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Hot Wound Springs Design Characteristics
Hot wound springs are coiled from wire that is pre-heated to a red hot state. In most cases this is normally from wire larger than ˝ inch. The same helical spring design formulas discussed on our other design pages are used for their design, except the modulus is changed to compensate for irregularities in the bar surface and contour.
For compression springs and extension springs the torsional modulus becomes 10,500,000 psi instead of 11,500,000 psi. For torsion springs the modulus of elasticity becomes 28,500,000 psi instead of 30,000,000 psi. If these springs made of centerless ground bars then you can use the conventional values of modulus of elasticity (E) and modulus of rigidity or shear modulus (G). The steel that is normally used in these springs include the high carbon spring steels, AISI 1085 and AISI 1095. Also used are many alloy steels such as AISI 5160, AISI 6150, and AISI 9260. Alloy steel is recommended for bars over 1 inch in diameter for better hardenability.
STRESS Hot wound torsion springs should be designed to approximately 20% lower stress levels than cold coiled springs which have beneficial residual stress. This is because hot wound torsion springs do not have the same residual stress pattern. This chart shows the maximum allowable solid stresses for hot wound compression springs in static service. The values can be reduced by 20% for any type of fatigue application. This is due to the surface quality and decarburization of standard hot rolled bars. If these springs are designed to work at high stress levels they should be made from centerless ground material and shot peened. Calculations Calculations on normal hot wound springs will not be as accurate as on cold wound springs because of the increased material tolerance and surface condition. The maximum solid length should be calculated as the total number of coils times the bar size. If there is a heavy forge and grind the solid length can be reduced to total coils less ˝ coil, times the bar size. Manufacture Load tolerances can be improved by the use of centerless ground material and tighter manufacturing processes. This does, however, add greatly to the cost of manufacture. Practical manufacturing tolerances for hot wound springs are given in the ASTM specification A-125-65, “Heat-Treated Steel Helical Springs”. Commonly, the ends of the bars for hot wound compression springs are forged with a taper to reduce the amount of grinding on the finished spring. If the accuracy of squaring is not important then grinding may not be necessary and thus provide a considerable savings in cost. Stay tuned for updated information related to Hot Wound Springs. Our team and visitors to spring-makers-resource.net will be contributing. Got some info you want to share? Please, go to our Contact Page and send it our way. Don't miss any updated information! Stay in touch by subscribing to Spring Makers Resource e-zine. Return from Hot Wound Springs to Advanced Design
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