1、Testing of rubber and elastomers Measurement of vulcanization Characteristics (curometry) General workina Drincides Prfung von Kautschuk und Elastomeren; Vulkametrie, allgemeine Arbeitsgrundlagen Supersedes February 1971 edition In keeping with current practice in standards published by the Internat
2、ional Organization for Standardization (ISO), a comma has been used throughout as the decimal marker. - DIN 53 529 - Part 1 1 Curometry is the study of the vulcanization process in cross-linkable rubbermixes.The present standard specifies design features of instruments employed in curometry, namely
3、curemeters, and the requirements which such instruments shall meet. DIN 53 529 Part 2 specifiesa method of determining vulcanization characteristics and of evaluating cross-linking isotherms in terms of reaction kinetics and DIN 53 529 Part 3 deals with the determina- tion of cross-linking behaviour
4、 with the aid of rotorless curemeters. Scope and field of application 2 Concept Curemeters are test instruments which, on the basis of the strain produced in a specimen by their mechanical oscillation, make it possible to plot the course of vulcan- ization processes and evaluate cross-linking isothe
5、rms in terms of reaction kinetics (see DIN 53 501 for the concept “vulcanization“, and DIN 53 529 Part 2 in connection with the evaluation ofcross-linking isotherms). According to the type of strain which they produce, curemeters are classified either as a) linear shear curemeters (see figure I), in
6、 which speci- mens are subjected uniaxially to an alternating linear strain, or as b) torsion shear curerneters (see figure 2), in which specimens are subjected to an alternating torsional strain. This type of curemeter may be either rotorless or fitted with an oscillating disc. 3 Apparatus A cureme
7、ter assembly consists of the following compo- nents: a) reaction cavity (containing the specimen); b) device for applying strain to the specimen (drive c) heating device; system); Figure 1. Linear shear e- ,- Directions of motion - W of moving shear element In figures 1 and 2 d is the thickness 1 is
8、 the length 6 is the width y is the shear angle; h is the deflection of the moving shear element; P is the angular deflection of the moving shear element. d) device for measuring either the force or torque, or The above-listed curerneter components shall meet the requirements specified in subclauses
9、 4.1 to 4.4. Figure 2. Torsional shear strain strain of the specimen; I the linear or angular amplitude. , 4 Apparatus requirements 4.1 Reaction cavity 4.1.1 When cross-linking isotherms are to be plotted, the poor thermal conductivity of rubber mixes requires that the thickness of the specimen be k
10、ept to a mini- mum. The design of the reaction cavity shall hence be such that the thickness of the specimen does not exceed 5 mm (see figures 3 and 4). Preliminary tests shall, however, be conducted with the standard test mix in order to establish that the initial value F (see DIN 53 529 Part 2) ma
11、y still be reliably ascertained despite the thinness of the specimen tested. Continued on pages 2 to 6 Beuth Verlag GrnhH Berlin 30, has exclusive sale rights for German Standards (DIN-Normen) DIN 53 529 Part 1 Engl. Price group 6 Sales No. O106 09.85 Page 2 DIN 53 529 Part 1 4.1.2 Examples of react
12、ion cavities Temperature sensors Temperature sensors Specimen - Lad c-) v d is the thickness of specimen, or thickness of specimen at distance r,. r, is the radius of spec.imen. Figure 3. Reaction cavity of a linear shear curemeter 4.1.3 Cross-linking causes rubber mixes to contract in volume, with
13、the result that slippage may occur between specimen and cavity walls. It is thus recommended that provision be made to compensate for such shrinkage in the specimen. 4.1.4 The curemeter indication is produced by the oscillating strain applied to the specimen in the deforma- tion zone. The design of
14、this zone shall be such as to ensure that the stress on the specimen is distributed as uniformly as possible. It is thus specified that specimens tested in linear shear curemeters (figure 3) shall be of constant thickness d, and those tested in torsion shear curemeters shall have a constant ratio rl
15、d as shown in figure 4. Equivalent requirements shall apply to other types of curemeter. It is of particular importance for the determination of the shear modulus G that the dimensions of the defor- mation zone are kept to so closely that the error in the value of the shear modulus resulting from th
16、e specified dimensional tolerances remains less than 3% (see Ex- planatory notes). Note. When measurements are made in the curemeter, the linear range of the force (or torque) strain characteristic of the rubber mix should not be exceeded. In borderline cases, this shall be checked by plotting the c
17、haracteristic con- cerned after the apparatus requirements specified in subclause 4.1.3 (prevention of slippage) and subclause 4.1.4 (uniformity of stress distribution in the deformation zone) have been fulfilled. 4.1.5 The temperature distribution in the deformation zone shall be as uniform as poss
18、ible. When thermal equilibrium has been attained, the temperature differ- ences overall shall not exceed 3OC. 4.1.6 Provision shall be made for temperature control in the deformation zone by means of temperature sensors with low thermal dissipation. With the drive system switched off, the temperatur
19、e sensors shall be introduced into the specimen in such a way that the points of highest and lowest temperature in the deformation zone may be registered. Specimen Figure 4. Reaction cavity of a torsion shear curemeter The average specimen temperature is dependent on the type of apparatus used. Thus
20、 the temperature to be designated as test temperature shall be that which corresponds to the measured rate constant specified in DIN 53 529 Part 2. 4.1.7 The temperature measured in the wall of the reac- tion cavity is termed the reference temperature. I t is not identical with the test temperature.
21、 Once temperature equilibrium has been established in the specimen, the reference temperature shall not deviate by more than 2C from the test temperature specified in subclause 4.1.6. The temperature sensors used for measuring and con- trolling the reference temperature shall be easily remov- able f
22、or purposes of calibrating the indicating instruments; they shall form a close fit with the cavity wall so as to avoid dead time in the controlled system. The reference temperature shall be reached without overshoot within 3 minutes of the specimen being in- serted. Note. The reference temperature g
23、ives only an approx- imate guide to the test temperature, since the latter, for a given temperature gradient between the cavity wall and the test space, is also deter- mined by the thermal conductivity of the rubber mix and the tolerance of the temperature meas- uring instruments. 4.2 Device for app
24、lying strain to the specimen (drive system) 4.2.1 Elastic deformation of the drive system of cure- meters with a given linear or angular amplitude shall be as small as possible when subjected to load and temper- ature fluctuations. If elastic deformation does result from the loading of the drive sys
25、tem, then the relation- ship between the force or torque and the deformation of the system shall be linear. It shall be possible to insert the specimen with the drive in the zero position. The drive frequency shall lie in the range between a minimum of 3 min- 1 and a maximum of 1 O0 min- 1. The driv
26、e frequency shall be independent of the force or torque. As shown in figure 5, the areas A, and A, which are DIN 53 529 Part 1 Page 3 Time f- Figure 5. Examples of deflection/time curves of cure- meters In figure 5 Al andA2 are the areas delimited by the abscissa and the h is the deflection of the m
27、oving shear element; is the angular deflection of the moving shear element; s is the linear or angular amplitude of the moving shear element. deflection/time curve; delimited by the deflection/time curve and the abscissa, shall be congruent. In curemeters with a given linear or angular amplitude, th
28、e deformation of the specimen generally decreases as the force or torque increases, the reason being that a certain degree of elastic deformation occurs in both the drive system and in the force (or torque) measuring device (see subclause 4.4). This effect is termed reac- tion. The shear angles can
29、thus only be determined when the drive system is unloaded (.e. idling). When the drive system is idling, the shear angle amplitude (see figures 1 and 2) shall not exceed IO“. Preference shall, however, be given to smaller amplitudes such as 5, 2 or 1“ (see also note to subclause 4.1.4). 4.2.2 For cu
30、remeters with a given force or torque amplitude, the requirements given in subclause 4.2.1 shall be modified and applied appropriately. Reaction may also occur in such curemeters. In many cases, the loading amplitude acting on the specimen is increased as the shear modulus of the specimen increases
31、because, for example, the force dissipation in the readjusting springs that serve to determine the zero point of the linear or angular measuring devices is reduced when the strain displacement of the specimen decreases. 4.3 Heating 43.1 The accuracy class and the specified measuring ranges of the te
32、mperature indicating devices shall be selected so that within the range from 1 O0 to 200C the temperature can be measured to an accuracy of at least f 0,3“C. 4.3.2 The temperature control devices shall permit the adjustment of the reference temperature (see subclause 4.1.7) by 0,3Cor less over the r
33、ange from 1 O0 to 200C. 4.4 Device for measuring force or torque, or linear or angular amplitude 4.4.1 In the case of curemeters with a given linear or angular amplitude, the resistance of the specimen to strain shall be recorded with a force or torque measuring device with minimum displacement. The
34、 relationship between force or torque and elastic deformation of the force or torque measuring system shall be linear. The measuring device shall be calibrated with standard weights. The total error resulting from zero point error, sensitivity error, linearity and reproducibility errors, shall not e
35、xceed 0,5% of the measuring range selected (see Explanatory notes). It shall be possible for the force or torque indication to be traced in both directions on the curemeter recording device, .e. on either side of the zero line (see Explana- tory notes). The inertia of the measuring device shall be s
36、mall enough to ensure that the permitted total error of not more than 0,5% is not exceeded even at the highest frequency and amplitude of the drive. The measuring device shall have several ranges (see Ex- planatory notes). Note. 4.4.2 Two-way recording is required for the determina- tion of the appa
37、ratus characteristic (see subclause 5.1). Two-way recording is also recommended because it makes it possible to compensate for any shifts of the zero point of the force or torque measuring device and for any changes in the drive when the curemeter curves are evaluated (see subclause 5.2). For cureme
38、ters with a given force or torque am- plitude, the requirements given in subclause 4.4.1 shall be modified and applied appropriately. 4.4.3 Curemeter testing with the aid of a standard test mix of natural rubber (NR) and dicumyl peroxide (DCP) Testing of curemeters by the method specified in DIN 53
39、529 Part 2 shall produce the required values of reaction rate constant h(1), reaction orders and ac- tivation energy EA. 5 Correction of indications The curemeter indication may be affected by the reaction of the stiffness of the specimen (see subclauses 4.2.1 and 4.2.2) and this can lead to bias er
40、rors which shall be compensated by corrections if the results of a measure- ment (rate constant k (n), interaction constant a, shear modulus G, etc.) deviate by more than 2% as a result. Note. Correction is not required if the loading or deflec- tion of the specimen is kept sufficiently constant by
41、means of a control system as described in DIN 19 226. In the case of apparatus with a given linear or angular amplitude, correction influences the value of the shear modulus, the incubation time and the rate constant. If, however, in the case of curemeters with a given force or torque ampli- tude, c
42、onversion to a constant loading amplitude is made, then the results obtained from measure- ments of kinetic data remain unchanged as long as the apparatus characteristics are linear. Page 4 DIN 53 529 Part 1 5.1 Curemeter apparatus characteristics Apparatus characteristics shall be measured at regul
43、ar intervals (e.g. after 1000 hours operating time). 5.1.1 Apparatus characteristics of curemeters with a given linear or angular amplitude The apparatus characteristics indicate the gradual re- duction in the linear or angular amplitude of the moving shear elements, in mm, as the force or torque am
44、plitude F, in newtons or newton metres, increases as a result of the progressive stiffening of the specimens (see figure 6a). The apparatus characteristic s = f(F) is obtained by suc- cessively placing specimens of different shear moduli in the reaction cavity and measuring the linear or angular amp
45、litude at thewrface with a check instrument while the drive is switched on. It is permitted to use springs varying in resilience instead of specimens. When the apparatus characteristic is being plotted, the measuring Force or torque F N Nm A A 25 mm,O 15 10 5 OOO 2 4 6 8 10 12 14 min 18 -Linear or a
46、ngular Time t - amplitude S Figure 6a. Figure 6b. Figure 6. Measurement correction for curemeters with a given specimen deflection In figures 6a and 6 b F = f (t) is the curemeter curve (course of force or torque amplitude curve during vulcanization); F+ = f (t) is the cross-linking isotherm (curern
47、eter curve for so); F+ = f (t) is the cross-linking isotherm (curemeter curve for SN); Ft, Fl, FF are the values of curemeter curve and cross- linking isotherm at time t; s = f (FI is the apparatus characteristic: m is the slope of apparatus characteristic; EL is the linearity error of apparatus cha
48、rac- teristic; SN is the nominal linear amplitude h, or angular amplitude,; SO is the idling amplitude of linear amplitude h, or of angular amplitudep; St is the linear or angular amplitude when the curemeter indication Ft is obtained. error fors shall be less than * 1 % of the value obtained, and t
49、he measuring error for F shall be less than 0,5% of the selected force or torque measuring range. The apparatus characteristic shall be denoted by the following data (see figure 6 a): a) idling amplitude so, in mm, O; b) slope m of the apparatus characteristic, in mm/N or c) ratio SN/SO of the nominal amplitude to the measured d) maximum linearity errorEL, in mm or O. Note. The idling amplitude so shown in figure 6 is the O/N m. idling amplitude so; amplitude F = O. Ideally, the nominal amplitude SN is identical with so: SN SO - =I. 5.1.2 Apparatus characteristics of cu
