How does solvent welding work

Sounds pretty nifty but shipping,storing and handling those nasty solvent-based flammable chemicals can be the stuff of nightmares. Not forgetting to mention weakening the substrate, attacking areas outside of the bond and in general leaving a scruffy appearance which for clear coloured plastics gives a really poor finish.

Solvents appear cheap to purchase compared to adhesives — although when you add up how much you get through, the extra cost of shipping and storing plus also consumption of volatile solvent materials will most likely be considerably more. Solvent cement is popular for bonding and sealing PVC water pipes together, its use is widespread in the plumbing industry. Many manufacturers of clear displays so things like menu racks, display units, display boxes, signage, literature racks etc.

Due to tightening of materials handling in the workplace plus the drive to improve product quality, there is now a strong demand for clear, non-yellowing adhesive products. This forces the softened surfaces into each other when the joint is assembled. Because the socket is tapered, it is slightly larger than the pipe at the top. The resin in the cement is there to fill any remaining gaps, but is not necessarily an agent in the bonding process.

In order to create this described ideal fit, contractors must follow the appropriate steps. The physical solvent-welding process is quite simple.

There are four basic steps to prepare a pipe and fitting for solvent welding:. Once the pipe is properly prepared, a solvent cement that suits the piping application can be applied to the pipe and fitting following these four steps:.

While solvent cement only takes 30 seconds to set, the cure times are a function of pipe size, system pressure, temperature, moisture and humidity. The assembly must be allowed to set without any stress on the joint for one to five minutes, and the system should not be pressure-tested until minimum cure times have been met.

In order for solvent cement to effectively bond CPVC piping, some simple regulations and precautions should be followed, as shown in the chart to the right. The solvent-welding technique described is a process that creates a reliable piping system for your plumbing or fire protection needs. The solvent diffuses into the polymer, softening the surfaces and allowing interdiffusion of the polymer chains across the interface.

The weld is formed through the application of pressure. Since the solvent reduces the glass transition temperature Tg of the polymer, welds can be formed without the applied heat necessary in other welding processes.

Weld strengths approaching that of the parent material can be achieved, although the presence of residual solvent tends to result in some loss of strength in the joint region. The inside of the socket is slightly tapered, from a diameter slightly larger than the pipe OD at the entry, to a dimension at the base of the socket that is a few thousandths of an inch smaller than the pipe OD.

Thus, the pipe-to-socket match-up results in an interference fit more-or-less midway in the socket. Solvent cement is applied to the outside of the pipe end and the inside of the socket. The pipe is then pushed into the socket until it bottoms.