GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Engineering- Research & Development => Topic started by: pcairhunter on December 19, 2013, 08:52:33 AM
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I need to know what type of steal to use for a air tube o.d 1.250 x .125 wall I have tried to read on here as much as i can but too many suggestions. I have some DOM that's has a wall .095 but then I read somewhere not to use DOM! :-[ and sorta scared to try 7075 alum I want to be able to fill to 4000psi. the daystates have a working p of 250 bar and its the same size tubing that I would like to use. but who knows what type of tubing the daystates are made of! :-[Thanks guys in advance!
Paul
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.125 wall is really thick and could still have threads in it making the minor diameter less but still adequate. I like 4130 as it is very consistent and strong material, reasonably priced, easy to find and finishes nicely. It is what they use to build tube chassis and I use it to make all the Extension tubes I do for CO2 Tube guns like the QB/160 etc.
I do not like to thread tube OD's or ID's on High Pressure set-ups preferring to use Cap Head Allen Head in Shear (Usually 4 or more 1/4X20 TPI). FX uses this arrangement and I do on US FT and Hunter builds. It is a very good way to plug tubes without losing tube wall thickness.
4130 is going to be DOM(drawn over mandrel) as most tubing is.
TimmyMac1
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There are two major sub designations of what is commonly called DOM tubing (carbon steel)
The usual DOM which is welded on the seam and seamless (SMLS) This is commonly referred to as Boiler Tube and the welded version is hydraulic tube.
If you could find the seamless version it would be fine. It's hard to find in small quantities and it's a PITA to machine. The welded version however is playing russian roullete. Anyone who has worked on hydraulics extensively has seen a tube burst at operating pressures.
As Tim said 4130 is commonly available, you can even have it certified for about $20...go that route
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Thanks, guys!!!!!! :D
Tim… I should have called you! i use to live in California 4 years ago….i use to come by your shop and speak with you. I was the one that had the Beaumont .25 cal that you shot in your shop and you couldn't believe the power and how loud it was and i think you re did the crown for me also! You were always nice and great to deal with.
Thanks again guys! now i will go blow myself up!!! lol jk
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Thanks, guys!!!!!! :D
So 4130 seamless?
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.125 wall is really thick and could still have threads in it making the minor diameter less but still adequate. I like 4130 as it is very consistent and strong material, reasonably priced, easy to find and finishes nicely. It is what they use to build tube chassis and I use it to make all the Extension tubes I do for CO2 Tube guns like the QB/160 etc.
I do not like to thread tube OD's or ID's on High Pressure set-ups preferring to use Cap Head Allen Head in Shear (Usually 4 or more 1/4X20 TPI). FX uses this arrangement and I do on US FT and Hunter builds. It is a very good way to plug tubes without losing tube wall thickness.
4130 is going to be DOM(drawn over mandrel) as most tubing is.
TimmyMac1
Dear Tim,
What wall thickness do you use for the 4130 in a 3000psi application? When you talk about the 1/4-2 cap screws in shear it looks like in pictures of your USFT air tubes the cap is held in the tube by four, each at 90 degrees?
Best regards,
Scott
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What wall thickness do you use for the 4130 in a 3000psi application?
It depends on the diameter, it's the thickness/diameter ratio that governs the MSWP....
Bob
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I was about to order some of this as recommended by a fellow GTA member. Is it any good? DOM Mild Steel Tube A513 TYPE 5 1"x .065"
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That specification refers to electro welded and hot finished. It could be 10xx carbon steel or 41xx crmoly.
More than likely though it is carbon steel with tensile strength about 20.000psi lower than 4130
I would say not the best for a pressure tube.
Try these folks
Www.aircraftspruce.com (http://Www.aircraftspruce.com)
Certified crmoly tubing
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Thanks Sean. Does this tubing have a good finish for an oring seal?
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The CrMoly from Aircraft Spruce is extremely smooth on both ID and OD.... I use the 1.0" OD x 0.065 on my Hayabusa, it has a yield pressure of 9,400 psi and a burst rating of 14,500 psi....
Bob
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Thanks Sean. Does this tubing have a good finish for an oring seal?
Only aluminums will have extrusion error that could cause sealing issues with the Tubing and 70 durometer orings. To get 90 durometer to seal it needs to be smoother normally but it really depends on the amount of erosion the extrusion die has. Steels like 4130 have a very smooth ID so there should be no issue
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I would like to hear more about this topic.
One thing I am wondering is why 7075-T6 aluminum is not used for air cylinders. It has a yield of 73k and ultimate of 83k and would be quite a bit lighter than steel and quite a bit cheaper than Ti? Is there something else that would make it undesirable? Is the 10k difference in yield and ultimate just to close for comfort? I do see that its a bit harder to find.
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One word....Fatigue. :o Aluminum starts fatiguing the first time its used, sooner or later it lets go. Steel does not have this problem, if you keep steel away from the elastic limit, it never fatigues.
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This thread really covered this subject well... http://www.gatewaytoairguns.org/GTA/index.php?topic=61069.0 (http://www.gatewaytoairguns.org/GTA/index.php?topic=61069.0) some great information in that thread.
7075T6 aluminum is hard to source in tube; 2024T3 aluminum is easy to source as is 6061T6 aluminum but 2024T3 is better material for an air tube and close to 7075T6 for strength, a better choice than 6061T6.
For steel... 4130 as recommended by the guys here is the way to go.
Make sure you test the vessel or have the vessel tested before you use it and if the design of the air tube has sufficient space for it install a burst disk for insurance.
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Where would you have a cylinder tested and what do they do? And where do you get a burst disc and how are they installed?
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Burst discs are available from paintball regulator companies such as Ninja, and their dealers.... or on eBay.... The commonly available ratings are 1.8K, 3K, 5K, and 7.5K.... They are 3/8"-24 NF thread and require a hole with a square bottom about 1/4" deep with a small air hole (1/16" - 3/32") feeding pressure to the center.... They have a soft copper "crush face" on the bottom to make them seal.... Any dirt or grit will destroy the seal and may damage the sealing surface in the hole as well....
Bob
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Hydrostatic pressure vessel testing is a very common practice. Any dive shop can get a pressure vessel tested for you or you can search for a testing facility in your area.
Many air smiths use a hydraulic jack with a pressure gauge attached to test every air tube they make. You will need to supply end caps with your air cylinder with a standard pressure fitting for testing. To limit the amount of fluid required you can fill most of the space inside the air tube with a slug of Delrin or metal. There's an article called " In the Shop" on Dennis Quackenbush's website that shows how he tests his air tubes and a good discussion about the various metals he uses to make air tubes and air guns.
Standard test pressure is 5/3 of rated vessel pressure... a 3000 psi pressure vessel would normally have a 5000 psi burst disk installed and a 4,500psi pressure vessel would have a 7,500 psi burst disk installed. Burst disks are normally installed in the regulator or valve attached to the pressure vessel on the high pressure side. One of the nice features of the Mac1 guns (IMO) is a burst disk.
More information on burst disks can be found online or at NinjaPaintball.com.
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Ninja makes 1.8 and 5K Burst Discs and we use the Other makers discs when we need 3K.
Output side Burst Discs on HPA Tanks should match the Pressure vessel Test Rating or MWP of the Operating system.
On Tanks outputting 1200 PSI or less Mac1 runs 1.8K Output disc protection with 5K vessel protection.
On Tanks with output pressure of 3K down to 1200 they run a 5K burst disc on the output side because they no longer manufacture a 3K disc. I change all these out for 3K discs so the operating systems won't see pressure in excess of 3K should there be a reg failure.
CO2 systems altered to take regulated HPA should be aware the MWP of most CO2 systems is not over 3K but the HPA burst disc will be 5K on both the vessel protection and Operating system side when the Output pressure is over 1000 PSI. This does not adequately protect the operating system and it could be subject to an extreme overpressure if the Regulator has been over shimmed and unable to seal or has failed due to seal degradation.
I'd suggest the Regs that people use that has output burst discs with ratings higher than the Guns MWP the 3K disc should be swapped for the 5K as we do for all the Regs we sell.
WE get the 3K burst discs off CO2 Pin valves that are in the 12 and 24oz CO2 tanks we buy as we always change out pin valves for on/offs valves.
If you need 3K burst discs Mac1 can supply. We can also supply Mil-Spec 90's for the Ninja Reg Piston so your regulator will have the seals it needs to live a longer life. Ninja Piston uses a 012 and 008. I move the 70 durometer urethane they install into the second groove and put the Mil Spec 90 in the working position of the large side. The small side only has a single oring. I upgrade every Ninja Regulator I sell to Mil Spec 90's on the Reg Piston because in heavy users we have seen the stock items degrade.
I've got about 3 years experience with Ninja Regs and used a Ninja Regulator on my US FT Benchrest gun for 3rd place in the worlds Heavy Varmint BR match in 2011.
http://www.mac1airgunshop.com/burst-disc-p/psibd.htm (http://www.mac1airgunshop.com/burst-disc-p/psibd.htm)
Ninja discontinued their 3K burst disc, years ago now, likely because of poor demand and huge availability of substitute products. My first connection with Ninja was when I bought the 3K burst disc due to the competitions products being junk. Once the competition got the reliability up Ninja demand was weak as their is no other disc with as much turnover and worldwide production as the 3K disc.
TimmyMac1
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That's some cheap insurance to be sure... Peace
Pete