Rated puller rod / plates

[Equipment Stripper]

Hi all...
I'm not an engineer, just a 35yr trade experienced Heavy duty mechanic.
I have a few questions that I'm hoping you can help me out with.
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We often experience wear bushings pressed into the machine. The replacement of these bushings require cutting the old bushing and pulling it out, or pulling it out with plates and threaded rod, and then installing the replacement bushing by pulling it into place with a hollow core ram and rods and plates.
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I have worked as a "dealer" mechanic and in almost every scenario I have come across, we go get a piece of "grade 8" redirod, (also known as all thread and numerous other trade names). Then we take a piece of plate with a hole in the center and put it on the bushing and use some double nuts and put it through the hollow core cylinder and then pull out or in as required.
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Recently I came across a listing from "Caterpillar" in their tooling catalogue. They list them as "puller rod" and actually publish a specification rating for the size of the rod, ie 30 ton, 50 ton, 150 ton, etc. The rating of the rods changes with the length and the diameter of the rods. They also had a section of "threaded rod" "not to be used with hydraulic cylinders"
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In my experience with the redirod, we quite often break it, or pull the threads out of the nuts, or off the rods, through the plates, etc. Having a steel rod break with 60 tons on it and go flying through the air can be unnerving.
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No other tool manufacturer, or equipment manufacturer that I can find, list a source or part number for "rated" puller rod. Just the Caterpillar ones.
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I have attached pages from the Caterpillar catalogue that has the "threaded rod" specs and pic as well as the "puller studs" specs and pic (found on pages 10-4 and 10-5 respectively).
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If I want to order some threaded rod from a manufacturer, (other than Caterpillar) and want them to be certified for a "tonnage" strength to be compatible with the 30,60, 100 ton etc hollow ram cylinders, what should I be specking for materials?
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The second question I have, I want to make up a set of puller plates, to be used to pull against the bushings. I would like a set that can be used up to the 150ton hollow ram cylinder I have. So they would have a 1-1/2" center hole through them that I could bush down to fit the smaller puller rods. We usually torch cut a plate out of what ever material we have handy, and quite often they buckle etc. In this day and age, safety is starting to become a major requirement for all job sites. I would like to have a set that I can have premade and have in a kit. I'm thinking 1-1/4 thick would be enough, of say QT400? But here I'm just pulling stuff out of the air. For example, if the OD of the bushing I am pulling is 6" with a wall thickness of say 1/4" then I have an unsupported span of about 5-1/2" and a hole of 1-1/2" through it. How would one calculate what kind of material and thickness I would need so the plate doesn't buckle? (if this is unclear, tell me and I will try to make a sketch of what I am describing)

 

[desertfox]

Hi Equipment Stripper

One problem you will have is knowing what force you need to apply to extract the bearing and the force will vary depending on the amount of radial interference the bearing was originally designed to have on assembly, then there are all the materials you might encounter which you will need to use the bearing puller on.
So I am not sure you can do what you wish to do without knowing the extraction force before you start, there are formula for interference fits for installation and removal but over time this will change as the materials age and dirt and other stuff migrates into the joint.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[btrueblood]

"If I want to order some threaded rod from a manufacturer, (other than Caterpillar) and want them to be certified for a "tonnage" strength to be compatible with the 30,60, 100 ton etc hollow ram cylinders, what should I be specking for materials?"

Order studs in a rated grade, e.g. per ASTM A354 Grade 8, or ASTM A193 Grade B7. The supplier should be able to tell you the rated strength of the studs, or a least the minimum tensile strength of the material, from which you can calculate the breaking strength.

 

[dhengr]

Equipment Stripper:
I think I know what you are doing and about how you are trying to do it. But, there are a few hundred variations on the theme, so you really have to show use some sketches of the various parts and details, and how they fit together. The way the bushing fits in the machine bore, and what areas on the machine we can push or pull against, vary in the hundreds too, so you have to show the most common ones, so we know what we are dealing with. An example problem…, many bushings are pressed till they hit a keeper shoulder on one side/end of the machine bore i.d. This shoulder limits how much of the wall thickness of the bushing we can press against in one direction. What is the range of i.d’s., o.d’s, wall thk. and length of bushing you deal with, or wish this kit to work with? How tightly, an interference fit, do you usually make these bushings? Do you ever use heat or liquid nitrogen in the process? What size hollow hydraulic cylinders do you have, what stroke length, their other details, etc.? Within reason, I’d always use the largest puller which would fit through the bushing bore; so I didn’t have to do everything over because I needed a few more pounds.

I’ll bet that you would pay a premium buying this type of equipment from CAT, and it would be good stuff. But, there is no reason we can’t follow the good parts of their design. I’m pretty sure you can buy all the parts, or kits, from various mechanic’s tool supply houses, or make your own based on your exact needs. You do not want just any old all thread rod from a big box store. I would start with only a few pulling rods, as long as they would fit inside the bushing i.d., and the longest length you’ve ever needed. Fewer pieces allow the whole kit to fit in one box, not a truck load. I’d have a machine shop make me a bunch of round pls. with your largest center hole, and in .25” dia. changes, over your range of bushing dia’s., pl. thickness to be determined. Then, I would stack them up, pyramid/cone fashion to improve their spanning strength. For example, your 5.5” dia. span, for your 6” bushing might involve a 5.8” dia. first pl., with a 5.5” dia. pl. and a 5” dia. pl. backing it up. You can get by with somewhat thinner pls. by stacking them, and taking advantage of their combined strengths, and the way they distribute the loading. Maybe your back-up pls. should be thicker pls. in 1” dia. changes. You want high strength rods, and you want high strength, extra deep nuts, for extra strength and abuse of the nuts. Most of this stuff can be pretty easily worked out, strength wise, once you kinda hone in on how you want this system to work, and what parts are needed.