Thermal Cleaning is a process used to remove organic contaminants by the use of heat.  Considerations for thermal cleaning include:

  • Temperature Profile: Part metallurgy/design and chemical properties of the contaminant will determine the temperature profile, timing, and cool-down procedures to minimize damage potential for the part while providing effective cleaning.
  • Oxygen Potential or Atmosphere: Depending on part design and physical properties, a controlled oxygen atmosphere may be required to minimize damage potential. In other cases, oxygen atmospheres up to 21% may be needed to oxidize carbon-based contaminants.
  • Part Size and Configuration: The size and configuration of the filter or part to be cleaned may affect the type of equipment  such as Convection or Vacuum ovens used for processing.

Common Types of Parts used in Thermal Cleaning Processes

  • Filters
  • Static mixers
  • Piping
  • Canisters & housings
  • Metal plates
  • Tubesheets
  • Spinnerets

Carolina Filters offers a variety of customizable thermal cleaning methods to fit each customer’s needs.

Convection Oven:

Convection ovens are used under the conditions of normal atmospheric conditions, i.e. , 760 mbar. The cavity or part temperature is controlled by water spray or inert atmospheres. These ovens can be gas or electric fired.

  • Benefits of convection ovens include:
    • Available oxygen potential to facilitate oxidation carbon-based contaminant.
    • Custom sizing to accommodate a range of configurations, and dimensions.
    • Afterburner systems provide environmentally responsible processes to eliminate or minimize emissions resulting from oxidation & burning processes.
    • Low operating costs.
  •  Limitations:
    • Burning can occur on the part; as a result, convection ovens may not be the most ideal thermal cleaning option for fragile filter media and fragile parts.
  • Types of parts cleaned in a convection oven:
    • Extruder screws and parts
    • Heat Exchangers
    • Canisters and Housings
    • Metal Pads
    • Piping
    • Screens

Vacuum Oven:

Vacuum Ovens are used under conditions when a reduced oxygen atmosphere is preferred under vacuum.   For vacuum ovens that can be regulated, at some point in the process, the vacuum will decrease allowing an increase in oxygen potential to scrub out residual carbon material.

  • Benefits of Vacuum Ovens:
    • Minimization or elimination of burning on the metal substrate that prevents temperature excursions. For fragile parts, temperature excursions can be damaging to the substrate.
    • Ability to capture melt-off of polymers and sublime polyolefinic polymers – which reduces the amount of polymeric material that must be pyrolized.
    • Ability to maintain part temperature within ~5⁰C during the process.
    • Catalyst Blocks and After-Burner systems provide environmentally friendly processes to eliminate or minimize emissions resulting from oxidation & burning processes.
    • Low operating costs.
  • Types of parts cleaned in a convection oven:
    • Extruder screws and parts
    • Piping
    • Screens
    • Dies & Spinnerets
    • Filters – Fiber metal and screens
  • Limitations:
    • Sizing of ovens may not accommodate large parts or an assortment of polymers.
    • Some vapors or contaminants may poison catalyst blocks.

Molten Salt Bath Cleaning:

Molten Salt Bath Cleaning: A process used to remove scale, polymer, and/or carbon or degraded polymer debris from a part or filter. While there a many molten salt media formulations, CFI uses a eutectic mixture of sodium & potassium nitrate and nitrite salts.  When the solid salt mixture is heated to its melting point, the salt will melt and liquefy.  Parts are immersed in the hot melt and heated up to a pre-programmed set-point. The hot melt circulates via convection currents and will penetrate small openings and media packs removing contaminant.

The contaminant, if carbon based, will oxidize to carbon dioxide & water or move to the top of the salt for burnout.  Inorganic scale such as rust, carbon deposits, heat stains, etc, can be removed by processing the parts in salt. As the salt heats the part, the metal will expand allowing the scale to crack and be removed from the part.

  • Benefits
    • In comparison to oven processes, the salt bath medium acts as a heat sink if exothermic reactions occur; whereas, in an oven, there is no medium to absorb evolved heat in the case of rapid oxidation reactions.
    • Due to the liquid form of the salt medium, there is even heating across the part which reduces the potential of temperature differentials across the part which could result in warping.
    • Salt bath processes are faster than oven processes.
    • Thorough particulate removal is achieved with salt bath processes, as opposed to, oven processes.