Preparation of Test Pieces

Batches of all 39 compounds were mixed. In most cases 2 batches were needed, which were blended. 

Standard 2 mm thick sheets and type A compression set buttons were produced by compression moulding. 

The cure times used in 1958 for the original materials could not be derived from measurements in a curemeter as these instruments were only in the experimental stage. Hence, they were derived from a programme of curing for various times and measuring physical properties. The cure times for the new materials were derived from measurements on a Monsanto rheometer. 

Processing variables can affect to a very great extent the results obtained on the rubber product or test piece and, in fact, a great number of physical tests are carried out in order to detect the result of these variables, for example state of cure and dispersion. In a great many cases, tests are made on the factory prepared mix or the final product as it is received but, where the experiment involves the laboratory preparation of compounds and their moulding, it is sensible to have standard procedures to help reduce as far a possible sources of variability. Such procedures are provided by ISO 2393 which covers both mills and internal mixers of the Banbury or Intermix type, and also procedures for compression moulding. 

The standard does not specify such details as temperatures and mixing schedules, which must be taken from the particular material specifications or, presumably, agreed between the parties concerned. It is doubtless next to 

The tolerance allowed on mass of ingredients is fairly tight at 1% generally but down to 0.02g for sulphur and accelerators. For miniature internal mixers this reduces even further to 0.002g. There are limits on the difference between the sum of the masses of the ingredients and the final mass of the mixed batch of between + 0.5% and - 1.5%. Carbon black is required to be conditioned before use to remove moisture but it seems curious that this is not required for other fillers. 

A two-roll mill is specified fairly precisely in terms of dimensions, 150 -155 mm diameter x 250 - 280 mm long, with the front roll speed 24 1 rpm 

Three types of mixer are recognized, plus a miniature mixer which would provide just enough compound for a curemeter test and one sheet. Mixers types A] and A2 and the miniature device have non-interlocking (tangential) rotors whilst type B has interlocking rotors. Dimensions of the larger mixers are specified fairly precisely, including new and worn rotor clearances, and they are required to have temperature control, a system to record power or torque and a timer. The miniature mixer is only specified in terms of capacity, rotor speed and friction ratio but is required to control of temperature, indication of power and a timer. 

The cure conditions arrived at are presented along with the compound formulations in appendix 1. 

Trial mixes were made and checks carried out to ensure that the chosen conditions did produce 

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The methods for the preparation of test pieces (or products) and their subsequent history will influence the material properties. Consequently, it is important for any testing that all the moulding, storage, preparation and conditioning procedures are defined and carefully controlled. It may be worthwhile conducting preliminary trials. 

Except for work on complete products, a test piece must be formed before the test can be carried out. In many cases, the test piece can be directly moulded but, particularly when tests on finished products are concerned, the specimens need to be cut and/or buffed to some particular geometric shape (Figure 4.1). It is convenient to consider separately, first the mixing and moulding leading up to a vulcanised (or thermoplastic) test piece or test sheet, and secondly the preparation of test pieces from moulded sheets or products. The preparation of test pieces for tests on raw rubber and unvulcanised compounds will be considered integrally with those tests in Chapter 6. 

Although it is debatable whether mixing and moulding are strictly part of testing, particularly as these processes are often not under the control of the tester, there is no doubt that the preparation of test pieces from moulded sheet or products is part of the testing process. The most common operation... 

To stamp, for example, a dumb-bell from sheet requires only a die and a press, although a hammer has been known to replace the latter. There has been a tendency to treat stamping as so simple an operation as to merit little attention, despite the fact that the accuracy of the final test result depends very considerably on the accuracy with which the test piece was prepared. The necessary dimensions of the die are given in the relevant test method standard, for example ISO 375 for tensile properties, but there is ISO 235292 which deals specifically with the preparation of test pieces for physical tests. ISO 23529 now incorporates what was ISO 4661 Part 1 but ISO 4661 Part 2 still exists and deals with the preparation of samples for chemical tests. The British standard is identical to the ISO standard7. 

Mixing and moulding have been considered under the general heading of preparation of test pieces in Chapter 4. Where compounded but unvulcanised rubbers are to be tested, the same standard mixing procedures will be relevant together with further details relevant to particular polymers, as referred to in Section 1 above. 

Borroff and Wake48, and later Meardon49, developed a direct tension method which was claimed to more nearly measure the true adhesion between fabric and rubber. It is particularly useful for discriminating between adhesive systems, when the peel tests can be misleading. The main objection to the method is practical in that the preparation of test pieces is rather difficult. 

When studying the graphs, note should be taken of the scale used so that the degree of scatter is put in perspective. Despite the care taken in the preparation of test pieces and the testing, it is apparent that the scatter is significant and it would have been advantageous if more data points and more test pieces could have been afforded. 

It should be noted that most optical properties are greatly affected by the condition of the surface, so that the method of preparation of test pieces is most important and needs to be carefully controlled if comparative results are required. To obtain a very high standard of surface finish, molding against platens of borosilicate glass without a release agent has been recommended,... 

Testing of rubber and elastomers - Flexing endurance test, definitirHis, apparatus, preparation of test pieces (withdrawn replaced by ISO 132 2011)... 

ISO 11413 1996 Plastics pipes and fittings - Preparation of test piece assemblies between a polyethylene (PE) pipe and an electrofusion fitting. 

A.F.A. Rammer. Apparatus designed by the American Foundrymen s Association for the preparation of test-pieces of foundry sand in 1948 the Association changed its name to the American Foundrymen s Society. See A.F.S. and... 

Preparation of test pieces of welded metal for stress corrosion testing... 

One of the most important points of EN 1402 was the agreement about shapes and sizes of the test pieces. It was agreed to use for the preparation of test pieces the following three shapes ... 

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