DE1915739A1 - Device for measuring the viscoelastic properties of elastomers - Google Patents

Description

Case Glf) 4

GERMAN SEMPERIT GUMMIWERK GES.M.B.H., MUNICH

Device for measuring dor viscoelasbischsn Properties of elastomers.

The invention relates to a device for measuring the viscoelastic properties of elastomers with help forced resonance vibrations, where j ο a specimen on both sides in the axis of the moving coil of an electrodynamic Vibration transmitter is arranged.

The measurement of the viscoelastic properties of elastomers is essential for assessing their usability, as their suitability for many areas of application through these properties is determined. Particularly when using rubber cannabis seeds in tires, rubber or damping elements These properties are decisive for vibration isolation. Carrying out the measurement under the terms of the Intended use proper conditions is therefore crucial for later use. Pure development When it comes to the formulations of such elastomers, it is essential to test these ■ properties.

A number of devices have been developed and described for measuring these properties. However, all previous devices have Disadvantages, which they recognized today, are these measuring methods

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not allow the demands to be made to be justified. In principle, it "is not and methods, optionally in konstair! Sr Uechse'lverforßirng allow the previously professed devices ("? In · _.Β β sinusoidal deformation constant Y / egainplitude) of the test specimens of different hardness, to be tested and vex'gleichenden materials to measure, or to carry out this 1-measurement with constant Y / echsel force action (with, for example, sinusoidal force path constant force amplitude). If, however, this fundamental distinction is not observed, wrong assessments of the quality of different materials will result.

The viscoelastic properties are very much dependent on the test conditions under which they are measured. This dependency is different for elastomers with different compositions. It is therefore necessary to vary the test conditions within wide limits or, if this is not possible for technical reasons, to select the correct test conditions. For example, for the intended use of vulcanizates in car tires, it is necessary to combine the following test conditions. The temperature of the test body during the test must be between 100 and 150 ^° C. It must be ensured that these test bodies generate heat themselves during the test, especially if it lasts longer, and thus experience self-heating which differs from the test chamber temperature. For these reasons it is necessary to choose the shape of the test specimen appropriately, whereby a sufficiently large deformation of at least 10 % must be achieved even under pressure. Experience has shown that this is achieved by the fact that the test specimens are cylinders 20 to 30 mm in height and 10 to 15 minutes in diameter.

This large deformation of the test specimen, which requires relatively large forces, must nevertheless be achieved at high frequencies, v / ie they occur quickly on car tires. The frequency must therefore be between 50 and 200 oscillations per second. 9098 k 4/1 207

The tendon gap it is also used for development tests Examination essential, bringing all the procedures of liability between the KU-testing elastomers (vulcanizates) and the contact surfaces fall away «, ErfcliruogseeKafi will bc-i DrucksehwinFiuigen a simple and safe clamping by.-achieved that the Test cylinder through a pre-deformation or pre-tensioning between the clamped-in puddle, which is slightly larger than the Wcchaelverfortung or Yfechsellast acting on them.

In ei new known RosonraiK-testing device form eg two rubber · prüf body and the vibrating Apporatmasse an oscillatory ^ll J? EDCR-lla "rio" Däini) .CniiKf? Sy «te) fi" v / Olch "it through the inhomogeneous dif ferent. in! equation el or Erzvningenen, damped oscillation bescln / iobon was.

The solution of the differentini equation for the resonance case, ie if the test x-equence is equal to the natural frequency of the oscillating system, gives the dynamic module E ^{1 for i *}

E ¹

and for ¹ the loss module E "

X _{Q means} the vibration amplitude in the case of resonance, w _Q the natural angular frequency of the oscillating system, m the oscillating Hasse, P the deforming force to be applied and I / F the form factor from the length I and the area F of the test body. By measuring these quantities, the dynamic modulus of elasticity E ¹ and the dynamic loss modulus E "can be calculated. The method thus allows a direct determination of these two quantities of interest without detour via the determination of the loss factor or by planning out the hysteresis loop.

I. • m. 2 w_ O F.

With known devices, the measurement of the viscoelastic Properties only under constant feather deformation, i.e. constant V / egoiaplitudc take place, the respectively read the force required for this deformation can and in the ForiQol to calculate the two modules a ~ goes. In many cases it is necessary to obtain the Test conditions of the intended in practical use To equalize the stresses as much as possible, the measurement under constant tension, ie. applying a constant Perform force, and the deformation achieved thereby, if necessary to consider.

According to the invention, such a device is therefore provided suggest which the optional keeping constant the alternating deformation or dex * enables alternating force by the fact that in. the extended axis of a 'l' smoke coil as well as a position measuring device and at least on one side of the plunger coil in front of or behind your test specimen Force measuring device are arranged.

It is not necessary to apply a constant alternating force during the vibration measurement, but rather it must also be kept constant with the bias the test specimens have to be clamped so that they sit firmly between the test plates without adhesion. To therefore a To carry out measurement under constant alternating force, the specimens are initially clamped in such a way that by axial Compression, e.g. by means of a spindle, a certain Preload is enforced, the size of which on the force measuring device, e.g. a piezoelectric load cell, ge «· can measure and set. Now must also during of the vibration required for the measurement, the applied alternating force must be kept constant * This happens by keeping the alternating current flowing through the plunger coil constant. A power amplifier with a frequency-independent current output is expediently used for this.

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In the drawing, an embodiment is shown, based on which the invention is described in more detail below ..

The figure shows the scheme of a test device according to the invention. The resonance tester consists of an electrodynamic one Schwingungssystera with a moving coil 1. JSs can also zv / ei symmetrically arranged to a permanent on magnet Plunger coils may be provided. At both ends of a continuous rigid axle 2 to which the moving coil 1 is attached is, and which in axialpx * sighting dxirch on both sides arranged leaf springs can move freely within small limits of e.g. * 6 mm, plates 3 are used to hold test specimens 4- attached. The moving coil system acts as Schwingungsgebc; r simultaneously on both test pieces. the Voice coils are adjusted and adjustable RC audio frequency generator 5 with a downstream, adapted Power amplifier 6 fed, the change in the voice coil current takes place by changing the oscillation amplitudes at the RO generator 5 or by changing the gain on the power amplifier 6.

The current is read on a Röhrenvoltmetex ^ 7, the the voltage drop across one in series with the voice coils lying resistance 8 of 1 ohm measures. Dadux'ch corresponds to 1 volt after 1 ampere. By avoiding the direct measurement with a low-resistance ammeter Area-dependent internal resistance, an undistorted current measurement is achieved because the voice coil is adapted to the amplifier output is not changed by changes in resistance. Because the force in an electromagnetic system is proportional to the current flowing through, and this propox'tionalitätsfak-fcor remains constant in the system described by the arrangement mentioned, can be used for the evaluation Obtain the necessary deforming force by measuring the current are »ij & ie fregpeniz * rird not only on the imprinted dSk ^ e ^ eBchxiftuiag aid ^^ & eniersator ^ dismissed / sen ^ but

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digitally indicates the time per oscillation in microscopic circles. The resulting high accuracy is important because the dynamic Ε-module E ¹ is proportional to the square of the frequency. The measurement of the vibration amplitude takes place with the aid of an inductive Uegaufnehßers 10, the induced voltage of the vibration samplitude is proportional. The voltage is measured over a carrier fi ^ equenzmeßbrücke 11 with a Eöhrenvoltmeter 12, the scale of which is directly scaled to amplitude size.

A piezoelectric load cell 13 is under pressure electr. Charge to a charge amplifier 14. This charge amplifier converts the charge into a charge proporbionale Tension um, v / eDche cn a Röhrcirvülhaotei · or digital Voltinetex * can be read. At PxObenbeanr.iiruchuug with constant alternating force or with constant alternating deformation is a setting to a desired "force or. to a desired amplitude through automatic control kept constant. This avoids a drift in the force or amplitude during the tuning process for resonance. .

The clamping of the cylindrical test specimen 4 takes place symmetrically to the moving coil 1 between each plate 5 of the vibrating part and an adjustable plate 16. The Adjustability of the plate 16 by means of threaded spindles 1? and handwheels 18, enables pressure deformation of the two Test specimen 4 in the axial direction, their size when tested under constant alternating deformation with the aid of dial gauges 19 can be read. In the case of loading with a constant alternating force v / ird is also used to measure the pressure preload the piezoelectric load cell 14 already described used, including the charge amplifier 14 for the quasi-static measurement required here with a circuit for long-term constancy Is provided. The pre-load or * pre- The shape of the test specimen must be larger than idaue wished ¥ achsel stress-üng or ¥ ectselverfprfflungi. JDamil; aware! It is established that the test specimen pline feftoapg sltciher

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on plates J and 16.

To find the measured values, the setting of the vibrating system required for resonance. For this purpose, on an X-Y oscilloscope 20, the X deflection of the Current through the plunger coil or the 1 ohm resistor 8 falling across a 1 ohm resistor 8 connected in series with the plunger coil In-phase voltage applied «At the Y-deflection is a voltage proportional to the speed of the voice coil, which is tapped at a speed sensor 21 is »The moving coil itself could also be designed as a speed sensor. In case of re & onanz one receives a phase shift of 180 ° between current and speed and thus a collapse of the surface of the hysteresis loop on a straight or curved line. The measured values can be read in this state of the oscillating system.

The two test pieces are surrounded in their clamped location of chambers 22, a hot air stream can draw up to 150 ⁰ C by the mitte3.s elektr.Heizung and blowers. The temperature is controlled by these chambers made using thermocouples or resistance thermometers on a controller, the test specimens thus can be brought from room temperature to 150 ⁰ G to any desired temperature.

The evaluation of the measured variables voice coil current or vibration amplitude and resonance frequency takes into account the constants of the apparatus, such as the no-load resonance frequency of the vibrating system, by an electronic computer, which shows the results of the values of the dynamic Module and the loss module over the practically occurring ' Specifies the range of heights.

- patent claims -

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Claims (1)

Claims 1.! Device for measuring the visco-elastic natural ^ shafts of elastomers with the help of forced resonance vibrations, one specimen on each side in the axis of the moving coil of an electrodynamic Vibration encoder is arranged, characterized in that that the choice of keeping the alternating deformation constant or the alternating force in the extended axis of the plunger coil both a measuring device and at least one on one side of the moving coil in front of or a force measuring device close behind the specimen * are arranged, ' Device according to claim 1, characterized in that sUr is kept constant during the vibration measurement applied alternating force for the flowing through the plunger coil Electricity is a performance amplifier with a frequency that is unequal Current output is provided GERMAN SEMTERIT feUMMMERK GES .M.B.H. 909 8 U 4 Μ 207