coolant corrosion issues

[Gnome]

Hi all,
I was hoping for some advice regarding some coolant issues i've been having.

I have been using Shell Dromus B (http://www.shellusserver.com/products/pdf/DromusB.pdf) coolant for my milling machine and have been having issues with rust formation on my milling table and especially on Kurt Vices. If i leave the vice overnight s/u on the table, the vice will corrode the table surface and leave a black outline which can actually be felt with your nail. The vice will develop black markings on it where the jaws sit, even over the course of a days machining. My shop is not heated however there must be better products available. I have been decreased my mixture ratio from ~20:1 to ~10:1 with no success.

It should be noted that i have not changed out the coolant entirely in roughly 10 months and i don't have anything to check the exact coolant concentration. I am not sure if a contamination issue can cause this but i was hoping someone else would have some recommendations for way better corrosion resistant coolants.

95 percent of my machining is of aluminum.

Thanks for the input.

[Geof]

We use Dromus and on most of our machines run aluminum all the time. In our experience keeping the mixture more concentrated than the manufacturer's suggestions is needed to prevent corrosion.

The surface rust that occurs overnight does not occur if the coolant mix is above 15% and we often run at a slightly higher concentration, which also improves drilling and tapping when things are running fast. Your 20 : 1 and 10 : 1 is well below what we use.

The black corrosion is a different matter and we have found it to be variable. On some machines the vises stay in place for years and there is just a bit os staining when they are removed. On one machine within a few months the corrosion between the vise and table etched a ring in the table around a hole in the bottom of the vise. This is galvanic corrosion that you get between metals that are not identical and I have seen it on machines for years. It is possible that the stronger coolant mix has reduced the amount we see but that is difficult to say.

[Gnome]

Hi Geof,
Thanks for the reply. What would you recommend for concentration?
Do you have any other brands that you would recommend trying?

[Geof]

With Dromus go for between 10% and 15% I think.

The only other one we ever tried was Valcool and it reacted with rubber parts on one machine so we went back to Dromus.

If you do a search on CNCzone for Hangsterfer or Blaser you should find several threads/posts mentioning these. I have looked at Blaser but was not convinced the hassle of scrubbing out 18 machines to change to a different brand of coolant was worth it.

[Daleb]

We had this problem way back when we first started using water based oils on our CNC machines. When we called in the oil company (I can't remember who that was at the time) they said it was our water. We put filter on were we mix our oil & water and it has never happened again in 20 years.

[big_mak]

We use Novamet AL9000 I think is the number it's excellent for corrosion resistance we try and keep it around 8-10%. They are coming out with a line of coolant compatible Waylube as well so contamination isn't an issue.

[Grasshoppa]

I am testing Oemeta Novamet AL900 as well. Great stuff so far.

Other than that I use Houghton HoCut 795-B. So far, this is the best coolant I have ever used.