Finish mower blade

[trkbldr]

Junkman, take a look at mowproducts.com. I recently ordered blades for a 72" Woods finish mower as well as blades for an old Sears rider. The pricing is very reasonable. However, I can not give an opinion on quality as I have yet to use them.

 

[nomad]

I just visited the website given above (mowproducts.com) and searched the net for mower blades. So, there are so many mower blades out there. Why? or What gives?

Also, searched the net about mower blades and their technical reasonings on why they are designed so, but unable to find any detailed explanation yet. Just fyi. If anyone comes across such a web page, he/she can post here.

 

[Molerj]

I'm just wondering if you cut any grass or are just inquisitive? I have cut about 8 acres of grass for the last 10 yrs. & I haven't had that much interest in the aerodynamics of the blade. Heck, I've used probably 10 different riding tractors & twice that many push mowers over the yrs. /forums/images/graemlins/tongue.gif

 

[txdon]

Nomad, don't know if <font color="red"> this </font> is exactly what you are looking for but I found it interesting that they use a strobe light "to “freeze” blades for visualization under full dynamic conditions."

 

[nomad]

TxDon, I know Rover mowers - their products are mainly Walk-Behind and Ride-On Mowers - Their blades are like this given in this picture - I don't know if they are MFGing a 3-pt finish mower that we are talking about here.

I know also Gilmore Eng. and their "e3k" (from the net only of course.) Their this mower blade study, I suppose, is related to those lawn mower blades, not our 3-pt finish mower blades. I am emailing the web address of this thread to them now. If anyone from there to this thread comes and joins, he may enlighten us whether they also did somethings about our 3-pt finish mower blades.

As for their mower blade works; Rather than their stobe visualisations, I'd be interested in seeing their aerodynamic hot wire anemometry test details. For those who don't know about this technique; its principal is to measure the velocity using its relation to temperature/heat. So, this technique can also measure the turbulence (velocity fluctuations.) So, them Gilmores probably have the data of turbulence that we would also like to see in around our 3-pt finish mower blades. Okay, this data maybe a secret, but "similar studies in 3-pt finish mowers too were made" can be said in a public meeting (like we do here online

I believe Gilmores designed such blades taking also the air flow fluctuations/turbulences around their mower blades into account. (or, they only modelled the blades using cutting and lifting mechanisms and after the design, they measured/visualied air flow around the blade?) These two things are different; 1. designing an object/configuration without considering turbulent effects and then studying the turbulences around it - 2. designing a blade from zero according to a given flow type details including local turbulent regions. (2) is a really hard work. It's like that I will give you a painting (free hand, art painting) of a certain flow type with some special circulations/chaoses/turbulences in it and I'll ask you to design a blade which will create that flow type exactly. Why am I asking such a hard thing to be done by you? BECAUSE it has been claimed that "recyclings/re-cuttings a grass over and over" are being considered when designing these 3-pt finish mower blades AND to be able to that, you must do such a work (painting of air flow type - blade design) as I mentioned (2) that is a real hard work. And, recycling/re-cutting a grass blade over and over in the mower deck requires such a detailed hard work. I don't think Gilmores did such a study. Well, we'll see if anyone from there joins and tells us somethings.

Ps: my main goal in this thread is to talk about the finish mower details and also not to hear anymore about "air flow in general and re-circulations/turbulences in finish mowers are also being designed" - and to enlighten my farmer friends whose minds are confused by "some" manufacturers and by "some" dealers. No a generalized accuse here. Only "some", maybe /forums/images/graemlins/grin.gif

 

[nomad]

Another thing; I see Gilmores also did a noise study work.
Wondering what the noise level in decibels is permitted in the mowers. As far as I know, 120 db is critical for human ears - but, is there such a high noise level in the mowers?

 

[rambler]

Noise is dangerous to human hearing not on decibels alone, but on how long the exposure is.

As well, neighbors don't like loud machines next door to them so it becomes an issue of legislating politeness to the neighbors....

At one time 80 decibels was considered the max for longer-term hearing health. That may have changed.

As to the whirling blades, people like to have multching blades to chop up their lawn clippings, and so manufaturers made then to do so. How did they make them? Who cares. They just did.

--->Paul

 

[RayHope]

Hi All. Nomad emailed me asking to contribute to this thread. So here I go.

Gilmore Engineers is a consulting Engineering company. One of our repeat clients has been a local Lawn Mower Manufacturer in Australia.

About seven years ago, before I was working for Gilmore Engineers, Gilmore Engineers were asked to help with a performance problem that they were experiencing in Europe. The grass in some European countries was quite different to our grass, and they were not satisfied with the cutting performance.

We did quite a lot of work researching and testing (your are right, there is very little if anything published on this).

At that time we did some CFD (Computational Fluid Dynamics) analysis. This was limited by the software and computational power of PC's at the time.

We also did a lot of real testing of different blade shapes to see cut quality and also used clear mower decks to see what was happening.

The blade shape we came up with ended up cutting much better and also was much better at picking up and propelling the cut grass into the catcher. They named it the superior blade and now use it on almost all their models (not just the ones for Europe).

In the last few years we have worked on a noise reduction program. The EU has introduced noise restrictions for most outdoor machinery and these will be tightened further in 2006.

The main source of noise is the blades (we did tests to comfirm this). Software and computing power had improved leaps and bounds in the last few years and we were able to use CFD (Computational Fluid Dynamics) analysis much better.

Each blade model ran for almost a week (we needed a very fine mesh on the surface of the blades). We were able to compare the CFD results with actual noise measurement for the superior blade and a flat blade (which was much quiter, but no good for cutting and catching performance).

From the study we learnt alot about the flow around the blades and how this effects cutting and catching as well as noise. We were able to recommend some modifications to the superior blade which would reduce the noise enough to meet the 2006 requirements, and have little effect on cutting and catching performance.

New blades with these modifications have been tested and the noise reduction agreed very well with those predicted by our analysis.

Obviously all the results of the work are highly confidential and this is about as much as I can tell you.

We have not done any work on or for the Finish blades you are talking about.

Other work we have done includes improving the efficiency of Francis Turbines for Hydroelectric power generation and we are currently working on a project to generate power from ocean currents.

I hope this helps.

Regards
Ray Hope
Gilmore Engineers

 

[nomad]

Thanks for the contribution, Ray. I was expecting to hear some words from you and I got answers to some.

You say you have not done any work on or for the blades or our Finish mower. Our finish mower is less tech mower so I don't think there is such a study like yours about our finish mower.

</font><font color="blue" class="small">( We did quite a lot of work researching and testing (your are right, there is very little if anything published on this). )</font>

This (nonexistence/nonavailability of blade studies) was what I've been claiming. Since you did an extensive study you must have all publishments you were able to reach, or least you must have some research abstracts or, at least, you probably know from "verbal" sources who did what. Nonexistence/nonavailability of such works on mower blades which have been in the field for decades show that not much detailed studies on the mower blades. And, as I frequently said in this thread, very detailed studies are required to model the complex flow around the blade. I guess your blade (theoretical or analytical) model consists of the physical mechanisms of (1) cutting and (2) lifting the cut grass by propelling into the catcher. I mean you probably didn't include in the mathematical model of blade those complex turbulent local flows that will be very important for recyclying/re-cutting the cut grass several times (a process that's being claimed by someones here in our finish mower to be designed.) Since in your CFD studies you had to use a very fine mesh to study relatively simpler mechanisms (cutting the cut grass + lifting it to propel into the catcher), you people here, imagine how very very fine mesh should be used to study the flow details around the blade. Relatively "larger-scale" flow study like Gilmore Eng. did won't be enough to model that mechanism of recycling (re-cutting the grass several times.) - "Characteristic scale" that should be considered in such a theoretical, CFD and experiemental study of detailed air flow should be much less than the scale/size of the thickness of one thin grass blade in all flow region (not only boundary layer region) around the mower blade so that you can take small forces/effects in the air onto the cut grass blade which can move arbitrarily in the mower deck.

As a conclusion; As such a detailed air flow is REALLY hard work I'm sure about that there is no such a detailed study of recycling/recutting grass in our finish mowers. A model consisting of mechanisms of cutting and lifting the grass requires relatively larger scales (coarser mesh in CFD) and see (in Gilmore study as Ray said), even for such a larger scale study of theirs, they had to use very fine mesh in their works. Also, I believe they didn't use many many hot wires at the same time in their experimental studies - meaning that they didn't study "minor scales" or smaller scales in the flow. From what Ray says, I understand that their study is maybe most detailed study in the mower field- and imagine the other (finish) mower blade studies which are probably more coarser studies.

Ps: If I saw set of equations of your analitical model, I'd be sure about what mechanisms were taken into account. This should not be a secret to public in my opinion as scholars probably have such analitical models in their stores already. Maybe, I'm wrong. Maybe, you Gilmore and I together would do such a study about our finish mowers by modifying your analitical model a little to include some smaller scales around the blade and we could produce a finish mower with a universal blade which will also do recycling/recutting works /forums/images/graemlins/grin.gif

Ok. Thanks for your contribution to this community forum.
Regards,
Nomad

 

[Villengineer]

Nomad, You are the spin master. The guy from Gilmore just confirmed or at least gave circumstantial evidence to support everything I pointed out was wrong with your opinion, yet you spin it as if it supported your assumptions. He stated that: 1) Despite your arguments that they weren't or can't manufacturers are in fact taking fluid flow into account when designing blades. 2) I told you why the work wasn't published and he confirmed that it's trade secrets. 3) He gave no evidence that they were not in fact doing analysis of other blade functions, yet stated that there was more but was unable to discuss it further.
How can you still claim to be right or that the same work isn't being done on 3pt finish mower blades? The fact that 1 engineering firm hasn't done the work for every blade or mower manufacturer doesn't prove anything. Companies like Deere have their own engineering staffs full of very intelligent and well equipped engineers assigned to their various products. They are better positioned do this work than a consulting firm which has to take up the assignment cold.