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Plastic impellers...

29K views 123 replies 29 participants last post by  sscotsman 
#1 ·

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#4 ·
Plastic composites have come a long way, from aerospace to auto manufacturing, manufacturers choose plastic over metal due to space/weight/shape constraints and prefer it over metal.

In this case however the choice was made to cut cost, so no bueno.

Beside being brittle than metal I wouldnt want a plastic impeller just because of the lack of momentum/torque compared to a metal one.
 
#10 ·
I have No Problem with Plastic For Certain Applications, But I Don't Want it on My Snowblower. Period.
 
#12 ·
If I could build a snowblower out of plastic, I'd do it in a heartbeat. No rust, no chipping paint, stronger, lighter, lasts forever. Can be drilled, tapped, shaped in all different ways.

The reason it's not done, is because metal is CHEAPER. Plastic is more ridged, doesn't flex, no need for welds, can be done in one piece, can be designed much better. Metal is archaic. Not that it hasn't worked, but with today's technology plastics can out perform metals for every situation.

The range of plastics is really misunderstood. Ya know, bridges are made of plastic. I'm not talking bits and pieces here and there, I'm talking the WHOLE BRIDGE:

https://www.bing.com/images/search?q=frp+bridge&FORM=HDRSC2

I'm trying to build a new product for myself out of plastic, because it's better for my application, and it's way more expensive than building it out of metal. I've been researching this for over two years waiting for plastic to be competitive. It's not getting any better.

Ocean going yachts are made of plastic. Airplanes are made of plastic.

Stairs, I-Beams, Structural components.

https://www.bing.com/images/search?q=frp+structural+shapes&FORM=HDRSC2

Plastic does not automatically equal bad.
 
#11 · (Edited)
It would make adding the impeller mod a challenge if the machine needed one. On the other hand plastic might be a better choice if it holds up to ice chunks, frozen newspapers and the like IF it's lighter so less stress on the bearings and it is rustproof.

It's a knee jerk reaction hearing plastic and assuming it's cheap and of lesser quality than it's metal predecessor. Might be something we just need to see how it goes.
 
#13 ·
It would make adding the impeller mod a challenge if the machine needed one.
Why? Could be easier if the plastic is thicker, and perform better. OR, with plastic manufacturing process, you may not even need the mod.
On the other hand plastic might be a better choice if it holds up to ice chunks, frozen newspapers and the like IF it lighter so less stress on the bearings and it is rustproof
.

Plastics used correctly is, many times, more effective than metals. Now, clearly I'm not talking about engines, cylinders, bearings, etc.. For that you'd have to look at Ceramics, but for housings and such, yeah.

It's a knee jerk reaction hearing plastic and assuming it's cheap and of lesser quality than it's metal predecessor. Might be something we just need to see how it goes.
Usually borne from ignorance of what plastics really are.
 
#14 ·
Ceramic engine:



295HP 1.6 liter engine. Ceramic engines run hotter, don't need a cooling system, are more efficient, and last longer.

I bring this up because the mere suggestion of a ceramic engine, to parallel the plastic impeller, would be tantamount to saying "I won't have a coffee cup powering my blower"..

These pre-conceived biases without knowledge is just silly. I only know, because I've been trying to put out a stout plastic product and have no choice but to learn about it.
 
#15 ·
There are a lot of different plastics, absolutely, with different fillers for reinforcement. Plastic doesn't simply mean it's made out of recycled milk jugs.

But this is an application with cold temperatures (where plastics get more brittle), and sudden impact loads. I work with plastics at work, but this is not an application where they'd be my first choice.

My Toro 1800 single-stage electric has a plastic paddle. It works fine, and fortunately I've never had one break. They do show signs of wear, with grooves and notches in them, but they've held up. But I use it for the deck, which doesn't get chunks of ice like EOD.

I think the earlier comparison was fair. If you hit something solid enough that it bends a metal impeller, the odds are decent that it might crack a plastic impeller.

The plastic chute in my MTD worked well, no complaints. But I would not be comfortable with a plastic impeller, personally. If they turn out to be robust, and still running strong after 20 years, that will be great, and I'm happy to be wrong. But I'd rather not have one on my machine.

As just a single reason for that opinion, if a metal piece on my machine cracks, I can weld it. But if a plastic impeller cracks, the best I could do is drill a hole at the end of the crack, and hope it doesn't continue to grow.

I don't think lighter weight of the impeller offers the machine a big benefit. The bearing still takes most of its load from the snow being flung, rather than from the weight of the impeller. A plastic impeller *can* probably have tighter tolerances for concentricity of the blade tips, allowing a smaller gap to the impeller housing. But the impeller housing is the other half of that discussion, so I'm not convinced you'll suddenly see a nice tight fit.
 
#17 ·
Thing is, and I'm just going by what I read, I don't see a huge clamoring of people complaining about broken plastic impellers. Not being your first choice, I get that. Personally, a well constructed FRP wouldn't be a bad thing, po-tay-to, po-tah-to. It's used for bridges, and structural materials all the time. But where's the problems?

If I'm wrong, and many of these are breaking, it could be that plastic wasn't a good choice, or they picked the wrong plastic, or plastic wasn't the right choice. But I'm not seeing a lot of threads about shattered impellers, nor can I find anything in an internet search.
 
#16 ·
Plastic does not automatically equal bad.
Unless is comes from China, right? :)
 
#18 ·
I've haven't seen reports either. But then again, I didn't realize there were plastic impellers for 2-stage machines until this morning :)

As was pointed out to me recently in a thread about another new blower technology, just because there aren't many reports doesn't mean there aren't problems. There are probably millions of steel-impeller machines out there. But how many plastic-impeller machines are in use?

And for normal use, especially when still young, they're probably fine. My concern is when you suck in a big chunk of ice, or ingest a newspaper. And things will get worse over time, as the plastic ages, and becomes more brittle.
 
#20 ·
I've haven't seen reports either. But then again, I didn't realize there were plastic impellers for 2-stage machines until this morning :)
EXACTLY!!

As was pointed out to me recently in a thread about another new blower technology, just because there aren't many reports doesn't mean there aren't problems. There are probably millions of steel-impeller machines out there. But how many plastic-impeller machines are in use?

And for normal use, especially when still young, they're probably fine. My concern is when you suck in a big chunk of ice, or ingest a newspaper. And things will get worse over time, as the plastic ages, and becomes more brittle.
Fair nuff. I'll wait until we start seeing massive failures before I call it a failure. Metal fatigues over time, something plastic doesn't do.

On another note, what do you do in plastics, wondin' if I can tap your brain on what I'm trying to build. PM me if it's OK.

Thanks
 
#25 ·
at a a thickness metal is stronger than plastic on an industrial scale usage and manufacturing proceses, unless youre talking about some space age plastic or carbon fibre than cost would make it prohibitive, still dont think even those plastics can handle the abrasive nature of a snowblowerl. cars are still made of mostly metal because of the need for thin strong materials that dont crack or fatigue easily under stress or load
 
#28 ·
Metals are cheaper. I looked into doing carbon fiber for some of my products, now I'm looking at FRP, which is poor man's carbon fiber. It's not THAT expensive. It's used on ladders. Those colored ends. I think FRP would work fine, but I'm no engineer.

Saturn. :D Plastic fenders and such.

High end cars are using carbon fiber frames. BMW, for example, is using sections of carbon fiber. They are doing it because it's stiffer than steel, and improve handling.
 
#27 ·
Since it is so Widely Used Today, Nobody Notices Plastic Until it Breaks on Them....I flushed the Crapper the Other Day, and the Plastic Handle Broke. Replace it with a Metal One. Plastic Snow Shove Cracked. Plastic Choke Control Tower on Briggs Engine Broke, but I was able to Superglue it, and that's just the Recent Stuff....Did I mention How Much I like Plastic? Rant Over.

 
#30 ·
Plastic will fail. An airliner crashed in NYC [Rockaways} after leaving JFK. Alright, it got into a previous jet's vortex. They blamed it on "pilot error". But the tail vertical piece FAILED, why? Because it was frp. Just about any metal will stretch, or bend before it fails, frp will not. Just saying.
Sid
 
#31 · (Edited)
As for my general opinion, something that's spinning at around 600 to 1200 RPM and carrying a substantial load should not be made out of plastic. Plastic may not rust, bend/twist or need to be welded together, but most plastics if I'm not mistaken degrade over time. While they may be strong today, 10 years or so from now, they may not be. Whether it be from sun/UV damage or temperature, it seems like it's inevitable. I've even seen this happen to glass fiber reinforced nylon. Metal is definitely the way to go in this application. Let's not forget the weight. Loss of inertia on a plastic impeller may impact performance.
 
#32 ·
I can't say for sure whether or not this plastic impeller would fail. In this application was likely a cost-cutting measure as it is in an MTD a low cost leader in terms of "mainstream" manufacturers.

I know that Simplicity's efforts to incorporate plastic transmissions in some of their lower end models was/is a failure based on user reviews on the company website and Donyboy 73's vid I attached below. Then again in certain applications Toro seems to have done a good job incorporating extensive use of polymers in their machines and they are said to perform very well.

 
#38 ·
I didn't try to balance my impeller after making & installing my impeller kit. I did try to cut the rubber pieces to matching sizes, to at least minimize the impact on balance.

If you wanted to balance it, because you felt significant vibration, the "simplest" approach might be to add a little weight to one blade, then move it to the next, until the vibration is reduced. This is kind of a hack approach, but it requires minimal disassembly.

Or, for a better approach with more work, you can pull the augers assembly out, split the gearcase, and put the shaft on some level blocks (or a countertop, etc). Let the impeller shaft rotate until you find the area of the impeller that settles at the bottom. That's your heavy spot. Either grind some steel off the low area, or weld a little onto the others, until it's better-balanced.
 
#40 ·
A broken plastic impeller would be impossible to repair. Once plastic is broken or fractured, there is really no effective way of welding or gluing it back together. Not in the same way you can with metal ones at least. Centrifugal force comes into play as well and I don't think any sort of glue, adhesive or epoxy would hold up. Metal impellers are fairly easy to balance. Take the impeller off and mount it to a prop balancer, find the heaviest spot and add a bolt and a couple of washers to add some weight until the impeller rotates freely without leaning to one side. Weld them in place, grind a little off and you're done.

Injection molded plastic is much harder to balance as it tends to distort over time. I guess being so light weight it doesn't really matter but breaking is definitely an issue.
 
#42 ·
A broken plastic impeller would be impossible to repair. Once plastic is broken or fractured, there is really no effective way of welding or gluing it back together.
Which would be a problem if they were unreliable and breaking left and right. I have seen no evidence to support that. If you have to take it apart to repair, why not just replace, it's less work.

To say this is an admission that metal fails. It's up in the air if plastic fails at all. I'd like to see the MTBF for both plastic and metal.
 
#41 ·
I have never heard of failures of plastic impellers. It is, however, recommend not to install impeller kits on them.

MTD also tried using plastic wheels. Those got recalled because some of them were exploding. I think that was partly because people were over inflating the wheels though.
 
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#61 · (Edited)
jsup: I had an MTD for many years as well (1995 640F, sold it 4 years ago, still ran well, though it had a lot of surface rust) and the polymer chute was fine, just sprayed it with silicone spray once a year, it never really clogged. Personally I am still leary of a plastic impeller at this point, just seems like it can distort in certain conditions. It may be my prejudices towards plastic being of lesser quality and cheaper in many cases. Even the Toro chutes which seem awesome and are easy to use for a mechanically controlled chute. I have read they can stick in really cold conditions according to a vid I watched on YouTube today. I was always a fan of the Simplicity Pro Series, nice machines and built like tanks. Best of luck with it.
 
#62 ·
I had an MTD for many years as well (1995 640F) and the polymer chute was fine, just sprayed it with silicone spray once a year, it never really clogged. Personally I am still leary of a plastic impeller at this point, just seems like it can distort in certain conditions. It maybe my prejudices towards plastic being of lesser quality and cheaper in many cases. Even the Toro chutes which seem often I have read can stick in really cold conditions according to a vid I watched on YouTube today. I was always a fan of the Simplicity Pro Series, nice machines and built like tanks. Best of luck with it.
My MTD also has that polymer chute. Never cared for it and I hated how much it flexed in heavy snow, but it did the job faithfully for years, even before I had it. I just can't see the same material being used on something that does almost all of the work while spinning at a high RPM. That being said, I've never owned a metal chute snow blower until now. I have yet to really put both my Craftsman II and my Ariens to use but I'm looking forward to the next big snow storm.
 
#64 · (Edited)
A quick google search shows that John Deere used plastic in their 47" and 54" blowers around 2010 (unclear for how long).

I don't know if it's the same grade of plastic utilized by MTD ...perhaps there may be more mode(s) of failure highlighted in the tractor forums than snowblower forums.

How good is the 54 Snow Blower with Plastic Impeller
 
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