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Brush Hog Blades

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bobad1
Join Date: Sep 2003
Posts: 31 Eunice, Louisiana
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2003-10-03          65494


We can go to the moon, but we can't keep brush hog blades sharp. Has anyone tried hardfacing (Stellite or hollow tungsten carbide rods)on just the cutting edge of the blades? Even selectively carburizing and hardening the bottom of the blade would cause a self-sharpening effect. I read about amorphous steel 15 years ago, and it is very hard but not brittle. Perfect for hardfacing for the "self sharpening" effect. Anyone hear of it actually being used?




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AC5ZO
Join Date: Jul 2003
Posts: 928 Rio Rancho, NM 87144
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2003-10-03          65496


I have only used hardfacing rods on dirt and rock cutting blades. It is very difficult to grind, so I don't know if you would be able to sharpen it. Some of these have carbides and others are high nickel alloys.

If you just applied it to the bottom of the blade, it might tend to self sharpen as the bevel wears away, or it might just get to the point that the hardfacing just flakes off. It is generally applied so that the force directly presses against the front of the hardface bead.

Stellite might work, but it is also difficult to grind and generally needs to be applied by an experienced welder.

I think that the best option would be a good case hardening job. I use a powder called Casenite or something like that. You do the case hardening with a torch only. It should give you a hard edge and a soft core of steel to keep the blade from breaking. It can also be reapplied as the blade eventually wears through the hard case. ....


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Peters
Join Date: Feb 2002
Posts: 3034 Northern AL
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2003-10-03          65499


We still have a blacksmith in the area that will hammer out the blades and case harden in the forge. He is quite reasonable and does a good job. ....


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bobad1
Join Date: Sep 2003
Posts: 31 Eunice, Louisiana
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2003-10-04          65512


I was thinking that you could hardface the entire bottom of the blade. I have seen rock bits come out of a deep hole with the teeth still sharp. Also, bonding 1/16" of amorphous steel to the bottom of the blade would guarantee a sharp blade until the entire end wore off. I guess the great hope of amorphous metal has fizzled. ....


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bobad1
Join Date: Sep 2003
Posts: 31 Eunice, Louisiana
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2003-10-04          65513


Peters, That must be cool. Wish we had a smithy here! Shame on the mowing machine manufacturers for continuing to use 1930's technology. There's no excuse for having to sharpen blades every time I mow my field. Wonder if there would be a good aftermarket for better blades? ....


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AC5ZO
Join Date: Jul 2003
Posts: 928 Rio Rancho, NM 87144
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2003-10-04          65589


If you used hardfacing on one side of the blade only, you would put a lot of heat into the blade and I expect that it would shrink on the hardface side and you would probably get severe warpage. The hardface would crack, which is OK, but it would be very difficult to control.

Case hardening whether it is done by a blacksmith or with an oxy-ac torch and casenite will heat the blade evenly and warpage should not be a problem.

I do remember a project that I had years ago where we cut a groove in a piece of steel and filled the groove with stellite to make a long lasting cutting edge. That might work, because it would be completely inset, but it would probably be too expensive for commercial sales. I have also designed self sharpening cutting edges for medical devices, but they rely on metal to metal contact to control the wear surface. I don't know of a way to do that on a blade that swings freely through brush. ....


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DRankin
Join Date: Jan 2000
Posts: 5116 Northern Nevada
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2003-10-05          65611


Something else you can do to prolong the cutting edge is to stay away from high speed grinders. Anything that throws off sparks is making way too much heat and creates a brittle cutting edge.

Cooler methods work better. Like Mike, I have had good sucess with hardening compounds. ....


Link:   Kasenit

 

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AC5ZO
Join Date: Jul 2003
Posts: 928 Rio Rancho, NM 87144
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2003-10-05          65633


Mark brings up an excellent point. Depending on the steel, a high speed abrasive grinder may also heat the edge and anneal it. Some high alloy steels can become brittle.

You can use water to keep the edge cool, but it takes some experience to know how and when to cool the steel. For cutting tools, I grind them very slowly or in some cases sharpen them with a metal file. Edges put on with a metal files last are very tough.

Also, if you have overheated the blade and annealed it, it will never hold an edge after that for any period of time until you get past the soft spot you created or you can have the blade hardened again. Also, don't just assume that a guy that sharpens blades for a living is doing it just right. I have seen many guys at lawn mower shops grind blades and create red heat on the blade edge, which causes the blade to lose its temper. ....


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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2003-10-06          65657


Yep, I never touched my wood carving tools with a power grinder. I also didn't have a large slow speed stone wheel with a water drip so it took a lot of time. My neighbour rigged up one from an old wood lathe with different pulleys to slow it down even more.

I've been sharpening my riding mower blade with a stone on a Drimmel tool (probably the worst choice since the stones are small and the motor is very high speed) but I go very lightly and never for very long. I also don't let the blade go long enough to need a lot of grinding. I take out any dings with a file first. It seems to work OK but the heat problem for mower blades is a little less than for wood working tools since the edge cross-sections are much greater. You don't want to sharpen a mower blade too sharp or it won't last very long.
....


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