REASONS FOR HIGH WEARING OUT

• Armouring of 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. The 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 at the surface, compared to the remaining cross section of the layer. With increasing depth of nitriding the hardness of the nitrided layer decreases.The service life of armoured pieces is min. three times and even more higher in comparison with nitreded pieces of higher qualities of armoured layers.

After certain amount of time the signs of wear of the screws and barrels in extruders and injection machines become obvious. The increased requirements concerning the operating life of the screws, extruder barrels and injection machines will be based on:

• Utilizing of a new plastic materials and material mixtures
  - The frequent demands on the final product require the increased proportion on filling and reinforcement of the substance.
• The higher efficiency enforcement and new production technologies
  - In particular, the screws and barrels get exposed to the extremely high stress and consequently to a higher wear.

The experience has shown that the main causes for wears are:

• 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.
• The high temperatures during processing
  - Decrease the thermal strength and hardness of the screws and barrels.
• The extremely high pressures
  - Upon contact with high temperatures during material treatment, they overstress the screws and barrels over their limits.