Rubber Info

[drkucho]

Hello all

I am manufacturing rubber tires for radio controlled offroad trucks, i did my first tires with NR which have a very good grip but they dont last so much , the rocks and rough terrain worn them pretty quick.

Now im trying to find the best rubber choice to avoid premature wear without loosing grip (at least not much)

reading here and there found some nice tables which show rubber properties comparison, I found theese the most useful:

http://www.srp-rubber.com/materia.htm

http://www.tsrubber.com/en/compound_terminology.php

looking to them looks like CR (neoprene) , SBR and NBR are the best choice with good abrasion resistance and good tackyness

but there is something i dont understand: in SRP table , NR shows "Excelent Abrasion" what does it mean? i gues the field "abrasion" means "abrasion resistance" , but then NR is excelent on this? i think this data is just wrong , but i am not engineer so i cant be sure...

can anyone please confirm the abrassion resistance of NR is good or bad?

Also any extra info you can tell me about the best choice for my tires is highly welcomed

thanks a million in advance

 

[GrahamBennett]

Abrasion resistance comes mainly from the grade of carbon black used to fill the rubber. Having said that, abrasion resistance can be improved further by blending different polymers eg 70% NR with 30% Butadiene rubber.

 

[tom1953]

I'm sure that "Abrasion" in the SRP table does mean Abrasion Resistance, as most other references also show NR to be Excellent for abrasion resistance. NR is generally good for off-road tires because it's good for cut and abrasion resistance.

I'm not a tire expert, but I wonder if the quality of the natural rubber compound you're using can be improved to have better abrasion. BR (butadiene rubber) is also excellent for abrasion resistance, and is commonly used in blends with NR.

Another possibility is urethane; urethanes as a general category are also excellent for abrasion resistance, and you sometimes see them rated higher than NR. My company, TSE Industries, makes millable urethanes (Millathane®), processed on rubber equipment, that are used in applications that need excellent abrasion resistance and high mechanical strength. They're not the best for heat build-up, so if that's a factor other polymers would be better for the off-road tires. Millable urethanes are quite a bit more expensive than NR and other common polymers, also.



Tom Jablonowski, TSE Industries, Inc.

http://www.tse-industries.com

 

[drkucho]

thanks for such usefull answers !

the thing is to allow maximum grip i did my tires with NR 35 durometer, its dificult to find the balance between grip and long life...

i think i will do both things, to mix NR + BR (70%-30%) and to increase the durometer to 40 or 45 and will see how they perform and last

thanks again , if you have any other comments i will allways welcome !

 

[Compositepro]

The type and amount of curing agent is a major factor also. The degree of cure will be affected by cure cycle

 

[drkucho]

Compositepro,

sorry but i dont understnad you well, would you be so kind and say it again with other words?

maybe a direction to tell my rubber manufacturer?

 

[Compositepro]

Charles Goodyear is famous for developing "vulcanization". This is the chemical reaction of rubber with sulfur to crosslink the rubber. Other chemicals than sulfur can be used but non-crosslinked (uncured) rubber has relatively very poor properties. Uncured rubber will soften and flow when it get hot. This is useful for molding shapes but curing is done in the hot molds (usually arround 300F) to set the rubber. Natural rubber is just one ingredient that is amber in color. Rubber parts are made from rubber formulations that contain a dozen different ingredients. These formulated rubbers must be processed correctly to get parts with the desired properties.

 

[drkucho]

Thanks for your quick reply compositero

i asked my rubber manufacturer about their vulcanization method, they told me they do "oxide cure" , they say "it doesnt affect rubber properties" ... what do you think?

 

[tom1953]

They might have meant "peroxide". There are two primary cure systems for vulcanizing rubber: sulfur cures and peroxide cures.

Generally, sulfur cure systems give better abrasion resistance and physical properties, while peroxide cures give better heat aging and compression set properties. Within each type of cure system, there are numerous variations in the type and amount of chemicals used. A good custom mixer can advise the best cure system for your end product and manufacturing process.

If the compound you're using isn't cured with sulfur, you may want to evaluate a sulfur cured compound.


Tom Jablonowski, TSE Industries, Inc.

http://www.tse-industries.com

 

[drkucho]

thank you tom

 

[drkucho]

one more question, will the sulfur cure harm the takyness of NR?

 

[tom1953]

I wouldn't think the cure system would affect the tackiness of the cured compound.

That being said, with sulfur or peroxide cure systems, if ingredients are added that are above their solubility limit in the compound, they may bloom to the surface, giving a whitish powdery deposit on the surface. Undercuring the rubber (not giving it enough time or temperature to cure) can also promote blooming. But, a typical sulfur or peroxide cure system shouldn't bloom and affect tack.


Tom Jablonowski, TSE Industries, Inc.

http://www.tse-industries.com

 

[drkucho]

thanks a million

 

[drkucho]

i aksed my rubber manufacturer about sulfure curing, they told me the sulfure it is already inside of the rubber when they purchase the material, so it is not needed to add sulfure on the cure

is this normal? will sulfure inside the rubber cause the same sulfure cure properties?

 

[tom1953]

Do you buy mixed rubber compound from your rubber manufacturer and then you mold the tires, or does your rubber manufacturer buy mixed compound from another company?
It sounds like the sulfur and other ingredients are already mixed into the rubber compound when your "rubber manufacturer" buys the compound.
With the compound variations you're thinking of trying (raising the hardness and trying a blend of NR with BR), is that something your "rubber manufacturer" is doing, or their supplier, or you? Just curious . . .


Tom Jablonowski, TSE Industries, Inc.

http://www.tse-industries.com

 

[drkucho]

yeah... there is a little mess here...maybe i was not clear enough

i design the tires, and pay a rubber parts company to make moulds and final pieces, then , the rubber parts company buy the rubber from a rubber material supplier to make my parts

rubber part company told me that the rubber they buy from the rubber supplier is already mixed with sulfur (probably got this info from the rubber supplier)

and finally its me the one looking to increase resistance so its my idea to mix compounds, but not sure who will do the mix for me, the rubber part company i deal with OR the rubber material supplier

 

[drkucho]

i woudnt want to abuse , but looks like you missed my last question :

to use rubber compound with sulfure already on it , is exactly the same than curing the rubber with sulfure? should it cause similar properties to the final rubber part?

 

[tom1953]

The rubber formula you're using contains sulfur, and other ingredients, and the sulfur (along with the other chemicals) "cures" the rubber when heat and pressure is applied. Sulfur "curing" is not a process as such, but is the reaction of the sulfur and other ingredients during vulcanization, or curing. The compound, containing the sulfur cure system (sulfur plus accelerators plus activators), is then "cured" by a molding process, with heat and pressure.

It's probably a little confusing because "cure" refers to the type of chemicals that are used in the compound (either sulfur or peroxide) as well as the process or method of vulcanization/curing (by molding, for example).

If you do a search on the internet for 'rubber curing' or 'sulfur curing' you'll find some better explanations.

So, your question is referring to the same thing in different ways; sulfur is in the compound, and it is used to cure the rubber.

Tom Jablonowski, TSE Industries, Inc.

http://www.tse-industries.com

 

[drkucho]

i think i got what you mean , thank you very much

 

[polym3]

There is a definite trade-off between coeffient of friction and abrasion, and cut and tear resistance. To raise the abrasion resistance properties (as well as cut and tear resistance) you need to add a reinforcing agent, i.e. carbon black or amorphous silica for colored compounds. This naturally reduces the amount of rubber in contact with the ground and it's the rubber that gives you the higher c-o-f.

I have seen applications where the fact that the natural rubber wears is an advantage since it continually exposes fresh rubber which is where the grip comes from. If the tires are cutting or chunking out, you need to add a reinforcing filler.

As others have pointed out, the cure system is also important, and should be designed to give you the best possible dynamic properties.

It is common in the rubber industry to "extend" rubber compounds with non-reinforcing fillers like kaolin. Obviously this reduces the cost, but also affects the performance. Make sure that whatever you have specified is, in fact, what you are getting.

You cannot do better than natural rubber in this type application. Polybutadiene (BR) requires reinforcement (carbon black), even when blended with natural rubber. BR is great when used in a tire tread because of it's low heat build-up characteristics...but I doubt this is going to help your application.