We are the sole European distributor for Tohatsu Die Springs
Most problems that arise in the use of die springs usually result from improper application... failure to take advantage of and protect the features engineered into the spring.
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Die springs are produced under such careful controls that manufacturing problems have virtually been eliminated. Die spring failure is usually due to either poor spring design and manufacture, or incorrect application of the spring. The most common problem source is the use of die springs too close to, or beyond, the springs' physical limitations. The solution, of course, lies with careful selection of die springs for each application.
 Die springs are manufactured with ends ground and squared so that they stand on their own base and compress evenly under load. There is a positive relationship between the spring's outside diameter and the total length, which determines whether or not a spring will buckle under load.
Generally, if the free length is more than four times the mean diameter of the spring, it could have a buckling problem under compression. This is solved by providing guidance by a pocket, a rod, or both to reduce buckling. It is always recommended to provide guidance for any die spring.
Figure A provides information as to whether a specific spring with squared, ground ends is subject to buckling. The curve indicates that buckling may occur to a squared-and-ground spring, both ends of which are compressed against parallel plates, if the valves fall above and to the right of the curve.
Holes or pockets provided in the die for springs must be to a specified size. Springs increase in diameter as they are compressed. If the hole is undersized, a wearing or binding action will produce early spring failure.
Holes must have flat bottoms with square corners. This will allow the spring to work on a flat surface and provide uniform stress on the coils when the spring is compressed.
Working a spring over a rod provides good protection against buckling. Care should be taken to ensure the rod is smooth. If the rod is shorter than the spring, it should have a tapered nose so that there is no danger of the spring coils coming in contact with a sharp edge.
Care should be taken to make certain that any device used to contain or guide the spring is properly aligned on both sides of the die. Holes or rods that do not match can cause problems that create spring failure and damage to the tool.
Heat is a frequently ignored factor in spring failure or load loss. The maximum rated service temperature for our chromium alloy steel is 230°C.
Figure B: Approximate Percentage Loss of Load
Initial
Stress
MPa |
Carbon Steel |
Chromium Steel |
| 120°C |
177°C |
200°C |
120°C |
177°C |
200°C |
| 276 |
2.0 |
3.5 |
4.5 |
1.0 |
2.0 |
5.0 |
| 345 |
2.0 |
4.0 |
5.0 |
1.0 |
2.0 |
5.0 |
| 414 |
2.5 |
4.5 |
5.5 |
1.0 |
2.0 |
5.5 |
| 483 |
3.0 |
5.5 |
6.5 |
1.0 |
2.5 |
6.0 |
| 552 |
3.0 |
6.0 |
8.0 |
1.5 |
2.5 |
6.0 |
| 620 |
4.0 |
8.0 |
9.0 |
1.5 |
3.0 |
7.0 |
| 689 |
4.5 |
9.5 |
10.5 |
2.0 |
4.0 |
8.0 |
| 758 |
7.0 |
11.5 |
14.0 |
2.0 |
5.0 |
10.0 |
| 827 |
9.5 |
13.0 |
17.5 |
3.5 |
8.0 |
13.0 |
Figure B shows the percentage of load-loss due to heat and stress combinations. Thought should be given to the heat generated by the working die which can be significant in many applications. Heat absorbed by the tool can be transferred to the springs, resulting in a loss of load and premature spring failure.
Deflection beyond the manufacturer's recommendation can cause early spring failure. Check the press or die travel to be sure of the actual deflection to which the spring will be subjected. If it is beyond a safe limit, changes should be made without delay.
Each Metrol die spring is carefully engineered to perform within specific areas of work. Alterations to a spring, such as reducing its length or number of coils, grinding the inside or outside diameter, or placing restrictions on the movement of the coils can cause early spring failure.
Trying to alter a spring by grinding down its ends can change the temper of the material and negatively affect spring performance.
Altering springs from their manufactured state almost invariably leads to problems and failure. Our advice is: don't gamble an expensive die for a small saving on a cheap alteration.
Frequently, spring failure can be traced to corrosive elements. Reduction of material or pitting of the spring will reduce its useful life. Be alert to conditions that may effect the spring's surface such as rust, lubricants, soaps, chemicals, etc. Clean, protected springs give the best job performance.
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Metrol Springs can provide springs for strippers, pressure pads and other die components.
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