PTA Bimetallic Coating
The increase in the plastic material variety in extrusion and injection applications and the use of additives with high abrasive-corrosive effects shorten the life of the screws. For this reason, the screws’ pitch, which are in contact with the barrel and which are subject to wear, must be protected with a suitable coating.
Coatings made by standard welding methods cannot provide the desired corrosion resistance at high pressure and temperature. Porosity and cracks appearing in the welded area during simple gas or coated electrode welding significantly reduce work quality and wear resistance. However, with PTA (Plasma Transfer Arc) welding technology, you do not experience the shortcoming of welding. It has become the most preferred method in coating screw as it shows high resistance to corrosion, work quality, and welding material variety (powder alloy). Powder metals used with PTA include tungsten carbide and similar carbide alloys. Corrosion resistance is maximized with these carbides.
What is PTA?
Plasma transfer arc method is based on melting of special mixture powder metal in plasma arc pool and welding to surface. In this method, firstly powder metal is welded to the surface, then the creation of pilot arc behind tungsten electrode and nozzle and then it is finalized with the main plasma arch created between working part and electrode. Metallurgical conjunction between created arc, sub material, and hardened layer and there occurs very small warping because of high welding speed at the material.
The Comparison between Surface Hardening Methods and PTA;
Standard nitration hardened screws have a hardness depth of 0.4-0.7 mm, whereas bimetallic screws have a special surface having thickness of 1.5-3 mm with high corrosion resistance. Thanks to this technique, the lifetime of bimetallic screws is 2-4 times longer than that of standard screws.
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