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What are the key considerations when bonding or butt-fusing plastic flanges?
2018-03-07
In construction, plastic pipes are often connected to cast-iron flanges, iron valves, and other pipe fittings using plastic flanges. There are primarily two types of flanges: one is the injection-molded flange for diameters up to Φ315 (available in socket and adhesive versions), and the other is the socket-type flange made from welded or glass-fiber-reinforced composite materials, available in various sizes. When connecting these flanges, it’s crucial to first ensure that both the plastic and cast-iron flanges adhere to the same standards and have identical pressure ratings. Currently, the most commonly used standard is the national code, though users may occasionally opt for flanges following standards set by the Ministry of Metallurgy or other industry-specific guidelines. Commonly applied pressure ratings include 1.0 MPa, 1.25 MPa, and 1.6 MPa. Only when flanges with matching standards and pressure ratings are selected can their external dimensions—such as outer diameter and hole spacing—be properly aligned during installation.
Injection-molded adhesive flanges, also known as slip-on flanges, consist of three main components: the flange gasket, the flange seal, and the flange plate. When bonding injection-molded flanges, in addition to following the guidelines outlined in "How to Bond Plastic Pipes and Fittings?", you should also pay attention to the following key aspects:
1. Before bonding, first slide the loose flange onto the middle of the pipe, and then proceed with attaching the flange gasket. Otherwise, after the gasket is bonded, the flange may end up being pushed inward—specifically, one end features a Reuter expansion joint, while the other end already has the bonded gasket in place.
2. The orientation of the loose flange must be correct, as the two sides of the loose flange are different— one side is flat, while the other features a groove. This difference in design restricts the direction in which forces can be applied; therefore, the grooved side should face the mating flange on the opposite side. After bonding, allow sufficient time for the adhesive to fully cure before tightening the bolts.
When connecting a fiberglass-reinforced composite flange with other flanges, ensure that the screw hole orientations align properly. For instance, if one flange is already attached to the pipe, the composite flange being connected afterward must have its screw holes aligned directly opposite those of the previously installed flange; otherwise, the misaligned holes will prevent the bolts from passing through smoothly.
When tightening bolts, whether using injection-molded flanges or fiberglass-reinforced composite flanges, ensure that the flange centers are aligned on the same horizontal line. Additionally, both sides of the flange should be perpendicular to the pipeline, with uniform gaps between them. Be sure to use washers under the bolts to increase the contact area, and tighten the bolts symmetrically while applying even pressure—this will help achieve an ideal sealing effect.
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