Making a Venturi Suction Device for Cleaning Molds

Discussion in 'Foundry tools and flasks' started by Melterskelter, May 31, 2020.

  1. On some of my molds that have relatively deep narrow recesses blowing out loose sand and sand clumps can be a real test of patience as the clumps and loose sand tend to just blow back and forth but not out. A while back I made a very crude Venturi device to suck out sand and clumps and it worked pretty well as crude as it was. I wanted a more powerful and efficient design and did not find any suitable devices searching online. (I will not be amazed if someone posts a link to such, however.)

    So I looked up Venturi design and found that typically the entry angle is 20 degrees on each side for a forty degree included angle and 5 degrees on each side for a ten degree exit angle with the sucker entry just beyond the the narrowest point or, in some cases, at the distal end of the straight throat where entry and exit meet. Mine is not quite an ideal design as it has no straight section but is just an intersection of the two cones with the hole just past the intersection. Nevertheless, it is quite an improvement over the old design and will be a big help in doing the final mold cleanup prior to closing the mold.

    The small brass piece is soft slodered to the body of the Venturi and the two pieces of the body are silver soldered together with 55% silver solder.
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    One unexpected and very positive feature of this tool is that, besides being a neat little suction device, it makes a very handy blower too. I hold the Venturi in my hand with the compressed air blowing, but if I need to nudge a sand clump, say, I just put my finger partly over the exit of the Venturi and suddenly it is a blower. I use that feature all the time.

    Last edited: May 31, 2020
    joe yard, Chazza, TRYPHON974 and 2 others like this.
  2. Stevan

    Stevan Copper

    Very nice and beautifully made. I have had the same problem but my solution is a little simpler....but no so elegant. I have a 6 foot length of tube the size you have, I put it in the hose end of my shop vac and jam a rag in with it to seal it. It makes a very nice tiny vacuum.
  3. Thanks, Stevan. I don't have a shop vac at the foundry (more a limited space issue than a cost issue) and do have compressed air. If I had a shop vac handy, I'd use it as you do. Gotta say, the blower feature of this venturi is handy, however. Just by repositioning my hand it converts from suction to blowing which helps corral those little sand boogies prior to suctioning them.

  4. Billy Elmore

    Billy Elmore Silver

    Cool! We made some for the old hand floor when we had it it in production. I actually built these into a pattern that had deep pockets and very hard to fill out on our molding machine. I did it just as a test to see if creating a vacuum inside the mold would help to fill out the deep pockets. It worked incredibly well but the down side was that it created the impressions of the brass vents I used to pull the suction through on the inside bottom of the castings. They were not too hip on having the vents show up on the castings, so we eliminated them. But they are very useful and easy to make! Nice job on making those!
  5. oldironfarmer

    oldironfarmer Silver

    Great job Denis!

    It's called an eductor. Very available on the internet and everywhere else. They are also used in jet pumps (the jet is into the eductor) for water and for non-condensibles in steam condensers (air, etc.). Some power plant condensers operate at a high vacuum and steam jet air eductors are used to suck the air (and some steam) out of the vacuum of the condenser up to atmospheric pressure.

    Making your own is cheap and reliable and as Denis says you don't need a venturi shape, simple cones work. If you think about it, most of the gas burners we use without blowers are eductors, sucking air in by using the gas (propane, natural gas, hydrogen, etc.). We always have to restrict the inlet or lower the gas pressure to avoid sucking in too much air. They are more efficient than is necessary.

    You can also mix media, using air to educt sand into your sandblast nozzle for instance.

    Most everyone also probably has a blow gun with an eductor built in, the tube hangs down and can be used to suck up liquids to spray them. Hand held soap dispensers for washing cars and siding work this way.
  6. I do not doubt they are available and at reasonable prices. A plastic one should cost only a few dollars. I did a brief search online and found a few (costing more than 500 bucks) but I probably am not using the correct words in the search to get into the common-use educators. Where do you find them cheap?

    Cost was not necessarily the prime motivator in my build. It was something I wanted more or less immediately and took about an hour? to build. So I just fired up the lathe and mill and got er done.

  7. I think the answer to my question is to not use “eductor” but rather “Venturi suction”

  8. dtsh

    dtsh Silver Banner Member

    eductor, ejector, venturi pump, lots of names.

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