Underbody Coating
Under body coating is a process which used in OEMs to deposit a coating on the BIW upon which the paint is applied. This done so that the paint sticks to the BIW for a longer period of time.This underbody coating is of two types:
1.Powder Coating 2.Electrode deposition Coating or ED coating
1. Powder Coating
This is a type of under-body coating in which powder type particles which are dry are flowing directly over the BIW and then they are deposited or cured under the application of heating.A spraying machine is spraying the powder directly over the BIW and then this BIW is undergone heating for 20 to 30 minutes in heaters for an approx temperature of 150-200`c. Due to this application of heating the powder gets struck to metal plates cause of static electricty.This method is both automatic,manual and semi-automatic depending on the industry and the product which is to be coated.Since theparticles in the powder coating are very small and dangerous there is high risk of exposure to humans thus to avoid the direct contact of the powders the person assigned with this work is fully coverd and a mask is provided to them so that they can not inhale the powders. Before applying the powder coating the metal surface undergoes a pretreatment process so that the metal surface is free from rusting this procee is called the 7 TANK PROCESS.In this process a sheet metal has to undergo from 7 different tanks to freem the metal from any disinfectant or impurities thses 7 tanks are:Degreasing Tank,Water Rinse Tank,Derusting Tank,Water Rinse Tank-2,Surface Condition Tank,Phoshpate Tank,Passivation Tank.
2.Electrode deposition Coating or ED coating
Electrode Deposition coating or ED coating is a method that uses electrical current todeposit the paint on any BIW.The rails takes the BIW into the coating at an angle which is decided by the weight of BIW and the type of BIW plant.The angle at which it rotates isthe angle at which ED droplets are let downHence the body inside the BIW ae rotated in such a way that the no droplets are found inside and the complete part of the body is E deposited.The better the ED coating is the better corrosion resistant car becomes.The car also undergoes a heatng process and there are many hole to let the solution out and the remaing is heated thus BIW gets dry.Depending on the polarity of the part and the paint particles,ED coating is divided into two types Cathode Electro-deposition or the Anode Elcetrode deposition.Next the car will be went to paint process where either manually or automatically the the car BIW will be undergone painting process,underbody sealent and then for the inspection area.
Cathode Electrode deposition:
In this process charged particles from the paint moved to cathode under electrical forces. The ed depositioning is done until resistance gets build up giving the required amount of coating and thickness.The voltage in the Ed is used to control the amount of paint deposited.Cathode coating are the high performing coating with excellent corrosion resistance.This car gets rotated 360 in the electrolyte depending on the weight and industry. There are hole provided in the BIW so that the solution goes out of the BIW and then its's heated on high temperature to make it dry. These coatings methods have a lot of advantages some of thema are:More uniform and thick coating,complete paint utilization,good coverage at sharp corners and interior surfaces,not much human health hazard etc.
