Why Do Industrial Machinery Use Pneumatics Instead Of Electrics?

Why do industrial machinery use pneumatics instead of electrics?

 

Pneumatic solutions have special advantages over electric ones in terms of power density, reliability, hygiene, explosion-proof, and moisture resistance. In some specific industrial situations, pneumatic solutions will be cheaper, more reliable, or safer than electric ones.

 

① The control is very convenient (gas is compressible, pneumatic is too soft and difficult to control; hydraulic pressure is okay);

 

② Wires are more convenient and space-saving than pipes, and there is no need to consider sealing;

 

③ The control system is generally simpler and has cost advantages. For example, multi-channel electric-driven switch actuators can be directly controlled by PLC, while pneumatic power must first use PLC to control multiple solenoid valves (that is, valve islands), and then the solenoid valves control the actuators, creating one more control level. The system is complex and costly.

 

 

 

In many industrial projects that I have been involved in, the advantages of pneumatics are as follows:

 

1. High power density, light and compact.

 

Under the same system weight and size, the power that pneumatic and hydraulic systems can transmit is generally greater than that of electric systems. This is mainly because fluid actuators such as cylinders and hydraulic cylinders have simple structures and mostly direct-drive loads. However, motors of the same power have a large mass of magnets and copper wires, and heat dissipation must be considered. Generally, there must be additional space between the motor and the load. The volume and weight of a reducer are generally larger than a gas-liquid actuator of the same power.

 

2. Simple, reliable and durable.

 

The main reason is as mentioned in 1. Generally, the transmission mechanism of pneumatic systems is simpler than that of electric systems. In addition to being compact and lightweight as mentioned in 1, it also brings another benefit: fewer potential failure points and higher system reliability.

 

In addition, fluid transmission also comes with an innate skill: overload protection. Pneumatic tools generally will not damage the tools, but electric screwdrivers and electric drills will burn out the motor if they are blocked for a long time; pneumatic and hydraulic actuating equipment are also very resistant to mechanical impact, such as a sudden sudden brake. Or if you bump into something, the actuating system is rarely damaged, but the electric drive system driven by the motor and the reducer is very likely to damage the gears.

 

The overload protection function of the fluid transmission system comes from two aspects: 1. The fluid is naturally flexible and elastic, and the system has natural buffering capabilities; 2. The fluid circuit is generally designed with fluid protection components such as pressure relief valves, which will automatically Take protective action to automatically clamp the maximum output of the system.

 

The innate skill of overload protection further improves the reliability of the system. This is the main reason why pneumatic and hydraulic equipment are generally stronger and more durable than electric equipment.

 

 

3. Health is mainly in the fields of food and medicine.

 

Motors generally do not meet food and drug grade health and safety requirements: various insulating paints, adhesives, and rare earth alloys. There are also various supporting electrical equipment, wires, electronic controls, connectors; supporting mechanical transmission equipment, reducers, and transmission components. In addition to the various materials involved in electrical appliances that smell toxic, the various lubricating greases, seals, and adhesives involved in machinery all fail to meet food and drug safety standards.

 

Because of the limitations of materials science, existing electromechanical systems are inherently difficult to achieve food or even pharmaceutical grade safety if they are to meet performance requirements: Toxic materials are difficult to bypass. If you have to do it, you can only rely on sealing: seal all equipment that cannot be made of safe materials, and use food and drug-grade materials for exposed parts.

 

However, this type of production lines run continuously, and many production lines even run continuously for 24 hours. Can these seals withstand such high-intensity use while meeting food and drug grade safety? For example, the shaft seal of a motor with tens of thousands of rotations must not only have good performance, be highly reliable, and be able to withstand 24x7 continuous operation, but the materials used in the entire sealing system must also be of food and drug grade. It is very difficult to meet the food and drug grade requirements, and even if it can be achieved, it is still very expensive.

 

Pneumatic machinery generally uses stainless steel or aluminum alloy, several sealing rings, and several plastic pipes. There are not many types of materials required, and electrical requirements such as insulation and magnetism are not considered. The mechanical requirements for seals due to intermittent action are not that great. It is harsh in terms of materials, and it is easier for the entire system to meet food and drug grade health and safety requirements. It is currently the most mature solution.

 

What's more, it won't burn out due to overload, which also eliminates a huge health and safety hazard. The material itself meets health and safety standards. Even if something breaks, slag falls into the product, or gas leaks, there is a high probability that there will be no quality and safety accidents due to contamination. This is called intrinsic safety. Therefore, it is easier and cheaper to achieve food and pharmaceutical grade safety with pneumatic systems than with electric systems, so pneumatic components are widely used in the production lines of these two industries.

 

 

4. Explosion-proof.

 

Many electrical equipment theoretically have the possibility of sparking during use, such as plugging, unplugging and loosening connectors, various coils will generate counter-electromotive force, and capacitors on circuit boards may suddenly explode. It would be very dangerous if a fire occurs in a flammable and explosive environment, such as an oil refinery or a coal mine. Therefore, the electrical equipment used in such occasions has a technical level called "explosion-proof level." Electrical equipment that meets the requirements of this level needs to be specially designed to ensure that each electrical link will not spark, or to ensure that even if it is sealed and isolated, The ignition is also isolated from the explosive environment. It takes a lot of manpower and material resources to make these designs and pass these levels of test certification. Therefore, electrical equipment with explosion-proof levels is generally much more expensive than ordinary electrical equipment with the same specifications, and can even be several times worse.

 

As long as the gas in pneumatic equipment is properly purified, flammable gas is not mixed, and there is no direct collision of metals, there is essentially no possibility of sparks. The same is true for hydraulic equipment. Therefore, in situations with explosion-proof requirements, using gas or hydraulic pressure as power, and placing the pumps, solenoid valves and other electrical equipment that drive the actuators in a remote pump room isolated from the explosive environment can avoid the use of expensive explosion-proof equipment. electrical equipment, thereby achieving the purpose of reducing system costs.

 

What's more, for some customized special applications, ready-made explosion-proof electrical equipment may not be available. In this case, gas-liquid drive may be the only option.

 

 

5. Waterproof and moisture-resistant.

 

Electrical equipment used in industrial automation environments is generally inseparable from low-voltage direct current. Such as driving solenoid valves, driving relays, driving small motors, not to mention the microcontroller itself. However, there is a big problem with DC electricity: it is prone to electrochemical corrosion.

 

DC circuits exposed to humid environments are prone to this situation: moisture condenses on the conductors to form local solution pools, and the conductors form electrochemical corrosion driven by DC voltage. For example, although the drive current on the solenoid valve is a PWM wave, if you low-pass filter it, you will find that it has a large DC component. In the industrial control field, in addition to the power circuit, there are not many strict DC currents on other circuits. Most of them are waveform signals such as PWM. However, these waveforms, especially the waveforms of the power circuit, contain a large DC component, so they will be affected by humidity. Electrochemical corrosion occurs in the environment. The most likely place for this type of electrochemical corrosion to occur is at various joints of wires. Therefore, welding should be used as much as possible when wiring DC circuits. Directly wrapping metal wires together is very unreliable. It will either rust and break after a few days, or it will cause poor contact after a while. On the contrary, the pure AC circuit has strong corrosion resistance.

 

Pneumatic and hydraulic equipment naturally does not have this problem. In principle, it is naturally moisture-proof:

 

① It is not charged, there is no electrochemical corrosion problem of electric drive, and there is no need to consider conductivity. All metal materials can be rust-resistant stainless steel or aluminum alloy;

 

② The internal environment is filled with working medium (compressed air, hydraulic oil) and is under positive pressure, and the working fluid circuit is connected with drying and dehumidifying equipment (such as a cold dryer), so the interior of the house will not be affected by moisture from the external environment. Influenced. Therefore, many of the actuating mechanisms of automatic car wash rooms are hydraulic, because water is everywhere. The food industry is similar, but in order to avoid contamination caused by hydraulic media, pneumatics are used.

 

It is not that electric equipment cannot be made into moisture-proof equipment, but there is a price to pay for sealing: watertight equipment is definitely much more expensive than non-watertight equipment. Coupled with the advantages listed above (such as hygiene), pneumatics can have a cost advantage in specific application scenarios (such as in some high-humidity food processing workshops).

 

In short, electronic control is a major trend. The solutions on the market are rich and mature, and they will become more mature and low-cost in the future. The pneumatic system only has comparative advantages in some occasions with special requirements. Therefore, as long as there are no special requirements such as food hygiene, impact resistance, explosion-proof, and moisture resistance, the electric system should still be given priority when designing the system.