THE SCIENCE OF SOLVENT WELDING Lou Mihamou Director - International Sales Weld-On Adhesives, Inc. Presented by:

Solvent Welding as Science Welding is a scientific process Solvent welding is a form of welding that uses chemicals rather than heat to produce a bond When properly understood and implemented it is: Cost effective Reliable Resilient Strong Permanent

Cement & Primer: Cost vs. Value Less than 1% of the material cost in a plastic piping system, cement & primer play an integral role in a complete and functional fluid system

Preventing Misuse of Solvent Cement Understand Solvent Cements How it works What is in it The relevance of pipe and fitting dimensions and tolerances Factors that can reduce weld strength

How Solvent Cement Works

Solvent Welding is a chemical weld Typically welding needs heat to melt the parts and pressure so they flow into each other Solvent Welding is a chemical weld The melt occurs with chemicals rather than heat, and the radial pressure generated by the pipe/fitting interference completes the weld The right combination and proportion of solvents and appropriate radial pressure welds the pipe and fitting together

Solvent Cement: How it Works Joins pipe and fittings by fusing – not gluing Glues & Adhesives Glues bond to part A on one side and to part B on the other side If the two components are in actual contact with each other, there would be no glue left in between them and therefore no bond Solvent Cement Does not work properly when there is space between part A and part B. 80% of the bond strength in a solvent weld comes by fusing part A into part B.

Solvent Cement: How it Works The two components have ‘flown’ into each other Where is the Solvent Cement? Some components in a Solvent Cement penetrate, melt and/or swell the material, then evaporate Allows the substrates to regain crystallinity and with it all of their physical properties. With the addition of radial pressure pushing part A into part B, they become one solid block

Chemical Composition of Solvent Cements

Solvent Cement: What’s in it? Contains two primary components that can serve several functions: Solvents -Dissolve PVC & CPVC resin -Swell PVC & CPVC material -Control evaporation -‘Lubricate’ the joint Cements -Fill any gaps between pipe OD and socket ID allowing radial pressure to be generated throughout the joint

Dissolve PVC & CPVC resin. True Solvents Dissolve PVC & CPVC resin. -Because of their very aggressive nature they will penetrate deep into the pipe and fitting wall When appropriate, the difference between deep and shallow solvent penetration is easy to illustrate -Consider two wood boards, joined by a nail: Deep penetration allows for a more complete weld Depending on factors such as temperature and wall thickness, too deep of a penetration may increase cure time or compromise the integrity of the pipe and/or fitting

Swelling Some solvents are designed to swell the pipe and/or fitting wall Increases the interference between pipe and fittings Essential to create radial pressure which forces material from the two components to mix with and into each other Makes the surfaces more porous Allows deeper penetration of the solvents

Evaporation Control Some Solvent Cements include solvents with a high boiling point which slows the rate of evaporation Helpful for large diameter systems and for use in very hot weather installations For small diameter jobs where a quick cure time is needed or in very cold weather applications, these solvents are not as desirable

Lubrication Solvents don’t actually lubricate, they create conditions similar to lubrication Allows the full penetration of the pipe into the fitting socket in any interference‐fit connection Without Solvent Cement, it is difficult to bottom out an interference fit joint without damaging either the pipe, fitting or both After the solvent has been worked into the surfaces, ~1/3 of the wall thickness of the pipe OD and socket ID will be temporarily softened, minimizing resistance allowing the pieces to ‘mix’

Cements Cements must: Cement components include: Fill any gaps between the pipes and fittings Fill them with material that has sufficient density to act as a wedge and actually generate some radial pressure even in places where there are gaps Fill them with material which is compatible with the installation and performance of the operating system Cement components include: Resin Additives Fillers

Resin Same resin that is used for the pipe and fitting compounds Should have the same cell classification to ensure performance consistent with the rest of the system Because PVC Cement uses PVC resins with a lower cell class than CPVC, it is not able to handle the operating parameters of a CPVC system and should never be used with CPVC However, CPVC solvent cement can be used to join PVC pipes and fittings

Resin The amount of resin in Solvent Cement varies depending on the desired viscosity There is a saturation limit around the 20% mark ASTM standards require that a minimum of 10% of either PVC or CPVC resin must be used Two Solvent Cements one with 10% and one with 18% resin will both meet the standard, but they will perform differently in the field

Additives and Fillers Solvents and Cements perform the primary tasks in forming a Solvent Weld, but there are other considerations impacted by the ingredients in the Solvent Cement: Viscosity Stability Shelf life Color To meet these specific needs additional fillers, additives and stabilizers may be included in the Solvent Cement formulation

The Science of Weld Strength

Weld Strength: Fit Radial pressure is required to create fusion, which provides 80% of the weld strength Interference Fit Net Fit Loose Fit Radial pressure is achieved in PVC or CPVC systems using either a tapered socket (IPS systems) that produces an interference fit or extra heavy viscosity cements (DIN systems)

Weld Strength: Fusion Area Efficiency Voids and inclusions in the fusion area can reduce weld strength Voids and Inclusions may be caused by Angled pipe cuts Presence of burrs and filings on a cut pipe Less then full pipe insertion

Weld Strength: Fusion Area Efficiency Insufficient solvent cement coverage in the fusion area may reduce weld strength Reduces lubrication in the fusion area Reduces the likelihood of full pipe insertion Shortens the exposure of the fitting wall to the softening agent