DE3730398A1 - METHOD FOR ACCELERATED COOLING OF CASTING PARTS - Google Patents

Abstract

Subsequent to solidification, immediately after the greatest wall thickness of the casting has gone below the solidus temperature, the casting is separated from the mould and cooled at a rate of 18 to 20 K/min; upon reaching the temperature range of the transition from the preponderantly plastic to the preponderantly elastic condition in the greatest wall thickness, the casting is heated as quickly as possible to a temperature in the range below the eutectic transition and thereafter immediately cooled at 70 to 90 K/min. to a mechanical working temperature or to ambient temperature.

Description

Field of application of the invention

The invention relates to a method for accelerated Cooling of cast iron castings after the Solidification, which are used in all foundry plants can.

Characteristic of the known technical solutions

The central point of the casting manufacturing process is the Cast body formation, in which the liquid melt accordingly the geometry of the shape brought into the appropriate shape and by dissipating heat into a solid, form-forming Body is transferred. The process flow at the pouring point is decisive for the performance of the foundry, he sets the Conditions for the material and heat flow before and after technological molding and casting systems and has too high Manufacturing speeds and corresponding production capacities of modern foundries. The cooling sections  lengths of the molding lines resulted from the product from expl the cooling time of the individual cast body, the shapes flow number and the length dimension of the shape. If you keep that Heat transfer conditions between the casting and the mold, so increased production speeds lead to proportions tionally extended cooling sections. This corresponds to elaborate plant engineering solutions.

With the completion of the solidification, the form has its primary Design task accomplished. After a technologically time after completion of the solidification become castings separated by and form. After separation, others kick, mostly tightened heat extraction conditions. The technically real The heat removal rate that can be set is based on two criteria limited:

• 1. The temperature difference due to the different Wall thicknesses of a casting may be during the Cooling does not become so great that it increases too Internal stresses and, in extreme cases, distortion or stress crack comes.
• 2. In the case of structural changes in the solid state, it must not lead to an inadmissible increase in hardness.

Based on experience, the practical foundry operation usually proceed in such a way that stress and crack sensitive casting parts remain in the mold as long as possible, e.g. B. at Castings made of GGL up to temperatures <300 degrees Celsius. The amount of internal stress in a casting is dependent of its shape and the cooling regime. With complicated ge designed parts also occur when cooling in the mold Temperatures <300 degrees Celsius are still considerable tensions on. In extreme cases, the residual stresses significantly reduced by subsequent stress relief annealing.  

There have been numerous efforts to reduce the cooling times, especially for castings from iron-carbon foundries to shorten substances (Ruehl, R. et. al .: DD patent 1 41 123, DE-OS 31 00 028; Hilgeroth, DE-OS 33 23 839).

The proposed solutions are accelerated cooling of castings from iron-carbon materials from Temperatures <600 degrees Celsius from increased to own to avoid tensions and increases in hardness.

In the case of the Ruehl claim, the cast body and shape only separated after the eutectoid transformation. In the Hilge case The separation of mold and cast body becomes red at übereutek tooid temperatures, but then a Controlled cooling provided until the end of the eutek tooid conversion takes place slowly and only afterwards is accelerated. Thinner due to the cooling process Parts of the cast part take place for them the eutectoid Conversion much faster than in the stronger parts. This leads to conventional cooling of the cast body the form and also suggested by Ruehl and Hilgeroth procedure to ensure that the thinner casting par the highest, the strongest parts the lowest hardness exhibit.

Aim of the invention

The aim of the invention is to cool castings following the solidification a process shortening at ver to achieve better casting quality.

State the nature of the invention

The invention is based on the technical object, a Ver  drive to develop, which is a conventional way of working Significant reduction in cooling time and a decrease the cooling section length of modern molding plants at the same time early reduction in the spread of microstructure formation metallic matrix, the hardness and machinability as well as the Amount of residual stress allowed.

According to the invention the object is achieved in that the Cast body immediately after in the thickest wall the solidus temperature was fallen below by the Form separated and then immediately a controlled Ab cooling regime is subjected. Here, the casting with increased speed (18-20 K / min) in moving air cooled and as soon as the temperature in the thickest wall the temperature range from the transition from the predominantly plastic on the predominantly elastic material behavior of Fe-C- Alloys has reached 700 to 500 degrees Celsius, the same as soon as possible at temperatures in the area heated below the eutectic conversion. It will Heating times of <5 minutes are selected and a Temperature compensation between thin and thick castings lots or even higher temperatures in the thinner wall thick reached.

Immediately after reaching the temperature range below the Eutectoid conversion will rapidly cool the cast some (70-90 K / min) up to manipulation or room temperature performed.

The following advantages can be achieved with the method according to the invention be achieved:

• - the cooling time compared to conventional technologies can be reduced to about 10%
• - The residual stresses compared to the cooling in the mold  reduced to 100 degrees Celsius to 50%, d. H. on Orders of magnitude that otherwise only through additional Stress relief annealing can be achieved,
• - with Fe-C cast materials by accelerating the eutek tooid transformation in the thicker wall thickness of the casting the formation of the basic metallic structure between the strong and weak cast parts become more similar and thus differences in mechanical properties, in particular the hardness and thus the machinability reduced will.

Embodiment

The invention will be closer to the following embodiment are explained.

Castings in the form of a tenter frame are used in molds cast once from GGL 25. After a sub the casting temperature falls below the solidus temperature At about 1000 degrees Celsius, the casting becomes mold Cut.

With a conventional cooling in the molding box, the technologically possible unpacking temperature in the strong Cast part after 95 minutes at approx. 400 degrees Celsius reached.

After the separation of the mold and casting, the cooling air shower speed from about 0.4 K / s to about 2.0 K / s increased.

After temperature equalization between thin and thick cast batches, which by heating the Cast body at temperatures below the eutectoid temp reached in the annealing furnace, accelerated further  Cooling down. This cooling to room temperature is at Cooling rates of approx. 13 K / s in water with 1% Aqua-Plast made. The total cooling time is reduced to about 10 minutes.

Reduced in the cast according to the invention cooled the residual stress in the 20 mm cross-section is around 7.0 MPa In the 40 mm cross-section, the drop in residual stresses approx. 8.0 MPa.

The hardness difference between the 20 mm cross section and the 40 mm cross-section decreases during cooling speaking of the invention from 37 HB to 7 HB.

Claims (1)

Process for the accelerated cooling of castings following solidification, characterized in that the castings are separated from the mold immediately after the solidus temperature has fallen below the thickest wall thickness and then cooled at 18-20 K / min so that the castings when the temperature range from the transition from the predominantly plastic to the predominantly elastic material behavior in the thickest wall thickness is reached as quickly as possible to temperatures in the range below the eutectic conversion and then immediately cooled to manipulation or room temperature at 70-90 K / min.