Wall thickness ranges and tolerance

Table 8-7 Example of wall thickness ranges and tolerances for RPs...

Table 7-5. Example of Wall-Thickness Ranges and Tolerances for RP/Composite Parts... 

Referring again to Fig. 8.32, the nominal wall (W) can range fi om 0.080 to 1.000 in, with wall variations as low as 0.010 in for thin walls and 0.020 in for heavy walls. However, the wall thickness can drop to 0.060 in when the glass fiber content is less than 20%. Large variations in wall thickness can be tolerated. Inside radii (IR) should be a minimum of 0.250 in. Draft should be 1 to 3° to a depth of 6 in, 3° from a depth of 6 to 12 in, and an additional 1° for every 6 in beyond that. 

Schott supplied the mirror substrates for both X-ray telescope projects, namely ROSAT and AXAF. As far as production technology is concerned, the AXAF tubes, measuring up to 1274 mm in diameter and 991 mm in length, with wall thicknesses ranging from 17 to 24 mm, constituted the greatest challenge. Tolerances of 0.1 mm and axial runout of the front sides, as well as circular runout of the conical surfaces within 0.05 mm have had to be observed (see Fig. 4.53). 

The components of a pipe extrusion line include an extruder, annual die, calibration system, cooling system, puller, wind-up unit or stacker, and auxiliary equipment. The extruder typically has anL/D of 24 1 or greater and the screw design depends on the material. Conical twin-screw extruders are often used for poly(vinyl chloride). The diameter of the annular dies is 25 to 100 percent of the extruder diameter. However, the output of a pipe extrusion line is limited by the ability of the downstream equipment to cool the product and hold tolerances. Since extruder capacity is often underutilized, the same die may be used for a range of pipes of differing diameter and wall thickness. IVpically, a number of adapters and replaceable components are used with the same rear section of die. Dies with multiple outlets are employed when large-diameter extruders are used for small-diameter pipe. 

Achievable tolerances ranging 0.25- 2mm, and largely mold dependent. Wall thickness tolerances typically 20 per cent of the nominal. 

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