ISO 48-4:2018 download free.Rubber, vulcanized or thermoplastic — Determination of hardness — Part 4: Indentation hardness by durometer method (Shore hardness).
Introduction
ISO/TC 45/SC 2 established a principle that It would hi helpful For users ii standards on the same subject but coverrng dllIcrcnt aspects or methods were griiupcd together, preferably with an Introductory guidance standard, rather than being scattered throughout the numbering system. This has been achieved for some subiects. for example euremeters (1SF) 6502) and dynamic properties ISO 4664).
In 2017. it was decided to group standards br hardness and. xuhisesucnLly. it was agreed that they would he grouped under the 150411 niiniber, The new standards together with the previously numbered standards are listed bclnw.
— ISO 411-1: former ISO 111517
— 150 411-2: homer ISO 411
— ISO 48-3: tninwr ISO 27588
— ISO 411-4: former ISO 7619-1 ISO 48-5: hornier ISO 7619-2
— ISO 48-6: former 150 7267-1
— ISO 48-7: former ISO 7267-2
— ISO 48.8: lormer ISO 7267-3
— ISO 411-9: tornwr ISO 11189$
The hardness of rubber, as measured by a duronieter (Shore hardness) or .in IRHP pocket meter. is determined from the response of the rubber to an applied indentation The response is complex and will depend on:
a) the elastic modulus of the nihber
h) the viscoebstic properties of the rubber;
c) the thickness of the test piece;
d) the geometry of the indcntor.
e) the pressure exerted:
F) the rate of increase ol pressure;
g) the interval alter which the hardness Is recorded.
lkcausc aithiese factors. it is inadvisable to relate results using .i durometer (Shore hardness) directly to 18111) values, although correlations have been estihlished br some individual rubbers and compounds.
Durometers were originally portable hand-held instruments that have proved to he p.irtlctibrly convenient for making measurements on products, Ily now a lot of laboratories also use theni on a stand with a weight applied to the pressure loot in order to improve precision significantly.
NOTF ISO 4112 speullies hard,w-ss measurements for determination of hardness betwccn 10 18111) and
100 18110 Further information on thy relationship between the duromcter values and 18111) values is given in
References ISII6lrZI
WARNING I — Persons using this documeni should he lamiliar with normal laboratory practice. This docunieni does not purport to address all olthe salely problems. irany, associated with its use. his the responsibility of the user to establish appropriate safety and health practices and to determine the applicability olany other restrictions.
WARNING 2— Certain procedures specilled in this document might hwolve the use or generation of substances, or the generation of waste. thai could constitute a local environmental hazard. Reference should be made to appropriate ducunwutation on sate handling and disposal after use.
I Scope
ISO 48-4 specifies a method for determining the itidentation hardness (Shore hardness) of vulcanized or thermoplastic rubber using durometers with the following scales:
— the A scale for rubbers in the normaIhardness range;
— the I) scale for rubbers in the high-hardness range;
— the At) scale For rubbers in the low-hardness range and for cellular rubbers;
— the AM scale for thin rubber test pieces in 11w nurmal•hardness range.
2 Normative references
The Following documents arc referred to in the text iii such a way that some or all of their content on%(itutes requirements of this docunicnt For dated references, only the edition cited applies For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 48.9. Rubbe,: vuk’un,zed or thc’rrrwpiustfr — Determination of Iwrthwss — Part 9: calibratiot, and u’er,fEcuL Ion of hardness testers
ISO 23529, Rubber— Cteneruf piswedurc’sfrwpreporim and uinditaonmg test pieces lot physicultesi methods
3 Terms and definitions
No terms and definitions are listed in ISO 48-4.
ISO and IlC maintain terminolngical databases 11r use in standardization at the Following addresses-
4 Principle
An indentor at specilwd dinwnseons is pressed mb . test piece under a speifiect load and (he depth of Indentation measured. ISO 48-4 is converted to a hardness value by means ala specified relation,
5 Choice of durometer
When using do rurneters. the scale should be dioseii as follows:
— for values less than 20 with a type I) durnnieter: type A:
— tar values less than 20 with i type A duronwter: type A0;
— (or values over 90 wIth a type A durometer: type Li;
— for thin test pieces (less ihan 6mm thick): type AM.
6 Apparatus
61 flurornetcr types A, U and 40
These durometers consist of the components specified in JJ. to £1_S.
6.1.1 Pressure loot
The pressure fool br types A and 1) shall have a dumeter at 18 mm ± 0.5 mm and a central hole at diameter 3mm ± 0.1 mm. For type 40, the pressure loot shall have a minimum area of 500 mm2 with a central hole of diameter 5.4 mm t 0.2 mm. The tolerances on the dimension of the central hole and the requirement for the size of the pressure foot only apply to instruments used on a stand.
6.1.2 loden br
The indentor shall he formed train a hardenedsteel rod of diameter 1,25 mm ± 0.15 mm to the shape
and dimensions shown in Fgure liar type A durometers and FIu 2 for type Li duromvters. 1’pe 40
uurometers shall have a round endentor with a radius of 2.5 mm ± 002 mm in accordance with Figu 1.
6.1.3 IndicatIng devIce
This is a device for allowing the extent of protrusion iii the iint of the Indentor beyond the lace of the pressure foot to be read. It shall be calibrated directly In terms of units ranging from 0 fur the maximuni protrusion of 2.50 mm ± 0.02 mm to lOt) for zero protrusion obtained by placing the pressure fool and indciitar in firm contact with a suitable flat, hard surface (e.g. glass).
6.1.4 Calibrated spring
l’hls IS USed to apply a force. F. expressed In millinewtons. to the itidentor in accordance with one of the
following formulae:
— Far type A durometers:
F= 550 + 75II
where H5 is the hardness reading taken from the type A durunieter.
— For type F) duronwters:
F= 44511p,
where 11D is the hardnes. reading Lken 1mm the type fl durometer.
— Fur type AO durorneters:
F. SSO • 7511A0
where Is the hrdiwss reathng taken from the type AO dutunwtcr
NOTE The rubber industry uses the term equIIIun Icr the reLationships herein termed lormula. The term lormula is used to describe the table ol Ingredients In a rubber compound.
6.1 .S Automatic timing device (optional)
The timer shall be automatically activated when the pressure foot is in contact with the test piece and shall indicate the end of the test time or lock the test value at its completion. Use ot a timing device for the test time improves precision. When the instrument is used on a stand, the time tolerance shall he ±O,3s.
6.2 Durometer type AM
This duromcter consists of the components specified in 2d tn2.5.
6.2.1 Pressure foot
The pressure foot shall have a ilianieter f 4) rum ± 0,3 mm and a centr.il hole of diameter 1,19mm ±0,03mm.
6.2.2 lndentor
The indentor shall he formed from a hardened-steel rod of di.imeter 079 mm ± 0,025 mm to the shape and dimensions shown in Figure 4.
6.2.3 Indicating device
This is a device for allowing the extent of protrusion of the point of the indentor beyond the face at the pressure loot to he read, Ii shall be calibrated directly in terms of units ranging from 0 for the maximuni protrusion of 1,25 mm : (1.01 mm to 100 liii zero protrusion obtained by pLwtng the pressure foot .,iitf indetitor in firiii contact with a stiitabk’ flat, hard surface (e.g. glass).
6.2.4 Calibrated spring
This is used to apply a force, F, expressed in milliiiewttrns. 10 the Itidetitor in acwrdance with the formula:
F. 324 •
where “AM Is the hardness reading taken Ironi the type AM durometer.
NOTE The rubber industry uses the term equation for the relationships herein termed turmula The term lormula is used to describe the table of Ingredients in a rubber compound.
6.2.5 Autoniatlc liming device (option.il)
The Inner, it used, shall he automatkally acttvated wheti the pressure toot is In coiltact with the test piece .mcl shall indicate the end of the test tinie or lock the test value it Its completion. Use of a tintIng device for the test time Improves precision, The time tolerance shall be ±03 s.
6.3 Stand
6.3.1 The original concept of a duromeler was a portable Instrunwnt that could be used, for example. on a product in service. However, better precision caii be expected by using a stand with a weight centred on the axis of the indentor to apply the pressure toot to the Lest l)iLTe. Durumeter types A, Dand AO may be used either as hand-held Instruments or mounted on a stand, Type AM dLirometers shall always be mounted on a stand. Clearly, when a stand is used, the portability is last.
NOTE As a general trend, it can be expected that the precision will hslhiw the order:
Hand held duromewr Hand held durometer equipped with torce.calibratrd hand-gnp c fluromcter using a stand c Durnmeter equipped with a timer and using a stand.
Precision is affected by a number of lactors. including parallax error, time of load application, speed of applying the load to the foot and orientation of the test piece. A detailed study of the reproducibility of rubber hardness tests can be found in Reference (UJ.
6.3.2 The operating stand shall he capable of supporting the pressure-foot surlace of the durnmeler parallel to the test piece support table.
63.3 The stand shall be capable of applying the test piece to the indentor. or vice versa, without shock NOTE A inasimuni speed of 3.2 nm/s has been found to be suitable
6.3.4 The Lat,il iliass o[tlw dururneter antI extra itiass La overtoitie the spring farce shall be:
— kg for types A and Aft
— Sjkgfcrtypel);
— kgfortypeAM.
6.4 Durometer spring force calibration
The force values shall he in accordance with Thlo
7 Test pieces
7.1 General
Test pieces shall be prepared in accordance with 1St 23521).
7.2 Thickness
For the determination of hardness using type A, I) .nd AC) durometers. the thickness ol the test piece shall be at least 6 mm.
For the determination ot hardness using type AM durometers, the thickness of the test piece sh.ill 1w at least 1.5 mm.
For sheets thin ncr than 6mm and 1,5 rnni (sec above), the test piece may be composed of not more than three layers, in order to obtain the necessary thickness. Howevet determinations made on such test pieces might not agree with those made on single’laycr test pieces.
For ompararive-test purposes. the test pieces shall 1w similar.
NO1’I Mt’asairerncnts made on thin last pk’ces olsoit rubhcr will he in(Ii,rmed by the support tahicand will
give at result wlilih is us, high
7.3 Stirlace
The other dimensions oIthe test piece shall he suIt icient to permit nw,isurements at least 12 mm away from any edge (or types A and ft .ind IS mm and 4,5 mm away front any edge Iór type AO and type AM. respectively.
The surface ulthe test piece shall be Flat and parallel over an area sufficient to pennit the pressure loot to conic into contact with the test piece aver an area having a radius ulat feat 6 mm from the andcntor point for types A and ft 9 mm for type AU and 2.5 mm br type AM.
Satisfactory hardness determinations cannot he made on rounded, uneven or rough surlaces using durometers. however, their use in certain specialized applications is recognized, e.g. ISO 48-7 for the determirtailun oltlw hardness olrubber-tovered rolls. In such applications. the hmltatiuns to their use shall be dearly identified.
H Conditioning and test temperature
I’or all test purposes, the minimum time between vulcanization and testing shall 1w 16 h. Where practical. test pieces shall be conditioned immediately before testing fur a meflifliurn period oil h at one of the standard laboratory temperatures specified in ISO 23529. The same lemperatLire shall he used throughout any single test or series of tests intended to be comparable.
9 Procedure
9.1 General
Plate the test piece on a flat, hard. rtg,d surface (e.g. glass), Apply the pressure foot to the test piece, or s’lce versa, as rapidly as possible but without shock, keeping the foot parallel to the surface of the test piece and ensuring that the indentor Is normal to the rubber surface.
9.2 Test Lime
Apply a force in accordance with 6.33 and 2.3 suIt Icient only Lu obtain firm contact between the pressure loot and the test piece and take the reading at the specified time alter the pressure foot is in firm contact with the test piece. The standard test time is 3 s for vulcanized rubber and IS s for thermoplastic rubber. Other test limes may he used, provided they are stated in the test report. Rubbers of unknown types should he treated as vulcanized.
NOTI I A test time of iSs has been iniruduted for thermoplastic rul,her hec-ause the hardness valurcontlnuc”, todrerraw over Iongrr period ol 1mw ih,in lor vulraiiizril rubber, this lest time being the sanw .is that spcilied mr plast its in ISO H4B.
NOTI 2 II a tlow curve is recorded for at least 15 s (hardness every 0.1 s) br ni unknown material, the appropriate nwasuringtinw(3 sor ISs) can 1w selected instead ailtreating it as vuItaiiied
9.3 Measurenients
Make three (known material) or five (unknown material] measurements of hardness at different positions on the test piece at least 6 mm apart lot’ types A, P and AO and at least 0.11 mm apart for type AM. and determine the median value.
If the time interval alter which each reading was takeit Is dilferent from 3 a. record the individual values ol the indentation hardness togetlwr with the I nw interval after which each reading was taken. and determine the median value and the maxinuim ,inil tuinimitni values tthtaincd.
10 Calibration and checking
10.1 Cahlbralig,n
The instrument sh.ill he calibrated regularly using suitable instruments [or measuring force. Indentation depth and indenter geometry in accordance with ISO 4B9.
N4)Tl’ Abrasive material can siningly wear the itidenter, Therefore. recalibraijain air replatemeni ol the mndenser can he needed more o(tcn than the standard frequency.
10.2 Checking using standard rubber blocks1)
Press the Instrument against a suitable hat. hard curtace (e.g. glass) and .idiust, where possible. the reading on the sale to give a value of 100.
Continue the instrument check using a set of standard rubber blocks covering the measurement range. All adluslinents shall he niade in acr-nrdance with the manufacturer’s instructions. The set iii standard rubber blocks used shall consist ol at least three reference blocks in a suitable covered container away from light, heat, nil and grease. The reicrenec blocks shall he recalibrated once a year. or If the mean value deviates more than one unit compared with the certificate of the reference blocks. The calibration of the reference blocks needs to he done with a reference measurement device of an accredited laboratory. Instruments in regular use shall he checked a; least each week against standaril rubber blocks.
11 Precision
Sec Annex A
12 Test report
11w lest report shall include the following inlormalion:
a) sample details:
1) a full description of the sample and its origin:
2) a description of the test Piece, including its thickness and, in the case of a composite test piece, the iiumber of layers;
b) the test method used, i.e. the reference number ol this document (1St) 48.4:2018);
c) test details:
1) the temperature 01 test, and the relative humidity when the hardness of the material is dependent on the humidity;
2) the type of instrument used, Including whether it was hand’held or on a stand;
3) number of measurements;
4) the time which elapsed between the llrep.lratlon of the test piece and the measurernern of itS hardness;
5) detaIls olany deviaticm 1mm the standard procedure;
) details ol any operations nut specified in this docunwnt and any incidents likely to have had ,mn influence on the result:
d) the test result, expressed as,; whole number, together with the scale used. e.g. 75 Shore A (A75);
e) the date of the test.