bimetal

In the context of saw blades, what does "bimetal" mean?

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http://news.thomasnet.com/fullstory/8741
Bimetal Saw Blade outlasts carbon steel ten times over.
April 22, 2002 07:45 - Model 3861 Sandflex(R) NF(TM) bimetal bandsaw blade lasts 8 to 10 times as long as common milled carbon steel blades when sawing wood, plastics, and metals from foundry metals through alloy steels. Bimetal blade has high speed steel teeth beam-welded to spring steel back. Suitable for job shops and tool rooms, blades are available in sizes from 1/4 to 1 in. with 3 to 24 teeth-per-inch pitch.
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It's amazing what Google can find.
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I had that experiance today in fact i wiped out a plan steel one on 5 cuts of stainless ! I cut 50 pcs with a bimetal thats what the diffrence is! matrial is 3/4 round stock.I ran it slower with bimetal 29.00 for blade 64.500 .500 wide blade .020 thick
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I wonder if this "bimetal" concept is close to the concept of damasque steel.
i
wrote:

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Is that the deal where back in the middle ages they ran the hot blade through a slave to temper it? Damascus steel, if I'm not mistaken. Always wondered if that story had any truth to it.
Garrett Fulton
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Always
Probably did; brutal times, 'twere...
But damascus specifically refers to the method of forge-welding two different materials (in those days, probably high and low carbon steel from the uneven nature of the bloom iron used), flattening, folding and rewelding ad nauseum to get many layers (often hundreds) of alternating material to even out the properties a bit.
Come to think of it, how thin would the layers have to be before they diffuse into each other reasonably at the temperatures used for forging, and become homogenous? Say, alternating layers of 1020 and 1090, and a long anneal (several hours) at 2000F or so. Anyone?
Back on topic, what's the advantage of bimetal over HSS? I noticed the yellow-painted HSS hacksaw blades are cheaper at Ace than the bimetal (carbon steel of course is cheapest, but nuts to that!). I haven't had one break on me after the usual abuses of normal uses, just a few teeth chipped as any would.
Tim
-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @ http://webpages.charter.net/dawill/tmoranwms
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Less likely to snap. I bent over a few of them a couple of days ago, in a Sawzall. 'No way that solid HSS would have taken that without snapping off.
So, why doesn't the narrow HSS strip on a bimetal blade snap, you ask? I don't know. I think it's something like the metal strap you use on the outside of a piece of wood you're steam-bending to extremes. Constraining one edge of it may make the difference.
-- Ed Huntress
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What makes you think they don't snap?
John Martin
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off.
I bent six of them over in the last week. They didn't snap. Also, I've used bimetal blades in my bandsaw for years, and they don't snap.
Ed Huntress
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I'm afraid, Ed, that you're missing your own point.
They do snap - frequently.
Yours snap - frequently.
Not the blade, but - just as you said - the HSS edge. The edge, however, is narrow enough that a few cracks in the HSS part will not cause it to separate from the carbon or alloy steel backing. The backing itself is tough, rather than hard, and won't crack.
Make sense now?
The same thing happens with carbon steel blades, except that they are the same material throughout. The teeth and the backs are hardened differently - or at least tempered differently.
My father in law was in the tool business, manufacturing hacksaw and bandsaw blades among other things. I once showed him some old carbon steel hacksaw blades I had, on which the company name was spelled incorrectly. He looked at one carefully, and then started flexing it. You could hear the blade crack in many places, but it stayed in one piece. He allowed that, although it was a counterfeit, it was at least hardened and tempered somewhat properly.
John Martin
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I posted a reply to this the other day, but it seems to have gotten lost in the ether, so I'll risk everyone's ire and do so again.
They do snap - frequently.
Yours, in fact, snap - frequently.
Read your question again. You were talking about the narrow HSS strip on a bi-metal blade, not the blade itself. And a snap in the HSS strip doesn't necessarily cause the entire blade to snap.
The hard and heat-resistant HSS edge with the tough and flexible alloy or carbon steel back is the best of both worlds. The same thing is done with solid alloy or carbon steel blades, through the use of differential hardening and/or tempering processes.
My father-in-law worked for a company which manufactures, among other things, hacksaw and bandsaw blades. I once showed him some old carbon steel blades I had on which the company's name was spelled incorrectly. He looked one over pretty carefully, asked where I had gotten it, and, when I explained it was from my grandfather's tool chest and datedfrom probably the 1950s, breathed a sigh of relief and said that there were some counterfeits being made then, probably in Mexico. He then proceeded to flex it pretty strongly, and you could hear it cracking like a bowl of Rice Krispies. Stayed in one piece, though, and he allowed that whoever had hardened and tempered it knew at least a bit about what they were doing.
Of course, it also depends somewhat on the blade. On a fine-toothed blade, there will always be a continuous HSS strip below the tooth gullets. On a coarse blade, the gullets may be milled right through the HSS strip.
John Martin
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off.
Yabbut... I'm pretty rough on tools, and I didn't break one. How truely terrible are these people at tools that they break these!? ;o)
Tim
-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @ http://webpages.charter.net/dawill/tmoranwms
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a
Didn't break one what? Saw blades? Carbon steel, or 100% HSS?
Ed Huntress
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HSS. I've broken teeth, but no blades. I *know* I can't break bimetal or carbon blades, I've bent those before. ;)
Tim
-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @ http://webpages.charter.net/dawill/tmoranwms
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On Sat, 25 Dec 2004 00:53:02 -0600, "Tim Williams"
......and in reply I say!:
remove ns from my header address to reply via email
Easy to break. And not truly terrible either. All it takes is a workpiece to move or even the cut to close or twist for some reason.
If you have bent other types of blade then you have simply been lucky not to break HSS. It simply does not bend much.

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Huh. My work must not be that evil then ;)
I have a high tension hacksaw frame, FWIW.
Tim
-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @ http://webpages.charter.net/dawill/tmoranwms
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Tim Williams wrote:

As I stated in another post. Unlikely.

The actual term damascus was first used to refer to a type of steel known also as Wootz. It was a crucible steel that got at least some of its useful properties as a rsult of some of the trace elements in the make-up of the ore it was smelted from. The Europeans first encountered it in the region of Damascus.
Now the term is used to describe what would be more accurately called pattern welded steel.
The Japanese smiths used a process more along he lines of what you describe above, sorting fragments of higer and lower carbon steels and welding them together to achieve their end product. Some old sword blades from there exhibit paterns that show the layers clearly, while others do not. A lot of the variations can be accounted for by the master/ apprentice training system, and that the variuos makers kept their techniques secret from one another.

It takes very few folds (from personal experience)to get a homogenous product. Or at least one that does not readilly show its layers, when etched. Many, if not all the folks doing pattern welded steels today are using at least one high nickel alloy in the mix to prevent the layers from homogonizing. Several makers are welding knife billets up out of layers (lots of layers) of shim stock thickness, to avoid having the losses that come from repeated heats and welds.
Two straight carbon steels such as you propose above would not show much if any pattern after about three weld cycles, if you were dealing with work of a size suitable for a blade.
There is a really good book out called(IIRC) The Craft of the Japanese Sword that has a reaaly good series of photos of the entire process, starting with mining the ore, right through the final finish, with an explanation of the tradesmen involved in all the steps along the process. Shows good pics of the selection and sorting of the various carbon content chunks that get welded into the billet. It also shows a good representation of the economics involved in multiple welds in the forge, as it discusses the losses due to scale, etc that are assosciated with the forge welding process. While it deals with Japanese swords specifically, it does show some of the problems that any smith must deal with to produce a decent sword blade in the forge.
Cheers Trevor Jones
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On Wed, 22 Dec 2004 22:54:16 -0600, "Tim Williams"

Actually that's a lousy way to temper a blade -- unless you can get it all the way in at one time.

Well, not exactly. Or at least not originally.
We have to distingush three things here which are all called 'damascus': True damascus, or wootz, steel; pattern welded steel now commonly called 'damascus'; and damascene, which is a surface treatment.
Damascus (from the city that was the terminus of the silk road -- most of the original blades probably came from India) was a homogenous crucible steel with was worked in a superplastic state to produce exceptionally fine blade. The crucible steel, called 'wootz' was made by a process which originated in India and India remained a major source for the metal. However the process of forging damascus blades (and I believe the technique for making the steel as well) spread to the Middle East.
The obvious characteristic of a damascus blade was the patterning on the surface produced by the process. This became a mark of a high-quality blade.
Pattern welding by welding bars of different steels together is an ancient technique practiced just about anywhere steel was made and worked, including northern Europe. The Europeans couldn't make true damascus, but they could imitate the patterning and produce superior blades with pattern welding.
When the process of pattern welding enjoyed a resurgence in the 19th Century, the pattern welded still was referred to as 'damascus'.
The thing that causes most of the confusion is that modern smiths refer to pattern welded steel as 'damascus'. Knowledgable smiths and collectors use the term 'true damascus' for real damascus steel and simply 'damascus' for pattern welded material.
Damascene is a surface treatment that can be applied to any metal to produce a repeating pattern. It is a common decorative technique in jewelry makings.
If you want the full low-down ask over on the knives group.
--RC
"Sometimes history doesn't repeat itself. It just yells 'can't you remember anything I've told you?' and lets fly with a club. -- John W. Cambell Jr.
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snipped-for-privacy@TAKEOUTmindspring.com wrote in
snip

So...which one of these discriptions apply to "damascus barrels" that's an honest question BTW.
granpaw
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