Repairing Plows, and Welds on Plows



I am employed in the welding business full-time, and every winter we see lots of snowplows come in for repair work - often while it is snowing! It's always because something either broke or bent, rendering the plow
unusable, and it's got to be fixed NOW because there are contracts to keep.

Most of the time, the customer was using the plow the way they always do when all of a sudden, something broke or bent, putting their plow out of service. Upon taking a close look at the unit, it becomes obvious that -
except in a few instances where someone has done something completely insane with it - none of these plows broke "all at once". The structural failure was merely the end result of the normal fatigue process found in any fabricated part.

At a glance, a fabricated assembly such as your plow A-frame looks like a solid, immovable object. In fact, there is a certain amount of flexibility to it - if it couldn't flex at all, it would break. A couple of good examples are the frame on your pickup and a tree swaying in the wind. And if they flex too far, they either bend or break! Steel has a
certain amount of "elasticity" to it, this being the ability to deflect under load, then return to its former position. Beyond this point, once it's bent it stays bent! As well, if bent back and forth at the same spot
continuously, steel will eventually break. This is known as "metal fatigue" and can be easily seen by straightening out a paper clip and bending it back and forth in the same spot until it breaks. Before it breaks, tiny cracks will appear on the surface of the metal.

Although the deflection under load isn't visible to the eye on your plow, it's there - just like it is with big machinery. Every winter one of our good customers (an aggregate company) overhauls their equipment. We generally see quite a bit of repair welding work on their big loaders, among other things. Most of this work involves repairing cracks. Under the stress of daily operation, the steel buckets and frames on these machines flex back and forth and cracks appear in areas where the stresses are concentrated. This is generally at either end of a weld, near a hole or at a sudden change in direction. Because the machines are "overdesigned", some cracks are not a big problem: there is enough  strength left in the remaining structure to safely carry the load. That's why they make sure they get looked after every winter. The cracks are like the tiny cracks that appear before the paper clip actually breaks. If left long enough, the loader bucket or frame will break.

That's the case with the plows we end up repairing. Besides the damage that caused it to be "out of service", other signs of fatigue are evident. Generally cracks have started at either end of some of the welds, in more severe cases some welds are cracked all the way through. Sometimes things are bent, too. In any event, not enough strength was
left in the remaining structure to carry the loads imposed by plowing, which meant some part of the plow ended up absorbing more stress than it was designed for, and either broke or bent as a result.

One solution would be to make everything heavier, and add more bracing. The problem with doing that is twofold. 1], your plow would end up being so heavy a pickup truck couldn't carry it (by the way, we also do repairs
on the big highway plows and the same things happen to them) and 2], better that the plow be the "weak link" than the frame of your truck. In the "worst case" scenario of having to rebuild an A-frame for your plow,
it would take about a day, tops. Having to rebuild your truck would involve a lot more time and $$$.

Unless you do a v-e-r-y minimal amount of plowing, your equipment is going to see some "wear and tear" and begin showing signs of fatigue. Since they were designed to have the A-frame level with the ground when
pushing, plows really take a lot of punishment when stacking. Any sort of twisting action (one side of the blade higher than the other) is also something they weren't designed for, and depending on how rough the roads
are in your area just carrying your plow around can be hard on it!

So if making the plow "unbreakable" isn't practical, what is? The solution is to take a page from the book used by the aggregate company we work for, and inspect and overhaul your plow regularly.

When you get ready to put your plow away in the spring, give it a thorough inspection for cracks and anything that's bent. Then deal with any problems you find, right away! Any reputable welding company can handle this task, but if you're handy with a welding machine you can also do this job yourself: 

The most important thing to do when repairing cracks is to gouge ("vee") them out. The most common mistake we see on the plows that come in for repair is cracks that have had a quick bead run over top of them. It is important for the weld to get a good "bite" on the base metal on both sides of the crack. As well, any dirt and moisture down in the crack will make it difficult to weld. A decent 4" or 5" disk grinder is an excellent tool for gouging the cracks. It is also important to gouge and weld starting ahead of the crack and finishing beyond it. This way the crack has "disappeared". If part of the crack is still there, the stress will be concentrated in that area and the repair weld will crack again, soon.

Any good 220-volt stick welder will work well. If you have a MIG machine, the small 110-volt models are a little too light for this type of structural welding in my opinion. (They are great for doing repairs on the face of your moldboard though!) A larger 220-volt MIG machine should work fine. To make your job easier, do all the welding in the flat position. This may involve some disassembly of your plow, but that's OK - good time to check the bolts & pins too!

As far as "beefing up" your plow is concerned, keep in mind that if you make it t-o-o strong your truck's frame might become the "weak link". And don't be alarmed if next spring, you see some minor cracks starting back
up in the same areas - that is where the stresses are concentrated. The key is to catch & fix the small cracks before they grow into big ones & weaken the structure. If it works on big loaders, the same approach will certainly work on your pickup plow.

If you're out plowing and hit something a little harder than you expected (curb, frozen bank etc) but everything seems OK, give your plow an inspection as soon as you can. There may be some new cracks as a result
of the "big hit" and fixing them right away is your best insurance against a breakdown during the next storm.

Hope this information can help you "keep plowing" next time it snows!

Written By:

Rob Nagle
Ontario, Canada

 

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