Protection systems of the titlting mechanisms at the rolling trains.

Miklos, Imre Zsolt ; Alic, Carmen Inge ; Miklos, Cristina Carmen 等

1. INTRODUCTION

This paper presents the study of the hook tilting mechanism from the Blooming 1000's rolling train. To this mechanism, due to a wrong operation, it could happen that, on one side, when the hooks are going down, they jab into the bloom, and on the other side, when the hooks are going up, they can hang in the roller table. This can damage the component elements by producing additional loads. In case of the tilting mechanism from Blooming 1000, the main connecting rod is fitted with a minimum resistance section, by two safety bolts, which break-up when additional loads appear. The connecting rod's cross-section is presented in fig.1 (***, 2003). The tilting mechanism's protection by safety bolts is convenient at first sight, only that it presents some disadvantages. Thus, in the moment of bolt's break, due to accidental additional loads, the rolling process should be interrupted, whilst the broken bolt is removed and replaced with a new one. This operation is difficult, due to the difficult access to the section with bolts.

The above presented issues have been previously studied, and to solve them, there were proposed several technical solutions. To design this, is necessary to know the force value from the tilting mechanism's connecting rod. The blooms' tilting mechanism works with shocks and, therefore, the efforts condition from its elements can be only determined when the dynamic coefficient is known very well. To have a real situation, the experimental method is accepted (with tensometer stamps).

[FIGURE 1 OMITTED]

After measurements, is obtained the maximum force values from the mechanism's connecting rod in the following conditions: idle run, loaded run, and bolts' break (Zamfir & Elczner, 1982). Unfortunately, these studies were not completed.

The authors have continued these studies by research, design and execution of an automatic power limit bolt with tapered blocking bodies; also they have made experimental tests in operating conditions. The results are satisfactory, following further to be implemented on the tilting mechanism.

2. DESCRIPTION AND WORKING OF THE AUTOMATIC POWER LIMIT BOLT

The schematic of the automatic power limit bolt, with tapered blocking bodies, is presented in fig. 2. The pressing force Q from the compression spring (4) is calibrated depending on the maximum regime force from the connecting rod. When force F from the connecting rod exceeds a certain pre-value, the blocking bodies (3) will be pushed outside the transversal seats, compressing the springs until their release from the two tapered bores. After additional load is ended, the compression springs will push back the blocking bodies into the connecting rod's tapered bores. Thus, the connecting rod's mid-section of the is displaced by the exterior one, allowing the effort's end, making the automatic power limit bolt to enter the next kinematical cycle.

Taking into account that the connecting rod's critical force (the spring's pressing force) is very big and because the spring's space is limited (for a little deformation), is recommended to use compression ring springs, which satisfy the conditions below.

3. CALCULATION AND DESIGN OF THE AUTOMATIC POWER LIMIT BOLT

For the automatic power limit bolt, is noted by F the force from the connecting rod when the bolt is breaking up, and the bolt's load diagram is presented in fig. 3. On each blocking body will act half of the critical force, F/2. The blocking body's load diagram is presented in fig. 4.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

By notations from fig. 3 between the distributed force F/2 and force P which pushes the blocking body into the tapered bore, the following relation can be written (Miklos, 2005):

P = F/4 x (sin[alpha] + [mu] x cos[alpha]) (1)

Forces which act on the blocking bodies (fig. 4) will be: P, respectively [mu]P, spring's pressing force Q and [N.sub.1], [N.sub.2] (the slide-way reactions) respectively [F.sub.1] and [F.sub.2] the friction forces in the slide-way. From the forces' balance condition, results the relation of the force P depending on Q and the geometrical measures of the tapered blocking body.

P = Q/[cos[alpha]] - [mu] x sin[alpha](1 + 2xb/1 - [mu]xa/1)] (2)

From the relations (1) and (2) is determined the spring's pressing force value, Q:

Q = F x [cos[alpha] - [mu] x (1+2xb/1 - [mu]xa/1) x sin [alpha]]/4(sin[alpha]+[mu]xcos[alpha]) (3)

Next, the problem is to choose the optimal value of a angle of the bolt's tapered body, respectively to determinate the limit value to avoid the stuck phenomenon in the connecting rod's tapered bore, in working conditions. The sticking of the blocking body into the connecting rod's tapered bore is produced when the denominator from relation (2) is null, respectively force P tends to infinite. Taking into account these specifications and the fact that [alpha] angle can't have negative values, the range where a angle can take values is:

0 < [alpha] < arctg 1/[mu]x(1+2xb/1 - [mu]xa/1) (4)

The relations (1)-(4) were solved by a computing program, which allows to know the maximum values of [alpha] angle, [[alpha].sub.max], where appear the stuck of the blocking body into the connecting rod and spring's pressing force Q, for different values of friction coefficient [mu] (different pairs of materials), respectively the geometrical measures of the tapered blocking body.

Keeping constant the geometric measures, for different values of the friction coefficient between the tapered blocking body's material and the connecting rod's material are obtained different limit values for the blocking body's angle.

[FIGURE 5 OMITTED]

For the analyzed tilting mechanism's real case, admitting [mu]=0.15, will result the maximum angle where appears the sticking danger: [[alpha].sub.max] = 78.68 [degree] (Miklos, 2001).

4. EXPERIMENTAL TRIALS

Because the main connecting rod of the tilting mechanism has a big length (2480 mm), for the experimental trials it was considered just a portion from connecting rod, respectively the portion on which is assembled the automatic power limit bolt.

The experimental trial on the automatic power limit bolt with tapered blocking bodies was performed on the universal machine of tensile and pressure tests, (Miklos, 2001) the trial diagram being presented in fig.5.

From the experimental trials results that the bolt is broken at values between 50200 and 50750daN of the connecting rod's force, to the calculated (53010daN) (Zamfir & Miklos, 1999).

5. CONCLUSION

Further the above research can be concluded that the presented protection system runs properly in real operation conditions and is proposed to be located on the tilting real mechanism from the Blooming 1000 rolling train. As future research, is foreseen to adapt this protection system also to other similar mechanisms from steel industry.

6. REFERENCES

Miklos, I. ZS. (2001). Contributions to improve the technological performances of the bloom tilting mechanisms at the rolling trains, Doctorate Thesis, University from Petrosani, 2001

Miklos, I. ZS. (2005). Mechanisms. Mechanisms analysis, "Mirton" Publishing House, ISBN 973-661-743-2, Timisoara

Zamfir, V.; Elczner, G. (1982). Kinematic and dynamic analysis of the blooming 1000's hook tilting mechanism, Research contract no. 270/1982, Hunedoara, 1982

Zamfir, V.; Miklos, I. Zs. (1999). The kinetostatic analysis of the tilting mechanism at the 1000 mm rolling train. UPT's Scientific Bulletin, Vol. 44(58), Fascicle 2, Page 275 - 282, ISSN--1224-6077

*** (2003) Technological instructions for the Blooming 1300 and 1000 mm rolling trains, Vol. II, Arcelor Mittal Hunedoara, Plant no.4--Rolling Mills, Hunedoara, 2003