Rod mill Introduction

The rod mill is a mill in which the grinding body loaded in the shell is a steel rod. Rod mills are generally of the wet overflow type and can be used as primary open-circuit grinding. They are widely used in the primary grinding of artificial stone sand, mineral processing plants, and power departments of chemical plants. The rod mill is an asynchronous motor connected with a small gear through a reducer, which directly drives the surrounding large gears to decelerate and rotate, and drives the rotary part to rotate. The shell is equipped with an appropriate grinding media—steel rods. Under the action of the machine, the material to be ground continuously enters the inside of the shell from the feeding part, is crushed by the moving grinding media, and the product is discharged out of the machine through the force of overflow and continuous feeding, so as to proceed to the next process.

Rod mill structure

Trunnion: The trunnion (hollow shaft) of the rod mill is a steel casting manufactured in our metal casting workshop. It mainly plays the role of supporting and connecting the shell, it is the passage for the material to enter and exit. When the ball mill is operating, the trunnion is floating on the bearing bush with the aid of the forced high pressure lubrication system.

Bearing Bush: rod mill bearing bush ensures the smooth rotation of the ball mill and empowers the ball mill to maintain optimal grinding conditions. It is equipped with a forced lubrication system and also cooling system. It has alloy surface and 3 rolling rods on the bottom to make sure when the ball mill trunnion moves, the position of the bearing bush can be adjustable.

Hood Cover: The discharge hood of the rod mill is installed at the discharge end of the ball mill, and there is a screen inside. After grinding, the material with a qualified size will enter the discharge hood through the screen and enter the next process. There is a vent on the upper part of the discharge hood, and a discharge funnel on the lower part.

Diaphragm: The ball mill Diaphragm (compartment plate) is fan-shaped plate or bow-shaped grate plate fixed in the rod mill with bolts. Its function is to divide the ball mill into two or more chambers, the material moves to the next compartment through the openings on the grate plate. The function of the compartment plate is to prevent the grinding media running from one compartment to another compartment, so that the materials can be reasonably finely ground.

Liner: The function of the liner is to protect the shell of the ball mill and the trunnion, some special-shaped liners can also design to lift the grinding media to a certain position. According to the shape of the liner, it can be divided into flat liner, beaded liner, corrugated liner, ribbed liner, stepped liner, etc.

Rod ball mill transmission: Central drive ball mill refers to the arrangement of the driving mechanism for the mill. In a central drive configuration, the motor and gearbox are positioned at the center of the mill, usually between the grinding chamber and the mill shell. This design is in contrast to an edge or end drive configuration where the motor and gearbox are situated at one of the ends of the mill. Central drive transmission systems typically involve a motor that powers a gearbox, which then transfers the rotational energy to the mill's main shaft. The central drive design can provide advantages in terms of power distribution and efficiency compared to other drive arrangements. It can also offer better control over the mill's operation.

PLC control system: A PLC is a digital computer-based system that is designed to control various industrial processes automatically. In the context of a ball mill, a PLC is used to monitor and control parameters such as temperature, rotation speed, air flow, fuel flow, and other critical variables that affect the performance of the ball mill and the quality of the products being processed. 

Design principles of rod ball mill

Rod mill is used when 80% of the particle size of the product is required to be less than 2.0% to 0.5 mm. The product particle size of the rod mill is generally not more than 4.7 mm, and the minimum is not less than 0.4 mm. The feed particle size of the rod mill is 80%. Less than 20 mm to 4 mm, the maximum particle size of the ore can reach 50 mm. Due to the material of the grinding rod and other reasons, the length of the grinding rod cannot exceed 6.0meters, otherwise it will cause bad effects such as disordered rods.

When the ore is fed into the rod mill, the coarse particles are at the ore feeding end, and the fine particles are at the ore discharge end, the rod group cannot be completely parallel and inclined during operation, which is also a reason for limiting the length of the grinding rod.The crushing ratio of the rod mill is 15:1 to 20:1.

Because the grinding rods of the rod mill are in line contact, the large materials are firstly ground, which has a selective grinding effect, so the product particle size range is narrow, the product particle size is uniform, the phenomenon of over-grinding is less, and the grinding efficiency is higher.

Advanced manufacturing Equipment: Tongli has over 100 set of large-scale mechanical processing equipment, especially a 5.3x18-meter fully numerically controlled horizontal lathe to ensure the processing accuracy and concentricity of the ball mill.

Heat treatment: Tongli heavy machinery is equipped with a large annealing furnace of 6.5x6.5x20m and a large sandblasting room, which can conduct overall heat treatment and sandblasting on the ball mill to ensure the service life and appearance of the ball mill.

Process Control: Tongli has its own metal casting foundry, starting from the raw material to the finished product, Quality in every detail, from start to finish.

Lubrication system: Tongli ball mill is equipped with force lubrication system, there is an oil station equipped for thetransmission part, another oil station for the gearbox to ensure smooth operation and prolong service life of the ball mill.

Cooling system: The main bearing bush is equipped with a water cooling system, and a cooler is also installed in the lubrication system to forcibly cool the lubricating oil.

Transmission connection: Tongli’s ball mill is equipped with a transmission connection, which is welded on the cylinder and machined together with the ball mill shell to avoid assembly errors and ensure the concentricity of the ball mill.

Specifications of rod ball mill

Note: * Mill diameter refers to the inner diameter, while the mill length refers to the effective grinding length.

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Industry Knowledge extension:

What is the difference between rod mill and ball mill?

Rod mills usually use steel rods with a diameter of 50-100mm as the grinding medium, while ball mills use steel balls as the grinding media. The length of the steel rod is 25-50mm shorter than that of the cylinder, and high-carbon steel with a carbon content of 0.8%-1% is often used. Made of steel; the amount of rods loaded is about 35%-45% of the effective volume of the rod mill. The horizontal plane of the rods is about 100-200mm below the centerline of the cylinder.The ratio of the length to the diameter of the shell of the rod mill is generally 1.5-2.0, and the inner surface of the liner on the end cover should be a vertical plane. The purpose is to prevent and reduce the chaotic movement, bending and breaking of the steel rod in the shell. Ensure that the steel rod moves regularly. The ratio of shell length to diameter of the ball mill is small, and in most cases the ratio is only slightly greater than 1.Rod mills do not use grid plates to discharge ore, but use overflow type and open type ore discharge; the diameter of the trunnion at the discharge end is generally larger than that of ball mills of the same specification. The cylinder speed of the rod mill should be lower than the working speed of the ball mill of the same specification, so that the medium in it can work in a cascading state

What is the difference between Open-circuit and closed-circuit ball mill?

Closed-circuit grinding refers to that in the grinding operation, the material is fed into the mill and then classified after one grinding, the ore with unqualified particle size is returned to the mill for regrinding, and the ore with qualified particle size is sent to the next stage. The closed-circuit mill has a high crushing rate, and the quality of the obtained product is high. At the same time, the output of the closed-circuit production is relatively large, but its disadvantage is that the production process is relatively complicated and the input cost is high.The production process of the open circuit mill is relatively simple, and the input cost is low. And its disadvantage is that it has low production efficiency, because the qualified fine powder cannot be removed in time, so it produces a large energy consumption during production.

What is the difference between ball mill and vertical roller mill?

Both ball mills and vertical roller mills plays a vital role in the cement grinding plant. Ball mills are versatile and cost-effective, suitable for various materials and simple to maintain. On the other hand, vertical roller mills offer superior energy efficiency and particle size control, making them ideal for cement and ore grinding applications. The choice between the two depends on specific requirements, budget constraints, and technical expertise.

How to install A Ball mill?

The first step of ball mill installation is to Install the base frame of the ball mill. The base installation uses a large number of metal partitions as base pads, prepare metal partitions with different thicknesses in advance for backup. After the base is installed, the worker can adjust the position of the base and the number of partitions according to the actual situation, the width of the partition cannot be less than 80mm, and the external exposed part should exceed at least 10mm In order to move the baffle, after the location of the baffle is determined, a welding operation is required. After the ball mill chassis is installed, it is necessary to accurately measure the levelness and level of the chassis with a spirit level and a tracking instrument.