Estandar RMA

7/29/2019 Estandar RMA

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In the early 1900s, all around the world, rubber

products and manufacturing suddenly began to

flourish. Decades after the “vulcanization”discovery, rubber was finally beginning to

fulfill its 20th Century prophesy as a major

supplier to both the automotive and industrial industries.

Here in the USA, the Rubber Manufacturers

Association (or RMA) was established in 1928.

Although having many directives with its

rubber manufacturing constituents, this tradeassociation was empowered to catalog and qualify various rubber products as to their quality and

expected performance … aspects that, to that date, varied widely within the industry.

The RMA later went on to establish specifications for rubber used in “flat” belting products …

identifying each according to a specific “grade.” Originally, there were three such RMA gradeclassifications … #1, #2, and #3. Each wasqualified according to a minimum cover tensile

and elongation, along with minimum cover and

carcass ply adhesions.

Over the years that followed, the flat belting

picture has changed significantly. Yet, the RMA

grade specifications have changed little!! As aresult, there tends to be a great deal of confusion

about today’s compounding “grades or qualities.”

How many are there?? What exactly do theymean?? And how do they apply to compound

selection?? Can they be “combined??”

To answer some of these questions, and to keep current with today’s compounding

“classifications,” let’s review each of the primary grades that are fundamental to Conveyor and

Elevator belting. You’ll see that each grade tends to be broadly categorized under either a“General Purpose” or “Special Purpose” label.

Tire demand

drives rubber

production

RMA qualifies rubber “grades”



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“““GGGeeennneeerrraaalll PPPuuurrrpppooossseee””” GGGrrraaadddeeesss

RMA Grade Designations …

Today, we refer to the existing “RMA Grade” classifications (last updated in 1994) as a reference

to “General Purpose” compounds. RMA’s Flat Belt Technical Committee provides aspecification for end-users entitled “Conveyor Belt Cover Characteristics and Classifications.”The properties, test values, and minimum requirements included serve as a guideline for acceptable

performance for these basic of all field applications.

• RMA “Grade 1” …

o Was RMA’s 1st rubber

“grade classification”

o Referenced as Cut/Gouge

Resistant rubber , with good

abrasion resistance

o Now qualified by min tensile(2500 psi) and elongation

(400%) values @ break

o The RMA guidelines suggestthat the cover will consist of

Natural or Synthetic rubber,

or blends thereof, suitable for applications involving sharp and abrasive materials or severe loading conditions.

Note 1 … The properties of Natural rubber are extremely important in this

grade! In its purist form, the compound should be 100% Natural rubber ,

with little dilution from extenders.

Fenner Dunlop offerings include … Matchless, Grade I, Matchless Plus, and Grade M

• RMA “Grade 2” …

o Was RMA’s 2nd rubber “grade classification”

o Primarily referenced as a Wear Resistant rubber

o Now qualified by min tensile (2000 psi) and elongation (400%) values @ break

o The RMA guidelines suggest an elastomeric composition similar to Grade I …

providing excellent service with abrasive materials, with somewhat less cut/gouge

resistance than Grade I.

Fenner Dunlop offerings include … Giant, Grade II, and Giant SAR

• RMA “Grade 3” … No longer specified!! Originally referenced as an “economy”offering (a 50/50 blending of fresh and reclaimed rubber), this grade category eventually

disappeared in the early 1970s as market expectations gradually outdated it.

Typical RMA I

Application



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As originally structured, this rubber grading system was a reasonably effective way of

“qualifying” a belt’s expected field performance. However, what once worked well years ago

(with predominately Natural rubber and cotton carcasses) is no longer as meaningful.

With advanced polymer and textile technology, today’s flat belting products have much different

performance indicators. They are also much better products … in many cases exhibiting physicalsthat the early RMA references simply could not have imagined. (As an example … Dramaticimprovements in adhesion levels have long ago

obsoleted the adhesion references that were once

an RMA Grade criterion!)

Bottom Line … The once pertinent

RMA Grade classifications, now based on merely tension and elongation values

alone, are no longer the best indicators of

any compound’s performance!

Today, the spirit of the “RMA Grades” is

to simply differentiate between the two

principal “General Purpose” application options: 9 “Grade 1” … best possible Cut/Gouge resistance!

9 “Grade 2” … best possible Abrasion resistance!

Note 2 … The test methods for Fenner Dunlop Americas Conveyor and Elevator belting and

its rubber covers are based on testing in compliance with ASTM D378-91 and ASTM D412-92.

“““SSSpppeeeccciiiaaalll PPPuuurrrpppooossseee””” GGGrrraaadddeeesss

Out of necessity, World War II accelerated the development of Synthetic rubber. With “Allied”

access to Natural rubber virtually severed, a major emphasis was placed on the making of

Synthetic rubber. By the end of that war, after just four years, Synthetic rubber production in theUSA alone increased over 100 fold!!

With the advent of Synthetic rubbers, came the opportunity to “chemically” create polymers and

compounds that could meet specific needs … needs that could never have been met with Naturalrubber alone. While there is only one chemical type of “Natural” rubber, there are more than

twenty different chemical types of “Synthetic” rubber.

Within each Synthetic polymer type, there are often many distinguishable grades or qualities

offered. Each grade or quality references a specific rubber-performance expectation … and aretherefore cataloged as one of several “Special Purpose” grades. With Conveyor & Elevator

belting, here are some of the more prominent of those compound grade categories.

Typical RMA II

Applications



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MSHA (Mine Safety Health Administration) …

Major fires, causing untold personnel and property loss, have always been a “mine site” issue.

During the 1950s, several world-wide government regulatory agencies … principally the NCB in

Great Britain, and the United States

Bureau of Mines (USBM) … began toimplement strategy designed to minimize

these tragedies.

In the USA, the result was “Schedule 28”

(later referred to as “Schedule 2G”) … afederal regulation mandating a fire

resistant standard for all rubber destined

for use in underground mining/conveyingoperations. The USBM began to require

that all belting sold in such underground

service must pass their new “flameretardency” tests … and be appropriately

branded, as such.

Note 3 … Today, MSHA has replaced the USBM as the agency that regulates the flameretardency test in the USA… which is now cataloged as “30 CFR 18.65.” In Canada, their

governing flame retardency test is referenced as “Can\CSA-M422-M87.”

Note 4 … When such “flame testing” was first implemented, Scandura solid woven PVC

products were amongst the first belt offerings to pass their respective flame testing

requirements … both in the USA, and in Great Britain.

Many early PVC industrial conveyor belts, liked that produced by Scandura, were 2G compliant.

However, DuPont’s “Neoprene” (due to the same inherent chlorine content as in PVC) was thefirst … and for many years the only … commercially available rubber polymer that could beeconomically compounded to pass 2G. It wasn’t until the early 1970s that belt manufacturers were

finally able to compound more cost efficient SBR and BR rubbers to satisfy the federal flame

retardency test.

Fenner Dunlop offerings include … F, FAR, MSHA/FR, SFAR, FF, FFAR, LT/FR,

FF-CSA, FFAR-CSA, FFOR, and FORP

Important to understand, however … that “flame retardency” is NOT the same as “flame proof .”

All elastomeric belts WILL burn!! Flame “retardant” ones are merely qualified to “self-

extinguish” when the source of the flame is removed or will no longer propagate the fire!

Oil (and sometimes Acid) Resistant …

In the presence of oil, or oil-based contaminants, standard compounded rubbers will “swell” and

degrade … resulting in a genuine loss of “physical” properties (abrasion, adhesion, tensile, etc).

MSHA Application



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Soon after WWII, existing “oil resistant” technology combined with newly available Synthetic

rubbers to legitimately offset rubber degradation when in contact with such undesirablecontaminants.

Today, several different polymers are

used and/or blended together (including Neoprene and Nitrile) to offer differing

degrees of resistance to such absorptionand deterioration. Typically … compounds containing the highest levels

of Nitrile concentration will offer the

greatest resistance to oil degradation.

It is important to understand that NO

compound is totally resistant to oildegradation! Oil resistant offerings will

merely withstand contact with such

volatiles and contaminants for a longer time before compound degradation (and ultimately belt

demise) takes place.

Fenner Dunlop offerings include … MOR, ORN, SOR, ORP, FORP, FFOR, and

Uscothane

Heat Resistance …

As contact temperatures increase, rubber experiences an acceleration of the oxidation (or aging)

process. When those temperatures rise above 180-200oF, an unprotected cover compound will

tend to get hard . Eventually, will most of these will likely crack . Besides an overall degradation,the cover cracking can lead to undesirable “carry-back” issues. The hardening aspect canaggravate splice life (e.g., cover fill-in adhesion, etc).

With the proper blending of standard SBR and BR rubbers, compounds in the early 1950s couldoffer resistance to heat degradation up to 250

oF, or so. Today, some of these compounds are still

in service … while now combining their

very moderate heat resistance with goodabrasion resistance.

For higher temperatures, those

approaching 350o

F, “Butyl” rubber wasinitially used. However, in the 1970s, this

problematic compound was slowly being

replaced by EPDM for such extreme highheat resistance. Besides processing

somewhat better in the factory than

Butyls, EPDMs “hardened” when heataged … often considered more desirable

in field service than “softening” (as Butyls

tended to do).

Oil Resistant Application

Hot Service Application



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Today, Fenner Dunlop uses a variety of EPDM and EPR polymers to optimize heat resistance.

This was done to achieve more consistent heat resistance throughout the entire high temperaturerange!

Similar to the “oil resistant” story, NO compound is totally resistant to heat degradation! So-called

“high heat” offerings will merely endure higher temperatures, and possibly for a somewhat longer time, before such compound/belt degradation takes place.

Fenner Dunlop offerings include … Sahara, Sahara SAR, and Super Sahara

Note 5 … For BOTH “heat and oil,” Fenner Dunlop offerings include Sahara OR (SHOR),

and Super Sahara OR (SSHOR)

Static Conducting …

As belting interfaces with the various conveyor components, the resulting friction can produce a

“static charge.” Standard rubber compounds tend to act as “insulators,” and inhibit the release of any such static. As this static builds up, any subsequent discharge can result in a “spark.” In some

dusty/dry enclosures … grain elevators, munitions factories, fertilizer plants, etc … that spark could lead to a devastating explosion!

With concern over such “spontaneouscombustion” explosions in the early 1970s,

OSHA instituted qualifying guidelines on all

belts destined for such “static-induced” service.They mandated that all belts utilized in such

service would have to pass an “electrical

resistance” test … having a maximum surfaceresistivity. (Today, that maximum resistivitylevel is set at 300 mega-ohms). Upon passing

that test, such belts would be deemed “static

conducting”…and suitable for this service.

Fenner Dunlop offerings include … FORP

FDA (Food & Drug Administration) …

This government agency regulates belt surfaces that

come in contact with “consumable” goods. These beltsare typically “light-weight” and “color-pigmented” (non-

black). Ingredients contained in these products are

therefore FDA approved.

Fenner Dunlop offerings include … FDI

and FDP

Static Conducting Environment

(Grain Terminal)

Typical

FDA

Application



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SSSuuummmmmmaaarrryyy ……… “““GGGrrraaadddeee ooorrr QQQuuuaaallliiitttyyy”””

Over the past six decades, the era of Synthetic

rubber has evolved. Compound performance

has vastly improved. New, and often

overlapping, compounding needs are

continually being addressed and satisfied. Asthey are developed, these new compounds will

be categorized just as existing ones have … into

one or more “grade or quality” classifications,

consistent with their performance

expectations! Fenner Dunlop Americas

expects to not only participate in this process,

but to pioneer and benefit from it as well.

Belt selection requires both carcass and cover/compound choices … and within each of these

separate categories, the available options can be

staggering. Most compounds will cross-referenceinto more than one “grade” category. When selecting

the proper compound, all compound requirementsmust be factored together … and requested, as

such!! No single grade reference is likely to fulfill

that, and provide the “elastomeric value” needed!

As the compounding/grade aspects of Conveyor and

Elevator belting continually change, questions are bound to arise. To assure that you’re both current

and properly informed, don’t hesitate to give us a

call. We’ll analyze your needs, and help provide ameaningful solution. In the final analysis, thatrapport is certain to be a “win-win” … for all of us!!

* * * * * * *

Geoff “Small G” Normanton

Corporate Director of Technology

George “Big G” Frank

Manager, Application Engineering

September 2005

Estandar RMA

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