Metal or plastic body?

[sawtooth]

I previously worked for a supplier for John Deere. Not sure now but in early 2000 they were pushing to change over as many components as possible to plastic in tractors and mowers. Main reason for this was to remove as much cost as possible from each product. I remember one piece in particular which was a structural piece for the hood of a 4000 series tractor. As metal it was very stiff but they went through 3 versions of a plastic one that when the hood was raised gave the feeling of a very cheap and wimpy hood support. I was very surprised they left it that way. They were even celebrating the fact it was converted to plastic material. Very junky in my opinion though. The material was a nylon 6 with 33% glass filler.

 

[MHarryE]

I have a different view than all the others. Plastics allow much more flexibility in the design so curves can be sculpted into the shape for clearance purposes. An example is our JD 7720 - sculptures sides provide tire clearance while increasing visibility. Cost - generally higher with plastic depending on the plastic type of which there are zillions. Seams don't show rust, paint doesn't peel, scratches don't turn into dripping red rust. Stiffeners can be molded into the plastic making the plastic lighter. Fading is a selection process - plastic doesn't mean fading unless the manufacturer opts to go for faded paint. That is a cost decision whether metal or plastic and customer feedback is the ruling factor. But if you are prone to doing something like dropping a tree over your tractor, it is going to be less expensive to pound out the crumpled sheet metal vs replacing the broken plastic.

 

[paulfun9]

I previously worked for a supplier for John Deere. Not sure now but in early 2000 they were pushing to change over as many components as possible to plastic in tractors and mowers. Main reason for this was to remove as much cost as possible from each product. I remember one piece in particular which was a structural piece for the hood of a 4000 series tractor. As metal it was very stiff but they went through 3 versions of a plastic one that when the hood was raised gave the feeling of a very cheap and wimpy hood support. I was very surprised they left it that way. They were even celebrating the fact it was converted to plastic material. Very junky in my opinion though. The material was a nylon 6 with 33% glass filler.

Now they can celebrate the fact that I spent my money on a Kioti rather than than an other JD.!

 

[Cherokee140]

I have a different view than all the others. Plastics allow much more flexibility in the design so curves can be sculpted into the shape for clearance purposes. An example is our JD 7720 - sculptures sides provide tire clearance while increasing visibility. Cost - generally higher with plastic depending on the plastic type of which there are zillions. Seams don't show rust, paint doesn't peel, scratches don't turn into dripping red rust. Stiffeners can be molded into the plastic making the plastic lighter. Fading is a selection process - plastic doesn't mean fading unless the manufacturer opts to go for faded paint. That is a cost decision whether metal or plastic and customer feedback is the ruling factor. But if you are prone to doing something like dropping a tree over your tractor, it is going to be less expensive to pound out the crumpled sheet metal vs replacing the broken plastic.

Shape has nothing to do with it, metal can be stamped into any shape you want...ever see a VW bug?

There is really only one reason to make it out of plastic, cost. It is cheaper for them to make it out of plastic....all the way around. From the equipment needed to make the part to the material the part is made from. Anyone that has every played with vacuum forming can tell you that.

I do agree that it will not rust, but it will get brittle and crack. I know that from experience with my JD lawn mower and its plastic hood....only 3 out of the 7 mounting tabs are left and it has duct tape now holding it on.

They are doing it to make the bottom line better for them all the while charging us even more for the part. Thanks but no thanks.

 

[gphil12873]

Well when they really started making out of plastic the price of steel was thru the roof. The price has came back down to tollerable levels...but the tractors hasnt....go figure.

 

[KennyG]

I probably ought to stay out of this but some of this discussion isn't making sense to me. Is anybody really sure that a plastic body part is cheaper than steel? Stamping out sheet metal parts is dirt cheap. The type of plastics used on body parts looks to me like a pretty sophisticated material. If plastic is so cheap why don't all our cars have full plastic bodies?

My tractor is only 4 years old, so I can't say for sure how it will stand up but I do know that if it had a metal hood it would have some dents at this time but because it's plastic it's in perfect condition. Maybe some plastic body parts do have problems, but I take care of a couple of Honda snowblowers that are probably 25 years old and the plastic body parts are in better shape than the metal parts. Motorcycles have been using a lot of plastic parts for over 30 years now and they seem to hold up fine if you don't crash.

Some people have talked about flimsy, but my plastic parts seem heavier and more rigid than a lot of metal parts.

 

[gphil12873]

well would you ride around at 75 mph in a plastic bodied car....or ride around in a 17 mph tractor? That isnt even a fair comparision. I just know steel was very expensive five or six years ago. Plastic has a place but not tractors I dont think.

 

[D7E]

I have a different view than all the others. Plastics allow much more flexibility in the design so curves can be sculpted into the shape for clearance purposes. An example is our JD 7720 - sculptures sides provide tire clearance while increasing visibility. Cost - generally higher with plastic depending on the plastic type of which there are zillions. Seams don't show rust, paint doesn't peel, scratches don't turn into dripping red rust. Stiffeners can be molded into the plastic making the plastic lighter. Fading is a selection process - plastic doesn't mean fading unless the manufacturer opts to go for faded paint. That is a cost decision whether metal or plastic and customer feedback is the ruling factor. But if you are prone to doing something like dropping a tree over your tractor, it is going to be less expensive to pound out the crumpled sheet metal vs replacing the broken plastic.

I agree with nearly all of this but regardless of brand I find the paint comes off plastic worse than steel . The fenders on JD's , The hoods on NH 40 series and TM's can look like dairy cows and our cat backhoes have almost no yellow left just black plastic on the hoods . But then with tractors like the mf 2000 series that were very prone to the cabs rotting out and didn't have bolted fenders plastic is a lot better than cutting out and welding in panels !

 

[Baby Grand]

My personal preference is for metal, just because I have a good idea that that means steel of some suitable grade. If designed right, primed & painted properly, it will last and last. Dents & bullet holes can be fixed with relative ease and a new shot of primer & paint will protect it for many more years. The paint fades in the sun, but the steel is impervious to UV damage.

When you say "plastic", that could mean any of thousands of compounds - some very good and others, not so good. Almost all plastics degrade in sunlight, so it should really have a coat of paint to limit the damage. A carbon fiber hood would be nice - very strong and light weight up high, bringing the center of gravity down a tiny bit. But it would cost much, much more than steel. A polystyrene hood would probably last a few months before cracking and cost a little more to make than a disposable milk jug. The material the tractor company decides to use will be somewhere in between those two extremes, and will probably have some percentage of filler, like glass fibers, just to complicate the comparison. Fixing any plastic part requires a lot of skill and careful material matching/selection.

So, steel is simple and works. Plastic - not necessarily so, but maybe, sometimes.

 

[k0ua]

I thinks that some of problems with the plastics come in the attachment points. That seems to be the most problems with cracks forming at the tabs where hoods rotate around the bolt axles etc. If they could solve these problems then perhaps most people would look at plastics in a more positive light. I haven't had any problems yet with my JD, but it is still fairly new, with low hours and is garage stored.