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

2. 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

3. 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

4. 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

5. How Solvent Cement Works

6. 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

7. 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.

8. 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

9. Chemical Composition of Solvent Cements

10. 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

11. 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

12. 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

13. 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

14. 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’

15. 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

16. 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

17. 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

18. 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

19. The Science of Weld Strength

20. 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)

21. 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

22. 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