With sourcing of sand from natural sources such as rivers and coastlines outlawed in many African countries, manufactured sand is proving to be the most economical and ecological alternative. Yet, the production of sand using conventional crushing solutions such as vertical shaft impact (VSI) and cone crushers has its limitations.
Before VSIs became as common as they are now, cone crushers were preferred, but they are an uneconomical way of producing sand. The downside is that for cone crushers to produce sand, one needs to crush with a very tight closed side setting (CSS), which by its nature is not economical because of the extremely high wear it causes, plus some other adverse operating conditions as a consequence of this requirement like high power demand and continuous ring bouncing condition due to the fines generated, with further damages to the machine main components.
While the VSI has proved itself as the ultimate sand-maker, producing high-quality manufactured sand with a consistent shape and gradation, it is inherently a power-hungry machine, which makes it unfavourable, especially in an environment where energy efficiency is becoming a principal parameter. Depending on the application conditions, VSIs high circulating loads and wear rates, could make the operation cost intensive.
In addition, the VSI is highly dependent on constant feed material, which means there is a high possibility of excess fines. To mitigate excess fines in sand-making, washing has become a go-to solution for ultra fines removal. Given the water shortages in southern Africa and several other regions on the continent, washing is often out of the question.
Considering these challenges, Francois Marais, sales and marketing director at Pilot Crushtec, believes that the introduction of the HRC 8 marks a new era in manufactured sand and aggregate production. The HRC 8, he says, has a completely different crushing principle from other conventional solutions such as impact crushing.
The HRC 8 uses a method of inter-particle comminution by drawing in a bed of material between two rotating rollers. The rollers, one of which is in a fixed position and another floating, generate an extremely high pressure that is applied to the layer of material between the rolls, extruding the feed material down to the desired smaller grain sizes. The HRC 8’s adjustable pressure allows customers to vary the curve grading for finer or more coarse grading.
Closing the gap
Some six years ago, Metso became the first global aggregates equipment manufacturer to introduce an HPGR crusher in manufactured sand and aggregates. Oldemar Meneses, product manager, HRC Technology at Metso, says the move was informed by the realisation of a gap in the market for a machine that could produce fines with fewer unwanted microfines (0,075 mm) in the final product. Customers, he says, were also looking for a machine suitable for difficult applications where waste material from the crushing and screening processes (material with low mass gradings, difficult to crush by a VSI or other types of compression crushing) could be processed to obtain a high quality sellable product.
“To help customers address these pain points, the HRC 8, based on Metso’s existing HRC 800, was introduced in 2018, specifically for the manufactured sand and aggregate industry. The HRC 8 works in applications where traditional cone and VSI crushers cannot. It can handle material that is small in size and very difficult feed materials that are challenging to process by any other technology, even those with high abrasiveness, low crushability, high moisture and fines,” explains Meneses.
The uptake of the technology in the sand market has been remarkable. To date, Metso has some 130 HRC machines operating in the world, with 80% in manufactured sand, and the rest in quarrying and reprocessing.
The ultimate sand-maker
The HRC 8 is the ultimate solution for the manufactured sand market where fines must meet a defined end product specification. The quality of sand can be adjusted and optimised, thus reducing the amount of cement and asphalt required in concrete mixes or asphalt. The machine produces a gradation according to customer needs and delivers a perfect cubical shape for concrete and asphalt sands.
In some applications, non-sellable waste materials can be reprocessed by the HRC 8 to correct the gradation curve and particle shape, converting them into high-value sellable products. This not only addresses the cost factor, but also speaks to the manufactured sand sector’s drive for sustainable operation.
“In typical sand-making with VSIs, for example, there is generally a high percentage of ultra fines – the unwanted 0,075 micron material, which calls for wet processing. Due to its ability to produce very fine material with fewer unwanted microfines in the final product, we believe that in some applications, the HRC 8 may eliminate the requirement for washing,” explains Marais.
Key benefits
Based on customer feedback from Metso’s global installed base, Meneses tells Quarrying Africa that customers in the manufactured sand market have particularly commended the HRC 8 for its throughput, energy efficiency, reduced operating costs, as well as safety and ease of maintenance.
The HRC 8 can provide a notable increase in throughput. The flange design maximises the amount of material that is crushed by pulling the feed into the crushing zone. This method prevents the material passing the rollers and increases efficiency and throughput. The patented arch-frame, on the other hand, eliminates downtime caused by skewing. One can also adjust the speed and pressure of the machine depending on the material conditions and application requirements.
“Depending on the reduction ratio, the size being produced and the screening efficiency, we have most operations in the sand manufacturing market running the machine at 60-80 tonnes per hour (tph), which is a remarkable throughput,” says Meneses.
Thanks to the ability to handle a continuous stream of material, HRC’s are considered to be energy efficient grinding machines in general. The HRC 8 goes a bit further; it directs the feed material straight to the crushing zone and adjusts the speed and pressure in order to avoid energy wastage.
The machine uses a combination of high pressure and a unique patented roller design to achieve a fine grind with minimal energy input. The arch-frame roller design eliminates the need for a spring-loaded frame, which ensures even pressure distribution across the whole width of the rolls, resulting in sound performance and longer wear life.
“The reduced power required to run the machine compared to traditional impact and even cone crushers is another big benefit of the HRC 8. To provide context, where customers would traditionally require 250-300 kW of power to produce 50 t of manufactured sand, they now use only 120 kW with the HRC technology. In fact, the machine consumes up to 50% less power in sand production compared to other technologies for the same volume of net product,” explains Meneses.
Equipped with a robust wear protection system, the HRC 8 minimises maintenance downtime and extends the operational life of the machine. The wear protection system includes carbide studs on the rolls and a wear-resistant feed system.
“The machine runs at a very low speed – a maximum of 32 rpm – resulting in reduced roller wear. As a result, some of the customers running this machine in manufactured sand only replace their wear parts once every six months or once a year, depending on application. Customers have found this machine to be almost maintenance-free because the number of replacement parts is minimal,” says Meneses.
By reducing energy consumption and increasing wear life of components, the HRC 8 helps lower operational costs. Its efficient grinding mechanism also reduces the need for secondary crushing, further cutting down operational expenses.
“Due to the low speed at which the rolls move, there is also very little machine vibration and far less wear on the manganese parts. You can imagine the operational benefit of only having to change the manganese wear parts once every year, for example. On VSIs, in some cases these may need to be changed every week depending on the application. However, it is important to note that there is still a place for other crushing solutions – for some customers, a VSI will still be suitable for their operational needs.”
During the design of the HRC 8, Metso cast a special focus on safety and ease of maintenance. The key to improving safety during maintenance is to minimise the need for maintenance. With the HRC 8, maintenance downtime has been reduced by using robust components, while high-pressure rock-on-rock crushing enables long wear-life of the manganese tyres. The patented split shaft allows for the tyres to be replaced quickly, without full machine disassembly, making the changeout of wear components easy and effortless.
The machine is also encapsulated with guards to eliminate the risk for operators during operation – the operator cannot access the moving parts.
First machine
Ahead of the official launch, Pilot Crushtec has brought the first HRC 8 into South Africa. Marais tells Quarrying Africa that the machine will be mounted on a mobile tracked chassis, making it the world’s first tracked HRC 8. In addition, Pilot Crushtec will also have on offer a static module on a skid frame, complete with handrails and walkways.
“The tracked approach will allow for ease of machine movement on or between sites, especially during the demo period. We will be trialling the machine on various local customer sites to prove its effectiveness,” concludes Marais.
