1. Heating temperature, holding time and cooling method: The phase transition temperature of the tin bronze plate from α→α+ε is about 320 ℃, that is, the heating temperature is higher than 320 ℃, and its structure is a single-phase structure, until it is heated to 930 The liquid phase structure appears around ℃. Considering the equipment used, the degree of oxidation of the workpiece after heating, and the actual processing performance of the workpiece after heat treatment, after on-site comparison and verification, the heating temperature of ( 350 ± 10) ℃ is more appropriate. The heating temperature is too high, and the workpiece is seriously oxidized.
If the temperature is too low, the strength and elasticity of the workpiece are high and the toughness is obviously insufficient, so it is not suitable for forming. Due to the large amount of furnace loading (230kg/35kW pit furnace), in order to make it heat through and obtain a certain strength and toughness, so as to facilitate the subsequent bending processing, the workpieces in each furnace need to be kept warm for about 2 hours after reaching the temperature. It can be air-cooled, or the workpiece can be left in the tempering barrel to cool slowly.
2. Identification of the effect of annealing treatment: Due to limited conditions, two methods can be used to easily identify the treated workpiece. One is to observe the color of the workpiece, that is, the well-treated workpiece changes from the original brass color to blue-black. The second is that the processed workpiece can be directly judged by bending it by hand. When bending, if the workpiece can be bent while having a certain strength and elasticity, it means that the annealing effect is good and it is suitable for forming. On the contrary, the strength and elasticity of the workpiece after treatment are high, and it is not easy to bend by hand, indicating that the annealing treatment effect is not good, and it needs to be re-annealed.
3. Equipment and furnace loading method: In order to achieve the purpose of temperature uniformity and anti-oxidation, tin bronze material workpieces are generally not suitable for processing in box furnaces without stirring fans. For example, under the condition of the same furnace load (furnace power is 230kg/35kW), the workpiece is treated in a box furnace without stirring fan and a pit tempering furnace with stirring fan, respectively. Under the same annealing process conditions of heating at ( 350 ± 10) ℃, holding for 2h and then air-cooling, the results of the two treatments are very different.
The workpieces treated with the box furnace have different brilliance, high strength and insufficient toughness, which are difficult to be bent. After processing the same batch of workpieces with a pit tempering furnace, the brilliance is more uniform, and the strength and toughness are suitable, which is conducive to subsequent processing operations. Therefore, for enterprises with limited conditions, the annealing treatment can be processed by a pit furnace, and a tempering barrel with a large capacity can be used for charging. The workpieces must be placed neatly to avoid deformation of the underlying workpieces due to pressure.
Post time: Jun-08-2022