Stabilisation of isocyanate cross linked polybutadiene binder

Isocyanate cross-linked hydroxy terminated polybutadiene is used as a binder for solid rocket propellant. Rocket motors containing this propellant require a storage life of at least 20 years. During storage it has been found that the important rubbery properties of the binder can be lost due to oxidative cross-linking of the polybutadiene chains. This could cause catastrophic failure when the rocket motor is required. At present the bis-hindered phenol Calco 2246 is used as a thermal oxidative stabiliser, but it's performance is only adequate. This has led to the search for a more efficient stabiliser system. To hasten the evaluation of new antioxidant systems the use of dynamic thermal analysis was investigated. Results showed that a tentative relationship existed between predictions by thermal analysis and the long term oven ageing for simple single antioxidant systems. But for more complex systems containing either autosynergistic or mixed antioxidants no relationship was observed suggesting that results for such an "accelerated" technique cannot be used for the purpose of extrapolation for long term performance. This was attributed to the short time and more aggressive condition used (hjgher temperature and oxygen rich atmosphere in thermal analysis) altering the mechanism of action of the antioxidants and not allowing time for co-operative effect of the combined antioxidant system to form. One potential problem for the binder system is the use of an diisocyanate as a cross-linking agent. This reacts with the hydroxyl hydrogen on the polymer as well as other active hydrogens such as those contained in a number of antioxidants, affecting both cross-linking and antioxidant effectiveness. Studies in this work showed that only antioxidants containing amine moieties have a significant affect on binder preparation, with the phenolic antioxidants not reacting. This is due to the greater nucleophilicity of the amines. Investigation of a range of antioxidant systems, including potentially homo, hetero and autosynergistic systems, has highlighted a number of systems which show considerably greater effectiveness than the currently used antioxidant Calco 2246. The only single antioxidant which showed improvement was the partially unhindered phenol y-Tocopherol. Of the mixed systems combinations of the sulphur containing antioxidants e.g. DLTP with higher levels of chain-breaking antioxidants, especially Calco 2246, were the most promising. Also the homosynergistic mix of an aromatic amine and a phenol was seen to be very effective but the results were inconsistent. This inconsistency could be explained by the method of sample preparation used. It was shown that the efficiency of a number of antioxidant.s could be dramatically improved by the use of ultrasound during the mixing stage of preparation. The reason for this increase in performance is unclear but in the case of the homosynergistic amine/phenol mix both more efficient mixing and/or the production of a novel mechanism of action are suggested

Design and analysis of a 2-DoF split-stator induction motor

A two degrees of freedom (2-DOF) actuator capable of producing linear translation, rotary motion, or helical motion would be a desirable asset to the fields of machine tools, robotics, and various apparatuses. In this paper, a novel 2-DOF split-stator induction motor was proposed and electromagnetic structure pa- rameters of the motor were designed and optimized. The feature of the direct-drive 2-DOF induction motor lies in its solid mover ar- rangement. In order to study the complex distribution of the eddy current field on the ferromagnetic cylinder mover and the motor’s operating characteristics, the mathematical model of the proposed motor was established, and characteristics of the motor were ana- lyzed by adopting the permeation depth method (PDM) and finite element method (FEM). The analytical and numerical results from motor simulation clearly show a correlation between the PDM and FEM models. This may be considered as a fair justification for the proposed machine and design tools.