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Stainless Steel in Shredder

This topic contains 31 replies, has 13 voices, and was last updated by  Tom 2 months ago.

5
Bill billa14

Stainless Steel in Shredder

11/07/2018 at 15:20

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

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11/07/2018 at 16:58
2

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

11/07/2018 at 17:53
2

for now you could reduce wear as described here. i have no long-term data on this but using classic cutting tool basics seems definitely feasible.

@davehakkens, @xxxolivierxxx, would be nice to have at least a link to hand picked list of important forum topics in the public ‘machines’ section of the site to avoid exactly this sort of desaster. 200 euro average price tag on the laser cut with 6 months lifespan is more likely what most of us can’t effort :-). I am already afraid about that my clients re-claim their money from me…
g

warrior
11/07/2018 at 19:28
3

I’ll set this topic as sticky. Unfortunately, I can’t speak on regards of inox steel usage on the shredders because all shredders I have build are made with torched Mild Steel and they show zero signs of wear, even without applying Guenter’s knive upgrade

starter
13/07/2018 at 01:03
2

There are different types of Stainless Steel, however the fact that a lot of stainless is non magnetic already creates a problem for the machine shops as the baled thickness can not easily be ground.  The chuck that holds the pieces are generally magnetic based.  The next item is the process used to cut the material, laser cutting actually produces a harder edge, however it also produces a burr, unlike the waterjet.  It would seem sensible to use a tool steel such as American grades A2.  O-1 steel is less expensive and can be oil quenched and tempered in a home shop.  A2 is best hardened at a proper heat treat shop.  Hardness process requested should be Vacuum Harden, Temper to 58-60RC, process for cutting either waterjet prior or after heat treat, leave .010 on the thickness for grinding.  Wet Grind on a proper surface grinder if available.  O-1 will warp during treatment and a good tool shop can grind it flat and take the warp out, oversize may need to be .035, depending on the warpage per test.  European materil equivalants can be found in “the Key to Steel” global material conversion book.  The cheapest would be to use Mild steel, use it and if there is wear, then it can be carburized to induce a hardness.  We are in the process of building a stainless shredder and it is not simple, especially as we are reducing the cutting clearances, so everything has to fit perfectly.  I hope this helps,
cheers, Mirco, Ontario Canada.

warrior
15/07/2018 at 22:03
2

@mirco Indeed, making a shredder is not as simple as cutting the parts and assembling them, there is a LOT of adjustment needed, grinding, shimming, dissasembling, reassembling, tightening, before your shredder is ready to use.

Finding perfectly calibrated steel sheets is pretty much impossible, so a belt grinder comes pretty handy for reducing the thickness of the parts as close as possible to the design measures.

starter
17/07/2018 at 04:59
2

Hi Olivier,
agreed the fit up needs careful planning, a good CAD system and methods to manufacture the plates so the stack up works out.  We are currently working on reducing the cutting clearances tolerances and altering the blade designs slightly in order to attempt to increase efficiency.  I am a Tool and Die maker by trade and worked in Tooling Engineering for one of the largest Auto Parts manufacturers in the world.  The materials are available in the correct sizes, especially in imperial units here in Canada.  So the design needs to suit the supply, ie. Europe metric and North America Imperial (Yes even Canada) Imperial, stock materials are often imperial sized.  And yes if you are real good with a belt sander and have a week to spare you can likely get it done.  Even bolts and nuts are generally cheaper in Imperial units.  I work in either measuring units and understand the advantages.  The key is knowing a few things about metallurgy and the availability of the thicknesses and tolerances, including the manufacturing method.  Cost plays into it of course.    Less than .001″ (.0254mm)  is the type of tolerance that will be required for each blade and opposing cutter if you are looking for a .010″ or less cutting clearance (distance between the moving shredder blade and opposing fixed cutter) between the blades.  Careful  planning and material selection can avoid much sanding and fitting.   As with 13 or 14 blades the stack up error will accumulate and then the shimming and adjusting will never end or take another week….  Planned and accurate sizing will allow the stack to work without shims or belt sanding.   Which size is the best cutting clearances we have not determined, but generally in steel cutting it is a function of the type of material and the shear strength.  I am going to take a guess here and say that .010″ or just over .25mm per side will be suitable for most materials, if the clearance is to large or to small the efficiency window may be missed.  Changing the cutting clearances involves a basic re-design of the overall cutter box, shaft and or number of blades used.  We will be adding 2 or 3 additional blades when we complete the refurbishment of ours to fit into the current box.  We are also adding two counter blades on each end as a blade just running on the outside does not have an opposing cutting edge in the current design – that can`t be the best we can do for efficiency and stopping the thing from jamming.  A reversing switch and an E-Stop is a must have on the motor.  Once we figure out a nice method we will post…
Food For Thought…. Best Regards,
Mirco

starter
21/07/2018 at 02:36
2

I wonder if you could have a tooth ‘cap’ made of tool steel.  See if you could attach it near the end of each tooth with a screw (use a non-perminant thread locker or ‘lock-tight’ type material) so you can remove/replace it when it wears.

 

A similar thing is used in wood plainers with little square ‘carbide inserts’, so they can be turned for 4 fresh blade faces.  They are readily available in the USA at Walmart, Amazon, and many tool web sites and stores.  They are pretty inexpensive.

new
21/07/2018 at 14:08
1

@servant74
Please an example link to best understand.
Thanks

starter
21/07/2018 at 14:21
1

https://www.youtube.com/watch?v=-bOkqHZesnQ

This shows a wood plainer and someone changing the carbide insert.  I hope this helps.

starter
24/07/2018 at 05:10
2

Hi Servant, I like your thinking with the cap, it is definitely something to be explored and would work if we can mass produce these caps.  I am actively thinking about this to evaluate if that is a sensible overall savings.  At present if we make the blades of the correct material (availability, heat treatment for longevity and financial realism for most of us)then we can evaluate if caps or inserts will give an advantage.  Of the top an advantage of inserts is if a metallic hard object were to accidentally fall into the shredder  it could damage the blades.  If the blades and the overall design reduces plastic friction it should not degrade the blades for a very long time under normal use.  Entire blades can be replaced and maybe relatively cheap (maybe similar to the price of an insert and screw if we finalize and optimize the design).  This all should be tested and evaluated.  I am interested to design an insert system when time permits, and I think I may have an idea of how to do this economically, again design, make, test  and evaluate.  I think optimizing the shredder blade shape has to come first, then we know how the insert needs to be shaped.  The current design has already evolved and will soon evolve further as we all gather feedback and tell each other what fails and gains we have had.  I am still struggling to understand how the plastic was able to wear the stainless blades discussed prior – was it stainless?  was it laser or waterjet cut?  Was it hardened?  I believe a properly heat treated tool steel blade will give the desired precision and longevity at a reasonable price, just got to test and find the way, one step at a time.  Inserts is a definite viable possibility, I think sintered carbide inserts as seen in some planer video links posted here are overkill for this application for a smaller scale project and too expensive to make it feasible plus if they chip or break the pieces will get into the plastic and possibly wreck other blades or inserts while getting hurled around the shredder…

Just my thoughts, have been dealing in heavy stamping and metal cutting since the 80s where we pierce through sometimes 1/2" thick sheet steel for 100s of thousands  or even millions of parts with stamping dies, more often than not a good tool steel piercing through steel, day in and day out may last for 100 000 pcs (not plastic but steel piercing!) before needing just a minor sharpening and shimming!  So if the cutting clearances and process pressures are distributed correctly for the product to be shredded and the materials are suited to the task, and the assembly is optimized then we should get much more than the equivalent of 100 000 stamped parts should we not?  Maybe inserts will help, I may think there is a chance – good thought to be tested, we might be surprised at the results after 1 year or so.  Lets gather all the pitfalls from al lthe shredders and fix and optimize – can we do that?  We need a pitfall category for the shredder to optimize! @davehakkens
Best Regards,
Mirco.

starter
24/07/2018 at 05:24
3

Hi Anne, I will be in Spain (Malaga) in September, we should talk….

new
24/07/2018 at 09:21
2

@servant74
Many thanks very clear now.
Ciao

24/07/2018 at 12:09
2

@mirco: sorry to tell you that I’m fully occupied. I do however have some vacation first 2 weeks of Sept. I will be on trip in the basque country that time. Please send me a private message, I can delegate you to my new precious plastic student who can call you, in spanish 🙂

starter
24/07/2018 at 19:00
1

@anne, it was just a thought.  My Spanish is pretty rusty and I am also pretty occupied, just eager to meet some Precious Plastic members in different Countries when the opportunity presents itself – no worries,
Mirco.

starter
26/07/2018 at 08:27
1

Thanks for raising this questions @billa14
I was planning to order laser cut parts for a shredder yesterday and then read this thread and I’m now not sure what to do.
It seems odd that this topic hasn’t been raised by anyone before (that I’ve noticed anyway) as the shredder design has been out for a long time now. Is it possible that this is an unfortunate rare occurrence which has affected @billa14. I notice that he/she hasn’t added any further responses on this thread and there’s no detail of exactly which stainless steel was used or pictures of how the blades have worn. Have the blades got thinner (through rubbing the neighbouring blade) or just worn away along the cutting edge?
As has been pointed out there are many types of stainless steel. I don’t know a lot about metallurgy (I’ve forgotten most of what I was taught over a decade ago now) but based on this page it sounds like a martensitic type would be good.
https://www.bssa.org.uk/faq.php?id=10
Has anyone else reported a similar wearing problem?
Two related points to consider (touched on above):
Should we be applying a hardening process to the blades?
Would it help if the blades were sharpened? A 6mm wide leading edge can’t be the most efficient way to cut through plastic. Sharpening would also reduce the torque required but may result in faster wearing if the wrong material was used.

helper
31/07/2018 at 13:16
2

thanks  Bill,  for the  photos.
I have sent you some  photos of the  wear
approx 1000 milk bottles a month on average without cordial bottles meat trays etc

Attachments:
warrior
31/07/2018 at 14:25
3

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.

starter
31/07/2018 at 18:58
2

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.

starter
01/08/2018 at 13:35
1

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

starter
01/08/2018 at 14:45
1

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

starter
04/08/2018 at 11:04
2

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

starter
04/08/2018 at 13:58
1

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.

new
06/08/2018 at 02:37
1

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?

starter
06/08/2018 at 03:48
1

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 <grin>).  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.

 

 

starter
06/08/2018 at 03:54
1

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!

starter
06/08/2018 at 08:24
1

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.

warrior
06/08/2018 at 23:38
2

@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

starter
06/08/2018 at 23:42
2

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.

starter
15/08/2018 at 10:10
0

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 🙂

 

 

starter
31/08/2018 at 08:03
0

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!

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