Principle

A drum flaker is a type of cooling and solidification equipment used to convert molten or concentrated liquids into solid flakes by cooling a thin film of the material on the surface of a rotating, water-cooled drum. The principle of operation is based on indirect heat transfer by conduction, where heat is removed from the molten feed as it comes into contact with the cool surface of a metal drum, causing rapid solidification. The solidified layer is then scraped off by a doctor blade as flakes, which are collected for packaging or further processing.

Drum flakers are commonly used in the chemical, food, and pharmaceutical industries for converting molten or semi-molten materials such as fatty acids, waxes, resins, soaps, sulphur, detergents, and plastic additives into uniform solid flakes for easy handling, storage, and dosing.

Principle of Operation

The working principle of a drum flaker is based on indirect cooling through conduction.

• The molten product (feed) is evenly applied as a thin film onto the outer surface of a slowly rotating, hollow, water-cooled drum.
• As the drum rotates, heat is conducted from the hot product film through the metal wall of the drum to the cooling medium (usually water) circulating inside.
• This causes rapid solidification of the molten material into a solid layer.
• The solidified layer adheres lightly to the drum surface until it reaches the scraper or doctor blade, which continuously removes it as flakes.

The cooling rate and film thickness are controlled by adjusting parameters such as drum speed, feed rate, cooling water temperature, and feed applicator design.

Construction

A drum flaker consists of the following main components:

• Drum (Cooling Cylinder):
  The core component of the drum flaker is a hollow, rotating metal drum, usually made of stainless steel or carbon steel, with a polished, smooth surface. The drum is mounted horizontally and rotates at a low speed (1–10 rpm). The drum’s interior is equipped with a cooling system, where chilled water or brine is circulated through the drum’s shell to maintain a uniform surface temperature, typically between 10°C and 25°C. The drum diameter usually ranges from 300 mm to 1,200 mm, and the length varies from 500 mm to 3,000 mm, depending on the capacity.
• Feed Applicator System:
  The molten feed is applied onto the surface of the rotating drum through an applicator system, which ensures the formation of a uniform, thin film for consistent flake formation. Depending on the nature and viscosity of the product, different applicator designs are used:
  • Overflow Weir (Dip Feed): The drum is partially submerged in a feed trough, allowing the molten material to adhere as a thin layer when the drum rotates.
  • Doctor or Applicator Roll: A rotating applicator roll transfers the molten film from a feed tray onto the drum surface.
  • Spray or Splash Feeder: Nozzles spray the molten feed directly onto the drum surface.

The film thickness can be adjusted by controlling the feed rate and applicator gap.

• Cooling System:
  Inside the drum, cooling water, glycol, or brine is circulated continuously through the hollow shell. The cooling medium enters through a rotary joint and exits through an outlet, ensuring efficient heat removal. The temperature and flow rate of the cooling medium are precisely controlled to achieve desired solidification rates.
• Scraper or Doctor Blade:
  A stationary scraper blade, made of hardened steel or bronze, is positioned tangentially to the drum surface. As the drum rotates, the solidified layer of material is scraped off in the form of thin flakes. The blade pressure is adjustable to ensure clean scraping without damaging the drum surface.
• Discharge and Collection System:
  The flakes fall from the scraper into a collection hopper or conveyor belt, which transports them to a crusher, packaging unit, or storage bin. Some systems include a vibratory conveyor or rotary screen for cooling and classifying the flakes before packing.
• Drive Mechanism:
  The drum is rotated by a motor and gearbox assembly, typically via a chain or belt drive. The speed of rotation (and hence residence time) can be controlled using a variable frequency drive (VFD).
• Frame and Enclosure:
  The entire assembly is mounted on a rigid steel frame with adjustable leveling supports. The drum may be enclosed in a casing to retain heat, prevent contamination, and collect vapors if the feed contains volatile substances.
• Instrumentation and Control:
  A control panel regulates the drum speed, cooling water temperature, and feed rate. Temperature sensors monitor both drum surface and cooling medium temperatures to ensure consistent operation.