4 Items Need to be Known on Limestone Powder Grinding Line
As the calcium carbonate rock whose main component is calcite，limestone (CaCO3) is the main constituent of karst. It is the gray or gray-white sedimentary rock formed by the accumulation of biological shells or bones in the sea and lake basins.
With the wide application in building materials, highways, metallurgy, and chemical industries, the limestone powder grinding industry has developed rapidly and achieved good economic benefits. So, what do you need to know before engaging in limestone powder grinding?
This article will share the relevant content of the limestone powder grinding from the following four aspects, hope it will be helpful to you.
- 1 Introduction of limestone powder grinding
- 2 Applications of limestone powder
- 3 Selection of limestone powder grinding machines
- 4 Two things to be noticed in limestone powder grinding
Limestone powder grinding line in site
Introduction of limestone powder grinding
To engage in the limestone powder grinding industry, the most important thing to understand is how the limestone is ground into the powder. Limestone powder (calcium carbonate) ground into different fineness can be roughly divided into two types: light calcium carbonate and heavy calcium carbonate.
Therefore, according to the types of limestone powder, methods of limestone powder grinding can also be divided into light calcium carbonate powder grinding and heavy calcium carbonate powder grinding.
|Types of limestone powder||Light calcium carbonate||Heavy calcium carbonate|
|Appearance||Various regular shapes||Irregular shapes|
|Distribution of particle size||Narrow||Wide|
|Particle size||0.5-15 μm||0.5-45 μm|
|Bulk density||0.5-0.7 g/cm3||0.8-1.3 g/cm3|
|Whiteness||92%-95%, few reaches to 97%||89%-93%, few reaches to 97%|
|Moisture||Fluctuating, 0.3%-0.8%||Stable, 0.2%-0.3%|
|Application||Large filling content, as a volume filler||Small filling content, for modification or reinforcement|
Light calcium carbonate powder grinding method
Light calcium carbonate is an important basic chemical raw material and is mainly used as a functional filler for modification or reinforcement. Here are the processing steps of light calcium carbonate powder:
Process of light calcium carbonate powder
- 1 The raw limestone is burned into calcium oxide (CaO) and carbon dioxide.
- 2 Then the calcium oxide is digested with water to generate calcium hydroxide (Ca (OH)2).
- 3 Passed into carbon dioxide, the calcium hydroxide can be precipitated with calcium carbonate.
- 4 Being dehydrated, dried, cooled, ground, and sieved, at last, light calcium carbonate is produced.
Through calcining, carbonizing and pulverizing, this method of light calcium carbonate grinding is called carbonization.
Relying on the chemical reaction process, this method has a long flow, large energy consumption, serious pollution. Besides, the instability of performance severely restricts the application of light calcium carbonate.
Heavy calcium carbonate powder grinding method
Limestone rock can be directly used as the heavy calcium carbonate after grinding. Therefore, the dry production method is the most used method for heavy calcium carbonate. Steps are as following:
Process of heavy calcium carbonate powder
- 1 After removing the gangue, use a crusher to crush the limestone into a certain particle size
- 2 The crushed limestone is further ground with a grinding machine to obtain fine limestone powder.
- 3 The powder separator selects and collects the fine limestone powder that meets the fineness requirements.
Having stable performance and environmental protection during the processing, heavy calcium carbonate is bound to be widely used.
With the development and changes in the requirements of related application fields and downstream industries, heavy calcium carbonate has evolved from fine powders mainly based on d50 = 74 μm and d97 = 45 μm to ultra-fine powders and ultra-fine active powders.
The ratio of heavy calcium and light calcium application in some developed countries has reached 4: 1. Therefore, light calcium production will disappear sooner or later. To engage in the limestone powder grinding industry, it is wise to choose heavy calcium carbonate grinding.
Applications of limestone powder
Limestone can be applied to many fields after being ground into the fine powder and obtain considerable economic benefits. In recent years especially, the limestone powder grinding industry has gradually become popular.
Applications of limestone
Being crushed into a smaller certain size, limestone can be directly used as construction aggregate in the construction industry and can be sintered for use in steel plants after grinding.
While the uses of calcined high-quality lime (calcium carbonate) have expanded widely such as:
Being used as a slag-making agent for steelmaking, 1 ton of steel consumes about 40-50 kg of lime. And being used as raw materials for calcium carbide production, almost 1 ton of ash need one-ton lime.
Light calcium carbonate or nano calcium carbonate powder, depending on the fineness, can be used for paint or plastic product additives, and be used in papermaking, pharmaceutical, rubber production. The economic value of nano-scale calcium carbonate is quite objective with the price from several hundred to more than one thousand dollars per ton.
And the different uses of heavy calcium carbonate powder with different fineness are in the following：
|Within 200 mesh||—||Feed additives with a calcium content of more than 55.6%|
|250-300 mesh||≥85%||Raw materials for plastic, rubber, paint, waterproof material|
|350-400 mesh||≥93%||Make gussets, downspouts, chemicals|
|400-600 mesh||≥94%||Be used for toothpaste, soap, etc.|
|800 mesh||≥94%||Used for rubber, plastic, cable, PVC.|
|1200 mesh||≥95%||PVC, PE, paint, paper primer, paper surface|
Selection of limestone powder grinding machines
As the most important part of the limestone powder grinding, the choice of the grinding machine will directly affect the fineness of the limestone powder. So how to choose the most suitable one?
According to the input size, output size and needing capacity, the powder grinding equipment in the current market can be roughly divided into 3 types: Raymond mill, HGM German high-efficiency powder grinding mill, and three-rings and medium speed micro powder mill.
Besides, the methods of powder processing can also be divided into 3 types: coarse powder grinding, fine powder grinding and superfine powder grinding according to the fineness of the finished product.
Three types of powder grinding equipment
Coarse powder grinding
The recommended powder grinding equipment for coarse powder grinding is Raymond mill, which is also the most popular powder grinding equipment in the market.
As one of the most mature grinding mills, Raymond mill can grind more than 280 materials with Mohs hardness of 9.3 or less and moisture below 6% spread from mineral, chemical, construction to many other industries.
With finished powder fineness range from 80 mesh to 325 mesh, Raymond mill can meet the fineness requirements of limestone powder in most industries.
In addition, with the development of technology, the structure and function of Raymond mill are also improved. The specific improvements are as following:
- The traditional part of the powder separator has been changed from in-cavity dragging to external-cavity hanging transmission, which strengthens its stability and durability.
- The grinding roller rotates and whirls around the center shaft as well, so that Raymond mill can work under greater grinding force and higher running speed.
- Being formed into a bucket shape, it can protect the airbox and air duct from blockage.
- The electrical system adopts centralized control, which reduces human capita.
Structure of Raymond mill
The new Raymond mill with the above improvements not only improves the grinding efficiency greatly but also consumes less energy. With a capacity of 8-176 tons/day and good performance at a low price, it is more suitable for the small powder grinding plant.
Fine powder grinding
HGM German high-efficiency powder grinding mill is a new type of powder grinding machine which is designed by the latest international processing technology and concepts. The working principle is shown in the following:
Working principle of HGM grinding mill
- The spring pressurization device can not only increase the grinding force but also extend the service life of the grinding ring and grinding roller, which saves the maintenance cost effectively.
- The air duct designed in an arc shape makes the air inlet smooth and reduces the resistance. And the internal outlet direction is easy for the dispersion of the material.
- More accurate, the speed of the separator is controlled by frequency conversion, so the effect of fine powder sorting is better.
Compared with the traditional Raymond mill, HGM grinding mill has a larger capacity with 40 t/h and further reduces energy consumption. Therefore, it is the best choice for large-scale powder processing plant.
While the more advanced technology means higher prices, so HGM grinding mill is more suitable for the project with sufficient budgets and higher requirements of fineness and capacity.
Superfine powder grinding
As a representative machine for superfine powder grinding, the fineness of three-rings and medium speed micro powder mill can reach about 2000-3000 mesh. However, so fine its output size is, the capacity is only 500-7000 kg / h.
Cause the powder is so fine, its application and amount of use are very limited. As a result, three-rings and medium speed micro powder mill is not the mainstream equipment for powder grinding industry.
When choosing the powder grinding machine, you can refer to the following comparison table:
|Grinding degree||Coarse powder||Fine powder||Superfine powder|
|Machine||Raymond mill||HGM grinding mill||Three-rings micro grinding mill|
|Capacity||0.3-7.3 t/h||0.4-40 t/h||500-7000 kg/h|
|Output size||80-325 mesh||80-800 mesh||400-3000 mesh|
Two things to be noticed in limestone powder grinding
Ensuring the grinding efficiency and reducing dust pollution are the two most important aspects during the powder grinding. Ensuring grinding efficiency is the first factor for obtaining the expected economic benefits, and reducing dust pollution is an important measure of protecting the environment and achieving sustainable development.
Ensuring the grinding efficiency
After deciding the powder grinding fineness, the grinder capacity is a very important step that affects the profit. Ensuring the capacity has great significance for improving economic benefits. Then how to ensure the grinding efficiency of the grinder in the grinding operation?
Control the spindle speed: it is one of the aspects that affect the powder rate cause the
spindle speed reducing will lead to the reducing of grinding speed. And it
would be affected when there is a lack of operation power and when the
transmission belts wear out.
Therefore, during the powder processing, it is necessary to notice whether the grinder has sufficient running power or not and replace the worn transmission belt in time.
Check the wearing parts: The wearing parts such as the blade, grinding roller, and grinding
ring of the grinder being severely worn will also decrease the powder output
Therefore, checking and replacing the wearing parts is also an important part to ensure grinding efficiency.
Check the pipes: Being not well sealed, the air duct will be blocked, then the dust
would increase. With the negative pressure imbalance, the powder transport rate
will decrease, which reduces the powder output rate of the grinder.
As a result, the seal of grinder needs to be checked carefully before working. Once the air duct is blocked, stop the operation and dredge the pipeline in time.
FTM powder grinding equipment
Reducing dust pollution
Dust pollution is one of the most common and difficult problems in powder grinding. Dust pollution can be reduced from the following aspects:
- Adding an aerosol dust removal system at the inlet of the grinder is an important way to reduce dust pollution. While the amount of water needs to be controlled strictly cause the grinder would be blocked if the moisture of material is more than 10%.
- Take a closed approach among parts of the grinding line to prevent dust leakage.
- Choose a high-quality dust collector. Dust collector plays a very important role in the powder grinding, which affects the discharge of dust directly.
FTM dust collector
The non-renewable and non-creative of limestone determine the "expensive" trend of high-quality limestone powder. With quality depending much on the degree of limestone resource, the production of high-quality heavy calcium carbonate is the "stability anchor" of the lime industry in the future.
Fote Heavy Machinery (FTM), as one of the biggest manufacturers for mining machines with more than 37 years’ experience, we have introduced much advanced technology from both Germany and America. Also, we have more than 300 professional engineers to design the most suitable powder grinding equipment for your project.
Any questions about the limestone powder grinding are welcome to ask our professional engineers. We are looking forward to your inquiry.
Powder grinding equipment designed by FTM