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Internal Surfaces Internal Surfaces

Summary

  • Failure mode Powder coated surfaces can become damaged if not cleaned
  • Durability feature Coatings should be tested to prove resilience. Steel panels will be higher performance.
  • Cost

Good practices

  • Good practicesCoatings tested to prove resilience
  • Good practices Stainless steel

Bad practices

  • Bad practicesCoating onto dirty or rusty steel
  • Bad practices Use of abrasive and aggressive cleaners

Key facts

  • 15% of microwaves are replaced within 3 years because they fail or are unreliable. 

Icon key

  • Failure mode Failure mode
  • Durability features Durability features
  • Cost saving Cost saving
  • Low cost Low cost
  • Cost neutral Cost neutral
  • High cost High cost

Key failure modes

  • Most lower-priced microwave ovens have powder coated steel surfaces internally and externally.
  • This coating must be applied correctly for long life, but if food residues remain on the surface this can get very hot and damage the coating.
  • More expensive ovens may use stainless steel panels for internal and external walls as these are easy to keep clean, do not rust and are not easily damaged.

Early Life

  • Incorrectly applied powder coating, e.g. if the metal surface is dirty or oxidised

Later in lifetime

  • Lack of appropriate cleaning techniques lead to localised heating around food residues

Specification for improved performance

The specification below provides the recommended improvements needed to improve product durability. They are ranked from bronze to gold based on the effectiveness of the change in improving durability, with bronze being the minimum and gold being the maximum.

Check coating quality using salt spray

  • The surface coating adhesion and corrosion resistance of powder coated steel can be assessed using the test procedure provided below (BSI BS EN 60068-2-52).

Additional adhesion tests; acrylic interior panels

  • Carry out adhesion testing (EN ISO 16276-1 and EN ISO 16276-2) in addition to salt mist cyclic testing to BS EN 60068-2-52.

  • Acrylic interiors are increasingly common and are reasonably durable.

Stainless steel or ceramic / enamel interior panels

  • Stainless steel will give the best performance although needs to be kept clean to prevent corrosion.

  • Ceramic / enamel surfaces are also very durable.

Testing to demonstrate performance

The tests below demonstrate appropriate coating adhesion:

BSI BS EN 60068-2-52 “Environmental testing Part 2: Tests Test Kb. Salt mist cyclic (sodium chloride solution)”

  • Detects gaps in the coating and also assess the coating’s adhesion. If gaps exist, corrosion will occur and the coating may peal off.
  • Coatings should be largely unaffected visually after 96 hours testing.

Additional tests for coating adhesion:

EN ISO 16276-1 “Corrosion protection of steel structures by protective paint systems - Assessment of, and acceptance criteria for, the adhesion/cohesion (fracture strength) of a coating - Part 1: Pull-off testing”

EN ISO 16276-2 “Corrosion protection of steel structures by protective paint systems - Assessment of, and acceptance criteria for, the adhesion/cohesion (fracture strength) of a coating - Part 2: Cross-cut testing and X-cut testing”

Cost implications – Internal surfaces

Improved reliability of components can reduce early returns and improve brand reputation which, in turn, can lower business costs and increase long-term sales.

To calculate overall cost savings for your business, use the WRAP cost/benefit analysis tool (currently in draft form and available on request).

Saving

Neutral

Internal coating
Most domestic ovens use powder coated internal surfaces and these should survive the normally expected lifetime at no extra cost, as long as they are applied correctly, pass the required tests and are maintained correctly by the customer. 

Low cost

High cost

Stainless steel panels 

Commercial ovens and some more expensive domestic models use stainless steel panels which will be more expensive than powder coated mild steel.