Process pulling force

Extrusion. In general, extmsion is the process of forcing a polymer melt through a die (104,105). Typical extmsion appHcations include initial resin pelletization after manufacture and production of film, sheet, pipe, tubing, and insulated wire. The HDPE extmsion temperature is around 150°C, the pressure 40—50 MPa (5800—7250 psi). An extmsion production line usually consists of an extmder (mono- or twin-screw) with a die at the end, a cooling and shaping device, a pulling device (a roUer), and a cutter. 

Figure 10-8. Upon exceeding an average pulling force of 80 17 pN, helix B and loop AB are unfolded (n = 31). (d) Helices C and B unfold in a three-step process. First, helix C unfolds at 108 26pN, thereby lengthening the stretched polypeptide to 158 aa (blue fit). Second, loop BC is pulled into the membrane at 116 33 pN (green fit). Third, helix B unfolds at pulling forces above 87 31 pN (n = 9). (e) Schematic drawing of the unfolding pathways found. The total number of force curves shown corresponds to 88...

Dembo et al. [1988] developed a model based on the ideas of Evans [1985] and Bell [1978]. In this model, a piece of membrane is attached to the wall, and a pulling force is exerted on one end while the other end is held fixed. The cell membrane is modeled as a thin inextensible membrane. The model of Dembo et al. [1988] was subsequentlyextended via a probabilistic approach for the formation of bonds by Coezens-Roberts et al. [1990]. Other authors used the probabilistic approach and Monte Carlo simulation to study the adhesion process as reviewed by Zhu [ 2000]. Dembo s model has also been extended to account for the distribution of microvilli on the surface of the cell and to simulate the rolling and the adhesion of a cell on a surface under shear flow. Hammer and Apte [1992] modeled the cell as a microvilli-coated hard sphere covered with adhesive springs. The binding and breakage of bonds and the distribution of the receptors on the tips of the microvilli are computed using a probabilistic approach. 

Dow has developed a pultrusion simulation modeling (PSM) service designed to help fabricators achieve higher levels of productivity and reliability. Process variables such as pull speed, part and die temperature, heater output and pulling force can affect the quality of pultruded components. The PSM tool allows fabricators to predict processing performance for specific applications, and is accurate to within 10% of actual performance. The tool has been validated in customer trials and allows the pultrusion process to be optimized quickly. 

Drawing is a plastic deformation process in which the cross-sectional area of a part is reduced by the contemporary action of a pulling force and a converging die. 

In any case, a pulling force is applied to the part at the exit area, and this strongly differentiates the process form extrusion, in which a pushing force is used. 

A major disadvantage of pultrusion parts consisting only of unidirectional fibers is the minor strength and stiffness in cross-direction. Thus, woven fabrics can be applied to the process. In order to prevent warping of the textile, the woven fabrics have to be placed between some pull-force resistant fibers (e.g., some unidirectional fibers orientated in process direction). 

The investigation of pulling forces during the thermoplastic pultrusion process has been widely neglected in research, although it is an important... 

There are always fibers necessary, which are aligned in process direction, in order to carry the pulling force. 

In contrast to the pultrusion process, the production speed and the maximum size of the profile are not limited by the required pulling forces. Due to the use of release films, there is no adhesion between the polymer and the surface of the mold. Furthermore, the friction between the release film and the tool is minimized because of the semi-continuous operating principle of the CCM process. 

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