Looking for steel alloy best suited to wood chipping and grinding?

R

Rob Canada

Joined
Jun 8, 2012
Messages
6
Hi folks.
I apologize if I am in the wrong area for this question but there seems to be a wealth of knowledge here and the tools we use are often referred to as knives.
I design and build industrial mulching machines that are used for clearing vegetation without burning. I am currently building a compact steel tracked rear engine mulcher that has a horizontal axis drum with carbide tipped tools as the cutters. I would like to experiment with different alloys that I can use to manufacture prototype tooth. Rather than using a carbide tip tooth I would prefer using something that can be sharpened with a grinder to keep an edge as opposed to using massive torque and inertia to force a blunt piece of carbide through the tree. Of course this wont last as long but they will require far less energy and fuel to chip and grind up woody debris. The tooth must be able to come in contact with the ground and resist dulling for a reasonable period of time between sharpening. The purpose of this tooth will be to chip up the majority of the trees at or slightly above ground level and then we would switch to the carbide tool drum to finish off the job by mulching the material into the ground.
The fact is most of the wood is chipped/mulched above ground and the dull carbide tools are very inefficient at this. I also wish to try some full length blade prototypes for jobs that are in low growing brushy hedge type species. Using current tools this type of growth tends to wrap around the drum and tear rather than get sliced up.
I suspect ideal properties of the steel for this purpose would be similar to a good quality knife except perhaps a little less brittle. In the event of a glancing rock strike it would have to bend rather than shatter. I would like to be able to recycle the steel after the edge has been used completely. The idea is that only the leading edge of the knife or tooth would be made of this alloy to minimize cost. The majority of the tool would be made of AR plate alloy, similar to a grader blade or excavator bucket tooth. I just discovered I cant post pictures on here yet so unfortunately I cant illustrate what I have built in the past.
Any suggestions would be greatly appreciated!
Thanks,
Rob
 
Jikes! In knife terms your application would be categorized as extremely abusive. Again in knife terms you are going to need a very "tough" steel, but to get that level of malleability you'll need to run the steel pretty soft. The extremely chip resistant (tough) steels are things like S7, L6, CPM 3V, and M4, and you'll have to have a wide bevel angle to put plenty of steel behind the edge. The closest "knife" comparison would be an axe, which are run at perhaps Rockwell C values of 56 or below. If you grind a hardened steel you run the risk of changing the heat treat significantly, which is where a "high speed steel" tool steel alloy that gives hot work hardness might be required. Off the top of my head that leaves you with something like M4, which is abrasion resistant, tough, and has the hot work hardness properties you need. You're into the classic problem of balancing abrasion resistance versus sharpening time, but again your application is going to place more stress upon the edge than any conventional knife is going to see. Good luck!
 
Thankyou. It is quite an abusive situation to maintain any form of sharpness. I still believe that even when the leading edge is dulled to 2 or 3 mils thick it would be a significant improvement in production relative to fist shaped rounded off blocks being forced through the tree.
As for the heat of sharpening being detrimental to the heat treating. Would it help at all to use a water cooling stream while re-sharpening?
 
We could all give our opinions but wouldn't the services of a metallurgist/engineer be a little more useful in the long run? The "chipper" steel is Latrobe A8(mod), which is a slightly modified form of A8 steel. That might get you close but you are still going to do better with a real engineer instead of a bunch of knife knuts, or knife maker/knife knuts. :)

Good luck.

Joe
 
look up the companies that make such machines. saw them featured in "sharpest blades in the world" --youtube. there was this monster mulcher that was employed to clear fallen trees in 'orlens' after katrina.
 
Thank-You all for the response to my questions. I have designed, built and collaborated on several prime movers designed to power mulching heads. The actual head has always been sourced from others and of course the metallurgy of the teeth is always proprietary information. In response to the need for more efficient cutting performance in small dense brush we have decided to try a new approach.
The prototype machine and mulching apparatus that I am now building will be able to take advantage of a knife style tooth by design. I have already CNC manufactured the prototype teeth from the same AR plate that I used for the actual drum. Once we determine the most efficient knife shape and angle we will be testing the material. I can't get too deep into the design here but there are counter cutting protrusions involved as well.
I have often found that grassroots enthusiasts have valuable insight to offer when researching a specific topic. I searched this forum for metallurgy threads before posting and found it to be great reading for someone like me with minimal knowledge on the subject.
I have had several recommendations from our steel salesmen and will running field tests for at least 6 months ( extreme cold weather included) to identify the best performing products for this purpose. I came here to get some suggestions from knife experts and add them to the growing list of alloys to consider for field testing.
 
upload the pics to something like imageshack or photobucket and link them here. A8 or Viking is probably going to be recommended as Mastiff said - maybe an 8% Cr steel as well, like Cruwear, 3V, DC53, PD#1, etc. They will get you higher wear resistance with still good levels of impact toughness. I think tool dimensions, specific operating conditions, and cost constraints are really going to have to be articulated first.
 
Just some thoughts. What sort of aparatus do you use to sharpen these blades? I can imagine you'll be trying all sorts of steels before you arrive at a finished product, but depending on how you plan on sharpening them some of the more exotic wear resistant steels will probably make sharpening such a machine unfeasable even if you disregard the lack of toughness. (s125v, s90v).

Some of the new particle metallurgy D2 and M4 derivatives were my first thought, M390 or CPM D2, tougher than regular D2 steel and a finer edge, but still retains much of the wear resistance that D2 is famous for. CPM M4 and similar steels like Bohler s690 are favorites in cutting competition knives, and I'm guessing will represent the hardest and most wear resistant steels that might still have adequate toughness.

CPM 3v is likely one of the toughest steels used in knives, I'm not sure how it compares to something like A8 or S7 for shock resistance. In thinner profiles it has an odd tendency to "flop" over at the edge or ripple even at high hardness, depending on the thickness of the blade and edges this may not be an issue at all.

There's also alot of steels out there that knife people aren't very familiar with for various reasons. I was browsing through some datasheets and saw Latrobe Duratech 9, it runs much softer than most folks like their knives to be, aorund RC 53, but has phenomenal toughness and wear resistance characteristics. Spec sheets don't tell the whole story of course, on paper s30v should be more resistant to chipping than the majority of stainless steels that came before it, yet it has a bad reputation for chipping easily at the edge. Good luck with your project, it sounds like an interesting machine.
 
I will try and upload photos asap.
If you wish to see an earlier version in action I have a couple of videos on Youtube under my user name : rohaymico These videos will show you the configuration and an idea of the performance using standard FAE carbide tipped teeth. The blade style teeth will be used for smaller timber similar to the Black Spruce and tamarack shown in the longer clip. My customers have a great deal of clearing to do in sub arctic forests like these. They will not be used for grinding stumps and larger timber into the ground as shown in the other videos. Thankyou for the excellent suggestions! I have already googled up many pages describing the properties of the alloys you folks have suggested! High performance will greatly offset the capital cost of the material due to the great expense of working in these very remote areas. In an earlier test using sharpened teeth that we made out of grader blades, production increased by over 50% in dense black spruce. We made them with a waterjet table and actually ground the edge on them with angle grinders. The result of that test is what inspired me to build this head.
 
I just got Yoda's Post, Thankyou! It sounds like there are some very interesting alloys out there in the world of knives. I have a habit of searching for answers in less than obvious places and I have already received more info here then from our metal suppliers.
The sharpening apparatus is still on the drawing board, however it will be powered by the machines aux hydraulics and will be indexed on a jig that quickly attaches to the mulching head chassis. The video on youtube may provide a better picture of the machine configuration then my text description!
Rob
 
Do you have any measurements on how much heat is generated in the grinding? With the high speed operation and the insulation of all the wood chips and dirt, those big heat sinks that will be the teeth could get really hot and stay that way, maybe enough to affect hardness if your steel isn't alloyed enough. That of course isn't an issue with carbide teeth. I know I wrecked some chainsaw blades quickly cutting dirty wood near the ground. First they dulled, then got hot very quickly due to the increased friction of reduced cutting efficiency, then quit cutting completely. It would take this larger tool longer to heat up, but also longer to cool down.
 
Rob Canada,

To answer an earlier question of yours, yes - wet grinding is superior for sharpening both steels and cemented carbide hardmetals. Tungsten carbide is far less sensitive to heat than steels are because the cobalt matrix is not heat-treated for hardness like the iron matrix of high carbide alloy steels. Tungsten carbide does not rely on the hardness of its matrix the way alloy steels do. However, the extreme heat of sharpening dry can weaken a fine edge on carbide and also injure the diamond sharpening wheels. Your application does not call for a fine edge, but if you use steel the temper must be maintained by cooling. High wear steels are very hard to grind, so they can get hot fast.
 
Thanks for drawing my attention to the heat issue during sharpening. There will be many compromises and it will be interesting to observe how each different alloy performs side by side. The insights about sharpening and heat while operating are exactly the type of info I was hoping to get here.
 
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