PRODUCT CATEGORIES

Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

Vacuum Brazing Furnace

Which process should be used for quenching after vacuum carburizing?

Vacuum carburizing and quenching is widely used in power transmission and fuel system components of automobiles, transmission components of trucks and off-road vehicles such as gear sleeves, pinions, etc., transmission and power system components of aviation and spacecraft, and other components such as hydraulic pump cams, Bearings, valves and other industrial products.

The use of vacuum carburizing and quenching can usually eliminate slow cooling, reheating, and subsequent pressure quenching and sizing quenching. Copper plating or impermeable coating on the selected surface can prevent carburization of the surface.

Vacuum quenching + gas quenching

The vacuum carburizing and gas quenching system can greatly reduce the quenching deformation of workpieces of various sizes, especially compared with atmospheric carburizing and gas quenching. For example, comparing the tooth profile scribing of the gears of the automobile transmission system after two different processes of atmospheric carburizing and oil quenching and low-pressure vacuum carburizing and 15Bar nitrogen quenching respectively, it can be found that the distortion of oil quenching is larger and more serious. Difficult to control.

Low pressure vacuum carburizing and gas quenching for components such as silent gears can make the machining process more economical and easier. It is very important to reduce the quenching distortion of the workpiece without sacrificing the metallurgical, mechanical and physical properties. Therefore, it is imperative to replace oil quenching or salt bath quenching with gas quenching under the condition of ensuring cooling capacity. We firmly believe that the gas quenching method is very likely to replace the oil quenching method currently used by some heat treatment equipment in the near future.

Another reason why the gas quenching method can be the best choice is that we can adjust the cooling rate by changing the gas pressure, selecting different cooling gases, and changing the flow rate of the gas. A few days ago, it was thought that using the lowest possible air cooling pressure could reduce distortion.

Vacuum quenching + oil quenching

In many cases, oil quenching is one of the best processes to achieve good results, especially when the effective size of the workpiece is large and the alloy content of the material is low. In order to minimize the quenching distortion, the typical temperature range of the quenching oil in the oil tank is 55~190℃.

Configuration of oil quenching equipment

Since the equipment factor is the most important factor affecting the product quality stability in the heat treatment production process, the variability caused by the equipment should be paid attention to. Understanding and controlling the effects of various aspects of the heat treatment process is important for making deformation predictable (repeatable). The main focus should be on the following aspects: charge size/weight (uniformity); workpiece orientation (flat or vertical); heating rate; holding time and temperature; process selection (strengthening method, source of carbon); quenching Choice of medium (type, temperature, quality); design of quench tank (capacity, agitation).

In the oil quenching process, the size of the quenching oil groove not only affects the instantaneous heating rate of the quenching oil, but also affects the maximum heating rate of the quenching oil, but this effect is limited. If the workpiece has a small contact area in the quenching oil, then there is no obvious advantage to having a large capacity oil sump. From this aspect, the variability caused by the equipment is determined by the following factors: the circulation method used (blade agitation or pump spray), the circulation method, the heating method of the quenching oil and the capacity of the oil tank (heating rate). It also includes the type of quenching oil, heat transfer characteristics, initial temperature, and cleanliness of the oil pool (type and content of contaminants). When oil quenching is used after vacuum carburizing, a certain pressure should be applied to the surface of the quenching oil in the oil tank, which can affect the formation of oil vapor and help control the deformation of the workpiece.

Configuration of gas quenching equipment

During the gas quenching process, equipment-induced variability includes: whether the quenching chamber is a double or single chamber, the size of the quenching chamber, the internal design of the quenching chamber, the power of the fan motor, the heat transfer capacity of the heat exchanger, the gas and the cooling system design, fan design, etc. The gas quenching chamber of the double-chamber gas quenching furnace is an independent chamber (cold chamber) isolated from the heating chamber. This is not only because of the fast heat transfer, but the design of the quenching chamber can be optimized so that both maximum heating efficiency and maximum cooling efficiency can be taken into account.

The volume of the gas quenching chamber should be as small as possible (typical size is 3m³) to reduce the consumption of cooling gas. Especially when the cooling gas is no longer recycled, usually when nitrogen is used as the cooling gas, the size of the recirculation system (compressor and gas storage tank) should also be minimized. The interior design of the cold room should be as simple as possible to ensure high reliability and low cost, and must comply with ASME pressure vessel standards. Note that the power of the cooling fan motor should meet the requirements of the cooling gas circulation, but its size is limited by the cooling capacity of the cooling water.

The design of the heat exchanger of the gas quenching system must be suitable for high pressure air scouring and good heat exchange performance. When a thick workpiece with a large surface area is gas quenched at 20 bar, the heat dissipation in the first few seconds of the quenching process is particularly large. Thus, improper cooling water flow, low water pressure, or low flow rate will cause the cooling water to vaporize/boil in the heat exchanger. To make matters worse, blocked cooling water pipelines can cause damage to pipelines and heat exchangers due to rapid pressure build-up.

Controlling the temperature of the cooling water is important for consistent results throughout the year. In summer, the temperature of the cooling water in the heat exchanger will be high, and when the Rockwell hardness of the core of the workpiece is tested after quenching, a little soft spot will appear. Workpieces made of low hardenability steel are prone to the above situation.

Usually, for gas quenching, it is sufficient to keep the temperature of the cooling water below 27°C. However, for thick workpieces or some more difficult alloys, in order to obtain high core hardness, the temperature of the cooling water should be kept below 15 °C. Monitoring the water temperature at the outlet of the cooling water system during quenching is an excellent measure of cooling efficiency.

Related vacuum furnace brands: The vacuum oil quenching and gas quenching furnace produced by SIMUWU is a high-quality product for the vacuum heat treatment process of gears and other auto parts. The good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum heat treatment process, and the oil-cooled air-cooled system is efficient. Stable, ensuring uniform quenching and small deformation. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.