Scraper blades of snow removal equipment are originally considered as wear (spart) parts due to their degradation they face during their operational life. However, in order to prevent direct wear degradation of these parts while improving the equipment efficiency, manufacturers have worked on the modification and the design by adapting and fixing wear pads on the rear of the scraper blades in such a way to raise them slightly above the ground level. This way of proceeding protects the blade when these pads are wearing.
Aggregates of solid particles, asphalts, sand are ice that detach from the pavement and shoulder edges slide and scratch the underside surface of the wear pads during snow removal operations. Thus, the predominant wear mechanism in such a situation consists mainly of abrasion. The wear surface is characterized by various scratches of variable depth and parallel to the moving direction. The wear depends on pad material properties and the different operating parameters such as pressure, nature of ground, sliding distance or contact time, environment, etc.
In the light of greater amplitude of sliding movement, the wear debris are mostly evacuated from the contact zone (pad/ground), some other ones are embedded on the surface prior to detaching with the progression of wear. The damaged surfaces exhibit grooves and traces of plowing parallel to the direction of movement. Wear rate is becomes roughly steady over time. Wear volume increases with the applied load (pressure) and the travelled distance.
Wear pads: materials and fabrication:
Wear pads are generally made of either fully hardened steels or from hardfaced steel base metal. In fact, the hardfacing technique consists of his last option is considered as the preferred choice to confer a higher abrasion resistant to these critical parts, leading to increase their technical lifetime and also the equipment efficiency. According to the wear conditions described above, the materials that must be selected for hardfacing consists of ferrous alloys similar to high chromium white cast irons with the addition of strong carbides-forming elements (Nb, V, W). The typical microstructure of this type of hypereutectic alloys with a high fraction of primary carbides imbedded in matrix of austenite and secondary carbides. The high carbides concentration leads the abrasive particles to slide on the wear surface instead of indenting and abrading the matrix.
As per the previous experiences, it turns out that hardfacing deposited following a dot pattern have better spalling resistance in comparison with continuous hardfacing layers deposited on the same base metal. In addition, the selected hardfacing material must be compatible with the base metal. Welding must be carried out in a way to ensure a minimum penetration and to prevent the lack of fusion on the edges of prepared holes.
Preparation and welding
- Piercing of holes of 1/4” deep and 1/2 – 3/4” diameter as per a pattern of holes on the underside surface of the wear pad;
- Chamfering of the hole edges
- Filling and hardfacing with Sodel 2045 Plus, Sodel 2024 Plus or other products according to the base material and the recommended strategy
For hardfacing, proceed as follow :
- Preheat to 400°F;
- Strike the arc on the bottom of the hole and start to fill the hole with a circular movement from the edge towards the centre;
- Deposit an excess thickness of 2-3 layers after filling the hole;
- Let cool down to the room temperature;
- Grind out the outer periphery of the hardfacing to render it in the form of a rivet head.