Which joint involves no melting of the materials, merely using a chemical bond in thermoplastic piping?

The joint that involves no melting of the materials and relies solely on a chemical bond in thermoplastic piping is indeed the plastic adhesive joint. This type of joint is formed by applying an adhesive that chemically interacts with the surface of the thermoplastic materials, allowing them to bond together without the necessity of heat or melting the materials. This is particularly advantageous in situations where maintaining the integrity of the original materials is critical and where the application of heat could potentially cause harm or alteration to the pipes.

In contrast, plastic solvent cement joints involve the use of solvent to partially dissolve the surfaces of the thermoplastic before joining, essentially merging them through a melting process, which is a different mechanism altogether. Plastic heat fusion joints require heating the materials until they reach a molten state to allow for fusion, which is again a melting process rather than a chemical bond. Mechanical joints, on the other hand, rely on physical means, such as screws or bolts, to connect the pipes without any chemical or thermal changes.

This understanding of the different joining methods is essential in mechanical applications, especially when selecting the appropriate method based on the materials and the operational environment.