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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
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