Applications > Application Recommendations with Oxyacetylene
Application Recommendations rods and cored electrodes for hardfacing - hardfacing


AgroCrom / AgroTung



APPLICATION GUIDE OXYACETYLENE


Protected self alloy has a melting point of about 1050 ° C and makes possible the application oxyacetylene torch.


Equipment required:


Oxygen Acetylene cylinders and pressure regulators:


Oxygen: 4 bars - Acetylene: 0.8 bars of pressure.


Peaks: (approximate consumption / diameter)


     Pico Nº 3: 600 litros / hora - d 1,75 mm

     Pico Nº 4: 1000 litros / hora - d 2,20 mm

     Pico Nº 5: 2000 litros / hora - d 3,00 mm


1.- Preparation of the surface to recharge:

Removing rust, dirt, grease, oil and other contaminants from the surfaces to be welded.


Previous recharge should be removed if:


Are unknown, are incompatible with the material to be deposited, no pores, no cracks, deformed or have been hardened by work (impact wear).


The removal must be carried out by grinding the workpiece and repaired if necessary.


It requires a good foundation and it may therefore be necessary to remove the parts showing signs of fatigue, highlights or surface irregularities.
The cracks in the base metal must be removed or drill down to find firm material and rebuild using compatible electrodes. If the base metal is cracked, dig until you find firm material, drill the ends of the crack and fill.


If the surface has worked impact should be removed approximately 3 mm from the surface before rebuilding (build up) and recharge.


Poor preparation of the base metal may lead to delamination of the contribution.


Base metal may be unknown or contain foreign objects (excess sulfur) affecting the contribution of the alloy; this is solved by cleaning the surface and applying a "buttered" or intermediate layer with a low alloy electrode, basic (AWS E-7018) before applying the hardfacing alloy. The preparation requirements are stricter when it applies recharge torch.


2.- Preheat the surface


Before the recharge, the welder must consider the size of the piece, its shape, characteristics and use.


Suggestions:


Manganese steels; should be preheated to 100 ° C, but should NEVER exceed 260 ° C. Higher temperatures (preheating and interpass) causes manganese carbides form austenite grain edges reducing the hardness of the deposit.


Cast iron; high preheating temperature requires. A good rule of thumb is to heat the piece until a dull red.


Carbon steel and low alloy; preheating in some cases it may be necessary to prevent cracks, delamination, or in the base metal under the cord.


3.- Method hardfacing:


To recharge torch, we recommend using excess acetylene. The outer cover should be three times the size than the size of the inner cone.


A flame fuel decreases the melting temperature of the surface and protects the base metal excess oxidation during recharge.


This is called "called 3 X" because the arrow is 3 times the size of the cone. See photos.


Peak numbers 3 to 6 are used depending on the diameter of the tubular rod and the size of the part to recharge. Nickel base alloys require neutral flame.


Rendering the surface "sweat" (deep red) or is the beginning of the merger by excess acetylene.


The flame should form a 45 ° angle with the surface of the workpiece and also the rod 45 of the surface on the opposite side.


The flame should oscillate from side to side of the material. The tip of the rod should not be withdrawn or removed during the melting process. The procedure must include the coating thickness required for maximum wear resistance.


Welding position:


Horizontal
Contribution downward angle 15 °, thickness decreases
Contribution upward angle 15 °, thickness increases.


Thickness of the deposited material:


Avoid excessive intake of material recharge, this can cause cracking or detachment in service.
If excessive thickness is needed, use a suitable material previously reconstruction up to the required dimensions.
Heating the tubular rods for over an hour at 100 ° C to remove the presence of moisture which can cause pores in the support.


Deformation:


The heat generated by the intake process can cause deformation of the parts.
Use appropriate methods of clamping and welding.
Provide material alternately to prevent overheating of a point.


4.- Cooling / post heating


This is the best method to control the recharge base metal dilution because oxyacetylene flame temperature is much lower than the electric arc, thereby melting the rod and the preheating of the base metal is easily controlled.


Cooling procedures:


Austenitic steels; should be welded with low temperature between passes and cooling is not a factor to be controlled.


Martensitic steels, the goal is the complete formation of martensite or other metallurgical phase. Generally, the part must be air cooled to 120 ° C from the welding temperature. This ensures to achieve the desired structure and prevents cracking. Hydrogen is always a potential danger and therefore it is advisable to keep the workpiece at a temperature of 120 ° C for 2 to 3 hours, allowing the escape and prevent hydrogen embrittlement of the workpiece.


Postheating:


This term generally comprises ease tensions and mild.
This is done below the critical temperature of the filling material.


The usual post-heating is made at temperatures between 450 and 650oC. The appropriate time and temperature vary according to the result sought and is generally considered one hour per 2 cm thick. While it is possible to observe a slight decrease in hardness (1-3 points HRc), there are occasions where the hardness increase is called secondary hardening temper usually occurring at low temperatures is observed.


VERY IMPORTANT:


Fumes from the normal use of these products contain amounts of Chromium, Manganese and the tungsten carbides that can be harmful.


ADJUSTMENT OF FLAME:


  1. Short flame with excess oxygen. * Not recommended.
  2. Llama very long, insufficient oxygen. * Not recommended.
  3. Called short, excess acetylene. * Recommended prevents oxidation.