1、 .#gj!j# Manlffact.uring Standards .c c SirLT BATH MOLTEM - SAFETY PRSCAUTIOBS II OPERATIOB OF Scope and Aim This.Manufacturing Standard relates to molten salt bath operations and contains technical requirements for the equipment to be used, its installation and the operating procedures to be adopte
2、d. Its primary aim is to prevent accidents, injuries to health and environmental pollution. This Standard is based on: InFoB: Vrecautions in the use of Molten Salt Baths for the Heat Treatment of Metals“ - H.M. Factory Inspectorate Form 850 eXHbB0 InFoG: “Guideline for the operation of Cyanide Beat
3、Treat Dept. and similar activities! as issued January 1963 and-the publication of the Ministry of Labour and Social Affairs, . . dated August 17, 1965 (legal requirements). 2 Hazards at Molten Salt Bath Operations The principal hazards to be considered are :- a) Explosions due.to physical reactions
4、b) Explosionsdue to chemical reactions cl Fires due to contact of molten salt with combustible materials d1 Burns resulting from contact with molten salt e) Gassing from nitrous fumes f) Poisoning from ingestion of toxic materials or inhalation of toxic fumes and gases. . . 3 Technical Safety Requir
5、ements 3.7 Workshops 3.1.1 Workshops in which heat-treatment with molten salts is conducted, and particularly those containing cyanide, must have a minitnum floor area of 2Gm 2 , and a minimum height of 3 m. The actual floor area should be related to the number of furnaces or baths and the quantity
6、of work. Basements and similar rooms must not be used. Workshops shdld, by preference, be located in non-combustible buildin. If that is not possible, the baths must be surrounded by a non-combustible wall or a tiled pit(s) of sufficient volume to contain the total contents of the baths. Such catch
7、pits must be kept clean and dry at.all times. Menufachwig Admlntstratlon PfiOCESS FiDERE?RX DATA U-hTx-8000 JULY 1990 Page 1. ! I. : ,. ;z_c ,. . :. ._,.; Manufacturing Standards m ; 3.1.2 3-1.3 3.1.4 3.1.5 3.3.6 3.1.7 3.1.8 As a protection against spitting during heating up or cooling down, the bat
8、h should be fitted with a cover. Covers for baths should be of sheet steel - so designed that they cannot fall into the bath. Water must not be allowed to contact molten salts. To ensure that this cannot happen the molten salt baths shall be located at a suitable distance from any source of water. w
9、hen water based quenchants or washes are required in these areas then the water for these purposes shall be piped via rigid pipes to the quench or wash tanks. There shall be no water-pipes, leaky roofs or non-waterproof ventilation over the salt baths. Floors must be easy to clean, and must not incl
10、ude grooves, pores or indentations nhere salt residues may accumulate. In order to facilitate washing, floors shall be laid with a slope to drainage points. Direct drainage into municipal sewage systems is . strictly prohibited. Salt baths shall be covered before any * washing of the floor takes pla
11、ce. . Adequate general ventilation must be provided to control ambient temperatures to a reasonable level and to control air contamination. Ventilation rates below 15 air changes per hour will not normally be adequate for these purposes. Lighting intensities should be 500 lux or more. Adequate nashi
12、ng facilities to include skin cleansers, hot water and towels shall be provided for the operators. Locker rooms shall be provided, equipped with two-compartment lockers for the storage of clothing and overalls.(Manufacturing Standard E-VB002 and G-VBOO2.) At the entrances to heat-treatment areas, wa
13、rning signs according to USNool shall be prominently displayed, indicating “no unauthorised entry“ and “no smoking“. Appropriate signs and instruction forms shall be prominently displayed in the workshop. Che 6.11 Consumption of food in the working area is forbidden and a separate rest room, immedia
14、tely adjacent to the workshop shall be provided where operators may smoke and eat meals. Manufacturing Administration Page 2. PROCESS REFERZI?CE DATA U-HTX-8GOO JULY 1990 Y.“. AdnIl”. F Temperature Control of the Salt Bath Fuily automatic temperature controllers , or at least automatic excess temper
15、ature devices which stop the heating immediately the bath rises more than a few degrees are recommendiy Eul Y P Manufacturing Standards w a 3-5 tire Protection Bquipment and Emergency Action Molten salt bath heat treat and cleaning departments shall be equipped with dry powder extinguishers based on
16、 sodium hydrogen carbonate or carbon dioxide. The use of extinguishers with water, foam or other wet chemicals are prohibited. Signs to this effect must be adequate to warn uninstructed Fire Fighters of the danger from the use of water based quenchants. The salt bath heating source shall be shut-off
17、 immediately a fire is discovered. Dry sand is to be kept readily available to dam liquid salt.streams in case of an emergency. 3.5.1 Beat treatment baths without cyanide salts. Under no circumstances should water be allowed to penetrate into molten salt baths. Roof level sprinkler systems to protec
18、t the building are to be kept in service. Where necessary, non-combustible hoods are to be installed above the baths to prevent water from contacting the molten salt. 3.5.2 Heat treatment baths with cyanide salts Under no circumstances should water be allowed to penetrate into molten salt baths. No
19、water pipes or sprinkler pipes are allowed above these areas. In the case of rearrangement or new installation of baths, existing pipes are to be dismantled. when extinguishing cyanide heat treatment bath fires suitable breathing apparatus and protective clothing as recommended by the Medical and Sa
20、fety activities shall be worn. 4. . Precautions in Use 4.1 Hater The accidental introduction of water into molten salt baths, giving rise to “steam explosions“, is a most serious cause of accidents. Every precaution must be taken to prevent the contact of water with the salt bath, all articles intro
21、duced into the bath must be free of moisture and preheated. Fresh salt added to the bath shall be dry and preferably added to the cold bath on start-up, if it must be added to molten salt an all-metal container shall be used. Salts shall not be added direct from paper bags or sacks, these may fall i
22、nto the bath causing fire or explosion. MenulecturIng Admlnistmtbn PROCESS FiEFEREHCE 3ATA u-HTX-8000 Page 4 JULY 1990 Yn. *ddn. Euq Set% 71 Y . . - .j& Manufacturing Standards P 4.2 Acids ThB r&ion of acids with cyanide and other salts (see 3.3-4 ) may cause the evolution of highly toxic gases and
23、must he avoided. 4.3 Air enclosed in tubes or hollow objects which are immersed in the bath may escape with violent expansion causing spattering of molten salt. Where hollow work has to be heatTtreated, care must he taken to ensure that entrapped air can escape. 4.4 carbon Free or chemically combine
24、d carbon in contact with some molten salts (ones of an oxidislng nature) can give rise to SeriOUS explosions. Carbonaceous materials must be kept away from these baths. The introduction of cyanide compounds (which contain carbon) into a nitrate bath (which is oxidising) will cause a violent explosio
25、n. 4.5 Free of Oil and Grease All pa&s to be treated shall be free of oil, grease and paraffin residues: 4.6 Metals The heat treatment of aluminium alloys must be carried out with extreme care as any overheating of the bath, particularly in the presence of loose oxide scale, may result in an explosi
26、ve reaction. The presence of Magnesium in alloys may be particularly dangerous. 4.7 Temperature Control With all molten salt baths, and nitrate baths in particular, close control of the bath temperature is necessary. The correct operation of control devices should he checked at least daily. 4.8 Bath
27、 Operation When starting up a bath, the melting of the salt must be very gradual to avoid local overheating with local generation of gases, which may cause explosions or splashing. . When cooling a bath to the solid state, iron rods should be placed vertically in it and removed just before solidific
28、ation, to provide vent holes. For extended shut down, emptying of the bath is preferable, C%S Appendix 2). Stock should be suspended in the bath and not allowed to rest on the bottom. Msnufacturlng Admlrdstratlon JULY 1990 ?ROCESS REFERENCE DATA u-rrx-0000 Page 5. P. Manufacturing Standards w 4.9 4.
29、10 4.10-l 4.10.2 4.11 5. 5.1 5.2 - Liquid Effluents 5.3 5.4 Bath Maintenance Baths should be dredged using perforated scoops or other suitable appliances at least once a week, and every bath should be emptied, cleaned and thoroughly examined at least once every 6 months. Cleaning The floors of salt
30、bath heat treatment departments should be cleaned daily at the changing of shifts, and at the end of shift. Exhaust ventilation systems are to be cleaned regularly to remove deposited dust, and to paintain efficiency. Use of Poisonous Salts The receipt, storage, and distribution of poisonous salts m
31、ust be strictly controlled by the Supervisor of the area. Envlroumental Control Disposal of Salts Fdr the disposal of poisonous salts and liquid effluents attention should be paid to : FoB: Health h Safety Manual Section IV, Topic 2 Waste Disposal“. FOG: Procedure “Disposal of Industrial Wastew,IR/5
32、9. Containers whibh have held poisonous salt mixtures are to be disposed of by approved disposal agents. Liquid effluents containing poisonous salts are to be collected in sumps of adequate size, and discharged into the sewage system only after adequate treatment. If treatment is not available in th
33、e plant, disposal must be arranged as in 5.1. Cleaning of Containers Containers in which poisonous effluents have been handled are to be cleaned immediately after emptying. iiarniag Notices All areas and receptacles containing poisonous materials or effluents are to pe marked with appropriate warnin
34、g signs (see Manufacturing Standard USNOOl). ManulacWrlng Admlnlstratlon U-FrIx-8000 JULY 1990 Page 6. PROCESS REFERENCE DATA -m Manufacturing Standards liedlth and Safety 6.1 tis&iction af Bmployees it is of particular importance that all employees associated with these processes be we11 trained, a
35、nd instructed to follow the laid d,owu operating and safety procedures. This training shall be repeated at regular intervals. The instructions to be displayed shall include: . FOB: “Precautions in the Use of Molten Salt Baths for the Heat Treatment of metals“. Form a50 HtSO. “Cyanide PoiSonin F&m 38
36、5. HMSO. “Nitrate Salt Baths“ Form 849. HMSO. 6.2 FoG: kCyanide Instruction Sheet Cl”. (Format*D 945). . Protective Clothiq . Ali salt-bath operatives must wear suitable protective equipment for head, face, hands and body. These will be recommended by the Medical and Safety activities, but will norm
37、ally include helmet, visors, gauntlet gloves, aprons and boots. Gloves and aprons will normally be made from heat-resistant leather. 6.3 AprovaI of Plans The Occupational Health Department shall be informed in advance about the installation, m-building, expansion, or disamntl%ng of molten salt bath
38、operatibns, so that the appropriate measures for health, safety or waste disposal may be initiated at an early stage. . Manutacturing Admtnlsttition u-EI!cx-aooo PROCESS REFERENCE DATA JULY 1990 &.Y“ M V Page 7 m 7009Lb0 0048087 3TT m P . Manufacturing Standards e . . APPBBDIX I Preoautions recommen
39、ded for elaetrioal heatinK equinment used in connection uith nitrate salt baths The following recommendations apply to all electricaIly heated nitrate salt baths: 1. Each individual resistance heater unit should be provided with automatic excess current protection, arranged to disconnect the supply
40、from the heater if the current exceeds the normal value by an amount as small as practicable. 2. Where resistance heating elements are used, provision should be made for the application of reduced heating during the melting period, to ensure . gradual melting of the salt without local overheating. 3
41、. Immersion heaters should be installed so that they can be readily removed from the bath to facilitate cleaning of both heaters and bath. The arrangement of the heaters should be such that they are kept clear of any sludge that may be deposited between intervals of cleaning. 4. Electrode heating eq
42、uipment should be fitted with means for automatically disconnectingthe supply as quickly as possible from the electrodes if the current exceeds the normal value by an amount as small as practicable, and guards should be fitted to prevent accidental short circuit of the electrodes by the charge or ot
43、herwise. The guards should interfere as little as possible with the circulation and even heating of the salt. The following additional precautions should be adopted in nitrate salt baths used for the treatment of aluminium alloys: 5. An earthaetecting device should be fitted which should indicate wh
44、en an earth fgult occurs on the heater and preferably, should automatically cut off the electricity supply when the leakage exceeds a pre-determined value. The scale of the indicator should be of the order of O-15A. 6. Provision should be made for the following measurements to be taken regularly at
45、least once a month, while the heaters are hot: (0 The insulation resistance of each unit of the heaters (ii) The ohmic resistance of each unit of the heaters A written record of the results of all such tests should be kept. 7. - If immersion heaters are used on a direct current supply, non-linear re
46、sistors suitable for suppressing over-voltages likely to damage the equipment should be connected across contactor coils and relay coils. Manufacturing AdmhlstmUon u-HTx-aooo PROCESS REFERENCE DATA Page 8. JULY 1990 g$:y- EM Y m 7007lIb0 008088 23b m - (aigm Manufacturing Standards P . UPBNDIX IX Me
47、thods of emptying nitrate salt baths Nitrate salt baths should be emptied, cleaned and thoroughly examined at least once every six months. Various methods are in use to remove the nitrate from . the bath: 1. 2. 3. 4. A few firms allow the molten salt to solidify and then employ a pneumatic drill to
48、break it out. This avoids manipulation of the salt in the molten state but may, in a busy factory, involve delay. The drill must be used carefully to avoid mechanical damage to the bath. Baling into metal trays by means of. a metal container attached to a long solid iron handle is a method frequentl
49、y employed. With large baths a container suspended from an overhead travelling crane and provided with a tilting device which can be operated from a distance is so× used. Siphon devices are available which can empty molten nitrate from a salt bath rapidly, but the receptacles must, of course, be at a level below that of the salt to be emptied. The pragticability of pumping molten nitrate by specially constructed pumps has been demonstrated. Attention must be paid in the design of such pumps to the avoidance of lubricants such as oil or grease and to the av
