Hello and welcome to a new processing hack blog post, in particular on how to clean you injection mold in an optimal way.
Dry ice cleaning (Dry ice blasting) is an efficient, non-abrasive method for cleaning injection molding tools that allows for faster cleaning cycles and reduced production downtime. The process involves propelling solid carbon dioxide (CO2) pellets at a high speed toward the mold surface, which removes contaminants through a combination of kinetic energy, thermal shock, and gas expansion (sublimation).
Key Benefits
Minimal Downtime: Molds can be cleaned in-place (in-situ) and at their operating temperature, eliminating the need for cooling, disassembly, reassembly, and reheating. This can reduce cleaning times by up to 75% or more.
Non-Abrasive: Dry ice is a soft medium that sublimates into a gas upon impact, so it does not damage or erode delicate mold surfaces, intricate details, or critical tolerances (Class A-D finishes). This helps prolong the lifespan of valuable tooling.
No Secondary Waste: Because the dry ice turns directly into CO2 gas, there is no water, chemicals, or blasting media residue left behind. The only cleanup required is the removed contaminant itself, which can often be simply swept or vacuumed away.
Improved Product Quality: Cleaning molds more frequently and effectively ensures consistent venting and cavity shape, which helps prevent defects like flash, short shots, and splay, leading to lower scrap rates and higher part quality.
Environmentally Friendly and Safe: The process reduces or eliminates the need for harsh chemical solvents, improving workplace safety and environmental compliance. The CO2 used is often a reclaimed byproduct from other industrial processes.
Cleans Complex Geometries: The process can reach into hard-to-access areas, crevices, and fine vents that are difficult to clean with manual methods or other media.
Apart from dry ice cleaning, there are three more cleaning technologies which can be utilized. I have listed them in Table 1.
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| Table 1: Comparison of injection tool cleaning technologies. |
How It Works
The cleaning action is based on three main principles:
- Kinetic Effect: High-velocity dry ice pellets physically impact and dislodge contaminants.
- Thermal Shock: The extreme cold temperature of the dry ice (-78.5°C or -109.3°F) causes the surface residue to shrink and become brittle, breaking its bond with the warmer mold substrate.
- Gas Expansion: Upon impact, the dry ice pellets instantly sublimate (turn into gas). This rapid expansion of CO2 volume creates microscopic "mini-explosions" that lift and carry the dirt particles away from the surface.
Implementation
Manufacturers can either invest in their own portable dry ice blasting equipment (machines and a supply of dry ice and compressed air are needed) or utilize third-party contract cleaning services. Leading equipment manufacturers like Cold Jet offer a range of machines and accessories tailored for delicate to more aggressive cleaning applications.
Example Cleaning Methods for PPS-GF / PPS-GF+MD Mold Deposits
Cleaning mold deposits from a Polyphenylene Sulfide (PPS) reinforced with glass fiber (GF) and mineral (MD) and/or impact modification often involves a combination of chemical and physical methods. The high service temperature and chemical resistance of PPS require specific cleaning considerations.
- Chemical Cleaners (During Production): Specific solvent-based, fast-evaporating mold cleaners are effective for use while the mold is still in the injection machine.
- Apply the cleaner to the top of the open mold and let gravity help the product flow down, flushing away contaminants. These cleaners work by dissolving greases, oils, and gas deposits, which are common byproducts of the molding process.
- Products like Slide Resin Remover are used during production to "mold off" stubborn deposits in subsequent cycles.
- Physical Assistance: Chemical cleaning is often best when combined with a physical cleaning action.
- For light deposits, a clean, lint-free shop rag can be used for wiping.
- For strongly attached or heavy deposits, use a soft, non-damaging tool like a bamboo, copper, or brass spatula or brush to avoid scratching the mold surface. Metal abrasives can also be used with caution.
- Offline Cleaning (Tool Room): When the mold is removed for thorough cleaning, stronger, fast-evaporating cleaners (often hydrocarbons and naphthas) may be used to dissolve resins and greases. These can be followed by a mold polish/cleaning compound with mild abrasives for a final sheen.
- Advanced Method (Dry Ice Blasting): As explained above, dry ice blasting is a highly effective method that can remove deposits without disassembling the mold from the machine. It works by freezing and air-blasting the contamination off the surface.
- Frequency: Clean frequently. Small amounts of deposits are easy to wipe away; once they accumulate, they can become corrosive and require more aggressive measures.
- Post-Cleaning Protection: Because PPS outgassing can be acidic, always follow cleaning with a rust preventive if the mold will be idle for more than a few hours.
- Solvent Selection: Ensure the cleaner is compatible with your mold temperature. High-evaporation solvents (like hydrocarbons) are best for offline cleaning, while slow-evaporating ones provide better "soak time" for thick deposits.
Thanks for reading & #findoutaboutplastics
Greetings,
Herwig
Literature:
[1] https://blog.coldjet.com/dry-ice-blasting-vs.-alternative-cleaning-methods
[2] https://www.findoutaboutplastics.com/2016/12/optimizing-your-injection-moulding.html
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