FAVIMAT+ ROBOT2 and AIROBOT2

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Automatic linear density, crimp and tensile tester for single fibres

Test section FAVIMAT+
Test section FAVIMAT+

The design of the FAVIMAT+ takes into account any needs to combine single-fibre linear-density measurements and tensile tests with different crimp test methods into a single testing instrument. All of these tests are carried out on the same fibre section. Transferring the fibre from one testing device to another is, therefore, no longer necessary. This results in a significant reduction in both operator input and expenditure as well as a reduction in possible fibre damage when compared to multiple measurements carried out on alternative independent devices.

The FAVIMAT+ incorporates two additional measuring systems located in the tensile testing section. The high-resolution load cell enables accurate adjustment of specified pretensions, as well as the measurement of extremely low tensile forces when determining fibre crimp properties or testing nano-structures. To ensure highest measuring accuracy, computer-aided calibration of all measuring systems can be carried out automatically.

The FAVIMAT+ testing methods

Linear-density test

The FAVIMAT+ automatically determines the linear density of single fibres using the vibration method, e.g. according to ASTM D 1577. With this testing method the resonance frequency of the sample is measured at constant gauge length and known pre-tension; the data ob- tained is then used for calculating the linear density according to the following formula:

Tt = FV / (4 · f2 · L2)

Tt = linear density 
FV = pre-tensioning force 
f = resonance frequency 
L = test section length

A possible influence of bending stiffness and fibre cross-section can be analysed by means of an au- tomated pre-test and can in general be eliminated for series testing.

Determination of crimp geometry

A further measuring system with opto-electronic sensor integrated in the FAVIMAT+ enables the creation of a digital image of the crimped fibre, which is held between the two clamps, and the subsequent evaluation of the crimp geometry regarding crimp number and crimp amplitude.

As applicable to mechanical crimp properties, size, shape and regularity of the crimp geometry sup- ply important information regarding the crimping process during fibre production. In addition, these values give information on further processing of the fibres and the properties that can be expected from the intermediate- and finished products.

Static tensile test and examination of mechanical crimp properties

Tensile testing of single fibres represents one of the most important quality control testing methods in chemical-fibre production. In addition to the (linear density-related) breaking force and breaking elongation, other parameters such as modulus, intermediate values of the force/elongation curve, e.g. force values at specified elongations, work to rupture or characteristic values for elastic- and plastic deformations, can be obtained.

With a known material density the effective fibre cross-section and breaking stress values, e.g. in MPa as generally used for reinforcement fibres (carbon, etc.) can directly be determined.

Crimp test
Crimp test
Crimp stability test
Crimp stability test

An additional important value determined through tensile tests are the mechanical crimp properties of a fibre, which are characterized by the following parameters: crimp elongation, crimp removal force, and crimp stability. Further international accepted crimp measurement methods (e.g. JIS standard, VIBROTEX method) are available as options.

Tensile tests conducted within the range where crimp is removed from the fibre require a high-resolution force-measuring system that also enables sufficient measurement accuracy for tensile forces within a range even below 1 mN. The FAVIMAT+, as a consequence, is equipped with a compensating force-measuring system developed by Textechno.

In addition, to having an extremely high resolution of 0.0001 cN for a measuring range of 220 cN and fully automatic calibration, the system is characterized by high stability against external vibrations.

For crimp tests, in particular where there is a need to avoid any external influences on the measurement, e.g. breath of the operator, the FAVIMAT+ is equipped with a recessed testing section that is isolated by a motor-driven sliding glass window.

The actual test section comprises the measuring- and draw-off clamps, which open and close automatically. The clamp jaws are tightened by spiral springs, and the clamping force can be steplessly and reproducibly adjusted over a wide range. The gauge length between the clamps can be varied between 0 and 100 mm.

Test sequence

Depending on the task in hand, either one of the four tests or a combination of two, three, or four tests can be carried out on a single clamped fibre.

Cyclic load-, relaxation-, and creep testing

An optional software offers various possibilities for hysteresis- (cyclic load or elongation), relaxation-, and creep testing. These methods can be combined with the linear-density test.

Friction testing

Exchanging the draw-off clamp against the special friction appliance allows tests of friction properties fibre to metal (or other materials). Evaluation includes a graph of friction-force along the fibre and determination of the coefficient of friction.

Clamping systems for different fibre types

The FAVIMAT+ standard clamps are suited for all textile- and most technical fibres including glass, carbon, basalt and Aramid. For very short samples special clamps with jaw faces of only 2 mm height and an innovative short fibre insertion mode enable tensile tests of short cut fibres up to minimum lengths of 3 mm. An optional pressure amplifier is recommended for high-tenacity material like Polyvinyl alcohol (PVA) as used in concrete reenforcement.

A further special clamp for manual sample insertion is equipped with force reduction bollards in order to avoid slippage between the jaw faces or breaks at the clamps on testing very critical material such as ultrahigh molecular weight Polyethylene (e.g. Dyneema, Spectra). For such applications a high-resolution load cell with a force range of 1.200 cN is available.

The ROBOT2 and AIROBOT2 automatic fibre feed units

FAVIMAT ROBOT 2
FAVIMAT ROBOT 2

If the crimp stability test is included in a testing cycle, testing of a single fibre may take several minutes, depending on selected loading and relaxation times. As a consequence, the operator has to wait until the next test can be initiated. This clearly demonstrates the advantages of an auto- matic supply of test specimens.

For this purpose the automatic unit ROBOT2 can be added to the FAVIMAT+. ROBOT2 comprises a sample storage unit and a transfer clamp, the latter for transferring the single fibre from the storage unit to the test section, and a suction system for removing the waste fibres after each test. The sample storage unit contains up to 20 magazines, each of which can accommodate 25 individual fibres. Therefore, the total capacity of the unit amounts to 500 fibres. Depending on the test requirements, the fibres are suspended in the magazines using tongs-shaped pre-tensioning weights, e.g. equating to the standard pre-loading for tensile tests, or paperweights for crimp tests. Magazines are equipped with an automatic identifi- cation system. They can be removed and reloaded during a running test series.

The AIROBOT2 is a variant of the ROBOT2 auto- matic fibre feed unit. Here the fibres are loaded pneumatically into the magazine in a semi-auto- matic loading unit. When being transferred from the sample storage unit into the FAVIMAT+ test section, the fibres are slightly pre-tensioned by a suction device. The AIROBOT2 does not require pre-tensioning weights, resulting in a further sub- stantial increase in test preparation efficiencies.

Efficient testing with FAVIMAT+ (AI)ROBOT2

Transfer clamp and magazine
Transfer clamp and magazine

The time required for testing a single fibre on the FAVIMAT+ including feeding and removal of the fibre amounts to approx. 35 sec (force-elongation test with 20 sec breaking time and linear-density test). The full programme including crimp stability examination has a duration of up to 4 min. Operator time required, therefore, amounts to approx. 4.5 ... 30 hours for 500 fibres when using the FAVIMAT+ without automatic sample feed. During conventional testing with separate testing instru- ments and visual crimp counting the overall testing time may be even substantially longer.

When FAVIMAT+ and ROBOT2 are combined, the work of the operator is reduced to introducing the fibres into the storage magazine and, where applicable, attaching the pre-tensioning weights. After appropriate operator training it can be assumed that the loading of 500 fibres into the storage magazines will require approx. 80 min. In case of the AIROBOT2 this time is even further reduced to about 45 min. In an extreme case this corresponds to a reduction in working time of more than 95 %. When comparing the above figures, the enormous rationalization effect of the FAVIMAT+ (AI)ROBOT2 is evident, which results from the combination of different test methods into a single instrument, together with automated sample feed and -disposal and the large capacity of the sample storage unit.

Testing methods

Measurement of linear density with the vibration method
Static tensile test, cyclic load testing, creep- and relaxation trials
Measurement of mechanical crimp properties
Crimp number and -geometry measurement
Friction testing

System components

Test section:

One pair of single-fibre clamps, also suited for other narrow test specimen
Continuously adjustable gauge length 
0 – 100 mm
Draw-off clamp speed 0.1 – 100 mm/min, 
return speed 300 mm/min, 
max. travel of draw-off clamp 100 mm
Additional vertically movable measuring head that automatically swings into the test section, comprising two measuring systems for the measurement of linear density and the determination of crimp geometry.

Measuring systems:

Force measuring device, resolution 0.0001 cN, measuring range 220 cN, other ranges available on request
Elongation measuring device, 
resolution 0.1 μm
Linear-density measuring system with acoustic initiation of the fibre vibration and opto-electronic recording of the resonance frequency
Opto-electronic measuring system for digital recording of the fibre geometry.

(AI)ROBOT2:

Fibre sample storage unit for a maximum of 20 magazines, each with a capacity of 25 single fibres
Transfer clamp (AI)ROBOT2 to FAVIMAT+
Loading unit for fibre introduction into the magazine with pre-tensioning weights (ROBOT2) or pneumatics (AIROBOT2)

TESTCONTROL:

PC system for controlling the test processes and for the evaluation of the measured data, connected via USB interface
Input of all parameters for testing and measured-data evaluation on the PC, saving of selected parameter sets of test conditions under code words
PC for easy integration within any network type.

Further technical data

Mains supply:

220 V, 50 (60) Hz, current requirement
approx. 1.5 A.

Compressed-air supply:

6 bar, 10 l/min., with (AI)ROBOT2 50 l/min.

Lacquer finish:

RAL 9006/5002.

Dimensions:

Height 600 mm, width 600 mm, depth 540 mm, approx. 85 kg (FAVIMAT+)
Height 1125 mm, width 880 mm, depth 600 mm, approx. 90 kg (ROBOT2).

Technical contents can be subject to changes by Textechno.