When it comes to the important process of removing contaminants from molded plastic parts, there are a variety of different methods available. However, as society becomes more and more concerned with environmental protections and sustainable practices, it’s worth exploring those processes that do not make use of chemicals or abrasive materials. One such process utilizes dry ice, which can be used to remove contaminants from a variety of surfaces and substrates.
Plastics Decorating sat down with Steve Wilson, global business unit manager for Cold Jet, LLC, to discuss the dry ice cleaning process and the advantages it offers compared to other processes.
How does the dry ice cleaning process remove contaminants from molded plastic parts?
There are three principles involved in the process of cleaning with dry ice. The acronym I.C.E. helps to explain the process.
1. Impact – While dry ice particles have little hardness – around 1.5 to 2.0 on the Mohs Scale of Hardness – when accelerated, they create what is called the Kinetic Energy Effect. Kinetic energy is measured one-half mass times velocity squared. Both of these variables (mass/dry ice particle size and blast velocity) are controlled and adjustable by the user, depending on the nature and amount of contaminant, as well as the hardness of substrate being cleaned.
Dry ice particle sizes are selected via the machine controller and can vary from nearly snow (micro particles) up to 3.0 mm in diameter but generally do not exceed 1.0 mm in most surface preparation solutions. The velocity of the dry ice particles is created via the dry ice cleaning system’s nozzle and is controlled by an adjustable blast pressure chosen by the user. Stand-off distance and angle of impingement can also have an influence on kinetic energy and are controlled via the programmed robot path.
2. Cold – Dry ice is very cold: -109°F. Unique to dry ice cleaning, the cold particles cause the various contaminants to embrittle (shrink) and to lose their bond strength with the various substrates. Essentially, it’s the coefficient of expansion and contraction principle between the two different materials (substrate and contaminant).
3. Expansion – The last contribution to the cleaning process is another unique principle of dry ice cleaning. Upon impact the dry ice particles will sublimate, expanding volumetrically upwards of 700 times in size, as multiple micro explosions occur on the substrate. These micro explosions on the surface lift the contaminants from the substrate.
In summary, I.C.E.: Micro crack the contaminant with some impact, embrittle the contaminant with cold and blow it off with the expansion of the dry ice particles.
Is the dry ice method limited to certain applications?
The principles of the ice cleaning process itself remain constant. But the process is very adaptable, largely dependent upon the amount of kinetic energy that is needed to remove any given contaminant. That is where the process itself is adapted for certain applications. Contaminants can come in many forms, such as fingerprints, dust, mold release agents, etc. The dry ice cleaning process is adapted to each level of cleaning requirement needed and the nature of the substrate itself.
For example, contaminants, i.e. dust, have a very weak bond strength, while some substrates have a lower Rockwell hardness than others. In such an application, smaller dry ice particle sizes will be utilized at lower blast pressures. When contaminants are stubborn, the dry ice cleaning process can be adapted to meet those requirements, whereas other cleaning methods are not so easily adjusted. This is how the dry ice cleaning process can be best for a variety of applications.
What are the advantages of using dry ice over other process to remove contaminants?
The biggest advantage of using dry ice is the fact that it is dry. It eliminates aqueous and solvent-based methods and the associated costs that go along with those other methods – reclamation, scrap from incomplete parts drying, etc. The user no longer needs that large dryer, which consumes lots of plant footprint and energy to operate. The operating cost of a dry ice cleaning system is generally around 50% of traditional aqueous systems.
Another advantage of the process is the ability for the user to manufacture the dry ice just in time. This is especially useful for automated, turnkey systems. There is no need for bulk dry ice storage and manual loading into the system. Users simply have a local gas company install a liquid CO2 tank in their facility and produce their own CO2 as needed from that liquid.
Furthermore, CO2 has a lower surface tension than many aqueous fluids, so it can clean very small and complex geometries of various parts. When dry ice sublimates (“E”), it leaves no solvent residue behind. When working with a new part design, parts no longer require weep holes needed with aqueous cleaning methods.
Dry ice cleaning systems also easily integrate into existing paint lines, utilizing existing robotic systems. The automation and consistent delivery of dry ice particles provide a repeatable cleaning performance. Dry ice cleaning systems also are Industry 4.0 ready with Cold Jet CONNECT™ capability, to connect into existing plant monitoring systems and for remote predictive maintenance.
Finally, users of dry ice cleaning systems also can utilize their manufactured dry ice pellets to clean their JIG’s. With the use of a stand-alone blaster, dry ice pellets can be used to clean JIG’s on-line, on an as-needed basis. There is no need to maintain multiple sets of JIG’s and coordinate their removal and reinstallation from the paint line for off-site cleaning. Furthermore, there is no more need to deal with large amounts of paint build-up on the JIG that causes part handling issues.
Steve Wilson is the global business unit director-plastics, rubber and composites for Cold Jet, LLC. As a former plastics business owner, he has over 35 years of experience in injection and compression molding, extrusion, blow molding, thermoforming and rotational molding. He began his career at Milacron’s plastics machinery division, serving in manufacturing, product line management and a variety of sales/marketing roles. Wilson has written numerous white papers on dry ice solutions for various applications, many of which have been published in industry magazines. He is a member of SAE, the Rubber Division of ACS and currently serves as president for the Ohio Valley Section of the Society of Plastics Engineers. He holds a bachelor’s degree in business administration from Cedarville University and an MBA from Xavier University. For more information, visit www.coldjet.com.