Page 29 - CFCM Sept-Oct-2020_Neat

Alloys like tin zinc provide enhanced corrosion protection
and lubricity. Zinc nickel provides up to 10 times the galvanic

protection on steel that zinc does while offering better
resistance to other chemicals such as fertilizers for agriculture

applications and chlorides for saltwater exposure.

the plating system set-up. were shipped in. There are two typical electrochemical battery.
Heat-treated parts present certain process flows in zinc plating: The finish has endured due to the
risks that must be accounted for and reliability of the process, the cost
require best practices to ensure the RACk SYSTEM effectiveness of the finish, and the avail-
integrity and safety of the part when Soak Cleaner – To remove soils, ability of the process. It endures despite
put into use. If a part is hardened and grease, oil, etc. ever growing regulatory pressures such
then machined, ground, cold formed Electro Cleaner – To loosen and as RoHS, REACH, ELV, and other laws
or cold straightened after being heat- remove oxides and scales and other and directives. In the 1980s, tightening
treated, that part should be stress tenacious contaminants. regulations and the need for better
relieved by baking prior to pretreatment Acid Activation – To finish corrosion protection and replacements
and plating. Media blasting such as glass removal of any oxides and metallic for toxic processes such as cadmium
bead and shot peening as well as thread contaminates and to activate the and hexchrome chromates let to a new
rolling impart a compressive stress on substrate for zinc. wave of research. This research led to
the part which actually improves the zinc Plate – Parts are plated to the invention of hexavalent chrome free
function of the part and therefore it thickness specified for the corrosion passivates and zinc alloy coatings that
would not require a stress relief bake resistance required. improved on the zinc electroplate while
prior to pretreatment. Chromate/Passivate – To add the providing environmentally friendly
Parts with scale may first require specified conversion coating to alternatives for many environmentally
descaling before processing to pro- provide the finish and corrosion unfriendly processes.
mote good plating adhesion and an resistance required. Alloys like tin zinc provide
aesthetically pleasing finished part. Seal (if required) – To further add to enhanced corrosion protection and
This may include welded fabrications, the corrosion resistance and if re- lubricity. Zinc nickel provides up to
heat-treated parts with heavy scale, hot quired to impart a specific coefficent 10 times the galvanic protection on
rolled steel, and thermal deburred or friction to modify torque tension steel that zinc does while offering bet-
parts. There are several options for properties of plated part. ter resistance to other chemicals such
descaling including alkaline descalers, as fertilizers for agriculture applications
acid descalers and pickles, and media bARREL SYSTEM and chlorides for saltwater exposure.
blasting or tumbling. (most common with fasteners) When done properly and with the
Acid pickling should not be done Soak Cleaner proper attention to alloy constituents
on heat-treated parts as this process Acid Activation and alloy condition, zinc electroplating
can impart a condition called hydro- Electro Cleaner is an easy choice for applications
gen embrittlement, which can render Weak Acid – To neutralize the throughout virtually every industry. As
the steel part very brittle due to the alkaline electrocleaner and keep a finisher, make sure you get all the
entrapment of hydrogen gas in the parts active for plating. information to properly pretreat, plate
steel. Unfortunately, this defect is zinc Plate and post treat the parts. As a manu-
typically not discovered until failure Chromate/Passivate facturer looking to get your parts
occurs after the part is put into use Seal (if required) plated, make sure you provide the
and under load. Media blasting is the finisher with all the information
preferred method for scale removal Throughout the world, zinc is one needed to provide a process that
on hardened steels. They are usually of the most widely used corrosion- utilizes best practice to yield the
the most costly methods as well. inhibiting coatings. It has been elec- desired quality zinc plating finish. n
Most parts do not require the pre- troplated onto parts since at least the
treatments described above and are start of the 19th century when electro Paul Fredericks is Founder and CEO,
typically processed through the plating galvanizing research was sparked by Aerospace Metals LLC. Jeff Logan is
President, Saporito Finishing.
line right out of the containers they Alessandro Volta’s invention of the
www.cfcm.ca CAnADIAn FInISHInG & COATInGS MAnuFACTuRInG 29