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Cone drill bit with threads to drill in hard rock formations?

  1. Aug 12, 2018 at 7:06 AM #1
    i designed a cone drill bit with right hand thread to give friction and grab inside to give pulling force. my question is can this type of cone drill bit drill hard rock formations like normal tricone drill bits with teeth or the cone drill bit will be weak to penetrate hard rock formations .

    Attached Files:

  2. jcsd
  3. Aug 12, 2018 at 8:25 AM #2
    One test is worth a thousand opinions......

    You can easily test your idea. Get a hardened steel screw, such as a drywall screw. Cut the head off, chuck it in a drill, and try it on a rock. Try soft rock first, such as limestone. You will quickly learn if the idea is valid.
  4. Aug 12, 2018 at 9:03 AM #3
    Three cone bits are rarely used these days, in comparison with two decades ago. Fixed cutter bits using Polycrystaline Diamond Compacts are the norm. Durability is a key issue and the PDC provides this. How do you envisage your design offering equivalent durability? What hydraulic design do you intend for cuttings removal?
  5. Aug 12, 2018 at 1:56 PM #4
    i didn't think it all through i was just seeing if the cone will perform like pdc if it is made of same material as pdc drill bits.
    i guess like you said its about durability so if it's made out of pdc then it will work. right?
  6. Aug 13, 2018 at 7:58 AM #5
    I would not give a categorical "no", but there are several issues and potential issues. I'm happy to work through some of these with you, if you wish.

    Now, you cannot make the cone of PDC. That is far to brittle and there is no practical way of adhering the diamond to the supporting bit body. The key word in PDC is Compact. The polycrystaline diamond layer is bonded to a tungsten carbide substrate by means of cobalt, which forms an interlinked phase between diamond and TC. These compacts, which range in size from 8mm - 19mm are then mounted in the body which is either steel or a tungsten carbide matrix material. Since you are targeting hard rocks, the latter would be the appropriate choice.

    Given all that, one major problem then lies at the point of your cone. This would be protected by a single PDC cutter. Moreover that cutter is presented parallel to the rock so that it drills by grinding, not shearing. One of the major benefits of PDC bits is that they drill by shear. Rocks are, generally, about half as strong when subjected to shear compared with compression. So, even if your point cutter provides adequate duability you have sacrificed rate of penetration. You might consider a chisel shaped cutter, as the technology is now up to producing simple shaped PDC. (The problem is exacerbated by the interbedded character of almost all drilled formations. This means that, at times, the point will be in hard rock and the other cutters in comparatively soft rock. The applied weight on bit will be alomost entirely on that lead cutter, with greatly increased risk of wholesale failure, or at least chipping.)

  7. Aug 13, 2018 at 9:25 PM #6
    i mean covering the whole cone and it's threads with polycrystaline diamond layer and the original cone and threads are out of TC. regarding the shear drilling,
    the cone drills by the thread grabbing onto formation with rotation and the point of the cone seperate the rock or you can say penetrate it and split it in half and then the whole cone grinds the remaining with every inch of the whole cone is in contact with formation on it's own at same time.

    the material and pdc i think is no issue as its doable but i would love if you could explain more about the shear drilling, my point is
    think of trying to drill in say butter with a tall cone like cylinder and with a fork.

    it's easier with with the cone like cylinder as penetration is easier and drilling continues as it moves with the threads. but with a fork the empty spaces between teeth like the pdc drill bits will leave remainings (cuttings).

    also keep in mind that the picture i attached is the cone inside the formation, the formation has same shape as cone so point of cone will sit on same area as the point's.
    every mm of the cone is facing the formation on it's own at same time.

    i'm trying to explain the picture i have in my head.

    let me know what you think.

    thank you
  8. Aug 18, 2018 at 11:12 AM #7


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    @ ahmed11.
    1. The grinding of every fragment into a fine powder requires much more energy than is needed to produce big fragments. Fine grinding is not only expensive and unnecessary, but it heats the bit and greatly reduce service life of the equipment. I suspect your cutter design grinds too finely to be economic.

    2. To remove rock fragments efficiently, remove one rock fragment at the time. Allow each fragment to fall into the hole vacated by the cutter or the previous fragment. Repeat that process. I cannot see how your design will allow the escape of big fragments.

    3. Avoid a flat face to face confrontation with solid rock. You cannot simply push rock out of the way with infinite force because there is an immovable mountain behind it. You must provide a high local pressure against it, then jump back. The mountain will respond by immediately pushing a fragment into the space vacated by the cutter pressure. By repeated loading the rock, unloading fractures form inside the rock, parallel with the local surface. Those fragments, once separated, can then fall out. How can your design produce the bit pressure variation usually generated by point percussion.

    4. In shallow holes compressed air may both drive and cool the cutters, then remove the spoil. In deeper holes water may be used. The deepest holes require a higher density fluid such as drilling mud that will flush and float the spoil from the hole. In your design I see no obvious path for the fluid flow in or out, needed to flush the hole.
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