Screw, outside diameter

Concentricity Term to describe two circles or cylindrical shapes having a common center and common axis, such as the inside or outside diameters of a barrel or outside diameters of the surface and bearing surfaces of a screw. Deviation from concentricity is referred to as runout. Also refers to the relationship of all inside dimensions to all outside dimensions usually expressed in thousands of inch or millimeter FIM (full indicator movement). Deviation from concentricity is usually referred to as a runout. The concentricity should allow for the maximum part tolerance. The geometry of the part should help indicate the tolerance applied. 

The first time that a new screw is instaiied into an extruder, it is important that the screw be instaiied into the machine at room temperature. If the outside diameter of the screw is siightiy too iarge or if it has an unacceptabie yet smaii bend in it, the... 

Figure 10.31 The surface grinding process where a grinding lathe removes excess hard facing material from the outside diameter of the screw (courtesy of Jeffrey A. Kuhman of Glycon Corporation)...

The holding power of screws can be affected by the size of the pilot drill-hole, the depth of screw engagement, the outside diameter of the screw, and quality of the bone [Cochran, 1982 DeCoster et al., 1990], Therefore, the selection of the screw type should be based on the assessment of the quality of the bone at the time of insertion. Under identical conditions, self-tapping screws provide a slightly greater holding power than non-self-tapping screws [Tencer et al., 1993]. 

L/D ratio See screw length-to-diameter ratio, leach To extract a soluble component from a mixture by the process of percolation. See percolation, leachate A contaminated liquid that drains from landfills and must be treated before entering the environment. It can contain decomposed wastes, decomposition byproducts, heavy metals, or bacteria. See geomembrane, lead 1. The distance in an axial direction from the center of an element such as a screw flight at its outside diameter to the center of the same flight. See directional property. 2. A heavy metal, Pb is hazardous to one s health if inhaled or swallowed. Its use is restricted. In plastics it is found in certain products, such as additives. Pb can be used in safe environments since it has excellent performance properties, such as resisting attack by many corrosive chemicals and is impervious to x-ray and gamma radiation. See hazard x-ray. 

The die is held in a holder known as a die stock, which has a centred screw for adjusting the size and two side locking screws which lock in dimples in the outside diameter of the die, Fig. 2.20. The die is inserted in the holder with the split lined up with the central screw. The centred screw is then tightened so that the die is expanded, and the two side locking screws are tightened to hold the die in position. 

Conventional feeder screws have full-face flights welded to a centre shaft or tube. Uniform pitch screws are sometimes used in simple feeding applications. In order to secure differential intake of product along the axis of a screw, a range of techniques can be adopted, either individually or in combination where appropriate. Typical constructional features are (see Fig. 4.5) stepped pitch variable pitch stepped or taper centre tube or shaft variable screw diameter part ribbon or shaftless construction. (Occasionally the construction is stepped on the outside diameter.)... 

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