Monthly Archives: June, 2010

Understanding Airgun Spring -Part1

Spring! A simple word but not that simple a subject.

The intention of this post is to enlighten fellow “air gunners” looking at spring replacements for their air rifles to better understand some basic technicalities of springs while selecting the same.

To start with, let us study 3 different springs. For a slightly in-depth understanding, we will look at their chemical compositions and manufacturing processes as well.

Spring used for sock absorber

Spring used for shock absorber

shock absorber spring -close-up

A closer look at the surface of this spring reveals a quiet uneven and rough surface. Unfortunately, an untrained eye will not be able to pick the difference as these very springs, when they hit the market are usually polished. The spring steel used in these types of springs is usually cheap and has carbon content of between 0.50% to 0.80%. These springs also have a different drawn process compared to springs that are fit for Air Guns. The spring wire being perfectly round in these springs is questionable. These springs are also not capable of taking high stress, and therefore on load, it will set very quickly.

Carbon content is not the only factor that plays a roll in making spring steel better or worse. Percentages of Mn, Si, P, S, Cr and V are also very vital to the end result of the spring steel quality. A simple difference between high tensile steel and low tensile steel boils down to stringent quality control on the ratio of the above said chemicals and a “better drawn” process.

Furnished below is the drawn process:

For general shock absorber spring:

  • Wire Rod
  • Heat Treatment
  • Pickling –> Wikipedia
  • Drawing
  • Oil Treatment
  • Inspection
  • Wire Forming

In addition to the above, for a good Air Gun Spring, the following additional processes is introduced after Drawing.

  • Heat Treatment
  • Pickling
  • Drawing

The picture below shows a spring made from good quality steel using the above 10 steps of the drawn process with the right quantum of carbon and other chemicals mentioned earlier. This is very evident when one closely inspects the surface (Please compare the previous photographs and the ones below).

  • Airgun Spring

Airgun Spring -Close

Even if both the spring steel were to go through the same 10 steps in the manufacturing process mentioned above, the low carbon steel spring cannot attain the same smoothness as the high carbon steel. This is because there is a tight bonding between the metal and carbon.

In addition, elasticity can be increased in a good spring wire through a process called low temperature annealing. Most spring maker are either not aware of this process or choose to avoid it due to the high costs involved and the resultant increase in production cost.

Left -Shock absorber; Right - Airgun Spring

A comparison of the two spring steel quality side by side:

Close-up

Air gun springs available in the country are made from Shock absorver grade steel (seen on the left). This is largely due to the manufacturers lack of knowledge in spring engineering.  It is not uncommon to hear praises for springs like Cherokee, G Smith and many unknown brands for their quality. I have closely inspected these springs and they tell a different story. I have found all equally bad! I have heard people say that during installation these springs are extremely hard to install and later they become soft or slack. One thing is for sure. A good spring never changes its state so quickly.

There is a misconception among many air gunners that the hardness of a spring is directionally proportional to its power potential. “The harder it is, the better the spring will be”.

Please click on the following link to get an idea of what I’m trying to convey and for an idea of Plasticity (I do not wish to go in detail on this topic). http://en.wikipedia.org/wiki/Plasticity_(physics)

The third spring is good for working under high temperatures, and has a different chemical composition and manufacturing process and is usually very expensive. Due to high resistance of fatigue under high temperatures, this spring will last very long. The surface is smooth and very similar to the air gun spring we studied earlier, and is hard to differentiate with the naked eye!

That’s all for now folks!

Hope this little article helps you in choosing the right spring for your baby.

P.S: Part II will give more dept…..

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