DE4104986A1 - Treating cast iron@ boilers, etc., for reduced residual stress formation - includes cooling boiler slowly and uniformly in insulated continuous heating furnace using conserved specific heat - Google Patents

Abstract

A process for cooling cast iron boilers or similar hollow bodies comprises removing the member from the mould after solidification at temps. above 600-650 deg.C and placing the member in a heat insulated continuous heating furnace. The member is then slowly and uniformly cooled to about 500 deg.C as a consequence of the conserved specific heat. USE/ADVANTAGE - Residual stress formation on cooling is reduced without the additional step of annealing which reduces costs.

Description

The invention relates to a method according to the preamble of claim 1.

Cast iron boiler sections and other hollow bodies cast with cores in a mold can have high residual stresses due to their geometry. Usually work they are not negative. However, it can happen that the residual stresses exceed a maximum, which then leads to mechanical damage to the hollow body can lead. This is particularly uncomfortable with boiler sections if the damage only occur during operation on the finished boiler block. Then there are elaborate assembly work required to remedy the defect.

Studies have been carried out to determine whether the cooling time in the form affects the degree of internal stress of boiler sections. Here there was no clear influence of different cooling times on the formation the residual stress is determined. This supports the well-known idea that to reduce the residual stresses that occur only by stress relieving or to be eliminated. According to previous knowledge, this is the only way reduce the tensions if they cannot be accepted. However, annealing is a complex and expensive process step, and with regard to the separate procedure and with regard to the Energy expenditure.

A possibility is to be created to avoid the residual stresses to reduce a separate annealing process.  

The method according to the invention consists in the application of the Claim 1 measure mentioned.

It was found that the residual stresses in the cast iron boiler sections reach their full final value after a certain time after casting. They do not change during the further cooling period. The critical Phase in which the form cannot be intervened therefore runs from Solidify until certain temperature values are reached. The boiler members will now after solidification at temperatures above 600-650 ° C the mold taken, d. H. as long as the formation of residual stresses in their first Stage is. The actually critical temperature zone is in a heat insulated Pass through continuous furnace. As a result of the inherent heat preserved here, it then takes place an evenly slow cooling, which builds up residual stresses encountered. Instead of an uninfluenced cooling in the mold, a quasi adiabatic cooling, whereby of course the temperatures in the continuous furnace are to be set specifically. A separate annealing process is avoided. Only when Temperature values around 500 ° C have been reached, which no further increase in the If you expect more residual stresses, the casting is quickly cooled.

Claims (2)

1. A method for the targeted cooling of cast iron boiler members and comparable hollow bodies for the reduced formation of residual stresses, characterized in that the boiler members are removed from the mold after solidification at temperatures above 600-650 ° C and fed to a heat-insulated continuous furnace and that they after even slow cooling down as a result of the conserved heat from about 500 ° C free cooling. 2. The method according to claim 1, characterized in that to achieve quasi-adiabatic cooling Temperatures in the continuous furnace using the internal heat of the boiler sections are kept at predetermined values.