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My guess is that would be a 3600 RPM motor. For the shredders here most use a gear reduction in the 30-60 RPM range. I don’t think you’d have good results trying to use that, for this application you really need low speed/high torque, not high speed/low torque in the case of a motor like you described.
Normally reversing contactors are a pair that are mechanically interlocked so that it’s physically impossible for both contactors to be energized at the same time. On a 3 phase motor, if you swap two of the wires, you will reverse the direction. So for “normal” direction, you’d pair L1-T1, L2-T2, L3-T3. To reverse the direction, you could set it up L1-T1, L2-T3, L3-T2 (or L1-T3, L2-T2, L3-T1, etc).
This is a good video explaining how it works. https://www.youtube.com/watch?v=nKDG3Ja4d8A
I googled your contactor, and to make this a reversing contactor you’d need the appropriate mechanical interlocking module: http://vistronica.com/images/Documentos/CJX2.pdf
For overload protection, a thermal overload would work. You would want to set it to the FLA (full load amps) of the motor, or maybe even 80% of the full load amps. Thermal overloads will allow for momentary spikes in power (for startup or sudden loads) but will trip if there’s a sustained high load. They are different from a breaker because a breaker will pretty much trip immediately if you exceed the amperage (to protect the wire), whereas a thermal overload will take much longer to trip, however there are instances where your thermal overload would trip but a breaker or fuse would not. Normally a thermal overload interrupts the “start” signal to the contactor, and shuts off the motor before it damages it.
You might be able to get creative with a thermal overload to reverse the direction of the motor if it sensed a high load. You would set the thermal overload relatively low value, and if the overload tripped it would direct power to the other contactor, and then when the overload reset it would then resume forward direction. This would take some tinkering and may not work ideally, but it would be a nice “non-electronic” way of doing it, and worst case you’d have a thermal overload to protect the motor in the traditional sense if it didn’t work.
To select the shaft size, I just went with whatever size the gearbox uses. You could do a calculation to determine the minimum shaft size, but I went this route because coupling the gearbox to the shredder shaft being equal size is a lot easier for a variety of reasons.
One thing I will note, it will NOT hurt to oversize the gearbox/motor in terms of torque.
I guess what I don’t have shown here is the 3/4″ diameter pipe is actually a valve (the tank will be pressurized at times), and the valve is actually a 1″ nominal but the bore of the valve is 3/4″ (ball valve). I am concerned that the screw may not be able to push/force the plastic through the reduced diameter, but maybe it’s not enough of a change that it could. After all if it can push molten plastic (which is not thin) through a tiny orifice to make string, maybe it would work for this.
Next week I will probably give it a try, I already have all the parts. This is the configuration I have to work with, I was just seeing if anyone had any specific suggestions that might lead to success sooner.. 🙂
I used a 5HP 3-phase motor with a VFD running single phase (220V 2-wire), so 2 leads on the input side of the VFD, 3 leads on the output side. 1800 RPM
Gearbox was a worldwide electric inline reducer: http://www.worldwideelectric.net/product-category/gear-reducers/inline-helical-gear-reducers/
First one was a 20:1, 76 RPM gearbox. This didn’t have enough torque for my shredder (larger than this) design, and moved very fast so if it jammed it was violent.
I then upsized to a 60:1 (28 RPM), this has plenty of power but my shaft was undersized, it sheared the keyway.
The coupling I ended up with is a chain coupling. https://www.mcmaster.com/#standard-shaft-couplings/=1av78pa
These work really well because it’s easy to adapt different size shafts together, they can handle some misalignment, are easy to assembly, and they’re pretty cost effective.
Just a quick update:
Based on my testing I will need to do a complete redesign of my unit. Originally the gearbox I used was about 75 RPM, which was too fast.. Whenever it would jam it had so much momentum it was very violent. I got a larger gearbox which moved the speed down to about 25 RPM and over doubled the torque, but then it applied so much torque that it sheared the keyway between the shaft and the coupling, so I will need to use a larger shaft with a bigger keyway. So by virtue of needing to change the shaft size, I will need to have completely different teeth, shaft, bearings, which basically means my current unit will need to be scrapped. Additionally, I learned that you want to make the cutting teeth as small of diameter as possible to maximize the force applied on the material.
Sometime in 2018 I am going to design a double-shaft shredder. See attached images (this is a Franklin Miller TM8500, look up their website if curious). This particular unit will work nicely with my 5HP motor and reduction gearbox (if anything, my gearbox might be a little oversized, so less throughput but less likely to jam and handle heavier material)
The PP shredder design works good but it’s easy to overload it. Its a very simple design that is effective. You have to make the teeth larger diameter so it actually grabs the material (compared to a double shaft which grabs the material and forces it toward the center). The larger you make the diameter the easier it is to jam. The double shaft design should be a lot more efficient and really it won’t cost substantially more. My application demands something with a bit more throughput than the PP shredder, hence my original redesign.
I have a feeling (but have no data to support this) that even doing a smaller shredder with a double shaft configuration (similar size to the PP shredder), it may not end up costing a much more because it’s more efficient you could run a smaller gearbox and motor, which is a very substantial portion of the cost.
If you want to save a little money, get the parts made out of A36 steel instead of stainless. That would take quite a bit out of the cost.
For a gearbox, just look up anyone who sells belts, pulleys, bearings, etc. They’ll usually carry a line of gear reducers and motors.
A 3 HP single phase motor will perform the same as a 3 HP three phase motor. The three phase motor will be more efficient and cost less.
I am using a 3 phase motor + VFD with a single phase connection input. Basically you give it single phase input, and it spits out the 3 phase the motor wants. The VFD doesn’t need to special, you just need to oversize it (because there are losses in the VFD when going from single phase to three phase).
I’m in a similar situation that I’m definitely not going to have 3 phase power installed.
For me, getting a VFD with a 3 phase motor was about the same price as getting a single phase with no VFD. Not to mention, without a VFD you’d likely want to get a reversing contactor to switch direction, or worst case get a single contactor to start the motor, so you’ll have additional cost there. Nice thing with the VFD you can easily increase speed, automatically program it to reverse direction if it overloads.
On the underside of my machine I have a 1/4″ mesh. I found that it cut everything the proper size, but the material would tend to stay on the mesh and not fall through. Plus, no matter what I did it seems like this thing always makes a mess. So I’m building a hopper to go underneath it to funnel the material close to the inside, and I’m going to attach a shop vacuum to the underside to draw the material out. I think this will help keep the mesh clean and help reduce the mess. The first image doesn’t show the attachment for the vacuum, I will probably try it without the vacuum first. To add the vacuum attachment, I’ll just weld in a small square piece and a pipe that I can attach a vacuum hose to. I think also in the future, using a rolled wire mesh of the proper size opening would work better than a plate with holes in it.
Below are a couple pictures of my final setup. I will post an update in a few weeks when everything is done being manufactured and I have a chance to put it together.
Update to my project. I finally got my bigger gearbox in and I modified the frame. In the pictures the blue one is the old one, orange one is the new one. I increased my torque about 3x (under 3,000 in-lb to over 10,000 in-lb), and reduced the speed from about 75 RPM to 25 RPM.
The new gearbox has a bigger shaft, and I didn’t want to have a new shaft machined (would have been a big redesign). Originally I used a straight coupling, so now I’d need some sort of adapter coupling. After some digging, I found these couplings (many other brands make them). https://www.ibtinc.com/wp-content/uploads/2015/07/Martin-Sprocket-Roller-Chain-Couplings.pdf These are readily available all over the place, and pretty cheap! Basically it’s 2 sprockets, a roller chain and a cover. The chain coupling is pretty forgiving in terms misalignment, and allows you to connect two different size shafts very easily. Nice thing is if I ever change my setup, I will only need 1 coupling sprocket and I’ll be back in business.
First run was with my original blade setup (3 teeth, all identical). Despite the extra torque, it still binds up easily. So I’m going to have new blades manufactured. My machine has 26 teeth in total, so with my current design I have 13 blades trying to cut simultaneously (which obviously requires a huge force). If you feed it slow on one side it cuts, but if you fill the hopper, it binds up easily. New teeth will 3 different blades and only 2 teeth, so now only 4 teeth will be cutting at one time. I think that will make a big difference.
I agree that it would be nice for something on the outside of the blades to grab onto the material. I am working on a new set of blades for my machine and I may give this a try.
Another thing that I noticed with mine is that sometimes material likes to get stuck between the blades and spacers. I’m thinking that next go-around I may add some cuts on the spacers to help grab material and drag it down (attached)
I also agree about the mesh, it gets clogged easily, and on my setup it’s really hard not to not get material everywhere.. So I’m gonna make a hopper that goes underneath, and I’m even thinking I may attach a shop vaccum to the bottom to help draw material through. I found on mine that the material is definitely chopped up smaller than the mesh is, but it just doesn’t want to go through the holes easily.
I’ve also posted an update on my original thread.
I’m not really following what you’re going after?
Remember the spacers and the cutting teeth are different thicknesses of metal to allow for clearance between them. In my design the cutting teeth were 1/4″, and the spacers were 5/16″, so you have 1/16″ (or about 1.5mm) total clearance between the teeth. So when everything is put together you won’t have any metal-on-metal contact. Also remember that if you want things to fit together tightly like that, you’re going to have to make the parts more accurately (which increases cost).
Personally I think it’s OK if the teeth on the shaft can float a little bit. Everything goes together pretty easy and tends to self-align..
When I put mine together, everything spun freely on the first go.
Personally if it were me, I would lean toward oversizing the motor/torque requirements than getting too little. Last thing you want to do is lock-up the motor, and you’ll take a LOT of torque to break any components inside the machine.
I really like my 3-phase motor with VFD, and was about the same price as a single phase motor without a VFD.
I did try offsetting the blades, and while it did help I still think I have issues with it trying to cut too much at a time. For testing purposes, I think I’m going to cut off one of the blades on the teeth so I can offset them more like how the original design (from here) is done.
I also had a failure of the gearbox. Fortunately the MFG is covering it under warranty, and I’m going to be upgrading it a unit with a lot more torque. My original gearbox had an output of about 4000 in-lb torque @ 75 RPM. I went back and reviewed my FEA results, and I think I can handle up to about 20,000 in-lbs torque. The revised gearbox is going to be around 20 RPM and about 13,000-16,000 in-lbs torque. Also, instead of using a solid shaft coupling, I’m either going to incorporate a torque limiter (clutch) or a belt drive to help reduce shock on the gearbox.
I suppose it could work, but I’m not really sure of the advantage. Getting parts cut on a laser really isn’t that big of a deal, and my guess it wouldn’t save you a lot of money. Not to mention with wider teeth, you’re going to be making bigger pieces.
I’d be surprised if you could 3D print plastic parts cheaper than having them cut from steel (unless you get free access to 3D printer and 3D print material).
I don’t think zinc (galvanized) steel would gain you much because the zinc wear and you’re left with mild steel. Also keep in mind galvanized steel generally has slightly different dimensions (since it’s mild steel + zinc plated).
Another option might be paint/coating (powdercoating/anodizing). Plastic isn’t terribly hard, so you could probably find some pretty good wear resistant paint that would last a reasonable length of time.
Sure. shoot me an email!
Honestly in hindsight, I wish I would have bought an electric garden mulcher/shredder versus building a shredder for the first go-around. You could buy one of those a lot cheaper than building one, although that’s not as fun and it most likely wouldn’t last as long.
I think part of the issue you’ll have is plastic is way more ductile and stronger than most “wood” products (branches, leaves, etc) so it’s a little different application. Still, there’s videos on youtube of people putting plastic through one of these types of shredders and it seems like it takes it pretty well, but you’d probably be limited on the size of what you could jam in there, versus this design.
I would recommend looking at “world wide electric” for the gear reducers.
Simply select the speed/torque you want, and then you will see the motor requirements.
Inline helical gear reducers should be a bit more robust and cheaper than a worm gear or helical bevel reducer, but takes up more space.
You can then source a C-face motor to suit your needs. Single phase motors above 2HP are expensive and sometimes hard to find. Keep in mind that 3-phase motors are quite a bit cheaper than single phase motors, and often times you can use a VFD + 3 phase to convert single phase to 3 phase. With a VFD you have the ability to do all your controls on the drive, so no additional switches/reversing contactors/etc are required, and you can adjust speed to your liking.
If I was to go back and do mine over again, I would have used a slower speed (higher torque) reducer and used the VFD to speed it up if I wanted more speed. For my shredder I thought that 80 RPM was a little fast, so I’m going to look at getting a different reducer to run more like 50-60 RPM.
@ramdhan2805 it is a lenze VFD. I ended up with a 10HP drive for 5HP motor based on some simple up-rating.. Since 3 phase power is defined as P=(sqrt 3)*(voltage)*(current)*(PF), and single phase power does not include the (sqrt 3) term, and assuming voltage and PF are nominally the same (safe assumption), you multiply your motor’s FLA by 1.73 to get the full current carrying capacity of the VFD. Pretty much any 3P VFD can do this, so just select whatever one is cheapest and easiest to get for you.
I also like your inline reducers, found those are cheaper and more robust than the angle gearboxes (either helical bevel or worm gear), at the expense of taking up more footprint.
@jonn, I used FEMAP. The only thing I really did was model the teeth and the shaft. Basically I did a fixed constraint on the end attached to the motor, did “rolling constraints” where the bearings sit. Overall it was a pretty basic analysis.
My email address is [email protected] if anyone wants to contact.
No I decided to use standard A36 steel for this build, just mainly due to cost.