Resin-treated compressed wood laminates (compregs) - Specification, Part 2: For chemical purposes
1989 Edition

According to the standard, compregs for chemical applications are classified into two main types based on veneer grain orientation: Type V, where the grain runs parallel to the load direction, suitable for tensile load components such as rods and turned parts; and Type VI, which has grain directions approximately equal and perpendicular across axes, ideal for applications requiring high compressive strength like sheets and blocks. The grain alignment is essential for achieving the desired mechanical characteristics.

Compregs intended for chemical usage must meet specific physical properties including a minimum specific gravity of 1.25, moisture content below 4%, and water absorption not exceeding 1.2% at 27±2°C. Mechanically, they must demonstrate minimum tensile strengths of 200 MPa for Type V and 100 MPa for Type VI, bending strengths of 200 MPa and 90 MPa respectively, along with specified compressive, shear, hardness, and impact strengths. These properties are verified through standardized test methods to ensure durability and performance in chemical settings.

Chemical resistance testing involves immersing specimens in 20% solutions of sulphuric, nitric, and hydrochloric acids for 12 weeks. Post-soaking, mechanical tests for bending, compression, and impact strengths are conducted. The compregs must retain a minimum of 75-80% of their original impact strength, 40-70% of bending strength, and 70-80% of compression strength depending on the acid type. This ensures the compreg’s suitability for prolonged exposure in harsh chemical environments.

The production process requires vacuum impregnation of veneers using alkali-catalyzed phenol or cresol formaldehyde resin or phenol formaldehyde film resin, ensuring a minimum resin content of 40% by oven-dry weight. The curing stage is conducted at temperatures between 135°C and 150°C, under bonding pressures ranging from 7 to 15 MPa. These conditions guarantee the compreg’s high density and chemical resistance appropriate for chemical industry applications.

For compreg boards, length tolerance is +6 mm / -0 mm, width tolerance +3 mm / -0 mm, and thickness tolerance is ±10% for boards under 6 mm thickness and ±5% for those 6 mm and above. Edge straightness and squareness are controlled within 2 mm per 1000 mm (0.2%). Rods have zero negative tolerance on diameter, with standard lengths and diameters specified. These tolerances ensure dimensional stability and fit for chemical-resistant applications.

Finishing must comply with varnish specifications as per IS 524:1983, and testing methods outlined in IS 525:1968. The varnishes provide essential protection to compreg surfaces, enhancing durability and chemical resistance. Manufacturers are also required to furnish certificates of conformity for finished machined components, confirming adherence to the standard’s finishing criteria.

Purchasers must specify the quantity, material type, exact dimensions including size and thickness, and provide detailed drawings with tolerances for components. They should indicate finish type—platten or machine finish—and surface treatments such as oil or varnish finish. Any additional special requirements must also be communicated. This ensures the supplier can meet exact specifications and quality standards as per the standard.