Mechanism of fire retardancy of polyurethanes using ammonium polyphosphate

In this work, we studied the mechanism of the fire retardancy of ammonium polyphosphate (APP) in polyurethane (PU). Indeed, according to the limiting oxygen index test, the efficiency of APP in PU coating was proven. On the one hand, thermogravimetric analyses showed that the addition of APP to PU accelerates the decomposition of the matrix but leads to an increase in the amount of high‐temperature residue, under an oxidative or inert atmosphere. This stabilized residue acts as a protective thermal barrier during the intumescence–fire retardancy process. On the other hand, spectroscopic analysis of the charring materials using infrared spectroscopy, MAS NMR of the solid state, and ESR enables better understanding of the carbonization process and, consequently, of the intumescence phenomenon. It has been shown that the char resulting from PU consists of an aromatic carbonaceous structure which condenses and oxidizes at high temperature. In the presence of APP, a reaction between the additive and the polymer occurs, which leads to the formation of a phosphocarbonaceous polyaromatic structure. Moreover, this char is strongly paramagnetic. The presence of large radical species, such as a polyaromatic macromolecule trapping free radicals, was demonstrated. Both of these characteristics help to explain the fire‐retardant performance of PU/APP. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3262–3274, 2001     

Grinding of microstructured functional surfaces: a novel strategy for dressing of microprofiles

For the grinding of microstructured functional surfaces called riblets, a novel dressing strategy using diamond profile rollers was introduced for the generation of microprofiles on vitrified grinding wheels. The purpose of the present study is to grind special designed riblets (microgrooves with a width of 40 μm and depth of 20 μm) on the surfaces of compressor blades with the purpose of drag reduction in turbulent flow. It is currently not possible to achieve the desired microprofiles on grinding wheels by profile dressing directly, due to the limited producible minimal profile tip geometry on the dressing roller. The new profile dressing strategy using a profile shift kinematic allows generating microscopic roof profiles with an ideal sharp profile tip. Compared with dressing using form rollers, the new dressing method using profile rollers offers a much higher dressing efficiency and process stability at dressing microprofiles.     

Production-based design of a hybrid load introduction element for thin-walled CFRP Structures

The project “Multi-Layer Inserts” (MLI) proposes a new design for inserts used in thin-walled CFRP structures. The proposed inserts consist of multiple thin metal sheets and is build up simultaneously with the laminate in an intrinsic hybridization process, eliminating time-consuming post-processing steps. Furthermore, at equal weight, such inserts greatly increase the bonding area between metal and CFRP in comparison to conventional inserts. This results in a significant increase of the loads that can be transmitted into the CFRP. The present work discusses how the shape of the metal sheets which the proposed inserts consist of influences the mechanical properties of the surrounding laminate. This influence is investigated by measuring the strain distribution during tensile tests by means of digital image correlation. The strain distributions around the following three different MLI design approaches are compared: An elliptical metal sheet, which is expected to be ideal in terms of mechanical performance of the overall structure; a cross-shape metal sheet representing a production-driven simplification which only requires the ability to perform cuts in individual tows perpendicular to the laying direction and can be performed by state-of-the-art AFP systems; and lastly, a compromise between manufacturability and achieved mechanical performance, a decagonal metal sheet design, which requires angled cuts of the fiber tows. It is shown, that the decagon is able to evenly spread the strain over a larger area and is therefore able to significantly reduce the maximum strain values compared to a cross-shape metal sheet, while still being automatable.     

Biomechanical characterisation of a degradable magnesium-based (MgCa0.8) screw

Magnesium alloys have been in the focus of research in recent years as degradable biomaterial. The purpose of this study was the biomechanical characterisation of MgCa0.8-screws. The maximum pull out force of screws was determined in a synthetic bone without corrosion and after fixed intervals of corrosion: 24, 48, 72 and 96 h. This in vitro study has been carried out with Hank’s solution with a flow rate corresponding to the blood flow in natural bone. A maximum pull out force (F_max) of 201.5 ± 9.3 N was measured without corrosion. The biomechanical parameter decreased by 30% after 96 h in corrosive medium compared to the non-corrosion group. A maximum load capacity of 28 ± 7.6 N/h was determined. Our biomechanical data suggests that this biodegradable screw provides a promising bone-screw-fixation and has great potential for medical application.     

Condition based maintenance planning of highly productive machine tools

The competitiveness of producing enterprises in high-wage countries is extremely dependent on the productivity of the production line. Consequently, the availability of machines displays an essential index. The aim of the research project ??Make-it?? (Condition Based Maintenance Planning of Highly Productive Machine Tools) was to improve the availability of machine tools. Therefore, within this joint project, new methods and approaches for condition based maintenance were investigated. Thereby, an important objective was to develop an innovative maintenance algorithm which enables to calculate the most cost-effective maintenance times based on a continuous prognosis of the remaining life time, maintenance costs, and potential failure costs. This paper describes the results of the developed maintenance approach. Within this paper, the fundamental mathematical foundations of the innovative, cost-oriented maintenance algorithm and the use of the data of machine condition are presented in the first part. Moreover, the implementation of the algorithm in a computerized maintenance management system is described. The validation of the cost-oriented maintenance planning by means of event-oriented simulation will also be part of this paper.     

Process stabilization with an adaptronic spindle system

For economical reasons it is necessary to reduce the machining time and to increase the process automation. This leads to the need for fast machine tools with high process stability in order to enhance the material removal rate. However, the machine often does not limit the process stability but the tool because of its compliance. This paper presents a new possibility of expanding the stable process range of long and slender end mills with an adaptronic spindle system. The system is able to position the spindle dynamically in the range of microns with three piezo actuators. In order to disturb the regenerative effect, which leads to an instable process, the chip thickness is modulated by a dynamic spindle actuation. This is realized by a superposition of vibrations of the tool in feed direction. In milling tests the degree of stabilization is verified for different superpositions. Hence, the stable process range could be improved for spindle speeds up to 5,000?rpm.     

Development of an advanced micro-positioning system for increasing operation accuracy: consideration of high pressure sealing

This paper presents the development of a micro-positioning system for the increase of operation accuracy of machine tools. A highly dynamic piezo-actuated micropump coupled with a hydraulic cylinder transforms small strokes of the piezoelectric actuator into a continuous piston movement. Fast-switching active valves direct the volume flow. Crucial for the functionality of the pump module is the sealing function of the membrane to isolate the piezoelectric actuator unit against high pressure fluid. Therefore, the requirements for foil membrane selection are investigated by means of a developed test bench. It is demonstrated that a successful test of foil membrane materials provides a closer insight into the entire valve characteristics.     

CFD modeling of the Wurster bed coater

In the Wurster bed coater, the wetting, drying, and circulation of particles are combined to produce a high quality coating. The drying and wetting conditions in a laboratory scale Wurster bed coater are modeled and compared with experimental data. A model combining multiphase fluid dynamics with heat and mass transfer is developed to model the particle and gas motion and the transport of thermal energy and moisture. A wetting region is defined, where a specified moisture content is set in the particle phase, above the jet inlet, to describe the injection of coating liquid. The simulation shows the characteristic circulation of particles in the equipment, as well as the behavior of the moisture in the system and agrees well with measurements. The simulation indicates how different process conditions influence the drying regions. The results show that most of the drying, under typical operating conditions, takes place in the Wurster tube. © 2009 American Institute of Chemical Engineers AIChE J, 2009