1.1 This specification covers two kinds of rolls used in machinery for producing corrugated paperboard. Rolls are fabricated of forged bodies and trunnions. The trunnions may be bolted or shrink assembled on one or both ends of the body. A seal weld may be made at the body/trunnion interface. Roll shells are made of carbon/manganese, or low alloy steel as hereinafter described, and are heat treated prior to assembly. Pressure rolls are surface hardened. Provision is made in Supplementary Requirement S1 for the optional surface hardening of corrugating rolls.
1.2 Corrugating and pressure rolls made to this specification shall not exceed 30 in. [760 mm] in inside diameter. The wall thickness of the roll body shall not be less than 1/12 of the inside diameter or 1 in. [25 mm], whichever is greater, but shall not exceed 4 in. [100 mm]. The wall thickness of the corrugating roll is measured at the bottom of the corrugations in the location of the trunnion fit. The maximum design temperature (MDT) of the roll is 600°F [315°C] and the maximum allowable working pressure (MAWP) is 250 psi [1.7 MPa]. The minimum design temperature shall be 40°F [4°C] for roll wall thicknesses up to 3 in. [75 mm]. For roll wall thicknesses over 3 in. [75 mm] to 4 in. [100 mm], the minimum design temperature shall be 120°F [50°C]. The maximum stresses on the roll bodies from the combined internal and external loading are limited to 18 750 psi [129 MPa] for the Class 2 pressure roll bodies, and 20 000 psi [138 MPa] for Class 1A, 1B, or 5 pressure or corrugating roll bodies in Grades 1 or 2. For the trunnions, the maximum stresses from the combined internal and external loading are limited to 15 000 psi [103.4 MPa] for Classes 3 or 4, or 20 000 psi [138 MPa] for Classes 1A, 1B, or 5 in Grade 2 only. The Grade 1 strength level is not permissible for trunnions.
1.3 Referring to Table 1, material to Classes 1A, 1B, or 5 shall be used for the manufacture of corrugating or pressure roll shells, and Class 2 shall be used only for pressure roll shells. Trunnions shall be made from forgings in Classes 1A, 1B, or 5 in Grade 2 strength level as restricted by Footnote B in Table 2 or in forgings in either Class 3 or 4.
1.4 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.
1.5 Unless the order specifies the applicable “M” specification designation, the material shall be furnished to the inch-pound units.
1.6 Except as specifically required in this standard, all of the provisions of Specification A 788/A 788M
TABLE 1 Chemical Requirements
| ||Composition, %|
|Class 1A||Class 1B||Class 2||Class 3||Class 4||Class 5|
|Carbon||0.45–0.60||0.40–0.60||0.55 max||0.35 max||0.35 max||0.50–0.60|
|Phosphorus||0.025 max||0.025 max||0.025 max||0.025 max||0.025 max||0.025 max|
|Sulfur||0.025 max||0.025 max||0.025 max||0.025 max||0.025 max||0.025 max|
|SiliconA||0.15–0.35||0.15–0.35||0.15–0.35 max||0.15–0.35||0.15–0.35 max||0.15–0.35|
A When vacuum carbon deoxidation (VCD) is used the silicon content shall be 0.10 % maximum.
TABLE 2 Tensile Requirements
|Class||Grade||Yield Strength, minA||Tensile Strength, min||Elongation in 2 in. or 50 mm, %, min||Reduction of Area, %, min|
|1A, 1B or 5||1||130||||150||||12.0||30|
|1A, 1B or 5||2B||65||||100||||14.0||30|
|3 or 4||...||30||||60||||22.0||55|
A 0.2 % offset.
B For trunnion application, a maximum tensile strength of 125 ksi [860 MPa] applies for Grade 2 of Classes 1A, 1B, or 5.