Undercut elements

A cut perpendicular to the axle of a self-wiping screw element shows the same free cross-section at any point independent of the screw pitch or pitch direction. If this needs to be enlarged to improve product intake, the contour of the intermeshing profile may have to be abandoned in some cases. These undercut or double undercut elements (Fig. 12.12) offer 15 to 30% increase in the product volume, but increase the risk for product building up on the un-cleaned flanks of the elements. 

Conveying elements with single or double-flighted self-wiping profiles and undercut profiles differ substantially regarding certain factors relevant to the extruder conveying capability, i.e., free volume and conveying efficiency (Fig. 12.13). 

FIGURE 13J36 (a) Density distribution as measured by a quantimet in the r ion of an undercut in a die pressing Cu powder. Data taken from Perdman and Roman [78, p. 43]. (b) Density distribution predicted by finite element methods. Taken from Bortz-meyer [82]. 

West et al. [51] simulated shape changes in through-mask electrochemical micromachining. The degree of undercut was predicted for vertictilly-walled cavities of different aspect ratios, assuming primary current distribution. The boundary-element method was used. 

The lower film is etched by the solution subetching the upper layer as well. The magnitude of undercutting is regulated (depending on the circuit complexity) by the component ratio of the solution for etching the lower semitransparent film. The dimensions and smoothness of the edges are determined by elements produced in the lower layer of the semitransparent film (base film). 

Because the simple dexel model is not able to represent undercuts in direction of the dexel elements, an extended model is used for most implementations, where more than one element can be stored at each grid position. 

Polymerization with more than raie species of monomer, which can react with (Mie another, forming a copolymer. Either a male element in die that produces a hole or recess in a part, a part of a complex mold that molds undercut parts (cores are usually withdrawn to one side before the main sections of the mold open), a channel in a mold for circulation of a heat-transfer medium or the central part of a laminate. 

Samples and standards, in the form of the ignited oxide powder, are mixed with graphite powder which acts as a spectroscopic buffer, and prevents the formation of molten globules which tend to be ejected from the electrode cup. This mixture is loaded into an undercut graphite cup electrode. Direct-current arc excitation is employed, and the spectra of samples and standards are recorded on suitable photographic plates. Intensity ratios of selected line pairs are determined photometrically. The concentration of the element sought is read from an analytical curve that relates the logarithm of the concentration to the... 

External undercuts normally have to be demolded using lateral moving elements. Sliders, splits and core pullers can be used for this application. 

Thin-gauge products are often flexible enough to be pulled from minor undercuts, such as detents. If necessary, ejector pins or rings are used. Moveable mold elements are used with undercuts of thick products or for plastics that are stiff at product removal time. Simple moving elements are hinged to swing away as the product is withdrawn. For severe undercuts, pneumatic cylinders are activated to move elements away as the product is pulled from the mold cavity. Orphan mold elements exit with the product are removed and are reassembled in the mold for the next cycle. 

Structural elements, polysilicon for resistors and wires, and nitride for electrical insulation. The nickel sidewalls can be further coated with a thin gold layer to improve the electrical conductivity for improved electrical contact in relays. Structural elements can be released by either using sacrificial oxide or undercutting with trenches formed in a bulk KOH etch. An example of a microrelay formed in the MetalMUMPS process is shown in Figure 1.15. A cross section showing all of the layers used to fabricate the relay is shown in Figure 1.16. 

Anchors without end plates (Fig. 11) consist of a metallic profile that is embedded in the masonry and can transmit loads to the substratum by mechanical locking, friction, bond, or a combination of these three (EUgehausen et al. 2006), rather than use of an element such as a plate, a key, or a peg. Mechanical locking can be obtained, for instance, by undercut, namely, shaping the end part of the hole and introducing an anchor with an end shape so as to result larger than the rest of the shaft. Friction systems, instead, consist of torsion or displacement-... 

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