• Welcome to engineeringclicks.com
  • Molded plastic part design for radial pressure

    Discussion in 'The main mechanical design forum' started by hank1090, Dec 23, 2015.

    1. hank1090

      hank1090 Member

      Joined:
      Dec 2015
      Posts:
      5
      Likes Received:
      0
      Hello everyone,

      I'm designing a cylindrical plastic adapter with mounting features on two ends, to grip a stiff tube from the inside. I would slide the tube on the adapter from one end, so I need to have features in the adapter that flex radially and apply internal pressure to securely hold the tube. There has to be no independent rotation of the tube, since this assembly will be rotated by a motor through the mounting points on the adapter.

      The problem is getting radial features that can flex and be moldable too. I'd appreciate any help or ideas.

      Thanks,
      Hank.
       
    2.  
    3. s.weinberg

      s.weinberg Well-Known Member

      Joined:
      Nov 2012
      Posts:
      58
      Likes Received:
      0
      Don't know your application, but the first thoughts that come to me are:

      A. A pneumatic or hydraulic bladder that would expand to grip the tube.

      B. Slotted, or otherwise separate, portions making up a cylinder, with a hole in the center. Press a conical rod up through the center (or have a conical hole and a straight rod, or both conical - depending on your application) for a firm radial grip. The rod can be driven by a set screw or something similar.

      C. Fingers with cylindrical outside edges. Expand with any of the various options available for grippers.

      Hope something there helps.
       
    4. AndySmallman

      AndySmallman New Member

      Joined:
      Jan 2016
      Posts:
      1
      Likes Received:
      0
      Does it need to be watertight? Do you have access once assembled to tighten the screws/nuts as per the first reply? Or should it be push fit?
       
    5. nishantc07

      nishantc07 New Member

      Joined:
      Jan 2016
      Posts:
      1
      Likes Received:
      0
      I don't have any idea about your application, but would suggest:
      1. Try hydraulic coupling or hydraulic bladder as suggested above or,
      2. If both shafts have enough thickness, then try inner grooves on outer shaft and outer grooves on inner shaft, most probably this will restrict the shaft rotation and can give you good fitting, or.
      3. You can go for third element i.e. key. First machine your shafts according to fit after that, use key for gripping and to restrict radial movement of the shafts.
      Hope you find something helpful.
       
    6. hank1090

      hank1090 Member

      Joined:
      Dec 2015
      Posts:
      5
      Likes Received:
      0
      [​IMG][/URL][/IMG]
      Thanks for your suggestions everyone. To better explain my application, this rough sketch shows what I have in mind. It's supposed to be a plastic part. The two ends have a hex shaped boss sticking out to enable a connection to the motor using transmission elements. The arms in the middle are a rough representation of what I'm looking for, features that will flex as I push the tube in. The only problem here is structure, a central beam would do it but then the design becomes rigid. The tube is a stiff cardboard material.

      There is no requirement for this part to be waterproof. Also, I'm trying to find a design for this without the use of fasteners.

      Here's the link for a clearer image: http://s11.postimg.org/mc30v5m0z/IMG_2308.jpg
       
    7. robertjeffery

      robertjeffery Active Member

      Joined:
      Dec 2015
      Posts:
      28
      Likes Received:
      0
      Can you add a little more information why it needs to flex?

      Is it so that the motor doesn't have to be inline with the tube? if so a universal joint???

      Is it because you cant be certain that the tube is straight and true? if so maybe something like a self adjusting 4 jaw chuck???
       
    8. hank1090

      hank1090 Member

      Joined:
      Dec 2015
      Posts:
      5
      Likes Received:
      0
      It is supposed to be just one molded part (hence the flexing arms), and the adapter connects to a plastic pulley, belt drive and small right angle gears. The tube is certainly straight and true, similar to the roller in a paint roller. After the tube slides in and is secured, the adapter snaps in to the main housing.
       
    9. Erich

      Erich Well-Known Member

      Joined:
      Feb 2012
      Posts:
      223
      Likes Received:
      2
      You can form 3 flexible arms just as you have sketched with an open and shut mold.

      Make your arms 120 degrees apart. One is located at 12 o'clock. The underside is formed by steel that comes up from below.
      The other two are at approx. 4 and 8 o'clock. The top and inside of these are formed by steel coming down from above. The outside is formed by bottom half of mold.

      Leave enough room between features so the steel can shut off on each other with a 10-15 degree angle.

      As the tube ID varies, the overall length will change, your mounting methods will need to accommodate.

      The bore for the hexes will need to be formed by a slide on each end.

      The hexes could be formed on the slide or by the open and shut action of the mold.
       
    Tags:

    Share This Page