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Designing for Plastic Longevity

When designing to improve plastic part longevity, it is imperative to consider what the part will go through on a day-to-day basis, as this will affect how long it will last. First consider the level of stress or load that a part will be subject to and secondly the length of time that the part will experience stress, load or other pressures. If a plastic part is continually loaded or placed under pressure the structure of the part will change over time and this is referred to as creep. Other factors affecting a parts’ longevity that must be considered at the point of design include wear, weathering and fatigue.

 

Creep

Creep is a crucial concern when designing plastic parts that will be subject to long-term loading, creep is when a plastic part is stressed over a period of time and will not return to its original state. Creep is dependent on the level of load or stress and the amount of time this is applied, it can either be extreme deformation or breakage of the part. When designing parts that will be subject to long-term loading, using creep data can be effective to ensure that the parts do not rupture, yield, or deform excessively over their required service life. It is worth considering when designing plastic parts, that the rate of creep for filled and fibre reinforced polymers is notably less than that of unfilled polymers.

The level of creep a plastic part is likely to experience can be determined by:

  • Material – different materials will experience different levels of creep
  • Degree - The level of stress or load that is applied to the part
  • Time – the length of time in which the part is experiencing the stress factors
  • Environment – this not only includes temperature (high and low) but certain chemicals when exposed to plastic cause the polymer to creep

 

Wear

Wear refers to the gradual erosion of a material which has been subject to friction over a period of time. Friction usually occurs at the point of contact between two or more materials, often seen on components with bearings or gears. Erosion is typically present when surfaces with varying coarseness are in contact and therefore cause wear.

 

Fatigue

Fatigue occurs when a repeated strain or stress causes the failure of a plastic component. The load or level of stress does not have to be high in this instance but it is the amount of time the component is subject to the stress that causes the failure. Parts most at risk of fatigue include, those subject to vibration or repeated impacts or flexion.

 

Weathering

Long-term exposure to the elements of weather conditions can affect a materials’ properties and colour of the plastic part. Some plastic materials are more suited to the outside, such as acrylics and have properties suitable for the environment. Other plastic materials are less suited to the outside, in fact many plastics have poor long-term resistance to the outdoor elements and require the use of stabilisers or coatings to increase their suitability to the elements.

 

Our designers have years of experience designing parts and will always consider the longevity of the part and its day-to-day requirements. Considering the above factors, our design team will review the design, materials used and advise as to the best approach to ensure your part is best adept for its future role. 

Speak to a member of our design team today, for help and advice when designing for plastic part longevity.

 

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Looking for more information? Check out our blog, News & Views for useful articles, tips and tricks on plastic injection moulding.