Once again, it’s time to break out the lawn mower, garden rake, pruning shears and garden tiller. Ever wonder what all these tools could have in common with the long-handle shovel, edging tool and the broadcast spreader besides sounding like a lot of springtime work? All of these tools are heat treated for durability.
While shovels and rakes have been around a long time, lawn mowers were invented in Britain in 1830 by Edward Beard Budding. The development was brought about from our need for leisure. Several sports had just been invented in Britain that required a flat, soft playing surface including croquet, cricket, soccer and rugby. Necessity dictated that the grass was more uniform in length, and like many other inventions necessity was the mother of the mower.
Not all mowers have hardened blades. It depends on the type and manufacturer as to whether the blades are hardened. The reason for hardening mower blades is to prevent them from becoming dull. A dull blade makes the equipment work harder and damages the grass. Manual and motorized reel-type mowers all appear to have five induction-hardened blades. This type of mower, popular earlier in the 20th century, seems to be making a bit of a comeback.
Rotary mowers have a veritable potpourri of blade choices. Some are hardened to high hardnesses for better wear with little consideration to the resultant brittleness. Others are not hardened at all, and it is difficult to hold a sharp cutting edge on these blades. Still other blade manufacturers control the alloy composition and heat-treating process closely enough to assure that the blades have the proper hardenability for long life without brittleness. One manufacturer of aftermarket mulching-mower blades advertises the use of 10B38 steel heat treated to a Rockwell hardness of RC-50 for safety and durability.
In addition to the obvious wear factor, proper heat treatment is key because a blade in a lawn mower travels over 200 miles per hour, or 19,000 feet per minute. If the blade is too brittle and encounters an immovable object at that speed, catastrophic failure can occur. If this happens, blade pieces will be expelled from the mower at the same speed. Needless to say, injury is likely.
The same is true of items the mower encounters such as stones, sticks or toys. When these items leave a discharge shoot they can cause serious injury to people nearby, the operator or even cause damage to personal property. While on the topic of safety, care should also be taken when handling gasoline. Did you know that, combined with the correct amount of air, one gallon of gasoline has the explosive effect of 83 pounds of dynamite? So, never fill the tank on a hot mower and carefully wipe up any spills.
After cutting the grass you may need to fertilize the lawn or edge along the sidewalk. In either case, parts of this equipment may also be heat treated. The gear on a good broadcast spreader is made from heat-treated steel, as are the blades on a steel-wheel edging tool. Of course taking some dead wood out of the low-hanging branches will require the right pruning tool, which is also fully heat treated to be able to maintain sharp cutting edges.
Most all of the parts mentioned thus far are hardened and tempered steel. The type of steel and exact heat treatment depends on the configuration, application and size of the specific part. Parts might be batch hardened, quenched and tempered, or could be induction hardened, quenched and tempered to the proper combination of hardness (for wear resistance) and ductility to prevent breakage.
Hopefully you are motivated to put the winter behind you and dig into the yard work ahead. And whether you’re digging or cutting, now you know that proper thermal treatment makes the job easier and safer.IH
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