Home

About Us

Cast Components

Formulations

Products by Application

Support

Downloads

Determine the Cause of Cracking in an Epoxy or Urethane Cast Component

 

A Quick Check List to Determine the Cause of Cracking in an Epoxy or Urethane Cast Component:

If the problem is recent, the Number 1 step is to check if anything has changed in your process. Do not assume! Check! - Take the show me how you do it approach!

 

Some common things to look for are:

  • Are you using the proper mix ratio? (i.e. new or different operator)
  • Are you mixing thoroughly? (i.e. new or different mixing method)
  • Material mix temperatures (check with a probe)
  • Oven temperatures (don’t trust the gauge, measure inside the oven)
  • Changes in part design (corners, sharp edges etc.)
  • Look for new shortcuts in various parts of your process

 

Some of the usual reasons for epoxy or urethane cracking before and during thermal cycling are as follows:

  1. Fillers not evenly distributed in the mix
  2. Insufficient mixing of resin and hardener mixture (this will result in resin or hardener rich areas within the mix causing different rates of hardening within the mixed product)
  3. Sharp edges on the part (this would result in micro cracks being initiated during gellation which would fully develop as the material cures or during thermal cycling).
  4. Incorrect mix ratio resulting in higher exotherm, faster gellation, more shrinkage (i.e. too much resin, too much hardener or visa versa)
  5. Improper cure resulting in excessive shrinkage (cure temperature too high)
  6. Incorrect oven temperature or excessive zoning in the oven (hot spots)
  7. Vast variation in epoxy wall thickness in the casting
  8. Different heat capacity of internal components resulting in different rates of gellation
  9. Inadvertent thermal cycling of the cast unit before full cure. This is a very common occurrence (i.e. taking the part out of the mould after gellation and putting it on a cold surface (bench top or concrete floor) for a period of time before placing it into a curing oven)
  10. Improper combination of material cured properties (i.e. tensile strength and % elongation)

 

In the case of heat cure products, a quick intermediate solution may be to stage cure the casting. This is done by starting cure at a lower temperature than the cure temperature specified by the supplier (i.e. 60oC or 140oF for a 120oC specified cure) for one hour or so followed by one hour at 80oC and so on until the specified cure temperature is reached. Stage curing will allow the epoxy or urethane to gradually solidify in a more relaxed state with less built in stresses.

In most cases it is also helpful to “post cure“the casting. This is done by exceeding the supplier’s specified cure temperature by 10 to 20o for an hour or so. This will force the reaction to be completed and develop maximum strength.

Keep in mind that most formulators take the “if it isn’t broken, don’t fix it” approach, therefore, if it worked before it is likely that something changed in your process.

 

Phone: (+1) 905.673.0510
Toll free North America: 1.800.563.3769
This email address is being protected from spambots. You need JavaScript enabled to view it.
 
6380 Viscount Road,
Mississauga, ON L4V 1H3. Canada