If properly stored, transported and used electrodes will form weld deposits with low hydrogen content.
If not, hydrogen porosity can lead to hydrogen cracking (cold cracking) if the component welded is under strain, vibration or load.
General background
When welding carbon-manganese and low alloyed steels cold cracking (often referred to as hydrogen crack-ing) can occur. These cracks gener-ally form in the coarse-grained, heat-affected zone (HAZ) of the base plate.
The most important factors which influence the risk of hydrogen crack-ing are:
• Chemical composition of the steel
• Cooling rate
• Hydrogen content of the weld metal Hydrogen is always present in small quantities during welding and is a prerequisite for the occurrence of cold cracking.
The most common sources of hydro-gen are:
• Moisture in the electrode coating
• Moisture in the air
• Condensation, rust, oil, paint or primer in the welding joint area.
By following the recommended stor-age, and procedures for handling and redrying , the moisture level in electrode coatings can be minimised, along with the associated risk of cold cracking.
Hydrogen levels are measured as ml H/100 g weld deposit and typical levels for different electrode coating types are as follows:
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box and have become damaged by moisture pick-up can be redried at a temperature of 300–350 °C for 1–
hours. Redrying should be restricted to a maximum of 3 cycles.
Re-dried basic electrodes can be stored in a heated cabinet at 80 °C without further moisture pick-up.
Stainless steel electrodes which have been stored outside of their electrode
Welding electrodes should be stored in their original package.
Preferably in a de-humidified area or in a heating cabinet.
Heating Cabinet at 80 °C
Minidryer 300–350 °C
Worksite All basic electrodes and stainless steel electrodes should be re-dried before use. Always do when there is application requirements.
Rutile electrodes normally no need for re-drying.
Observe recommended re-drying temperatures and holding times for Unitor electrodes stated on box label
Unused electrodes should be re-dried before being returned
to the heating cabinet. Max exposure
time for electrodes in the open is 8 hours.
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136
Storing and re-drying
Minidryer-350
The Minidryer-350 is designed to restore moist electrodes, or to pre-dry electrodes before welding when this is required. The dryer may be used with electrodes of both 350 and 450 mm length. With the cover in an open position, the electrodes will protrude approximately 40 mm and are easily accessible.
The Minidryer-350 is equipped with
m primary cable and plug. It has a thermostat for continuous selection of the temperature from 100 to 350 °C (1 °F to 66 °F).
The dryer is very robust in design and are all-over insulated with 40 mm mineral wool. It can also stand permanently in a tilted position. When the dryer is in a tilted position, the cover cannot stand open, but always closes to prevent the intrusion of unwanted moist air. When the dryer is tilted, a rim around the opening prevents rainwater from entering.
Caution:
Use gloves when handling warm electrodes from inside the Minidryer-350. No chemical products are to be used in the dryer. This product should be used for drying electrodes only.
Ordering Information:
Minidryer-350.
Product number: 094-63787.
Spare Parts:
H Heating element.
Product number: 094-637835.
The heating element is rated 00W.
There are two of this elements inside the Minidryer-350 (400W).
This heating element can also be used for the old Unitor Minidryer.
T Thermostat w/reg. knob for Minidryer-350.
Product number: 094-637843.
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The Minidryer-350
Type Mains Heater Primary Operating Width x Depth x Height Electrode Net Voltage Output Current Temperature Inner Dimensions Outer Dimensions Capacity Weight
V W A °C mm mm kg kg
Mini- 30, 400 1.8 100 to 350 Ø100 x 460 170 x 170 x 570 8 7
dryer- 50/60 Hz 350
COATED ELECTRODES
Re-drying time is measured from the point at which the re-drying temperature has been reached. After re-drying, the electrodes can be returned to a heating cabinet and kept at a minimum temperature of 70 °C (158 °F).
Unitor Heating Cabinet-85 (094-637850)
85 °C (185 °F) can be used for this purpose.
Mild steel rutile and rutile / organic electrodes such as GPO-30 N normally need no re-drying Re-drying covered electrodes more than three times is not recommended.
* The copper coating will oxidize during the process, butt this will not influence the performance of the product.
Re-drying of Electrodes
Customers are recommended to re- dry low hydrogen electrodes before use whenever there are application requirements relating to weld metal hydrogen content and / or radio-graphic soundness. This information is given on the box label for the individual electrodes. Failure to follow these recommendations may produce pores and weld failure.
Unitor Minidryer-350 (094-637827)
100–350 °C (1–66 °F) can be used for this purpose.
Recommended re-drying temperatures, holding time two hours, for Unitor electrodes: ALUMIN-351 N Not needed from
sealed packing.
Open packing: redry at 80 °C (176 °F) 1 hour.
CH--38 10°C (48 °F) 1 hour ACA-384 180°C (356 °F) 10 hours*
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138
Storing and re-drying
The Heating Cabinet-85
This cabinet is specially designed as a ships’ store for repair and maintenance electrodes.
A thermostat allows for stepless setting of the temperature from 30 °C up to 85 °C (86 °F up to 185 °F).
The cabinet contains five shelves and every shelf is removable. The shelves are slanted to prevent the content from sliding out when the door is opened in rough seas.
The active parts in this oven are enclosed in a unit located in the bottom of the oven. This unit can be easily removed as one unit.
The Heating Cabinet - 85 have 100 mm mineral wool in the bottoom and 50 mm in the top and side walls.
The oven has a simple yet rugged construction, and can be transported with a fork lift truck.
Caution:
Use gloves when handling warm electrodes from inside the heating
cabinet. No chemical products are to be used within the heating cabinet.
Ordering Information:
Heating Cabinet-85 Product number: 094-637850 Spare Parts:
H Heating element for Heating Cabinet-85
Product number: 094-637876 T Thermostat w/reg. knob for Heating
Cabinet-85
Product number: 094-63 78 84 3.01
Type Mains Heater Primary Operating Width x Depth x Height Electrode Net Voltage Output Current Temperature Inner Dimensions Outer Dimensions Capacity Weight
V W A °C mm mm kg kg
Heating 30, 500 1,3 30-85 460 x 50 x 860 564 x 640 x 1095 350 70
Cabinet- 50/60 Hz 85
The Heating Cabinet -85
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Ship quality steel and cast steel:
SPECIAL-303 N ,5 mm 1 package 4,1 kg SPECIAL-303 N 3, mm packages 8, kg SPECIAL-303 N 4,0 mm 1 package 5, kg Ship quality steel, horizontal,
high recovery:
LHH-314 H 5,0 mm 1 package 5,5 kg Ship quality steel, vertical
down welding: Stainless steel, stainless to
mild steel, compound steel:
18/8-31 N ,5 mm 1 package 1,7 kg
A complete‘mini-store’ for covered electrodes, including 7 packages of electrodes selected to cover all normal welding applications on mild steels, ship quality steel, stainless steels, ‘problem steels’, cast iron, copper alloys and aluminium.
• Compact design with easy access to contents, and separate room for the welding handbook.
• Sturdy, corrosion resistant
construction from electrogalvanized steel plates, with final coating by powder spraying and baking, and with zinc/yellow-chromate passivated shelves for optimal corrosion and scratch resistance.
Dimensions:
600x600x300 mm
free distance above cabinet 310 mm.
Weight with electrodes 110,5 kg
Contents and Applications Areas Instruction and information:
Unitor Welding Handbook:
Sheet metal and thin walled pipes:
SPECIAL-303 N ,0 mm 1 package 1,7 kg General mild steel repairs,
all positions:
GPO-30 N ,5 mm 1 package 5, kg GPO-30 N 3, mm packages 10,8 kg GPO-30 N 4,0 mm 1 package 5, kg General mild steel repairing,
horizontal, high recovery: Electrode cabinet
complete 094-670000
Electrode cabinet
empty 094-669994
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changes can be expected within the near future. In America one refers to AWS (American Welding Society) for classification of electrodes. Because of this we will mostly refer to EN and AWS in the Nomenclature for Welding Consumables.
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The European Community for Standardization has developed a new nomenclature in welding, Euronorm EN. This nomenclature replaces the current European standards like DIN, BS and NEN. Several new standards have come in force already and more
EN 499 Covered electrodes for manual arc welding of non alloy and fine grain steel DIN 1913
BS 639
NEN 560
DIN 859
EN 757 Covered electrodes for manual metal arc welding of high strength steel DIN 8556
BS 96
EN 1600 Covered electrodes for manual metal arc welding of stainless and heat resisting steel NEN 3581
DIN 8575
BS 493
EN 1599 Covered electrodes for manual metal arc welding of creep-resisting steel NEN 3580