What kind of steel is used in heavy duty mower blades for excavators?
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  1. #1
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    Default What kind of steel is used in heavy duty mower blades for excavators?

    Hey Guys,

    We have a customer that has an over sized mower attachment (don't know the real name of it) for an excavator. He uses it to cut grass, shrubs and trees up too 10" diameter with.

    We have tried O1 and 4140 Treated and drawn to 55, 50 and 45 Rc.

    The cutting edge itself we started at 30 deg but I noticed it was wearing into a steeper pitch. Last set I cut @ about 37.5 deg.

    We coated the last set with tungsten carbide hard face and treated to 50 rc on the blade and used the 37.5 deg angle on the cutting edge using 4140. He was able to get about 10 hours of run time before he had to flip the blades and start using the other side which was a big improvement from the stock blades that came on the machine "2 hrs".

    Any of you guys have suggestions to make the blades last longer; material cutter angle, coatings ect?

    Thanks for reading

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    I used to make different blades and knives for a big heavy equipment manufacturer. These were prototype runs in different mat'ls, same types of knives. They started with AR400, tried a few runs of that. Then tried Hardox 400. Last ones I made were S7. Some of the Hardox knives were released for production, so it must have worked (at least for something).

    Knowing what those knives were going to be doing, I always thought that S7 would have been my choice.

    AR is some wicked shit to machine, whether you're cutting through a HAZ or not. Nasty stuff. Hardox was definitely easier on the carbide.

    Note-

    Each part, whether prototype or production release, had to have the mat'l engraved in the part. That is their practice, so I'm sharing no secrets here.

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    Tell him to stop running the blades in the dirt so much , I have a friend that has several forestry mowers, sidewinders, and a mulching head on a boom. He gets several days out of a set of teeth before he replaces them.

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    I just sharpen them on our bobcat mower, but it does maybe 1-2" thick saplings, tops. Its pretty quick just to sharpen them, even daily. Then again 2 hours doesn't even get you to lunch.

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    Must be why Woods mowers use chain flails.

    Tom

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    I agree on the s7 as well. Very good resistance to impact damage. The only thing left to do is to test some edge design and away you go.

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    Something else... After sharpening many mower blades, too sharp can be bad. You make them too sharp and the edge dulls/nicks faster.

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    There's a brush mower manufacturer in my neck of the woods. Their web site says their blades/knifes are made from 5150. Not sure what that is exactly? Maybe is goes by a more common name?

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    5150 is a spring material used to make leaf springs, or at least used to.

    Edit:; 5160 and 1566 is common spring materials I've specified for leaf springs in the toy box I play in.

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    How about hard-facing the edges with one of the high-manganese maraging alloy rods designed for impact and abrasion resistance (the stuff used for excavator teeth and bucket edges)? This might be an improvement over the tungsten carbide facing you're using now, because it would be solid material rather than little bits of carbide, and quite possibly tougher than the matrix the carbide is deposited in.

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    Quote Originally Posted by sfriedberg View Post
    How about hard-facing the edges with one of the high-manganese maraging alloy rods designed for impact and abrasion resistance (the stuff used for excavator teeth and bucket edges)? This might be an improvement over the tungsten carbide facing you're using now, because it would be solid material rather than little bits of carbide, and quite possibly tougher than the matrix the carbide is deposited in.

    The material we are using now is going on in in big puddles not little bits. Are we using the same product?

    I think I would like to venture into the s7 hardox 400 material.

    Anyone have an idea of cutting edge angle? I want to try to take the blade's edge to a 40 or 45. Will it still cut grass at that angle?

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    Having ran a similar attachment on a machine. Ours had knives attached to a shaft that with inertia would swing out. We made our knifes from hardox 400, mechanic made a second set so we could just change them then sharpen dull ones at will.

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    Me thinks the operator is pushing that machine pretty hard to kill a set every two hours. Just because a machine is rated to "take trees up to 10 inches" doesn't mean it should do it all day long, and most importantly you need to keep it out of the dirt and rocks. I used to be a sub operator one crew that ran Tiger mowers. We could fell a full size tree up to that diameter if we wanted. Once it was down you could run back and forth and buzz the limbs off. Buck it up with a saw and flip the sections over and get the limbs on the back side. Usually we were only mowing with some occasional samplings, but those Tiger's could do it at 7+ miles per hour. The tractors got fueled, everything was greased, and the blades sharpened with an angle grinder every night. Those mowers ran 6 hour days, 5 days a week, 6 months a year and as I recall they changed the blades no more than once a year. All the blades I recall seeing on various mowers of this type had a twist in them so they mounted flat to the plane of travel and then angled up say 30 degrees or so. Is this really a mower or brush cutter that has a wheel? Those work more like a stump grinder.

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    Quote Originally Posted by alonzo83 View Post

    Anyone have an idea of cutting edge angle? I want to try to take the blade's edge to a 40 or 45. Will it still cut grass at that angle?
    I have a fairly stout bush hog, it will cut up 4" trees OK. For 2 years or more the operator was sharpening the wrong side of the blades, he was sharpening the following edge instead of the cutting edge. The cutting edge wound up with about a .125 radius and it still cut grass and weeds. The mowed area looked crappy a week or so after being mowed when the mangled plants started to grow back, but it was short. I'd think a sharp 45° should work better than that at least.

    I discovered what he was doing when it lost a blade and I put 2 new ones on.

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    I worked on a couple big deforesters a few years ago that were that size or just a bit bigger. We worked with atlas copco and ... I can't remember the other company... To get the deforesters up and running for the US Forest service. 37.5* was a magic angle, but not ground sharp. We left about .085-.1" before starting the angle if my memory is correct. I don't recall the material used, that had been sorted out early on by the engineering team, we were mainly messing with the hydraulic system and trying to deal with the vibrations all those knives developed in a light cut, hence playing with the cut angle.

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    Very interesting thread.

    I built my own brush cutter this summer,(skid loader mounted) and My-O-My how it finds rocks
    just like a magnet.

    Even though I'm the builder and owner, so I baby it a bit more than
    a hired hand would, the nature of brush cutting is running the
    cutter into places that are full of nasty stuff like rocks.


    "Keep it out of the dirt ?" easier said than done.

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    I sharpen the blades on my two bush hogs at 45 degrees and they work fine. I agree with what someone said that if you are not taxing the machine more then what it was designed to do then the blades don't need to be overly sharp. My bush hog will cut small trees up to about three inches in diameter with blades that are as dull as the side of your hand. I'm not saying this is a great practice but you would be surprised at how dull they can be and still get the job done. Now cutting what this machine is doing is a hole different ball of wax of course. I have never even seen a rotary type cutter that would cut ten inch trees. I've seen plenty of sheers and hydraulic saws that do it no problem but that must be one hell of a mower.

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    AR500 steel is used for armor plating, steel shooting targets, and for blades on graders and bulldozers. The key strength is the abrasion resistance on top of the hardness.

    There are more steels than AR500 that have improved abrasion resistance, but AR500 is simply the steel I have experience with. I figure if it's good for a dozer blade and for graders, it should handle dirt, grass, sticks and stems.

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    A tip I learned long ago. The sharper the blade is, the easier it will cut. BUT, you don't want that on a bush hog! The sharp blade will bend the sapling over a bit and slice it off. As it stands back up, you've got a nice sharp spear that will puncture a tire. Less likely to happen with a blunted edge.


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