Machinery's Handbook, 31st Edition
352 Disc Springs chromium-vanadium alloy steels such as AISI 6150 used in the United States. Similar alloys such as DIN 1.8159 and DIN 1.7701 (Germany) and BS 735 A50 (Great Britain) are used in foreign countries. Some disc spring manufacturers in the United States also use chromium alloy steel AISI 5160. The hardness of disc springs in Groups 2 and 3 should be 42 to 52 RC. The hardness of disc springs in Group 1 tested by the Vickers method should be 412 to 544 HV. If disc springs must withstand corrosion and high temperatures, stainless steels and heat-resistant alloys are used. Most commonly used stainless steels in the United States are AISI types 301, 316, and 631, which are similar to foreign material numbers DIN 1.4310, DIN 1.4401, and DIN 1.4568, respectively. The operating temperature range for 631 stainless steel is − 330 to 660ºF ( − 200 to 350ºC). Among heat-resistant alloys, Inconel 718 and Inconel X750 (similar to DIN 2.4668 and DIN 2.4669, respectively) are the most popular. Operating temperature range for Inconel 718 is − 440 to 1290ºF ( − 260 to 700ºC). When disc springs are stacked in large numbers and their total weight becomes a major concern, titanium α - β alloys can be used to reduce weight. In such cases, Ti-6Al-4V alloy is used. If nonmagnetic and corrosion resistant properties are required and material strength is not an issue, phosphor bronzes and beryllium-coppers are the most popular copper alloys for disc springs. Phosphor bronze C52100, which is similar to DIN material num- ber 2.1030, is used at the ordinary temperature range. Beryllium-coppers C17000 and C17200, similar to material numbers DIN 2.1245 and DIN 2.1247 respectively, works well at very low temperatures. Strength properties of disc spring materials are characterized by moduli of elasticity and Poisson’s ratios. These are summarized in Table 1. Table 1. Strength Characteristics of Disc Spring Materials
Modulus of Elasticity
Material
10 6 psi
N/mm 2
Poisson’s Ratio
All Steels
0.30
28-31 193,000–213,700
Heat-resistant Alloys
0.28–0.29
17 16 17 18
117,200 110,300 117,200 124,100
0.32 0.35 0.30
α - β Titanium Alloys (Ti-6Al-4V) Phosphor Bronze (C52100) Beryllium-copper (C17000) Beryllium-copper (C17200)
0.30 Stacking of Disc Springs.— Individual disc springs can be arranged in series and paral- lel stacks. Disc springs in series stacking, Fig. 3, provide larger deflection S total under the same load F as a single disc spring would generate. Disc springs in parallel stacking, Fig. 4, generate higher loads F total with the same deflection s than a single disc spring would have. n = number of disc springs in stack s = deflection of single spring S total = total deflection of stack of n springs F = load generated by a single spring F total = total load generated by springs in stack L 0 = length of unloaded spring stack Series: For n disc springs arranged in series, Fig. 3, the following equations are applied: F F S s n total total # = =
L H n t h n 0 # # = = + ^ h
(1)
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