Friction welding is a popular process for joining metal and polymer work pieces by rubbing them against each other. This way, friction heat is generated in a zone of the faying surfaces, thinner than ...1 mm. After cooling down, the heated surfaces establish a tight and strong bond. To improve this joining process, a method is desirable allowing measuring generated temperature and shear stress in the zone between the joining work pieces. Unfortunately, this is a very difficult task because the welding zone cannot be accessed with a sensor without significantly altering the process and thereby the desired measurement results. This paper describes how shear stress and temperature change generated by rubbing polymer pieces in a friction welding machine have been measured between the faying surfaces by employing sensor foils from the piezoelectric and pyroelectric polymer polyvinylidene fluoride (PVDF). This way, heating and cooling rates, pressure rise of the pneumatic system, frequency rise of the starting machine, the duration of starting and stopping, the damping of the vibrations after the drive was stopped, and the stress generated by the pullback of the machine head have been measured. A careful characterization of the sensor was necessary to enable distinguishing the measured voltage due to straining, shearing and temperature change.
Phosphate toxicity is a major threat to cardiovascular health in chronic kidney disease. It is associated with oxidative stress, inflammation and the accumulation of calcium phosphate commonly known ...as calcification in soft tissues leading to functional disorders of blood vessels. An improved calcification propensity test for the assessment of phosphate toxicity was developed, which measures the velocity of calcium phosphate mineralization from colloidal precursors in vitro. This so called T50 test measures the transformation from a primary into a secondary form of nanosized colloidal plasma protein-calcium phosphate particles known as calciprotein particles. The T50 test in its previous form required a temperature controlled nephelometer and several hours of continuous measurement, which precluded rapid bed side testing. We miniaturized the test using microfluidic polymer chips produced by ultrasonic hot embossing. A cartridge holder contained a laser diode for illumination, light dependent resistor for detection and a Peltier element for thermo control. Increasing the assay temperature from 37°C to 75°C reduced the T50 test time 36-fold from 381 ± 10 min at 37°C to 10.5 ± 0.3 min at 75°C. Incorporating sputtered micro mirrors into the chip design increased the effective light path length, and improved signal-to-noise ratio 9-fold. The speed and reproducibility of the T50 chip-based assay run at 75°C suggest that it may be suitable for rapid measurements, preferably in-line in a dialyser or in a portable microfluidic analytic device with the chip inserted as a disposable cartridge.
•Approximate calculation of forces between magnets.•Simple equations for cuboid magnets.•Magnetic forces as a function of their normal and lateral distances.•Only two parameters approximately ...describe the forces between magnets.•Comparison with measurements and FEM.
Equations are presented roughly describing the forces between cuboid magnets in normal and lateral direction as a function of their relative position. The equations are adapted to the forces measured with a tensile testing machine and obtained from finite element calculations. From the conservation of energy, a relationship between the magnetic forces in normal and lateral direction is derived. The equations may help designing machines containing solenoids or permanent magnets.
Ultrasonic Hot Embossing Schomburg, Werner Karl; Burlage, Katharina; Gerhardy, Christof
Micromachines (Basel),
06/2011, Letnik:
2, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Ultrasonic hot embossing is a new process for fast and low-cost production of micro systems from polymer. Investment costs are on the order of 20.000 € and cycle times are a few seconds. ...Microstructures are fabricated on polymer foils and can be combined to three-dimensional systems by ultrasonic welding.
Ultrasonic fabrication of fiber reinforced plastics made from thermoplastic polymer films and carbon or glass fibers enables cycle times of a few seconds and requires investment costs of only some ...10,000 €. Besides this, the raw materials can be stored at room temperature. A fiber content of 33 vol % and a tensile strength of approximately 1.2 GPa have been achieved by ultrasonic welding of nine layers of foils from polyamide, each 100 µm in thickness, and eight layers of carbon fibers, each 100 µm in thickness, in between. Besides unidirectional carbon fiber reinforced polymer composite (CFRP) samples, multi-directional CFRP plates, 116 mm, 64 mm and 1.2 mm in length, width and thickness respectively, were fabricated by processing three layers of carbon fiber canvas, each 300 µm in thickness, and eight layers of polyamide foils, each 100 µm in thickness. Furthermore, both the discontinuous and the continuous ultrasonic fabrication processes are described and the results are presented in this paper. Large-scale production still needs to be demonstrated.
It has been shown that the formation of calcium phosphate crystals can be detected in patient blood using a polymer microchip manufactured by ultrasonic processing. Ultrasonic processing is recently ...evolving for the fabrication of low-cost microfluidic devices from thermoplastic polymers. The formation of calcium phosphate crystals can be measured in the blood serum of a patient both optically from a change in turbidity or in electrical resistance.
A time of flight sensor has been equipped with a sensing wire parallel to the flow direction (flow parallel wire, FPW). A heat pulse is generated with a coil in the flow channel. The FPW has a center ...tap allowing its upstream and downstream parts to join in a half bridge. When a heat pulse passes the FPW, a large output peak is generated. The time between heat pulse generation and recording the peak maximum is only marginally affected by the properties of the fluid. With a combination of two FPWs, a measuring range of approximately 0.01–0.5 m/s can be achieved.
Vortex whistles generate a tone with a frequency which is a monotonically increasing function of the flow rate. This effect can be employed for flow sensors which do not need any lead-through into ...the fluidic channel because the frequency can be measured outside with a microphone. Flow measurements with vortex whistles can be performed both with gases and liquids. For comparatively small flow velocities the frequency is proportional to volume flow and only a weak function of temperature and fluid properties. The investigations presented here show that at high flow rates the frequency increases with the density of the gas. Micro whistles designed similar to organ pipes were also investigated. However their frequency is not proportional to flow velocity but is bowed similar as a root function. Therefore it is not very sensitive as vortex whistle at larger flow rates.
•Vortex whistle is employed as remote micro flow sensor without electronics.•Flow measurement with vortex whistles can be performed both with gases and liquids.•Output is a weak function of temperature and fluid properties at small flow rate.•For large flow rate the output is not linear.•For lager flow rate the output is a strong function of fluid properties.
Ultrasonic thermoforming of micro structures is similar as usual thermoforming, but the heat required for softening of the polymer is at least partly generated by ultrasonic vibrations. Cycle times ...as short as a few seconds are achieved by ultrasonic thermoforming and not much more than a commercially available ultrasonic welding machine is required for the process. This paper describes the process window of this fabrication process for polypropylene foils, 200 µm in thickness, as a function of preheating of the tool. Best results have been obtained at room temperature. Since the process is a function of temperature, it is concluded that production should be performed with a tool preheated to 45 °C to avoid an influence by a changing room temperature. The overall size of the samples is limited by the size of the available sonotrodes. The experiments described in this paper were performed on an area of 2 × 2 cm
2
, but larger sonotrodes with an area of, e.g., 8 × 12 cm
2
could also be employed. The size of the process window is a function of both the properties of the polymer and the inclination angle of the side walls of the structures on the tools.
We present a polycarbonate-based microfluidic device that was rapidly manufactured by ultrasonic hot embossing and welding. The fabrication of microstructures using ultrasonic processing allowed the ...embossing of micrometer-sized structures in polymer films by molding from a master die; this process was completed within seconds. The short manufacturing time required using this process and its ease of reproducibility allows rapid prototyping of custom-made microfluidic devices. Through ultrasonic fabrication, disposable microfluidic devices were newly designed and manufactured within a working day. The feasibility of these devices was demonstrated by cultivating yeast cells. The cells remained viable within this system for at least 22 h. Enhanced green fluorescent protein (eGFP) expression was initiated by providing the cells with a supply of the inducer galactose. The present study not only shows the potential of microfluidic devices fabricated by ultrasonic processing but also discusses their capability for use in microbial analysis.
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