Replacing your blades

[bertsmobile1]

Any metal to metal contact has the ability to create a tight bond as it rusts together. It doesn't take much rust to seize a bolt and it's the rust you don't see that causes the problem. When this happens, you must break the bond between the two metals to get the bolt free. Heating up the bolt so that it swells can and does break the bond, but not always. Hitting the hot parts with penetrating lubricant will cause metals to shrink and often will suck some of the penetrant deep into the threads. It might take more than one or two cycles of heat and cold to get the bond to break. Steel also becomes plastic with heat. Heat the head enough, and the bolt will stretch a bit, releasing any pressure. You can argue with the physics all you want, but that's how it works. We call it the "hot wrench" for a reason. Do be careful though... heat can and will be transmitted through all metals and things like seals can be adversely affected. Just use reasonable care and you should be fine.

However, the absolute best way to bust things loose is prevention, prevention, prevention. Using anti-seize is an easy, cheap and incredibly effective way to prevent metals from creating any kind of bond. The carrier (grease) used in anti-seize will keep water out preventing any rust. In addition, the tiny, tiny flecks of a disimilar metal that can't rust does the rest and will continue to act as a lubricant should the grease dry out. Yeah, you don't like this and yet it seems that you have more than your share of stuck bolts. Perhaps you should give it a try. What have you got to loosen???

I was, at one time, an ASE Master Certified Auto & Truck Technician. My first job in the automotive world was back in 1969 and I spent 30 years in the service bays and learned how to deal with stubborn fasteners. I even moon lighted as a small engine mechanic and have never, ever met a blade bolt that would not come off. I'm the guy people would take their broken bolts to, because I know how to get them free without ruining the part.

Since I have been repairing mowers for a living I would have replaced several thousand blade bolts and am yet to come across one with the slightest amount of corrosion on them apart from on the outside of the head where they are exposed to the acid from the cut grass. They lock in because they self tighten in use .
It is a pure a simple case of dynamic loads causing the blade to rotate on the spindle and because the bolt head can not slip on the blade as it is under spring tension the bolt tightens.
This is also plain physics, the spindle is rotating in one direction and the blades resist the rotation so tighten .
Blade bolts fitted into a spindle never ever rust solid in place.
They can not do this unless fitted wet as the hole is blind , points up and the spindle / blade / washer / bolt interface is airtight when done up to the recommended torque.
Blade carriers on the other hand do rust in place because they are open to the atmosphere so you can get an oxidizing agent in there, usually water to start a galvanic cell and allow corrosion to occur
Or if you want to sound knowlegable, allow the high energy steel to revert to a lower energy state according to the laws of thermodynamics.
metals that have the same crystal structure or are in fact the same will form oxides that will grow into each other and form a single oxide layer.
Weather this is a problem depends upon thinsg like the strength of the oxide and the volume increase of the oxide, which in the case of rust is the big problem as rust is very very weak.
This is usually not a big problem unless it is a metal like stainless steel where the oxide is particularly strong, we call this gauling if it is on a fastener or stiction if it is something that is supposed to be a sliding fit.
Zinc carb slides are notorious for stiction & stainless bolts for gauling but neither of these are applicable to blade bolts .

Heating nuts & bolts works because one part gets heated more than the other part so it moves with respect to the other part and this movement can cause a fracture line to happen through one of the oxide to metal interfaces if and only if the amount of differential movement is sufficient .however, if not heated to red hot where a phase change causes a massive volume change, the amount of actual expansion is quite small. Like every process it has places where it is very appropriate and places where it actually makes the problem worse and a blade bolt is one of these cases.

I do use grease , copper, nickel & graphite anti sieze but being properly trained,only in places where it is appropriate to do so and then because I am properly trained the tension applied to the fastener is reduced to the appropriate level to compensate for the reduction in the dynamic friction between the contact faces of the threads .

A blade bolt into a spindle is not an appropriate place to use any type of thread lubricant because it MAKES THE SELF TIGHTENING WORSE even if the fastener was only tightened to 62.5 % of the printed dry thread torque to compensate for using copper anti sieze .
If the bolt is done up to the full listed tension then it will already be over tight and unless the anti sieze was also under the head, where it should never go the bolt will be a lot harder to remove and you run the risk of breaking the bolt because they are only grade 5 ( on commercial ) or standard ( on domestic) grade bolts thus you run the real risk of necking the shaft under the head thus allowing the bolt to fail under use.

Now I rarely bother to play the "qualificatins game" on the web because readers should read all of what is posted then make up their own minds not blindly follow the person with the higher quaifications.
But as you think it is appropriate I started off my career as a metallurgist, graduating with a higher diploma, followed with an undregraduate degree in metallurgy and one year of a masters in materials science which I never got around to fininshing .
Add to that post graduate diplomas in NDT and a stand alone radiology diploma , followed by a radiation diploma so I could rent isotopes to x-ray welds in pipes followed by a diploma in accoustic emissions , then audiology
diploma ( for workers comp ) and a diploma in adult eduction so could teach TAFE students part time. to be able to sign off on defense work NATA required me to get further qualifications in microscopy & metallography so as one of my ex- business partners used to say, more degrees than a thermometer .

But again people should read a post , work it through for themselves then try what they think is appropriate as this is the web & I could really be a 12 year old girl who gets her jollies by fooling people on line.

 

[The Chairman]

but being properly trained

Properly trained to use anti-seize? The water came out of my nose when I read this. That's too funny. Who did your training? Was it University or industry sponsored? Here's the only direction you need: a little dab'll do ya.

Weather this is a problem depends upon thinsg like the strength of the oxide and the volume increase of the oxide, which in the case of rust is the big problem as rust is very very weak.

Actually, it depends on the friction coefficient generated by the bond and the contaminate. When you're putting a lot of pressure, it doesn't take much to really jam things up.

FWIW, I live in Florida. It's not unusual to have very high humidity as you assemble things. Anti-seize is the way to go for me.

.however, if not heated to red hot where a phase change causes a massive volume change,

No. This is false. In college, I apprenticed in a machine shop and that was a great study in metals for me. Right after, I ran a materials science lab and machine shop for UF's college of architecture where that hands on learning was formalized. We had a 60,000 psi Tinius Olsen Stress Strain machine, where we could stress various items to failure. Adding heat was amazing. All metals have a modulus of elasticity. When stressed it will go through predictable ranges of being elastic like a rubber band and then being plastic, where permanent deformation occurs. 250F is enough for most steels to severly alter that modulus so that the steel enters the plastic stage almost rather quickly. This is why fires in steel buildings are so catastrophic. You don't need to go anywhere near "cherry red" in order to get that bolt a little loose.

 

[bertsmobile1]

Way way back I adopted the practice on not getting into spats with people on forums. particularly as like this one they tend to get way off topic & become both boring & confusing and thus no help to the original poster.
Thus as previously mentioned it is up to the reader to make their minds up.
There are places where copper anti sieze is the correct thing to use
There are places where graphite is the right stuff
There are places where nickle is the right stuff
there are places where plain old grease is absolutely fine
and there are places when anything on the threads should be avoided and the fastener should be done up dry
And Hustler 27's blade bolts is one of these cases
This is what training to use never sieze is all about not how to apply it, any monkey can do that and many monkeys do with absolutely no understanding of what they are doing .

As for the temperature dependence of elastic modulus, that has been the topic of millions of papers from undergraduate level right up to Phd level and it is specific to the alloy being used and the method of production of the item , grain size & orientation and the direction and type of loading.
It is also totally irrelvant to this situation.
A good engineer knows hundreds of equations & formulea .
A proficient one knows when & where to apply them

And a ceiling fire can run well over 1000 deg C and the fire strenght of steel truss roofs is dependent upon the type of steel in the truss, it's cross section on weather it is cold or hot rolled or extruded , open or closed section etc etc etc and yes you are right in one thing. fire men hate walking on a steel framed roof.
However they suffer from a double whammy because like bridges with insufficent expansion plates the uncontrolled EXPANSION of the hot steel can cause a failure and it is a bigger problem than heat reducing the stiffness unless you are talking about RSJ's riveted to cast plates and these need to get really hot .
many people mix up stress relief which will cause wrought structures to fail with softening of the steel which should never happen under 400 deg C in plain carbon structural steels

 

[Tomster]

My blades look like the OP's after 7 hours of mowing, not 7 years! I usually get to sharpen them once and then they are pretty much worn away. I use an impact every time to take them off and then put them back on. Once I hit something with the left side blade and it took a lot more effort to get that bolt loose, but it finally moved. My neighbor came over to get help changing his blades for the first time on his gravely (I think). The first two came off with the impact no problem, but we had to get a cheater bar to remove the left one.

 

[The Chairman]

it is specific to the alloy being used

Le sigh... not really. Heat changes each and every alloy. Yes, the degree that it changes might differ, but heat will have an affect on any steel. On every steel. Especially carbon steels. The best way to relieve stress in most any steel is to heat it and let it cool. That's pretty universal. You seem to think this can't work, yet the metallurgy and physics disagrees with you. Again, it's why we call a torch the hot wrench.

And a ceiling fire can run well over 1000 deg blah, blah, blah, blah...

This is argumentum per deluvium... how does any of this matter to the one bolt we are heating? Can we stay on topic?

Again, I have to ask what "training" you got for anti-seize? Was it university or industry sponsored training? I'm guessing it's more apocryphal OJT with someone telling you what THEY think is true. I have been to product seminars by two manufacturers, and the amount of time they spent on anti-seize was pretty minimal. I've been successfully using anti-seize since 1969 when I first worked in a shop. For what it's worth, I can find absolutely no reference to using or not using anti-seize by Hustler. Apparently, they don't see it as a problem either way.

Let's consider some more physics. Bolts are held in by friction caused by tension. Sometimes, we add a lock washer or loctite to increase that friction to stop bolts from inadvertently backing out. When you tighten a nut, the the tension or stress between the bolt and the surface increases with the friction of the threaded components. Tighten it too much, and you get galling, which is a deformation caused by excessive friction in the threaded components. Even a tiny bit of galling can make the removal of any fastener far more problematic. The force needed to remove a fastener with galling and/or corrosion is amplified by the normal friction in the fastener.

Anti-seize was developed to inhibit any galling and corrosion. In fact, the application of anti-seize affords a small reduction in the torque needed for a fastener to achieve full holding power. Over tighten the fastener, like when hitting a stump, and the strength of the bolt, ie the stress between the head and the underlying surface, will be the limit for how much the blade overtightens tightens. Anti-seize will reduce the chance of it galling or seizing and you having to cut off the bolt. Amazingly, it's why they call it "anti-seize". Amazingly x2, it works as advertised, unless you fail to use it and have to keep cutting bolts off. Here's a definition of the stuff...

from www.Wiktionary.org :

Noun
anti-seize (plural anti-seizes)

A compound used on threads, bolts, gaskets and other mechanical joints to prevent seizing and galling, to improve installation, removal and disassembly, and to prevent corrosion.​

About "spats". Unless it devolves to name calling, which I haven't done to you, it's not a spat but a disagreement. We disagree on two issues and we're both pretty passionate about that. That's what's great about a forum. You can read two or more sides of an issue and decide who is right and who is not. You have set yourself up as being "the authority" and yes, I have indeed challenged that. I'm not going to demean you and hopefully, I can expect the same from you. I've asked for clarifications (twice now) as to the nature of your training, but I absolutely feel no ill will towards you. Except for your treatise on burning buildings, both heating bolts and using anti-seize are germane to this topic.

 

[bertsmobile1]

I am here to learn just as much as anyone else.
When I see some thing that is wrong I like to correct it because what goes on the web stays there forever.
In the same vein when I post something that is factually wrong and others correct me I try to acknowledge it and modify the incorrect post.

If I wanted to set myself up as an authority then I would have included my full credentials in the footer of my posts but you will have noticed there is nothing there, not even the business name to affirm I am in fact currently a mower technician . On occasions I do mention that x number of cases have presented with this problem but apart from that it never gets a mention, on purpose. What is posted on the web should always be taken at face value and the reader should decide what is fact, what is fiction & what is urban myth.

Debates like this can very quickly go into esoteric levels where we could argue about the definition of gauling for instance and the different between gauling and mechanical surface welding .
There is nothing wrong with heating fasteners to facilitate their removal, I do it all the time, when it is the right thing to do.
There is nothing wrong with using anti-sieze , when it is the right thing to do

Now if Hustler 27 was trying to undo a deck bolt , a head bolt , or any other statically loaded bolt then heat is an appropriate mechanism to use as the fastener would most likely be corroded in place.
THis includes any fastener subject to varying stress like head bolts & muffler bolts.
But this is not the case
Hustler has a blade bolt that is under dynamic loading in a direction that causes the bolt to tighten in use.
Applying anti sieze to this bolt will facillitate over tightening by lowering the friction co-efficient even more than a dry thread would do.
If anything it should get a touch of low strength lock tite to prevent over tightening during use, some thing I never thought about till writing this post but will give a try the next time one of the problem child mowers comes in for a blade change.

Hustler27's bolt could be anything from 1/2 turn to 2 1/2 turns over tightened . much more than this exceeds the torsional elastic yield point of the steel & the bolt will start to neck & break the head off.
From what you have already posted you should be aware that forces applied on 2 planes drastically reduces the elastic yield point. This is why metal spinning works , not that it is used much now days.
For heat to work the shaft of the bolt has to expand more than the spindle, blade & washers to a length of at least 1/2 turn to relieve the pressure that the head of the bolt is applying to the shank of the bolt and that just is not going to happen without getting well & truely into forging temperatures and phase changes .
If the spindle used tapered roller bearings like a lot of the better old stuff did then it would have a nut on the blades and in that case heat would be appropriate but in this case it is not.

And metallurgy is an applied science involving physics, chemistry & engineering so yes I did study fasteners at both university & trade school levels and this included things like making lead bolts for cyrogenic use ( mine failed by the way ) and all sorts of weird things . We had to calculate the stresses on individual threads , yield stress on the thread roots & deformation of the thread face.
Nuts & bolts are a lot more complicated than most would think.

Overtightened heads get chopped off because it is the quickest & easiest way to remove them if my 1300 ft lb rattle gun will not shift them
Takes about 5 to 10 minutes and can be done by any one at home with an average home owners tool kit .
I used to take mowers up to the machinery shed, fire up the Boomwade compressor , lift the mower with the tractor then hit them with the 1" rattle gun.
Some came out but most broke .
Close examination of the ones that came out showed deformations in the plating under the head signifing that there had been some movement between the head & shaft so the bolt was compromised in any case thus could not be reused hence it became a pointless waste of a 1/2 hour and now only gets done if 2 or more bolts refuse to loosen with my rattle gun.

 

[Ken22]

Bertsmobile1. I got a metallurgy ticket back in the 70's and followed you through your explanations. Spot on. I torque all bolts and know the value of doing so. I went trucking in the 80's and one of my customers supplied Kopr-Kote to the oil industry and gave me a pail. He warned me to torque 1/3 less. I was always leery about using it where torque was important as in mower blades and wheel nuts for example. I use it a lot where bolts don't need to come off often. Or holding two pieces of metal together. This was my rule of thumb.
A friend of mine brought me his Kubota ZTR to replace the blades a couple years ago. I grabbed my torque wrench and tried to torque to the manual's specs and it wouldn't tighten. I asked him if anyone put the blade on with an impact wrench and he was proud to tell me the last guy did and really gave it to the bolt. I told him the bolt was stretched and I wouldn't put them back on. He cussed but got new ones.

 

[bertsmobile1]

That is freaky,
I got my diploma in 72 , higher diploma in 73, BsApSci in 75 then started a delivery business in 88 when the metals industry collapsed and land prices skyrocketed so raiders bought out most of the metal business to sell off the real estate at massive profits.
Still a member of Aust Institute of Metals , an associate of American Society of Metals , American Foundrymens Society and a couple of other local associations.
Never lost the passion but one has to eat and delivery drivers always were paid more than technical staff.

 

[The Chairman]

So, for the end user: you have at least two methods of approaching this dilemma. The one that works for you, works for you.

I'm wondering if I don't have that issue because invariably, some anti-seize gets on the bolt face. Rather than spinning the bolt when it hits an obstruction, the blade spins under it. All I know is that it works for me and I'll continue to keep applying it as needed. It works as advertised. I had a few times where I had to really use a breaker bar to loosen the nut. After I started using anti-seize, I haven't had an issue with it at all. My 18V Ryobi Impact zings it right off and then it zings it back on. I sharpen or replace blades every 8 hours or so, which is a single mowing.

 

[StarTech]

Just wondering when the threads will so worn that you will need parts.

I get in mower with blades so worn that you would definitely they have been off in years. Matter of fact I got sitting in my junk mower a Honda mower that has about a 12" long blade that should be 21" and the customer was only complaining that it was hard to start.

I think that one might just needing a slight touch-up to make it cut like new again.