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Old 06-26-2019, 09:32 AM   #1
Mikel_24
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Rubber band properties, marketing lingo and related issues

I was about to write this in LewyJFreediver's post about roller gun bands but finally I decided not to (so as not to highjack that thread)

The thing is that a few years ago I started hearing about different adjectives used to describe the behavior of rubber band material.

Progressive, reactive, etc. you know them all. I find hard to believe this more than just marketing lingo used to boost sales of a certain product.

Personal perception and opinions is one thing, and fair standarized testing is a whole different one.

Many many maaaaaaaaaaaaany moons ago I recall an article in a Spanish magazine (called Apnea) about lab testing a few rubbers from different makers. I still own that magazine (although I would have to find it as it is in my parents place).

When I say lab testing, I mean it. The testing was conducted by Josetxo Errondosoro (industrial engineer by trade) and some of the parameters tested for all the rubbers where the following:
- Force graph required to stretch a certain lengh of rubber to an X percentaje (it is not linear)
- Force (graph) released by the rubber after a certain amount of time stretched to a certain % (not linear either)

I recall that the G20 and S45 rubbers from Cressi Sub were the most eficient ones, being the ones that were able to release the most energy after being stretched for a while (compared to the force required to stretch them, that is). Other makers did much worse, releaseing only 50% of the energy required to stretch the bands (load the gun) which somehow shows that the quality of the rubber just wasn't there. either that or that the elastic threshold value had been surpased, therefore degrading the rubber.

Durability of the rubber was not tested as this was not a long term test. Although they tested the rubbers to destruction stretching them until they snapped.

It is easy to get the idea that certain rubber pushes the shaft in a gun in a more uniform way and without a jolt or recoil, simply because the rubber gets tired while being loaded for a while not releasing too much energy to the shaft. Easily tagged as "progressive" when the reality is that it is "shitty".

On the other hand, a rubber that is able to release most of the energy required to load it would be tagged as "explosive" or "reactive" when the truth is that THAT rubber at THAT % of stretch is more efficient, therefore releaseing more of the energy required to load it, to the shaft when the gun is shot.

Has anyone lately LAB TESTED any rubber in a similar way as Josetxo Errondosoro did long time back?

Mikel
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Old 06-26-2019, 06:32 PM   #2
popgun pete
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Re: Rubber band properties, marketing lingo and related issues

Rubber tends to vary between different batches. When I worked in the tire industry the rubber compounding (chemistry) guys used to talk about the variability in natural rubber from different sources in terms of the trees and plantations from around the world, the natural rubber or latex always varied slightly in its properties when the next shipment arrived. The job of the compounders was to tweak the formulations to ensure standard properties for the required tasks as you had tread rubber, bead area rubber, sidewall rubber and various fillers and spacers in a tire that required different mechanical and wear or fatigue properties with a mix of synthetic and natural rubbers. Now speargun band rubber will be a much simpler formulation, but these problems will still exist as the rubber trees are different varieties depending on where they are growing around the world.

Mori conducted some testing of band rubber many years ago and a websearch will probably find it. Here is something similar if you search on "Power Band Test" on another spearing forum.

Last edited by popgun pete; 06-26-2019 at 06:42 PM.
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Old 06-26-2019, 06:58 PM   #3
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Re: Rubber band properties, marketing lingo and related issues

Something to read: https://www.researchgate.net/profile...erformance.pdf
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Old 06-27-2019, 01:31 AM   #4
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Re: Rubber band properties, marketing lingo and related issues

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Originally Posted by popgun pete View Post
.....Rubber tends to vary between different batches. When I worked in the tire industry the rubber compounding (chemistry) guys used to talk about the variability in natural rubber from different sources ........

Mori conducted some testing of band rubber many years ago and a websearch will probably find it. Here is something similar if you search on "Power Band Test" on another spearing forum.
Hello Pete,

I am familiar with the rubber industry (to some extent) because I worked for a year in the Bridgestone truck tire factory in Bilbao (Spain). At the office anyways, but I got to do a few trips arround the whole facility and the explained me the whole process.

I certainly understand what you mean. Some properties require additives to tune them up. But as far as I know, the only additives given to the bands were meant to provide more UV protection, color or harder shore. But I have always been told that the purest the latex in the compoud, the better.

Maybe I didn't explain myself the right way in my first post but, which precise properties (meassureable) are required for a rubber to be called progressive or reactive or whatever. I think it will be much clearer for the buyers to analyze load force and released energry graphs.

I will search for those test you are talking about right now. Thanks!
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Old 06-27-2019, 02:12 AM   #5
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Re: Rubber band properties, marketing lingo and related issues

Good question Mikel! I have been wondering about these terms and what they really mean as well.
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Old 06-27-2019, 11:15 AM   #6
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Re: Rubber band properties, marketing lingo and related issues

I'm following this thread.

I've tried many band materials, and the G20 from Cressi were way too explosive. S45 were better. The best I've tried by far is Primeline small ID (Amber core/black shell). A nice punch and durability mixture whitout too much recoil.
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Old 06-27-2019, 05:34 PM   #7
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Re: Rubber band properties, marketing lingo and related issues

Some terms used to discuss elastomers https://pslc.ws/macrog/elas.htm are defined, however there are others that are not. Properties that are able to be tested for to characterize a given material have their own definitions which you can see here https://physics.info/elasticity/.

“The quantity that describes a material's response to stresses applied normal to opposite faces is called Young's modulus in honor of the English scientist Thomas Young (1773–1829). Young was the first person to define work as the force displacement product, the first to use the word energy in its modern sense, and the first to show that light is a wave. He was not the first to quantify the resistance of materials to tension and compression, but he became the most famous early proponent of the modulus that now bears his name. Young didn't name the modulus after himself. He called it the elastic modulus. The symbol for Young's modulus is usually E from the French word élasticité (elasticity) but some prefer Y in honor of the man himself.

Young's modulus is defined for all shapes and sizes by the same rule, but for convenience sake let's imagine a rod of length ℓ0 and cross sectional area A being stretched by a force F to a new length ℓ0 + Δℓ.

Tensile stress is the outward normal force per area (σ = F/A) and tensile strain is the fractional increase in length of the rod (ε = Δℓ/ℓ0).

The proportionality constant that relates these two quantities together is the ratio of tensile stress to tensile strain —Young's modulus (E)."

F/A = E.Δℓ/ℓ0 or σ = E.ε

Terms like progressive stretch don’t seem to be defined, after doing a search, but in speargun band parlance the notion is that the band produces a gradual increase in force as we continue to draw it back. That sloping ramp of increasing force with increasing elongation is exhibited by most band rubbers, however some bands seem tough to start and are hard to stretch and that means the force level ramps up very quickly. To power a spear shaft to be flung through water which is 784 times denser than air we need stored energy and that requires force and displacement and for the latter we require the band to elongate to cover nearly all the length of the spear.

Bands that do not stretch out to any appreciable length are of no use in a speargun as we want a long power stroke for the wishbone and the force ramping up too quickly is of no practical use if we cannot draw it back. Alternatives where we can use a windlass with a ratchet detent to crank back more resistant bands may make those band materials more useful, but ultimately we need to load a gun maybe twenty times in a given session with our bare hands and with a gun not encumbered with gadgets.

Another aspect to consider is the bands narrow as they stretch, they thin out and at some point the force applied over the diminished cross-section is going to start the band yielding in that it will not recover its original length. The most important factor in a speargun is reproducible shots as then we can develop an auto-shoot response where in our mind’s eye we can see the spear’s course and the fish swimming into it with convergent line shooting or “shooting from the hip”. Therefore the bands need to be consistent in their performance from shot to shot over several hours in the water and from day to day, thus they need to quickly recover.

Last edited by popgun pete; 06-27-2019 at 05:59 PM.
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Old 06-28-2019, 01:25 AM   #8
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Re: Rubber band properties, marketing lingo and related issues

Great expalantion Pete. If we get to the point, soon we will be having more formulas in the posts than plain jane text.

I will try to find the charts I was talking about so I can picture exactly what I was talking about.

And yes, I think we should stick to what is sold as speargun rubbers with a diameter of 14 to 19mm.

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Old 06-28-2019, 01:41 AM   #9
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Re: Rubber band properties, marketing lingo and related issues

You can see the charts on the Spearing Forum under the name "Power Band Test". For some reason the URL if posted here gets asterisked out and you cannot click on it. Here are some of the charts. There are a lot more!
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Last edited by popgun pete; 06-28-2019 at 01:49 AM.
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Old 06-28-2019, 04:30 AM   #10
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Re: Rubber band properties, marketing lingo and related issues

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Originally Posted by popgun pete View Post
You can see the charts on the Spearing Forum under the name "Power Band Test". For some reason the URL if posted here gets asterisked out and you cannot click on it. Here are some of the charts. There are a lot more!
I saw those charts but that"s not exactly what I am talking about. Bands should be maintaines stretched for a while to see the decrease in tension. That's, in mu opinión, something that tells apart good from bad rubber!
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Old 06-28-2019, 08:03 AM   #11
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Re: Rubber band properties, marketing lingo and related issues

The tests looked into band soak as well, you need to read the thread which runs to two pages. Rubber exhibits hysteresis in that there are losses in the material as when you stretch it you never get back out all that you put in when the band is released. Another way of looking at band soak is to hang a weight on a rubber strand and over time the strand will get even longer as the material relaxes so that the initial elongation at that loading will now be too short to maintain that force level.

On a cocked speargun we fix the elongation when we set the wishbone in the spear wishbone notch, or on the shaft tab, but the force that we used to pull it there is not held by the band, but starts to tail off until it reaches a steady but lower value. If you want the most from your bands then shoot as soon as possible, but of course this is not always practical unless you cock your gun only when you see that fish are around that you want to shoot. The latter approach may work OK if you have a single or two band standard gun, but try doing that with a five or six band cannon or a multi-stage cable rollergun. Inverted rollerguns are cable rollerguns and to avoid confusion that is what they should be called.

When the "Dreamair" cable gun is released band soak will be a thing of the past as there are no elastomeric energy storing components in that gun, instead only a pneumatic "air spring" in a totally closed system.
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Last edited by popgun pete; 06-28-2019 at 08:32 AM.
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Old 06-28-2019, 05:43 PM   #12
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Re: Rubber band properties, marketing lingo and related issues

If you find a good batch of band rubber and can get more of it then buy a long coil of it and put it is a big round biscuit tin with a tight press fit lid with a handful of tire-makers talc thrown in (don't use perfumed talc!). Shake the closed tin and tip it around a few times to distribute the talc, don't use too much talc as talc sucks softeners out of the rubber. Then put it in a cool location away from light and heat. Don't freeze it and keeping the lid closed keeps fresh oxygen getting in as little as possible. UV and oxygen and atmospheric pollution does in rubber, so the more that you can isolate it the better. Buy a pair of band scissors or cutters to chop lengths off clean, they have a blade that squeezes against an anvil that is made of a hard elastomer.
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