Anodizing: plenty steps, a lot of solutions

Anodizing: plenty steps, a lot of solutions

The aluminium anodizing process requires the right pump and filter solutions. As a result of increasing quality specifications, OEM’s or manufacturers look for solutions which can optimize their  installations at a fair price. We totally understand this way of thinking. However, we find it even more important that the quality of pumps and filters ensures a long product lifetime, and with that, the lowest total cost in the end possible.

The process of aluminium anodizing contains electrochemical conversion of metal surfaces into corrosion-resistant, durable finishes. Next to aluminium, also magnesium and titanium can be anodized. Anodizing aluminium surfaces takes several steps, which call for specific equipment. For the anodizing industry, Hendor provides an array of pump and filter systems which assist in the anodizing process.

Hot Seal filtration
Surface smut regularly occurs in the anodizing process. This smut necessitates labor intensive post-treatment. In addition, contaminated baths require replacement and re-heating. Hot seal baths are typically filtrated at 1-1,5 turnover per hour to avoid sealing smut. Due to the high temperature (generally 96-100 °C), manufacturers use stainless steel cartridge filter pumps. But, in our opinion, this is not the most optimal choice. Hendor provides a very robust PP horizontal disc filter system with mechanical seal pump which well withstands the hot seal bath temperature, because it is made from Simona® high-grade Alpha PlusTM PP.

The advantages of PP filter systems over stainless steel filter units are:

  • Significantly lower investment costs
  • Lower operating costs due to use of low cost filter paper
  • Less energy losses due to PP’s excellent thermal insulation properties
  • No corrosion of pump and filter
  • Less disposal costs (cartridges are chemical waste)
  • Ease of handling due to partitioned filter disc stacks

Hendor’s PP horizontal disc filter systems are standard available with capacity up to 30 m3/h. Though initially developed for hot seal application, these filter systems are also well suited for use with cold seal baths, electrolytic coloring, and rinse tanks.

Filter media
For hot and cold seal, coloring tanks, and rinse tanks, both cartridge filtration and disc filtration can be used – we supply both. But, we recommend using discs. Why? The use of filter paper results in low filter media costs, low waste volume, and lower disposal costs. Down time of the filter unit is avoided by having an additional disc stacks available for immediate exchange.

Residual oil and grease removal
Organic contaminants, originating e.g. from the extrusion process or subsequent handling prior to the surface treatment, can pollute baths and lead to inferior anodizing and/or coloring quality. Hendor provides a special PP filter unit with specially activated adsorption fibers. These fibers are made of plasma-charged PP, which adsorb the non-emulsified oils and greases up to 5-6 times their own weight. Using this effective filter system results in:

  • Improved anodizing and/or coloring process
  • Improved product quality
  • Longer bath lifetime / less costs involved in chemistry
  • Less water usage

Bath circulation / agitation
For an optimum and homogeneous anodizing process, and subsequent stable product quality, sufficient bath circulation/agitation is of utmost importance. Rather than using a large circulation pump, a smaller sized pump in combination with eductors can be used. Due to the venturi design of the eductors, the resulting circulation flow can be 5 times the pump input.

Pump / eductor systems are ideal to replace conventional air agitation thereby avoiding the inherent disadvantages associated with air agitations. The advantages of using pump/eductor tank circulation are:

  • Less to no acid mist above the tank (sulphuric acid mist is carcinogenic)
  • Bath conductivity improvement leading to faster processing
  • Lower energy consumption
  • More stable process due to less temperature variation
  • No dirt intake by polluted pressurised air

For bath circulation we advise our well-known robust vertical PP pumps. In those situations where the tanks do not allow sufficient space for these vertical pumps, the special Out-of-Tank versions can be used, thereby maintaining the advantages intrinsic for Hendor’s vertical pumps without requiring tank space. Due to the single, stainless steel shaft, oversized motor bearings, and absence of bearings or seals in the volute, these pumps are very reliable and can essentially operate maintenance-free. Pumps and eductors are available in various sizes to suit each bath geometry.

In sum, we provide several solutions for the anodizing process: robust PP horizontal disc filter system with mechanical seal pump, disc filtration and filter paper, special PP filter unit with oil adsorption  fibers, vertical pumps (in tank or out of tank) and eductors.

In case you are interested in more details about one specific product, feel free to contact the Hendor team.

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