Explosive Welding Process: A Step-by-Step Guide

Explosive Welding Process A Step-by-Step Guide

1. Surface Preparation of the Welding Material

The joint of explosive welding must have overlapping or tightly fitted bonding surfaces with the same geometric shape. This bonding surface must be flat, smooth, and clean. The cleaner and smoother the bonding surface is treated before explosive welding, the higher the strength of the explosive weld joint.

Before explosive welding, the workpiece should be flattened and any defects on the joining surface should be checked. The required surface roughness depends on the properties of the metal being welded. The smaller the surface roughness value, the better, generally requiring a surface roughness value of Ra≤12.5μm.

Although the metal jet formed during explosive welding can remove the oxide film on the metal surface, the thickness of the removed film is only a few micrometers to tens of micrometers. Thicker rust and oxide layers cannot be thoroughly removed, thus affecting the bonding performance. Therefore, the dirt on the welding surface should be removed before installation.

Common cleaning methods include chemical cleaning, machining, polishing, sandblasting, and shot blasting. Workpieces cleaned on the same day should be subjected to explosive welding on the same day. If welding cannot be conducted on the same day, the workpiece should be sealed with oil, and cleaned with acetone or similar before explosive welding.

The impact of different treatment methods on the bonding strength of titanium/stainless steel explosive welded composite plates is shown in Table 8-4.

Table 8-4 Impact of Different Treatment Methods on the Bonding Strength of Titanium/Stainless Steel Explosive Welded Composite Plates

Titanium Plate Thickness
/mm
Stainless Steel Thickness
/mm
Gap
/mm
Amount of Explosive
(g/cm2
ConditionShear Strength
/MPa
Base Plate Surface Treatment Method
31851.4Explosive State402Grinding Machine Polishing
Explosive State349Grinding Wheel Polishing
Annealed State240
5186.51.6Explosive State370Grinding Machine Polishing
Explosive State230Grinding Wheel Polishing
Annealed State133

2. Constructing the Base

The sieved sand is piled to form a sand base for the welding workpiece, with a height of 200~300mm, and a surface area equal to or slightly larger than the area of the base plate bottom.

3. Placement of Base Plate and Cladding Plate

First, place the base plate on the sand base, maintaining the original shape of the sand base. Then, wipe the welding surface of the base plate with emery cloth and clean it with alcohol to ensure surface cleanliness.

Clean the cladding plate’s welding surface with emery cloth and alcohol, then lift (or carry) it onto the base plate. When placing, the welding surfaces of the two plates should contact each other. Note that the length and width of the cladding should be 5~10mm larger than the base plate. Similar extra extensions should be considered when welding pipes and tube sheets.

4. Setting Gap Columns

To maintain the distance between the base plate and the cladding, insert a screwdriver into the gap between the cladding and base plate from the periphery, then pry the cladding upward a certain distance, and place a gap column of a certain length in the gap. Place a gap column every 200~500mm at the edge of the base plate.

After setting up the gap columns, if the area of the composite plate is not too large, a gap distance is formed between the two plates, with the length of the gap column as its size. This distance is the same and uniform at any position between the two plates.

However, if the area of the composite plate is larger, the gap distance at the geometric center of the two plates could be very small, or the two plates could even be in contact.

Therefore, before placing the cladding, a certain number of gap objects of certain shapes and sizes should be evenly placed on the bonding surface of the base plate to ensure uniformity of the entire gap between the base plate and cladding.

5. Applying a Buffer Protection Layer

After the cladding is supported on the base plate, use a brush or roller to apply water glass or grease on the upper surface of the cladding (which will be in contact with the explosive). Sometimes, rubber material is used as a buffer layer. This thin layer can buffer the explosion load and protect the cladding surface from oxidation and damage.

6. Placing the Charge Frame and Laying the Explosive

Place the prepared wooden or other material explosive frames on the cladding, with the inner edge size of the frame slightly smaller than the outer edge size of the cladding.

The explosive is divided into main explosive and detonating explosive. After placing the charge frame, put the main explosive into the frame with tools, then use a scraper to spread the piled main explosive evenly, while constantly measuring the thickness of the explosive to ensure uniformity.

To improve the detonation and propagation ability of the main explosive, place 50~200g of high-speed detonating explosive at the position where the detonator is inserted. The detonating explosive can also be placed at the predetermined position before the main explosive is laid.

7. Inserting the Detonator

After laying the explosive, insert the detonator into the position of the detonating explosive, contacting the surface of the cladding. To prevent the focussing effect of the front end of the detonator from creating a pit in the corresponding position of the cladding after detonation, a small piece of rubber or other flexible material can be placed under the detonator.

8. Explosive Welding

In the case of using a pyrotechnic detonator, insert the fuse into the detonator, clear the items on the site, evacuate the staff to a safe area, and detonate the explosive through the detonator with a detonator to complete the explosive welding process. When using an electric detonator, its two leg wires should be connected with the two strands of the detonation wire.

The length of the detonation wire (i.e. ordinary wire) depends on the safety distance. After connecting the two wires, twist the two wire ends of the other end of the detonation wire together. Finally, depending on the amount of explosive and the presence of barriers, mark out a danger zone with a radius of 25m, 50m, or more than 100m.

During explosive welding, the metal jet generated in front of the impact point of the contact interface, and the deformation and acceleration of the cladding when the explosion occurs, must be completed progressively along the entire welding joint, which is a basic condition for obtaining a solid explosive welding joint. Therefore, the detonation of the explosive must be done gradually.

If the explosive detonates all at once, the entire cladding and base plate collide, and even with high pressure, good bonding cannot be achieved.

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