Mixing by weight?

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PostPosted: Sun May 12, 2024 9:07 am
So, my preferred method of mixing is by weight, but obviously the spec sheets give volume as the ratio.

Products are Shop Line JP37x epoxy and VP2050 high build.


Anyone have any data?

Other than just me weighing and measurin to establis ratios?g?



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PostPosted: Sun May 12, 2024 10:27 am
My trouble is that I've discovered I've been using too much hardener miging by weight.

I expected the graduations on my mixing cups wasn't accurate, so I thought the scale would be better. I was right and wrong.

20240512_111508.jpg


That's what I've got to work with. HF cup system and mixing cups from my supplier. Using water, I wanted to verify the graduations. When comparing the oz/ml marking to actual, the graduated cups had error, but where pretty consistent 5-10 grams. The Harbor Freight cup was worse. More error the fuller it got. Up to 10% off at 600ml.

So then I just used the 4:2 or 2:1 scales and checked again. These scales are easy to interpret on the mixing cups, but the HF system isn't very intuitive. Both of them seem closer to the right amounts, but I'd rather use the oz scales so I can get the most product in my cup each time.



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PostPosted: Sun May 12, 2024 11:12 am
To establish my specific gravities, I'm filling my container to the 200ml mark and taking actual gram measurements.

So, with water =1gm/ml, I have 189grams. That establishes the error in the graduations on my vessel. Basically 5.5%. Volumetric correction factor of 1.0582, I think

With product A, it weighs 257 grams and product B weighs 176 grams, at the 200ml mark.

I'm thinking that by applying that correction factor to the A and B weights, it will give me their corrected values. Which would be 272 and 186

So that would be the weights for a 1:1 mix. 2:1 would be 272 to 93 or 514 to 186


Make sense? Anyone double check my numbers?



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PostPosted: Sun May 12, 2024 11:21 am
Bonus question is "what was my actual mixing ratio?"

When mixing them 2:1, I was using too much hardener. Basically 514:257. But that's 71 grams too much.

38% too much, it seems. What's the ratio?

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PostPosted: Sun May 12, 2024 6:56 pm
If you want to check mix ratios accuracy,
use one of these, they are straight up and down
so very accurate to measure.

https://www.ebay.com/itm/263465562378?i ... R6rCzfPtYw
JC.

(It's not custom painting-it's custom sanding)



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PostPosted: Thu May 23, 2024 9:02 am
I just had a rather disappointing conversation with my paint supplier.

But, let me backup 1st...

Through a facebook group, I found a guy(body shop sales mgr) who sent me a Formula Recipe for my JP377, which showed the mixing amounts in grams. Just what I wanted. :worthy:


I followed up on that and asked him if he could get me the same information for 3 more products - sealer, base and clear. He said he would prefer that I contact my supplier. So I did.

The salesman there said he had never been asked the question I was asking - regarding mixing by weight. He and another tech called up the sheet for clear, which was what I had already, and said that 4:1 is the mix rate. Said same for volume or weight, which I know is not correct, but I didn't push it.

I mentioned that perhaps the body shops have different software than the suppliers and even referenced the sheet the 1st guy sent me. He didn't know anything about that.

So anyway I wonder if anyone here could get the formula recipe in grams for them? Shopline JP337 and JC630. The basecoat is JB. :neutral:


Thanks



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PostPosted: Thu May 23, 2024 11:55 am
the reason why the tech people said no one asked the question is because you don't mix products that way. the only thing you mix by weight is the color formula itself.
you have two real world options.
1st buy good quality mixing cups.
the 2nd is my preferred way. I use metal cans I take a can opener and cut the ring off that the lip is held on by. I then use the metal factory mixing sticks that have the ratios printed on the sticks. when I'm done with the can I wipe it out then put it in the gun washer clean it. I will use a can a few times then gets put in the trash. with the mixing stick I just keep it clean many of them I have for a few years then get new ones.



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PostPosted: Thu May 23, 2024 1:25 pm
I'm not sure about that...

Here's what I'm looking for.
Screenshot_20240523_141908_Samsung Notes.jpg



My understanding is that it's available here...

Jobshop software. Paint Manager XI
https://www.ppg.com/refinish/en-US/colo ... manager-xi


Screenshot_20240523_142302_DuckDuckGo.jpg



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PostPosted: Thu May 23, 2024 1:31 pm
Regarding your method...

For example?
Can you mix 50 ml of product accurately? And without waste?

When I see that formula is available as i posted, my question really seems quite simple. I can't believe it's uncommon.

Say a body shop needs to repaint 1 door. Software says they need "X" amount for the job. So you mix it. Exactly With the graduated cups and sticks, you're gonna have to choose a larger amount, probably. With extra left over.


I really don't mean to be argumentative, but my question is reasonable.


When the products are over $200/gallon I don't want to waste very much if I can help it.

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PostPosted: Fri May 24, 2024 9:51 am
Your question is reasonable, but you're over-thinking it.

I have an Axalta Cromax system and that gives me formulae for any product, in grams, for whatever quantity, in litres, that I want to mix. Easy because colours are always mixed by weight. But other products, like primers and clears are mixed by volume. Fortunately, in the Cromax system, all the TDS show both weights and volumes but some other Axalta products don't, as is the case with a lot of products from other manufacturers.

So, if I don't have the weights I have two options. Firstly to mix by volume in a graduated cup or to mix in a non-graduated container (like a straight sided tin or plastic bottle) using a measuring stick, or a simple steel ruler. Or, secondly to measure out a given quantity, say 100ml of each of the components and record the weight, then use those weights/ratios to weigh out the actual mix that I will be using. This is useful for high build primers and similar and is basically what you're trying to do.

However, unlike colours, where the quantity of each tinter is critical to colour accuracy, with clears and primers it is not. If the TDS says mix 2:1 clear to hardener and you mix 2.1 to 0.9 it will make little to no difference to the end result. Obviously you want to be as close as you reasonably can, but don't get hung up on "to the gram" accuracy.

Bear in mind that in a shop environment I might buy 5 litres of clear and get 2.5 litres of medium hardener plus 2.5 litres of slow (or fast) hardener as well. Mix on the day will be according to ambient temperatures but, over time I know that my mixes are sufficiently accurate, even allowing for occasional use of some hardener to use in something else, like some basecoat. I've added a screenshot of the TDS for my favoured clear and you will note that it can be mixed 2:1 or 3:1 with different hardeners, according to application.

As for mixing the exact, to the gram or millilitre quantities, nobody does this. Every panel is different - in size and in shape, so the recommended quantities per panel are very approximate. Many years ago I learnt to spray so that I could achieve a given thickness, in µm, as is specified in the TDS. Checked with a paint thickness gauge then and I still double check, especially if I'm using a different gun, or fluid tip or aircap. Accuracy within 10% on a 60µm clearcoat DFT is 6µm and that's fine.

I know, just looking at a panel, pretty much how much basecoat or clear I'll need to achieve the thickness I want and I usually mix a little more than I think I'll need. A small amount of waste is normal and acceptable, certainly better than running out and having to mix more halfway across a panel.

Sure, not everyone can do this, but there are plenty of charts and tables out there that will give approximate quantities for typical small, medium or large panels. Start with one of these as a guide.

696S_TDS.jpg
Chris
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