HVLP viscosity cup

[Chris Stromberger]

Do any HVLP users out there use the viscosity cup? I have been experimenting with oil paints and some waterborne poly. The poly registered a fairly high viscosity with the cup that came with my Fuji, but I am able to successfully spray it without thinning (using a #4 tip). I'm wondering if I will always get better results adhering to the manual's viscosity numbers. Eg, for oil paint they say 20-25, I think (don't have the manual in front of me). The oil I am using is off the charts viscous out of the can. I am thinning to the paint mfgr recommendation, and it still is showing a high viscosity number wit the cup (like 70 or so if I recall). Just wondering if those viscosity numbers are hard rules--do people here follow them as listed in the book? Do you generally ignore the mfgr thinning recommendation when spraying with HVLP and thin to the "official" recommended viscosity?

Thanks,
Chris

[Byron Trantham]

Chris,
I use an Apollo system and have the Zahn #2 cup. Until I adhered to the viscosity numbers, ie thinning, I had all kinds of trouble. I learned about the importance during one of those mini-seminars at your yearly wood working shows. I went home, tested the material and found that that after 10% thinning, the material atomized beautifully. Now I don't spray squat until I test the material.

[Dennis Peacock]

Chris,
I use an Apollo system and have the Zahn #2 cup. Until I adhered to the viscosity numbers, ie thinning, I had all kinds of trouble. I learned about the importance during one of those mini-seminars at your yearly wood working shows. I went home, tested the material and found that that after 10% thinning, the material atomized beautifully. Now I don't spray squat until I test the material.

Oh man....Excellent advice and right on the money too!!! :)

[Mike Hill]

I have been using some Sherman Williams NS Lacquer and am trying to determine what it's viscosity should be for spraying. The instructions say it does not need thinning, but 10% thinner can be added. I printed a data sheet for the product from their web site, but no viscosity number. So I am left with trial and error. Any recommendations on where to find this number?
Mike

[Chris Stromberger]

Not sure. I have noticed on some product's MSDS (data sheet) there is a viscosity number in units of "KU" I think, but not sure if you can translate that into "viscosity cup units". I just go by the sprayer's recommendation. Mine came with a viscosity cup and most things seem to require 20-25 on their cup, according to the sprayer manual. So I have been thinning until I reach that viscosity.

[Byron Trantham]

I have been using some Sherman Williams NS Lacquer and am trying to determine what it's viscosity should be for spraying. The instructions say it does not need thinning, but 10% thinner can be added. I printed a data sheet for the product from their web site, but no viscosity number. So I am left with trial and error. Any recommendations on where to find this number?
Mike

Mike,
Your gun instructions should tell what viscosity is required for the various needles they supply. Further they shold tell what viscosity scale they are referring to. Mine is a Zahn #2. I have a Zahn cup (came with gun). You fill it and time how long it takes to empty. That time then tells you which neddle to use. If the time is longer than the needles you have, you have to thin it until the time is correct. With the proper viscosity, the material should spray very well. If its too thick it will splatter comming out; too thin it will run like crazy. You can PM me if you wish and we can get into details.

[Byron Trantham]

I was sitting here re-reading this thread and decided to try and consolidate the viscosity information into a form that makes sense (I hope).

First, viscosity is its simplest terms, is how thick/thin the material is based on some standard and is measured in time. If a paint manufacturer states the viscosity without stating the method used the number is useless. I use Zahn #2 because that is what came with my gun. there are other way to measure viscosity but the procedure is the same.

Second, you need to know what you gun manufacturer uses as a standard, Zahn or what ever, to measure viscosity. Again, mine uses Zahn #2. Your gun should come with more than one needle/nozzle set. If not, you may have to buy additional sets to accommodate various thicknesses (viscosity) of paint.

Third, your gun manual should have a chart that states the viscosity (time) for each needle set. Mine came with four needles, #1 - #4. #1 is for dyes and some stains and the time to empty my Zahn #2 cup is 10-15 seconds. Needle #2 takes 15-18 seconds; #3 18-23 seconds and #4 25-30 seconds.

Fifth, fill cup and measure how long it takes to empty. Take that time and look at your chart and match the needle/nozzle set that most closely matches the time. If your time is longer than any needle/nozzle set you have you can either thin the material OR buy a bigger set. I do not recommend that you thin material more than 10-12%. Beyond that and you start degrading the paint.

If you are like most of us, you will tend to keep using the same material to finish your projects so once you know which needle to use you won't have to do it the next time. If you buy something you haven't used in the past measure the viscosity. I don't trust any numbers on paint cans!

I think the best advice I can give you is to get very familiar with your guns characteristics. If you think you need more needles/nozzles, contact your manufacturer for the parts. Also, if it is not clear what system they use to measure viscosity, again contact them and find out. Also, make sure you have the equipment to measure the viscosity.

[Chris Stromberger]

Third, your gun manual should have a chart that states the viscosity (time) for each needle set. My gun (Fuji MM4) only mentions one set of viscosity numbers, different according to material. Eg, "primers 30-40", etc. No indication of numbers correlated to tip sizes. Also, I don't think it mentions what kind of viscosity cup it came with (Zahn or Ford etc).


I do not recommend that you thin material more than 10-12%. Beyond that and you start degrading the paint. This is the part that worries me. I'm spraying oil based enamel paint, and I have to thin the heck out of it to get it down to the proper viscosity. I'm dealing with loss of sheen in the satin enamel due to the amount of thinner I have to add.

[Byron Trantham]

My gun (Fuji MM4) only mentions one set of viscosity numbers, different according to material. Eg, "primers 30-40", etc. No indication of numbers correlated to tip sizes. Also, I don't think it mentions what kind of viscosity cup it came with (Zahn or Ford etc).

This is the part that worries me. I'm spraying oil based enamel paint, and I have to thin the heck out of it to get it down to the proper viscosity. I'm dealing with loss of sheen in the satin enamel due to the amount of thinner I have to add.

Absolutely contact Fuji. I am sure the numbers you have are for the needle/nozzle provided. Find out if they have larger needles and a Ford/Zahn cup to measure the viscosity recommended for the needles they do offer. You're on top of this, you just don't seem to have the correct needle for the paint you are trying to spray. Thinning is last resort but can certainly be necessary. Are you using a turbine? If so, how many stages?

[Chris Stromberger]

I will contact them to get more details. It's a 4-stage turbine system. I'll post here if I get anything interesting from them.

[Byron Trantham]

I will contact them to get more details. It's a 4-stage turbine system. I'll post here if I get anything interesting from them.

Chris, a four stage unit should allow you spray just about anything including latex but you need different needles for different materials. I'm using a regular air compressor and a conversion gun. I works fine but the compressor runs it's ... off. Next month our yearly wood show happens and I am pretty sure the "biggie" this year is going to be a four stage Apollo.:D

[Chris Stromberger]

Got a reply from Fuji. The viscosity cup that comes with their system is not any of the standard varieties, it's just their version I guess.

And re the different viscosity numbers for different air cap sizes, this was the reply: "Each aircap size does not need a different set of viscosity numbers - it's the paint viscosity that determines the amount of thinning necessary and the viscosity numbers"

Now I'm even more confused! :confused:

[Byron Trantham]

Got a reply from Fuji. The viscosity cup that comes with their system is not any of the standard varieties, it's just their version I guess.

And re the different viscosity numbers for different air cap sizes, this was the reply: "Each aircap size does not need a different set of viscosity numbers - it's the paint viscosity that determines the amount of thinning necessary and the viscosity numbers"

Now I'm even more confused! :confused:

Chris, I am sorry to hear their answer. I doesn't make sense. Most paint does not come with viscosity numbers and if they do, its related to one of the standards like Zahn or ford. The air cap does not control how much paint is sprayed only the fan pattern. The needle hole controls how much is sprayed (with the same air pressure). My set does come with one other air cap and it is used with my largest needle #4. I don't have any advice here. I hope you can work it out.

[Chris Stromberger]

Hmmm, ok. Their "air caps" come with needles also. I guess they change the cap a bit for each needle size too. Well, thanks for the help. I'll keep experimenting!

[Byron Trantham]

Hmmm, ok. Their "air caps" come with needles also. I guess they change the cap a bit for each needle size too. Well, thanks for the help. I'll keep experimenting!

Hey, that's good news because there is a relationship between the needle/air cap size and viscosity. You can buy a Zahn #2 cup. There should be a chart out on the net somewhere that relates needle diameter and viscosity. Heck, if you want I can measure mine in thousands and provide the recommended viscosity for each needle diameter from my chart. Buy yourself a Zahn cup and keep track to see what times are best for your needles. Let me know if you want my information as a starting point.

[Chris Stromberger]

Absolutely would love to see your viscosity chart. Thanks. Any idea where to find a Zahn cup online?

The Fuji needle sizes are:
#3 = 1mm
#4 = 1.4mm
#5 = 1.8mm
#6 = 2.2mm

[Byron Trantham]

Absolutely would love to see your viscosity chart. Thanks. Any idea where to find a Zahn cup online?

The Fuji needle sizes are:
#3 = 1mm
#4 = 1.4mm
#5 = 1.8mm
#6 = 2.2mm

Heres mine:
#1 .75mm Inks dyes stains 16 seconds
#2 1.00mm "all purpose", thin lacquers, water based finishes 16-18 seconds
#3 1.5mm Catalyzed lacquers, conversion varnish (what ever that is) 18-24 seconds (I need the A or B air cap)
#4 2.0 mm thined laytex paint, heavy primers 24-35 seconds (I need my B air cap)

These are not a dead match but will sure give you a starting point. I'll search the net for a Zahn cup. You're getting closer. I really is a big help to get the viscosity right. When its right it goex on so well. When its wrong you have a frustrating mess. A Fugi is a good unit.

[Chris Stromberger]

Thanks for the info. I'll get some of the larger needles and try those with this oil pant.

[Byron Trantham]

Thanks for the info. I'll get some of the larger needles and try those with this oil pant.

I'd wait until you can measure the present viscosity. It may work with the 2.2 mm needle with a LITTLE thining.

[Mike Hill]

Byron: Following you discussion has helped me a lot. I never did get a reply from Porter Cable. Not surprised.

I have 2 needles and caps:
#1. 1.5mm for high solids, multipurpose.
#2. 2.0mm for medium to high solids. Based on your chart, using a Zahn 2 cup I can get close to what I need for viscosity.

Make sense?
Mike

[Mike Hill]

I just did a search on line for Zahn Cups. The least expensive I found was $103.00! Now I am wondering why I did not buy a gun that had the cup included :)

[Chris Stromberger]

I guess that explains why my gun came with its own "proprietary" viscosity cup, made of plastic. The Zahn ones I see online are made of stainless steel, come with a "cetificate of calibration" and are sold by scientific instrument places.

[Byron Trantham]

For those of you looking for a Zahn #2 cup, you can get one from Apollo. The contact is J. Danderand. $19.95 + shipping. Email them at jdanderand@hvlp.com

Hope this helps.

[Mike Hill]

Byron: Thanks for the lead. I was able to get an aluminum Zahn #2 cup for $19.95 from Jason. A lot better than $103.00 :)
Mike

[Edward Oleen]

Ah Ha! Another victim of the deviousness of paint manufacturers, or somebody.

I'm in the throws of starting to spray coatings - in my case AquaZAR Interior Water-based Polyurethane, from UGL. The stuff is labeled as 55-60 KU.

Now what is a KU? After an afternoon spent on the web, I find (on Wikipedia) that KU means Krebs Units, and is used solely with a Stormer Viscometer. This is industrial production testing equipment, and way out of our price range - I suppose, 'cause I haven't seen a price for the stuff.

I haven't yet found a conversion table from KU to anything else, but a call to DuPont (the number on the can) got me talking to a gentleman who informed me that 60 KU is about 70 seconds using a Ford #4 cup. He found this out by looking up the viscosity of some substance (I don't remember what it was, if he even told me) in two tables, one in KU and the other in Ford.

I bought a viscometer - after going to loads of paint stores. The one I finally got was a bit dusty, but it seems to work okay. It is a Dupont M-50, which corresponds to a Zahn #2, which, in turn, corresponds to a Ford #4.

Of course this is only tangential to your question, but it is some sort of a start. What I think is that the maker of your spray equipment supplied a viscometer with no identification, and there are several different ones out there. The "number" for a Ford or Zahn or whatever relates to the diameter of the hole in the bottom. I've seen cups advertised with interchangeable tips - probably at interchangable prices: they'll give you a cup and tips and you'll give them your bank account.

I did find a table containing the conversion equations for Zahn Cup #'s (#1 thru #5) to "Kinematic Viscosity in Centistokes". Here it is...

..Converting Cup Time (seconds) to Kinematic Viscosity in Centistokes
Zahn Cup #1: V = 1.1(t - 29)
=> Zahn Cup #2: V = 3.5(t - 14) DuPont M-50, Ford #4 equivalent
Zahn Cup #3: V = 11.7(t - 7.5)
Zahn Cup #4: V = 14.8(t - 5)
Zahn Cup #5: V = 23t

I've used the Capital letter "V" instead of the Greek letter "nu" for the number in Centistokes.

A "centistoke" is one one hundredth of a stoke.

I don't know just how equivalent "equivalent" is.

I have no intention of going into an explanation for Stokes vs Poise vs... If you are either interested or a masochist, go to Wikipedia and search for Viscosity.

So far nothing for Ford cups.

I think that what I'm going to do is simply thin the product, keeping track of how much thinner I put in it, until the product sprays okay. THEN - and only then - I will measure it's viscosity, record the number, and thin future purchases to the same number.

The coating manufacturers seem to not give a damn about making their stuff easy to use, what with the various number systems in use, with no correlation. I fear that it is time for somebody - NIST, maybe? - to step in and require a standard, and that the manufacturers be required to list the number on the product containers, the spec sheets, etc.

I mean - there are standards for most everything else we use: lumber, power, fasteners, tools, etc. Granted that many of the standards are voluntary, but the coating manufacturers have been around for a long time and still give us a mess.

[Bill Neely]

I posted this link on the other thread. Hopefully it will relieve some of the stress:

http://www.clearcoproducts.com/pdf/library/Viscosity-Conversion-Chart.pdf

[Curt Harms]

I mean - there are standards for most everything else we use: lumber, power, fasteners, tools, etc. Granted that many of the standards are voluntary, but the coating manufacturers have been around for a long time and still give us a mess.

I suspect the reason there are no commonly available standard because spray finishing by consumers is a somewhat new phenomenon and a small % of a manufacturer's sales. Pro shops have 'internal knowledge' gained from experience or from manufacturers' reps and don't need published standards.

[John TenEyck]

It's more practical to get a viscosity cup and use it to measure your incoming product, and then adjust it for your spray equipment, as required. A Ford #4 cup is typically used for many products that can be sprayed with an HVLP setup, and that's what I use. I measure the viscosity of every gallon of finish I get and write it on the lid. You'd be surprised how much the viscosity varies from one can to the next of the same product. From charts readily available on-line I know, for example, that a viscosity of around 45 seconds should spray well through a 1.8 mm orifice gravity feed HVLP conversion gun and it does with mine. So if I get a gallon of finish that measures 60 seconds I know that I'll need to thin it if I want to use that setup. From experience, I know that I'll probably have to add about 6% H2O for that product, so I'll add 4 or 5%, check the viscosity, and add more if required until I measure something close to 45 seconds.

Even if the manufacturers listed the viscosity of their products on their PDS, and many do, you shouldn't expect the actual product you get to be exactly that number. At best, it's a guideline.

John