According to Cold Jet, when traditional cleaning methods detract from uptime and overall profits without achieving an optimal level of clean, the trend among foundry industry leaders is to explore dry ice cleaning as a cleaning alternative for core boxes and moulds.
The plants that have switched from abrasive blasting media or manually cleaning with wire brushes to dry ice blasting have experienced a cleaning system like no other.
What used to take several workers hours to clean now only takes one worker minutes and the cleaning standard is on a completely different level: as one user put it, the moulds look brand spankin new.
In an industry where time is money, a cleaning system that yields effective results quickly can offer $250,000 in annual productivity gains and is fast becoming the application of choice in the foundry industry.
The value of dry ice blasting in foundries:
This cleaning application is a non-abrasive, non-flammable and nonconductive cleaning method which means that in the foundry industry machines can be cleaned online while hot.
Actually, with dry ice blasting, cleaning while the machines are hot yields effective results because the of a thermal shock effect.
Since there is such a difference in temperature between the dry ice particles and the hot machine surface, the contaminant/refractory coating on the machine becomes immediately brittle when blasted, and the bond between it and the machine surface is broken.
The contaminant/coating is then easily removed. A pitfall in using traditional blast media like sand versus dry ice blasting is that the parts have to be removed to a tooling room to be blasted because the hot temperatures on the lines might cause sparking of the media. However, this is not a concern when cleaning with dry ice.
Dry ice blasting leaves no secondary waste like solvents or blast media. By eliminating secondary waste, workers are not vulnerable to slipping on the grit media, nor do they have to worry about eye injuries from the atmospheric contaminants or exposure to toxins.
Not to mention workers comment on the cooling effect they experience with dry ice blasting.
With dry ice blasting there is no secondary waste to clean up eliminating downtime and waste removal costs.
The actual cleaning with traditional methods is time consuming enough; having to clean up after cleaning just increases the downtime.
It does not damage electrical or mechanical parts. Since dry ice blasting is dry and non-abrasive, production machines can stay on while they are being cleaned.
There is no damage of shorting electrical components. In addition there is no risk of damaging parts, like vents. Because the vents are not damaged during the cleaning application, they do not need to be replaced, thus cutting down on time and costs associated with replacing them.
Removes refractory coatings and other contaminates without altering the integrity of the mould.
Since dry ice blasting just removes the contaminant, the mould or core box itself is not damaged. This means the equipment is restored to like-new conditions.
Since dry ice blasting yields a smooth as a feather result, the end product is consistently of high quality, eliminating scrap and the costs associated with it. Moulds cleaned with dry ice media not only produce a better quality product, they do it faster.
Dry ice blasting systems can be used for general and preventative maintenance. When not being applied to foundry specific equipment, dry ice can be used to clean power cabinets, splatter on walls, paint, etc. It also can be incorporated into a preventative maintenance plan.
When consistently used it has been proven to extend machine life, reduce part breakage and overall it makes sure that machines are reliable to keep up with demand.
How it works:
Instead of using abrasive blast media like sand or bead which can grind the urethane on moulds or damage vents on core boxes, dry ice blasting uses dry ice which is accelerated at supersonic speeds, creating mini explosions on the surface lifting just the contaminant, like a refractory coating, without damaging the core box or the mould itself.
As the dry ice particles hit the surface of the contaminant, it sublimates, or becomes a gas. Since the dry ice sublimates, little impact energy is transferred to the coating making it non-abrasive as well as effective.
In one instance, when dry ice blasting was applied to a mould, the mould was cleaned online when the temperature was 29°C.
It took one worker 10 minutes to clean the entire mould and temperature only dropped to 18°C and so the refractory coating could be immediately reapplied.
Within fifteen minutes of the coating reapplication, parts were being made.
When it comes to shell core moulds the dry ice blasting is so fast that moulds can be cleaned at 260°C without even having time to cool down, eliminating the need to reheat them.
Dry ice blasting is so efficient that cleaning time, and subsequently labour costs, can be reduced by up to 75%. Workers can be reallocated to other plant areas. And plant productivity can increase up to 50%.
One dry ice blasting user reported that by cleaning just five of their core boxes with this cutting edge application, they were saving $105,000 yearly from labour savings and productivity alone. This does not include the added savings from eliminated tool wear, waste removal costs, or vent replacements.
Another company reported no vent damage to date since implementing their dry ice blasting process.
Dry ice blasting systems:
Direct acceleration (single hose) system:
Dry ice pellets enter the air stream at the hopper rather than at the nozzle like they would for a 2-hose (Venturi) system. This allows for pellets to be accelerated the length of the hose, exiting the nozzle at more than 900 ft/sec.
This means dry ice blasting can offer high aggression but still non-abrasive cleaning. But if less aggressive cleaning is what is needed, a switch of a dial allows the operator to reduce the air pressure and ice feed rate thus reducing the pellet velocity.
Application-specific nozzles, just as the single hose offers control of blasting levels, so does the choice of nozzles. The nozzle selection can affect the blast aggression as well as the distribution of ice on the surface to be cleaned.
The longer the nozzle the stronger the blast aggression and subsequently the cleaning capabilities, and the wider the mouth of the nozzle means a greater distribution of dry ice particles meaning a wider area can be cleaned.
Fire safe sleeves are available. Since moulds are cleaned while hot and online, dry ice blasting systems offer the preventative option of having a fire safe sleeve for the hose. This eliminates whatever concern the operator had about the hose operating under the mould’s harsh temperatures. With this option shell core moulds can be cleaned while they are still 260°C.
Systems are small, light weight and portable. Dry ice blasting systems can be pushed by one worker right up to the mould that is to be cleaned which results in saving time and the extra labour costs of having to disassemble the mould and take it to the tool room to be cleaned.
Even though the machines are portable, they still need access to an air supply, offering 70-90 psi.
Low operating costs. For a single hose system dry ice costs $1.65/pkg and is consumed at a rate of 0.7kg/min. In comparison, glass media is estimated to cost $2pkg with a consumption rate of 2kg/min.
Environmentally safe/lean manufacturing:
Dry ice blasting is consistent with Toyota Production System (TPS)’s process management philosophy centered around reduction of process variation.
Dry ice blasting can be used as a tool to eliminate waste, improve quality and production time and the reduction of costs.
Cleaning with dry ice meets the ISO 14000 environmental standards by eliminating the negative effect that previous cleaning methods had on the environment, because dry ice/CO2 does not release harmful chemicals into the environment.
Also this cleaning method is nontoxic, meaning employees are not exposed to toxic chemicals or atmospheric contaminants from the blast media. This results in lowered liability for the company since the contaminants and toxins are eliminated.
Dry Ice FAQs:
How do I get it?
- There are local distributors who sell high density block and dry ice pellets.
How much does it cost?
- Approximately $1.65/pkg with contract
- Approximately $2pkg without a contract
How do I need to store it?
- Dry ice is not a stockable media. It is usually delivered in 200kg – 300kg insulated totes. Sealed it will last 5-7 days. Once opened the dry ice should be used in 3 days for the best blasting results
Are there any safety concerns?
- Dry ice should never be handled with bare hands since it is -79°C media
- Blasting in a well ventilated area since CO2 displaces oxygen
Using safety gloves and typical plant ventilation systems easily overcome these safety concerns