Blenders: A Tip, Tip Speed

[dcarch]

It occurred to me that I can share this with you:

What makes a blender work is the difference between the speed of the blades’ tip and what you are trying to blend. The bigger the difference, the better the end result. An expensive counter top blender can achieve over 30,000 RPM.

A hand stick blender cannot go very fast because of portability and low power. Most of them are about 15,000 RPM. A stick blender goes much slower inside liquid, especially thick liquid, probably less than 8,000 RPM.

You can get much better end results for blending if you try this technique, even with blending thick liquids:

With the blender turned on, insert the blender in and out of the liquid. When the blender is out of the liquid, it achieves max blade speed immediately. When you plunge the blender at max speed into the liquid, the liquid is at 0 speed, maximum blending occurs. Very quickly, the blade slows down by the liquid, then you lift the blender out of the liquid again. In and out, in and out, keep repeating.

dcarch

[Shalmanese]

This only works well in the specially provided container the blender comes with. If you try it in a pot on the stove, it's a good way of finely decorating your kitchen walls with an even layer of soup.

[Chris Hennes]

Actually, Shalmanese, I've found that if you angle the head right you can create some quite intricate patterns, not just an even spray

[_john]

any ideas about how to measure tip speed at home? I'm guessing you would need a high speed camera.

[Shalmanese]

any ideas about how to measure tip speed at home? I'm guessing you would need a high speed camera.

If you're at all musically inclined, you can figure it out by the tone it's generating. For example, 15,600 RPM is 260 RPS which is 260Hz which is middle C. ~8,000 RPM is the octave below middle C and ~30,000 RPM is the octave above middle C.

Edited April 20, 2012 by Shalmanese (log)

[_john]

i'll record my blender and look at the spectrogram

[_john]

There seems to be a solid tone right around 3.7khz that rises slightly as the motor gets going. That can't be right can it? 3,700*60 = 222,000. This is for an old cuisinart "super blender"

[goodkidwe]

Interesting information on how to make blender work quickly. I would have a try next time.

[Tri2Cook]

Actually, Shalmanese, I've found that if you angle the head right you can create some quite intricate patterns, not just an even spray

And, when it's 2am and you're not paying the attention you should be while trying to get prep work done for an unexpected catering job for the next day, it can also help you discover that the face doesn't necessarily acquire that heat-resistance the hands build up over time. Not that I would know anything about that...

[Shalmanese]

There seems to be a solid tone right around 3.7khz that rises slightly as the motor gets going. That can't be right can it? 3,700*60 = 222,000. This is for an old cuisinart "super blender"

The 3.7Khz appears to be something else, I'd focus on that line between 500Hz and 1Khz. That seems like a far more likely candidate.

[Shalmanese]

I just tested my Braun stick blender and it was a G# which is ~200Hz so about 12,000 RPM. My Waring Pro countertop blender was 350Hz (21,000 RPM) on low and 500Hz (30,000 RPM) on high.

Edited April 20, 2012 by Shalmanese (log)

[dcarch]

The accurate way to find out RPM is by using a tachometer.

John, the 222,000 RPM is not possible with electric motors. What you are seeing was most likely harmonics of the blade(s) made with the number of holes around the blade housing.

Shalmanese, 21,000 RPM on low and 30,000 RPM on high are possible with counter top blenders (Universal motors).

Perminent magnet motors (common with immersion blenders) are difficult to be made for high power and high RPM because few have internal ventilation holes to evacuate the heat generated.

dcarch

[CFT]

You can use an adjustable speed strobe light to measure rpm: http://www.ehow.com/how_5021934_use-strobe-light-measure-rpm.html

Basically adjust strobe frequency until the blade appears stationary.

Edited April 20, 2012 by CFT (log)

[haresfur]

It occurred to me that I can share this with you:

What makes a blender work is the difference between the speed of the blades’ tip and what you are trying to blend. The bigger the difference, the better the end result. An expensive counter top blender can achieve over 30,000 RPM.

A hand stick blender cannot go very fast because of portability and low power. Most of them are about 15,000 RPM. A stick blender goes much slower inside liquid, especially thick liquid, probably less than 8,000 RPM.

I think there is a bit more to it than this. I assume by "blending" you mean chopping or liquifying - reducing the solids to smaller bits or to muck. Blenders also blend - or stir stuff together. Counter top blenders needs to blend the material together and pass it through the blades and that's their Achiles heel. The blades are designed to try and do both things. With a stick blender you do the mixing bit so the blades are more knife-like. It seems to me that helps them make up in part for the wimpier motors.

But the real difference in tip speed is both the rpm and the blade diameter. For a given rpm a large blade will have a higher tip velocity than a small one. I have no idea what the difference in rpm is, but a small motor can drive a small blade pretty fast and I think it takes a lot more oomph to move a large blade at high rpms. That doesn't mean that your average stick blender isn't underpowered for the task, but so is your average counter top blender.

Then there's an inertia effect. If you try to make a smoothie with a stick blender (as my DB does since I blew up the Kitchen Aid) it is pretty hard to whack apart ice cubes with a light blade, no matter how fast it is going. Can't be too good for the motor.

I find that with reasonably soft materials just moving the stick blender slowly through the soup works pretty well, although I do use the plunge technique sometimes. If only my Dalmatian had wings so she could clean the ceiling as well as the floor...