Perfect vacuum sintering step by step [1/4]

This is the first part of an article that provides a comprehensive description of vacuum debinding and sintering giving you much opportunity to expand on this topic. Through a step-by-step approach, I want to make sure you are equipped with the technical knowledge to successfully master the challenges that lie ahead. I will also provide some useful tips on how to make the most suitable choices for your application and ensure you achieve perfect sintering.

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Advantages of vacuum sintering

Components that require sintering are often delicate, intricate, and easy to botch. Sintering involves the heat treatment of a material powder in order to ensure correct coalescence of the individual particles. This inter-particle bond is guaranteed by the atomic diffusion that is thermo dynamically favored by high temperatures. This treatment is essential for obtaining a high quality of the end material in terms of density, porosity and mechanical resistance. The properties of the end product, in terms of the surface finish of the part and mechanical properties, can be improved by carrying out sintering in a vacuum furnace. This will guarantee a reduction in oxidization of the individual particles and their subsequently improved coalescence.

Pressing of metallic powders, metal injection molding (MIM), 3D printing, and other similar technologies can benefit greatly from the superior quality and flexibility of vacuum sintering.

Sintering in a vacuum is an efficient way for making special shape components, greatly reducing machining purposes. The benefits of vacuum sintering can be summarized as follows:

• Clean, bright parts
• Superior quality
• Fewer defects
• Easy maintenance
• Production flexibility

Debinding: the first critical step of sintering

In order to go into the sintering phase without defects, the part needs to be debinded. So, the first decision regards the procedure for debinding the parts. The debinding process removes the primary binding material from the molded component. Typically, there are steps to the debinding process, and the part goes through more than one cycle to ensure as much of the binding material is removed as possible before sintering. The exact process depends on the kind of binder used. Apart from binders for which there are specific procedures, most of them are heat type processes, possibly preceded by a preliminary stage in water.

The question then arises of whether to carry out debinding in the same furnace as the sintering or to use a more specific furnace. The answer is open to interpretation and requires the assessment of various factors, including clean process requirements, fragility of parts, use of manpower, production requirements, energy consumption, and required process atmosphere. All of these factors are important for making a choice whether or not to perform debinding and sintering in the same furnace. And I will now analyze all of them in detail.

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Debinding and sintering: how to choose the ideal furnace

• Clean process requirements. Generally speaking, debinding and sintering are, to some extent, in conflict with one another, because debinding is an intrinsically &#;dirty&#; process, which means that substances other than the metallic powder we want to bring to coalescence, inevitably find their way into the furnace, while sintering must be as clean as possible, in that any substance other than the metallic powder can negatively alter the product's characteristics. As we will see further, there are highly effective techniques for resolving this conflict and performing both treatments in the same furnace. That said, it is advisable to check that these are suited to your application. If the binder that you use is particularly &#;difficult&#; or your application requires a higher than average purity, it may be necessary, or at least advisable, to carry out debinding in a separate furnace.
• Fragility of parts. It is worth remembering the parts become extremely fragile after debinding, and could break due to vibrations when being moved from one furnace to another. However, this can easily be resolved by carrying out a pre-sintering in the debinding furnace (which must be capable of reaching the required temperature, higher than that for debinding alone).
• Planned use of manpower. When debinding can be done in the same furnace as sintering, advantage can be taken of this opportunity to avoid using the manpower required to move parts from one furnace to the other. If the production requirements are high, this advantage could be extremely important, as it would mean that the furnace can be loaded in the evening, the debinding and sintering process completed and the completed parts removed the following morning without the need for a night shift. On the other hand, if there is only a minimum amount of production that can be carried out during the day and/or staff are in any case on duty for other reasons, this advantage becomes less relevant.
• Required productivity. If the production is so limited that it can be completed by a single small furnace, the purchase of a separate furnace for debinding could be an excessive financial burden, considering that below a certain limit, the cost of the furnace cannot be further reduced by lowering the useful volume. If, on the other hand, production is high, or if it increases significantly, in order to cope with this increase, purchasing a debinding furnace, which is undoubtedly less expensive when compared with the useful volume, could make financial sense. In this respect, it is also worth considering that the time required for thermal debinding can be longer than that for sintering, which is worth bearing in mind when determining furnace capacity. For example, if the debinding time is double that of sintering, then the capacity of the debinding furnace should also be double, in order to prevent bottlenecks. As well as volume ratios, that the ratio between individual lengths must also be studied, in order to facilitate transfer of the load from one furnace to another.
• Energy consumption. All other conditions being equal, it is obvious that carrying out both processes consecutively in the same furnace would deliver advantages in terms of energy-saving, as a saving would be made in the process of cooling the pieces in the debinding furnace and re-heating them in the sintering furnace. However, it is worth bearing in mind that the amount of energy consumed by the debinding furnace can be significantly different from that of the sintering furnace. Take, for example, the case of a typical hot-wall debinding furnace with a retort in which the load is processed, with the resistor fitted externally and a substantial layer of ceramic refractory material. If we compare its consumption with that of a graphite sintering furnace, we might find that they are quite similar, so the point made above might, in fact, be valid. If, however, the sintering furnace were metallic, and in particular, if the partial pressure level used during debinding were high, the consumption of the metallic sintering furnace would turn out to be higher, due to the limited efficiency of the metallic shielding in the presence of convection.


• Required process atmosphere. In previous comments we speculated that the debinding furnaces would be significantly cheaper than the sintering furnaces. This is certainly true if the process atmosphere is inert (typically vacuum, argon or nitrogen). If, on the other hand, an atmosphere with inflammable gases were required, such as hydrogen, for example, the safety measures applied could make the cost difference less significant, and the other points in favor of performing both processes in a single furnace would then prevail.

Do you have any additional questions about the debinding process? Just ask and I'll be happy to help you with useful information and tips about debinding and sintering.

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Vacuum sintering furnace is mainly used for sintering technology of semiconductor components and power rectifier devices. It can be used for vacuum sintering, gas protection sintering and conventional sintering. It is a kind of novel technology equipment in the series of special equipment for semiconductor industry. It has a novel design idea, convenient operation and compact structure. It can also be used in vacuum heat treatment, vacuum brazing and other processes in other fields. What note does vacuum sintering furnace have to use?

I. necessary skills for the use of vacuum sintering furnace

Vacuum sintering furnace is after vacuum filling hydrogen protection condition, by using the principle of intermediate frequency induction heating, the high temperature of tungsten crucible in the winding, by heat conduction to work on, suitable for scientific research, military units for hard metal such as tungsten, molybdenum and its alloy powder sintering molding. The installation site of electric furnace should meet the requirements of vacuum hygiene, the surrounding air should be clean and dry, and good ventilation conditions, the working site is not easy to raise dust. Vacuum furnace

Daily use skills of vacuum sintering furnace:

1. Check whether all parts and accessories in the control cabinet are complete and intact.

2. The control cabinet is installed on the corresponding foundation and fixed.

3. Connect the external main circuit and control circuit according to the wiring diagram and refer to the electrical schematic diagram.

4. Check the movable part of the electric appliance, and it should be free from jamming.

5. The insulation resistance shall not be less than 2 megohm.

6. All valves of the vacuum furnace must be in the closed position.

7. Control the power switch in the off position.

8. Manual pressure adjusting knob counterclockwise rotating head.

9. Put the alarm button in the open position.

10, according to the plan complete equipment of circulating cooling water connection, recommend that users always in and out of the device ShuiGuanChu access another spare water (or water), to prevent the circulating water has a power failure or lead to seal burn out.

Special attention should be paid to the following points when using the vacuum sintering furnace:

1, due to the mold, generally by the user should bring along their own, mold material selection basically high purity graphite, its pressure limit is 40 mpa, recommend that users use under 30 mpa safer, pressurized before should calculate the area of the upper and lower punch mould, and then converted to pressure, the specific formula is as follows:

The system allows pressure (ton) = top or bottom punch area * 30MPa

2. The thermocouple is tungsten-rhenium type, which will be brittle and untouchable after use. If damaged, it should be replaced in time. The model is the W2.

3. In winter, attention should be paid to the problem of keeping warm of circulating water, otherwise the water pipes will burst easily.

4. After use, the furnace body should be kept vacuum, because the heat preservation layer in the furnace is susceptible to moisture, and the vacuum should be maintained so that the vacuum can be pumped faster next time.

5. Due to the complexity of the equipment, it is recommended to use the equipment exclusively and exclusively, and strict pre-use training and post-use inspection for the novice should be carried out.

6. This hot-pressing furnace can also be used as a vacuum sintering furnace. When used in a vacuum sintering furnace, please note that after the crucible is placed in the furnace, don&#;t forget to cover the small cover between it after the cover of the heat preservation screen is put on. Otherwise it will burn out the electric furnace.

7, should be cleaned before operation observation window, clean the furnace wall, observe the water pressure, there is no damage to observe furnace graphite, electricity observation instrument display is normal, after testing the hydraulic system can work normally.

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8. The meter should be sent to the metrology department for calibration after one year of use.

Emergency method of vacuum sintering furnace

Cooling water anomaly

1. Confirm that the heating power has stopped.

2, leaking, outside the furnace cooling water exception, should take emergency measures, as soon as possible if you can guarantee the water, please continue to keep the vacuum, such as not take emergency measures to keep the original state, confirm the equipment to cool down.

3. When the cooling water is abnormal, the equipment is in a stop state and the emergency cooling water is immediately connected.

4, in the high temperature (over 200 &#; high temperature) shall be deemed to be, if the cooling water stop, if not an emergency water, water-cooled electrodes, heat exchanger, vacuum chamber and the pump shell may be damaged.

Stop compressed air

1. When abnormal alarm of compressed air occurs, the equipment is in a stopped state, and it should go to the spare compressor room as soon as possible to restore it to work.

2. In case of abnormal alarm of compressed air in vacuum, and the recovery takes a long time, the vacuum shall be terminated to stop the equipment.

All of a sudden power failure

1. In case of power failure, if the water is cut off, the spare cooling water shall be immediately connected to the water source.

2. If the equipment can be restored as soon as possible when it is not heated, heated and cooled, restart the equipment and keep running for a long time.

3. If the device is being heated and cooled, it can be restored as soon as possible, and restart the device. If it takes a long time, it will remain the same and allow the device to cool down naturally.

The heating power is off

1. The water is low, and when the water pressure is lower than 0.15mpa, the pressure gauge will alarm.

2. Ground fault.

3. Vacuum discharge. The connection between the water-cooled electrode joint and the heater must be firmly connected and well insulated from the reflection screen.

4. If the pressure in the furnace is 13.3-66.5Pa (this vacuum is easy to discharge). The reason of power failure can be regarded as the discharge caused by dielectric breakdown.

The aerated gas (argon or nitrogen) stops

1. Before the start of vacuum extraction, if the gas has been filled for a long time or cannot be filled, please confirm whether the gas pipeline is blocked.

2. If there is no problem with the gas pipeline, check the action of the solenoid valve and the gas charging valve. In order to ensure the safety of the equipment associated with it, the inspection shall be carried out after all the stops.

3. When the air filling into the vacuum chamber cannot be stopped, all gas systems including the gas supply valve and the distribution pipe shall be closed when the pressure relief valve ACTS as the pressure relief valve.

4. Confirm whether there is any air leakage in the gas filling pipe, if any, it will affect the product quality.

Vacuum chamber pressure deteriorates

1. When the vacuum exhaust time is longer than usual, the equipment should be stopped for inspection. According to the influence of different state of the vacuum indoor structure to lower the air, there are also cases of increased pressure.

2. Confirm the influence of air leakage and air release through pressure rise test or helium leak detection.

The above content is to introduce the necessary skills and the use of vacuum sintering furnace daily emergency method, in a vacuum and protective atmosphere, and for some metals, ceramics and refractory metal heating intermediate compound powder sintering, to obtain a certain density and has a certain mechanical properties of materials, generally USES two kinds of process; There is pressure sintering and no pressure sintering. Pressure sintering has the characteristics of high temperature, high vacuum and high thermal pressure

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