AlumiRod - more shots and a HUGE weight savings!

Jump to latest Follow Reply
Doug-T

Doug-T

Member
Feb 19, 2019
287
17
Orygun, United States
I'm always tinkering and modifying things to my liking. Motorcycles, RC stuff, boats, houses, guns, air rifles, etc. About a month ago I ordered a 5' section of 1.25" 2024 aluminum tubing to make two longer Mrod air reservoirs, one for my best friend/shooting buddy, Wade, and one for myself. I'm only a hobby machinist so I asked another air rifle friend "Chuck" to machine my reservoir. We started it last night and he finished and dropped it off today and what a beauty it is. The stock tube is over 36 ounces. The aluminum tube is 4" longer than stock and still only weighs 15 ounces. After the regulator and gauge block go in it should be 21 ounces lighter than a stock Mrod and I estimate I'll have 37% more air capacity than the stock tube with the same reg/block. I'm debating leaving it matte aluminum or Cerakote it flat black.

I think I'll call it...............AlumiRod. 

YtzZFJd.jpg
[/url][/img]

y2jmfwH.jpg
[/url][/img]

kQSNBzX.jpg
[/url][/img]

skHLP6l.jpg
[/url][/img]
 
I think you are very unsafe. You have probably created a virtual bomb. First 2024 AL is not a high strength alloy. In fact 2024 has very poor fatigue resistance in all its hardness states. Every time that tube is pressure cycled, it has less strength left. There is a very good reason why aluminium scuba tanks have limited pressure ratings and effective life. You should have done your homework. See the Barlow formula below. This formula is a rough rule of thumb. The real number is a product of many things like surface finish, nicks and dings, because they all are stress concentration zones and fatigue centers. Please consider the consequences of that tube exploding on a range and injuring the people around you. The following lawsuits would financially cripple you for the rest of your life.

BARLOWS FORMULA - Theoretical Bursting Pressure for Tubes P = Internal Pressure PSI S = Fiber Stress of Tube PSI P = 2si T = Wall Thickness in Inches D = Outside Diameter in Inches Example smls 304A269, 3" O.D. x .065 wall, tensile 85.000 PSI 2 x 85.000 x .065 =11.050 = 3.683 PSI Theoretical bursting pressure 3 3 Theoretical Weight Per Foot Formula (A) Round Steel Tube O.D. minus wall, times wall times (factor) 10.68 Example: 3" O.D. x .065 wall steel tube 3 - .065 (=2.935) x .065 (=.1908) x 10.68 = 2.037 lbs per ft (Square and rect. steel tube factor is 13.60) (B) Round Aluminum Tube O.D. minus wall, times wall, times 3.1416 (factor) times alloy factor Example: 3" O.D. x .065 wall, 6061 aluminum tube 3 - .065 (=2.935) x .065 (=.1908) x 3.1416 (=.5994) x (alloy factor) 1.176 = .7049 lbs per ft Aluminum alloy factors: type factor (Square and rect. alum, tube factor is 4.000) 3003 1.188 2024 1 .J200 5052 1.164 6061 1.176 6063 1.176
 
Upvote 0
scary But i had a failure as well , where a 500 cc bottle came apart and busted my foot , I will never buy from China , I learned some mess with labels for pressure ratings to increase profits and they are like a bomb I thought i went deaf , what happened to me was I filled a bottle I heard a small leak



I put the bottle near my ear to listen and toughed the gage and boom ,it went down like a bullet on my foot , and the gage went threw my celing missing my ear by a fraction
 
Upvote 0
I had an aluminum tube machined out of 2024-t aluminum for my marauder long ago, anodizing is not necessary either...2024 aluminum @ the same spec as factory has been tested to beyond 10,000 psi meaning its safe @ 3,000 psi factory recommended fills...fwiw.



My un-anodized tube looks the same as it did 1.5 years ago when I had it machined, if you fill with dry air much like you're supposed to...there is no need to worry about corrosion within our lifetimes...in fact there is/was more corrosion on my OEM tube 1 year after use, its not uncommon to see some pitting or corrosion in OEM tubes.



I believe the fatigue rate of 2024 aluminum would incur failure at over a million cycles, to which I have filled 50/1,000,000...shame my tube only has 999,950 fills left before it must be decommissioned.



Barlows formula also suggests it won't fail and is safe to fill to factory recommended fill...



-Matt


 
Upvote 0
First, as a fellow modder and tweaker, let me say that air tube looks very nice! Congrats on the design and machining. Having said that, it is important to know whether the 2024 aluminum you are using is tempered or un-tempered and which temper was used. Tempered 2024 aluminum has a significantly higher yield and tensile strength than un-tempered 2024 aluminum. Once you know the temper, you can obtain the yield and tensile strength for that temper (from the internet) and plug those numbers into the Barlow calculation as suggested in the Steve-I post above. That formula is explained in many places on the internet and is worth understanding. It will give you some idea of the safe working pressure, deformation pressure and burst pressure of your cylinder. Cylinder wall thickness is integral to this calculation, which is why that information was requested in one of the earlier posts.

Good luck with your project !






 
Upvote 0
Steve-1.

Please, before you type 1,000 words ranting about my project, please don't make assumptions.

Assumption #1. You mentioned 6061 aluminum. This is a soft alloy, used for decorative things like flashlights. 2024 is aircraft grade and is used in all sorts of air and hydraulic pressure vessels. It has copper as part of the alloy and is much stronger.

Assumption #2. You mentioned 0.065" wall thickness. Not sure where this number came from. I'm using 0.095" wall thickness, the same as the stock tube, nearly 50% thicker than your assumption.

Assumption #3. 3" tube diameter. Why would use this number except to make a horrible example of failure? I'm using the same 1.25" diameter as the stock tube. OD and wall thickness are directly related in strength of pressure vessels. A very small diameter tube can handle very high pressures with thin walls. Think of your car's brake lines or new diesel engines running 23kpsi through a pipe the size of a pencil.
 
Upvote 0
Steve-1 Your calculations would be very unsafe fortunately he used the correct material and tube dimensions to stay well with in the calculated safety zone. Its easy to do it wrong and just as easy to do it right, we have two engineers on staff and we do not take anything for granted its all well thought out and calculated. Stay safe and have fun guys. P.S looks good Doug-T but if left raw have it clear anodized it will help prevent oxidization that happens very quickly on alloy under pressure.
 
Upvote 0
scary But i had a failure as well , where a 500 cc bottle came apart and busted my foot , I will never buy from China , I learned some mess with labels for pressure ratings to increase profits and they are like a bomb I thought i went deaf , what happened to me was I filled a bottle I heard a small leak



I put the bottle near my ear to listen and toughed the gage and boom ,it went down like a bullet on my foot , and the gage went threw my celing missing my ear by a fraction
Click to expand...


That's horrible! Did you make a post of details such as the condition, the make of the bottle and valve and the seller you went through as a PSA? 
 
Upvote 0
You must log in or register to reply here.
Top Bottom
Back
Home
Forums
Resources
Menu