Posted by: dal_johnson ® 10/29/2006, 16:48:35 Author Profile eMail author Edit

I'm trying to do a force analysis on the pins in an oilfield manual tong. For those that don't know, a manual tong is basically like a very large self clamping pipe wrench. It has it's teeth and latches that you attach around the pipe, and then the hydraulics are run to the lever arm, the grip tightens on the pipe and the threads are tightened or loosened. I will know what the tong is rated for, and as such know the torque (moment) at the pipe itself. If you were looking straight down (axial) on the pipe you would see that the tong has 5 pins holding the teeth and latches together around the pipe. At the position of the highest torque these 5 pins are located around the pipe, not in an even distribution (differing angles) the each pin has a different center-to-center distance from the center of the pipe (base point). Does anybody know of a way to translate to moment to figure out the force on the pins when the tong is fully loaded. It can't be a simple moment arm calculation to each pin, as each pin to working together and won 't see the full effect of the torque individually. I thought there may be a way to take an individual center-to-center distance and apply it as a percentage of the total of all center to center distances, but that wasn't working out. I've attached a scan of a hand sketch. I hope it works and will help to show the arrangement. Any advice, thoughts, or formulas are greatly appreciated.

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Re: pin forces from torque on a manual tong
Re: pin forces from torque on a manual tong -- dal_johnson	Post Reply	Top of thread	Forum

Posted by: dal_johnson ® 10/30/2006, 10:45:14 Author Profile eMail author Edit

please any help??

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Re: Re: pin forces from torque on a manual tong
Re: Re: pin forces from torque on a manual tong -- dal_johnson	Post Reply	Top of thread	Forum

Posted by: swearingen ® 10/30/2006, 13:09:00 Author Profile eMail author Edit

A clearer, well-dimensioned sketch is required.

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Re: Re: Re: pin forces from torque on a manual tong
Re: Re: Re: pin forces from torque on a manual tong -- swearingen	Post Reply	Top of thread	Forum

Posted by: dal_johnson ® 10/30/2006, 13:43:12 Author Profile eMail author Edit

The dimensions aren't known. They will be measured off of each individual application. It's the method of analysis. I know the sketch is pretty bad, the main points are that the tong grips around the pipe and provides its rates torque. The tong is made up of links that are pinned together around the pipe, and when the force is applied (to provide the rated torque) the links self-clamp and then the entire assembly works as a wrench. When the tong is at full capacity, I am trying to determine a method to calculate the force on each pin around the pipe. Each pin of the linkage is at a different center to center distance from the pipe, and these distances will be physically measured at the time of analysis. Once these center to center distances are known, along with knowing the rated torque of the tong, is there a method to translate this moment to the pins. The problem is in how all of the pins are working together, so no single pin will see the full effect of the applied torque. I've also been trying to look at it as a static analysis for the links around the pipe, since when it is fully loaded the assembly should not move relative to it's components. I am trying to consider the pipe as the pase point, but am unsure if I should call it a fixed point of a pin joint, and if I should then use an imaginary connection of each linkage pin back to the center of this pipe. Yet again I apologize for the skecth. I have added a picture of a tong. Hopefully it will help more. The dimensions "A", "B", and "C" are not relevant here, they were just on the picture. You can see the 5 pins that I am trying to determine the forces for, and there the center of rotation (pipe) will be. Hopefully that will help to explain things more, and once again any help is appreciated.

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Re: Re: Re: Re: pin forces from torque on a manual tong
Re: Re: Re: Re: pin forces from torque on a manual tong -- dal_johnson	Post Reply	Top of thread	Forum

Posted by: swearingen ® 10/30/2006, 17:45:41 Author Profile eMail author Edit

Now I understand how it goes together. It's actually simpler than you may think. This is just like the steel band type you can buy for removing car oil filters, but instead of a band, it's some heavy links with pins. Start with the two pins connected to the lever arm. The forces in those pins can be solved by taking moments around one of the pins. Example: if I call the left-most lever arm pin A and the right one B and the point of load application C, then start by taking moments around A. B = C x (distance C to A) / (distance B to A) Understand that this will be approximate, but quite close, because the resultant forces in the pins won't be quite perpindicular to the lever arm, but they will be close. Use the same method all the way around, but using the pressure point on the pipe as another force that you have to solve for. They are all determinant.

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Re: Re: Re: Re: Re: pin forces from torque on a manual tong
Re: Re: Re: Re: Re: pin forces from torque on a manual tong -- swearingen	Post Reply	Top of thread	Forum

Posted by: Kelly Bramble ® 10/30/2006, 18:17:32 Author Profile eMail author Edit

Similar too: /manufacturing_spec/torque_wrench_1.htm

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Re: Re: Re: Re: Re: pin forces from torque on a manual tong
Re: Re: Re: Re: Re: pin forces from torque on a manual tong -- swearingen	Post Reply	Top of thread	Forum

Posted by: dal_johnson ® 10/30/2006, 18:06:52 Author Profile eMail author Edit

You have no idea how thankful I am right now. I'm also kicking myself for looking for more then there was. Thanks for the help.

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