Hot Dip Galvanizing

The WIM Pre-Gal process is more than chemicals.

It is the combination of good control over the process tanks and chemicals that will remove the costly annoyances of poor control, poor cleaning, high acid use, spotty pickling, bad rinsing, high iron or sulfates in the flux, excessive spitting, popping, dross formation, the list goes on and on.

Hot Dip Galvanizing Tank

The basic principle of Hot Dip Galvanizing is to bring a clean metal surface in contact with clean molten zinc.

A Clean Metal Surface

The cleaner the surface the better the formation of the zinc coating over the steel. It is the careful control over the preparation steps that effect the efficiency of the cleaner, pickle, rinses, flux, kettle, and ultimately the quality of the galvanized product.

Testing

Preparation starts with a plan to test, adjust, and record all the chemicals used to clean, pickle, rinse, and flux in a timely basis. For some the testing is done at the beginning of each operating shift, others at intervals that historically show that a change has happened in concentration and requires a test and adjustment of chemicals.

Preparation Process

The preparation process includes an alkaline cleaner tank, and its rinse, the pickle tanks and their rinse tank, and the zinc ammonium chloride flux tank for “dry” galvanizing or a cover flux on the kettle for “wet” galvanizing.

Cleaner Tank

We recommend a good alkaline cleaner to remove oils and other contaminates that may be on the steel when it is brought in from the customer. Dry clean work with only mill scale or welding scale with no greasy or oils soils can be pickled directly.

Don’t try to make an acid pickle do what should have been done by the alkaline cleaner! It only contaminates the acid that much sooner reducing its productive life.

Cleaner Rinse

After cleaning the load should be rinsed thoroughly removing all loose soils and oils. The rinsed load is then well drained reducing the amount of residual alkaline solution into the acid pickle.

Pickle Tank

WIM® acid additives are designed to provide a cleaner, scale free pickled surface though the use of inhibitors, surfactants and special surface conditioning agents that reduce the rate of iron build-up while removing all the oxides.

  • Better pickling when the iron is high
  • Welding scale easily removed
  • Tank life can be increased
  • Maintain production at the lowest safe temperature
  • Cleaner surface yields a better coating

WIM® acid additives are combination additives of inhibitors, wetters, and surface conditioners that remove scale faster.

  • Scale is removed faster
  • The inhibitor is able to protect sooner
  • Wetters flush away loose scale and iron salts
  • Surface conditioners remove hard to pickle oxides
  • Iron drag out to other tanks is diminished

Our main concern when pickling is the iron salts that can carry through the preparation process. WIM® additives are specifically made to minimize this salt drag out even though the additives can pickle to a higher safe iron concentration before dumping or acid recovery. The superior wetting system used in a WIM® Acid Additive helps flush away these salts reducing iron drag out throughout the preparation steps.

Pickle Rinse

Years ago, it was common practice to see fresh water being added to the cleaner and pickle rinse tanks and a steady overflow at the other end to a sewer. The pH was constant and pickle residuals were washed away. Today that is not the case and Fe build-up in the pickle rinse contributes to Fe drag out to the pre-flux tank, ultimately to the kettle forming unnecessary dross.

WIM Inc. has special rinse additives that help knock down excess Fe from the steel as it is being rinsed. Less Fe is then introduced to the pre-flux, reducing the burden of the pre-flux to deal with this unwanted iron.

  • Fe builds at a slower rate in the pre-flux
  • Flux life is increased
  • Less downtime treating for sulfates and iron in the pre-flux
  • Better control over iron throughout the preparation steps

Zinc Ammonium Chloride Flux

WIM® Flux Additive can be added to either the Wet or Dry method of fluxing the steel.

WET: WIM® Flux Additive is added directly to the flux as it is spread over the kettle surface.

  • The kettle flux is more frothy
  • The kettle flux is more active
  • Is less “gummy” longer lasting
  • WIM® Flux Additive can be added to either the Wet or Dry method of fluxing the steel.

DRY: WIM® Flux Additive is added directly to the flux tank with each addition as it is made up or maintained.

  • The flux is run at the lowest safe Baume` for galvanizing
  • The flux forms a film of flux sealing the surface
  • Oxidation between the flux and kettle is reduced
  • Steel enters the kettle with less spitting & popping of molten zinc
  • Less iron is introduced into the kettle
  • Dross formation is lower

The WIM® Pre-Gal Process is a series of steps and specialty chemical additions that aid the galvanizer with a cleaner pickled surface, improved rinsing and special additives for the zinc ammonium chloride flux that better fluxes the steel for dipping.

  • Less iron is carried over to the kettle
  • Steel enters the kettle quietly with less spitting & popping
  • Molten zinc quickly and smoothly flows over the cleaner steel surface
  • The zinc/iron alloy is more ductile and adherent
  • The end product is often more cosmetically appealing to your customer
  • Dross formation is reduced

These WIM® additives make up the Pre-Gal Process

  • 1249 Alkaline soak cleaner
  • WIM® 2X acid additive *
  • WIM® accelerating acid additives
  • WIM® RNRB Rinse Additive
  • WIM® Flux Additive

Cleaner

1249 Alkaline cleaner is designed for job shop situations where a wide variety of soils and mill residuals are one the steel. It can run as low as 6oz/gallon and 140F. Cleaners of this type generally are most effective at higher temperatures. The 1249 is very effective @ 180F and 8 – 10 oz/gallon.

Acid Additives

WIM® 2X and WIM® 76 are combination inhibiting acid additives with added surface conditioners and wetters to quickly remove scale for faster efficient pickling. When combined with the WIM® accelerating additives tank life can be further extended, immersion times decreased or temperatures can be reduced.

When used with acid recovery units they are most effective in combating the inhibiting effect of iron in the pickle. The returning acid will pickle fast even with the returning iron at 3 – 4%.

WIM® 69 and the Naxid℠ Series are specialty acid additives that accelerate the rate of scale removal. Our companion PowerPoint® program ACCELERATORS outline these products in greater detail.

The additives are unique in that they rapidly work on the soluble oxides only and when these soluble oxides are removed the acceleration reaction stops and the inhibitors in WIM® 2X or similar WIM® additives take over protecting this now clean steel surface.

Rinse Additive

WIM® RNRB is a specialty additive to be added to the rinse tank and tie up residual Fe that is introduced from the pickling process. Originally developed for reducing flash rust after rinsing in a continuous strip line these additives have found a new home in reducing iron carryover when pickling for hot dip galvanizing.

Reducing the drag out into the flux these additives lengthen the life of the pre-flux and present a surface better prepared for the fluxing reaction.

WIM® Flux Additive

WIM® Flux Additive is a specially formulated combination of surfactants that lowers the surface tension of the flux while providing a tight flux film over the steel preventing excessive oxidation between the flux tank and the kettle. The superior wetting system allows the galvanizer to use the lowest safe range of flux in solution.

The flux dries faster and enters the kettle quieter with less danger to the worker from flying molten zinc.

The tight film reduces further the potential of unnecessary iron being brought into the kettle thus reducing dross formation over time.

WIM® Flux Additive is a specially formulated combination of surfactants.

The superior wetting system allows the galvanizer to use the lowest safe range of flux in solution.

The recommended addition rate of a zinc ammonium chloride pre-flux is generally 3 pounds per gallon. The standing inventory of flux represents a sizable amount of flux in solution. Adding the WIM® Flux Additive we recommend 2 to 2 ½ pounds per gallon. The dollar savings in flux can be substantial.

The flux dries faster and enters the kettle quieter with less danger to the worker from flying molten zinc.

Moisture in the flux and wet flux trapped due to the design of the article being dipped will splash molten zinc when entering the kettle. The WIM® Flux Additive forms a flux film that dries quickly so the steel entering the kettle is less able to spit or pop. At the same time the molten zinc flows evenly over the surface of the steel forming a good hot dip galvanize.

The tight film reduces further the potential of unnecessary iron being brought into the kettle thus reducing dross formation over time.

One pound of iron forms 15 pounds of zinc. Therefore, reduction in iron to the kettle is paramount. The WIM® Flux additive film is a tight film that prevents or retards oxidation between the pre-flux and the kettle. Dross, will be reduced in proportion to the reduction in iron being carried through to the kettle. We estimate 5 – 10% reductions using the WIM® Flux Additive along with the Pre-Gal Process are typical.

The basic principle of Hot Dip Galvanizing is to bring a clean metal surface in contact with clean molten zinc.

The WIM Pre-Gal Process is more than chemicals, it is the combination of good control over the process tanks and chemicals that will remove the costly annoyances of poor control…poor cleaning, high acid use, spotty pickling, bad rinsing, high iron or sulfates in the flux, excessive spitting, popping, dross formation, the list goes on and on. You would be surprised how much better you can make your end product. The next slide shows what that difference can be.