ok... first things first.....
The second heater ( PRODHEAT110 )is the more logical choice as they "regulate" the water to 110F. Of course... for 32 gallons, this may be taxing for just one element. I'd say that one will be good per 10 gallons otherwise you may not get that temperature up from a cold start. It may even be as low as 5 gallons per heater, I don't know the specs on this one to be quite honest with you. I would assume just for giggles on this one... that if you were going to be doing this on a constant basis, 3 heaters from a dead stop at room temperature would heat up a tank of the solution nicely.
With that said...... traditionally in an industrial situation, the iron phosphate is set up into a large washtank in stages. Temperature is "targeted" to be approximately 140F but there's always a loss of heat value when factoring in the ambient air temperatire, heat loss due to surrounding part and tank wall temperature, etc. The temp usually settles down to 120F.... so you won't be that far off base in your "tank" configuration. Usually the higher temperatures dissolve oils faster and create a quicker chemical reaction from phosphate to substrate which is why you have that "higher end curve" going. I personally see no difference between 160F for 30 seconds and 110F for 7 minutes. (much like the cure schedule on a powder if you pay attention!).
Next we have your question about how a phosphate leaves a finish. Well... chemically speaking, the "salts" or phosphates from your solution are attacking your substrate on a microscopic level. Oils are washed away and the pores of the metal are exposed. Therefore, leaving room for the structure of the phosphate to reside in. This is what is known as chemical oxidation. (use this example if it helps you.... put a piece of copper out on the ground. Nice and shiny, right? After years of rain, the water and natural "salts" or "minerals" in the air turn the copper green through oxidation. Phosphating is no different. Your metal is steel, your vehicle is the water, and your "salts and or minerals" are the phosphate. Same process, just that the time has been sped up due to heat and concentration of chemical reaction in a shorter time frame. Period). Anyways... when your part leaves it's phosphate wash, it is then rinsed to stop and neutralize the chemical reaction from happening. You do this simply by rinsing it with clean water. Then the part is dried. Either via an air-gun, or heating in a warm oven. NEVER wipe the water off or for that fact.... touch the phosphated steel with your bare hands. The reason is this : you have just applied a crystaline structure and washed the metal of any oils. When you touch it, the structure has been knocked down and the oils from your skin are left on the metal. Basically, you just reversed the process of which you just applied. Hang it from a hook and dry it properly. What you will be left with basically is a piece of steel that through the magic of phospating, looks for the most part blue. It's not unusual to see red,yellow,green,orange,etc.... but traditionally.... the colour left behind is a sort of bluish steel. All that happened here was the light bouncing off and refracting off of the surface of that crystaline structure. Different chemicals (or salts) will refract light differently. So don't be surprised when you see your part look sort of tye-dyed,lol. It's supposed to look that way. A pleasant (albeit brief) thing that just happend is this in a nutshell.... salts are minerals. Logic dictates that minerals turn to metals under the right conditions. So basically... you just degreased the part, filled the voids with chemically treated "metals" and not only primered the part, but "smoothed out" the conductive surface from applying a like minded "metal" evenly across the surface. Period. Of course... this leads us to your next question....
Does phosphate change the appearance of the metal in any way. Well... just to go over what I said. Basically, yes. You've "oxidized" your part chemically speaking. For steel, iron phosphate makes a "blue" because it is a ferrous (metallic) metal. Zinc Chromate (PRODALCHROME880) for aluminum will "yellow" in appearance. Can it be taken off after you've coated? sure it can! It's like any other oxidation. Just reverse the process. Wipe down with something acidic or base to release the bond from the structure and buff it to a shine. If you have areas where you have raised lettering on a valve cover, let's say? coat the entire thing and just take a flat sander and sand until you hit metal. Finish off with a high grit paper to get shine if you wish. You may be able to mask the part AFTER you phosphate or chromate, as the "detergent" will basically get underneath your masking and release the glue from the tape. Just be careful handling an already phosphated piece if you are going to do that,k?
I think I basically answer your questions,no? Just keep in mind... iron phosphate for steel,zinc chromate for aluminum. That's the general rule. Hope that helped and didn't make you more confused,lol.... Russ
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