The Thermal Spraying Process Has Requirements for The Size of The Workpiece

Overall, the thermal spraying process does not impose significant restrictions on the size of the workpiece, but the size and shape of the workpiece will directly affect the process

The difficulty and cost of selection and implementation.

We can understand it from two perspectives: "how small can be sprayed" and "how large can be sprayed", and the shape of the workpiece is also an important factor.

I. Considerations for "Small Workpieces"

The main challenges for small workpieces (such as screws, cutting tools, small shafts, and medical device parts) lie in fixture design, thermal management, and coating uniformity.

1. Fixture design: It is necessary to design meticulous and durable fixtures to firmly hold small workpieces and ensure that they do not fall off or deform during high-speed rotation or the movement of the spray gun. Meanwhile, the fixture should be as small as possible to avoid blocking the spraying area.

2. Thermal management (key factor) : Small workpieces have a small heat capacity. Under the high temperature of the spraying flame or plasma jet, the temperature will rise rapidly. Excessively high substrate temperature can lead to:

3. Thermal damage to the substrate: such as annealing, which leads to a decrease in hardness.

4. Sharp increase in coating stress: The thermal expansion coefficients of the coating and the substrate do not match. After cooling, huge thermal stress will be generated, causing the coating to crack or peel off.

5. Solution: Forced cooling measures need to be taken. The common one is to use a compressed air cooling system to cool the non-critical areas of the workpiece while spraying. For very small parts, it may even be necessary to carry out spraying inside a temperature-controlled box.

6. Coating uniformity: For small workpieces with complex edges and corners, ensuring that all surfaces requiring coating are evenly covered without overspraying or shadow effects requires robot path planning and workpiece rotation.

So, small workpieces can be sprayed, but usually require more meticulous tooling, stricter temperature control and higher operation skills, and the cost is relatively high.

Ii. Considerations for "Large Workpieces"

The main challenges for large workpieces (such as large rolls, ship propellers, turbine blades, and large valves) lie in equipment capacity, on-site construction, and internal stress.

1. Equipment capacity

(1) Spraying equipment: Standard spraying equipment is used in laboratories or workshops. For large workpieces that exceed the lifting capacity of the workshop door or the crane, on-site spraying is required.

(2) Mobility: On-site construction requires mobile spraying systems, power supplies, air sources and dust collection systems.

(3) Accessibility: The spray gun must be able to reach all the surfaces of the workpiece to be sprayed. For large components with deep holes or complex inner cavities, specially designed extended spray guns may be required.

2. On-site construction environment: The on-site environment (temperature, humidity, wind speed) is more difficult to control than that in the workshop and will affect the quality of the coating. Wind prevention measures are of vital importance because wind can interfere with the spray jet, cool the molten particles and lead to a decline in coating quality.

3. Accumulation of internal stress: When a coating is deposited over a large area, the internal stress of the coating (including quenching stress and thermal stress) will continuously accumulate. If not properly controlled, huge stress can cause macroscopic cracking of the coating itself or deformation of the entire workpiece.

Therefore, large workpieces can be sprayed and even constructed on-site, but they rely on specific mobile equipment and pose higher requirements for process control and environmental management.