JPH03224641A - Roller mill - Google Patents

Abstract

PURPOSE:To prevent the development of self-excited vibration based on vibration at pulverizing part, particularly stick slip phenomenon without lowering pulverizing capacity of a roller mill by pressurizing the roller with hanging load of a weight arranged at tip part of a tension rod. CONSTITUTION:In this roller mill, by hanging down the weight 24 at the tip part of tension rod 16, pulverizing load with a spring is eliminated, and a pulverizing roller 3, upper and lower pressurizing frames 11, 12 and weight 24 are made to the dead wt. pulverizing load. Successively, fixation of the rod 16 and the frame 11 is constituted with two positions in a supporting point 29 of the rod 16 connected with pin and a supporting point 30 supporting horizontal part of the rod 16 from lower part. That is, the hanging load at lower part of the weight 24 is directly acted to the frame 11. Therefore, by increasing ratio of the pulverizing load with the dead wt. to the whole pulverizing load, vibrating characteristic in the structure, particularly, number of natural vibration is varied, and as the development of self exciting vibration at the pulverizing part is obstructed, abnormal vibration in the whole structure can be restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a roller mill for pulverizing coal, cement clinker, or raw materials for chemical products, and particularly to a vibration-proof structure for a roller mill that is highly practical.

[Conventional technology]

Coal-fired boilers use low-pollution combustion (low No.

Low unburned height M) and rapid load fluctuation operations have been implemented, and as a result, the amount of coal fed to the pulverizer (mill) has expanded and fluctuated, etc.
There is now a need for more flexible operations.

One type of pulverizer for pulverizing lumps such as coal, raw materials for cement, or raw materials for new materials, is equipped with a pulverizing table that rotates at low speed and multiple pulverizing rollers that rotate on its own axis. There is a vertical roller mill, which has recently solidified its position as one of the representative models.

Hereinafter, the structure of a conventional roller mill will be explained using a longitudinal cross-sectional view in FIG. 3 and a cross-sectional view in FIG. 4.

As shown in Fig. 3, this type of roller mill consists of a crushing table 2 that rotates at low speed in a horizontal plane within a cylindrical casing 1, and a state in which the crushing table 2 is pressed against the crushing table 2 (this pressing force is hereinafter referred to as the crushing force). It is equipped with a plurality of crushing rollers 3 that rotate under the load (referred to as load). The grinding table 2 is
The motor 4 is fixed to and driven by a motor output shaft 5 and a vertical shaft 7 that rotates at a low speed via a speed reducer 6. Further, the rotation shaft 8 of the crushing roller 3 is supported by a roller bracket 9 provided on the top of the crushing roller 3.

The roller bracket 9 has an upper and lower pressurizing frame 11.1 provided at its upper part and having a spring lO between them.
2 through a pin 13 called a roller pivot. The crushing load, which is the main factor governing the crushing performance, is the crushing load due to the own weight of structural members such as the crushing roller 3, the upper and lower pressure frames 11 and 12, and the crushing load that connects the upper pressure frame 11 and the foundation mat 14. Pressure spring 15
This is given as the resultant force of the crushing load caused by the downward spring of the tension rod 16 attached.

The material to be crushed 18 that is supplied to the center of the crushing table 2 from the supply pipe (chute) 17 moves toward the outer periphery on the crushing table 2 in a thinly wound trajectory due to the centrifugal force caused by the rotation of the crushing table 2. , and is crushed between the crushing roller 3 and the crushing race surface 20 located on the upper surface of the crushing ring 19 inserted on the outer peripheral side of the crushing table 2. Hot air 21 is guided to the base of the mill casing 1 by a duct (not shown), and this hot air 21 is blown up through an air throat 22 between the outer circumference of the grinding table 2 and the inner circumference of the mill casing 1. ing. The powder and granular material after pulverization is moved into the mill casing 1 by the flow of this hot air 21.
It dries as it rises inside. The powder and granules transported to the upper part of the mill casing 1 are classified into coarse particles that fall down by gravity (primary classification), and the slightly finer particles that have passed through this and further rise are placed in the upper part of the mill casing 1. The particles are classified again by a cyclone separator or a rotary classifier 23 (secondary classification), and particles having a predetermined particle size or less are further conveyed by hot air 21. In the case of a boiler, the pulverized coal is sent to a pulverized coal burner or a pulverized storage pin (not shown). In addition, the powder particles having a predetermined particle size or more that have been sieved out in the secondary classification fall onto the grinding table 2, and are ground again together with the new material 18 that has just been fed into the mill, and this grinding action and classification action are combined. Repeated.

On the other hand, the method of applying the crushing load in the roller mill will be explained below.

As mentioned above, the crushing load in the roller mill is due to the crushing load caused by the weight of the crushing roller 3, the upper and lower pressure frames 11.12, etc., and the pressure spring 15 that connects the upper and lower pressure frames 11.12 and the base mat 14. The crushing load is applied by a downward spring of the tension rod 16 through the crushing force.

The standard value of the ratio of the crushing load due to own weight to the total crushing load is about 0.4, and due to the dynamic action occurring in the crushing section,
The crushing load due to this own weight also fluctuates.

This situation will be explained using FIG. 5(a). In other words, the crushing load increases or decreases around the initial setting amount (referred to as a static component), but this fluctuating component is herein referred to as a dynamic component. The causes of such dynamic components will be explained.

One of the causes is due to the expansion and contraction of two springs (the pressure spring 15 and the spring 10 between the upper and lower pressure frames 11, 12) caused by the vibrational displacement of the crusher components. Another cause is that the load due to the weight of the crusher component increases or decreases around the weight of the component due to an inertial force proportional to the vibration acceleration of the component. These two become the dynamic components of the crushing load. In this way, the dynamic characteristics of the two types of loads that contribute to the crushing load (load due to the spring and load due to own weight) are completely different.

FIG. 6 shows the relationship between the mill load of the roller mill (supply of material to be crushed N per unit time) and the dimensionless vibration level at a representative point of the mill casing 1.

When operating under a high load, the vibration level is low and there is no problem as shown in Figure 6, but when operating under a low load, that is, the supply amount of the material to be crushed 18 is reduced and the powder layer under the crushing roller 3 becomes thin. , the sliding phenomenon between the crushing roller 3 and the crushing race 20 (
(referred to as stick-slip phenomenon), and automatic vibration occurs. As a result, the vibration level of the entire structure increases or the vibration propagates to the surrounding area.

[Problem to be solved by the invention]

As described above, conventional roller mills do not take vibration prevention into consideration, and there are problems with the structural reliability of the mill body or the environment around the mill in terms of vibration and noise.

The present invention aims to eliminate such conventional drawbacks,
The purpose is to provide a roller mill that can prevent vibrations in the crushing section that cause such problems, especially self-supporting vibrations caused by stick-slip phenomena, without reducing the crushing performance of the roller mill. It's about doing.

[Means to solve the problem]

In order to achieve the above-mentioned object, the present invention provides a weight at the tip of a tension rod, and pressurizes the tension rod by the hanging load of the weight.

[Effect]

The increase in the ratio of the crushing load due to its own weight to the total crushing load changes the vibration characteristics of the structure, especially the natural frequency, and prevents the occurrence of automatic vibrations in the crushing section, reducing abnormal vibrations of the entire structure. can be suppressed.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a longitudinal sectional view of a roller mill according to an embodiment of the present invention;
FIG. 2 is a cross-sectional view taken along the line ■--■ in FIG. 1.

In FIGS. 1 and 2, reference numerals 1 to 23 indicate the same components as those of the prior art.

24 is a weight suspended from the tip of the tension rod 16, 25 is a pit, 26 is a horizontal stopper, 27 is a vertical stopper, 28 is a pit cover 29 is a support point of the tension rod 16, and 30 is a fulcrum of the tension rod 16. .

In such a structure, the difference between the roller mill shown in FIGS. 1 and 2 and the roller mill shown in FIGS. 3 and 4 is that in the conventional roller mill, the spring 10 and the pressure spring 15 are However, in the roller mill according to the embodiment of the present invention, a weight 24 is suspended from the tip of the tension rod 16 to eliminate the crushing load caused by the spring, and the crushing roller 3, upper
This is the point where the crushing load of the lower pressurizing frame 11, 12 and the weight 24 is the own weight.

The tension rod 16 and the upper pressure frame 11 are fixed in the same manner as in the conventional one, but as shown in FIG. It consists of two points: a fulcrum 30 of a tension rod 16 that supports it from below. That is, based on this principle, the downward hanging load of the weight 24 acts directly on the upper pressurizing frame 11.

Next, regarding the installation of the weight 24, even if a solid weight 24 made of steel is used, its volume will be close to 10 m3. Therefore, as shown in FIG. 1, a pit 25 was provided in the base mat 14 around the mill casing 1, and the mill casing 1 was suspended therein.

It is advantageous to store the weight 24 in the pit 25, since installing the weight 24 of 10 m3 on the foundation pine 4 would obstruct the work.

Further, as shown in FIG. 2, by dividing the weight 24 into about three pieces and suspending each weight 24 from three places, installation work and maintenance can be facilitated. Furthermore, by constructing each weight 24 from a plurality of thick plates as shown in FIG. 1, it is not only easy to handle the weight, but also allows one's own troops to finely adjust the crushing load. Note that a horizontal stopper 26 is provided within the pit 25 in order to restrain the horizontal movement of these weights 24. Further, as shown in FIG. 1, a vertical stopper 27 is provided close to the lower surface of the weight 24 so that the weight 24 can remain horizontal even if one of the tension rods 16 is damaged in the worst case.

The mechanism of automatic vibration, the conditions under which it occurs, and how to prevent it will be explained below. As an example of automatic vibration in a structure, a belt conveyor 31 as shown in FIG.
Examples include the sliding vibration of the one-mass spring system excited by the frictional force, or the vibration of a group of tubes excited by a cross-flow (hydroelasticity 2). The characteristics of this type of vibration are that an energy supply source that does not have a specific period (the movement of the belt conveyor 31 in the case of sliding vibration, a uniform flow in the case of hydroelastic vibration) comes from a certain mechanism (in the case of sliding vibration). Energy is supplied to the structure by frictional force (force exchange due to fluid-structure interaction in the case of hydroelastic vibration), and the structure is excited at a frequency corresponding to its natural frequency.

In that case, as shown in Figure 9, the vibration of the structure induces an increase in dynamic loads (fluctuations in frictional force and fluid force), and as a result, the vibration of the structure further increases, resulting in a repeating loop. Become. When this is applied to the vibration of a roller mill, the rotational movement of the grinding table 2 becomes the energy supply source, and the slippage (stick-slip) between the grinding table 2 and the grinding roller 3 provides a mechanism for transmitting energy to the structure. , resulting in vibration and crushing of the crushing section components as shown in FIG.

A self-oscillating loop will be formed due to the dynamic component of the load.

Next, conditions for generating automatic vibration or methods for preventing it will be explained using a roller mill as an example. The fluctuations in the grinding load induced by the vibrations of the grinding section components have a certain time delay. This is evaluated by the time delay between the vibration speed Jli of the components of the crushing section and the dynamic component F of the crushing load, as shown in FIG. 10(a), and this is expressed as Δt. The condition for automatic vibration is that the amount of work ΔW performed in one cycle by the dynamic component F of the crushing load is positive, that is, Δw=: fF large dt>O() Therefore, as a method for preventing automatic vibration, the structure All you have to do is change the natural frequency of the object so that 6w<Q. FIG. 10(b) shows a case where the condition of 6w<Q is realized by lowering the natural frequency, and the embodiments of the present invention also fall under this, as will be described later.

Next, the vibration behavior of the roller mill will be specifically described.

FIG. 8 is a frequency spectrum of horizontal vibration acceleration data of the mill casing 1. For conventional roller mills,
At low loads (mill load 25%), large amplitude vibrations occur as shown by the curve in Figure 6, but at that time the 8th
As shown by curve A in the figure, the component near the natural frequency has a remarkable peak, indicating that this vibration is automatic vibration. On the other hand, when the mill load is 80%, the 6th
As shown by curve B in the figure, the vibration level is low and the frequency spectrum is gentle. The detailed mechanism of this is unknown, but when the load is low, the powder layer between the grinding roller 3 and the grinding table 2 becomes thinner, and the sliding state is reduced as shown in Fig. 1θ (b
This is considered to be because the condition (ΔW>0) for generating self-excited imaging shown in ) must be satisfied.

Next, we will specifically discuss how the aforementioned structural changes associated with improving the method of applying crushing loads are related to changes in the vibration characteristics of the mill and furthermore, to prevention of self-help vibration.

FIG. 7(a) shows a vibration model of a conventional roller mill and a roller mill according to an embodiment of the present invention, which focuses on expressing the vibration behavior in the vertical direction, where the vibration is large, particularly for the components of the crushing section. be. Follow.

The vibration model for the advanced technology roller mill is based on the rigidity of the components of the crushing section (the crushing roller 3, the pressure frame 11, 12, the crushing table 2, etc.), the crushing table 2 and the vertical shaft 7 that drives it, etc. The spring 1 (2) represents the rigidity of the spring 1 shown in FIG. It is given by the following formula.

On the other hand, in the roller mill according to the present invention, as shown in FIG.
It is 0. In addition, since the crushing part components and the weight 24 move together if the expansion and contraction of the tension rod 16 that connects them is ignored, the model becomes a model in which the mass Δm of the weight 24 is added to m in the conventional structural model. . Therefore, its natural frequency fb is given by the following equation.

If we take the ratio of fll and f, we get: The natural frequency of the roller mill according to the present invention is smaller than the natural frequency of the roller mill of the conventional structure. According to experimental results, the natural frequency of the conventional roller mill is 2.
5H2, the natural frequency of the roller mill according to the example is 12H
2 and fh/f-=0.48 According to the roller mill according to the embodiment of the present invention, the curve C in FIGS. 6 and 8
As shown in curve A, the vibration is smaller than that of curve A.
It is clear that automatic oscillations are not occurring because there are no clear peak-to-peak frequencies like these. This means that the natural frequency of the roller mill of the present invention is approximately 1 of that of the conventional structure.
This is considered to be because the relationship between the vibration of the components of the crushing section and the dynamic component of the crushing load deviates from the automatic vibration generation condition, as shown in FIG. 10(b).

It has been confirmed through experiments that there is no significant difference in crushing performance between the present invention and the conventional structure, and this is because the static components of the crushing load in both are almost equal, as shown in Figure 5 (b). This is also a natural result.

〔Effect of the invention〕

According to the present invention, automatic vibration is suppressed, the vibration level is reduced, and the minimum load of the roller mill can be reduced.
It becomes possible to operate the roller mill in response to load fluctuations.

[Brief explanation of drawings]

1 and 2 are related to an embodiment of the present invention. FIG. 1 is a longitudinal cross-sectional view, FIG. 2 is a cross-sectional view taken along the line ■-■ in FIG. 1, and FIGS. 3 and 4 are conventional This shows the technology's roller mill, and Figure 3 is a vertical cross-sectional view. Figure 4 is IV-IV of Figure 3.
Fig. 5(a) is a cross-sectional view taken along a line. (b) is a simplified model diagram of the behavior of crushing load, Figure 6 is a characteristic curve diagram showing the relationship between amplitude ratio and mill load, Figures 7 (a) and (b) are vibration model diagrams of a roller mill, 8th
The figure is a characteristic curve diagram of dimensionless amplitude and dimensionless frequency, Figure 9.
Figures 10 (a) and (b) are explanatory diagrams explaining automatic vibration, Figure 11 is a characteristic diagram showing the relationship between amplitude ratio and load due to own weight/design value of crushing load, and Figure 12 is a general diagram regarding automatic vibration. It is an explanatory diagram. 1... Mill casing, 2...
...Crushing table, 3...Crushing roller, 8...Rotating shaft, 9...
Roller bracket, 11... Old upper pressure frame, 12... Lower pressure frame, 13.
1 old... pin, 14... basic mat, 1
5. Old... Pressure spring, 16...
...Tension rod, 19...Crushing ring, 24...Weight. Figure 8 Atsushi 2 Figure 4 Atsushi Figure 8 Atsushi Tsuta Figure (0) (b) Dynamic component diagram Mill load (%) Atsushi 7 Figure (a) Figure Dimensionless frequency diagram Figure 1

Claims (1)

[Claims] A grinding table that rotates on a base mat, a grinding ring located on the top surface of the grinding table, a grinding roller that rotates on the grinding ring, a roller bracket that holds the rotation axis of the grinding roller, and a roller. In the mill casing, there is provided a pressurizing frame that supports the bracket from above through a pin, and the pressurizing frame and the base mat are connected by a tension rod via a pressurizing spring, and the object to be crushed is crushed. A roller mill characterized in that a weight is provided at the tip of a tension rod, and pressure is applied by the hanging load of the weight.