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Jordan is the writer of the blog with a broad knowledge of this industry. Most importantly, he hopes to help you in your projects sincerely.

What are the differences between ball mill and rod mill?

Author : Jordan Last Updated : Nov 23, 2019

Ball mill and rod mill are the common grinding equipment applied in the grinding process. They are similar in appearance and both of them are horizontal cylindrical structures. Their cylinders are equipped with grinding medium, feeder, gears, and transmission device.

similar appearence and working principle of ball mill and rod mill

Similar appearence and working principle of ball mill and rod mill

The working principle of ball mill and rod mill machine is similar, too. That is, the cylinder drives the movement of the grinding medium (lifting the grinding medium to a certain height then dropping). Under the action of centrifugal force and friction, the material is impacted and ground to required size, so as to realize the operation of mineral grinding.

BALL MILL VS ROD MILL: what are the differences between the two devices that are so similar and how to select suitable equipment? Please find the answer in this article.

Differences between ball mill and rod mill

Different in performance

Ball mill

It can be divided into two types of ball mills according to the discharging ways, overflow discharge ball mill, and grate discharge ball mill.

FTM ball mill

FTM ball mill

Grate discharge ball mill

Grate discharge ball mill can discharge material through sieve plate, with the advantage of the low height of the discharge port which can make the material pass quickly so tha t to avoid over-grinding of material. Under the same condition, it has a higher capacity and can save more energy than other types of mills;

It is better to choose a grate discharge ball mill when the required discharge size is in the range of 0.2 to 0.3 mm. Grate discharge ball mill is usually applied in the first grinding system because it can discharge the qualified product immediately.

Overflow discharge ball mill

Overflow discharge ball mill is designed with no sieve plate so that the ore pulp can be discharged directly without filtration. It is very simple in structure and convenient in maintenance.

Though there is no sieve plate, the discharge pipe is cast with reverse threads, which makes that the large ores and balls are hard to discharge from the ball mill machine.

Overflow discharge ball mill can grind ores into the size under 0.2 mm, so it is very suitable for the second grinding system. The capacity of it is about 15% lower than grate discharge ball mill in the same specification, and the loaded grinding medium is also less than that one.

Rod mill

FTM rod mill

FTM rod mill

It can be divided into three types of rod mills according to the discharge methods, center and side discharge rod mill, end and side discharge rod mill and shaft neck overflow discharge rod mill.

Center and side discharge rod mill

It is fed through the shaft necks in the two ends of rod mill, and discharges ore pulp through the port in the center of the cylinder. Center and side discharge rod mill can grind ores coarsely because of its structure.

This kind of rod mill can be used for wet grinding and dry grinding. "A rod mill is recommended if we want to properly grind large grains, because the ball mill will not attack them as well as rod mills will."

End and side discharge rod mill

It is fed through one end of the shaft neck, and with the help of several circular holes, the ore pulp is discharged to the next ring groove. The rod mill is mainly used for dry and wet grinding processes that require the production of medium-sized products.

Shaft neck overflow discharge rod mill

It is fed through one of the shaft necks and discharges materials through the other shaft neck. It can be used for wet and dry grinding and also for the first grinding system.

The diameter of the shaft neck is larger than the diameter of the feeding port about 10 to 20 centimeters, so that the height difference can form a gradient for ore pulp flow. There is equipped with a spiral screen in the discharge shaft neck to remove the impurities.

Different in grinding medium

Grinding medium of ball mill

The ball is used made of several materials:

Grinding medium of ball mill

Grinding medium of ball mill

  • 1High manganese steel

    It has high toughness, good manufacturability and low price. The surface layer of high manganese steel will harden rapidly under the action of great impact or contact. The harder index is five to seven times higher than other materials, and the wear resistance is greatly improved.

  • 2Low carbon alloy

    It has high toughness, good manufacturability and low price. The surface layer of high manganese steel will harden rapidly under the action of great impact or contact. The harder index is five to seven times higher than other materials, and the wear resistance is greatly improved.

  • 3High carbon and high manganese alloy

    It is made of several elements such as chromium and molybdenum, which has high hardness and good toughness. Under the same work condition, the service of this kind of ball is one time longer than the high manganese steel ball.

Grinding Medium of rod mill

Grinding medium of rod mill

Grinding medium of rod mill

The rod of diameter from 50 to 100 mm is often used as the grinding medium, and the filling rate of rod mill is 35% to 45%, while filling rate of ball mill is 40% to 50%。

Rod is mainly made of several materials:

  • AHigh carbon steel

    After the professional technology straightening and quenching processing process, a high carbon steel rod has high hardness, excellent performance, good wear resistance and outstanding quality.

  • B42 Cr Mo steel

    It is improved based on the 40 Cr steel, which makes the wear resistance is about the 1.3 to 1.5 times of 40 Cr, but the price is only 1.1 times of 40 Cr.

Different in application

Ball mill and rod mill: wide range of applications

Ball mill and rod mill: wide range of applications

Ball mill

  • 1Ball mill has a wide range of applications. It can grind metal ore and non-mental ores, which is suitable for hard materials, such as quartz, gold ore, copper ore, iron ore, potash feldspar, etc.
  • 2Ball mill is also can be applied in the industries such as cement, construction materials, fireproofing materials, chemical fertilizer, ore beneficiation, glass and ceramics. And the fineness of the finished product can reach 800 meshes.

Rod mill

  • 1Rod mill can be used as the fine crushing equipment to replace short-type cone crusher when crushing soft ores. It has a simple configuration, less costs and low dust pollution, which can save a lot of investment in dust removal machines.
  • 2When the tungsten ore, tin ore or other rare metal ores are selected by gravity separation or magnetic separation, rod mill is often used to prevent over crushing.
  • 3In the two-stage grinding process, rod grinding machine is generally used as the first grinding equipment, which has the advantages of larger production capacity and higher efficiency.

Recommendation of ball mill and rod mill

Ball mill and rod mill are suitable for different materials

Ball mill and rod mill are suitable for different materials

1. Selection by material's hardness

Ball mill has a strong adaptation of material, and it is suitable for grinding hard materials, such as slag, iron ore, copper ore, etc.

Rod mill is suitable for grinding brittle material, such as rare metals.

2. Selection by required particle size

The steel ball of ball mill and the mineral material are in point contact, so the finished product has a high degree of fineness, but it is also prone to over-grinding. Therefore, it is suitable for the production with high material fineness and is not suitable for the gravity beneficiation of metal ores.

When the required particle size of the finished product is less than 0.5mm, it is recommended to use a ball mill.

The steel rod and the material are in line or surface contact, and most of the coarse particles are first crushed and then ground. Therefore, the finished product is uniform in quality, excellent in particle size, and high in qualification rate.

When the finished product size is required to be 1 to 3mm, it is recommended to use a rod mill.

3. Selection by the work site

In the design of the dressing plant, it is usually necessary to design the floor plan of the grinding workshop in advance, so it is necessary to consider the shape and size of the equipment.

The cylinder shape of the rod mill and the ball mill is different: the cylinder of the rod mill is a long type, and the floor area is large. The ratio of the length to the diameter of the cylinder is generally 1.5 to 2.0;

The cylinder of the ball mill is a barrel or a cone. And the ratio of the length to the diameter of the cylinder is small, and in most cases the ratio is only slightly larger than 1, and the floor area is small, too.

Therefore, it should be considered whether the equipment installation conditions can be met when selecting.

FTM--profesional ball mill and rod mill manufacturer

FTM--profesional ball mill and rod mill manufacturer

The above is the main content of this article. The ball mill and the rod mill are the same type of machine on the appearance, but there are still great differences in the interior. It is very necessary to select a suitable machine for the production to optimize the product effect and maximize its efficiency.

Reference:

https://www.sciencedirect.com/topics/engineering/rod-mill

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