A scalper, or scalping screen is a machine used to separate mixed materials into different grades. These machines are at the core of most construction and quarrying operations, and are one of the most used pieces of equipment onsite. They work after a crusher or an excavator, which feeds material into the screener for sorting.
The purpose of a scalping screen is to pre-process material for different applications. For example, gravel that will be used in landscaping might require stones that are no bigger than 2 inches, and no smaller than 0.5 inches. A scalping screen could be used to remove any material that is coarser or finer than these sizes.
How does a screener work?
The simplest way to explain how a screening machine works is to think about it as a large sieve. When you sieve flour you place it into a mesh container so that no clumps of flour can pass through to your mixing bowl. You might also shake your sieve to help the flour work it’s way through the mesh.
'Scalping' refers to removal of larger pieces of material from the mix, exactly like our sieve. Scalping screeners use vibrating meshes to output different sizes of material. The meshes, or 'screens' are stacked in tiers, and the material dumped on top.
As the screens shake, smaller material falls through the holes in the mesh, leaving larger pieces on top. For fine screening applications (<6mm), the screens are usually on an incline, so any material that doesn't fall through each tier can tumble onto a conveyor to be carried away. For less fine screening, the throw of the decks will move the material on to the conveyors.
The graphic below shows how material is sorted through these screens.
The number of screens used is linked to the number of material grades output from a scalping screen. For example, if you want to turn a pile of mixed soil into 3 different sizes, you would pass the soil through two screens.
These screens come in a range of different sizes and can be hot-swapped out of a machine. Changing screen size will change the size of materials that are being fed out of the machine. When the aim is a high volume of fine material the size of the bottom screen will be the limiting factor. A lot of screening machines will use a tapered design, where the decks get smaller towards the bottom. This restricts the flow of fine material at the bottom of the machine, and can cause a bottleneck.
A screen with flat sides (like this SR124), will provide a larger bottom deck than a tapered machine. Meaning it can process material much quicker and more efficiently than a machine with a similar footprint.
Screeners may also use water as part of the sorting process, but this can come with some challenges. For example, protecting the machine from water damage, or safe extraction and post-processing of water used during screening.
Screening by stratification
By building up a material bed on a screen deck the material will stratify when the motion of the screen will reduce the internal friction in the material. This means that the finer particles can pass between the larger ones giving a sharp separation.
Screening by free fall
If we use the double inclination used for stratification (from 10-15 up to 20-30 degrees) we are in free fall, meaning that no particle layer can build up on the screen deck. The particles will now be sized directly via the screening media, giving a higher capacity, (or a more compact installation), but also less sharpness in separation. Optimal use when a large amount of fines shall be removed fastly.
Common materials for screening
There are a huge variety of materials that can be screened, but to give you an idea of the types of materials, here a few of the more common ones;
- Crushed rock
- Zircon sands
- Wood pellets
- Metals and metal slags
- Construction rubble
The type and condition of the material can also affect the performance of a screening machine. For example, if a material is wet it can sometimes bind and clog a machine. Or if a material contains a large amount of fines is may take longer to process with some machines.
Benefits of screening
Aside from the obvious benefit of having a more consistent end product size, screening can offer other benefits such as;
- Removal of contaminants from food products or animal feed
- Less dust production (more health and safety friendly)
- Less wastage of ‘fine’ products when material is processed further
- A portable screener can remove the need for material to be transported away from a site. It can instead be reused for other applications; saving money and time.
- Bi products of other processes can be re-used or sold to increase income
Scalping screens in particular have some extra benefits over other screening machines. They generally have a large screening area, meaning they can process a lot of material quickly. They can also be fitted with a large variety of screening media.
Scalping screens are very versatile, designed to handle a range of materials, from demolition materials and heavy quarry outputs, to finer soil applications.
Application of a scalping screens
Top soil preparation
Scalpers can be useful in preparation of top soil for use in the agricultural systems like greenhouses and basket gardening. Often the soil has to be prepared by controlling the grade (particle size), as there are grades that are too large to be used in these applications.
This improves the flow of moisture, and ease of handling the materials. Scalping screens have served as the most reliable machine for this use case. Especially in large-scale preparation of top soil; as they are fairly accurate, and require less operational costs.
Quarries mostly process soils and rocks. Often, when processing soil, large heaps will contain covered rock masses, and there is a need to separate the two. This has always called for the use of screening to pre-process the material. With a scalper screen, it is possible to separate the large heaps of soils from the rock masses quickly and cost effectively.
Crushing processes also generate rocks of different sizes. Here, it is often necessary to sort them for ease of use. For instance, the aggregate used in road surfacing are different to the aggregate laid in a foundation. Different buyers also prefer different aggregate sizes.
Scalping screens have revolutionized this sector. Sorting materials has become very cheap, making for a lower break-even point and more competition within the market.
Use of scalping screen in the demolition site
Demolition often involves the complete destruction of a structure. This is often done through explosives and wrecking balls.
After the demolition process is complete, the demolished materials are usually dumped. However, there are often some aggregates left over that can be useful in other construction sectors.
These materials are often embedded debris from the knocked structure, and it can be expensive to separate them.
By using a scalping screen, the aggregates can be separated from the debris, allowing for recovery of useful materials.
Scalping screens can do wonders for a demolition process. So much of the useful, non-biodegradable aggregates remain unaltered within the debris.
By grinding the materials into finer particles then washing them using running water, fine aggregates can also be recovered. This ensures any dust is removed, so the aggregates can be made good use of or even recycled in the erection of another structure.
Use of screeners in mining
Unlike quarrying (the opencast extraction of rock masses), mining involves the removal of useful ores from the earth’s crust.. Mining may also involve the separation of soil and gravel debris from those ores. This involves heavy duty operations that cannot not be attained through human labour.
A scalper screen makes it relatively convenient to separate the ores from the debris. Huge tones of soil materials are involved in the mining processes, as the required ores usually make up a small percentage of the mined material.
Scalping screens facilitate cost effective separation of the ores from the soil before transportation to a processing site.
Screens for recycling
Recycling involves the rehabilitation of a material for reuse. Even though most metals are biodegradable, it takes a long time for them to completely break down. Waste metal and plastic materials often pollute the environment when not recycled. This results in pollution and land dereliction.
Using a scalping screener, huge quantities of debris and waste can be screened to remove useful materials like iron and plastics.
Why should you buy a scalper?
There are so many machines that are useful for handling soils as well as rock materials. But if you trying to purchase every type of material process machine won't get you the best ROI.
For this reason, it's a good idea to opt for a more versatile machine. Scalpers can be used across various industries to process a variety of materials. This means that the potential run time of a scalper can be very high, since there is high demand for its use.
What size screener should you choose?
If you now think a scalping screen may be useful for you, how do you know what size to go for? As with everything, bigger isn't always better, and it's important to choose the right equipment to match your needs.
After selecting a material and appropriate machine type, you can start to work out a bed size based off how much material you need to output. If you only need 10,000 tonnes of material a week, there's no point purchasing a more expensive machine that can process 40,000 tonnes a week.
It's much better to work out the monthly/yearly material requirement and use your projected running hours to figure out what machine size fits your application.
If you need more information on what machine might be right for your application, you can also contact Machinery Partner. We have a team of machine experts that can help match you with the right machine, and ship it to you directly from the manufacturer.
Another thing to keep in mind is the end product. As mentioned above, multi-deck screeners can sort a few sizes of product products, as well as some oversize. So you could be producing multiple products with a single machine, which should be factored into your ROI (Return on investment) calculation.
How can you acquire a scalper?
Getting a machine has never been as easy as it is now. Thanks to the advent of the internet, sites like Machinery Partner have made the world a much smaller place.
We operate as a managed marketplace for heavy machinery. Allowing you to search for all kinds of heavy equipment, and have them shipped directly from the manufacturer to you.
We also have a directory of machines bought from us that are available to rent. So if you're not quite ready to take the plunge on that screener you've been eyeing up, you can rent a machine near you to try it out first.
If you enjoyed this, be sure to check out our other articles and guides.