Single Screw Vs Twin Screw Extruders: How To Choose The Right Extruder For Your Application

Single Screw Vs Twin Screw Extruders: How To Choose The Right Extruder For Your Application

Choosing an extruder is not simply a matter of deciding between a single screw or twin screw machine. 

The right choice depends on what you are putting into the extruder, what you want to produce and how the complete production line needs to operate. 

For some applications, a single screw extruder is the right solution. For others, the greater mixing capability of a twin screw extruder makes it more suitable. In some cases, the application may require a custom configuration. 

So how do you know which extruder is right for your process? 

The starting point is the material and the finished product. 

What is the difference between a single screw and twin screw extruder? 

Both single screw and twin screw extruders heat, melt and convey polymer through a controlled process to produce a continuous product. The key difference is how the material is processed inside the machine. 

A single screw extruder uses one rotating screw and is commonly suited to finished-product manufacturing where the raw material is supplied in pellet form. Telford Smith single screw extruders are used across applications including recycling, sheet, pipe and profile extrusion. 

A twin screw extruder uses two screws. Telford Smith's machines are co-rotating twin screw extruders, with interchangeable screw elements and barrel sections that allow the process configuration to be changed for different applications. 

Twin screw extrusion provides more intensive mixing, making it particularly suited to processes such as compounding and masterbatch production where powders, additives or other materials need to be incorporated into the polymer. 

But there is no universal rule that says one type is better than the other. 

The raw material and the finished product determine which extruder is most appropriate. 

When is a single screw extruder the right choice? 

Single screw extruders are ideally suited to many finished-product manufacturing applications, particularly where the raw material is already available in pellet form. 

Depending on the configuration, applications can include: 

• Sheet extrusion 
• Pipe extrusion 
• Profile extrusion 
• Plastic recycling and regrind processing 
• Film and other continuous extrusion applications 

Telford Smith offers single screw extruders with different screw designs to suit polymers including LDPE, LLDPE, HDPE, PP, HIPS, ABS, PET, PVC and Nylon. Screw options include metering screws, barrier screws, two-stage screws for venting and screws incorporating different mixing heads. 

The important point is that the screw should be selected for the material and application. 

A machine that performs well with one polymer should not automatically be expected to deliver the same result with another polymer simply because the extruder has the required output capacity. 

When is a twin screw extruder the better choice? 

Twin screw extruders are particularly useful when the process requires more intensive mixing or compounding. 

Telford Smith's co-rotating twin screw extruders are used for applications including: 

• Masterbatch production 
• Colouring polyolefins and engineering plastics 
• Alloying and filling polyolefins and TPE 
• Filling and reinforcing engineering plastics 
• Recycling regrind plastics 
• Biomass compounding 
• Plastic/wood composites 

They can also be used for finished products. Examples include applications such as UPVC pipe and wood-plastic composite boards. 

This is why choosing an extruder based solely on the finished product can be misleading. Two companies may manufacture similar products but require different extrusion systems because their raw materials, additives, formulation or processing requirements are different. 

Which extruder is better for plastic processing? 

There is no single answer. 

A better question is: 

What material are you processing, and what do you need the finished product to be? 

For example, a process using polymer pellets to manufacture a finished product may be well suited to a single screw extruder. 

A process involving powders, additives, fillers or formulations that require significant mixing may be better suited to a twin screw extruder. 

The application needs to be assessed as a whole. 

That is why Telford Smith's process engineers start with the customer's material and product requirements rather than simply selecting an extruder based on size or output. 

The 4 questions that need answered before selecting an extruder 

Before specifying an extruder, there are four basic questions that need to be answered. 

1. What is the finished product? 

The finished product influences the extrusion process, downstream equipment and the requirements placed on the extruder. 

A pipe, profile, sheet, compound or masterbatch may each require a different configuration. 

2. What polymer and additives are being used? 

Different polymers behave differently during processing. 

Additives, fillers and other materials can also change the processing requirements. 

The screw design therefore needs to suit the polymer and the required processing conditions. 

3. What form is the raw material? 

Is the feed material: 

• Pellets? 
• Powder? 
• Fibre? 
• Regrind? 
• A combination of materials? 

The physical form of the feed material can influence the feeding system and the type of extrusion process required. 

4. What output is required? 

Required output is an important part of sizing the extrusion system. 

But output should not be considered in isolation. 

A machine capable of producing a particular number of kilograms per hour is not necessarily suitable for every material or application at that output. 

The polymer, screw design, feed material and finished product all need to be considered together. 

Why screw design matters 

The screw is one of the most important components in an extruder. 

Its job is not simply to move material from one end of the machine to the other. Screw geometry is selected to suit the polymer and the required processing conditions so that the extruder can operate efficiently at the desired rate. 

Telford Smith offers different screw designs for different applications, with process engineers selecting the appropriate design and material of manufacture. Options include nitrided screws for standard polymer applications and bimetallic materials where greater resistance to corrosion and wear is required. 

This is one area where buying an extruder based purely on its advertised output can create problems. 

Can one screw process different polymers? 

It may be possible to process different polymers using the same machine, but that does not mean the same screw configuration will provide the same results across the entire range. 

Acommon mistake seen by the Telford Smith Team is to try to extrude different polymers using the same screw and expect the same performance. 

The screw needs to be matched to the polymer and application. 

That is one reason why two extruders with similar physical dimensions can be configured very differently. 

Don't forget the rest of the production line 

One of the most important points to consider when buying an extruder is that the extruder is only one part of the production line. 

The team at Telford Smith describes the extruder as a hot melt pump. The equipment around it determines how the material is fed, filtered, formed and ultimately converted into the finished product. 

Depending on the application, an extrusion line may include: 

Feeding → Extruder → Filtration → Melt Pump → Die → Cooling/Forming → Downstream Equipment 

The exact arrangement depends on the product being manufactured. 

For example, Telford Smith supplies extrusion equipment including melt pumps, screen changers, strand pelletisers, roll stacks, sheet hauloffs and other equipment used to build complete extrusion systems. 

The engineering team also works on complete machinery design, proof of concept, testing, manufacture, delivery, installation and training. Recent projects listed by Telford Smith include complete extrusion systems for pyrolysis feed, extrusion coating and natural-fibre reinforced products. 

Why does downstream equipment matter? 

Because producing the melt is only part of the process. 

The downstream equipment has a direct role in turning that melt into the required finished product. 

For example, a sheet extrusion line may incorporate an extruder, screen changer, melt pump, sheet die, roll stack, winder and control system. 

This means the extruder should be specified as part of the production process rather than treated as an isolated machine. 

What about custom extrusion systems? 

Not every application fits neatly into a standard machine configuration. 

Telford Smith also supplies custom extruders for applications including compounding, recycling, film, pipe, profile, sheet, wire and cable. 

A custom extrusion system may involve changes to the screw, barrel, feeding arrangement, controls, machine configuration or downstream equipment depending on the application. 

The objective is not simply to select the biggest machine available. 

It is to configure an extrusion system that matches the material, product, required output and production process. 

Should you buy a larger extruder for future growth? 

There is a good reason to think beyond today's production requirements. 

Telford Smith's advice is: Plan for tomorrow, not today. 

Where future production growth is expected, a larger screw diameter may provide additional capacity. However, the appropriate size increase depends entirely on the application. 

That means there is no universal rule that says a business should simply buy the next size up. 

The decision should consider the material, product, current output requirements and realistic future production plans. 

Buying for future growth also needs to be balanced against the cost of operating a machine that is significantly larger than the current process requires. 

Single Screw vs Twin Screw: A simple comparison 

This table is a starting point, not a substitute for application assessment. 

There are applications that do not fit neatly into one column. The same product can potentially be manufactured using different extrusion technologies depending on the formulation and process. 

What information should you provide when requesting an extruder? 

If you are asking an equipment supplier to recommend an extruder, having the following information ready can make the initial discussion much more useful: 

Material 

What polymer are you processing? 

Additives 

Are there fillers, pigments, fibres or other additives? 

Raw material form 

Are you feeding pellets, powder, fibre, regrind or a combination? 

Finished product 

What are you trying to manufacture? 

Required output 

How many kilograms per hour do you need to produce? 

Existing equipment 

Do you already have feeding, filtration, melt pumping, dies or downstream equipment that the new extruder needs to integrate with? 

The more clearly these requirements are defined, the easier it is to assess the appropriate extrusion technology and configuration. 

So, which extruder should you choose? 

The answer starts with the application. 

Choose a single screw extruder when the material and process suit single screw technology, particularly where pelletised polymer is being processed into a finished product. 

Consider a twin screw extruder where the process requires more intensive mixing, compounding or incorporation of powders, additives or fillers. 

But neither statement should be treated as an absolute rule. 

The polymer, raw material form, formulation, finished product and required output all influence the decision. 

And the extruder itself is only part of the solution. 

A successful extrusion process depends on the complete production line, from feeding and filtration through to the die and downstream equipment. 

Need help choosing the right extruder? 

Telford Smith has been supplying machinery and engineered solutions for plastics processing and recycling for more than 100 years. Its current extrusion range includes single screw extruders, co-rotating twin screw extruders, custom extruders and complete extrusion lines. 

If you are considering a new extruder, start with the four questions above: 

What is the finished product? 

What polymer and additives are being used? 

What form is the raw material? 

What output is required? 

From there, Telford Smith's experienced Team can assess the application and help determine the appropriate extrusion technology and configuration. Telford Smith provides engineering support from concept and design through testing, manufacture, installation and training. 

Speak with Telford Smith about your extrusion application, today.