rust preventitive needed..

Dear Tim:

99.999% Au should do it.

Seriously, avoid inclusions, eliminate as much carbon as possible, add molybdenum. Then watch carefully the chemistry you expose the waterjacket to during use.

David A. Smith

Waterglass would be helpful, but then again, waterglass is a constituent of most anti-freezes.

If the heat tranfer requirement is not overwhelming, filling the water jacket with oil would pretty much stop rusting....

Brian W

waterjacket

I doubt you want to cast a new part from selfmade metal. There are commercial products to add to the water to prevent rusting (google for details, I don't know a specific product). They are basic and contain suitable inhibitors. Otherwise you could try to etch the water jacket perfect clean and apply electroless nickel.

was poking around on google and found several "rust converter" products. Might give them a try.

Should have mentioned before that the system will run clean water (no additives allowed)... and of course the fix needs to be inexpensive. The customer is asking for a painted interior cavity, but all the paint folks say it won't work well. They all recommend filling the cavity with 2 part epoxy and draining it out leaving behind a good coating. Does not sound fun with 130 50# class 30 cast iron parts.

Dear Tim:

There was a method used in cast magnesium parts, in which the part was vacuumed out, then exposed to an epoxy, which would then be "drawn in" to all the pores in the metal. Might be a real pain on something as complex as an engine block.

Next, you could use a sacrificial zinc anode somewhere in the water flow path. The water won't stay "clean", but the cast iron won't develop much more than a nice patina.

Finally, shoot the S.O.B. that is requiring this be done.

David A. Smith

When I was in sales I had a saying, "The customer is always right even if he is full of s***." The trouble with giving the customer what he asks for is it is usually wrong and you are expected to make it right. If he wants the inside painted, have him tell you what kind of paint, the method of application and put it in writing in his specifications. That lets you off the hook when fails. If the customer wants it done correctly, then he must pay for the correct solution.

Now that I have gotten off the soap box maybe I can make a suggestion. One thing that you have not mentioned is temperature of operation. Is this for a gasoline engine? For this suggestion I am assuming (bad word) you have cooling water that is about 120-150 degrees F running through the piping.

Look up asphalt roof coating ( bituminous NOT plastic) types I, II, III & IV as used in home/building construction. These types refer to the softening temperature of the asphalt roof coating. Type I is 135-150 degrees F - too soft for your application, but the other types increase to above that range. Type IV is 205 to 225 degrees F. You can mask the areas not wanted to be coated and pour the asphalt coating into your cast iron fittings. Also, look up asphalt mastics and grouts. See ASTM standards: D450, D312 & D491. The bituminous has better bonding strength than the plastic for most applications. Test it if you decide to use it before committing the entire set of components.

what do you need this medium to do? Is this coating for storage or for operation? Is it moving fluid and what kind?

1) any coatings you put on the inside will likely insulate, they will likely be eroded by moving.fluid, and they will be corroded by water or contaminants in the fluid 2) do you have any control over the medium? use of a fluid that does not attack is the preferred option - de-ionized water comes to mind, as does food rated poly glycol, or automotive anti-freeze 3) you could use a food rated cold zinc like carballoy applied as a flush, but it will need to be renewed at frequencies dependent on the medium, geometry, and the flow rate 4) you can flush it with hot "cosmoline" or the like if it is for storage

straight water and heat will create rust, and moving water will remove coatings

- so usually one addresses the fluid rather than try to coat the cast iron.

Forget de-ionized water. I worked in a lab that used de-ionized water. It is expensive to maintain. The stored DI water had to cycle through the de-ionizers continuously to maintain the quality - greater than one megohm resistance.

To solve this problem we need more information of what is available, as I said above, such as operating temperature and the environment in general. With what has been presented we are guessing. That is not how one solves engineering problems. Tim get more information to us if you want reasonable answers to your question.

Jim Y

Since you have not given us much to go on, here is another suggestion. Because you are using this piping for cooling, you want the fluid to be in contact with the pipe as much as possible to remove the heat it picks up. Water, pure or otherwise, on the molecular level attacks anything it comes in contact with because the hydrogen atoms are on one (?) side of the oxygen molecule. For most cases that matter is ignored, but under the proper environment can affect the system over time. Heat and water with an iron based metal will form rust (Iron Oxide). One solution that my employer company used to get around those problems was to use Stainless Steel piping. To my knowledge, 304 and 316 Stainless Steel (CRES) seamless pipe comes in 1/4" through 4" nominal pipe size. Fittings are available. Pressure of the system will determine the type of connection - screwed, welded or flange. Welded and flange connections are easier to maintain in the long run. Threaded fittings are not reliable over 50 PSI in my experience.

When you consider cast iron, remember castings are not 100% solid metal. In the manufacture of castings, voids are created in cast metal during cooling of the casting that can propagate and leak in time. (I have had that happen in a bath tub faucet on a new fixture.) Castings do leak when used with pressurized water systems. Not many foundries X-ray their products.

Weigh the cost of maintenance costs in this project. CRES piping may have a higher initial cost, but the lost time for repairs to iron based material may be many times higher over the life of the system. We put in a cooling system for a rolling mill that the customer insisted the use of carbon steel (they rolled carbon steel). Within a year they had to replace a significant portion of the equipment due to the effect from heat and water. That meant they lost time in production in addition to the repair cost. Had they used CRES as I recommended, they would not have had the rust deterioration of the system. I think the cost of that first replacement would have justified the initial use of CRES.

Jim Y

By the way, the CRES pipe fittings are forged steel and not cast.

Jim Y

Because you are using this

as possible to remove

attacks anything it comes in

molecule. For most cases

over time. Heat and

my employer company

knowledge, 304 and 316

size. Fittings are

screwed, welded or

Threaded fittings

the manufacture of

can propagate and leak

Castings do leak when used

higher initial cost,

over the life of the

insisted the use of carbon

significant portion of the

production in

not have had the rust

have justified the

thanks to all.. yes the customer is being a bit obstinate about this.

The machine in question is actually a vacuum booster and the cavity is in the endplate that supports the bearings and closes the rotor chamber. The hot side will see 300-350 degrees F and the cooling water is about 70 degrees with very low flow (2 gpm or so). Since the unit (not the water jacket) operates under a high vacuum, heat load is low. The customer makes a companion product to this which is also water cooled. They put a shellac coating in their cavity and insist it works (I have seen warranty machines which have rusty waterjackets, but it is no use to argue). We are stuck with using water (not sure if DI or not) from an in plant circulation loop. It has no additives.

I think I'll look at phosphate dips this week. Should be inexpensive and work as well as the shellac.

Dear Tim:

Nothing will work for long. Sounds like you've got phase change to contend with also. If so, this will take out any coating anyway. You might suggest titanium...

David A. Smith

Given the new information, there is perhaps a better way - but first -

my rules of thumb - 1) when the problem takes more than ten minutes, go back to the basics -

- 2) identifying the problem is 90% of solving it

so since this one has only a few basics, we need to identify the problem - which is - protect the jacket -

you don't really want a coating, you want to protect the jacket -

and from what? protect it from "rust"

That means that if you can keep the molecule exchange at the minimum, the jacket damage is minimized.

So that in turn means if you remove the co2 contact or keep the surface potential below minimum required for exchange, the jacket damage is minimized

Thus, rather than try to block exchange and co2 access by adding a barrier that relies on thickness and insulating value to protect, I would design the jacket so I could have an external physical point to use as a drain for any charge on the jacket, thus keeping the jacket potential below the mv needed for rust. And so, being cheap, I would tap a blind hole in the casting exterior and screw in a pointed zinc rod, oriented into the air and at least a fourth of the jacket diameter beyond the jacket, to be a drain. And if I could, I might put a magnesium rod/web screwed into the jacket inside in the water path to help lower that potential and electrically connect the water to the zinc rod.

no mv diff, no transfer - no transfer, no rust.

FWIW:

The various 'rust converter' coatings do work, but there's a limitation; you have to let the surface rust first. Then, you apply the goop, let it dry, and use it or paint it. The stuff does not bond well to bright bare metal, i.e., new castings.

DI water is one of the most corrosive substances on Earth, because it contains no natural chemical buffers that would limit random pH excursions. At least demand tap water, or go into the 'special cooling jacket water' business. ;-)

-Mike-