Engineer Info Wanted...Temperature effects on Aluminum, Stainless & Titanium metals?

[Dueydog]

I own all three and the titanium seems to be the least effected by hot or cold temperatures.

For a control purposes I used a .689 for all three barrels and 10 balls from two different types of paint. I practiced Sunday in 100 degree weather and the aluminum barrel seemed to constrict to a smaller bore, but when I checked the titanium barrel the balls fit perfectly.

I didn't check the stainless until today in my house at 78 degrees, used 10 balls from each bag of paint, and all three barrels where identical at .689 bore.

There is a descrepency between the temps for the aluminum barrel. I understand that paint size changes, but why would the same paint fit the titanium barrel on the hot day and not the aluminum one?

What else could cause this?

I have read Tom Kaye's info and about everything else out there.

I tried two searches without results so please...NO FLAMES!!!

And please...NO OPINIONS! Only FACTS!

Thanks,
Matt

[Redkey]

coefficient of thermal expansion

Materials will shrink or expand as heated or cooled. The amount of expansion or contraction is stated as the change in length over the orginal length per degrees of temperature.

Steels have a Coefficient of Linear Thermal Expansion of between 0.000009 and 0.000012 in/in per degree C

Stainless Steel has a CLTE of about 0.000017 in/in deg C

Aluminum Alloys have a CLTE of 0.000022 in/in per degree C

Ti has a CLTE of 0.0000085 in/in per degree C.

in your example of 37.7 deg C to 25.5 deg C the change in temperature is -12.2 deg C.

to help with the visualization of this...
12 inches of Steel will shrink by 0.0015 inches
12 inches of SS will shrink by 0.0024 inches
12 inches of Aluminum will shrink by 0.0032 inches
12 inches of Ti will shrink by 0.0012 inches

since the barrel cross section is a hoop we'll need to unwind it to find the effective length of it. The inner barrel diameter is 0.689 inches which means the circumference is about 2.164 inches. (length = 2*pi*r)

so the change in the length of the unwound barrel will be....
Steel = 2.16373
SS = 2.16355
Alum = 2.16342
Ti = 2.16378

reversing the calculations gives bore diameters of the following
Steel = 0.68874
SS = 0.68868
Alum = 0.68864
Ti = 0.68875

so, as you can see the Ti barrel shrinks the least. However, the difference in diameter is about 0.0001 inches.

I suspect that any differences you noticed were due to the paintballs changing size as they are much more affected by changes in temperature and humidity. The gelatin shell has a CLTE of about 0.00003 in/in per degree C. I'm not sure on paint chemisty but I'll bet that it shrinks and expands with temperature changes.

hope this answers your question

[Dueydog]

Excellent info.

There is a descrepency between the temps for the aluminum barrel. I understand that paint size changes, but why would the same paint still fit the titanium barrel on the hot day and not the aluminum one?

What else could cause this?

Thanks again,
Matt

[Redkey]

paint variation?

if you start measuring the diameter of the paintballs you will find they are not very consistant nor are they truely round.

[Dueydog]

I guess I didn't make myself clear...

6 hours in 100 degree day:
Ten paintballs ALL FIT the .688 titanium boomstick nicely.
Same ten paintballs would lodge in the .689 aluminum CP barrel.
Had to use a battle swab to get them out they were so stuck.

After sitting in the house for about 24 hours @ 78 degrees:
Same ten paintballs AGAIN fit the .688 titanium boomstick nicely.
Same ten paintballs also fit the .689 stainless Freak insert nicely.
Same ten paintballs NOW fit the .689 aluminum CP barrel nicely.

I'm not concerned about exact bore and I understand paintballs fluctuate with temp and humidity.

My question is what is going on with the aluminum barrel?

As stated titanium fluctuates less, but is too small to matter.

So, what makes the titanium barrel fit paint more often than the aluminum one?

What makes the aluminum barrel change more than the titanium?

Thanks,
Matt

[Redkey]

try this...

Measure the diameter of the barrel to the nearest 0.001 inches at room temperature and then again at 120 F or so and see if the diameter really changes.

You could also measure the diameter of a couple paintballs at room temp, marking the orientation of the measurement so it can be duplicated. Then heat the balls up to 100 F (six hours) and measure them again.

How were the balls being stored? in sealed bags? in pods? perhaps in the hopper? where were you playing? was the humidity high?

[Jaguar45]

There is a problem in the situation which you describe, Matt. You say that in the heat, the paintballs fire through the titanium barrel fine, but lodge int he aluminium. The problem is that all three barrels EXPAND from their room temperature bores when the heat goes up, and the aluminium barrel expands more than the other two. Therefore, it cannot be the thermal expansion which caused the paintballs to get stuck inside the aluminium barrel. The only possible explanations, to my mind, for what happened are that the paint you put through the aluminium barrel was larger than the others or that the aluminium barrel didn't so much expand as deform in the heat, perhaps becoming slightly ovoid and thus trapping the paintballs.