cutting plastic dulls edge?

L

lulwut

Joined
Nov 15, 2007
Messages
49
I've heard a rumor that cutting plastic will dull a knife's edge really fast.

Can anyone verify or debunk this?
 
Plastic is a pretty abrasive material. Some of the steels with the highest wear resistance are made for working with plastics. There are both faster and slower ways to dull an edge though.
 
I don't have problems cutting plastic. My blades dull faster cutting cardboard. By plastic I am mean thick unpigmented polyethylene or polypropylene. Pigmented plastic is a different beasty. PVC pipe is pigmented with TiO2, so cutting that is like running your blade into sand, very abrasive as Larrin said. Most of the PE and PP I cut is unpigmented and I do not have problems with it.

Just my opinion, but I think it also partly depends on how you sharpen. I'd like to hear people's experiences with cutting plastic with different angles on their blades.

I think that if you put an acute edge on a blade (say sharpen at <15° per side) the edge can deform when cutting plastic. I think that if you have a somewhat more obtuse angle (say 15°-20° per side) then there is more steel to support the edge and you do not get so much deformation. Got no proof. Just a guess. I'd be quite willing to be proven wrong.
 
I would bet you're right, Knarfeng. I never thought of that until reading your post, but it seems plausible because there is so much tension being applied back to the blade when cutting plastic.
 
Depends on what type of plastic. I cut a lot of shrink wrap and saran wrap at work. The D2 steel has held up the best for this so far, but I have only tried 1050, 1085, 1095, Carbon V, 420HC, 440A, 440C, AUS8, H1, X15 T.N, 8Cr13Mov, 13C26, VG1, VG10, ATS34, and D2. All others besides D2 have dulled out very quickly against the saran wrap type plastic. I still have 5 or 6 others steels to try out.
 
I am a Supervisor in an Extrusion Plant where we produce flat sheet and profile extrusions. I have been EDCing some sample of the latest greatest folding knife for near 25 years while on the job. I don't believe that the Polypro's or the polyethelens DULL the edges of the knives I have used, but I have learned through the years what cuts better. Now assuming all knives are of the same sharpness at the cutting edge. The blades that are the thinnest seem to slip through the poly materials easier than the blades with thickining blade bodies. Also a factory style edge that the grind is very visible, cuts better then say a hand polished blade with a mirror finish. Bottom line is any knife that has a blade thickness and edge profile similar to a Utility knife is your best bet. I have GOOD luck with small serrated knives such as my Spyderco Cricket or my old DoDo. As for the wear, we use Stanley knife blades for long periods of time with great results, so I believe that Plastics (in Polymer or Co-Polymer) form are not that abrasive on blades...
 
Bubblewrap is one of those things that can make life miserable for non-knife owners, and I can tell you from personal experience that a good blade is necessary to cut through it. (I had a Gerber Paraframe that simply would not penetrate it.) Decent knives will have no problems, though. I have a knife with an ATS-34 blade that cuts it with no difficulty and doesn't seem to need sharpening afterwards. The same is true for my AUS8 blades. Fortunately, I don't need to cut this stuff often, but once the plastic is penetrated, the blade seems to glide right through it without a great deal of resistance. I'd think you'd have to cut through quite a bit of it, but one thing's for sure, some types of plastic are tougher than others. I've seen some of it that can be opened with a boxcutter, others that need something heavier.
 
Thick blister packs are tough for most knives to cut. Any of my knives will slice plastic bags or wrap for a long time, but a blister pack is another story. I still enjoy the irony of buying a knife in a blister pack ... and needing a knife to open it.
 
Confederate said:
Bubblewrap is one of those things that can make life miserable for non-knife owners, and I can tell you from personal experience that a good blade is necessary to cut through it. (I had a Gerber Paraframe that simply would not penetrate it.) Decent knives will have no problems, though. I have a knife with an ATS-34 blade that cuts it with no difficulty and doesn't seem to need sharpening afterwards. The same is true for my AUS8 blades. Fortunately, I don't need to cut this stuff often, but once the plastic is penetrated, the blade seems to glide right through it without a great deal of resistance. I'd think you'd have to cut through quite a bit of it, but one thing's for sure, some types of plastic are tougher than others. I've seen some of it that can be opened with a boxcutter, others that need something heavier.
Click to expand...

rhino said:
Thick blister packs are tough for most knives to cut. Any of my knives will slice plastic bags or wrap for a long time, but a blister pack is another story. I still enjoy the irony of buying a knife in a blister pack ... and needing a knife to open it.
Click to expand...

What the heck are you folks using that you have problems cutting bubble wrap or blister packs?:eek:

ANY of my knives, from a Gerber EZ-OUT to a 1960's Buck 110 to a Cheapie Frost chisel ground Chinese lockback will cut such things once I am done sharpening them. You aren't trying to use Tantos are ya?
 
I cut yards and yards of bubble wrap, stretch film and pallet straps every day at work. I've used knives in 440A, carbon and D2. The D2 keeps an edge at least 5 times longer than either of them.
I also cut a lot of Kraft paper and cardboard. In my experience, nothing kills an edge like cardboard, especially Chinese cardboard (I don't know what the hell they put in that stuff).
 
tapedeck74 said:
I cut yards and yards of bubble wrap, stretch film and pallet straps every day at work. I've used knives in 440A, carbon and D2. The D2 keeps an edge at least 5 times longer than either of them.
I also cut a lot of Kraft paper and cardboard. In my experience, nothing kills an edge like cardboard, especially Chinese cardboard (I don't know what the hell they put in that stuff).
Click to expand...

Cardboard is made from paper which is made from wood fibers. I suspect that the Chinese material may not be as fully processed, leaving larger chunks of wood in it. It may also have more clay in it.
 
knarfeng said:
What the heck are you folks using that you have problems cutting bubble wrap or blister packs? ... You aren't trying to use Tantos are ya?
Click to expand...
Heh-heh. Nice shot, there. Nah, I'm talking about heavy blister packs that are molded and sealed. I have some EZ-Outs, but too much of the blades are serrated to even try. My Paraframe lock almost failed and all the blade could do is put a couple of light scratches in the stuff.

My Cold Steel tanto and my CRKT tanto would cut it with some resistance, but my CRKT S-2's sharp point and keen edge worked the best. Nothing worked as well as I'd hoped, though. All the blisterwrap contained were some electrical cords and a somewhat less challenging pack containing an mp3 player.
 
I was talking about the really thick blister packs too. I didn't mean to imply that my knives wouldn't cut them. I was saying that opening a bunch of them will dull a knife significantly faster than cutting plastic wrap or plastic bags.
 
Filled or reinforced plastics would be abrasive others really not and that does not depend on the polymer. Of course some are more difficult to cut than others.

TLM
 
You must log in or register to reply here.
Back
Top