Armouring surfaces with hard metal materials shows several times higher mechanical and chemical resistance to wear in comparison with service life of the pieces passed to nitridation only. Armoured areas acquire increased resistance to excessive wear, high temperatures and pressures as well as to all non-plastic materials.
Hard metal weld overlay of the thickness up to 2,5 mm (according to the type of armoured layer) shows in its whole thickness a uniform indicated high hardness and resistance to wear compared to the nitriding layer (thickness approx. 0.3 to 0.5 mm) showing higher hardness only on the surface, compared to the remaining cross section of the layer. With increasing nitridation depth the hardness of the nitrided layer decreases. The service life of armoured pieces is minimally three times longer in comparison with nitrided pieces of higher qualities of armoured layers.
After certain amount of time the signs of screws and barrels wear in extruders and injection machines become obvious. Increased requirements concerning the operating life of screws, extruder barrels and injection machines will be based on:
Utilizing new plastic materials and material mixtures
- Frequent demands on the final product require an increased proportion on filling and reinforcement of the substance.
Higher efficiency enforcement and new production technologies
- In particular, screws and barrels get exposed to extremely high stress and consequently to higher wear.
Experience has shown that the main causes of wear are following:
Increasing weight proportion during filling and substance reinforcement
- Puts a stress on the upper area of screws and barrels and leads to the abrasion. The friction process in the screw - barrel system works adhesively. This leads to the recurrence of the corrosion process.
High temperatures during processing
- Decrease the thermal strength and hardness of screws and barrels.
Extremely high pressures
- In contact with high temperatures during material treatment, they overstress screws and barrels above their limits.