ASTM D15-72. Methods of Compound and Sample Preparation for Physical Testing of Rubber Products

Standard Formulas and Procedures-Natural Rubber 17.1 Standard formulas and time cycles for mixing for the following natural rubber com-pounds are given in Tables 3 and 4, respec-tively:

~ ~l~ Designation: D 15 - 12

Standard Methods of

American National Standard J 1.1 American National Standards Institute

COMPOUND AND SAMPLE PREPARATION FOR

This Standard is issued under the fixed designation D 15; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision A number in parentheses indicates the year

of last reapproval

These methods have been approved by the Department of Defense to replace methods 101 I and I iII of Federal Test Method Standard No 601 and for listing in the DoD Index Specifications and Standards Future proposed revisions should be co- ordinated with the Federal Government through the Army Materials and Mechanics Research Center, Watertown, Mass

02172

1 Scope

1.1 These methods specify standard

ma-terials, describe equipment, and prescribe

processing methods for evaluating

compound-ing materials in various types of polymers,

carbon blacks in natural rubber, and for

eval-uating butadiene (BR) and styrene -

butadi-ene (SBR) polymers

1.2 The methods are divided into three

parts and appear in the following sequence:

Part A Preparation of Rubber Compound

Standard Materials, Equipment, and

Preparation of Pieces from ber Vulcanizates Other than Standard Test Sheet

Rub-Part B Evaluation of Standard and standard Materials and of Commercially Available Rubbers

Non-Natural Rubber Styrene Butadiene Rubbers Neoprene Rubber

Butyl Rubber Nitrile Rubber Solution Polybutadiene Rubber Polyisoprene Rubber Part C Evaluation of Carbon Blacks in Na- tural Rubber

PART A-PREPARATIO: ; OF RcBBER Co:vtPoc: ;o

Standard Materials, Equipment,

and Processing

2 Scope

2.1 These methods provide a listing of the

reference compounding materials required to

formulate the compositions given in

subse-quent parts of this method, give the

proce-dures covering the weighing of the materials,

describe a standard two-roll mill and certain

of the operations concerned with mixing, and

describe an internal mixer and methods of

op-eration These procedures may be used to

evaluate nonstandard materials where

appli-cable; the evaluation of nonstandard SBR

polymers and carbon blacks are referred to in

Parts B and C, respectively

3 Standard Materials

3.1 The standard materials required for the

composition given in subsequent parts of the methods are as follows, and may be materials that are known to have properties identical with those of NBS standards, as supplied by the National Bureau of Standards However,

in case of dispute, actual standard material from the Bureau of Standards shall be used

Material Natural rubber Styrene butadiene rubber, Type 1500 Butyl rubber

Styrene-butadiene rubber (Type 1503) Nitrile-butadiene rubber

(33 percent acrylonitrile approx.) Zinc oxide

NBS Standard Sample No

Material

Sulfur

Stearic acid

Benzothiazyl disulfide

Tetramethyl thiuram disulfide

Channel black (EPC type)

Magnesium oxide

Phenyl beta naphthylamine

·Oil furnace black (HAF type)

Conducting black (CF type)

Calcium carbonate (precipitated)

4.1 The standard laboratory mill batch size

in grams shall be based on four times the

rec-ipe weight for all compounds unless

other-wise specified For the internal mixer, the

batch size in grams shall be equal to the

nominal mixer capacity in cubic centimeters

multiplied by the spt:cific gravity of the

com-pound

4.2 All materials shall be weighed

accu-rately to witl:tin I percent of the weight

speci-fied

4.3 The carbon black shall be conditioned

before weighing and mixing by heating in a

Type I B oven, as described in ASTM

Speci-fication E 145, for Gravity-Convection and

rum:d- Ventilation Laboratory Ovens2 for 1 h

at 125 ± 3 C The black shall be placed in an

open vessel of suitable dimensions so that the

depth of black is no more than I em (0.4 in.)

during condftioning The black conditioned

as above shall be stored in a closed

moisture-proof container until ready for mixing

5 Mill Mixing

5.1 Mixing shall be accomplished on a

lab-oratory mill having rolls between 150 and 155

mm (5.9 and 6.1 in.) in outside diameter,

with a working distance between the guide at

the nip of 25 to 28 em (10 to II in.) The speed

.of the slow roll shall be 24 ± 0.5 rpm, and the

gear ratio shall be I to 1.4 The mill shall have

facilities for maintaining the rolls at the

speci-fied temperature within the tolerances given

5.2 The clearance between mill rolls shall

be determined by means of two lead strips 10

± 3 mm (0.4 ± 0.1 in.) in width, at least 50

mm (2 in.) long and 0.25 to 0.50 mm (0.01 to

0.02 in.) thicker than the roll clearance to be

D 15

measured The lead strips shall be inserted, one at each end of the rolls approximately 2.5 em (I in.) from the guide, while a piece of compounded rubber, with Mooney viscosity in excess of 50 M L I +4, 100 C (212 F), approxi-mately 75 by 75 by 6 mm (3 by 3 by 0.25 in.)

in dimension, is passing through the center porton of the rolls The rolls shall be at the temperature specified for mixing After pas-sing through the rolls, the thickness of the lead strip shall be measured with an accurate micrometer or thickness gage Tolerances

on openings between the mill rolls shall be

±0.15 mm (±0.006 in.) for openings 0.6

mm (0.025 in.) or more, and ±0.05 mm (±0.002 in.) for smaller openings

5.3 The compounds shall be mixed with the rubber banded on the slow roll, unless otherwise specified, and the temperature at the middle of the surfaces of the rolls shall be measured during the mixing procedure suf-ficiently frequently to maintain the desired temperature (Note 1) Whenever % cuts are specified, the batch shall be cut three fourths of the distance across the roll and held until the bank just disappears (Note 2) When cuts each way are specified, successive 3

; 4 cuts shall be made from alternate directions allowing 20 s between each cut, unless other~

wise specified

NoTE 1-The batch may be removed tarily from the mill to measure the surface temper-ature on the front roll

momen-NoTE 2_-Donot cut any batch while free ment ts evtdent tn the bank or on the milling sur-face

pig-5.4 The weight of the mixed batch shall not differ from the total weight of all the mate-rial by more than ± 1.0 percent

5.5 The mixed batch shall be cooled to room temperature on a flat clean metal sur-face

6 Internal Mixer Mixing

6.1 Internal mixing shall be accomplished

in a laboratory internal mixer3

having a

nom-; 1974 Annual Book of ASTM Standards, Part 41

An internal mixer, Type B Banbury, manufactured by the Farrell Corp., Ansonia, Conn., has been found satis- factory for this purpose

ina! capacity of 1170 ± 40 cm3

with a slow rotor speed of 77 rpm and a gear ratio of I to

1.125

6.2 The batch size should be the volume of

the internal mixer measured in cubic

centi-meters (or milliliters) multiplied by the

spe-cific gravity

NoTE 3-lf an old or worn internal mixer is used,

the batch weight should be increased accordingly

Preparation of Standard Vulcanized

Sheets from Mixed Batches of

Rubber Compounds

7 Scope

7.1 This method applies to the preparation

of standard vulcanized sheets from mixed

batches of rubber compounds The mixed

stocks may be prepared in a laboratory by the

procedures outlined in Sections 2 to 6 of these

methods, or they may be factory-mixed

stocks, or they may come from any stage in

processing before vulcanization This method

describes the standard press, mold,

prepara-tion of stock, and procedure for curing sheets

8 Preparation of Stock

8.1 Compounds described in Parts B and

C shall be conditioned at a temperature of

23 ± 5 C (73.4 ± 9 F), preferably in a closed

container to prevent absorption of moisture

from· the air The period of conditioning shall

be as specified in Table I Where remilling of

the stocks is required, this shall be done by

passing the stock without banding and with

rolling and passing it endwise ten times through

the rolls of the mill described in 5.1 at the

same temperature used for mixing and with

a clearance between the rolls of 0.20 mm

(0.008 in.) Then, after adjusting the clearance

between rolls to 1.4 mm (0.055 in.), the stock

shall be banded on the slow roll, three "1

cuts shall be made each way, and the stock

shall be sheeted from the mill to give a sheet

after cooling approximately 2.2 mm (0.085 in.)

in thickness

8.2 Compounds mixed in the factory shall

be conditioned at 23 ± 5 C (73.4 ± 9 F) for

a minimum of I h The stock shall then be

remilled for 5 ± 2 min on the mill described in

5.1 at a temperature appropriate for the

par-ticular compound The mill shall be adjusted

to give a sheet after cooling approximately 2.2

D 15

mm (0.085 in.) in thickness and the stock shall

be sheeted from the rolls

8.3 After mixing or remilling, the sheeted stock shall be placed on a flat clean metal sur-face and slabs shall be cut at least 3 mm (0.12 in.) less in width and length than the corre-sponding dimensions of the mold cavity Di-rection of the grain of the rubber shall be marked on each slab Slabs of uncured com-pounds shall be within ±3 g of the weight given in Table 2 when cured in the mold de-scribed in 9.2

9 Apparatus

9.1 Press-The press shall be capable of exerting a pressure of not less than 3450 kPa (500 psi) on the cavity areas of the mold dur-ing the entire period of vulcanization, and shall have heated platens of sufficient size so that no portion of the rubber will be nearer than 75 mm (3 in.) from the edge of the plat-ens during vulcanization The platen shall preferably be made of rolled steel bored for steam heating Either a self-bleeding trap or

a small vent shall be placed in the exit steam line to allow steam to flow continuously through the platens If chamber-type platens are used, the steam outlet shall be placed slightly below the steam chamber so that good drainage is assured The conduction of heat from the hot platens to the press crosshead shall be reduced as much as practicable by means of a steel grid between them, or by other means The pressing surfaces of the platen shall be plane parallel to within 0.24

mmjm (0.003 in./ft) when the platens are at

150 C (302 F) and closed under full pressure, with a grid of soft solder or lead wire between them

9.2 Mold-The mold shall have cavity tions similar in dimensions to that shown in Fig I, which gives sheets approximately 150

sec-by 150 sec-by 2 mm (6 sec-by 6 sec-by 0.08 in.) The ities to within 6 mm (0.25 in.) of the edges shall be between 1.9 and 2.0 mm (0.075 and 0.078 in.) deep The corners of the cavities may be rounded with a radius not greater than 6 mm (0.25 in.) An alternative type of test slab mold made by the cutoff bar method with a lower plate thickness of 19 mm (0.75 in.) is shown in Fig 2 The molding surfaces shall be clean, highly polished, and hard chro-mium plated The cover of the mold shall be

cav-a flcav-at plcav-ate cav-at lecav-ast I em (0.4 in.) in thickness

and preferably hinged to the cavity section to

minimize scratching of the mold ·surfaces

In-stead of a separate mold and cover, the

cav-ities may be cut directly into the platen of the

press Unless required, a mold lubricant shall

not be used on the mold surfaces When a

mold lubricant is required, only a

residual-type lubricant which does not affect the cured

slab should be used, and the excess lubricant

should be removed by curing and discarding

at least one set of sheets A silicone-type

lubri-cant ~r a mild soap solution have been found

satisfactory

NoTE 4-A film of suitable material, such as a

nonlubricated aluminum foil, 0.1 mm (0.004 in.)

thick, may be placed above and below the sheets

in the mold to prevent contamination with

materi-als remaining in the mold from previous cures If

foil is used, compensation in weights of

unvulcan-ized sheets should be made

10 Procedure

10.1 Bring the mold to the curing

tempera-ture within ±0.5 C (±0.9 F) in the closed

press, and hold at this temperature for at least

20 min before the unvulcanized sheets are

in-serted Verify the temperature of the mold by

means of a thermocouple or other suitable

temperature-measuring device inserted in one

of the overflow grooves and in intimate

con-tact with the mold Open the press, insert the

unvulcanized sheets into the mold, and close

the press in the minimum time possible

NoTE 5-When the mold is removed from the

press to insert uncured sheets, precautions should

be taken to prevent excessive cooling of the mold

by contact with cool metal surfaces or by exposure

to air drafts

10.2 The time of vulcanization shall be

con-sidered to be the period between the instant

the pressure is applied fully and the instant

the pressure is released Hold the mold under

a minimum pressure of 3450 kPa (500 psi)

on the ·cavity areas of the mold during

vul-canization As soon as the press is opened,

remove the vulcanized slieets from the mold

and cool in water (room temperature or lower)

or on a metal surface (for items to be used for

electrical measurements) for 10 to 15 min

Then wipe dry the sheets cooled in water and

reserve for test In both of the preceding

op-erations take care to prevent undue stretching

or deformation

10.3 Store vulcanizates of compounds

pre-0 15 pared in accordance with Part 8 at a tempera-ture of 23 ± 5 C (73.4 ± 9 F) and for the times shown in Table I Test vulcanizates of com-pounds mixed in the factory between 24 h and

60 days after vulcanization

Preparation of Pieces from Rubber Vulcanizates Other than Standard

Test Sheets

11 Scope 11.1 This method applies to the preparation

of a piece from a rubber sample that is not a standard vulcanized sheet These procedures should be used in conjunction with procedures

in ASTM Method D 412, Tension Testing of Vulcanized Rubber,< or other standard meth-ods of test, or in specifications for a particular article

12 Samples 12.1 Samples shall be obtained, if possible, from the product to be tested, and in such case shall be selected in accordance with the requirements of the specification covering the particular material In case it is not practicable

to obtain suitable specimens from the finished article, the manufacturer shall, upon request, furnish samples approximately 150 by 150 by

2 mm (6 by 6 by 0.08 in.) which he certifies to

be of the same material and equivalent cure used in the finished article

12.2 In case the finished article is obtained

by injection molding, the manufacturer shall,

on request, furnish injection molded samples that he certifies to be the same material and equivalent in cure to that used in the finished article The size of the injection molded sam-ples shall be agreed to by both the manufac-turer and the purchaser

13 Age of Samples 13.1 All tests shall be made using material that has been aged at least 24 h and not more than 60 days after vulcanization, except that, when the date of vulcanization is not known, tests shall be made within 60 days after de-livery by the manufacturer of the article rep-resented by the sample

13.2 Samples that have been buffed shall

be allowed to rest at ieast 30 min before

speci-• /974 Annual Book of ASTM Standards, Part 37

mens are cut for testing

14 Separation of Rubber

\4 l In certain tests it is necessary to

re-move the rubber from the fabrics or other

materials before conducting the test The

sep-aration shall be performed without the use of

a solvent, if practicable, and without excessive

stretching of the rubber The separation shall

be made a little at a time while the rubber is

gripped near the point of separation If it is

necessary to use a solvent in the separating

operation, commercial isooctane shall be

used If isooctane is used, the rubber shall be

placed so as to permit free evaporation of the

solvent from all parts of its surface, and shall

be allowed to rest at least \ h before being

tested

15 Buffing and Preparation of Material

l S.l Samples of rubber shall be buffed

when necessary to remove unevenness of

sur-face such as fabric impressions or corrugations

caused by contact with fabric components or

cloth wraps used for curing that would

inter-fere with measurements of thickness or other

tests Buffing is also applicable to reducing the

thickness of materials where it is necessary to

do so before testing, the removal of glaze or

skin coats from rubber where it may interfere

mm (S in.) in diameter, and revolving at a speed of 2500 to 3500 rpm Larger wheels may

be used, provided the speed is adjusted to give

a surface speed equivalent to a \25-mm (S-in.) wheel operating at 2500 to 3500 rpm The grinder shall also be equipped with a slow feed, in order that very little of the material will be removed at one cut The face of the wheel shall be kept sharp during operation

I 5.3 Procedure-The speed of the abrasive

wheel shall be 1200 ±200m (4000 ±700ft)/ min Finish the final buffed surface uniformly and smoothly Remove very little material by any one cut so as to avoid damage to the rub-ber by overheating Do not carry the buffing beyond the point at which the unevenness of gage just disappears, except in the case of thick materials Where it is necessary to re-duce the thickness of a sample for prepara-tion of test specimens, it may be desirable to slice the material to approximately the desired thickness before buffing Samples of material for preparation of specimens for tension test shall be buffed in strip form before cutting out the specimen

PART R-EVALUATION OF STANDARD AND NONSTANDARD MATERIALS

AND OF COMMERCIALLY AVAILABLE RUBBERS

16 Scope

16.1 These methods are intended for the

evaluation of standard materials described in

Part A, Section 3, and of nonstandard

mate-rials in a variety of rubbers Standard recipes

and procedures are given for use in

produc-tion control of commercially available rubbers

17 Standard Formulas and

Procedures-Natural Rubber

17.1 Standard formulas and time cycles for

mixing for the following natural rubber

com-pounds are given in Tables 3 and 4,

respec-tively:

Number Purpose or Description

I A Compound for classification of natural rubber

2A Gum compound

3A Channel black compound

4A Calcium carbonate compound

SA Electrically conducting compound 6A Resilient compound, 40 durometer hardness

7 A Resilient compound, 50 durometer hardness 8A Resilient compound, 60 durometer hardness 17.2 Method of Mixing-For mixing natu-

ral rubber compounds, proceed as follows, using the time cycles given in Table 4, and maintaining roll temperature at 70 ± S C (158 ± 9 F):

17.2.1 Pass rubber through the rolls twice, without banding, at a mill roll opening of 0.20

intervals to maintain an approximately

con-stant bank When about half the pigment is

incorporated and all dry pigment in the bank

has disappeared, make one 3/4 cut from each

side Then continue with the balance of the

pigment Be certain to add the pigment that

drops through to the mill pan (Note 2)

17 2.4 Add stearic acid

17 2.5 Add other materials

17.2.6 Make three 3/4 cuts from each side

17.2 7 Cut the batch from the mill Set the

opening at 0.8 mm (0.033 in.) and pass the

rolled stock endwise through the mill six

times

17.2.8 For compounds 3A to 8A, sheet the

batch to a minimum thickness of 6 mm (0.25

in.) and weigh For compounds lA and 2A,

sheet to 2.2 mm (0.085 in.)

17.3 Preparation of Compounds:

17.3.1 Condition compounds lA and 2A

for I to 6 h after mixing, prepare slabs as

shown in 8.3, and cure as shown in 17 4 Do

not remill

17.3.2 Condition compounds 3A to 8A for

I to 24 h, rem ill in accordance with 8.1,

con-dition 1 to 6 h, prepare slabs as shown in 8.3,

and cure as shown in 17.4

17.4 Recommended Standard Cures-10,

20, 40, and 80 min at 140 C (284 F)

18 Standard Formulas and

Procedures-Sty-rene-Butadiene Rubbers, Nonpigmented

Types

18.1 Standard formulas for mixing the

styrene-butadiene rubber compounds are

given in Tables 5, 6 and 7 Time cycles are

listed in Table 8

· 18.1.1 Table 5 contains Type A

formula-tions These are written on the basis of 100

parts of oil-extended masterbatch when such

a masterbatch is evaluated This method of

recipe formulation is used for simplicity of

op-eration in everyday quality control testing

18.2 Table 6 contains the equivalent recipes

of Table 5 when the various OE-SBR's are

used in formulation 9B These formulations

are expressed on a 100 part rubber basis

Rubber refers to the commercial nonoil

ex-tended material with a few percent of

nonrub-ber content The formulations are expressed in

this way so the content of each material is

clearly indicated on the PHR (parts per

0 15

hundred rubber) basis Table 6 is therefore cluded mainly for information purposes 18.3 Table 7 contains Type B standard formulations These are consistent with cur· rent compounding practice in regard to sulfur and accelerator content The report should clearly state whether Type A or Type B stand-

in-ard formulations are used

18.4 Preparation of Compo!)ite Samples for Physical Testing-This procedure de-

scribes the method of making a composite sample of a specific lot of SBR for specifica-, tion testing It is not necessary for in-plant quality or control testing

18.4.1 Take samples for physical testing from the lot according to the procedure de-scribed in ASTM Method D 1485, Sample Preparation of Solid Raw Rubbers!

18.4.2 Blend a minimum of 1000 g of the unpremasticated bale samples by passing five times through a roll mill set at 3 mm (0.120 in.) Roll up the rubber between passes and pass endwise through the mill

18.5 Method of Mixing-The mill mix

batch size shall be determined by the batch factor shown in Tables 5 or 7 The batch size

is calculated by multiplying the formulation total weight by the batch factor For mixing nonpigmented styrene-butadiene rubber com-pounds, use the following procedure with the mill roll temperature maintained at 50 ± 5 C (122 ± 9 F) and the time cycle specified in Table 8

18.5.1 Band with mill opening at I mm (0.045 in.) and make 3/4 cuts every 1/2 min from alternate sides (All mill openings shown are approximate and should be adjusted to maintain a good working bank at the nip of the rolls.)

18.5.2 Add sulfur slowly and evenly across the rubber

18.5.3 Add stearic acid Make one 3/4 cut from each side after stearic acid is added 18.5.4 Add carbon black evenly across the mill at a uniform rate When about half the pigment is incorporated, open the mill to 1.25

mm (0.050 in.) and make one 3/4 cut from each side Then add the remainder of the pigment When all the pigment has been incorporated, open the mill to 1.4 mm (0.055 in.) and make

a 3 /4 cut from each side Be certain to add the pigment that drops through to the mill pan

18.5.5 Add other materials at a 1.4-mm

(0.055-in.) setting

18.5.6 Make three 3/ , cuts from each side

18.5.7 Cut the batch from the mill Set the

opening at 0.8 mm (0.032 in.) and pass the

rolled stock endwise through the mill six

times

18.5.8 Open the mill to give a minimum

stock thickness of 6 mm (0.25 in.) and pass

the stock through four times, folding it back

on itself each time Weigh the batch and record

the weight If outside ± 1.0 percent reject

the batch From the stock, cut enough sample

to allow for testing of compounded viscosity

as described in ASTM Method D 1646, Test

for Viscosity and Curing Characteristics of

Rubber by the Shearing Disk Viscometer.'

18.5.9 Sheet off at 2.2 mm (0.085 in.)

finished thickness, cool on a flat metal surface

ll\.6 Preparation ofCompounds in

18.7.1-Condition all compounds as prescribed in

Ta-ble I, rem ill factory mixes in accordance with

8.1, and prepare slabs in accordance with 8.3

and cure as shown in 18.7.1

18.7 Recommended Standard Cures:

18.7 I Stress-Strain Properties-Vulcanize

the sheets in accordance with Section 8 and 10

for 25, 35, and 50 min at 145 C (293 F) and

measure tensile strength, ultimate elongation,

and stress at 300 percent elongation in

accord-ance with Method D 412

18.7.2 Viscometer Cure-An alternative to

measuring the stress-strain properties of

vul-canizates cured for 25 and 35 min is the

meas-urement of the time of incipient cure and cure

index at 150 C (302 F) in accordance with

Method D 1646

18.7.3 Cure Meter-A second alternative to

measuring the stress-strain properties of

vul-canizates is the measurement of vulcanization

parameters at 160 C (320 F) in accordance

with ASTM Method D 2084, for

Measure-ment of Curing Characteristics with the

Os-cillating Disk Cure Meter.' Values of ts2, tc

(50), tc (90), M H and M L shall be determined

19 Standard Formula and

Styrene-Butadiene Rubbers,

Types

Pigmented

Procedure-19.1 Standard formula and time cycle for

mixing pigmented styrene-butadiene rubber

pig-19.2.1 Band the unmassed masterbacth on the front roll with the mill set at 1.4 mm (0.055 in.) and break down without cutting 19.2.2 Add sulfur and zinc oxide slowly and evenly across the rubber

19.2.3 Add stearic acid and make one %

cut each side after the stearic acid is added 19.2.4 Add the accelerator

19.2.7 Open the mill to give a minimum stock thickness of 6 mm (0.25 in.) and pass the stock through the mill four times, folding

it back on itself each time Weigh the batch 19.2.8 Cut from the batch enough sample

to allow testing for compound viscosity and viscometer cure in accordance with Method

D 1646, or for cure meter characteristics in accordance with Method D 2084, or both 19.2.9 Band the remaining stock on the mill and sheet off at 2.2 mm (0.085 in.) fin-ished thickness and cool on a flat dry metal surface for use in preparing vulcanized stress-strain sheets Prepare sheets in accordance with 8.3

19.3 Condition and Cure of

Compounds-Condition all compounds as prescribed m Table I Cure in accordance with 19.4

19.4 Recommended Standard Cures:

19.4.1 Stress-Strain Properties-Vulcanize

the sheets in accordance with Sections 8 and

10 for 25, 35, and 50 min at 145 C (293 F) or

20, 25, and 40 min at 150 C (302 F) (Note 6) and measure the tensile strength, ultimate

elongation, and stress at 300 percent elongation

in accordance with Method D 412

NOTE 6-The series of cures at 150 C (302 F)

does not necessarily give results equal to those at

145 C (293 F)

19 4.2 Viscometer Cure-An alternative

to measuring the stress-strain properties of

vulcanizates is the measurement of the time

of incipient cure and cure index at 150 C (302

F) in accordance with Method D 1646

19.4.3 Cure Meter-A second alternative

to measuring stress-strain properties of

vul-canizates is the measurement of vulcanization

parameters at 160 C (320 F) in accordance

with ASTM Method D 2084, Measurement of

Curing Characteristics with Oscillating Disk

Cure Meter• The frequency of rotary

oscil-lation of the cure meter disk shall be constant

at 1.7 Hz (100 cpm) Values of 15 (2), lc (50), lc

(90), M H and M L shall be determined

20 Standard Formulas and

Procedures-Neo-prene Rubber

20.1 Standard formulas and time cycles for

mixing for the following neoprene rubber

compounds are given in Tables II and 12,

20.2 Method of Mixing-For mixing

neo-prene compounds, proceed as follows, using

the time cycles given in Table 12, and

main-taining roll temperature at 50 ± 5 C (122 ±

9 F):

20.2.1 Band neoprene with mill opening at

1.5 mm (0.060 in.)

20.2.2 Add magnesium oxide

20.2.3 Add antioxidant (phenyl beta

naph-thylamine)

20.2.4 Add stearic acid

20.2.5 Add carbon black evenly across the

rolls at a constant rate, and open the mill at

intervals to maintain an approximately

con-stant bank When about half the black is

in-corporated and all dry black in the bank has

disappeared, make one 3/4 cut from each

side Then continue with the balance of the

black, being certain to add all the black that

drops through to the mill pan (Note 2)

20.2.6 Add zinc oxide

D 15

20.2.7 Add 2-mercaptoimidazoline

20.2.8 Make three 3/4 cuts from each side 20.2.9 Cut the batch from the mill Set the opening at 0.8 mm (0.032 in.) and pass the rolled stock endwise through the mill six times

20.2.1 0 Sheet off at 2.2-mm (0.085-in.) ished gage, cool on a fiat metal surface, and prepare samples for cure in accordance with 8.3

fin-20.3 Preparation of

Compounds-Condi-tion the compounds for I to 6 h after mixing, prepare slabs as shown in 8.3, and cure as shown in 20.4 Do not remill.·

20.4 Recommended Standard Cures-15,

compounds, proceed as follows, using the time cycles given in Table 14, maintaining roll tem-perature at 40 ± 5 C (104 ± 9 F): ·

21.2.1 Band rubber with mill opening of 0.65 mm (0.025 in.)

21.2.2 Mix carbon black and stearic acid and add evenly across the rolls at a constant rate Open the mill at intervals to maintain

an approximately constant bank When all the pigment has been added, make a 3

/4 cut from each side Be certain to add all the pig-ment that drops through to the pan (Note 2) 21.2.3 Add other materials

21.2.4 Make three 3/4 cuts from each side 21.2.5 Cut the batch from the mill Set the opening at 0.8 mm (0.032 in.) and pass the rolled stock endwise through the mill six times

21.2.6 Sheet off at 2.2-mm (0.085-in.) ished gage, cool on a fiat metal surface, and prepare samples for cure in accordance with 8.3

fin-21.3 Preparation of

Compounds-Condi-tion the compounds for I to 6 h after mixing,

prepare slabs as shown in 8.3, and cure as

shown in 21.4

21.4 Recommended Standard Cures-The

recommended cures for the recipes shown in

Table 13 are, respectively:

22.1 A standard formula and mixing

pro-cedure for the following nitrile rubber

com-pound is given in Tables 15 and 16,

respec-tively:

Number

IF' Gas furnace compound Purpose or Description

22.2 Method of Mixing-For mixing nitrile

rubber compound IF, proceed as follows,

using the cycle as given in Table 16, and

main-taining roll temperature at 50 ± 5 C (122 ±

9 F):

22.2.1 Pass rubber through the rolls twice,

without banding, at a mill roll opening of 0.20

mm (0.008 in.)

22.2.2 Band with mill opening at 1.4 mm

(0.055 in.) and break down

22.2.3 Add stearic acid

22.2.4 Add zinc oxide, sulfur, and

benzo-thiazyl disulfide

22.2.5 Make one 3/4 cut from each side

22.2.6 Add black evenly across the rolls at

a constant rate, and open the mill at intervals

to maintain an approximately even bank

When about half the black is incorporated

and all the dry pigment in the bank has

dis-appeared, make one 3/4 cut from each side

Be certain to add all the pigment that drops

through to the mill pan Then continue with

the balance of the black (Note 2)

22.2.7 Make three 3/4 cuts from each side

22.2.8 Cut the batch from the mill Set the

opening at 0.8 mm (0.032 in.) and pass the

rolled stock endwise through the mill six

times

22.2.9 Sheet off at 2.2-mm (0.085-in.)

fin-ished gage, cool on a flat metal surface and

prepare samples for cure in accordance with

22.4 Recommended Standard Cures-10,

pro-Number Purpose or Description

I H For evaluation of solution polybutadiene bers

rub-For mixing by Internal Mixer (Method A and B) use recipe weight outlined in 6.1 and 6.2 For mixing by laboratory mill, use a batch size four times the recipe weight-Method C

23.2 Method of Mixing-The mill handling characteristics of the polybutadienes is some-what more difficult than for other polymers Mixing is more easily accomplished in an in-ternal mixer Results from mill mixing in some instances may not correlate with results obtained from Banbury mixing The following three mixing procedures are offered:

Method A -Internal Mixer for initial and final mix

Method B Initial Internal Mixer with final mill mix

Method C -Mill mix

For mixing in an internal mixer refer to 6.1 for equipment description For mixing on a mill refer to 5.1 See Table 18 for time cycles involving each step of the mixing procedure 23.3 Internal Mixer for Initial and Final Mix-Method A:

23.3.1 Initial Mix Procedure-Stage 1:

23.3.1.1 Adjust the Banbury temperature

to achieve the discharge conditions outlined

in 23.3.1.4 Close the discharge gate, start the rotor, raise the ram, and charge the ingredi-ents as described

23.3.1.2 Charge one half the polymer, zinc oxide, carbon black, oil, stearic acid, and the balance of the polymer Lower the ram 23.3.1.3 Raise the ram and clean the mixer throat and the top of the ram Lower the ram 23.3.1.4 Discharge the batch at 165 ± 5 C (330 ± 9 F) or 6 min, whichever occurs first 23.3.1.5 Pass the batch immediately through a laboratory mill three times as de-scribed in 5.1 set at 5.0 mm (0.20 in.) and 50

± 5 C (122 ± 9 F) Check the weight of the

batch as described in 5.4

23.3.1.6 Rest the stock for 1

/2 h minimum

23.3.2 Final Mix Procedure-Stage 2:

23.3.2.1 Cool the Banbury with full

cool-ing water on the rotor to 40 ± 5 C ( 104 ±

9 F), start the rotor, raise the ram, and charge

the materials as described

23.3.2.2 Leaving the cooling water on and

the steam off, charge one half the

master-batch, with all the sulfur and accelerator

rolled into this portion of the masterbatch

before feeding to the mixer Add the

remain-ing portion of the masterbatch Lower the

ram

23.3.2.3 Discharge the batch at 110 ± 5 C

(230 ± 9 F) or 2 1/2 min, whichever occurs

first

23.3.2.4 Pass the batch immediately

through a laboratory mill described in 5.1 set

at 0.8 mm (0.032 in.) and 50 ± 5 C (122 ±

9 F)

23.3.2.5 Reroll the batch and pass the

batch endwise through the mill ten times

without banding

23.3.2.6 Sheet the stock to a minimum

thickness of 6 mm (0.25-in.)

23.3.3 Preparation of

Compounds-Condi-tion the compounds for I to 6 h after mixing,

prepare the slabs as shown in 8 I, and cure

23.4.1 Initial Mix Procedure-Stage I:

23.4.1.1 Follow the procedure outlined in

23.3.1

23.4.2 Final Mill Mix-Stage 2:

23.4.2.1 With the mill roll set at 50 ± 5 C

(122 ± 9 F) and 1.5 mm (0.06 in.) add the

materials as described Adjust the batch

weight to four times the recipe weight

23.4.2.2 Add the sulfur and accelerator

slowly to the batch

23.4.2.3 Make six 3/4 alternate cuts

23.4.2.4 Cut the batch from the mill and

set the mill roll opening at 0.8 mm (0.032 in.)

Pass the stock through the rolls endwise five

23.5 Mill Mix Procedure-Method C:

23.5.1 With mill roll temperature set at 50± 5 C (122 ± 9'F) and 1.3 mm (0.05 in.), add ingredients as described

23.5.2 Band polymer on front roll

23.5.3 Add zinc oxide and stearic acid evenly across the rolls Make two 3

/ 4 cuts from each side

23.5.4 Add the carbon black evenly across the rolls until 1/2 the carbon black has been added Open the rolls to 1.8 mm (0.07 in.) and continue the carbon black addition, being cer-tain that all the black that drops through to the mill pan is added Make two 3/4 cuts from each side, allowing 30 s between each cut

23.5.5 Add the oil slowly

23.5.6 Add the sulfur and accelerator 23.5.7 Make six successive 3

/ • cuts from each side

23.5.8 Cut the batch from the mill Set the mill roll opening at 0.8 mm (0.032 in.) and pass the rolled stock endwise through the mill six times and check the weight

23.5.9 Sheet the stock to a minimum ness of 6 mm (0.25 in.)

pro-Number Purpose or Description 1-1 Oil furnace black (HAF type) compound 24.2 Method of Mixing-For mixing poly-isoprene rubber compound 1-1, proceed as follows, using the cycle as given in Table 20, and maintaining roll temperature at 70 ± 5 C (158 ± 9 F):

24.2.1 Pass the rubber through the rolls twice without banding, at a mill roll opening

of 0.5 mm (0.020 in.)

24.2.2 Band the rubber on the front roll

with the mill opening at 1.4 mm (0.055 in.)

Make two 3 14 cuts from each side

NoTE 7 -Some types of polyisoprene go to the

back roll in which case the stearic acid should be

added and after incorporation can usually be

trans-ferred to the front roll Also tougher types may

re-quire slightly longer breakdown before addition of

other pigments

24.2.3 Set the mill opening at I 7 mm

(0.067 in.) Add stearic acid and that which

falls into mill pan Make one 3

14 cut from

each side

24.2.4 Add zinc oxide and sulfur and that

which falls into the mill pan Make one 3

14 cut from each side

24.2.5 Add half of the dried carbon black

evenly along the bank of rubber at a uniform

rate When about half the black has been

added, open the mill to 1.9 mm (0.075 in.)

When all the unincorporated black in the bank

has disappeared, make one 3 14 cut from each

side and then add the other half of the black

as above Sweep the mill pan and add the

black When all the black has been

incorpo-rated, make one "I 4 cut from each side

24.2.6 Add the accelerator, taking care to

avoid any loss Sweep the mill pan and add

until all the pigment is in the batch Make

three 314 cuts from each side

D 15

24.2 7 Roll the stock from the mill, weigh and record the percent gain or loss from the recipe batch weight If it is outside ± 1.0 per-cent, reject the batch

24.2.8 Set the mill opening at 0.8 mm (0.032 in.) Roll and pass the stock endwise through the mill six times

24.2.9 Sheet off at 2.2 mm (0.085 in.) ished thickness, cool on a flat metal surface, and prepare the samples for cure in accord-ance with 8.3 and cure as shown in 24.3.1 24.3 Recommended Standard Cures:

fin-24.3.1 Stress-Strain Properties- Vulcanize

the sheets in accordance with Sections 8 and

10 for 20, 30, 40, and 60 min at 135 C (275 F) and measure the tensile strength, ultimate elongation, and stress at 300 percent elonga-tion in accordance with Method D 412 24.3.2 Viscometer Cure-An alternative to

measuring the stress-strain properties of canizates is the measurement of the time of incipient cure and cure index at 150 C (302 F)

vul-in accordance with Method D 1646

24.3.3 Cure Meter-A second alternative

to measuring the stress-strain properties of vulcanizates is the measurement of vulcaniza-tion parameters at 150 C (302 F) in accordance with Method D 2084 Values of t."' lc(50),

lc(90), M H, and M L shall be determined

PART C-EVALUATION OF CARBON BLACKS IN NATURAL RuBBER

25 Scope

25.1 These methods are for testing carbon

blacks when incorporated in rubber They

may be used for checking the properties of

the blacks being produced by the

manufac-turers or for testing shipments of blacks as

received by a consumer

25.2 These procedures involve the

incor-poration of the black to be tested in rubber

along with the necessary auxiliary agents to

permit vulcanization, followed by testing All

materials except the black to be tested are

reference materials of controlled and uniform

properties as described in Part A of these

methods Along with each test black or series

of test blacks, a corresponding stock

contain-ing the reference black is included The

dif-ferences between the properties obtained on

the reference black and test black are noted

The methods do not imply that the reference

black has desirable properties nor that duction of blacks should be directed to match its properties The use of a reference black is simply a device to cancel the inevitable vari-ations in test results which are due to minor variations between laboratories in equipment, procedures, and ambient conditions

pro-26 Standard Formula

26.1 The standard formula and miXIng method for testing carbon blacks are given in Tables 17, 18, and 19, respectively

26.2 The carbon black shall be conditioned

de-~~~~ D 15

27 1.1 Set mill opening at 1.4 mm (0.055

in.) and adjust and maintain roll temperature

at 70 ± 5 C (158 ± 9 F)

27 1.2 Add rubber and band on mill

27 1.3 Add stearic acid and cut once each

way

Natura\ rubber' Zinc oxide (NBS 370) Stearic acid (NBS 372) Sulfur (NBS 37\)

Benzothiazy\ disulfide (NBS 373)

100.0 5.0 3.0 2.5 0.6 'Available from the Firestone Tire and Rubber Co Specially selected Liberian crepe with 600 percent modulu~

of 700 ± \00 psi when tested in compound \A

27.1.4 Add sulfur, accelerator, and zinc

oxide and cut twice each way The masterbatch may be prepared either in

27 1.5 Add black Open the mill gradually conformance with 27 I using a mill mixing

to maintain an approximately constant bank method or in an internal mixer as follows and cut three times each way after all the _using the time cycle as given in Table 24: ' black is in Be certain to add all the pigment 28.1.1 Regulate the temperature on the that has dropped through to the mill ·pan rotors and shell to obtain a dump temperature

27 1.6 Cut stock, roll, and weigh If the 28.1.2 Add rubber

weight is outside the tolerance of ± 1 percent, 28.1.3 Add benzothiazyl disulfide

27.1.7 Pass endwise six times at 0.8-mm 28.1.5 Add zinc oxide

(0.032-in.) opening and sheet off to 2.2-mm 28.1.6 Add sulfur

(0.085-in.) finished gage Cool on a metal 28.1.7 Dump

table top and prepare samples for cure as 28.1.8 Sheet immediately from the mill set shown in 8.3 at a mill opening of 6 to 10 mm (0.25 to 0.4 27.2 Internal Mixer-For mixing in an in.), and allow to cool to room temperature internal mixer, as described in 6.1, proceed before piling or stacking

as follows, using the time cycle as given in 28.2 For incorporation of black into the

27 2.1 Regulate the temperature on the batch size that is four times the recipe weight, rotors and shell to obtain a dump tempera- proceed as follows, using the time cycle as ture between 110 and 125 c (230 and 257 F) given in Table 25:

27.2.2 Add rubber 28.2.1 Set the mill opening at 1.4 mm 27.2.3 Add benzothiazyl disulfide (0.055 in.) and adjust and maintain the roll 27.2.4 Add stearic acid temperature at 70 ± 5 C (158 ± 9 F) 27.2.5 Add the zinc oxide and half the 28.2.2 Add masterbatch and band on mill

27 2.6 Add remainder of the black 28.2.4 Add black Open the mill gradually 27.2.7 Add sulfur so as to maintain a constant bank Be certain 27.2.8 Dump to incorporate all the black that has dropped 27.2.9 Sheet immediately from the mill set through to the mill pan After all the black

at a mill opening of 2.2 mm (0.085 in.) and a has been worked into the batch, cut three roll temperature of 70 ± 5 c (158 ± 9 F) times each way (Note 2)

Band, cut, roll up, and weigh If the weight 28.2.5 Cut stock from the mill, roll up, and

is outside the tolerance of ± 1 percent, re- weigh If the weight is outside the tolerance ject the batch of ±I percent, reject the batch

27.2.10 Pass endwise six times at a 0.8-mm 28.2.6 Pass through the mill endwise six (0.030-in.) opening times at a 0.8 mm (0.032 in.), cool on a flat 27.2.11 Sheet off at 2.2-mm (0.085-in.) fin- metal surface, and prepare specimens for ished gage, cool on a flat metal surface, and cure as described in 8.3

prepare specimens for cure as described m 28.3 For incorporation of black into the

28 Preparation and Use of Masterbatches ·

28.1 A masterbatch of the following

com-position may be used:

as follows, using the time cycle as given in Table 26:

28.3.1 Regulate the mixer to obtain a dump temperature between 110 and 125 C (230 and