Tractor backhoe - homemade

[Kyle_in_Tex]

Rooting for Croatia tomorrow.

 

[BFreaky]

Thanks. I hope we win the gold. Best rank till now was 1998. 3rd place...

 

[BFreaky]

The whole hydraulic system, and finally first metal parts...kingpost hinges. The thickest material on the bh because it has to manage all the forces generated by the boom

 

[Rustyiron]

Elec. joysticks!! :cool2:

Those valves look conventional? I'm sure you have a plan.:thumbsup:

 

[BFreaky]

It will be a mixed system. Joysticks will have metal cable connection with those valves and two switches each so I can divert lines via 6/2 electric diverter valves. Not to expensive but very efficient

 

[Renze]

For your info, the main boom of a Cat M314F we got in the shop last week, has 8mm top and bottom plates, all S355 quality. Havent measured the section height but its less bulky than your RK 525...

 

[BFreaky]

New bh will have 6 mm side plates and 8 mm top and bottom. How did you determine grade of steel on the boom?

 

[Renze]

New bh will have 6 mm side plates and 8 mm top and bottom. How did you determine grade of steel on the boom?

S355 is the only thing Cat uses... We modify booms and sticks for Cat and Hitachi importers, high reach demolition, long reach dredging, thats why we get the info when we need it for a modification.

Even the big mining excavators use just S355... If it has to last, you need more steel to lower the strain. High strength steel is only useful for static, or limited design life applications because the welds have the same, or worse, fatigue life before they start cracking, than S355...

HIAB truck mount cranes are Domex 700, but when you use those as a construction hoist crane instead of a truck loading crane, it will be cracked all over within 1.5 years because it will see the number of load cycles in 1.5 year which a truck mounted loading crane (used to self load a transportation truck as intended, not as a cheap alternative for a tele crane) sees in 15 years.


In civil engineering, the same fatigue life (or max strain) is used for S355 as well as the most exotic high strength steel. I contacted our steel supplier, and some research centers, and i found only some German research with hard, conclusive data about the differences in fatigue life between S690 and S355 base material (S690 base material only has a better fatigue life in low cycle, high strain fatigue) and in welded S690 and welded S355 (The S355 weld had a slightly better fatigue life)

 

[BFreaky]

Well I used S355 on rk 525 so you just convinced me not to buy Domex for this application. This will speed up my project because it will save me money. I've heard before about this cracking problem but figured they just don't wanna spend the extra money. Last time I used S355 J2 G3... is this the one? There are few types of it..

 

[Renze]

Domex is good, because of its fine grained structure. But S355 or S420 is the max you get in fatigue strength, Domex 700 is only good for hoisting rigs with limited load amplitudes. Furthermore, high strength steel has higher carbon which needs preheating to avoid cold cracking and/or hardening effects along the welds.

But i think any S355MC has similar properties to Domex 355

 

[BFreaky]

I will do it with S355. It turned up good last time. Only this time I've reduced the wall and bottom thickness and overall height of box sections. Max height on the first one is 340 mm, on rk 525 it was more then 400 mm. The point is to reduce weight to get more load capacity

 

[BFreaky]

I wanted to ask you which material are you using for the pins. I used 42CrMo4V but there is a problem with it...when you weld pin ends most of welds crack if there is some force... how do you solve that on your machines?

 

[dfkrug]

I wanted to ask you which material are you using for the pins. I used 42CrMo4V but there is a problem with it...when you weld pin ends most of welds crack if there is some force... how do you solve that on your machines?

What is wrong with mild-steel pins and replaceable sleeve bearings?

 

[BFreaky]

Everything . The point is to have hard pins to get as much uptime as possible. Bushings are cheap and can be replaced quickly but pins are not

 

[love4god]

outstanding work,the best fab work i have seen in awhile,congrads,,
godbless

 

[BFreaky]

Thank you love4god. I hope new one will be even better...at least that's the idea

 

[love4god]

your welcome Bfreaky
I will be watching for your new builds,,
Godbless

 

[Renze]

42CrMo4 hardened and ground, is by far the most used material for pins in earth movers. We allways lathe a small recess on the pin so the tab plate is aligned on a 2mm edge, then the rest is lathed to a 45 angle as thick as the tab plate minus aforementioned 2mm, so it can be welded flush.

42CrMo4V has a high carbon equivalent, so it easily gets hardening cracks in the heat affected zone, or HAZ. Mostly tabs are welded with high amps, high heat input so the mass of weld cools slower to the mass of the pin. In case of problems, preheating the pin and tab is the only way to get the same strength as a weld in mild steel.

 

[Renze]

Oh, and breaking tabs and locking bolts means that there is too much friction in the bushing, so that the rotating force on the hinge is transferred to the locking tab...

It usually indicates fretting due to lack of lubricant, or misalignment of the bores, or play on the bores so the locking bolt is loaded whenever the pin wobbles.

 

[Renze]

...to be able to take pins out, years from now, it is also good to lubricate also the static bores in which the pin sits (not just bearing surfaces) with Copaslip (copper grease) or Keralube (ceramic paste) to prevent fitting rust. I remember at the wheel loader factory, guys from the service department running all yelling into the production department, cursing the guys who forgot to put keralube on tight fits, because in 2 years the bores had corroded so tight that they had to torch the pin out of the hole....