What Is Extrusion Process?
Extrusion is a unique manufacturing technique where a die manipulates material to a definite shape. In this case, you can transform rubber into continuous shapes using an extrusion die.
When making extruded rubber parts, the tooling system here is the die.
Extruding Rubber Parts Benefits
- Economical way to manufacture rubber parts due to slightly low production costs
- Versatile product that can produce rubber parts in a variety of shapes
- Durable and long-lasting parts
- Reduces material wastage
- Rubber parts are lightweight
- Suitable for making uniformly shaped rubber parts
- Extruded rubber parts are flexible
- Better performance in various temperature conditions
Choosing Rubber Materials for Extrusion Process
Rubber materials come in different properties.
As a rule of thumb, you must understand your application requirements before choosing rubber for the extrusion process. Some application requirements may include;
- Pressure rating requirements
- Temperature resistance requirements
- Exposure to corrosive environments
- Shear forces
- Abrasion specifications
- Compression requirements
- Electrical insulation requirements
Let’s explore common types of rubber materials:
|Rubber Material for Extrusion Process||Properties|
|Natural rubber||· The main compound is latex
· Popular for better heat buildup properties
· Exhibits better fatigue resistance
|Ethylene propylene rubber||· Commonly known as EPDM or EPM
· It is a product of propylene and ethylene copolymerization
· It has diene, which helps in the curing process
· Excellent dielectric resistance
· Superior weathering resistance
· Offer better insulation
· Maintains superior mechanical properties both at high and low temperatures
· Better chemical resistance both at high and low temperature
· Popular in the automotive industry
|Silicone||· High-temperature application requirements
· Highly resistant to light, oxygen, and ozone
· It is resistant to moisture
· More expensive
· Mechanical properties are lower than organic rubber
· Suitable for most industrial applications, especially in the food and drug industry
|Halogenated Butyl Rubber||· Offer better chemical resistance
· Exhibits improved ozone resistance properties
· Compared to butyl rubber, the improvement reduces both water resistance and insulation properties
· Perfect for making O-rings and rubber trims
|Neoprene||· Commonly known as CR rubber
· The first synthetic rubber from DuPont
· Excellent aging resistance
· Chemically inert
· More durable than natural rubber
· Expensive due to more additives
· Common applications include sealing systems, gaskets, hoses, and weather-stripping seals
|Nitrile||· Commonly known as Buna-N or NBR
· Made from butadiene and acrylonitrile
· Common in extruding automotive parts and components
· Resistant to oils, grease, and most petroleum-based chemicals
· Naturally, they have a low tensile strength
· Characterized by low-temperature performance
|Butane rubber||· Mostly abbreviated as BR
· Excellent cracking resistance,
· Resists abrasion, oils, and most solvents
· Susceptible to ozone degradation
· Commonly used to make tires
|Styrene butadiene rubber||· The rubber is made from butadiene and styrene
· Superior abrasion properties
· Excellent thermal resistance
· Resistant to tear
· Suitable for gaskets and tire manufacturing
|Butyl rubber||· It is made from isobutylene and isoprene
· Highly resistant to aging
· Readily repels most chemicals
· Common applications include hoses, O-rings, trims, and gaskets
|Fluorocarbon Rubber||· Also, known as Viton or FKM
· Resists virtually all chemicals
· Superior mechanical properties
· Main applications include O-rings and sealants
|Isoprene Rubber||· It is a general-purpose rubber material
· Exhibits better heat buildup properties
· Excellent fatigue resistance
· Better impact absorption properties
|Polyurethane Rubber||· It has plastic and rubber properties
· Offer better chemical and abrasion resistance
· Available with varying tensile strength and compression set
· You can make shock absorbers, bushings, etc.
How Rubber Extrusion Process Works
Extruding rubber is a systematic process involving several processes. The complexity or number of stages will depend on the rubber part designs.
Ideally, the process entails:
- Designing extrusion die
- Preparing rubber material or compounding
- Rubber material pressurization
- Extruding rubber
- Vulcanizing rubber
Let’s look at these processes in detail:
Step 1: Design Rubber Parts
Knowing the exact rubber profile you wish to extrude is very important. It will help you design a suitable tooling system for your rubber part.
It doesn’t matter whether you want standard or custom rubber extrusions. You will design a suitable die for the extrusion process.
In short: Have suitable extrusion die for the rubber material.
Step 2: Prepare Rubber Material for Extrusion Process
You must understand your rubber application requirements. With this information, you will know the various performance properties of extruded rubber products.
- Heat-resistant gaskets in the food industry – go for silicon rubber
- Hoses with excellent aging resistance – choose Neoprene rubber
However, choosing rubber material for extrusion is never enough. You must prepare the rubber by adding various additive or subjecting it to certain processes.
This way, you will improve the intrinsic properties of rubber material. Usually, the process is called rubber compounding. That is, you can add:
- Vulcanizing/curing agents
- Special ingredients
Let’s summarize why these four elements are critical when extruding rubber:
|Type of Compounding Material||Function||Examples|
|Filler||· Improves tensile and impact strength
· Makes rubber tear resistance
· Can improve abrasion resistance properties
|· Carbon black
|Stabilizers||· Improves degradation and weathering resistance
· Enhances fatigue and tear properties by acting as antiozonants, while preventing possible oxidation
|Curing Agents (Vulcanizing)||· Helps in proper rubber vulcanization||· Peroxides
|Special compounds||· To achieve specific application requirements or modify certain properties||· Pigments to add specific color theme
· Oils that can improve rubber processing
· Fibers and resins to enhance the tensile strength of rubber
Step 3: Rubber Extrusion Process
First, feed the rubber material prepared in step 2 above in the hopper. From here, the rubber material will move to the processing changer.
Second, configure and switch on the machine. The shearing screws will begin to rotate.
As the screw rotates, they transform the rubber to a pliable state. There are two screw designs:
- Single screw
- Twin screw
So, which options should you choose for extruding rubber parts – let’s compare:
|Variable to Compare||Single Screw Extruder||Twin Screw Extruder|
|Machine price||Affordable||More expensive|
|Efficiency||Low||High with large output and faster extrusion speed especially for a homogenous mixture|
|Compounding||Average results||Offer better results|
|Maintenance||Simple and easy||A little complex due to the structural design|
|Mechanism for conveying material||Depends on the frictional force between the barrel and material||Counter-rotating motion of the twin screw extruder pushes material|
Note: For a simple rubber extrusion process, you can choose single screw systems. It is affordable and easy to control.
At times, you may use rubber strips in the extrusion process.
Third, as the rubber moves through the conveyor system, the action of the screws heats the rubber. Consequently, the rubber will be ready for extrusion. At the same time, the screw’s action subjects the rubber material to pressure.
Finally, the screws will force pliable rubber material through a die. The rubber material exits the die (tooling systems). It will conform to the shape of the die system.
The extruded rubber parts will leave the die system. You will vulcanize rubber making it harden. You can shorten the rubber vulcanization timeframe using activators and accelerators.
Again, before rubber vulcanization starts, you may maintain the temperature between 140°C and 160°C.
Your extruded rubber product will be ready for secondary operations and quality inspection. Depending on the specific features you may want the rubber parts to have, you can:
- Cut to size
- Coat, etc.
Although the processes may vary slightly, generally, this is how to make rubber extrusions.
How Plastic Extrusion Compares to Rubber Extrusions
Ideally, the extruding two materials are virtually the same. What differs mainly is the applications and property specifications.
Take a look:
|Rubber Extrusions||Plastic Extrusions|
|· Tear-resistant applications
· Applications requiring a significant amount of compression
· Recycling may be a challenge
· Rubbers such as silicone are high-temperature resistant
· Not stiff
|· May not withstand the high magnitude of tear
· Highly compressive forces may cause deformation
· Easy to recycle
· Tends to melt under high temperature
· Offer a reasonably good degree of stiffness
However, there are instances where you can extrude both rubber and plastics. Through co-extrusion you can easily make parts with both rubber and plastics.
Such components have unique properties such as soft and rigid.
Remember, co-extrusion is a sensitive process that requires engineers to consider many variables such as:
- Temperature for co-extrusion process
- Production cost
Applications of Extrusion in Rubber Parts Production
Extruded rubber products are available in many configurations. Common applications are:
|Applications||Examples of Extruded Rubber|
|Extruded rubber profiles||· These include pipes, tubes, rods, hoses, etc.
· Profile can be square, rectangle, or round
· Many shapes available include L, T, J, U, or custom options
|Rubber trims||· Rubber trims are installed on removable covers, windows, etc.
· They offer better protection for edges and surfaces
|Rubber seals and gaskets||· Extrusion is a perfect alternative for making rubber and sealing gaskets. Other processes for making rubber gaskets are injection molding and die cutting.
· Examples of rubber gaskets are the O-rings
|Rubber bumpers||· These bumpers are popular for abrasion resistance and shockproof properties|
|Rubber bushing||· Are perfect shock absorbers and prevent unnecessary vibrations – good examples are automobile suspension systems|
Ideally, you can use rubber materials in many applications such as:
- Piping sealing systems
- Automotive part assembly
- Vibration reducer applications
- Window and door sealing systems
- Pressure systems
- Storage systems
In short, from aerospace, food processing, chemical petroleum, to agricultural industries, rubber parts play an integral role.