Heat Treaters Put Platers On Hot Seat
Platers hate heat treaters. Yes it's true. Nothing personal and I'm sure you're all wonderful people but... What you do, or don't do, or don't tell me you do to the customer's parts drives me crazy.
It may seem to be inconsequential to you that a heat treating operation is done prior to sending parts to the platers. I mean after all, it's on the print, the material call outs are there and as a plater you have all kinds of cleaners, acids and activators at your disposal so quit your moaning and plate the parts. It's that simple. Isn't it?
It's a Mystery
Well maybe and maybe not. Sometimes yes and sometimes no. For some parts and materials this is always true and for others it's sometimes true and in a few cases it's never true. Why is that? Let me try to explain the mystery wrapped in a riddle inside an enigma.
Heat treating prior to plating gives a plater a lot to think about. Starting with the obvious, heat scales that form on the surface need to be removed and done so carefully so that the base material isn't harmed. If you heat treated a steel part and there was heavy black scale all over the part we could throw it in some 50% nitric and remove the scale lickety split. And when the smoky and noxious orange cloud cleared we'd see that the scale was completely gone along with 2-3 mils of base material. So the scale is gone but, we ruined the part as well. The plater needs to make a careful choice removing these baked on oxides in such a way that the scale comes off without taking too much of the base material with it. Copper and copper alloys use different cycles to remove scale, steel and stainless steel need different cycles. A plater needs a full palette of acids and alkaline cleaners to remove this visible scale. And we haven't even discussed how you properly prepare a part before you put it into some aggressive acidic or alkaline descaler.
What about scales we can't see? I have seen parts come back from heat treating looking clean as a whistle. Perfect right? Sometimes yes. Sometimes no.
And I Need Them Tomorrow!
I'm not sure how it happens but occasionally we have had parts show up (due in 24 hours or less by the way... Platers are the last stop remember) looking bright and shiny and appear to be easy to clean. When they come clean quickly and easily and pass a water break test life is good. But quite often the clean look is a disguise. There is something in the way. Whatever it is keeping that surface nice and shiny is also keeping our process chemistry from getting to the surface. Seemingly wrapped in an invisible coating that is impenetrable, every tank in the shop gets used with limited success and the surface water breaks like my Tesla at the car wash (if in fact I had a Tesla…).
Water break is what happens when water beads up on the surface rather than laying down in a sheet. When you drive your Tesla out of the car wash and the beads of water are all over the hood rolling around that's a good thing. When the part your trying to nickel plate does it it's a disaster. Water break means there is something between us and the surface and we need to get that off to successfully plate the part. Whether it's material related, due to something in the heat treat process, that the parts were done in an atmosphere that created something like an oxide on the surface but not an oxide... Honestly I'd rather have a part that was thick with black scale than this invisible condition. At least that I can see if/when I removed it. This is particular true with copper and copper alloys.
Some other events that cause platers to curse heat treaters? Baked on coolant and other organic material. Now I need to carefully balance an alkaline cleaner often with electrical current and the acids that will activate the base material and remove oxides. Acid won't necessarily remove baked on organics. Heat treated in stresses that can cause blistering in plating? Don't believe me? Look at the old QQ-P-416 Cadmium plating specification. I like this specification as it has a lot of info in it around heat treating, machined and heat treated in stresses, abrasive blasting to remove scale, pickling in acid, pickling in acid NOT being allowed, electrolytic scale removal with direct current and with reverse current. Take a look at paragraphs 3.1-3.2.3. Yes it's an old specification but it's dealing with an ageless problem.
My other favorite heat treating rants put less blame on the heat treater and more blame on the customer/machine shop sending dirty, oily parts to the heat treater. The baked on coolants and lubricants may have been easily removed prior to sending to the heat treater. A cleaner part may be easier to clean and activate prior to plating.
Chemistry Is NOT Selective!
Here's another of my all time favorite recipes for disaster... Send a part to heat treat and return to the machine shop with heavy scale. The part is then re-machined so that a critical surface is beautiful, smooth and shiny. Then send it to the plater. Now I have heavy black scale on 80% of a part and 20% of the part is perfect and do not, under any circumstances do anything to etch, attack, or dull down that surface. So magically I have to submerge the entire part in solutions designed to etch, attack and dull metals except for that surface that I can't etch, attack or dull down. Really? Next time you are boiling water think about sticking your hand in it but... Do not burn your middle finger. You can't. Chemistry is not selective. The whole part goes in and the scale free, critical surface is going to get attacked. You have complicated my process tremendously and in a completely avoidable way.
Switching heat treaters in the middle of machining an order may present a challenge as well. One heat treater cleans/preps/does parts in an vacuum routinely. Suddenly in the middle of a job a part we have been successfully plating for a week comes in and looks and acts completely different because heat treater #2 doesn't clean/prep/processes in a vacuum. This change may not be visible and suddenly I'm yelling at my operator for forgetting how to plate and having the lab spend hours analyzing the tanks and dumping acids because what worked so well up to now isn't working at all. I'm sure switching heat treaters in the middle of an order was done for the right reason but... Could you have told me?
These last 2 scenarios bring me around to the 3 most important things in business... Communication. Communication. And Communication. A lot the negative things we're talking about are avoidable if the machine shop, the heat treater and the plater all talk.
If changes are made, make a phone call. Have a big important new job that has to go to heat treat then plate? Lets talk first. Unusual condition or material or heat treat callout? Ask your plater or send in a sample so they can do some testing on something that's not worth $1000 and you desperately needed to ship on Friday. In fact you may be paying extra for something, heat treating in an atmosphere to minimize oxidation for instance, you think may help the plater when in fact I don't need or want that. Maybe I'd rather have the visible oxide I know when it's been removed rather than the invisible one that I can't see when removed or get to pass water break.
So in the end, the heat treater and the plater do not need to have a hate/hate relationship. The machine shop does not need to suffer. The parts do not need to be destroyed and... There's money to be made. The game of blaming the other guy or covering your butt or taking 100 extra costly steps can end and end well. A little communication, cooperation and preparation will go a long way to allowing cooler heads to prevail.