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- Austrell, Per Erik, et al.
(författare)
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Survey of Design Methods and Material Characteristics in Rubber Engineering
- 1999
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The unique properties of elastomeric materials are taken advantage of in many engineering applications. Elastomeric units are used as couplings or mountings between stiff structures. Examples of these are shock absorbers, vibration insulators, flexible joints, seals and suspensions.The development of computers and of analysis programs in this area has given engineers a new tool for the design of elastomeric components. Computer simulation by finite element analysis has become increasingly important, allowing the mechanical behavior of products with for complex geometries, as well as loading cases of different kinds to be evaluated. Computer simulations enable both static and dynamic aspects to be analyzed. These matters have been recognized by the manufacturers of rubber products and by their customers. The benefits are shorter time for product development and also quality improvements.However, the possibilities available for finding less complicated technical solutions at lower cost with the use of elastomers, has not been fully utilized. Rubber components could be employed more frequently in design if engineers were more familiar with materials of this sort.Part of the problem lies in education and in the dissemination of information. Engineers working in the design area tend to not be very familiar with elastomeric materials and their properties. The offerings of courses on the mechanics of polymers at schools and universities are very limited. Skillful engineers in this field have usually acquired their knowledge through many years of experience and not formal education.Moreover, the complicated nature of the material behavior involved makes it difficult to devise general design rules and design tools. Only recently have computers and analysis programs become powerful enough for the analysis of nonlinear elastic problems involving large strains.It is essential, if one is to become competitive in high-tech applications, to possess a thorough knowledge of computer methods, material models and test methods available.There has likewise been a lack of relevant data for the computer analysis of elastomeric materials. The design tools employed rely on the material models available and on the test data required for the calibration of these models. In many cases, the only information available for analysis is a value for the hardness of the rubber in question. The wide variety of rubber compounds is also a problem. The characterization of different materials is costly and time-consuming. There is thus a need for simple and reliable methods to characterize the different vulcanizates.
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| 2. |
- Bellander, Martin
(författare)
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High pressure vulcanization : crosslinking of diene rubbers without vulcanization agents
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High pressure vulcanization (HPV) is defined in this thesisas crosslinking of rubber materialsat elevated pressure andtemperature, without the use of any vulcanization agents. Thisis atotally new vulcanization technique, not used in theindustry today. The HPV technique,however, has an interestingpotential since no hazardous chemicals need to be handled,thematerial does not contain any additives. The phenomenon thatcertain rubber materials can be crosslinked in this way wasobserved already in the 1960s, but there has been a lack ofknowledge of the underlying reaction mechanisms, kinetics, theresulting network structure and also the correlation betweenthe molecular structure and the physical properties ofthesematerials. The purpose of this thesis is to increase theknowledge of high pressurevulcanization, with respect toreaction kinetics and mechanisms, network structure andphysical properties.A low cis-polybutadiene was used as a model material forcrosslinking at high pressure (10-290 MPa) and temperature(240-250°C), and comparisons were made withperoxidevulcanizates. Both unfilled and carbon black filledsamples were studied. Nitrile- and styrene-butadienerubber werealso crosslinked successfully. Crosslink density is a centralconcept inthis thesis and was evaluated by swellingmeasurements. The microstructural changesoccurring duringvulcanization were studied by Fourier Transform InfraredSpectroscopy(FTIR) and 13 C solid state nuclear magneticresonance (NMR). The mechanical propertieswere investigated bydynamic mechanical thermal analysis (DMTA), tensile testing,and permanent set and stress relaxation measurements.Theprogress of the reaction proved to be well controlled by thetreatment time, temperature and pressure, resulting inmaterials with widely different properties within onesinglecompound due to the possibility of controlling thecrosslink density during the vulcanizationprocess. The reactionmechanism was shown to be of a radical type, and vinylunsaturations inthe polybutadiene are consumed concurrentlywith the crosslink formation. The effect ofpressure on thereaction is a decrease in molecular mobility, which results inhighercrosslinking reaction rate due to a decrease intermination reactions. When a carbon black filleris introduced,the number of polymer-filler interactions is increased due tothe ability of thepolymer to penetrate the carbon blackstructure under pressure. The mechanical properties areas goodas those of peroxide vulcanizates, and especially theresistance to deformation inservice-use at elevatedtemperatures suggests that the resulting material may be usedin gasketand seal applications. In spite of the difficulties ofmould sealing that arise at elevatedpressures, it was possibleto obtain vulcanized samples by common injection mouldingwithproperties comparable to those obtained by traditionalvulcanization.Keywords:High Pressure Vulcanization, Vulcanization,Crosslinking, Pressure, Elevated Temperature, Polybutadiene,Carbon Black, Rubber-Carbon Black Interactions, CrosslinkDensity, Peroxide Vulcanization, Injection Moulding,Nitrile-Butadiene Rubber.
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