how to straighten steel after welding:5 Tips and 3 Methods

Straighten steel after welding require 5 processes to follow such as : Heat straighten at 1200°F, 20° angle, repeat. Hot mechanical straighten at 1000-1200°F yield point, bend opposite distortion. Repeen weld bead with 1-2 lb ball-peen hammer. Clamp, balance welds, minimize heat input (<30 kJ/in), preset opposite distortion. Avoid >1400°F, overwelding. Use oxyacetylene torch, temp sticks, hydraulic press, hammer. Wear PPE.

Straightening distorted steel after welding is essential to maintain the dimensional accuracy and structural integrity of the welded component. In this comprehensive guide, we will explore advanced techniques and specifications for the DIY user to effectively straighten steel after welding.

Methods for Straightening Steel After Welding

There are three primary methods to correct distortion in steel after welding:

1. Heat Straightening
2. Hot Mechanical Straightening
3. Repeening

Let’s delve into each method in detail.

Heat Straightening

Heat straightening is a widely used technique that involves applying controlled heat in specific patterns to the distorted area of the steel. This allows the metal to expand and contract in a way that counteracts the distortion. Here are the key steps and considerations for heat straightening:

• Equipment:
  • Oxyacetylene torch: Use an oxyacetylene torch with a heating tip, such as a rosebud or single orifice, for precise heat control. Adjust the flame to a neutral or slightly reducing flame to avoid oxidation.
  • Temperature measuring tools: Use temperature sticks or an infrared thermometer to monitor the steel temperature during heating. Temperature sticks melt at specific temperatures, indicating when the desired range is reached.
• Preparation:
  • Marking: Use a soapstone, chalk, or permanent marker to draw lines or triangles on the steel surface to guide the torch movement. A typical angle is 20° on each side of the bend centerline. Measure and mark the lines accurately to ensure even heat distribution.
  • Cleaning: Clean the steel surface to remove any dirt, grease, or scale that may interfere with heat transfer. Use a wire brush, grinder, or abrasive pad to expose the bare metal.
• Heating Technique:
  • Torch movement: Apply heat in a steady, sweeping motion along the marked lines. Maintain a consistent distance between the torch tip and the steel surface, typically 1-2 inches. Keep the torch moving to avoid overheating any specific spot.
  • Temperature control: Aim to heat the steel to around 1200°F (dull red) without melting it. Monitor the temperature using temperature sticks or an infrared thermometer. Place the temperature stick on the heated area and observe when it melts, indicating the desired temperature range.
  • Heating pattern: Focus the heat on the inside of the bend or the convex side of the distortion. Apply heat in a triangular pattern, with the apex of the triangle pointing towards the center of the distortion. Adjust the size and spacing of the triangles based on the extent of distortion.
• Cooling:
  • Air cooling: Allow the steel to cool slowly by air, avoiding quenching. Quenching can cause rapid contraction and cracking. Use a fan or compressed air to promote even cooling if needed.
  • Monitoring: Observe the steel during cooling for any movement or straightening. The heated area expands and upsets the surface, and as it shrinks during cooling, it pulls the steel straighter.
  • Repetition: Multiple controlled heating and cooling cycles may be required to achieve the desired straightness. Repeat the process, focusing on the remaining distorted areas until satisfactory results are obtained.
• Precautions:
  • Temperature limit: Avoid heating the steel above 1400°F or holding it at high temperatures for too long, as it can degrade the microstructure and properties of the steel. Use a temperature stick rated for 1400°F to ensure you stay within the safe range.
  • Safety gear: Wear appropriate personal protective equipment (PPE) such as welding gloves, safety glasses, and heat-resistant clothing to protect yourself from heat and sparks.

Hot Mechanical Straightening

Hot mechanical straightening involves heating the steel to near its yield point while simultaneously applying an external bending force in the opposite direction of the distortion. This method requires careful control to prevent cracking of the steel. The steps for hot mechanical straightening are as follows:

1. Heating:
   • Use an oxyacetylene torch or induction heater to heat the distorted area of the steel to a temperature close to its yield point, typically around 1000-1200°F for most structural steels.
   • Monitor the temperature using temperature sticks or an infrared thermometer to ensure consistent heating.
2. Bending:
   • Apply a controlled bending force using mechanical means, such as a hydraulic press, beam bender, or jacking system, in the direction opposite to the distortion.
   • Position the bending equipment securely and align it with the distorted area.
   • Apply the bending force gradually and steadily, monitoring the steel for any signs of cracking or excessive deformation.
3. Cooling:
   • Maintain the bending force while allowing the steel to cool gradually. Avoid rapid cooling or quenching, which can cause additional distortion or cracking.
   • Use insulating blankets or cooling clamps to control the cooling rate if necessary.
4. Repetition:
   • Repeat the heating, bending, and cooling process if necessary until the desired straightness is achieved.
   • Adjust the heating temperature, bending force, and cooling rate based on the results of each cycle.
5. Precautions:
   • Yield point: Determine the yield point of the specific steel grade you are working with to avoid overheating or underheating. Consult the material specifications or use reference charts.
   • Bending equipment: Ensure that the bending equipment has sufficient capacity and is properly maintained to handle the required force and temperature.
   • Safety: Wear appropriate PPE, including heat-resistant gloves, face shield, and protective clothing, to safeguard against heat, sparks, and potential mechanical hazards.

Repeening

Repeening is a technique that involves hammering along the weld bead to stretch and elongate it, counteracting the shrinkage caused by welding. Although repeening is not as precise as heat straightening, it can be effective for minor distortions. To repeen the weld:

1. Hammer selection:
   • Choose a hammer with a rounded or slightly convex face to avoid damaging the weld. A ball-peen hammer or a hammer with a radiused face is suitable.
   • Select a hammer weight that allows for controlled and precise striking. A weight between 1-2 pounds is commonly used.
2. Hammer technique:
   • Strike the weld bead along its length, focusing on the areas with the most distortion.
   • Apply consistent and controlled blows to stretch the weld metal and counteract the shrinkage.
   • Adjust the angle and direction of the hammer blows based on the desired straightening effect. Striking at a slight angle can help redistribute the metal more effectively.
3. Weld bead preparation:
   • Ensure that the weld bead is clean and free from slag, spatter, or other contaminants that may interfere with the repeening process.
   • Use a chipping hammer or wire brush to remove any excess material or irregularities.
4. Repetition:
   • Repeat the hammering process along the entire length of the weld bead, focusing on the distorted areas.
   • Regularly check the straightness of the steel using a straightedge or measuring tools to assess the progress.
5. Precautions:
   • Weld integrity: Be cautious not to strike the weld bead too hard or repeatedly in the same spot, as it can weaken the weld or cause cracking.
   • Surrounding area: Protect the surrounding base metal from accidentally hammer blows, as it can cause dents or damage.
   • Safety: Wear safety glasses and gloves to protect yourself from flying metal fragments and impact.

Tips for Mitigating and Controlling Distortion

In addition to the straightening methods discussed above, there are several preventive measures you can take to minimize and control distortion during the welding process:

• Restraints:
  • Use clamps, jigs, strongbacks, and other restraining devices to hold the workpiece in the desired shape during welding and cooling.
  • Position the clamps strategically to provide maximum support and resistance to distortion.
  • Ensure that the clamping force is sufficient to overcome the shrinkage forces generated during welding.
• Balanced Welding:
  • Balance welds on both sides of the neutral axis to evenly distribute the heat and stress.
  • Employ backstep, block, or other specialized welding sequences to control distortion.
  • Divide the weld into smaller segments and alternate between them to allow for gradual heat dissipation.
• Minimizing Heat Input:
  • Reduce the weld size and heat input by using smaller electrodes or lower amperage settings.
  • Select the appropriate welding process and parameters based on the material thickness and joint configuration.
  • Utilize intermittent or skip welding techniques where possible to minimize heat concentration.
• Presetting:
  • Preset the workpiece in the opposite direction of the expected distortion before welding to compensate for the anticipated shrinkage.
  • Determine the amount of presetting required based on the material properties, weld size, and joint design.
  • Use hydraulic jacks, wedges, or other mechanical means to apply the presetting force.
• Avoiding Overwelding:
  • Excessive weld size and joint restraint can increase residual stress and distortion. Avoid overwelding and use appropriate joint designs.
  • Follow the recommended weld sizes and profiles specified in the welding procedure or industry standards.
  • Use weld gauges or measuring tools to ensure consistent and appropriate weld sizes.

By implementing these preventive measures, you can significantly reduce the occurrence and severity of distortion in your welded components.

References:

(SWPS) FOR SHIELDED METAL