Flexometer

It can be concluded from this study that Perkalink 900 can be used as a cross-linker in XllR and could provide the additional advantages such as, better high-temperature compression set and lower heat built up in Goodrich Flexometer test over HVA-2. 

FIGURE 14.19 Goodrich flexometer heat buildup at 100°C after 30 min (load 108 N, stroke 4.45 mm, frequency 30 Hz). 

The important vulcanizate properties demanded by this application, low heat buildup, and low dynamic set have been determined in the Goodrich Flexometer test. The compound containing the antireversion agent exhibits a marked decrease in heat buildup and dynamic permanent set (Figures 14.21 and 14.22). 

The rise in temperature which occurs when mbber is deformed. The energy used in deformation is not fully returned when the mbber recovers its original shape and the lost energy shows as a rise in temperature of the mbber. See Flexometer, Hysteresis and Resilience. 

ISO 3616 2001 Textile glass - Chopped-strand and continuous-filament mats -Determination of average thickness, thickness under load and recovery after compression ISO 4603 1993 Textile glass - Woven fabrics - Determination of thickness ISO 4604 1978 Textile glass - Woven fabrics - Determination of conventional flexural stiffness - Fixed angle flexometer method... 

Flexometers or heat build-up fatigue apparatus operate in compression, shear or a combination of the two and various designs have been in use and standardised, particularly by ASTM, for many years. The test piece geometry and deformation cycle used are, inevitably, somewhat arbitrary and this perhaps contributed to it being much later before there was an international or British standard method. 

The ISO rotary flexometer and the Firestone both operate by superimposing a cyclic shear deformation onto a static compressive deformation but the cyclic action of the two machines is not the same. The ISO apparatus is derived from the St Joe flexometer, which at one time was included in the ASTM standard (up to 1962). 

The Firestone flexometer method in D623 is not very specific. The standard test pieces are in the shape of a frustum of a rectangular pyramid but the use of any suitable shape is permitted when cut from products. The apparatus operates at 800 cycles/min and a range of compression loads and amplitudes of oscillation are possible, but no particular conditions are specified. The test piece is fatigued until a definite, but unspecified, decrease in the height of the test piece is reached, which is supposed to represent the onset of internal porosity. Parameters such as temperature rise and changes in compression are reported. 

The specification of the ISO rotary flexometer is not much better. It uses cylindrical test pieces and operates at 14.6 or 25 Hz. The axial compression can be either constant stress or constant strain and loading conditions are... 

BS903 Parts A4946 and A5047 are identical to ISO 4666 Parts 1 and 3. There is no British equivalent to the rotary flexometer, simply because such an arbitrary apparatus was not considered worthy of standardisation and it is not used in the UK. 

A draft is now being progressed in ISO TC 45 for a fourth part of ISO 4666 to cover constant stress flexometers. There is no doubt that there should be a method to allow testing at constant stress but perhaps the most encouraging thing about this new work is that the apparatus is based on modern instrumentation and not on some arbitrary and historical mechanical device. Unfortunately, at the time of writing, the draft needs a great deal of work before it could be called satisfactory. 

A servo hydraulic dynamic fatigue machine can, clearly, be used for testing under constant strain as well as constant stress conditions and this would be preferable to the traditional mechanical instruments. Interestingly, a comparison has been made of dynamic mechanical properties measured on a new version of the Goodrich flexometer and a servo hydraulic tester48. 

BS 903 Part A49, 1984. Determination of temperature rise and resistance to fatigue in flexometer testing (basic principles). 

DBP adsorption (Pre-compresseda) cc/lOOg Resilience (Yerzley method) % Heat rise (Goodrich flexometer) °C... 

Filler dispersion is a property that determines how well the filler partciles in a given rubber compound are dispersed as a result of the mixing process. This relates to carbon black dispersion as well as the dispersion of nonblack fillers such as silica, clay, calcium carbonate, titanium dioxide, etc. Also rubber curatives such as sulfur and accelerators can be poorly dispersed (commonly these ingredients are added late in the mixing cycle). Poor dispersion makes a mixed stock less uniform, and commonly the cured ultimate tensile strength will have more variability. Poor dispersion can affect other important cured physical properties such as abrasion, tear, and fatigue resistance, flexometer heat buildup, and other dynamic properties. 

An unfortunate confusion of terminology in rubber testing should be noted. The term flexometer has traditionally been generically applied to apparatus for heat buildup tests, whereas such apparatus generally work in compression or shear or a combination of the two. 

Flexometer tests are used to determine thermal stability under dynamic straining conditions. Measurements include temperature rise after a specified period of cycling, set and creep, and in some instances the time or number of cycles to failure in the form of thermal runaway or test piece destruction. In contrast to fatigue cracking tests, heat buildup tests... 

The principles of flexometer testing are described in ISO 4661/1 (BS903, Part A49). The best known test machine is the Goodrich compression flexometer described in ISO 4661-2. (BS903 A40 and ASTM D623). An alternative is the rotary flexometer of ISO 4661 2 a specific example, the Firestone flexometer, is specified in ASTM D623. 

Askea. D.. DM properties from the BFGoodrich Flexometer 11. ACS rubber division meetings 5 93. Paper 63 and 10 95, Paper 100. 

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