AR plate and heat

Date 02-12-2009 03:32

I am not familliar with Your machine, but on an old Asplund My friend had the blades were made from A2 tool steel and heat treated to 57 Rockwell "C". The machines He presently has use fully hardened tool steel blades too. If You are going to use this commercially You might re-think about it.

By Wrench Tech (**)

Date 02-12-2009 04:03

Thanks for the reply. I'm in quite a hurry (well the customer is) to get this thing running so I' thinking of buying the first set of cutters and building the second set once he's up and running. By the tone of your reply I'm guessing you don't think building a set is a good idea. I know building this type of cutter is commonly done but I'm interested to know what your concern might be. This type of brush cutter consists of a rotating drum with 24 floating cutters held in by four shafts. The drum is 50 inches long and 24 inches in diameter, weighs 2000 pounds and runs at about 1500 RPM. You mount it on an excvator instead of the bucket. For all I know the cutters are cheaper to buy than to make. If so I'll never build them. Still, I'm quite interested in the effects of heat on hardened steel...... Tom

By DaveBoyer (*****)

Date 02-12-2009 05:42

You are working on an entirely different type of machine than I was thinking of, so use Your best judgement. My friends machines are like You see the tree guys using when they cut around the power & phone lines.

I am not familiar with this type of machine, but it sounds like the blades just beat the brush apart and don't rely on a really sharp edge. The other type of machine needs sharp cutting edges to work properly, that is why they are fully hardened tool steel.

When You torch cut and weld quenched & temperd material You do have to take into account what will happen in the heat affected zone [HAZ]. If the area heated above non magnetic cools fast enough it can become brittle hard, if it cools slowly enough it will be soft. Any part heated above the temper temperature, but not above non magnetic will be softer than the specification.

You will need to follow low hydrogen weld practices when You weld this material.

By Wrench Tech (**)

Date 02-12-2009 05:58

Dave, I intend to tack the pieces up, preheat to approx 250 degrees (spit bounce temp) and weld it up with E71T-9 045 wire with CO2 gas. Sound about right to you? What do you think that'll do to the temper of the QT500 cutting edge? I mean do you think I should be concerned about the method used to cut the QT500 when you consider the process I intend to follow in welding the pieces together? I'd appreciate your opinion. Tom

By DaveBoyer (*****)

Date 02-13-2009 05:17

I am guessing that the weld is far enough away from the actual cutting edge that the weld won't make any difference. I am not familiar with QT500 You could probably go to about 600*F without softening the material. If You can find a recommended welding procedure for this material You would be wise to follow it, particularly if it calls for post weld heat treating. If You posted a picture or drawing of the part it would help too. Do these get sharpened to a sharp edge & kept that way or do they beat the brush to death?

By Wrench Tech (**)

Date 02-13-2009 14:28

Dave. There have been a couple of surprises. When I get to the cutter building stage I'll post a photo. Thanks. Tom

By Kix

Date 02-13-2009 16:16

If you're not going to build a ton of these things, then you might want to research and cost compare. Waterjet would be your best bet for cutting and keep the properties of the steel out in the cutting area. Like Dave said, the welding area will more then likely be to far away to effect the cutting edge. Do you have a waterjet?

By Wrench Tech (**)

Date 02-14-2009 03:15

No. And, in fact, i'm not even familiar with the process. I've done the cost comparison and found the materials are about the same cost as new cutters but the ones you build last longer, some of the pieces are reusable and are double edged as opposed to the single edged new ones. There are 24 cutters in a set which lasts from 3 days to 3 weeks depending on ......you know....whatever. I plan to have a set in use and a spare set. I don't know how sharp they have to be but the operator occasionally touches them up with a disk grinder. When one side gets down you pull the shaft and turn the cutters around and go back at it. The actual cutting edge is a piece of 1 inch flat bar cut at 45 degrees. As I said when I get to that stage I'll post a photo or 2. Think I'll just flame cut the first set with a beetle. Quicker, accessible, available localy.

By DaveBoyer (*****)

Date 02-15-2009 19:11

There is something to consider that might be a really big fly in the ointment, and that is liability for these cutters if one breaks in operation and results in injury. Is Your but covered?

By Wrench Tech (**)

Date 02-15-2009 23:44

Well, for one thing, they break all the time whether you build them or buy them. All you gotta do is hit a rock or a stray piece of steel or a stump or something. The operator can feel the drum vibrating because it's out of balance and he knows it's time to change a cutter. This thing is used to clear large areas of brush like under major powerlines etc. Not the type of thing you'd use in populated areas. Anyway most anything I weld could break and cause an injury. It's the same for all of us....isn't it?

Don't take offence, Dave, but if you look at the subject of my original post you'll see that I was asking about the effects of heat on the hardened plate with regard to keeping the cutter reasonably sharp. So many times I read a post that goes this way and that. It winds up so far from the original posters concern that he/she must be wondering just how they got here from there.

But to answer your question, I'm not worried about my butt at all. I've welded hardened plate to T1 and mild steel so many times that wound up in extreme conditions (Excavator buckets for eg.) that I'm just not worried about it. When I get done it would take a force that would break anything to break these cutters.

By DaveBoyer (*****)

Date 02-16-2009 05:15

A simple field expedient way to get an idea how hard or soft the flame cut edge will be is to flame cut a piece and test it by whatever method You have, a file being a pretty good indicator. Then grind of 1/64 and test again. Repeat untill You are through the HAZ.

By Kix

Date 02-16-2009 13:38

I think you will be fine flame cutting the piece by what you are describing. You will eventually get back into harder material as you grind and sharpen the chewing toofs. ;-)

By makeithot (***)

Date 02-16-2009 02:53

They are awsome machines WT have worked on similar and for the most part have used what ever was at hand harder the better of course as the thing is going to wear out any way. My main concern more, then any thing would be the balance. ie: so that the parts wear out evenly. In regards to heat treat we use to go to 750 if memory serves me and just weld away. My understanding of the effects without pre heat would be a hardend HAZ which to some degree would be good for wear, but not so good for the ductility of the thing which as you most likely know leads to cracking. Also if you don't have it already get "The Procedure hand book of arc welding" from lincoln it has a wealth of info which explians the effect of heat on hard and mild steels. For the most part though it has alot to do with the hardenability of the steel and what has been alloyed to it etc. This also combines to give you the right pre-heat for spicific materials.The book is great though I have yet not been unable to find an answer to any question that I had, and written so an eliterite such as myself can understand.