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Clean Molds & Endplates

“My boss is always on my case to keep my molds clean.  They’re a pain!  Does it really matter?”

Yes, it does matter.  If your molds look like the ones below, you have some work to do.

Figure 1: Dirty Molds.

Required for Certification

The checking of mold assemblies is part of the proper annual verification/calibration of a gyratory compactor.  And to check them, requires that they be clean. Not only does the standard require them to be clean, they must be clean to receive an accurate measurement.

AASHTO T312 Section A1.1 states “Minimum frequency of this evaluation [the evaluation of the molds as a check for compliance] is 12 months or 80 hours of operation.”

AASHTO T312 Section A3.1.1 states in part “Confirm that molds are thoroughly cleaned” and Section A3.1.2 states in part “The mold bore shall be free of residue …”

Molds are measured to thousandth of a millimeter. That is a resolution of 0.001 mm.  They are required to have an inside diameter from 149.90 to 150.20 mm measured at three locations along the bore (AASHTO T312 Annex A).

Properly cleaning molds can require much time and effort.  But, taking a few minutes after each use to remove debris and asphalt binder from the mold and end plates is a good investment.  It will prevent a much greater exertion of effort to remove binder that has been baked on over time.

End Plate Binding

A buildup of asphalt binder on the mold and mold endplates reduces the available space between them and increases the friction resistance of the surface.  Occasionally customers call Pine because they are having a problem with their gyratory compactor only to learn that the end plate is binding in the mold because of the molds weren’t properly maintained.  A thorough cleaning of the endplate and mold resolves the problem.

What Does Pine Recommend?

  1. Pine Service Technician’s use two products to clean and maintain molds—WD-40 or Purple Power.  Always read the product Safety Data Sheet before opening a cleaning product. Wear gloves and safety glasses when using these cleaning products.
    • WD-40 works well as a general, daily use product. It cleans and protects the molds from rust.
    • Purple Power cleaner/degreaser is tough on built up asphalt cement. In the event of mild to severe asphalt cement build up, soak the mold in a bucket of Purple Power overnight. The residue will soften and wipe away.  This works superbly based on recent experience.
  2. Wear gloves and safety glasses when using these cleaning products.
  3. Hand razor-blade paint scrapers can be used to remove a thin layer of build-up. Angle the paint scraper and rock it back and forth in the mold. Use caution to not scratch the bore of the mold.
  4. Do NOT use a wire brush or wheel. It will scratch the molds and increase the bore diameter. Remember molds are measured the 0.001 mm.
  5. Do NOT superheat the molds to “burn off” the residue. Molds are heat treated in a way that makes the resistant to temperature change. Extreme heat beyond the normal asphalt range can change the molecular structure of the steel and cause it swell or warp.

Want to Learn More?

Visit our website or talk with one of our specialists at 724-458-6393.

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