Grapple pins

Date 01-30-2015 05:12

Hello wrenchtech, I used to work for a heavy equipment manufacturer quite some time back and that's what they used on the majority of the pivotal areas on a lot of the equipment that we built. 4140 TGP (turned, ground, and polished) was what they often used. This included clam-shell buckets, log grapples, and a host of other stuff. There are likely better choices out there now, yet this is a choice that has been used in the past with reasonable success I would say. Best regards, Allan

By wrenchtech (*)

Date 01-30-2015 05:32

Thanks. I'll let you know how things work out.

By aevald

Date 01-30-2015 05:43

One thing I might add however, if you are going to do any welding on these pins, such as adding keeper plates, stop plates or other items, you may wish to use sufficient preheat (I believe around 600 degrees and with a slow-cool down, wrapped in KO wool, or buried in lime) and E9018 to E11018 stick electrode or possibly a 90,000 series flux-cored nickel wire. Without preheat/postheat and using lower tensile consumables you might have crack-issues on the pieces that you attempt to attach. Good luck and best regards, Allan

By aevald

Date 01-30-2015 15:21

I read Al's reply and certainly agree with the handling of the pin, however, a lot of the time the pin needs to restrained/locked into place on a part in order for it to rotate in another part of the system. Buckets are a prime example: they will "pin/retain" the pin to the ears of the bucket bosses to keep it stationary and allow the pin to rotate in the end of the boom as it is generally designed with bearing surfaces for this purpose. Just another variation that might need to apply. Good luck and best regards, Allan

By welderbrent (*****)

Date 01-30-2015 15:31

First, yes, 4140 is a good choice.

I second the cautions added by Allan and Al. Most heavy equipment will have one surface designed to carry load and support the pin while the other is designed to allow the rotation movement and wear at a reasonable rate while allowing for easy rebuild and/or replacement of parts (bushings, arms, brass inlay, etc) Homeowner equipment is not usually as well designed and wears out at all points of contact.

There are even times where the pin is the item designed to wear out and be replaced. Operators must be aware of slop developing in joints either way and know when to get it to the mechanic. Otherwise more time, parts, and expense are required to get back into working condition.

He Is In Control, Have a Great Day, Brent

By wrenchtech (*)

Date 01-31-2015 04:51

This grapple is hardly "homeowner" equipment.
Also, the reality is that although the hinge is fitted with pressed bushings that wear out and should be replaced, it usually is operated to destruction. Good thing for me, too. I make my living fixing such things. In addition, the pin bores in which the pin remains fixed still become really egg shaped over time. Hence the line boring.
Thanks for the reply.

By welderbrent (*****)

Date 01-31-2015 15:05

I was not suggesting it was homeowner, I used that as a comparison.

And I am well aware of the egg shaped holes requiring repairs over time and usually at total breakdown stages. I have done a fair share of similar repairs over the past 40 years. Everything from small equipment to LeTourneau Log Stackers. John Deere, Case, Cat, just about all of them at one time or another. Welding holes totally in and drilling and/or boring new ones. Welding with brass and boring to size. Welding and drilling or boring then inserting brass bushings. Building our own pins from whatever stock fit the bill, 3/4" to 4" diameter. Drilling for keepers, welding plates on one end. So many possible combinations and possibilities. Making the correct part harder than the others and making the easiest part to repair or replace be the one that wore out first. And the application always dictates how the repairs will be handled and what materials are best for the job.

Then the welding procedures come into play. Most repair welders I have worked around were terrible about pre-heat. Almost none if any, seldom sufficient. The heat affected zone breakage was so common it was pathetic.

BB

By wrenchtech (*)

Date 01-31-2015 05:09

These type of pins are usually attached by means of a tear-dropped shaped plate welded to the pin on the large end and fixed to the body of the grapple at the small end with a bolt. The bolt hole is larger in diameter than the bolt - large enough to just accommodate a bushing or spacer. A large flat washer under the head of the bolt is what keeps the pin from coming out and the bushing/spacer prevents the pin from turning in the fixed bores. Some small movement of the pin is allowed which keeps the keeper plate from breaking away from the pin. The pin is only just long enough to come flush at the other end. The keeper bolt is protected by a piece of steel bent around the top of the tear-drop. if the pin is made long enough to protrude beyond the body of the grapple it will get hammered against the body and the keeper pin will fail.

As for welding the plate to the 4140, I do use some preheat but that's about the only precaution I take. I haven't had any problems with the weld failing using either stick or dual shield wire.

Hope I described that all right. Maybe a picture would have been better than those thousand words I just wrote.

Thanks, Al for the reply.

By 803056

Date 01-31-2015 11:34

I've seen the keepers you are describing.

The AISI 4140 alloy steels do require significant preheat to prevent rapid cooling while welding. The 0.4% carbon plus the other alloying elements means it has a high carbon equivalency. High CE means it is easy to form hard, brittle martensite in the HAZ of the weld.

I do not recollect the diameter of the pins you are making, but I would use 500 degrees F as a starting point for the preheat temperature. I would anticipate your client complaining of keepers breaking loose if you fail to use sufficient preheat.

For this application where the loads on the welds are relative low; fresh out of an unopened can, E7018 or E8018 would work with SMAW, any bare wire would work with GMAW (spray transfer), and any E71T-1 would work with FCAW. I would opt for E71T-1C-JDH4 for FCAW to ensure a low hydrogen deposit.

Best regards - Al

By Blaster (***)

Date 01-31-2015 18:56

I used to manufacture excavator buckets. The bushings for the pins were made of 4140, 7 inch OD if I recall. We turned the ID in our shop. Anyhow I think we used at least a 350 preheat. May have been 500 - that was a long time ago. Anyhow I don't recall ever having a warranty return or claim regarding the bushing welds.

However we also built compaction wheels. I remember a return where the pin the wheels were welded to (4" I believe) snapped in half at the weld toe in a brittle fashion, like a piece of chalk. Almost certainly a preheat issue as that was not not a common problem and we built 2 or 3 compaction wheels per week.