Welder safety and protection

During the entire welding operation, the welder needs to constantly contact the electrical device. For example, when replacing the welding rod, the welder's hand will directly touch the welding rod. At the same time, a large amount of time will stand on the weldment to operate, and the no-load voltage of the welding machine generally exceeds With the safe voltage, the probability of getting an electric shock increases. What is more dangerous is that the welding power supply is connected to the 380 / 220V power grid. Once the equipment fails or the high-voltage part is damaged, the high-voltage power in the network will be directly lost to the welding clamp, weldment and welder casing. , causing welder's electric shock accident. Therefore, the electric shock accident is the most important dangerous accident in the welding operation. Especially in containers, pipelines, cabins, boilers, and steel structures, metal is surrounded by them, and there is a greater risk of electric shock.

According to the way the human body touches the live body and the way the current passes through the human body, the shock can be divided into the following situations.

(1) Low-voltage single-phase electric shock   The human body touches the electric shock accident of a phase charged body on the ground or other grounded conductors and other parts of the human body.

(2) Low-voltage two-phase shock   At the same time, the human body touched the electric shock of the two-phase electrified body. At this time, since the human body can receive voltages as high as 220V or 380V , the danger is high.

(3) Step voltage shock   When the live body is grounded and a current flows into the ground, the current generates a voltage drop in the soil around the ground point. The voltage that appears between the two feet around the ground point is called a step voltage. The resulting electric shock accident is called a step-voltage electric shock. A high step voltage may occur near a high-voltage fault ground or near a ground device where large current flows.

(4) High Voltage Shock   For high-voltage electrical equipment above 1000V , when the human body is too close to it, high-voltage electrical energy penetrates the air and causes the current to pass through the human body. At this time, it is accompanied by a high-temperature arc that can burn people.

First, the welding contact electrical mechanism

1 , safety voltage value

Under normal circumstances, the minimum allowable current for men is 9 milliamperes, and for women, 6 milliamperes. In the case of quick-disconnect protection with protection against electric shock, the short-term allowable current of the human body can be considered at 30 mA. Human body resistance can be considered from 1000 to 2000 ohms. Accordingly, the upper limit of a predetermined safe voltage state value: in normal operation, or fault conditions, should not exceed two conductors or any alternating current (50 Hz to 500) between a conductor and ground 50 volts rms. One of the criteria for this rule is that the human body allows a current of 30 mA and the body resistance to be 1700 ohms.

2 , a power shock

AC welding machine primary voltage is generally single-phase 220 volts or three-phase 380 volts, power frequency 50 Hz. Voltage value greatly exceeds the safety voltage (50 V AC), the greatest risk is the frequency band, a great danger of electric shock.

3 , output welding voltage and electric shock

According to national standards, AC welding machine no-load voltage ≤ 80 volts, the actual general is 70 ~ 90 volts. Obviously, the no-load voltage of the 70- to 90- volt AC welder is also greater than the upper limit of the safety voltage ( 50 volts), and people are equally at risk of electric shock. In addition, because of the wet environment, the wet skin, and the long time of electric shock, the voltage of 70 to 90 volts will increase the risk of electric shock.

Second, the cause of welding contact with electricity

1 、 Causes of direct contact with electricity during welding

(1) The hands or parts of the body are exposed to live parts such as electrode holders, welding rods, welding torches, etc. while replacing electrodes, motors, welding workpieces, and the feet or other parts of the body are not well insulated to the ground or metal structures, especially in the container pipelines. In places where there is rain, humidity, or where the body has a lot of sweat, welding can easily occur.

(2) An electric shock has been caused by the exposed hands or parts of the body touching exposed wires, terminals, wires, plates, and wires or cables that have been broken or have failed insulation.

(3) Electric shock caused by welding near a high-voltage power grid.

2. Reasons for electric accidents between contacts during welding

(1) The electric welding equipment leaks electricity, and the human body touches the shell that was charged due to electric leakage and the electric shock occurs.

Reasons for leakage of welding equipment:

1 Coil leakage due to insulation damage due to rain or moisture.

2 The device generates heat or corrosive substances due to overload or internal short circuit, resulting in reduced insulation and leakage.

(3) Electrowelding equipment causes mechanical damage to the insulation of the coil or lead due to vibration or impact, and the damaged conductor is connected to the iron core or casing and leaks.

4 Due to the chaotic management of the workplace, small metal objects (such as iron wire, iron chips, bolts, nuts, welding rods, and the like) were dropped into the wire, and the wires were touched at one end, and the other end hit the case or iron core and leaked.

(2) Insulation damage between the primary winding and the secondary winding of the arc welding transformer, mistakenly connecting the output end of the transformer to the power grid on the input side, or wrongly connecting an arc welding transformer with an input voltage of 220 volts to the 380 volt power grid, The human body touches the bare conductor of the welding circuit and the electric shock occurs. Improperly connecting the phase line to the device chassis will cause the device chassis to become live and an electric shock will occur.

(3) Electric shocks are caused by cables, switches, etc. that have been damaged by insulation.

(4) An electric shock occurs due to the use of metal structures, pipes, rails, overhead crane hooks, or other metal objects in the factory building as welding circuits.

Third, the welding equipment safety requirements and inspection

1. The no-load voltage of the welding equipment must meet the requirements of the welding process and at the same time ensure the safety of the welder's operation.

2. The power or capacity of welding equipment can meet the normal welding under a given welding condition, and a separate control device is provided. The control device should be able to reliably cut off the dangerous current of the equipment to ensure safety. Installation space for welding equipment and attachments should ensure easy and safe operation.

3. The insulation resistance of the live parts of the welding equipment to the ground, the shell, the phase and the phase, and the wire shall not be less than 1 megohm.

4. There must be intact isolation and protection devices for exposed parts of the welding equipment, such as protective covers and insulation panels.

5. The structure of the welding equipment is reasonable and easy to maintain. The joints and connectors should be firm and reliable.

6. Under normal condition, the metal shell of the welding equipment without electricity must adopt protective measures of zero protection or grounding.

Fourth, the safety requirements and inspection of welding tools

1 , welding cable

(1) In the rubber-insulated outer layer of the multi-filament copper core, the insulation resistance must not be less than 1 megohm.

(2) The cable should be light and flexible, and it can be bent and twisted freely to facilitate the welding operation.

(3) The cable should have good resistance to mechanical damage, oil resistance, corrosion resistance and other properties to meet the needs of the welding work environment.

(4) The length and cross section of the cable shall be selected according to the provisions of the welding work conditions to avoid overload.

(5) It is best to use the entire cable. When used with short roots, the number of joints should not exceed two. Copper conductors shall be used for joints and the resistance shall be small, and the joints shall be wrapped with insulating cloths.

(6) The contact between the cable and the equipment, welding clamp, torch, and workpiece should be good.

(7) The cable should be checked regularly for its insulation properties, and it is usually appropriate to use it once every six months.

2 、Pliers

(1) The structure is light and easy to operate.

(2) The insulation performance and heat insulation performance are better.

(3) The connection to the cable must be simple and secure, and no wires should be exposed to prevent electric shock.

3 , personal protective equipment

Welders' personal protective equipment includes: overalls, protective gloves, insulated rubber shoes, and insulating pads.

(1) The length of the protective gloves must not be shorter than 300 mm. The use of soft leather or canvas. Protective gloves should be kept intact and dry.

(2) Insulated rubber shoes should be kept intact and dry.

(3) The mask should be made of metal material as little or as little as possible, and non-useful metal parts should ensure that they cannot touch the human body during normal use.

(4) Work clothes should be kept completely dry, the cloth should be strong and wear-resistant, and the fire resistance should be good, and no static electricity should be generated.

(5) In welding of boilers, containers, pipes, etc., insulation pads should be used to prevent electric shock. Lights must use safe voltage power, and should not exceed 12 volts in general .

V. Safety Measures for Preventing Electric Shock

1. Strengthen the electrical safety technical education for welders.

2. The connection and dismantling of welding equipment and power lines and the electrical maintenance of welding equipment must be performed by electricians. Welders are not allowed to handle them without authorization.

3 , do a good job of isolation and protection. Welding equipment should have good isolation and protection devices to avoid contact with live sports people. The terminal out of the box shall be covered with a protective cover; the device with the pin hole connector shall be concealed in the plane of the insulating plate; the length of the power cable of the device should be as short as possible, generally no more than 2 to 3 meters. If there is a temporary need for a long power cord, isolate it with a porcelain bottle on a wall 2.5 meters above the ground . Do not drag the power cord to the ground. Keep at least 1 meter between the equipment and between the equipment and the wall. A wide passage; the passage between the welding equipment and the power transformer must not be less than 1.5 meters in width .

4 , to maintain good insulation. For welding equipment, power cords, welding cables, and welding tools, etc., the insulation properties (including insulation resistance, pressure resistance, leakage current, up-down loss, etc.) must be regularly checked.

5 , install automatic power off device.

6 , to strengthen personal protection, so that protective clothing, protective gloves, insulated rubber shoes and other safety requirements.

7. Take protective grounding or zero-crossing measures.