The extrusion head cleaning is a crucial operation in regular maintenance of these complicated tools. Intermediate cleaning of the machines shall be carried out when necessary e.g. in case of material/colour change or poor blend of the components etc. The previous molten polymer is simply pushed out from the system by a purging agent or compound without cooling the line.
In case there are hard-to-remove build-ups or burns the die head shall be disconnected and disassembled for the deeper cleaning and inspection of the parts.
Extrusion head deep cleaning
There are different reasons why an operator shall stop the production for the deep cleaning of the machine, for instance:
- Polymer burning and sticking to the die head flow surfaces. This primarily happens due to high shear stress, inadequate lubrication, and/or improper processing conditions. Factors like excessive temperature, insufficient heat transfer, and contamination can also contribute to these issues.
- Foreign objects and contaminants. Despite all precautions contaminants may enter the system and stick to the screws and die head’s surfaces e.g. from poorly filtrated recyclate, damaged filters, contaminants from the polymer silos, etc.
- Additives conflict. This may happen when changing from one raw material to another and types of the product. Sometimes, the additives conflict with each other forming clots of gel-like substances, often sticky. This will require to stop the machine for deep cleaning incl. the screws.
- Purging compound burning. When stopping and parking the machine for longer time, the operator introduces a compound into the system to protect the die head from corrosion. Compounds of poor quality can burn and stick to the walls when reheating the machine. As a result the machine shall be stopped for the immediate deep cleaning.
The purpose of the extrusion head cleaning is to remove polymer buildup from the flow areas and channels, polish the surfaces, inspect the condition of the die head, replace and lubricate bolts, make required repairs or schedule the refurbishment, if needed. In any case it shall be carried out, at least, once a year either manually or in pyrolysis oven.
Manual cleaning
Onsite the extrusion heads cleaning is often performed manually. For cleaning the polymer out the die shall be hot. It is either cleaned right after the stopping the machine or later when reheated again. Therefore, it is important to provide the personnel with proper heat-resistant protection and respective tools to avoid heat-related injuries and mechanical damages of the die surfaces especially flow surfaces.
The following tools and items could be useful for your cleaning procedures:
- An adequate lifting device (overhead cranes, die flipper or similar)
- A disassembly kit with all required tools like drills, wrenches, etc.
- A working surface strong enough to support the weight and temperature of the die parts e.g. an adequate rotating table, etc.
- A heating cabinet for keeping your die hot, a heat gun
- Cleaning supplies like are copper gauze, Coratex or other cleaning agent, brass scrapers of various sizes, brass brushes, die gap cleaners, abrasive pads, heat-resistant gloves for handling hot die components. All required items you can buy from FINTER’s store.
The manual cleaning of the die is time critical and -consuming. Once the parts of the die are separated, the polymer shall be removed as quickly as possible. Having everything ready and couple coworkers, equipped with the right tools, might be a good idea.
Thermal cleaning
Thermal cleaning, also known as pyrolysis, involves the use of the high-temperature ovens to remove organic contaminants like polymers, paints, and coatings from metal parts. This process decomposes the contaminants into smaller molecules, making them easier to remove in environmentally friendly manner.
This is how it works:
- Pyrolysis oven: Die head parts are placed inside the pyrolysis oven. Depending on the oven dimensions the die head can be cleaned assembled or disassembled into smaller parts. Then oven is heated to temperatures 300-600°C.
- Controlled Atmosphere: The oven is often operated in a controlled atmosphere, typically with low oxygen levels or in complete vacuum. This allows to clean parts without damaging them.
- Decomposition: The heat causes the organic contaminants (plastics, paints, etc.) to decompose into smaller molecules, leaving behind ash or a residue that can be easily removed.
- Afterburner: A post-combustion chamber (or so called ‘afterburner’) is used to burn off any remaining gases, ensuring environmentally responsible cleaning.
Pyrolysis is gentle on the tools, shortens the maintenance breaks and makes your processes more sustainable and efficient. The extrusion productions either invest into having own oven or outsource their cleaning services.