Stainless Steel in Shredder

Using Stainless Steel in the shredder is a real NO NO
I have been using mine for about 6 months now and has worn badly
The teeth have about an 1/8″ gap in front of them now so not cutting well at all and the sides well there is about 18thou gap on each side of the teeth to the guide
If you are going to build one please make sure you use a lot harder steel of some sort to lessen the wear

hi,
could you please add some pictures please ? it’s a sensitive topic for many of us…

Well,as a shredder manufacturer,the life of the blade is usually 6-8 months. If the wear is serious, you can consider replacing the new blade.

source:
HSS molybdenum:

https://www.azom.com/article.aspx?ArticleID=6174

HSS tungsten:

https://www.azom.com/article.aspx?ArticleID=6193

stainless steel (SAE 304):

https://www.azom.com/article.aspx?ArticleID=965

aluminium 6061:

http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=ma6061t6

Steel SAE/AISI 1045

https://us.misumi-ec.com/pdf/press/us_12e_pr1255.pdf

https://www.azom.com/article.aspx?ArticleID=6130

https://www.steelindopersada.com/2016/11/heat-treatment-of-carbon-steel-aisi-s45c-steel-grades.html

Hardness unit: hardness vickers

I choose stainless steel 304 and common steel 1045 because they’re mostly used in daily life.

<span style=”color: #000000;”>Just reference, feel free to critize 🙂

but, to be note: wearness properties actually is not all about hardness, there are others parameters like size, angularity, applied load, crystality, etc.

One further comment, and two questions, please!
After reading through this thread, is there any justification left for choosing stainless steel? It doesn’t sound too catastrophic to have a can of WD40 sitting next to shredders to give non-stainless parts a squirt now and then, if they are laid up, and not being used for a long time.

During normal operation, the rubbing action of material passing through should surely keep rust at bay! I am assuming that any oil on the plastic is undesirable, so… Is lubricating the metal parts during normal operation best avoided? OR, if a small amount of WD40 gets onto the plastic, will this be removed when the shredded plastic is washed? Related to this is the question, how do you experienced guys treat plastic containers that have had engine oil, brake fluid, etc in them? Must they be washed with solvents / detergents *before* they’re added to the mix to be shredded?

My second question is, does anybody know of shredder blades that are made from engineering ceramics? My intuition still recoils from the idea of using ceramic in a tough engineering environment, but people who work with them insist that some of them are very hard, resilient, and perfectly machineable. Ceramic kitchen knives stay sharp for a long time! Some sushi chefs use them. Does anyone know if engineering ceramics would cut well, & be long-lasting in this environment?

Hi, everybody! I am new here, and this is my first post!
Hope I don’t say anything too stupid!
I am not yet familiar with the current design of this shredder, but looking at the photos in this thread, when building this machine wouldn’t it be better to make the blade-spacers thinner, adding a number of shims to make up the width? In my view this may help initial setting up of the blades (move shims around), but also, when wear starts creating gaps between the blades, these can be closed up again by removing some shims (in the static set). Also, any damaged moving blades could be ground flat again instead of buying new ones – once again followed by removing spacer shims from the static set to compensate for material lost from the refurbished moving blade.

Regarding the topical questions of ‘wear’, and ‘material hardness’, I was going to make two points, but by the time I read the rest of the thread, good comments from andyn and mirco got there first. Andyn, when I saw the photos I was also of the opinion that the dents and chips were most likely caused by foreign matter, like metal or stone. Hard plastic would surely be more likely to jam up the works, than remove chunks of steel! In my small-scale experimental efforts up to now I have hand-washed all plastics, so I know that no dirt has got through. But, when working with waste plastic in larger volumes, is it ever possible to fully ensure that no sand or stone chips get through?

On the hardness question, rather than trying to bolt hard ‘teeth’ onto a 5mm wide blade, I prefer Mirco’s suggestion of tig-welding on hard material. The blade can be ground flat & sharpened afterwards.  I knew that you can get hard rods for Manual Metal Arc welding, so when the teeth wear down on earth diggers, hard metal can be welded-on to build them up again. I did not know (and am pleased to learn) that such rods are available for TIG as well. Tig could do a neat job here.

Last, I’d like to mention that having worked around copper mines, I have seen industrial diamonds frequently brazed onto large drill bits. Those bits frequently drill granite, and withstand a lot of punishment! The brazing is generously applied to cover the diamonds, but will soon wear down until you get to the hard stuff. On this relatively modest scale diamond dust could be considered, and need not break the bank. Or maybe tungsten carbide tips could be brazed on, along the lines of the suggestion by servant74. Is it possible to buy tungsten carbide powder? What I prefer about the idea of brazing-on hard *powder* – as opposed to hard tips – is that a broken-off hard tip will cause more damage in the machine.

ewanenj, if I understand your idea of ‘sharpening’ correctly, your suggestion sounds good to me! I mean that instead of the current, straight leading edge of the blades being repeatedly smacked and shocked (and blunted?), they could be ground to a V, so they first pierce, then continue to slice through on both sides. Leading with a centre-point may (or may not) help to keep the blades centered as well.
Oh Dear! I was just winding this up when a new thought arrived… Why not also grind the *side* of each blade at an angle, to a sharp cutting edge? Then, instead of aiming to pass each moving blade through the centre (creating 2 gaps), have the sharp edge actually rub against a static-blade’s similar sharp edge, so that they cut like a guillotine? With the shredder design as it is, I don’t see so much cutting going on! Much more of ‘tearing’! With square-on blades ‘smacking’ the plastic, and gaps (however small) between the blades… That’s not how scissors cut! The current design looks well suited to shredding paper (which doesn’t mind being torn), ot to breaking up glass (that responds to being hit). I suggest that plastics would respond better to being pearced and sliced.
OK. I’m done! I hope that some of you will comment. Thanks, folks! I found the past 2 weeks of reading here most interesting!

So… at this point in this discussion, stainless is not recommended but hardened steel is ok?

 

I have been speaking with our metal supplier and it seems hardened steel is not difficult for us to switch to if this is necessary and possibly it will make the machines final price cheaper. We have been working with 400 stainless steel so far but for machines we sell we would like to be sure we are making the best effort we can to provide a good, durable product.

 

This post took me by surprise I must say and the fact it is now sticky at the top of every forum raises big alarm bells for me but some of the comments from others saying they have not had similar problems etc suggest this is not necessarily an issue for everyone.

 

Some clarity would be great 🙂

 

 

Hello Billa,
I have build a shredder and my Job is Tool and DIe maker and Tooling Engineer, I own my own machine shop here in Canada.  We have just build a shredder, also following the instructions.  In defense if the original design, it is not an industrial design as such, it is more of a hobby design.  It is not possible to create the perfect design for all materials out there at a reasonable cost.  From a Tool and Die perspective dealing with stamping metals (!) not soft plastic the material of choice for blades would be tool steel which is hardenable, the stainless you used is fairly soft, and it does “work harden” however the type of “work done there’ would never harden it in short order.  It still seems that I am looking at tool marks caused by un-jamming and would be surprised if the marks were created by the hard plastic parts.  Fitting is something that has to be done properly and I don`t believe that the current “hobby” design goes into sufficient detail if you intend to use this design for a more industrial purpose.  It was mentioned that inserts could be placed on the blades, surely possible, but I again argue that the cost of that vs. new blades or having someone that understands (is an expert) tool steel cutting edge welding with a TIG (Tungsten Inert Gas) welding machine and hardened welding filler rod can repair all these edges and make them much more industrial than what you have.  We do this type of welding so I understand it well.  In fact stamping dies (even large dies the size of Cars) stamping through thick metal can be welded and ground with hand tools using this type of repair.    I believe Dave Hakkens and Team are working on a more industrial design, and we are also working on something here in Canada, as soon as current projects are completed and we can find some funding for testing and R&D develpment, we will of course post any upgrades which will be based on the current design.  I do not see this conclude here until late 2018.

@ewanenj They work perfectly but develop thin rust stains over time. You need to take care of them at least once a month with some WD40 and a steel brush

Great idea with the paper comb template.
I notice that several people in the Bazar are selling non-stainless laser-cut parts for the shredder, (@xxxolivierxxx is one). Has anyone got any feedback on how well this works in the long-term?
Rehardox, I wonder how well it resists wearing against itself.
@michael5254 asked for the download link, it’s here:
https://preciousplastic.com/en/videos/download.html
Note that there is an upgrades folder which has modified versions of some machines/parts.

A new thought on a solution.  I suggest put one sheet of paper (or other similar material) in the shreader down as low as you can get it, with the top of the paper secured in the hopper with some tape.  Turn the shreader, and get a new profile for the comb.  Then cut a new comb to replace your old one.  This one should match your still continue working until you get a different solution for the teeth or you can afford new teeth from a different material,   Once the teeth are replaced, you could use your old comb.

 

I hope this helps!

Michael5254,

 

I don’t think there is anything wrong with the current plans.  The discussion is basically metalurgy.  Stainless is pretty soft and brittle at the same time.  The idea of using Hardox is a good choice, even if it isn’t stainless, it is pretty much hardened steel but some flexability (think of a hard shell with a soft gooey center ).  Hardox is used in mining and earth moving equipment, it is better suited than most stainless steel products for its abbrasion resistance in harsh environments. … Just my thoughts.  Don’t be afraid to go ahead, just use either the suggested material or Hardox type steel. … Take care.

 

 

Being a brand new member and have not found out where to download the manufacturing drawings I have no input but think I will hold off for a while to see if this is a problem and if it can be easily overcome. Can someone point out to me where the drawing downloads are?

I don’t think hardox is stainless is it? How important do people think the stainless aspect is?
Reading the discussion above, I agree that the photo looks like metal-on-metal wearing. If no metal has been dropped in the machine then the most likely scenario seems to be that the blades have managed to move/bend whilst shredding and have scraped against each other. Thicker or shorter or stiffer blades would be less vulnerable to this risk.

Hi, you can use HARDOX 400.
Best regards
@vr76

Billa14,
I am sure your friend meant well, but unless he understood the material characteristics, he may have made an unfortunate material choice.  I still think that if you can get small ‘bolt on’ pieces of tools steel cut to the right size, and properly hardened, you can still get lots of use out of the current machine by bringing the profile back into specification.  If you can ‘bolt on’ the tooling, it could be replaced when it wears out (everything wears out, it just may be sooner or later).

Tool steel can be ground with a regular tool grinder and drilled with normal taps and drills.  Hardeining is not super hard, but getting somone that hardens tool steel normally (even making knives) can do this pretty easily.

Best wishes, … Jack

Well Mirco
I will have this to say in response to your message, I do appreciate what you have said and will everyones comments as they come in.

When we got this shredder made it everything was done by a laser cutter and it was fitted perfectly with very little clearance at all just enough to not grab or grind anything when turning  the clearance was very minute.

This shredder has definitely had NO steel any where near the machine let alone near the blades, it has had strictly plastic and plastic only through it.  How do I know this well I am the only one that uses it.

I don’t know if you have a shredder or have used one but a lot of the cordial bottles which are (no.1)  you put through have very hard necks and bottoms and quite often will jam the shredder if it is not cutting the plastic the right way, milk bottles I do are (no.2).

You said about the clearances we went by the PP specifications and built exactly to them.
It is 5mm 304 Stainless Steel that we used to build it. An engineer friend of ours advised that this might be good to use so we used it.
If as you say it was the wrong material why wasn’t it stipulated what to use in the instructions?
People like us go by the instructions because we know no better, so put all the instructions and information out together for us to build to.
As far as the screen goes I have never fitted one I just put it through 3 or 4 times to get the size I want so there is no problem as far as the screen goes.
Unless I am assured that there is a stainless steel that works a lot better than the 304 we used in this machine then I will be looking into something different to use.
The principle of the machine no doubt works well.

Cheers
Billa14

Hmm, that does not seem like plastic wear for the most part.  it does not match even the shredder blades hitting in all aspects although some side wear suggests that.  Is it possible that some of the indents on the blade counter parts have been damaged when the shredder jammed by a screwdriver or similar?  is it possible that foreign objects that are not stainless steel have gone through the machine?
In any regard the design needs to be re-evaluated we are working on that in our own little community group, although it can`t be our focus right now due to some other priorities in the group.  Will post thoughts and potential resolutions once we can do some testing with modified parts.
The clearances look Excessive particularly to the top, it does not look like wear it looks like it was always large with some wear.
The material definitely is the wrong type of stainless without heat treat, it is much to soft.  Not all Stainless can easily be heat treated.
Is this Stainless type 300 or 400 – ie. identified by properties such as is it Magnetic?  Is there confirmation of what type of material this was when purchased? Or even a material Certification?  These are often available upon request, in some cases free with purchase, but you have to ask.

Got a picture of the Milk Jugs before shredding?
What does the screen look like?  Do you use a screen?

Best Regards,
Mirco.

Wow! that looks pretty beaten up!

 

Though a lot of the dings in the fixed blades look like they have been hit by the rotating blades, note the ‘sawtooth’ pattern particularly on the 2nd photo, 5th, 6th and 8th slots from the left. This could cause chips of steel to be ground off which then cause the smaller dents lower down the slots in subsequent revolutions. I would not expect to see this type of wear caused by the normal shredding of plastic, that would look like a very even dulling of the sharp edges. I think this has been caused by steel on steel, the blades being too loose and able to move and hit each other. It could also be caused by the blades hitting the mesh screen, or by extremely contaminated material being shred. But I think the real giveaway is the pattern left on the fixed blades.