Page 21 - CFCM Nov-Dec-2020 Final_Neat

Left: CO2 snow blast cleaning device offers parts cleaning suitable for all industries.

THE PRETREATMENT PROCESS is designed to prepare a surface, ultimately leading to nonpolar (low-energy)
product’s surface for painting, plating or other types of in- surfaces. Activation, which refers to the modification of
dustrial finishing, and is probably one of the most important the component’s top molecular layer, can convert these
processes on the way to a finished product. If a plant is nonpolar (low-energy) surfaces into polar (high-energy)
applying paint or powder, it allows for the proper adhesion surfaces, making these activated surfaces more wettable
of the coating to the substrate and sets up the long-term for improved coating.
success and durability – or not – of that coating. The company offers components for flame silification,
The surface cleaning process removes unwanted layers plasma or flame treatment surface activation.
or particles from component surfaces. This can be done in a With flame treatment, plastic workpieces are flame-
variety of ways such as CO2 blasting, dust removal/ionization, treated with a gas burner prior to coating to improve the
water-based cleaning, or degreasing. surface tension, Venjakob says. Not a form of heat treatment,
flame treatment relies solely on the chemical effect of the
MECHAnICS gas flame.
Venjakob’s CO2 blasting machines can be used as a This breaks the molecular bonds in the surface of the
standalone solution or installed upstream into existing treated substrate so that oxygen and oxygen-containing
processes. The company recommends this process for groups can attach themselves to the broken chains. “In this
guaranteed residue-free cleaning of components and way, polar groups are generated in the originally nonpolar
thus flawless coating. material that enable the reliable adhesion of printing inks,
CO2 blasting can be done by snow blasting or using coatings, adhesives, and more,” Venjakob says. “The
dry ice on small 3D parts to large workpieces in large development of polar groups increases the surface energy
batches. of the treated substrate, which can also be measured.”
With snow blasting, a cold burner produces its own dry
ice from liquid CO2. The cleaning blast consists of a mixture CHEMISTRy
of CO2 snow particles, CO2 gas that’s not converted into PPG offers a line of pretreatment products such as multi-
particles and compressed air. metal safe cleaners, ambient temperature cleaners, iron,
Dry ice cleaning works in a way that’s comparable to zinc, and ambient temperature phosphates, as well as thin
abrasive blasting or hydroblasting. Solid CO2 pellets (solid film treatments that strengthen and protect metal substrates,
carbon dioxide, often referred to as “dry ice pellets”) are the company says.
used rather than water, sand or other abrasive materials. The PPG VERSABOND Pretreatment is a fast, kinetic-
Made from a mixture of compressed air and dry ice parti- efficient zinc-phosphate pretreatment system that improves
cles, the cleaning jet hits the surface to be cleaned at high corrosion resistance on mixed-metal substrates. PPG says
speed. It is suited for metal, plastics, glass, ceramic, and manufacturers realize the benefits of extended bath life,
building materials. reduced sludge and lower processing temperatures.
TTX offers all sorts of multi-stage pretreatment equip-
ment. Using spray, immersion or a combination of pre-
treatment methods, dirt, oils and contaminants are removed
from the product’s surface and phosphate or conversion
coatings are applied to help prevent corrosion and increase
paint adhesion, the company says.
Systems can be customized to suit any electrocoating,
powder coating, liquid spray-painting, cleaning, pretreat-
ment, or heat-treating operation.
Pretreatment systems are PLC-controlled, have automatic
startup and shut down programs and are designed with
computer-aided rinse ratios allowing reduced water usage
and in some cases, a zero discharge system, TTX says.
Once a workpiece is clean, it will likely undergo a sur-
face activation process.
Many materials don’t have the necessary surface tension
for further processing such as bonding and coating,
Venjakob says. Potential reasons include surface imper-
fections resulting from flaws or pores or possibly the
chemical composition of the substrate, which may result
in substance or processing aid diffusion on the component Operating principles of CO2 blasting technology.

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