw extrusion, such as rotational direction, degree of intermeshing, and so on.

The twin screw extruder has 2 varieties and they are also further subdivided as follows:

a. Intermeshing extruders

· Counter-rotating

· Co-rotating

b. Non-intermeshing extruders such as

· Counter-rotating

· Co-rotating

· Co-axial

3. Tubing extrusion

Tubes and pipes are extruded using this method of extrusion. Air with a positive internal pressure can also be used in this process. After departing the die, the tubes or pipes are dragged into a cooling tank, where they are generally water-cooled.

4. Blow film extrusion

This type plastic extrusion line can be used to make plastic film tubes using a continuous sheeting process. The melt from the film tube is cooled before it leaves the die, resulting in a semi-solid tube that is blown to a suitable size and film thickness. This method is employed in the production of items like shopping bags.

5. Sheet film extrusion

In this plastic extrusion line plastic sheets or films that are too thick to be blown are extruded using this method. The sheets are drawn and cooled through a sequence of cooling rolls after exiting the die, which helps regulate sheet thickness.

6. Over jacket extrusion

Wire coating is done with this form of extrusion. The wire is drawn into the die’s centre in this procedure. When a high level of adhesion between the wire and the coating is required, pressure tooling is employed.

The wire is covered with molten plastic while in the die and is pressured when it exits the die in this manner. Jacketing tooling is utilised if adhesion is not required. The melt covers the wire as it exits the die in this way.

How to select a plastic extruder?

The following are a few things that you must see while selecting any plastic extruder:

1. Track record of success

Reliability and experience are important things to consider when selecting a manufacturer. You must be confident that your chosen manufacturer will be there and able to assist you throughout the extruder’s operational lifetime.

A long and successful track record is the best indicator of a manufacturer’s dependability and industry experience.

2. Quality of components

Consider manufacturers who only employ high-quality components from globally recognised brand names when it comes to the numerous components used on an extruder machine. If a component has to be improved, repaired, or replaced in future, there will be no issues locating or integrating a spare part.

3. Quality of service and support

The term «quality» refers not just to the extrusion machine itself, but also to the continual support provided at every step along the road. A good business will follow through on its promise of excellent customer service by offering assistance throughout the purchasing process.

Nanjing Cowin Extrusion Machinery Company Ltd was formed by the optimization and reorganisation of the twin-screw extrusion industry’s leading team. It is a multinational, high-tech limited corporation specialising in the production of polymer material processing equipment.

In China, this company is considered to be one of the best extruder manufacturing companies. It was founded in Nanjing, Jiangsu Province, in 2012. The company employs more than 50 people, including ten technical R&D engineers, twenty machining and assembly workers, 18 management and sales teams, and five after-sales support teams.


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