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Heating element Heating element

Summary

  • Failure mode Heating elements can fail early if they are badly assembled.
  • Durability feature Bus-bar connections instead of cords can save costs.
  • Cost

Good practices

  • Good practicesUse elements pre-brazed onto plate from reputable suppliers
  • Good practices Test new designs for 20
  • Good practices000 cycles

Bad practices

  • Bad practicesKettle manufacturers should not buy separate elements and plates because they are likely to be unreliable

Key facts

  • The return rate can be as high as 30% for a bad design.
  • 22% of consumers check on-line reviews before buying to avoid unreliable brands.

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

UK kettles use three types of heating element.

  • Concealed resistance coil below a flat plate
  • Immersed resistance coil
  • Printed “thick film” heaters.

Early life

  • Heating elements can fail early if they are badly assembled, damaged during manufacture or are faulty.
  • Noisy kettles are frequent complaints in on-line reviews and this can have a variety of causes. These include the surface finish of the metal plate that covers the element, kettle design, scale deposits, power rating, etc.
  • A micro-roughened surface will create many small bubbles that will be quieter than large bubbles produced on a smooth surface. Sound is measured in decibels (dB) and as a guide, 60dB is relatively quiet and 80dB is quite noisy for a kettle. Specifying a maximum of 75dB should avoid too noisy designs.

Later in lifetime

Elements may fail if damaged in use or by excessive scale build up. Scale can also cause the kettle to become increasingly noisy.

Specification to ensure adequate 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.

Concealed elements; institute quality control procedures; provide instructions for scale removal

  • Use integrated concealed elements brazed to base plates from reputable suppliers.
  • Use management standard such as ISO9001 to develop good factory quality control procedures to avoid damage from impacts, distortion, being dropped. Ask local technical teams to carry out random inspections.
  • Clear instructions to users that they need to regularly descale kettles in hard water areas.

X-ray inspection of heating elements; low noise textured surfaces

  • X-ray a random sample of elements to ensure that the coils are evenly spaced and are not too close to the outer metal enclosure.
  • Proprietary surface finishes are available, otherwise ensure surface is micro-roughened. Measure noise level to ensure complies with specified maximum dB value.

Testing to demonstrate performance

  • Kettle testing as described for lids will also test heating elements. The test used is fill/boil/empty with lid opening and closing and this is carried out for the required number of cycles for kettles. Descale as necessary during test.
  • Noise can be measured with a decibel meter.
  • X-ray inspection of parts is routine in many electronics factories but examiners need to be trained to identify poor quality elements. Inspected parts should be compared with known good parts.

Cost implications

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

Weld control contacts to bus-bar

Use bus-bar connections instead of cords. These use less parts (e.g. no crimps) and are quicker to attach.

Neutral

New design testing

Testing will identify fatal flaws. Independent kettle design assessment and durability testing can be obtained free of charge from some manufacturers of kettle controls if sales volume are sufficiently high.

Quality control

Good quality control and change control should be standard procedures.

Low cost

Quality control

X-ray inspection can be sub-contracted if not available at factory. 100 elements can be inspected in one day so the cost per kettle if, e.g. 0.1% of elements are checked to ensure batch quality and consistency will (we estimate) be ca. $0.01 per kettle.

High cost