[garylb]

Hi,
I have just come back to work after a few days off and found rust on the table of my mill where the coolant has dropped onto it. This obviously means that the concentration is too weak. I always mix the coolant to 5% and it doesnt take long before the coolant is like water and causes rust on the machine. How is the concentration getting weaker? i would have thought that the water would evaporate causing the concentration to increase. Does anyone have any advice? It doesnt seem right that i have to keep adding neat coolant oil to increase the concentration all the time

[txcncman]

Does your coolant advertise it contains rust-inhibitors? Mixing coolant at 5% does not mean it stays stable at 5%. Use a refractometer to actually test your coolant that is in use.

[garylb]

it states that it has good anti-corrosion properties and should be a concentration of 5%. I do use a refractometer and when i do a coolant change i wash the sump before adding the coolant but within maybe a couple of months the coolant seems to have diluted

[txcncman]

I do not know your shop operation. Shops I work in have multiple operators/machinists. Anyone can go top off a coolant tank with straight water because they are too lazy to mix coolant.

[txcncman]

What concentration it is measuring now is what is important. Not at what concentration you mixed previously.

[garylb]

i am the only machinist so i know that the machines arent getting topped up with water. I wonder whether its due to the machines not being used everyday and this is causing the problem somehow?

[txcncman]

I have seen some coolants "separate out" after sitting unused for a period of time.

[garylb]

on my lathe it was 2% and i only replaced the coolant about 6 months ago id say. As for the lathe it doesnt even read as it is bascially dirty water

[garylb]

I have seen some coolants "separate out" after sitting unused for a period of time.

this is what i was thinking. Does this mean i should just add neat oil or will this cause even more problems with the coolant? will it make it unstable?

[txcncman]

As good maintenance habits, machines should be cycled frequently, even if not being currently used, to keep parts lubricated and coolant circulated.

[txcncman]

I would not purposely add oil to coolant. It is certainly acceptable to wipe exposed steel with oil.

[garylb]

but if i dont add neat coolant oil to get the concentration back up to 5% i will have to change the coolant every 2 months which isnt very cost effective. I think the answer is to run the coolant pump everyday to keep it moving. The top of the coolant in the sump is covered in a brown skim so im sure this is the cause

[txcncman]

Final comment on coolant. The brown skim is way oil and other contaminants. What will happen over time to coolant concentration depends on actual chemicals in the coolant and outside conditions present. My experience says that with heavy use, water is expelled from the mixture causing concentration of coolant to increase. Thus plain water must be added to maintain proper concentration. It might be possible with synthetic or semi-synthetic coolants and light use to have the coolant "flashing off" and leaving water behind, causing concentration to decrease. Synthetic and semi-synthetic coolants usually contain glycol, similar to alcohol.

Just cycle your coolant pump while adding a cup of raw coolant at a time and rechecking %.

[garylb]

Thanks for your help!

[ELM3060]

If it's a case of the coolant separating, can you set the coolant pump up so it cycles over, only put the nossle into a return hose, or could you add a small agitator to the tank. Connect it to a timer so it cycles over for 10min every second day.

[garylb]

If it's a case of the coolant separating, can you set the coolant pump up so it cycles over, only put the nossle into a return hose, or could you add a small agitator to the tank. Connect it to a timer so it cycles over for 10min every second day.

i was thinking of just turning the machine on and pressing the coolant on button and leaving it running for a while but the using an agitator sounds like a good idea. That way i dont have to turn the machine on

[txcncman]

@Gary - That would be acceptable. But it is also good to run the spindle through its speed range, and move the axis around too. Do whatever you have time to do to take care of your tools and they are more likely to be ready to take care of you.

[djr76]

You might have large amount of bacteria/fungi growing in your coolant also causing the rust issues. To combat that problem, keep oil skimmed off and I plumbed a 0-30 psi regulator (had on hand) into my existing air system with a flow control and ran a few lines into my reservoir with diffusers on the ends to keep the coolant oxygenated. You can get test strips that you dip in coolant and incubate a few days to see if you have excessive growth, then a sump side bactericide might be needed like Triadine.

[underthetire]

One of the biggest problems I see with coolant is how it's mixed. You have 2 choices, jet mix, or add coolant to the water. NEVER put concentrate in a bucket then fill with water. The biocides in the coolant react with water, without enough water on mixing, the coolant gets too "hot" and will not bind well with the water. The lead chemist from GC Chemical was the one that explained this too me, not my opinion.

[garylb]

One of the biggest problems I see with coolant is how it's mixed. You have 2 choices, jet mix, or add coolant to the water. NEVER put concentrate in a bucket then fill with water. The biocides in the coolant react with water, without enough water on mixing, the coolant gets too "hot" and will not bind well with the water. The lead chemist from GC Chemical was the one that explained this too me, not my opinion.

This is part of the reason where i have been going wrong i believe. I spoke to the manufacturer of the coolant who told me you should add the oil to the water whereas i had been adding the water to the oil. I had always done it this way and have always had the problem so i will now try it the other way round to see if it makes a difference