1. Shielded Metal Arc Welding Principles
Chapter 11

2. Objectives List the percentage of usage of SMAW in the industry.
Name the components that make up the schematic representation of the shielded metal arc.
Know the maximum arc temperature of an SMAW electrode.
List the four constant current welding machines.

3. Objectives
List the common type and uses of constant current welding machines.
Name the power supply ratings.
Name the characteristics of the four basic types of welding machines.
Choose the correct cable size based on the application.
List the welder’s safety equipment.

4. Shielded Metal Arc Welding (SMAW)
Manual arc welding
Heat for welding generated by electric arc established between flux-covered consumable metal rod (electrode) and work
Called stick electrode welding
Combustion and decomposition of electrode creases gaseous shield
Protects electrode tip, weld puddle, arc, and highly heated work from atmospheric contamination
Additional shielding provided by covering of molten slag (flux)
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5. SMAW
American Welding Society
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6. Process Capability
Shielded metal arc welding one of most used of various electric arc welding processes

7. SMAW Advantages Equipment less complex, more portable and less costly
Can be done indoors or outdoors, in any location and any position
Electrodes available to match properties and strength of most base metals
Not used for welding softer metals
Not as efficient in deposition

8. SMAW Operating Principles
Sets up electric circuit
Includes welding machine, work, electric cables, electrode holder and electrodes, and a work clamp
Heat of electric arc brings work to be welded and consumable electrode to molten state
Heat intense: as high at 9,000ºF at center
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9. Welding Process Electric arc started by striking work with electrode
Heat of arc melts electrode and surface of base metal
Tiny globules of molten metal form on tip of electrode and transferred by arc into molten pool on work surface
After weld started, arc moved along work

10. SMAW Operating Principle
American Welding Society
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11. Welding Power Sources
Each type of power source has fundamental electrical differences that best suit particular processes
Welding machine
Must meet changing arc load and environmental conditions instantly
Must deliver exact amount of electric current precisely at right time to welding arc
Available in wide variety of types and sizes

12. Welding Power Sources
Also known as power supplies and welding machines
Two classifications
Output slope
Whether constant current or constant voltage
Power source type
Transformer
Transformer-rectifier
Inverter
Generator

13. Type of Output Slope Two basic types Constant current Constant voltage
Referred to as variable voltage
Constant voltage
Referred to as constant potential

14. Output Slope
Relationship between output voltage and output current (amperage) of machine as current increased or decreased
Also called volt-ampere characteristic or curve
Largely determines how much welding current will change for given change in load voltage
Permits welding machine to control welding heat and maintain stable arc
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15. Output Slope
Indicates type and amount of electric current designed to produce
Each arc welding process has characteristic output slope
SMAW and GTAW require steep output slope from constant current welding machine
GMAW and FCAW require relatively flat output slope from constant voltage power source
Submerged arc welding adaptable to either slop

16. Typical Output Slopes
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17. Four Types of Power Source
Engine-driven generators
Powered by gas or diesel combustion engine
Can be found with a.c. or d.c. electric motor
No longer being manufactured and rarely found
Transformer-rectifiers
Use basic electrical transformer to step down a.c. line power voltage to a.c. welding voltage
Welding voltage then passed through rectifier to convert a.c. output to d.c. welding current
May be either d.c. or a.c.-d.c. machines

18. Four Types of Power Source
A.C. transformers
Used to step down a.c. line power voltage to a.c. welding voltage
Inverters
Increases frequency of incoming primary power
Constant current, constant voltage, or both
Produce a.c. or d.c. welding current

19. Power Sources Important to select right power source for each job
Table 11-1 "Common types and uses of arc welding machines" should be studied
Study of job indicates whether a.c. or d.c.
Shielded metal arc welding and gas tungsten arc welding must use constant current machine
Gas metal arc prefers constant voltage machine

20. Constant Current Welding Machines
Used for shielded metal arc welding and gas tungsten arc welding
Current remains fairly constant regardless of changes in arc length
Called drooping voltage, variable voltage, or droopers
Load voltage decreases as welding current increases

21. Constant Current Output Slope
Constant current welding machines
Steep output slope
Available in both d.c. and a.c. welding current
Steeper the slope, the smaller current change
Enables welder to control welding current in specific range by changing length of arc

22. Constant Current Output Slope
Some jobs require steep volt-ampere curve
Other jobs use less steep volt-ampere curve
(A), (B)
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23. Open Circuit Voltage
Voltage generated by welding machine when no welding being done
Machine running idle
Arc voltage
Voltage generated between electrode and work during welding
Load voltage
Voltage at output terminals of welding machine when arc is going
Combination of arc voltage plus voltage drop in welding circuit

24. Open Circuit and Arc Voltage
Open circuit voltage runs between volts
Drops to arc voltage when arc struck
Arc voltages
Range: 36 volts (long arc) to 18 volts (short arc)
Determined by arc length held by welder and type of electrode used
Arc lengthened, arc voltage increases and current decreases

25. Open Circuit and Arc Voltage
Open circuit voltage on constant current machines higher than on most constant voltage machines
Arc voltage depends on physical arc length at point of welding and controlled by welder
Shielded metal arc welding
Gas Tungsten arc welding
Arc voltage much lower than open circuit voltage

26. Motor Generator Welding Machines
Usually supply only direct current
Can be made to supply a.c.
Most constant current type
Used chiefly for shielded metal arc welding and gas tungsten arc welding

27. Motor-Generator Welding Machine
Hobart Brothers Co.
Sturdy steel lifting eye
Calibrated dial for easy, fine adjustment of heat and relation between voltage and current
Outer wheel and dial for selecting desired welding range
Large voltmeter
Stop button
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28. Motor-Generator Welding Machine
Hobart Brothers Co.
Ground cable connector
Optional steel guard
Pressed steel bearing cap
Heavy-duty ball bearings
Arc welded copper
squirrel cage rotor
Motor stator
Heavy steel fan
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29. Motor-Generator Welding Machine
Hobart Brothers Co.
Steel frame
Fourpole "Multi-Range" generator
Heavy-duty metallic graphite brushes
Large commutator
Arc welded steel frame
Heavy-duty ball bearings
Pressed steel bearing cap
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30. Motor-Generator Welding Machine
Hobart Brothers Co.
Steel turret top with removable cover
Removable steel covers
Large ammeter
Heavy-duty single unit steel shaft
Polarity switch
Welding cable connector
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31. Motor Generator Welding Machine for SMAW
Instruction on the Name-plate
The Lincoln Co.
Variable voltage control
Polarity switch
Constant voltage
Toggle switch
Current control
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32. External Construction of d.c. Motor Generator Welding Machine
The Lincoln Electric Co.
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33. Internal Construction of a D.C. Motor Generator Welding Machine
The Lincoln Electric Co.
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34. Motor Generator Desirable Characteristics
Have forceful penetrating arc
Versatile
Can be used to weld all metals that are weldable by arc process
Flexible
With proper electrode, can be used in all positions
Durable and have long machine life

35. Generators Classified by type of motor that drives generator
Consists of a.c. motor, d.c. generator, and exciter built on single shaft
The Lincoln Electric Co.
Miller Electric Mfg. Co.
Generators used in the field
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36. Sizes Determined on basis of amperage Range
100-ampere rated for home
1,500 ampere rated for use with automatic submerged arc welding equipment
Manual welding machine idle sometimes
Automatic power supply units 100% duty cycle
Should not be used at or beyond max over extended period

37. Maintenance
Contacts of starter switch and control rheostat should be inspected, cleaned frequently and replaced when necessary
Brushes need frequent inspection for wear
Check commutator for wear or burning
Rewound and turned on lathe
Main bearings on shaft inspected and greased at each 6-month period
Clean old grease out of bearing housings

38. Start and Stop Buttons Purpose of starting and stopping the motor
Start button black
Stop button red
Important buttons be engaged firmly

39. Polarity Switch
Electrode negative and electrode positive used in d.c. welding
DCEN (d.c. electrode negative)
Electrode connected to negative terminal of power source and work connected to positive terminal
DCEP (d.c. electrode positive)
Electrode connected to positive terminal of power source and work connected to negative terminal
Switch changes to either electrode positive or electrode negative

40. Volt-Ampere Meters Sometimes serve dual purpose
Can indicate polarity as well as current
Others, individual meters for volts and amperes
Some, single meter that indicates both volts and amperes
Button engaged to get individual readings
Would need second person for monitoring
Increased demand for additional devices so meters have been discontinued by some manufacturers

41. Current Controls Amperage Voltage Two types of dual control generators
Quantity of current
Determines amount of heat produced at weld
Voltage
Measure of force of current
Determines ability to strike an arc and maintain its consistency
Two types of dual control generators
Tapped-step current control
Continuously variable current control

42. Dual Tapped-Current Control
Coarse adjustment dial selects current range
Called steps or taps
Impossible to secure current value between two steps by setting dial between them
Fine adjustment dial trims current between steps
Whether set high or low depends on type and size of electrode, thickness of metal, soft or digging arc required, arc starting, restricting characteristics, and Position of welding

43. Dual Continuous Control
Coarse adjustment dial continuously adjusts current
Fine dial adjusts both current(amperage) and open circuit voltage
Operator adjusts output slope for given current setting by manipulating both coarse and fine adjustment dials together
Wheel or knob on both amperage and voltage setting devices gives welder continuous control of both

44. Engine Driven Generator
Miller Electric Mfg. Co.
Miller Electric Mfg. Co.
Capable of SMAW, GTAW, SMAW, FCAW and PAC.
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45. Remote Control
Welding machines may be installed in remote part of plant
Welder may adjust current without leaving job
Timesaving on work
Welder does not have to leave fabrication to readjust current

46. Air Filters Wear in arc welding machines costly Bearing wear critical
Cost of replacement parts and labor
Loss of production due to nonuse of machine
Bearing wear critical
May be reduced through use of air filter fitted on suction end of motor generator machine
Filter cleaned regularly
High pressure air, commercial solvent or steam

47. D.C. Transformer-Rectifier Welding Machines
Have many designs and purposes
Flexibility one reason for wide acceptance
Deliver either DCEN or DCEP
May be used for:
Stick electrode welding
Gas tungsten arc welding
Submerged arc welding
Multi-operator systems
Stud welding
The Lincoln Electric Co.
Miller Electric Mfg. Co.
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48. Transformer-Rectifier Machines
Have two basic parts
Transformer for producing and regulating alternating current that enters machine
rectifier that converts a.c. to d.c.
Third important part is ventilating fan
Keeps rectifier from overheating
Design improves arc stability and makes it easy to hold short arc which is soft and steady
No major rotating parts so consume little power

49. A.C.-D.C. Transformer-Rectifier Welding Machines
Permit welder to select either a.c. or d.c. and electrode negative or electrode positive
Switch
Permits welder to use only transformer part of machine for a.c. welding
Flipping switch then output current directed through rectifier which converts it to d.c. welding
High frequency arc-starting devices, water/gas flow controls, balance controls for a.c. operation, remote control often built into machine

50. A.C.-D.C. Transformer-Rectifier Welding Machines
Miller Electric Mfg. Co.
The Lincoln Electric Co.
A 300 amp model shown in use
The Lincoln Electric Co.
A 300 amp a.c.-d.c. GTAW/SMAW machine.
Portable SMAW/GTAW welding machine
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51. A.C. Transformer Welding Machines
Most popular a.c. welding machine
Function of transformer
Step down high voltage of input current to high amperage, low voltage current required for welding
Especially suited for heavy work
The Lincoln Electric Co.
Miller Electric Mfg. Co
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52. Advantages of a.c. Power Sources
Reduces tendency to arc blow
Can use larger electrodes
Resulting in faster speeds on heavy materials
Lower cost
Decreased power consumption
High overall electrical efficiency
Noiseless operation
Reduced maintenance

53. D.C. and A.C.-D.C. Inverter Welding Machines
Portable, lightweight, and versatile
May be either constant current, constant voltage or both
Can perform several different processes
Miller electric Mfg. Co.
The Lincoln Electric Co.
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54. Cost Comparisons: Arc Power Sources
Three main areas
Cost of purchasing equipment (nearly equal)
Operating efficiency
Motor generator machine: 52-65%
Transformer-rectifiers: 64-72%
Inverters: 85%
Maintenance
Motor generator machine: replacing parts, lubrication
Transformer-rectifiers and inverters have no moving parts
See Table 11-2
for more comparisons

55. Multiple-Operator Systems
Can be installed away from work site and be connected to control panels close to welding operator
When using direct current, all welders must weld with same polarity
Miller Electric Mfg. Co.
Most installations are d.c.
Power: 600-2,500 amperes
Cost less, saves space and cable, lowers operating cost
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56. Power Supply Ratings Standards set
The National Electrical manufacturers Association
Occupational Safety and Health Administration
Provide guidelines for manufacture and performance of power sources
Rated by
Current output
Open circuit voltage
Duty cycle
Efficiency of output
Power factor

57. Current Output Rated on basis of current output in amperes
Amperage range
200 amperes or less for light or medium work
Over 2,000 amperes for submerged arc welding

58. Open Circuit Voltage Maximum allowable used for manual welding
80 volts for a.c. or a.c.-d.c. machines
100 volts for d.c. machines
Very smooth output (less than 2% ripple)
Automatic machine welding
Some constant current machines rated up to 125
Constant voltage types normally rated from 15 to 50

59. Duty Cycle
Percentage of any given 10-minute period that machine can operate at rated current without overheating or breaking down
Rating of 100% means machine can be used at rated amperage on continuous basis
Required by continuous, automatic machine welding
Rating of 60% means machine can be used at its capacity 6 out of every 10 minutes without damage
Satisfactory for heavy SMAW and GTAW

60. Efficiency
Relationship of secondary power output to primary power input
Indicated in percent
Determined by losses through machine when actually welding at rated current and voltage
Average efficiencies
Motor generator welding machines: 50%
Transformer-rectifier: 70%
Inverter: 85%

61. Power Factor
Measure of how effectively welding machine makes use of a.c. primary line power
Primary power used divided by amount total drawn
Expressed in percent
Three-phase d.c. transformer-rectifiers: 75%
Single-phase a.c. power units: 55%
Welding machines can be purchased with power factor correction

62. Power Cable
Conductors of ample capacity and adequately insulated for voltage transmit power
Necessary to ground frame of welding machine
Portable cable with extra conductor fastened to machine frame on one end and solid ground on other
Important cable adequately insulated with tough abrasion-resisting insulation
Stand up under rough usage in welding shops

63. Electrode and Work Cable
Required to complete electric circuit between welding machine and work
Electrode cable (welding cable) attached to electrode holder
Work cable attached to work
Rubber-covered multistrand copper cable generally used
Must have high flexibility
The Lincoln Electric Co.
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64. Cable Core Construction
Woven of thousands of very fine copper wire
Greater the number of strands the more flexible
Components
Wires stranded for extra flexibility
Paper wrapping around wires allows conductor to slip within robber covering when bent
Extra strength from open-braided reinforcement of extra cotton cords
Special composition and curing of heavy rubber covering
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65. See Table 11-3 to help choose the right size of welding cable
Work Cable
Not necessary to have flexibility of electrode cable
Usually same cable used
Important considerations
Amperage of welding machine
Distance from work
Larger cable
Greater the amperage and greater the distance
Resistance increases as diameter of cable decreases
See Table 11-3 to help choose the right size of welding cable

66. Cable Lugs Required on both electrode cable and work cable
Soldered or fastened mechanically
Connections MUST be tight and secure
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67. Work Clamps
Variety of structures to be welded; many types of clamps may be used
Copper hook, heavy metal weight, C-clamp
Specialized work clamps
Rotary type
Lenco dba NLC. Inc.
This clamp stops twisting and turning of welding cable where work rotates. Clamp welded to part, thus permits work clamp to be attached in seconds. It is generally used in fabricating tanks, pressure vessels, and on weld positioners.
Lenco dba NLC. Inc.
Lenco dba NLC. Inc.
Spring loaded
C-clamp
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68. Quick Connector Attached to ends of different lengths of cables
Allow quick and easy attachment to any length cable
Lenco dba NLC. Inc.
This connector has cam-type action that ensures positive stop
and lock and cannot come loose or accidentally fall apart.
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69. Metal Electrode Holders
Device used for holding electrode mechanically
Conveys electric current from welding cable to electrode
Insulated handle protects hand from heat
Jaws of holder grip electrode at any angle
Made of metal with high electrical conductivity and ability to withstand high temperatures
Lenco dba NLC. Inc.
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70. Metal Electrode Holders
Jaws can be replaced with new ones
Should be light in weight, well-balanced and have comfortable grip
Size of holder must be in line with size of welding machine
Fully insulated so stays cool even with high duty cycles

71. Spring Type Electrode Holder
Lenco dba NLC. Inc.
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72. Short-stub Electrode Holder
One-ton pressure contact
High welding current conductance
Special extruded copper-alloy body
Cable connections
Entirely insulated
Bernard Welding Equipment Co.
Holds electrodes burned to very short stub.
Twist-type locking device permits electrode- gripping power in excess of 2,000 pounds.
Lifeguard insulation
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73. Angle-head Electrode Holder
Shorter and lighter
than other holders of comparable capacity.
Jackson Products Co.
Available in sizes of 400 and 600 amperes and takes electrodes from 1/16 through 5/16 inch in diameter.
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74. Other Electric Arc processes
Generates heat for several major welding processes
Gas tungsten arc welding (GTAW)
Gas metal arc welding (GMAW)
Arc cutting utilizes much of same equipment as arc welding

75. Carbon Arc Welding
Welding heat comes from arc formed between base metal and carbon electrode or arc formed between two carbon electrodes
With or without addition of filler rod
Carbon electrodes available: 1/4, 5/16, 3/8 inch
Alternating current: amperes
Metal electrode holders not suitable
Carbon electrode hotter than metal electrode

76. Twin Carbon Electrode Holder
Metal shield to protect welder's hand from intense heat.
Two leads are required because the arc is created between the two electrodes.
Larger than the metal electrode holder
The Lincoln Electric Co.
Holder is water cooled
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77. Atomic-Hydrogen Arc Welding
Process in which electric arc surrounded by atmosphere of hydrogen
Gas shields molten metal from oxidation and contamination from the air
Transfers heat from electrode to work
Arc formed between two electrodes
Temperature produced by arc: 7,500ºF
Current supplied by a.c. welding transformer
Hydrogen supplied in cylinders

78. Atomic-Hydrogen Electrode Holder
General Electric Co.
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79. Atomic-Hydrogen Arc Welding
Metal of same analysis as being welded can be deposited
Welds may be heat treated
Unusually smooth, ductile, nonporous and free from impurities
Surface free from scale
May weld hard-to-weld metals
Advantages: increased production, low operating cost, and low maintenance cost

80. Hand shield so person may hold shield in front of face
Hand and Head Shields
Brilliant light caused by electric arc contains two kinds of invisible rays which injure eyes and skin
Ultraviolet
Infrared
Rays affect eyes within 50 feet; and skin any distance within 20 feet
Fibre-Metal Products Co.
Hand shield so person may hold shield in front of face
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81. Hand and Head Shields Also called hood or helmet Dependable protection
Attached to adjustable headband
Allows it to be moved up or down as wearer desires
Dependable protection
Both hands free to grasp electrode holder
Partial protection
Must also wear leather or nonflammable cap for adequate protection
Fibre-Metal Products Co.
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82. Hand and Head Shields
Constructed of heat-resisting, pressed-fiber insulating material
Shields fully molded at top and bottom to protect head and neck
Usually black to reduce reflection with window frame to hole protective lens
Fibre-Metal Products Co.
Chrome leather helmets ideal for hard-to-get-into areas.
Wilson Products
Flip-front welding helmet permits welder to inspect and brush weld without lifting the hood.
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83. Head Shield Lens Sizes: 2 x 4.5 or 4.5 x 5.25
Colored to screen out ultraviolet, infrared rays, and most of visible rays
Variety of shades of color
Density depends on brilliance of arc
Varies with size of electrode and volume of current
Side exposed to weld pool protected by clear polycarbonate plastic cover lens
Protect costly filter lens from molten metal spatter and breakage (replaced when pitted and clouded)

84. Auto-darkening Electronic Filter Helmet
Useful when working close quarters, doing high production work, or avoiding inadvertent arc strikes
Single shade or variable shades
Filter can switch from light to dark in less than 1/10,000 of a second
Battery powered
May have solar battery booster .
Jackson Products Co.
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85. Safety Glasses Should be worn
Also behind hood to prevent severe arc flash reaching eyes
Can Absorb more than 99.9% harmful ultraviolet rays
Worn by others who work with welders
Light in weight, well ventilated, and comfortable
Lenses have light tint (Not dark!) and tented side shields
© RobCrandall/The Image Works
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86. Protective Clothing Gloves to protect hands
Made of leather or some other type of fire-resistant material
Leather capes, sleeves, shoulder garments with detachable bibs, aprons
Split-type apron if sitting down
No place to collect hot particles
High-top shoes
Leggings and spats
Department of Labor
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87. Protective Clothing 100% cotton or wool
Miller Electric Mfg. Co.
100% cotton or wool
Thick enough to prevent injurious untraviolet rays from penetrating to skin
Long sleeves
Shirts buttoned to neck
Shirttails tucked
Cuffless pants long enough to cover top of leather boots
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88. Protective Clothing
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89. Further Protection Ear Protection Flume Protection
Full ear muffs that cover entire ear or ear plugs
Dangers
Noise
Hot weld spatter or slag entering ear canal
Flume Protection
Always use proper ventilation to keep head out of fume plume