Toll Milling and Mineral Processing -
A Guide to Equipment, Services, and Applications
Processing minerals requires specialised machinery that’s suited for the type of mineral being milled. There are quite a few machines for mineral milling that each has a unique specialisation. In order to achieve the highest quality according to specifications, it’s essential to have and use the proper machinery. Toll milling is the exchange of custom milling services and other processing services for a fee or toll. This guide is a review of some of the machines we use in our cutting-edge milling facilities. By familiarising yourself with this equipment, you can get a better idea of what services and machines you’ll need.
Every mineral has its own set of characteristics that determine what type of processing is needed to break them down to the chosen specifications. Specifications will generally identify a size range that the particles must be for a certain application. The proper machine(s) must be used depending on the mineral or ore, its hardness on the Mohs scale, its abrasiveness, etc., and the desired result.
Using the wrong machine for milling and processing can result in improper processing and wasting of the mineral ore or worse, costly damage to the equipment. It is imperative that you know and use the machine that is right for your purposes. This knowledge is less vital when you’re hiring experts to mill your materials, but some companies might consider purchasing the machinery themselves to cut the cost of hiring millers.
So How Much Does it Cost to Buy the Equipment yourself?
The cost of mineral processing equipment is high enough that you should not invest in the machinery if processing is not part of your daily business. This is simply because the return on investment will not be high enough to justify the capital expenditure if you’re only using your machine occasionally. It might seem like a clean solution for those who regularly require custom milling services, but the equipment is just too expensive to be a practical solution.
Another aspect to consider when deciding whether or not to purchase your own milling equipment is the increased safety hazards these machines can create within your facility. The unforgiving power of crushing and grinding machines require intensive training for inexperienced personnel. That means increased labour hours and possibly higher insurance costs. Before buying your own mill, it is crucial that you review all of the effects, both positive and negative, that it will have on your business as a whole.
Purchasing and implementing the necessary machinery yourself is cost-intensive and probably not as convenient as it might seem, considering the facilities, labour, and maintenance. For most industries, the most cost-effective solution is to build a relationship with a reliable, experienced, and reputable mineral milling company for toll milling. These experts will know exactly what machine you need to achieve the results you’re looking for with the mineral or ore you have in mind.
African Pegmatite is a mineral mining, milling, and processing company with decades of experience servicing five continents with 100% customisable shipments. Our cutting-edge facilities contain all of the standard machines listed in this guide, as well as some not mentioned here and some that were custom designs and built for our factories. Our experts are always available to assist you, whether you need help determining what specs you need for your applications or the best shipment size and frequency for your budget and production schedule.
Mineral Processing Equipment
African Pegmatite uses all of these machines regularly for the processing of a full range of minerals. Each type of mill specialises in a particular type of material or a particular type of milling. There are crushers and grinder that produce slightly different results. There are mills that wear materials down through attrition and those that are gravity fed. One thing that’s true of virtually every machine we employ is that they can be set to produce ground or crushed rocks, aggregates, minerals, and ores to your exact specifications, which is crucial when using these materials for industrial purposes like water filtration, pigmentation, and more.
Ball Mill Services
The ball machine crushes materials using centuries-old principles of grinding that have been refined and applied to modern-day equipment. The machine contains various types of balls, depending on the mineral being processed, that grind and crush through repeated impact. The balls are usually chrome steel, but stainless steel, ceramic, and rubber can also be used for less common processing, like explosives. Flint pebbles are another common grinding media.
A large, cylindrical chamber lined with a particular material – either an abrasive-resistant surface or rubber – is partially filled with the balls and the minerals are placed inside the chamber, as well. The rotation of the cylinder causes the balls and minerals to remain in constant impact that slowly wears the mineral to a specific size or powder ratio.
Ball Milling is used in the processing of ceramics, paints, coal, pigments, feldspar, and more. In addition to grinding minerals down, a ball miller is often used to mix or blend materials. It can be used for wet or dry milling. Standard ball milling is performed by rotating the chamber around a horizontal axis. High energy ball milling involves a second, larger chamber in which the smaller agitates, sloshing the contents via centrifugal force. Both types of ball milling can be performed in batches or continuous operation.
A hammer mill is comprised of a steel drum that houses a horizontal shaft that rotates at high speed. Attached to the shaft are numerous hammers that crush the mineral as the shaft rotates. Some hammer mills have several large hammers while others have dozens of smaller hammers.
Generally speaking, all hammer types will be hinged so that they move with a swinging motion and have a very small gap between the extended hammer and the interior of the drum. Hammer mills have existed since 488 A.D. and were once water powered. This type of milling can be used as the primary milling process or can be used as a follow-up to achieve more precise results.
As the mineral is fed through the hopper, the hammers make repetitive impact at high speed and shatter the material. Crushed pieces are sifted through the bottom of the mill and can be process further or used depending on the requirements. In African Pegmatite’s facilities, this process is done on a large scale, but hammer milling can be done on a small scale.
Roller mills are one of the most effective milling machines when it comes to crushing calcite, feldspar, gypsum, clay, marble, glass, or other materials into a fine powder. The roller mill can easily meet the specification of 80 to 600 mesh and is widely used throughout the mining industry.
A roller mill works by grinding materials at high speed with a varying number of heavy, cylindrical rollers being spun around a central vertical shaft. The mineral is fed into the machine through a port in the side and is immediately crushed into powder by the large roller wheels.
A cone crusher is an efficient crushing machine that works by introducing the material into the top where it falls down towards a crushing cone that is pointed up. The cone rotates and agitates inside the cylindrical housing, crushing the mineral between the cone and the interior wall.
The cone can be set to a specific crushing size by raising it towards or lowering it away from the bottom of the cylinder. The crushed material falls through the gap between the cone and cylinder. Materials can be passed through multiple crushers to achieve specifications. Rocks are the most common material crushed in a cone crusher. The crushed rocks are typically used for landscaping, road work, mining, and erosion control.
A roller crusher is a very common type of crusher that’s used across many industries outside of mineral milling with various design alterations. For the purposes of mineral processing, a roller crusher consists of two grinding rollers that rotate in opposite directions towards each other with little space between them. Rocks, ore, or other aggregates are fed into the top of the roller crusher where they fall into the valley where the two wheels meet. The rotation forces the materials between the rollers where they are crushed and the fragments fall through the narrow gap. The size of the gap determines the results of the crushing.
There is another type of roller crusher called a high-pressure grinding roll or HPGR. This type of roller crusher reduces the mineral size through compressive and interparticle pressure. Measurements are figured mathematically beforehand.
Attritor mills are a type of ball mill that are sometimes referred to as stirred ball mills. They come in a variety of sizes for many different industries from labs to factory floors. Attritor mills are best suited for ceramics, food, pigment mixing, paper coating, iron production, glazes, pharmaceuticals, coal, and chemicals. The balls inside the attritor mill can be made of various materials, but must be stronger than the material to be milled.
A vertical centre shaft inside a cylindrical tank is fixed with arms that spin around the shaft at high speed. The arms can vary slightly in design. The tank is partially filled with balls and then the mineral is introduced. When the arms spin, they make impact with the material and the balls, both of which fly around the tank making impact with each other at high speeds. If the material is softer than the balls, it will be pulverised into a fine powder.
The jaw crusher is the primary crusher type used in the mining and ore crushing industry. It is made up of two panels that are arranged in a V shape with a small gap at the bottom. The size of the panels and gap depends on the specifications for the rocks, ore, or other aggregates to be crushed. One of the panels in the V configuration oscillates towards and away from the other panel. This allows bits of rock or other material to fall further into the V when the panel moves away, and then be crushed when the panel moves back in. The crushed fragments fall through the gap at the bottom of the panels. This sort of chewing motion gives the jaw crusher its name.
Custom Milling Services and Toll Processing
Familiarising yourself with some of the machinery used in mineral processing and toll milling is the first step towards establishing a solution that works best for you and your business. These are a few of the machines we have at our disposal, ready to process your ore and minerals to exact specifications that will ensure optimal performance in your applications. Will this equipment and the other machines we have not mentioned here, we can fulfil any milling request, regardless of mineral hardness or abrasiveness. In subsequent articles, we’ll discuss the functions of each machine in more detail, including what services they allow us to offer.
Toll processing allows you to get professional class results and optimal performance from your milled materials without adding the complication and high capital expanse of a purchased mill to your business. Use our services when you need them, saving you time, money, and resources. You can rely on our team and our equipment to provide the service you expect and deserve.
Contact African Pegmatite today to speak to a toll milling expert about your needs for your minerals and ore. We are located in South Africa and provide mining and milling services for industries across five continents, working closely with our valued clients for both short projects and ongoing services. Our advisers will be happy to offer assistance in determining what specifications are best for your applications and what machine and processing services are best for your specifications.