Coating to Reduce Friction Inside 3D Printed Nozzle

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Tim
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Coating to Reduce Friction Inside 3D Printed Nozzle

Postby Tim » Tue May 17, 2016 10:23 am

If I were to 3D print a nozzle for a home made blaster using Shapeways' "Polished Strong & Flexible Plastic" (Nylon), what would be an ideal NON-PERMANENT coating to reduce friction inside the nozzle? Assume that the nozzle in question attaches and detaches easily.

Shapeways' Polished Strong & Flexible Plastic is fairly smooth, but has a texture you can feel. It is not nearly as smooth as a machined or injection-molded part.

I am soliciting suggestions for a non-permanent coating for the following reasons:

- If I attempt a permanent coating and I do not like the results, I just wasted the part.

- I already have a couple options for permanent coatings if non-permanent coatings are not ideal (XTC-3D, Molykote).

Non-permanent coatings came to mind because I rub candle wax on the metal runners of my Flexible Flyer sleds. The wax is a temporary lubricant, but it lasts all day. Without the wax, ice builds up on the runners (latching on to the imperfections in the steel I suppose). After just one run down a hill, it appears as if the wax has been rubbed off, but it remains within the imperfections, disallowing the build-up of ice.

My hope for a non-permanent coating within a water nozzle is that the water washes away excess coating, while leaving deposits of the coating within the imperfections for a reasonable period.

Tim

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Re: Coating to Reduce Friction Inside 3D Printed Nozzle

Postby SSCBen » Tue May 17, 2016 10:39 am

Sounds really nice. PVA has been used for similar purposes before, but it dissolves in water, so it's not an option. I assume you've considered the various support-only materials for 3D printing and found none of them to be good. I might suggest looking into low temperature hot glue, because it can be be made smooth and usually you can peel it off solid objects.

Looking forward to the final result!

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Re: Coating to Reduce Friction Inside 3D Printed Nozzle

Postby Tim » Tue May 17, 2016 11:18 am

Hi Ben,

I do not need a material to co-print the nozzle with. I am just looking for suggestions for lubricants or other coatings that I can rub or slather on the inside. Just curious what might be best suited for what I am trying to accomplish (vasoline, food grade silicone, wax, etc).

Thanks,

Tim

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Re: Coating to Reduce Friction Inside 3D Printed Nozzle

Postby SSCBen » Tue May 17, 2016 11:48 am

I was thinking you could use the support material to smooth out the nozzle.

I doubt softer materials like vaseline or wax would stay in the nozzle well enough to work. Silicone sounds like a reasonable option.

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Re: Coating to Reduce Friction Inside 3D Printed Nozzle

Postby Drenchenator » Tue May 17, 2016 1:34 pm

Hi Tim,

How smooth is your 3D printed surface in the first place? If it's quite rough, I'm afraid no material will adhere to it for very long, and it likely would not form a very streamlined shape even if it did. It sounds like a more permanent solution would be a better bet (some kind of permanent seal or coat, or even sanding, depending on the material).
The Drenchenator, also known as Lt. Col. Drench

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Re: Coating to Reduce Friction Inside 3D Printed Nozzle

Postby Tim » Tue May 17, 2016 5:18 pm

Hi Andrew,

I cannot quantify the level of smoothness, but below is a link to an image showing something printed in this plastic. It would be polished by Shapeways just like the item on the right in the image.

http://static1.sw-cdn.net/rrstatic/img/ ... ompare.jpg

VR,

Tim

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Re: Coating to Reduce Friction Inside 3D Printed Nozzle

Postby Drenchenator » Tue May 17, 2016 8:13 pm

Thanks for the picture. The surface is definitely rough, but not really that rough, honestly. That means that it might not even be necessary to worry about any sort of coating, because under some circumstances, the wall roughness does not affect the friction much.

This is gonna get a little technical. The roughness itself would increase the friction by encouraging the flow to become turbulent (or more turbulent for the matter). Turbulence definitely increases the drag compared to a laminar flow. But the flow is likely already fully turbulent.

Predicting how much drag the nozzle creates is complicated, but for a straight pipe it can be reduced to two parameters: the Reynolds number (which measures the flow's inertia compared to the effects of viscosity), and the scaled roughness height (which measures the depth of the roughness compared pipe diameter). The Moody diagram shows qualitatively how both of these parameters affect the overall friction. Without any numbers, it's difficult to say exactly how whatever you are planning will work, but it's easy to see that under some circumstances, provided the roughness is not too great, it really does not affect the flow that much at all.

So long story short, even the best coating may be unnecessary, or it may be totally necessary, but it really depends on the degree of roughness compared to the nozzle diameter. I don't have any recommendations as to the coating, but I just thought that you should keep this point in mind as you design and build.
The Drenchenator, also known as Lt. Col. Drench

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Re: Coating to Reduce Friction Inside 3D Printed Nozzle

Postby Tim » Tue May 17, 2016 9:42 pm

Very good points. As you indicated, a coating may be critical or pointless. How can I best design the nozzle to mitigate the effects of my anticipated roughness to reduce the potential need for a coating? Would it be beneficial to make the nozzle as short as possible? In other words, would a sudden contraction be best? I could correct and scale the coordinates published by Theobald. The third radius he listed in his 1981 article is clearly a typo, but I can fit his other coordinates with a 4th or 5th-order polynomial. Perhaps it would be better to fit the major contraction with one polynomial and the final sweep at the outlet with another polynomial.

VR,

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Re: Coating to Reduce Friction Inside 3D Printed Nozzle

Postby SSCBen » Tue May 17, 2016 10:33 pm

There are few English language research papers on the effect of surface roughness. As I recall, the Russian hydraulic mining papers consistently state that a smooth surface is necessary for a coherent jet. And I vaguely recall one (French?) paper that said even short rough patches can have a noticeable effect. This is why I have not tried to 3D print nozzles. A CNC lathe or mill with some smoothing/polishing after cutting probably would be ideal.

I didn't notice that typo in Theobald's paper, so thanks for pointing it out. I think there are some other problems with some of his range plots, and his breakup length data seems odd when plotted with other similar data too.

I'm interested in seeing how well the 3D printed nozzle works. But I think a fairly sudden large contraction (diameter ratio greater than 10 if possible) with a very short orifice is most likely to be better. The contraction should be smooth if possible, but as I recall some of the data I have suggests that even non-smooth instantaneous contractions can do really well.

Here's a plot with the only data I have on the effect of the contraction.

nikonov_issledovaniia_1968_fig_8.png
nikonov_issledovaniia_1968_fig_8.png (22.24 KiB) Viewed 671 times


This is from a hard to find Russian book. Not much detail is given in the text, unfortunately, but the plot is the diameter ratio vs. the fraction of maximum breakup length you can get. Larger ratios clearly are better, but the effect saturates.

Also, I'm not sure whether Theobald's shape is entirely valid if the proportions aren't maintained, but it should still be good if you scale it with different proportions.

Edit: In terms of minimizing the effect of the roughness, a large contraction should help. First, the contraction usually has a turbulence reduction effect (this is why it improves breakup length). Second, a large contraction necessarily means a large diameter pipe, which would make the relative roughness smaller.

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Re: Coating to Reduce Friction Inside 3D Printed Nozzle

Postby Tim » Wed May 18, 2016 4:58 pm

Hey Ben,

Thanks for sharing; that chart is interesting. Are you suggesting I use a 2.5" ID pipe to supply a 1/4" nozzle outlet? That doesn't sound very practical for a water blaster. It would waste much water after each trigger squeeze assuming the supply pipe/barrel is after the valve. The Theobald ratio is more practical for both fire suppression and water guns. Nonetheless, I understand your point: the greater the ratio, the better.

VR,

Tim

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Re: Coating to Reduce Friction Inside 3D Printed Nozzle

Postby SSCBen » Wed May 18, 2016 5:10 pm

You're right, it's not practical to have that sort of contraction at the nozzle. That's part of the reason why fire protection researchers like Theobald looked into the effect of nozzle shape. Theobald's goal (flat velocity profile) is independent of the effect the contraction has, though. The contraction has a turbulence reduction effect. So ideally you would have both a flat velocity profile and low turbulence. You might be able to lower the turbulence with a "laminator"/"flow straightener" too.

Also, I don't think the contraction necessarily needs to be from the pipe right in front of the nozzle to the nozzle. You could have a larger diameter pressure chamber (3 inches would not be uncommon) leading to a relatively short normal diameter pipe (3/4" or 1/2") leading to the nozzle. The effect of an intermediate contraction is not clear. I suspect it's not as good as a single contraction, but still valuable. If the path has a bend in it, that'll generate swirl and turbulence, both of which most likely outweigh the benefit from the contraction. So your pressure chamber should be one type which allows a straight path to the nozzle (rubber bladder or air pressure with separating piston).

Edit: I am working on a design that has a large contraction, but it's built around that idea, and is definitely non-standard. The effect of a large contraction has been on my mind lately as I've picked up this hobby again, so I forgot that it takes a special design to actually use.

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Re: Coating to Reduce Friction Inside 3D Printed Nozzle

Postby Tim » Thu May 19, 2016 12:00 pm

The effect of a stepped contraction is an interesting thought. This is inherent to certain homemade soaker designs as you pointed out. I suppose an inline stepped contraction would not lend itself as well to soakers based on SuperCAP, UberSoaker, Dusty’s Water Gun, etc. However, these designs (even scaled-down versions) have a relatively large water capacity. Therefore, water conservation is not paramount. On these water guns, perhaps a single, 10:1 contraction is not impractical. Rather than using something like JLspacemarine’s laminator, it’s feasible to affix a large-diameter assembly that more-closely resembles a homemade water fountain laminator. Those laminators commonly employ a 1/2” or 5/8” supply (garden hose).

VR,

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Re: Coating to Reduce Friction Inside 3D Printed Nozzle

Postby SSCBen » Sun May 22, 2016 7:19 pm

Tim wrote:The effect of a stepped contraction is an interesting thought. This is inherent to certain homemade soaker designs as you pointed out.


"Stepped" contraction is a good way to put it. I think I'll adopt that term.

Tim wrote:Rather than using something like JLspacemarine’s laminator, it’s feasible to affix a large-diameter assembly that more-closely resembles a homemade water fountain laminator. Those laminators commonly employ a 1/2” or 5/8” supply (garden hose).


The fountain laminators are interesting. The people who make them talk a lot about the effect of the laminator, but I am yet to see anyone mention the effect of the contraction, which I suspect is just as significant as the laminator.

I do recall, however, that fountain building folks do not like straight injection into a laminator. Here's a quote from Mark Fuller's famous patent:

Each method cited above uses axial or radial water intake to the nozzle region. Such a method produces a great deal of turbulence in the fluid just upstream of the nozzle.


Personally, I find this hard to believe. But I do know that Mark Fuller has done a lot of tests on these nozzles and I suspect the devil might be in the details of the pipe enlargement.

Anyhow, I just found another paper (this time in English!) which suggested that roughness has a strong effect on breakup. They recommended using electroformed nozzles made from nickel. I am not at all familiar with this manufacturing technique, but it seems like something which could plausibly be done at home (!), so I will look more into it. I'll email you a copy of the paper later if you'd like, Tim.

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Re: Coating to Reduce Friction Inside 3D Printed Nozzle

Postby Tim » Mon May 23, 2016 10:24 am

“Stepped Contraction” - I’ve coined my first phrase! Sweet!

I agree; the value of the contraction is understated, and perhaps the value of a tangential injection is overstated. However, we must admit that the tangential injection is not a detriment, especially because it is followed by a large diameter and flow-straightening members. Perhaps you and I place too much emphasis on axial injection.

A fountain-type laminar nozzle may allow us greater design flexibility. The following pops into mind…

- 2.5”, 3” or 4” diameter nozzle
- Radial (not axial, not tangential) penetration to attach supply from backpack
- 90-degree elbow on the inside of the penetration to achieve tangential injection
- Manual spring-return ball valve or shower valve on the outside of the penetration
- Simple modification of the valve handle to allow direct trigger-like actuation

The valve would be perpendicular to the large nozzle pipe to give the in-hand feel of a gun. If we are not overly concerned about turbulence at the nozzle inlet, we don’t need to actuate the valve fully. The valve needs to be open enough so that the outlet of the nozzle is the limiting orifice. The adequateness of partial actuation significantly reduces the complexity of valve handle modification. Handle modification may not even be necessary, depending on individual preference.

Electroforming nozzles is an interesting concept! Yes; please send me a copy of the paper. Thank you.

VR,

Tim

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Re: Coating to Reduce Friction Inside 3D Printed Nozzle

Postby SSCBen » Wed May 25, 2016 11:20 am

I'm pretty skeptical of the "tangential injection" idea's applicability to water guns. The laminators have an associated pressure drop which fountain designers usually don't seem to care about, and tangential injection basically guarantees that you need longer laminators, and hence more pressure drop.

My guess is that there's a better way to do it if you need to go from a smaller diameter pipe for a larger diameter one. I imagine that axial injection with guide vanes in the expansion section, for example, would be superior to tangential injection. The problem likely comes from flow separation in the expansion (which could create turbulence), and there are some other ways to avoid that as I recall (see the book "Boundary layer theory" by Schlichting). I specifically remember that experiments were done to determine what expansion angle is acceptable to avoid flow separation. But that can be avoided entirely with guide vanes.

You're absolutely right that this offers some interesting possibilities about the valves, though. It's definitely worth looking into whether we really need a valve with a good flow path, as that tends to severely restrict ergonomics. If it's possible to use a more ergonomic valve and "clean up" the flow from it, that could very well revolutionize homemade water guns.

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Re: Coating to Reduce Friction Inside 3D Printed Nozzle

Postby Tim » Fri May 27, 2016 4:55 pm

Reeling the conversation back to 3D printed nozzles…

I had these Theobald nozzles printed with 3/4” and 1” NPT inlets. The initial diameters of the Theobald profiles match the ID’s of the 3/4” and 1” pipe nipples that I have. The nozzle ends have the external geometry of a 3/4” camlock fitting. I initially did this because all of my other ideas looked too much like sex toys once I modeled in a 6” long pipe nipple. Now, I’m thinking I can actually attach a female camlock and fill through the nozzle if I’m not terribly concerned about a fast fill.

Image

Image

Image

Image

I fully realize that the relatively weak, 3D-printed Nylon may break, but I figured I’d try it for fun anyways. Now I just need to make a blaster to try them on. I am going to make a CAP-based water gun. I want to incorporate an ergonomic firing mechanism because this seems to be a priority for most people judging by Ben’s survey. Once I have something built and my 3D printed nozzles blow up, I’ll test other nozzle ideas that we’ve been discussing.

VR,

Tim

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Re: Coating to Reduce Friction Inside 3D Printed Nozzle

Postby SSCBen » Sat May 28, 2016 2:30 pm

Thought I replied to this. Very nice work, looking forward to seeing these tested. How much did they cost?

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Re: Coating to Reduce Friction Inside 3D Printed Nozzle

Postby Tim » Mon May 30, 2016 1:14 pm

The 3/4" NPT nozzle is $20.24 including shipping if you choose Shapeways' extended manufacturing option.

The 1" NPT nozzle is $27.33 including shipping with the extended manufacturing option.

I was able to test the 1” NPT nozzle a bit, which has an outlet diameter of about 0.23”. I attached the nozzle to the end of a 6” long pipe nipple. I have 20-mesh screens at each end of the nipple and straight drinking straws inside. I tested at 40 PSI and 70 PSI. The blast looked very intimidating in person, but the stream was not as cohesive as I had hoped. I should probably coat the inside of the nozzle with XTC-3D and try again.

Below are some images at 70 PSI (40 PSI did not look a whole lot different).

Image
Image
Image
Image
Image
Image

EDIT: Just to clarify, I shot this from my CAP blaster that is in progress, not a garden hose.

VR,

Tim

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Re: Coating to Reduce Friction Inside 3D Printed Nozzle

Postby Tim » Sun Jun 05, 2016 5:16 pm

<insert double post here>

Ben suggested via email that I should test a drilled end cap for comparison to the 3D printed nozzle. I drilled a PVC end cap with a diameter that is within thousands of an inch of the printed nozzle's outlet.

I could not convince anyone to go out in the rain with me to test today. So unfortunately, I do not have photos of the end cap test from a similar perspective as the test of the printed nozzle. However, I was able to take the video below.

https://www.youtube.com/embed/7Wc090vMK ... ty(highres)

Visually, the stream looked about the same to me.

VR,

Tim
Last edited by Tim on Tue Jan 17, 2017 3:02 pm, edited 1 time in total.

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Re: Coating to Reduce Friction Inside 3D Printed Nozzle

Postby marauder » Mon Jun 06, 2016 9:53 am

Wow! That looks very impressive. Do you have a picture of your homemade? This looks seriously effective. What kind of range do you get on that thing? The shot time and stream size are impressive.
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