# Symons Cone Crusher Failure Analysis

## 1. Preface

Symons cone crusher has been widely used in crushing process because of its large processing capacity and fine crushing size. However, in actual production, some failures often occur due to manufacturing, installation and maintenance. For example, the capacity of a new replaced Symons cone crusher is smaller than the previous one, and the crusher is often “material stocking”, resulting in a lower capacity. Additionally, the main shaft sometimes has cracks and even fractures. The problem can be solved by analyzing the working principle, movement law and force situation of the crusher to find improvement measures to prevent such failures.

## 2. Symons Cone Crusher Structure and Working Principle

The structure of the Symons Cone Crusher is shown in the following figure, where the working mechanism consists of a movable cone and a fixed cone. The cone of the movable cone is pressed onto the main shaft, and one end of the main shaft is inserted into the conical hole of the eccentric sleeve. When the eccentric sleeve rotates, it drives the movable cone to make a swinging motion. In order to ensure the swinging motion of the movable cone, the lower surface of the movable cone is made into a spherical surface, and is supported on a spherical bearing. All the gravity of the movable cone and the main shaft are supported by the spherical bearing and the frame.

## 3. Processing capacity decreased

### 3.1 Analysis of the causes

To understand the cause of symons cone crusher “material stocking”, we must first understand the conditions of stable operation. The so-called stable operation of the crusher cone means whether the dynamic cone on the spherical bearing can be overturned, if it is overturned, the crusher is not stable operation.

When the symons cone crusher is running, the crushing cone axis makes a conical movement to the center line of the body, and its cone top is the spherical bearing center O. O point always remains stationary during the movement of the crushing cone, so the movement of the crushing cone can be regarded as the rotation of the rigid body around the fixed point.

In addition, the crusher must be operated in such a way that the main axis of the crushing cone and the centerline of the crusher intersect at the center of the sphere. Otherwise, the normal operation of the crusher will be destroyed. It can be seen that during the operation of the cone, the intersection of the cone axis and the centerline of the frame, O1, must coincide with the spherical center O of the spherical bush, which is a prerequisite for the normal operation of the cone, refer the following figure.

Also in order to ensure that the crushing machine cone does not fall over, in the maintenance, must make the entire spherical bearing contact area of 2 / 3 in the outer ring, 1/3 of the inner ring area is not in contact, after a period of operation, can reach the full area of uniform contact.

The production capacity of closed circuit crushing can be calculated by the following empirical formula:
Q closed = KQ open = KK1K2q0bδ /1.6( t /h)
Where Q closed – capacity of the crusher for closed circuit crushing, t /h;
Q open – crusher capacity at open circuit crushing, t/h
K – coefficient of average feed size refinement in closed circuit;
K1-Ore fragility coefficient;
K2-Ore size correction factor;
q0-capacity per unit width of crusher discharge opening, t /( mm-h) ;
δ – Stack density of crushed ore, t /m3;
b – width of ore discharge opening at crusher production, mm.

In practice, it can be assumed that the nature of the ore is unchanged for a certain period of time, and the crusher has been selected so that K, K1, K2, q0, δ are fixed values, and the crusher capacity is only related to the width of the discharge opening. However, if it is a new crusher, whether the crusher cavity type (mainly the crusher parallel belt length) is correct or not will also be a factor affecting the crusher capacity.

Therefore, to find out the reason for the unstable capacity of the crusher, we can start from whether the crusher cavity shape and discharge opening width meet the production requirements, and the discharge opening width is related to the position of the eccentric bushing bore axis and eccentric angle.

If the eccentric sleeve cone hole axis position is not correct, offset or eccentric angle is not correct, it will cause the O point and O1 point can not coincide, causing the dynamic cone instability and overturning during the operation. When the discharge opening is not adjusted to the required size during production, the cone will collide with the fixed liner, and the gap between the opening of the crushing chamber and the discharge opening will not gradually change from large to small or from small to large, but will suddenly change from large to small in an irregular manner, which will not be able to crush the ore effectively, and will not be able to reach the proper capacity of the crusher. If the cavity shape is not correct, the length of the parallel belt of the crusher will be different, which will also affect the capacity of the crusher.

### 3.2 Effective measures

A. The capacity of the crusher can only be guaranteed by ensuring the stable operation of the moving cone. If the eccentric axis is not correctly positioned or offset when manufacturing the eccentric sleeve, the relative position of the bowl tile and the eccentric sleeve can be adjusted by increasing or decreasing the shim between the bowl bush and the bowl bush support to achieve the coincidence of O1 and O point.

However, if the difference between the eccentric axes is large, the difference between O1 and O is too much. In addition, the up and down adjustment of the bowl-shaped bush will cause the gap between the main shaft and the taper hole to change. Therefore, the bowl-shaped bush support is not allowed to have a large amount of adjustment. Or the O1 and O points do not coincide due to the incorrect eccentric angle, which can only be solved by replacing the eccentric bushing with the correct eccentric angle and axis position.

B. If there is a problem with the cavity of the crusher, first find out whether it is the fixed cone or the moving cone, and solve it by replacing the parts.

## 4. Main shaft cracks or breaks

### 4.1 Reason analysis

To understand the cause of cracks or fractures in the main shaft, first perform a force analysis on the main shaft, and consider the main shaft and the cone as a whole for force analysis, refer the following figure. When running with load, the main shaft of the crusher always rests on the thick side of the eccentric sleeve, the maximum crushing force Pmax acts vertically on the lower edge of the surface of the moving cone, and the reaction force P1 of the eccentric sleeve to the main shaft acts on the lower end of the main shaft and in the horizontal direction, and with the maximum crushing force intersects at the O2 point. According to the principle that the three forces are balanced and intersect at one point, the reaction force P2 of the spherical tile to the cone must pass through the O2 point and the center O point of the sphere. And the maximum crushing force Pmax is:

In the formula where
G, self weight of the fixed cone;
n, number of springs;
K, spring stiffness;
p, the initial pressure of each spring;
f0, Friction coefficient of material on the liner;
np, Spring preload;
Lp, the force arm of the crushing force on the contact point between the spring and the frame;
Lf, Friction force on the contact point between the spring and the frame;
R, np Force arm of the contact point between the spring and the frame;
h0, additional compression of the spring.

It can be seen from the above formula that after the crusher is selected, the maximum crushing force is only related to the preload of the spring. When the cone crusher is working, the main shaft can be regarded as a cantilever beam with a concentrated load at one end, so it is not difficult to see that when the preload force of the spring is small, the crushing force of the cone crusher is also small, that is, the force of the main shaft is also small. It will be smaller, but it cannot be broken for harder ore, and the production capacity is lower; when the preload of the spring is larger, the crushing force of the cone crusher will be larger, and the main shaft will be stressed.

Therefore, when the non-crushed material enters the crusher, the spring is compressed, the force on the main shaft increases, and the bending stress increases. If the main shaft strength is insufficient, it will cause the main shaft to break. In addition, because the fit between the main shaft and the cone is an interference fit, if the interference is too large, stress concentration will occur, resulting in fatigue failure of the main shaft. The poor manufacturing quality and improper material of the main shaft itself will cause the main shaft strength to decrease and break.

### 4.2 Effective measures

A. During maintenance, adjust the springs according to the range specified by the manufacturer, and each group of springs should be adjusted to the same extent. If the spring is tightened to a certain extent, the support ring still jumps frequently, and the reason must be found, and the solution cannot be solved by re-tightening the spring, so as to avoid excessive compression of the spring and increase the pre-tightening force. When entering non-broken objects, the crushing force increases, it is easy to cause the accident of the main shaft to break.
B. When manufacturing the main shaft, the defects of stress concentration should be avoided.
C. When assembling the main shaft and the body, the interference cannot be increased in order to increase the firmness between the main shaft and the body, so as to avoid the excessive interference and serious stress concentration, resulting in the fracture of the main shaft.

## 5. Conclusion

Practice has proved that after the implementation of this series of measures, the “material stocking” problem of the Symons cone crusher has been solved, and the main shaft fracture failure has been significantly reduced.