Badly Engineered or Good Marketing?

After using a popular “blender” for approximately nine months the blades no longer span as fast (audibly) and there would be a faint burning rubber smell after use. When the manufacturer was contacted I was informed that the base with the blades was a consumable item and they expected them to be replaced every six months.

Now the blender is a great design as the blade section screws onto the top of the liquid container. This brings two benefits, firstly it eliminates one extra seal compared to older blender designs and two it also allows larger diameter blades to be used which also circulate the contents of the container much better.

Back to the problem of the worn out blade section. A replacement was ordered so the old section was going to be thrown away.

A perfect time to do a tare-down and fault diagnosis.

p1010264   On tare down a few things were noticed:

  • The two bearings may be a bit undersized for the job.
  • The rubber lip seal may have been installed the wrong way round.
  • The seal design is not the best for this type of purpose.

p1010265   This picture shows the wear on the shaft where the lip-seal was riding.

p1010266   This was the lip seal as it would have been installed. These types of seals are commonly installed in engines where an input or output goes through, keeping engine oil inside and keeping dirt and contamination out. They work well in that installation. As installed on the blender they would have the benefit of any pressure inside the container adding to the sealing force on the lip seal.   If it were installed the other way round it would do a better job at keeping dirt out but wouldn’t have any lubrication between the shaft and seal unless some was put there at the factory.
Where they do not work well is that the contents of the container are generally fruit, vegetables, nuts and liquid. This creates a media with lots of small, solid, abrasive food particles that get inside the lip and wear the shaft and the seal. Eventually liquid gets past the seal into the already heavily loaded bearings and leads to a rapid failure.
From an engineering point of view this is bad.

From a marketing point of view this is fantastic!

So what would be a better idea (from an engineering point of view without wanting to sell lots of disposable product)?

Typically in pumps that have to move an abrasive liquid, and even in older blenders, the design would use an end face seal or ceramic shaft seal. Any liquid lubricates the seal while any particles getting into the seal face are forced back out again.
They do have the disadvantage of being more expensive than rubber lip seals.

 

 

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