NOTE: The processes discussed below are a non partisan overview of the technology involved. This is intended to be a process awareness tool. SPRS will welcome any inquiry concerning a specific process as well as potential supply of overlay material for these processes.

Oxy-acetylene torch process:

This process is quite often considered as “old fashioned”, and even qualified as “antiquated” because of its lack of apparent sophistication. And yet, it is the most effective application process for tungsten carbide based products. These products are always dual phased: matrix and tungsten carbides. One phase, the matrix, melts at a temperature much lower than the other phase, the tungsten carbides themselves.

Advantages of this process:

  • The key factor in the oxy-acetylene process is that the heat generated by the flame of the torch allows to bring the matrix in which the tungsten carbides are imbedded, up to the melting point, and thus create a metallurgical bond with the substrate, while staying far below the melting point, (metallurgical properties altering level), of the tungsten carbide particles.
  • The equipment required is simple and very inexpensive as compared with other processes.

Drawback of this process:

  • The drawback of this process is that its efficiency relies heavily on the skills of the applicator. It is necessary to provide hands-on training for new applicators. SPRS does offer this training for Technogenia products.

Electric arc process:

The electric arc process is more familiar to professional welders. It is relatively easy to achieve an acceptable part by following the instructions on the products packaging.

Advantages of this process:

  • Many potential applicators are familiar with the concept of this process.
  • The parameters can be established and reliably reproduced.

Drawback of this process:

  • The high temperature of the electric arc is detrimental to tungsten carbide products, because it softens them during the application process. The original abrasion resistance properties are reduced by 4 to 7 times compared to the same product applied with the oxy-acetylene process (as proven by laboratory wear resistance testing).

H.V.O.F. process:

The High Velocity Oxy Fuel process involves projecting at high speed a product, which can include tungsten carbide particles, against a surface to be overlayed. The product is fused during the travel distance between the projection apparatus and the surface to be overlayed.

Advantages of this process:

  • The parts hardsurfaced with this process remain at relatively low temperatures. Consequently there is very little change in the overall dimensions or metallurgical properties of the base material.
  • The projection parameters can be defined and reproduced easily.
  • The overlay can be applied as a very thin coat.

Drawbacks of this process:

  • The bond between the base material and the overlay is a mechanical bond, which is weaker than a metallurgical bond. Consequently it is not suitable for high abrasion applications where impact can be present.
  • The overlay can only be applied as a very thin coat.

P.T.A. process:

The Plasma Transferred Arc process involves creating a flow of inert gas, brought electrically to a very high temperature (plasma) as a heat source to fuse and bond a metal based product (which can include tungsten carbide particles ) onto iron or steel parts.

Oddly enough, this is often considered as a product, and not as a process. Manufacturing specifications should include the process and the product to be applied by this process.

Advantages of this process:

  • This process allows to apply a relatively thick coat of overlay in one pass.
  • The application parameters can be defined and reproduced.
  • It can be automated.
  • It is a volume production equipment when set up.

Drawbacks of this process:

  • This process is somewhat deceptive because of its apparent simplicity.
  • It does require trained and experienced personnel to reduce problems due to poor bonding of the overlay to the base material. (This problem is very often ignored as the spalling of the overlay usually occurs very early after the parts are put into operation, and reduces their wear life.

LASER process:

This newer technology uses the energy of a laser beam to fuse and bond a product in powder form, onto a base material.

Advantages of this process:

  • It is particularly suited to automation.
  • Application parameters can be reliably defined and reproduced.
  • It is of particular interest in applications where material compatibility is difficult because of thermal expansion.

Drawbacks of this process:

  • It does require highly trained personnel.
  • The thickness of overlay applied in one pass is relatively low.