Mixing Tank

Mixing Tank

So you need a stainless steel mixing tank? Wonderful! But where do you start?

Well, first you’ll probably want to know that you have two basic options as far as material goes. You can get a tank made out of 304 stainless steel or 316 stainless steel. The first thing everyone wants to know about is price. 316 is generally 5-10% more expensive than 304. The question is whether or not you should invest that extra 5-10%.

If you’re mixing anything that is corrosive, you’ll want 316.

316 stainless steel has 2% of a material called “molybdenum.” When something corrodes it is slowly destroyed by chemical reaction. Most people will tell you that you need 316 for uses that involve salt water or other briny solutions because 316 resists the oxidization of iron that creates rust. However, 316 also resists the corrosion that happens when mixing sulfuric acids, chlorides, bromides, and iodides.

 

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The molybdenum in 316 helps resists corrosion since it increases the lattice strain of stainless steel (having a greater lattice strain means that it requires more energy to damage the steel chemically). Source: chemistryexplained.com

The bottom line is this: if you are using any chemicals that can corrode steel or mixing at a temperature higher than 212 degrees Ferenheit, you’ll probably want to invest in 316 stainless steel. If not, 304 is the way to go.

Once you have you material selected, you can start thinking about how you’d like to have access to your tank. Do you need an open top? Do you need a foldable lid? Does the tank need to be sealed for pressure purposes? Only you can answer these questions because it depends how you’d like to use your tank.

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Tank lids
From left to right: open tank, two piece lid, welded top.

Next you should consider what kind of tank head you want. A tank head is the engineer’s way of saying “the bottom of the tank” (this is highly ironic to me since a tank “head” is at the “bottom” of the tank). Most tank heads are angled in order to help with draining the product out of the tank once the process is finished. Tanks heads can be flat, conical bottoms, dished or sloped.

 

From left to right: cone, domed, sloped, flat.
 
From left to right: cone, domed, sloped, flat.

Flat-bottomed tanks are the easiest to make and are therefore the cheapest. Most people don’t need or want flat-bottomed tanks unless the tanks are huge (we’re talking 20,000 gallons huge). When tanks get that big, you usually set them on the ground and you’re not draining them from the bottom. When that’s the case, it doesn’t make economical sense to put money into getting an angled dish head.

Sloped bottom tanks are little more expensive because of the work it takes to cut and weld the tank in order to attach the head. Sloped heads make accessing the bottom of the tank easier, which is important if your drain is on the bottom of the tank.

Conical tank heads are more expensive than sloped tanks, again, because of the labor that it takes to shape the steel. Conical tanks are useful when you need to make sure you drain your mixture well before you start the next batch.

Finally, you have dished tank heads. These are the most expensive and most difficult to make. These tanks drain well and their shape is the most conducive for mixing since the rounded nature of the dished tank creates a better flow than a cone tank. However, the improvement in mixing is negligible unless the mixing is highly refined.

Next you should consider baffles. Baffles are simply pieces of metal that are inserted inside the tank the can break the flow of the tank in order to decrease the chances of vortexing (for more on vortexing you should check out our resource Mixer Basics – the Shaft).

 

This tanks has three baffles
This tanks has three baffles

Next, you should think about whether or not you need to heat or cool your tank. In order to heat or cool your mixture, we can weld stainless steel jackets around your tank that you can run heating or cooling elements through.

 

Left: a jacketed tank with dimples. Right: and open jacket.
Left: a jacketed tank with dimples. Right: and open jacket.

Finally, consider if there are any fittings on the tank that you might need. By fitting I mean manways, tri-clamps, NPT fittings, sprayballs, or flanges. If you need them to attached to your tank, just let us know and we can make it happen.

Now, you might be thinking, “But you never told me how big my tank should be.” And you’re right. Unfortunately you can’t simply ask “How much do you want to make?” and then we make the tank that big. There are power limits, intensity limits, and mechanical limits that have to be considered. Unfortunately these limits vary from project to project, and there is no one size fits all approach to getting the right sized tank. However, now that you know the basics of what you need, you can call our sales-engineers, tell them what you need your tank to have, and make them do all the sizing work. That’s the nice part about working with a company that loves doing custom tank design.

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tagged with stainless steel, Resources, mixing tank