Side Loading Of Compression Springs

[sbozy25]

Ok... I am not really sure how to phrase this question...

Has anyone here every tried to quantify the side loading that occurs in a compression spring? I ask because I have a few customers who are wanting me to tell them what the side loads are on the parts and how we plan to reduce it.

Well... our Instron will give me the test points, the load values, the position of said loads in an x,y,z coordinate system and the moments on these values. So I have been making graphs of these values and doing vector analysis to obtain my side load values. This works, but my god is it time consuming...

Next, after we figure these side loads we are all at a loss as to what to tell our coiler to do to correct these values. I mean there are so many factors that can go into the load value... hardness of the part, amount of coil clash, angle of the end coil, wire irregularities..... the list goes on.... No one is really sure where we should start looking... Anyone have any ideas?

 

[israelkk]

There is and will always be side load. Trying to minimize it and stuggle with it will increase the spring price many folds. Customers that insist on minimizing the side load do not see the whole picture of the system. A spring is only one part of the system and it should be simple and cheap. The solution is to use end fixing that will eliminate the side load effect. For example, many times for critical products where no side load is allowed on a part such as in a case of a valve spool, we arrange the spring load to apply through a small steel ball into a centered socket at the edge of the spool.

 

[sbozy25]

I understand, but this product line is a brake spring. It is under extremely high stress, and is a safety critical part. Unfortunately, side loads are a direct input to our fatigue life.

I suppose what I was wondering was this...

If you have calculated what your side loads are... how would you relate that back to the coiler? I know this question probably has a million answers... but I am at a loss for ideas. The only thing I can think of is making a matrix of the parameters affecting the load and change 1 at a time and test... Which will be expensive...

 

[israelkk]

I am a little bit confused are you worried that the spring exerts side loads on the brake or the brake exerts side loads on the spring?

 

[TVP]

sbozy25,

Obviously this is a complex subject, and you have the unfortunate task of making improvements in an area that does not have a simple formula, etc. I am assuming that these are cold coiled springs with a wire diameter less than 4 mm? What kind of wire are you using? Do you have a good understanding of the friction due to the wire/surface oxide/coating against the forming tools? This has a huge effect, and will be very important to quantify if you want to make any meaningful progress.

 

[sbozy25]

The spring sets in a cylinder located in the brake system. This cylinder is broken into 2 sections, top and bottom. The sections are seperated by a rubber diaphram. On the bottom side, air is pumped in and it actuates the brakes and keeps the spring in constant compression. However, if this air system fails the spring will engage against the diaphram and cause the brake to lock up. When this occurs the springs have a tendancy to exert side loads on the cylinder and the diaphram and this causes failure to the spring due to the impact....

 

[sbozy25]

TVP
Yes you are correct in the fact that it is not simple! Yes they are cold springs, however no... the wire size is up to 6mm. From there we will draw down to what size we require for each spring. They are made out of a very high quality Chrome Silicon wire with a smidge of vanadium for added strength. Yes, I do understanding of the cleaning, coiling, and coating process. What is nice, is we can place these springs in our instron and take them to the test heights and it will tell us loads at points and moments. What is hard is finding out how to relate that to the coiler to make them better!