Who Knew Cut Grass Would Be So Tricky To Move!

Like all publications, here at Hackaday we are besieged by corporate public relations people touting press releases. So-and-so inc. have a new product, isn’t it exciting! But we know you, our readers, we know you like hacks, and with the best will in the world, the vast majority of such things have nothing of the hack about them. Just occasionally though a corporate offering does contain a hack, and today we have a fascinating one from Charm Industrial, who are doing their best to make hydrogen from biomass. They were finding cut grass to be an extremely difficult material to handle, and their account of how they managed to feed it from a hopper into their machinery makes for interesting reading.

You might expect grass to flow from a conical hopper like an ungainly liquid, but in fact it readily clogs and forms bridges, blocking the outlet. Changing the design of the hopper made little difference, so they tried an auger. The auger simply compressed the blockage harder, resulting in the counter-intuitive strategy of running the auger in reverse. But even that didn’t work, leaving the area round the auger clear but the rest of the grass as a solid clump. Rotating plows were tried with multiple different profiles followed, but finally they settled upon a vibrating bin activator. It’s a crash course in materials handling, and though the Hackaday bench is likely to avoid having to handle cut grass except when emptying the lawnmower, it’s still worth a look.

We may have done very little with handling cut grass, but we’ve certainly taken a look at creating it.

20 thoughts on “Who Knew Cut Grass Would Be So Tricky To Move!

    1. Have you ever heard of the term “hodknocker”?
      A hod is a container, and a hodknocker is the person who bangs on the container to loosen up any material sticking inside when the container is being emptied.

    1. That’s where non-sparking metals are used, like brass. Expensive yes, but also conducive enough to also short out any potential static charge wheras PVC would build it up. Also using non-flammable gasses helps to reduce chance of combustion.

      The point of this story isn’t that they rediscovered the wheel, but the process methodology they used to achieve it.

  1. This is an entire subspecialty of engineering, complete with journals, meetings (and horrible politics, I”m sure). The journals carrying it range from fluids to powders to dedicated publications (https://www.tandfonline.com/loi/upst20). The solutions that pop up can range from wildly clever to hilarious.

    I worked with one installation that had a “bridging” problem (the product would form a compressed bridge over the exit of the hopper in the same way that sand arches are formed in geological formations). The solution? A pneumatically operated rod would periodically fire into the mass and break up the bridged material – essentially an automated kick in the pants.

    1. In both videos with the spiral feeders, they go through a lot of work to ensure that all parts are output with the same orientation, then just dump them haphazardly in a box. If that’s your desired results why not just dump straight in the box? I feel like I’m missing something obvious here.

  2. Grass clippings…. they bind, they bunch, they clump and they stick.
    In the right conditions it’s also a combustion hazzard, able to provide both its own kindling and its own heat source.

    Grass clippings are a terrible material if there ever was one.

    But when used as mulch (spread thin and applied regularly) it really makes broccoli plants thrive.

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