Become an expert in impact abrasion wear management
Impact abrasion, often called abrasion from impact or impact wear, stands out because it does not behave like other wear types such as pure abrasion. Simple abrasion involves removing material from the surface due to abrasive particles, while impact abrasion alters the internal structure of the substrate.
There are two possible scenarios:
- The substrate is hard and brittle, so the energy transmitted to the part fragments the substrate locally or breaks it completely.
- The substrate is ductile, in which case the energy transmitted to the part deforms the surface and modifies the substrate’s microstructure, thereby promoting further degradation by subsequent impacts.
The challenge in understanding impact wear is that it is often accompanied by other wear phenomena such as abrasion, temperature and metal-to-metal friction.
So, how can one distinguish impact abrasion from these other phenomena?
1. Extreme Impact Abrasion Wear
Addressing extreme abrasion without any other combined wear phenomenon is relatively straightforward and well-understood. The use of ductile or highly ductile materials such as manganese steels or hardened steels is recommended (e.g., DURSTEEL, CREUSABRO).
However, when an impact, whether moderate or severe, is accompanied by another wear phenomenon, it is crucial to measure the impact energy and devise a solution that addresses both the impact level and the additional wear issue.
Examples of Combined Wear:
- Impact Abrasion: In aggregate crushing, you might encounter very hard aggregates that are difficult to fragment and generate very few fine particles when fragmented (e.g., magmatic rocks such as granite). Alternatively, there could be aggregates that are easy to fragment and generate a lot of fine particles that can be abrasive (e.g., sedimentary rocks such as sandstone or limestone with a high silica content). The required solutions for these scenarios are quite different.
- Impact Temperature: In forging, a hammer transmits energy to the die upon impact, which is also subjected to high temperatures. The temperature creates thermal fatigue and the impact energy causes material displacement within the die, leading to metal-to-metal abrasion.
The best way to define an appropriate solution is to use a scale that considers impact abrasion or impact temperature and metal-to-metal friction to accurately identify the application. Once this is established, a thorough understanding of alloy elements helps in choosing the most suitable solution for the desired durability. Depositing a wear-resistant alloy by welding provides excellent protection and is commonly used for both repair and prevention of surface wear.
For more information, please see our Fundamentals of Hardfacing by Arc Welding booklet.
To illustrate wear by abrasive impact, let’s take the example of a gyratory crusher in an aggregate operation.
Gyratory crusher
Jaw crusher
Consider a gyratory crusher in an aggregate operation. A gyratory crusher consists of a crushing system with a vertical feed placed on top. The aggregate that enters the primary crusher is either extracted directly from the quarry or comes from a jaw crusher that provides an initial reduction of the mineral.
Crushing results from the interaction between a mantle and a concave. The concave is fixed, and the mantle is mounted on an eccentric mechanism that allows it to move in a circular path. This movement crushes the aggregate against the concave surfaces.
Fragmentation of the mineral occurs through compressive force. The surface of the mantle and concave is subjected to violent impacts and significant pressure during the crushing process.
As fragmentation progresses, more fine particles are generated. The more difficult the material is to fragment, the greater the impact, or “energy transmitted to the part”.
After primary crushing, there may be a series of crushers (secondary, tertiary, quaternary) to achieve the desired granulometry. Once the primary and secondary crushing stages have been completed, significant impact forces are no longer present.
In a porphyry quarry (railway ballast), characterised by the exploitation of very hard and abrasive stone, the primary gyratory crusher will endure significant impacts in the upper part of the mantle and concave, with moderate abrasion in the lower part. The secondary crusher will experience moderate impacts and increasingly severe abrasion.
In terms of durability, while manganese steel castings are ideal for the primary crusher due to their performance and cost-effectiveness, they may not fully adapt to the conditions encountered in the secondary crusher.
To increase durability and manage the impact of abrasion, we recommend switching to a hardfacing solution using welding, which will offer excellent wear resistance.
Despite this, caution is necessary – this surface treatment operation via hardfacing welding must be taken seriously due to the base metal and potential deformations caused by welding energy. Attention to detail is crucial.
In addition to offering good resistance to impact abrasion, it is entirely feasible, as part of a collaborative approach, to define a refurbishment/maintenance strategy with the operator. This strategy would involve hardfacing wear parts to improve the overall efficiency of the equipment.
The 3D drawings below were produced by Welding Alloys and show the profile of a cone before and after hardfacing.
3D plan of the cone before hardfacing
3D plan of the cone after hardfacing
2. Impact wear abrasion and temperature combined
2.1. Hammer forging
When considering the combined effects of impact and temperature, we will use the example of the production of car crankshafts. These components are forged using hammers in a step-by-step forging process.
Starting with a hot metal billet, each stage of the process brings the billet closer to its final shape through successive strikes. The billet is placed in a lower die, and as the upper die descends forcefully, it strikes the billet. Pestle forging involves minimal material displacement. However, the combination of high temperatures and the specific properties of the metal being forged results in significant surface wear.
This application has been extensively documented, and the solutions for addressing these stresses are well established. Building on this foundation, it is entirely possible to achieve a higher level of performance with a customised solution.