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I assume you mean the magic mixers!?
They have four screws, one in each corner. Each time you hit the magic mixer one screw will come out, so you have to hit it a total of five times before it blows up. It will, when it does blow up, cause an explosion similar to a wrapped candy, so that is useful. To hit them you either match candies next to them or hit them with striped candies.
If they start to shake it means they are about to spawn blockers. At this point, if you remove one of the screws by matching candies next to it the machine will reset and that is one way to stop it spawning blockers all the time, if you struggle to destroy it early on.
In some later levels the magic mixers produce the order, so just be aware of that as well. But mostly you are better off getting rid of them as early as you can.
Here is a screenshot of a magic mixer level.
In fact this is a hard one, as you can't get to them at the beginning due to the multi layered frosting.
On this shot I have removed one screw on the bottom right mixer, and if I match the purple or orange candies next to it I will remove another, maybe two. But I did fail the level on this try.
I hope this gives you a general idea. I can see why you liken them to a washing machine!