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Application of Vacuum Annealing Furnace in Annealing of Titanium and Titanium Alloys

In recent years, rare metal materials, especially titanium and titanium alloys, have been widely used in aerospace, navigation, nuclear power, petrochemical and other fields. These industries have extremely high requirements for the quality of titanium materials. Vacuum annealing is the intermediate and finished product production. Important process. Perform stress relief or recrystallization annealing in a non-oxidized and non-polluting state to eliminate work hardening and restore plasticity. There are many methods of heating annealing treatment, but the use of vacuum annealing to anneal titanium is a relatively new technology and process in the field of rare metal processing. It is clean with heat treatment, economy, pollution-free, non-oxidation, and small deformation.
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2. Performance Characteristics of Vacuum Annealing Furnace

2.1 Advantages of vacuum annealing furnace

Compared with general atmospheric annealing furnaces, why vacuum annealing furnaces are more suitable for annealing heat treatment of titanium and titanium alloys?

The main advantages are as follows:

1) The material hardly produces surface oxidation and pollution;

2) Not only can it retain the original surface quality, in most cases it can also improve the surface quality;

3) The wide operating temperature range is suitable for different treatment processes;

4) Small deformation of the workpiece;

5) Only a small amount of heat diffuses to the surrounding environment to greatly improve energy utilization;

6) Very low air pollution;

7) Safe operation and easy maintenance

2.2 The Main Performance of the Vacuum Annealing Furnace

The performance of the vacuum annealing furnace is mainly reflected in the following parameters: deflation, evacuation speed, ultimate vacuum and leakage rate.

2.2.1 Deflation

Outgassing is a phenomenon in which materials slowly evaporate in a vacuum. It is the main issue that needs to be considered in terms of vacuum performance. In a vacuum system, there may be molecular layers formed by the accumulation of liquid and gas on the surface of any solid material. These molecular layers gradually evaporate as the pressure decreases. Inert gases and volatile solvents outgas relatively quickly. Water vapor and oil will adhere to the surface and evaporate after several hours. Dust particles, porous materials and other foreign objects increase the surface area of the system and can cause more outgassing.

Temperature and radiation will provide enough energy for some absorbed molecules to move them off the surface. Increasing the furnace temperature will gradually release molecules that would otherwise remain on the surface at low temperatures. Therefore, the outgassing phenomenon will increase as the furnace is heated. Lowering the furnace temperature or maintaining a constant temperature can reduce this situation.

Keeping clean is the key to reducing outgassing. In addition, use inert gas or nitrogen to purge and remove the internal air, which can avoid the formation of a water vapor film when the surface of the system is exposed to the air. This effect can also be achieved by heating the inside of the furnace cavity after it is opened. Minimize the number of openings of the oven cavity, especially when not in use in humid weather, to maintain a vacuum. These measures can reduce the occurrence of outgassing and improve the performance of the vacuum annealing furnace.

2.2.2 Pump Down Speed

The evacuation speed is the time for the vacuum valve to open the vacuum chamber to reach the specified force when the furnace chamber is at atmospheric pressure. It is a method of measuring system performance under any pressure (including pumping heavy gas). In order to obtain reproducibility, the furnace cavity should be cleaned, emptied and vented, and each vacuum pump has been running for enough time to reach the full suction speed.

2.2.3 Ultimate Vacuum

The ultimate vacuum is the vacuum state obtained by actually completing the deflation. At this time, the gas flow caused by the leakage is balanced with the ability of the vacuum suction system to exhaust at a prescribed pressure. In order to maintain correctness, vacuum measuring instruments must be sufficiently sensitive and accurately calibrated.

Raising the furnace to its maximum temperature speeds up the deflation of the system. After heating the furnace under vacuum and cooling to room temperature, the true ultimate vacuum and leakage rate can be measured. The ultimate vacuum of the vacuum pump is called “Ultimate Low Pressure”, which is a good way to obtain the isolation performance of the suction system.

2.2.4 Leakage rate

Leakage rate refers to the rate at which the pressure in the vacuum chamber rises when the vacuum is closed. It includes two aspects, the rate of leakage and the rate of deflation. Leakage rate is the pressure rise caused by the flow of gas through the actual leak point in the cabin. The deflation rate (including virtual leakage) is gradually approaching zero as the cabin is emptied. Virtual leakage is the volume entrained in the vacuum bulkhead slowly leaking gas into the cabin.

The leakage rate is usually measured in micron mercury column (μmHg) per hour, and the leakage rate does not exceed 5μumHg per hour. Measure the furnace chamber pressure. When the speed rises, empty the furnace chamber and start the cycle heating. After the venting is complete, stop heating until the pressure remains constant (ultimate vacuum), then close all the vacuum valves and press the cycle stop button to isolate the furnace chamber. This can minimize the impact of closing the valve] while keeping the system balanced. After one hour, measure the vacuum again to calculate the pressure rise per unit time.

3 Application of Vacuum Annealing Furnace

3.1 Equipment Overview

Vacuum Annealing Furnace is applied for annealing and aging treatment of a variety of alloy materials, devices (tungsten, molybdenum, niobium, copper alloy, etc.), magnetic materials, electrical steel, magnetic alloy, stainless steel, heat-resistant alloys, copper and its alloys, hydrogen storage alloy, active and hard molten metal. It can also be used for vacuum sintering of magnetic material, diamond, hydrogen storage material reduction. The control system was controlled by PLC, temperature was controlled by intelligent temp controller, accurate control, high automation. User can choose auto or manual undisturbed switching to operate it, this vacuum furnace has abnormal condition alarming function, easy to operate.

3.2 Technical Parameters

When the furnace is clean, dry, empty and degassed, the following indicators can be achieved:

Max. Temperature: 1300℃

Temperature Uniformity: +5℃

Ultimate Pressure: 6.7*10-3Pa

Temperature Uniformity Size (W*H*L): 1100*600*3000mm

Loading Capacity: 3000Kg

Pressure raising rate: 0.67Pa/h