The chips and fine powder produced in the process of machining magnesium alloy have the danger of combustion or explosion. Because of the high thermal conductivity of magnesium, the friction heat can be quickly lost, and it is difficult to reach the ignition temperature. But in the finishing stage, because of the large specific surface area of the fine chips and powder, it is easy to reach the ignition temperature and cause combustion or explosion accidents.
In the process of magnesium alloy machining, the factors that affect the chip temperature rising to flash point or burning are: (1) machining speed; (2) high relative humidity; (3) too small feed rate or cutting amount; (4) too long pause time; (5) too small tool back angle and chip holding space; (6) high cutting speed without using cutting fluid; (7) metal cutting (8) magnesium chips accumulate around or under the machine tool, etc.
The central task of magnesium alloy safety production is to prevent combustion and explosion of magnesium dust, magnesium powder, magnesium scraps and light magnesium materials.
1、 Safety management requirements
(1) The production site requires high space, good natural ventilation, bright and spacious.
(2) Building facilities should be divided into several independent areas with relative safety distance.
(3) Inflammable and explosive materials are not allowed to be stored in and around the production site.
(4) The operation area and management area shall be equipped with corresponding fire-fighting facilities and equipment. The fire signs are obvious, easy to use, and should be maintained by special personnel.
(5) Strict fire and water control must be implemented in the operation area to prevent the generation of sparks and sparks.
(6) The installation of power lines and electrical equipment must comply with the provisions of national safety regulations, and be equipped with appropriate over-current power-off devices.
(7) The wire arrangement and joints must meet the requirements of the specification, and no random connection and erection is allowed, and the possible lightning protection and anti-static measures shall be taken. Dust collection equipment, exhaust fan and lighting must be riot proof.
(1) The operators must receive corresponding safety training before going on duty and pass the examination before going on duty.
(2) Before operation, operators must wear labor protection articles correctly according to regulations.
(3) Operators are not allowed to work with diseases or after drinking. Smoking is prohibited in the operation area, and fire, water and prohibited articles are not allowed to be brought into the operation area.
(4) The production site must be kept clean and free from oil and water stains. Magnesium scraps, magnesium slag, flash, light and thin materials must be cleaned up once every 2 hours, and transported away in special transit containers for harmless treatment.
(1) The warehouse of magnesium products and materials is suitable for miniaturization, segmentation and decentralization. The stacking height of magnesium ingots should not exceed 5.5m to prevent heavy losses caused by magnesium alloy fire due to excessive storage.
(2) The waste of magnesium should be stored in a special warehouse, and the stacking should not exceed 1.4m3, and it is suitable to be stored in a container covered with flame retardant.
(3) Oxidants, reducing agents and flammable substances should not be mixed with magnesium products and materials.
(4) It is strictly forbidden to bring fire source, fire and water into the warehouse to prevent magnesium products and materials from being drenched, soaked and damped, and keep ventilation and heat dissipation.
(1) Contents of fire safety measures. Safety first, combination of prevention and elimination. Three understandings and four abilities: know how to call the police; know the fire fighting knowledge of magnesium and magnesium alloy and the harmfulness of magnesium alloy combustion and explosion; know how to find hidden dangers; know how to set up and maintain fire fighting equipment; know how to call the police; know how to correctly use fire fighting equipment; know how to put out early fires.
(2) "Three uses", "Three Preventions" and "four harms" of magnesium fire protection. "Three uses" means "d extinguish" (Class D fire extinguisher), dry sand and covering agent; "Three Prevention" means fire prevention, waterproof and high temperature prevention; "four hazards" means strong light, high heat, rapid combustion and water explosion.
(3) Eight measures for magnesium fire protection: 1) use D-class fire extinguishing, dry sand and covering agent as early as possible to put out the initial fire; 2) alarm; 3) power cut; 4) cooling; 5) water prohibition; 6) air isolation; 7) escape from danger; 8) prevent fire expansion.
2、 Precautions in actual processing
Precautions for machining
(1) Keep the cutting tool sharp and the front and back corners are suitable;
(2) The strong chip of large feed tool is used to form thick chip and avoid small feed;
(3) When the feed rate is small, mineral oil cooling is used to reduce heat generation;
(4) At the end of the chip, the tool should be withdrawn immediately, otherwise the workpiece will continue to rotate to form small chips, which are easy to catch fire;
(5) Try not to use chip liquid, especially water-soluble chip liquid;
(6) In the case of high-speed chip production, compressed air or carbon dioxide gas can be blown;
(7) The machine tools near the processing machinery should be kept dry;
(8) Clean the chips frequently and store them in steel drums with covers;
(9) Before machining, the sand or other hard objects adhered to the casting should be clear;
(10) Avoid the tool hitting the steel inlay and causing sparks;
(11) Smoke and fire are not allowed to be near the processing area;
(12) It is not allowed to accumulate chips on the machine tool or work clothes. The dust and chips should be kept in a covered flame retardant container with labels;
(13) Ensure that there are sufficient fire fighting facilities where the operator can reach.
Precautions for grinding, grinding and polishing
(1) The operation is carried out in a dry state. When grinding fluid is necessary, acid free oil should be used to eliminate the powder immediately.
(2) the surface of chromate should not be lapping; the surface film of chemical treatment should be removed.
(3) In the grinding machine of magnesium, do not grind iron products and other spark prone materials, but use non-ferrous metal products. Special grinders shall be used.
(4) The workplace should be kept clean, dry and ventilated.
(5) The processing machine should be stable.
(6) Fireworks are strictly prohibited in the operation site.
(7) Use a special wet dust collector.
(8) The production site shall not wear shoes with iron spikes, and shall not use iron tools or strike.
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