[inmoteng]

Hello All,

We have been having problems with corrosion and pitting of 7075 aluminum parts machined on our CNC's. There are black and white spots with corrosion immediately following machining which leads me to beleive it is a coolant issue? We have also experienced this with parts washed right after machining. Has anyone else run into this?

Thanks,
Ed

[fizzissist]

... Boy, do you have a coolant problem. Do they actually show corrosion on the machine or do they wait till they're off the machine and being cleaned?

Maybe you need to hang a zinc bar in the coolant tank.....

How are you cleaning the parts?? Could that be the problem??

[inmoteng]

We noticed it happening on the machine as well as after washing. The parts are washed in simple green and water and then air dried.

Thanks

[fizzissist]

??? Are you using Simple Green in the machine, which ends up in the sump?

[inmoteng]

We wash the parts in simple green after machining. We use THE CUTTER EXP from Spartan Chemical in our VMC's.

[fizzissist]

We wash the parts in simple green after machining. We use THE CUTTER EXP from Spartan Chemical in our VMC's.

That fluid is recommended 20:1 for aluminum... I don't see anything about it that would result in corrosion on the machine.... too weird.

I'd send a sample of the coolant to the factory for analysis.

This is presuming you're dilution is correct (between 10 and 20:1), the water you're using is no less than regular tap-quality (at a bare min!!), the tramp oil is oil, and the coolant hasn't been in the sump for 5 years....

[underthetire]

Id find a water softener store or ACE hardware and get some strips to check your water and see what the PH is. Could be your coolant doesn't work well with your particular water, ive never heard of it so IDK.

[Geof]

Simple green is an alkaline cleaner, pH9.5 according to the manufacturer. All aluminum alloys will tend to corrode faster in alkaline solution.

[mactec54]

inmoteng

Your cutting fluid has chorine in it, this is what's causing your problem with the 7xxx series Q10,Fortal alloys, get a chlorine free cutting fluid & your problem will go away
I changed 3 months ago for having the same problem I went to Uitracut 380R chorine free, this is a very common problem
with these alloys

[inmoteng]

Thank you all for the great feedback.

What would be a better alternative to simple green for washing the parts?

Have you been happy with the Uitracut 380R for all materials?

[txcncman]

Dawn dish detergent and water for wash and then plain water for rinse.

[mactec54]

inmoteng

Yes Uitracut 380R has been really good on steel ,aluminum & plastic very good on the machine & tooling as well, but only time will tell, I have been using it for 5 months

[inmoteng]

Has anyone had experience with Hocut 795-H? My guys don't really like to go with anything synthetic.

[mactec54]

inmoteng

The 380R is a semi-synthetic, there is a big difference

The Hocut check with the company I think you need 795-B if you want this one, some of these cutting fluids have been aproved by Boeing,for aluminum,It also applies to most aircraft manufactures that is why it has the B at the end

[Delw]

Also if your getting it(black stains) on your machine put a ground rod into the ground. i makes a huge difference when your using tap water with your coolant.