Seven dangerous phenomena in the use of sheet metal CNC bending machine must be paid great attention
These problems are often encountered by us, but they are often overlooked. However, there are bigger problems, so it is very noteworthy.
Whether in our country’s relevant national standards or in the CE certification of EC mechanical and electrical products, it is an important part
of compulsory implementation. For “the safety of people and property, the consistency of control response and the convenience of maintenance”,
it is clear that “it is not appropriate to sacrifice the above basic elements to achieve high performance.” (IEC204.1, GB5226.1) However,
the following phenomena still occur in the actual maintenance and transformation work:
Phenomenon 1: Non-single power supply
Some CNC bending machine equipments add some mechanisms. Because of the convenience of wiring, or the action connection with other equipments,
the power consumption of the new mechanism is not from the power supply of the equipment to cut off the wire below the switch, but from the other leads,
which violates the standard stipulation of “connecting mechanical and electrical equipment to a single power supply” (GB/T5226.1-5.1).
When an emergency occurs, cutting off the power switch on the equipment can not cut off all the power supply of the equipment, which is a potential hazard to personnel.
Phenomenon 2: Unorderly connection of middle line to PE
Taking the national standard GB/T5226.1 as an example, paragraph 5.1 clearly stipulates that “within the electrical equipment, there should
be no connection between the middle line and the protective grounding circuit. The PEN terminal should not be used inside the mechanical cabinet.
We have encountered more than one case of modified machine tools, because of the need for AC220V power supply to increase devices, the three-phase
380V phase and the PE grounding terminal of the machine tool are directly connected to form AC220V, after adding three-phase electrical devices,
the middle line is connected to the PE terminal. Obviously, if somewhere is disconnected due to mechanical failure, the device becomes a charged
body with 220 VAC voltage to the ground. At this time, the equipment can cause direct electric shock injury to personnel.
Generally, CNC bending machine tool manufacturers according to national standards, “Only with the consent of users can use the midline.
Metal processing Wechat, the content is good, worthy of attention. When using the midline, it should be clearly shown in the technical documents
(installation drawings and circuit drawings) of the machinery, and a single insulating terminal marked with N should be provided for the midline.
Therefore, it is impossible to connect the middle line to PE in order to ensure the safety of production and maintenance personnel.
Phenomenon 3: Electrical equipment under-protection
In the national standard GB/T5226.1, thermal protection measures are required for motors with continuous operation of 0.5KW or above.
Failure of heat accumulation of motor is an important cause of motor burnout. In the process of machine tool equipment transformation,
the “time-current” protective device, which is not matched with the motor, is often not effective when the time constants of the protective
device and the winding of the protected device are quite different from each other. In our practical work, we can see that there are often
problems in the maintenance and transformation of machine tools.
Phenomenon 4: Insufficient protection level of electric cabinet
We have been entrusted with the acceptance of a modified equipment. The electrical cabinet of the equipment is about 800 mm in height
(about 1800 MM) and 800 mm in width. There is no door switch. Anyone can open the cabinet door and enter the cabinet without using
any tools. The protection level of the components in the cabinet is IP1.1. Obviously, the structure of the electric cabinet of the equipment
violates the following stipulations in GB/T5226.1-6.2.1: “Only under one of the following conditions can the protective case be opened
(i.e. door opening, cover, cover plate, etc.): a) The protective case must be opened by skilled technicians or trainees using keys or tools,
which may not be suitable for opening electrical equipment in operation.
- B) Cut off the live parts inside the shield before opening it; this technical requirement can be realized by the linkage mechanism
- between the door and the cut-off switch (e.g. power cut-off switch), so that the door can be opened only after the cut-off switch is
- opened, and the switch can be turned on only after the door is closed. (c) Only when the protection level of all live parts directly
- touched is at least IP2X or IPXXB (see IEC529), can the shells be opened without keys or tools and without cutting off live parts.”
- Metal processing Wechat, the content is good, worthy of attention. Therefore, the protection level of the equipment cabinet is far from “
- only skilled technicians can be allowed to enter and comply with special technical requirements (IEC364-4-41IEC-4-47IEC439-1).”
- The hidden safety hazards can be imagined.
Electric cabinet ventilation of CNC bending machine tools and other equipment has long been recognized as a “positive pressure”
mode in the world, but it has not been realized in some machine tool modification. We have encountered a domestic machine tool
with negative pressure ventilation. The cutting fluid on the tool holder enters the cabinet along the snakeskin hose. Moisture in cable trench,
dust during cutting and so on all enter the cabinet along the channels and crevices. The machine is used for about one year. There is a layer
of dirt and obvious water vapor (condensation) marks on the circuit boards and electrical parts in the electric cabinet. The frequent failure
of the machine affects the normal operation of the production. In GB5226.1-13.3, it is clearly stipulated that “the shell of the control
device shall generally have a protection level not less than
IP54 (see IEC529).” Therefore, we must pay a price for not acting according to the standard.
Phenomenon 5: Imperfect function of safety operation and protection
When the equipment with spatter danger does not have the function of protection door chain, it is necessary to confirm that
the operator’s hands have left the dangerous action area before the two hands control mode can be set up.
When the three-phase linkage circuit breaker is not installed in the burned electrical appliances due to the lack of phase and
three-way insurance is used separately, it directly constitutes a hazard to people and property.
Phenomenon 6: hidden danger of control line
As we all know, for persons involved