With the standardization of numerical control equipment, this work has always been considered as a matter for equipment manufacturers in product design and production. Therefore, it is often not paid enough attention in the process of equipment maintenance and renovation. Even the refurbishment design of the machine tool fails to mention its proper location. As a result, some equipment left behind in the maintenance, renovation and refurbishment of hidden dangers and regrets. With the continuous deepening of China's reform and opening up, domestic companies are increasingly using CNC equipment in the production process in order to adapt to market competition and improve their market response and response capabilities. In the increasingly important situation of maintenance and renovation work, the standardization issues in maintenance and renovation have had to be mentioned very urgently on our agenda. The following are based solely on "GB/T 5226.1 "Industrial Machinery Electrical Equipment Part I: General Technical Conditions" and "GB9061 "General Requirements for Metal Cutting Machine Tools"" and "JB4139 "Metal Cutting Machine Tools and Machine Tool Accessories Safety Protection Technology Conditions" "Standards, etc., illustrate the importance of standardization in the maintenance of equipment through examples of several problems.
I. About Personnel and Property Safety
This issue is very important. Whether in China's relevant national standards or CE certification of EC machinery and electronic products are all important contents of mandatory implementation. The “safety of personnel and assets, consistency of control response, and ease of maintenance†clearly stated that “it is not appropriate to sacrifice the above basic elements to obtain high performance.†(IEC 204.1, GB 5226.1) but in actual maintenance and renovation work, The following phenomena still appear:
Phenomenon 1: Randomly connect the midline to PE.
Only China's national standard GB/T 5226.1 is taken as an example. Section 5.1 clearly states that "In the interior of electrical equipment, there should be no connection between the neutral line and the protective grounding circuit. PEN's terminals should also not be used inside the mechanical cabinet. "We have encountered more than one case of retrofitted machine tools. Since the addition of the device requires an AC220V power supply, a phase in the three-phase 380V will be directly connected to the ground of the machine tool PE to form AC220V. After adding three-phase power devices, it will The center line it leads to is connected to the PE terminal. Obviously, if some place is disconnected due to a mechanical failure, the device becomes a live body with 220VAC voltage to ground. The device at this time can directly harm people.
In general, according to national standards, the machine tool manufacturer can only use the center line with the user's permission. When using the center line, it should be clearly stated in the mechanical technical documents (installation diagram and circuit diagram), and the midline should be provided with a single N. Insulated terminals are used.†Therefore, when the machine tool is being rebuilt, it must not be connected to the PE to ensure that the production and maintenance personnel are safe.
Phenomenon 2: Non-single power supplies Some devices add some mechanisms. Because of the ease of cabling, or the action associated with other devices, the power consumption of the new devices does not come from the underside of the device's power off switch. The "Standard for the Connection of Mechanical and Electrical Equipment to a Single Power Source" (GB/T 5226.1-5.1). In an emergency, disconnecting the power switch on the device does not cut off the entire power supply of the device. This is a potential hazard to personnel.
Phenomenon 3: The degree of protection of the electrical cabinet is not sufficient We have been commissioned to accept the acceptance of an equipment after transformation. The electrical cabinet of the equipment is one person high (about 1800MM) single door width of about 800mm, there is no door switch. No one can open the cabinet door and use it inside the cabinet without using any tools. The degree of protection of the devices in the cabinet is IP1.1. Obviously the equipment's electrical cabinet structure violates the following regulations in GB/T 5226.1-6.2.1: “The opening of the protective cover (ie, opening the door, cover, cover, etc.) is permitted only under the following conditions: a ) Shells must be opened by skilled technicians or trainees using keys or tools, and electrical equipment may not be suitable for operation.
b) Cut off the internal live parts before opening the protective cover; this technical requirement can be realized by the interlocking mechanism of the door and the cut-off switch (such as the power cut-off switch), so that the door can be opened only after the cut-off switch is opened and the door closed. Switch on. c) It is permissible to open the sheath without a key or tool and without cutting off the live parts only if all the live parts are in direct contact with a degree of protection of at least IP2X or IPXXB (see IEC 529). Therefore, the degree of protection of the electrical cabinet of this equipment is far from being "only allow skilled technicians to enter and comply with the special technical requirements (IEC364-4-41 IEC-4 IEC 439-1)." "Thinking of the hidden security risks from this.
Ventilation of electrical cabinets for equipment such as numerically controlled machine tools has long been recognized as a "positive pressure" method in the international community, but it has not been realized in the transformation of some machine tools. We once encountered a domestically produced machine tool and used negative pressure ventilation. The cutting fluid on the tool holders entered the cabinet along the snake skin hose. The moisture in the cable trench, the dust during cutting, etc. all enter the electric cabinet along each channel and gap. The machine tool used about one year or so, a layer of dirt on the circuit board and the electrical components inside the electrical cabinet, obvious signs of water vapor (condensation). The frequent failure of this machine has affected the normal production. It is clearly stated in GB 5226.1-13.3 that “the housing of the control device should generally have a protection level not lower than IP54 (see IEC 529).†Thus, it is necessary to pay for the non-standard operation.
Phenomenon 4: Under-protection of electrical equipment In the national standard GB/T 5226.1 thermal protection measures are required for continuous operation of 0.5kw and above motors. The failure of heat accumulation in the motor is an important cause of motor burnout. When the machine tool equipment is used in a process that does not match the motor: "time-current" protection devices, ie the time constants of the windings of the protection device and the device to be protected, differ greatly from each other, and often do not provide effective protection. We have seen in practical work that the maintenance and transformation of machine tools are often problems in this area.
Phenomenon 5: Control circuit burial hazards As we all know, for such signals involving people and equipment safety, such as emergency stop signal, overtravel signal, alarm signal, etc., should be “stop with power off†and “cut off the controlled device. All current-carrying conductors" (GB/T5226.1-9.4.2.1) We have encountered a privately-owned enterprise that has modified the design of the CNC machine tool. The limit travel switch uses the normally open contact, that is, when the machine tool does not exceed the normal working time, the line is "Disconnected" (low level). When the moving part overtravels the stroke switch, the circuit is closed (high level). During the debugging of the machine, the maintenance personnel is measuring the line, and the connected plug is unplugged. Can plug in, the result is always in the test line when the line is always open, the controller to confirm the machine "normal", so that the ball screw bearing housing crashed. It can be imagined that if the mobile chain is disconnected due to mechanical reasons during the user's use, who should bear the property loss or personal injury?
The "grounding of the relay coil side" in the control circuit has long been considered as an effective safety measure to avoid malfunctions. However, in some modified machine tools, the relay coils are provided with control contacts or one end of the power supply on both sides of the coil, and the contact point at the other end is very common. As the line is put on and off the machine tool equipment, if a certain part is short-circuited to the ground due to mechanical wear and insulation failure, the relay malfunctions and the consequences are unimaginable. It is worth mentioning that some electrical renovation designers, for the convenience of the diagram, often design the control output as an open collector circuit to directly drive the relay line diagram, but at the same time also buried the hidden dangers of the accident.
Phenomenon 6: Insufficient safety operation protection function When there is no protective door interlocking function for equipment that has splash risk, when it is necessary to confirm that the operator's hands have left the dangerous operation area, no two-handed control mode can be performed. When the phase loss causes the device to be burned without three-phase interlocking circuit breakers and three-way insurance is used, it directly constitutes a hazard to personnel and property.
Phenomenon 7: Inadequate warning signs Some modified machine tools have not been able to give corresponding warning signs in accordance with the requirements of GB 5226.1 - 18.2. It is often not well explained in the revised technical documents, and warnings were given only to the operators during the training.
Second, the convenience of maintenance
1. GB/T 5226.1 clearly states that “all aspects including guards, cutting/clamping, software and documentation together constitute industrial machinery†thus illustrating the importance of numerical control equipment for “documents/softwareâ€. It is treated as Part of the equipment is the "component" of the CNC equipment. The technical documentation plays a crucial role in the maintenance of the CNC equipment. The standard states that the manufacturer must provide the end user with the scope and content of the technical documentation. The change of structure must revise the original document to reflect the actual situation of the equipment, but in the actual work, it has been found that some machine tool equipment was rebuilt, especially some minor changes, and no corresponding revision or explanation was made on the relevant technical documents. The document is inconsistent with the actual situation. Some parts of the equipment have been changed several times to become "three nothing" products with wireless numbers, no device identification, no circuit or mechanical drawings. The formation of internal management and maintenance personnel between companies " The situation of non-self can't be repaired. And the equipment management department of general enterprises often The management of technical documents is rather strict, and the maintenance of “change records†has failed to attract sufficient attention.The longer the duration of this situation, the more serious the problem, the more obvious the dependence of CNC equipment on “concrete people†or specific maintenance units. As a result, the market competitiveness of enterprises has been reduced, and the development of enterprises has been restricted, so companies with numerical control equipment must pay special attention to whether the information provided by the transforming party meets the requirements of GB/T 5226.1─19 in the process of equipment reconstruction.
2. The weak awareness of standardization and the reckless implementation of national standards in construction do not add much to the cost, and it often takes only a little effort to pay a price. We once encountered a piece of equipment. The electrician tried to make the wiring easier. The line of insurance power was connected to the insurance gate and the load was connected to the insurance gate. When other personnel were repairing, after unplugging the insurance, they mistakenly believed that the insurance gate had been powered off. When the measurement was falsely alarmed, it was almost shocking. Obviously, failure to comply with standards will pose a threat to the safety of maintenance personnel.
We see that due to the large number of power connections and signal connections for machine tool equipment using plug connectors, there are also some problems with the use of plug-in connectors. If there is a violation of relevant safety standards, the plug on the incoming call side will be in the form of a pin and will be accepted by the receiving party. The plug uses the jack form, laying a hidden danger.
3. Failure to set device markings in accordance with the standards In some modified machine tool equipment, we found that the technicians of the technical renovation will directly write or stick the device identification on the device. In particular, some of the wearing parts will not be marked after maintenance and replacement of these devices, which will cause difficulties for the next maintenance work.
Third, understanding should solve the following problems
1. Being able to troubleshoot or achieve a function does not mean that you have the ability to repair or modify a CNC machine. Must also be familiar with the relevant national standards of the industry, especially for the content of personnel and property safety is clear and strictly enforced. For example, a clear understanding of JB4139 “Technical Conditions for Safe Protection of Metal Cutting Machine Tools and Machine Tool Accessories†and GB/T 5226.1 “Electrical Equipment for Industrial Machinery Part 1: General Technical Conditionsâ€. To meet the above requirements, only qualified to engage in the repair of CNC machine tools.
2. Standardization of repair or refurbishment work is very important. Many devices use 380V AC or 600V DC power supply, high voltage and high current, and many mechanical parts are associated with each other. In particular, numerical control equipment, if not carefully considered in the interlocking of protection and safety agencies, will eventually become a disaster.
Generally speaking, the state inspection and inspection of factory inspection and acceptance of machine tool equipment manufacturers is relatively strict, and some manufacturers of considerable scale have passed or tried hard to pass the "CE" safety certification of mechanical and electrical products and the ISO9000 series quality certification. Any new product design must be reviewed by the relevant standardization department. Therefore, it is relatively safe to install and use new machine tools and equipment (but some small-scale or some township and village enterprises also have to pay attention). However, when the machine tool is used for a long time, especially after several repairs or renovations, it can be ensured that the safety performance does not decrease. This is the responsibility of each equipment management and maintenance personnel and is the principle of our maintenance work. In JB4139 "Technical Conditions for Safe Protection of Metal-cutting Machine Tools and Machine Accessories", it is stipulated that any changes to the structure and function of machine tool equipment must comply with the requirements of this standard. Therefore, we must pay special attention to it.
3. Standardization is the guarantee of machine reliability. For many years, every person who is engaged in the production and processing of machine tools has put the reliability of the machine in the first place. Without reliability, there is no such thing as a CNC machine. The national standards have made more perfect provisions for the control methods, grounding methods, anti-jamming, fault tolerance, mechanical interlocking, and protection of dangerous components of CNC machine tools, effectively ensuring the safe and reliable operation of the machine tools. Our experience over the past few years has proven that the failure rate is low for machines with good standards. Conversely, failure rates for machine tools that do not comply with standards are high.
4. Effectively reduce maintenance costs. The time cost is the heavy head of the machine tool equipment repair cost. The CNC machine tool stop loss is generally 100-500 yuan/hour, and the large-scale machine tool is even thousands of yuan/hour. According to the requirements in the standard, complete and accurate, real technical data and complete maintenance records are important guarantees for quickly finding faults and shortening maintenance time. According to experience, according to the standard, the thinking is clear, and the road is familiar with traffic. On the contrary, there is no clue. If there is no record change, the wireless number, and no mark are more difficult to change in case of previous maintenance. Reliable protection measures are an important aspect of preventing damage to devices and devices. They often increase the number of protection links by a few tens of yuan in accordance with the standard requirements. This can avoid the loss of several hundred dollars or even several thousand dollars. Spare parts can be spared or not prepared. We have encountered accidents involving the burning of dozens of kilowatts of electric motors due to the lack of protection according to the standard, bringing high maintenance costs. There is also a device, the protection function is not perfect, there is no chain and alarm monitoring, running in danger, often is the mechanical movement of parts of the ground, hydraulic oil across the flow, a great waste, pollution of the environment, the monthly maintenance and shutdown several times, The manpower, material resources, and financial resources for workshop maintenance are mostly spent on this equipment.
The standardization work involves every equipment management and maintenance personnel, which is the embodiment of quality and technical capabilities. Let us work together to improve the standardization level of CNC equipment maintenance work and strive to cultivate a high-quality CNC equipment maintenance team.
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