Free Height Tolerances
Group |
t |
Tolerance for t (mm) |
1 |
<1.25 |
+0.10/-0.05
+0.03/-0.09 |
2 |
1.25 to 2.0
>2.0 to 3.0
>3.0 to 6.0 |
+0.15/-0.08
+0.20/-0.10
+0.30/-0.15 |
3 |
>6.0 to 14.0 |
+0.30/-0.30 |
Load Tolerances
The static load F must be determined at the proof test height of the Disc Spring. Calculation must be based upon the nominal material thickness of the Disc Spring t and not with the reduced material thickness t' . Measurements must be made during loading of the Disc Spring. The loading plates must be hardened, ground & polished. appropriate lubrication must be used during the testing
The tolerances on spring load
Group |
t |
Tolerance for t (mm) |
1 |
<1.25 |
+0.25.0 - 7.5 |
2 |
1.25 to 3.0 |
+0.15 |
>3.0 to 6.0 |
- 7.5 |
3 |
>6.0 to 14.0 |
+ 5.0 |
To ensure the specified spring forces, DIN 2093 allows the overall height tolerance to be slightly exceeded.
Theoretical vs Measured Characteristic of a Disc Spring
The characteristic of the individual Disc Spring is non-linear. Its shape depends on the ratio ho/t. At the lower portion of the deflection range the characteristic in practice depart slightly from the theoretical. When S/ho>0.75 the characteristic in practice again departs increasingly from the theoretical because the Disc Springs roll upon one another or upon the supporting surface and this leads to a continuous shortening of the lever arm. For this reason, the spring force is only indicated at Ss=0.75 ho in DIN 2093.
Tolerances for Spring Rates of Compression Springs
In standard compression spring applications, spring forces at the low and high ends of the scale normally determine the switching functions intended for a compression spring.
Practicable force tolerances as defined in DIN 2095, the established standard in many EU states and generally throughout the world, are stipulated for such applications.
In some cases, however, the decisive factor is specific force development after an adjustable switching point. This clearly relates to the increase or decrease in force per unit of spring travel, i.e. the spring rate.
Examples that spring to mind include spring balances, mechanical letter or diet scales
as well as suspension systems in automotive engineering applications.
Unfortunately, a very wide range of tolerances has been specified for spring rates to date.
In the United Kingdom BS 1726 is the standard, in America the M3 formula is used while in Japan JIS B 2707 is the decisive standard. All these standards apply to all types of compression spring and give rise to large discrepancies in specified tolerances.
In Germany, DIN 2096 Part 1 is the authoritative standard that applies only to helical springs on motor vehicle axles.
All the above formulae for calculating spring rate tolerance are outlined in Annex 1.
By considering the specified tolerances and comparing them to test results that were determined for ESF based on real springs in America, Denmark, Germany, France and Japan, we arrive at Annex 2.
The only effective way to derive correlations was to sort and compare all results corresponding to the number of active coils of the individual springs.
Trends indicate that the British formula for calculating spring rate tolerances as defined in
BS 1726 results in ever greater spring rate tolerances for springs with increasing number of active coils while the Japanese formula for calculating spring rate tolerances as stipulated by JIS B 2707 leads to precisely the opposite results, i.e. ever closer spring rate tolerances as the number of active coils increases.
In the same way as JIS B 2707, the German tolerance formula in accordance with DIN 2096 Part 1 for spring rates of vehicle suspension springs also leads to ever closer tolerances as the number of active coils increases.
The American M3 method indicates a trend similar to the Japanese JIS B 2707, however, it exhibits extreme values both for low as well as for high numbers of active coils.
With the aim of finding alternatives for an IWA document currently being prepared (i.e. tentative standard to ISO) for spring rate tolerances, the Japanese (end of March 2006) and the Americans (mid-April 2006) each submitted a revised proposal.
The Japanese proposed to split the spring rate tolerance formula of DIN 2095
THE TOLERANCE/COST RATIO
Acme Monaco is staffed and equipped to produce springs to extreme limits of precision. However, the end uses of most springs do not require more than "commercial tolerances."
These +/- allowances can result in economies while maintaining quality. Wherever commercial tolerances are acceptable, costs can be minimized. Commercial grade springs can often be produced on our automatic equipment. The following commercial tolerances are usually considered for springs like these shown.
MATERIAL SELECTION
Material can be selected as they relate to expected (a) cycles of stress, (b) temperature, (c) corrosion, (d) chemicals, (e) water and moisture, (f) special involvements. Commercial tolerances of materials vary with each wire diameter. For example: wire diameter .007" could be +/-.0002" while .090" diameter could be +/-.001"
DETERMINING FREE LENGTH
The overall length of an unloaded spring is its free length. The commercial tolerance of free length is determined by the Spring Index Number, which is the relationship of the spring diameter to the diameter of the wire from which it is made, and the number of active coils per inch (pitch dimension) in relation to the overall length. For example, a spring having 12 coils per inch with a Spring Index Number "10" has a free length commercial tolerance of +/-.030"
COIL DIAMETER
Coil diameter tolerance is determined by the diameter of the wire and the Spring Index Number. For example, springs made from wire with .035" diameter, having a index factor of "10", carries a commercial tolerance of +/-.007" for the coil diameter.
SINGLE AND MULTIPLE LOAD
Commercial tolerances of compression springs include +/- 10% of the load requirement. Springs with a multiple load carry a tolerance of +/- 10% on each load. For example, a spring with a free length of 2" working in the compressed state could have a specified load at 1 1/2" and also at 1". Commercial tolerance would be +/- 10% of each load
SPRING RATE
The spring rate is determined by the amount of force required to constrict a compression spring by one inch. Using the "LOAD" example, if the 2" free length spring required 1 lb. to compress it to 1 1/2", and 2 lb. to compress it to 1", its spring rate would be 2 lb., and its commercial tolerance would be +/- 3.2 oz. (+/- 10%).
GRINDING TOLERANCE
The grinding of compression springs provides squareness of closed ends. (Closed ends result from reducing the pitch of the end coils until they touch) The commercial tolerance for end grinding is +/- 3°
DISC SPRING TOLERANCES
TOLERANCE FOR THICKNESS MATERIAL C-1075 OR AISI 6150 Tolerances DO NOT Apply To Stainless See Note Below |
THICKNESS t |
TOLERANCE |
MM |
INCH |
INCH |
|
0.3
0.4 |
.0118
.0157 |
+.001
-.001 |
|
0.5
0.6 |
.0197
.0236 |
+.001
-.001 |
|
0.7
0.8 |
.0276
.0315 |
+.002
-.002 |
|
0.9 |
.035 |
+.002
-.002 |
|
1.0 |
.039 |
+/-.002 |
|
1.1
1.25 |
.043
.049 |
+.002
-.002 |
|
1.5
1.75 |
.059
.069 |
+.002
-.002 |
|
2.0 |
.078 |
+.002
-.002 |
|
2.25
2.5 |
.088
.098 |
+.003
-.003 |
|
3.0
3.5 |
.118
.138 |
+/-.004 |
|
4.0 to 16.0 |
.157 to .630 |
+/-.005 |
|
(Note: The tolerances shown in the table are for M series of material C1075 or AISI 6150. For tolerances on other series, such as Stainless, SP, AL, etc. consult factory.)
DISC SPRING TOLERANCES
OVERALL HEIGHT TOLERANCE |
Group |
Thickness Range
mm |
Thickness Range
inch |
Tolerance
mm |
Tolerance
inch |
1 |
less than 1.25 |
0.049 |
+0.10
-0.05 |
+0.004
-0.002 |
2 |
1.25 to 2.00 |
0.049 to 0.078 |
+0.15
-0.08 |
+0.006
-0.003 |
over 2.00 to 3.00 |
0.078 to 0.188 |
+0.30
-0.10 |
+0.012
-0.004 |
over 3.00 to 6.00 |
0.118 to 0.236 |
+0.30
-0.15 |
+0.012
-0.006 |
3 |
over 6.00 to 14.00 |
0.236 to 0.551 |
+/-0.30 |
+/-0.012 |
(Note: The tolerances shown in the table are for M series of material C1075 or AISI 6150. For tolerances on other series, such as Stainless, SP, AL, etc. consult factory.)
DISC SPRING HARDNESS RANGE:
FOR C1075 AND AISI 6150 |
Thickness of Disc |
ROCKWELL C |
MM |
INCH |
0.2 - 0.9 |
.008 - .035 |
46-51 |
1.0 - 4.0 |
.039 - .157 |
44-49 |
4.25 - 16.0 |
.164 - .630 |
42-48 |
For Stainless Steel and Inconel, consult factory
(Note: The tolerances shown in the table are for M series of material C1075 or AISI 6150. For tolerances on other series, such as Stainless, SP, AL, etc. consult factory.)
DISC SPRING TOLERANCES
OD and ID GUIDE CLEARANCE: |
OD / ID |
|
TOLERANCE(App.) |
mm |
inch |
MM |
INCH |
Up to 16 |
0.63 |
0.2 |
0.008 |
Over 16 - Up to 20 |
0.63 - 0.79 |
0.3 |
0.012 |
Over 20 - Up to 26 |
0.79 - 1.02 |
0.4 |
0.016 |
Over 26 - Up to 31.5 |
1.02 - 1.24 |
0.5 |
0.020 |
Over 31.5 - Up to 50 |
1.24 - 1.97 |
0.6 |
0.024 |
Over 50 - Up to 80 |
1.97 - 3.14 |
0.8 |
0.031 |
Over 80 - Up to 140 |
3.15 - 5.52 |
1.0 |
0.039 |
Over 140 - Up to 250 |
5.52 - 9.85 |
1.6 |
0.063 |
NOTE: Inside Guiding is preferred. Guide Bolts should be Rc55-60 ground and polished.
(Note: The tolerances shown in the table are for M series of material C1075 or AISI 6150. For tolerances on other series, such as Stainless, SP, AL, etc. consult factory.)
DISC SPRING TOLERANCES
OD / ID TOLERANCE: |
OD / ID TOLERANCES |
MM |
INCH |
Total Tolerances |
1.6 - 3 |
.060 to .118 |
.004 |
3.0 - 6 |
.118 to .236 |
.005 |
6.0 - 10 |
.236 to .394 |
.006 |
10 - 18 |
.394 to .709 |
.007 |
18 - 30 |
.709 to 1.18 |
.008 |
30 - 50 |
.1.18 to 1.97 |
.010 |
50 - 80 |
1.97 to 3.15 |
.014 |
80 - 120 |
3.15 to 4.72 |
.014 |
120 - 180 |
4.72 to 7.09 |
.016 |
180 - 250 |
7.09 to 9.84 |
.018 |
NOTE: For OD. Tolerance is Minus Value Shown. For ID. Tolerance is Plus Value Shown.
(Note: The tolerances shown in the table are for M series of material C1075 or AISI 6150. For tolerances on other series, such as Stainless, SP, AL, etc. consult factory.)
DISC SPRING TOLERANCES
LOAD TOLERANCE: |
|
THICKNESS RANGE |
TOLERANCE FOR LOAD |
GROUP |
MM |
INCH |
At Deflection=.75h |
|
1 |
less than 1.25 |
0.049 |
+25%
-7.5% |
|
2 |
1.25 to 3.00 |
0.49 to 0.118 |
+15%
-7.5% |
|
over 3.00 to 6.00 |
0.118 to 0.236 |
+10%
-5% |
|
3 |
over 6.00 to 14.00 |
0.236 to .551 |
+/- 5% |
|
(Note: The tolerances shown in the table are for M series of material C1075 or AISI 6150. For tolerances on other series, such as Stainless, SP, AL, etc. consult factory.)
