Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

Hi Guys!

When the frame on a riding mower is described as "drawn steel", exactly what does that mean? Is it a "quality" method of manufacturing the frame?

Thanks,

Marc

Rob,  You may be right? Here is something from a steel company..........Wilkinson Steel

Cold Finished
Description	Cold finished bars have a smooth scale free surface with precise dimension and straightness. These controls make it an ideal product for structural components in precision machinery and screw machine stock. Cold finished bars have higher tensile and yield strengths than hot rolled bar and also demonstrate a high degree of machinability.
Surface Finish	The surface of a cold finished bar is smooth, bright and free of scale. In many applications no further finishing is required and the absence of scale enhances tool life and promotes a cleaner operation.
Dimensional Accuracy	Exactness in size and cross section.
	Round Bar tolerance - plus and minus in inches:
	under .313	.001
	.313 to under .5	.0015
	.5 to under 1	.002
	1 to under 1.5	.0025
	1.5 to 4 included	.003
	over 4 to 4.5 included	.005
	over 4.5	.008
Straightness	The precise straightness of cold finished bar enables it to be put in applications where freedom from vibration, whipping and binding are desirable, with little or no rework. The straightness tolerance for any non-heat tested cold finished bar is 3/16" over a ten foot length.
Mechanical Properties	Show improvement by cold drawing. In comparison with hot rolled steel, cold drawn bars demonstrate higher tensile and yield strengths and higher hardness.
Machinability	Cold drawn bars enhance machining speeds, tool life and quality finish when compared to a hot rolled product.
Property Pages	AISI C1018
	AISI C1045
Sizes & Weights	Round Bar
	Square Bar
- top -

Hot Rolled / Structurals

Description

Merchant Bar Quality: a low carbon hot rolled steel sometimes referred to as "soft" steel or "mild" steel. Easily welded, machined and formed, it is used for general production, repair work, machine parts, welding jobs and bracing. It is not particularly recommended for forging, heat-treating or complicated machine operations. In producing Merchant Bar quality, only a minimum discard is made from each ingot, but bars of this quality should be free from visible piping. Seams and other surface irregularities may be present but are not objectionable for the purposes for which this quality is recommended. Chemistry is subject to ladle analysis only.

I wonder what they really are trying to say with this "sales pitch". If they are really serious, the salesperson should be able to easily explain why "drawn steel" is different and better than what else may be used in other machines.

The chart looks like cold drawn is harder, has a higher tensile strength (my understanding is resistance to bending) and a higher yeild strength (my understanding is how much does it take to pull it apart). How does forming or welding effect these properties? Since it also says harder, maybe that's why it seems to crack more easily.

When I think of a mower frame I think of a sheet bent into a channel, square or rectangular tube, or angle.

If you take a steel bolt for example, the sheer strength of the bolt anchored in concrete for example, is the force at which it would be sheared or broken in half from weight. The Tensile strength would be at what force in weight that same bolt anchored in concrete would be pulled strait out or become broken by the same type of force.

For example, if I had a steel bolt in a ceiling pointing strait down and applied enough force pulling downward on it, that would test it's tensile strength or "Ultimate Elongation" (stretching).  If I pulled sideways or horizontally on it, that would test it's shear strength, (pulling apart sideways). The same applies to steel in form of a bar, strip, channel, etc.

I have seen steel tested for these two strengths, and a third strength too. The machines they use are pretty cool. You would be amazed at the sound steel makes when it is pulled from both ends, stretches and snaps. Pretty loud!

Yield is more of a measurement of the amount of stress to produce an offset. For steel an offset is usually .02% change of it's original form. That's a very simplistic answer, it can get about as technical as a person desires. You can get into elasticity and all I have no desire for that, LOL.

As to which is better for a mower frame, who knows? There's so much more that goes into steel than just these few things. I strongly imagine very good as well as very poor frames could made of both.

Do I have yeild and tensile backwards?

Yep.