JP5870910B2 - Drum deterioration evaluation method and drum deterioration recovery method of drum mixer - Google Patents

Description

  The present invention relates to a drum deterioration evaluation method and a drum deterioration recovery method of a drum mixer.

  A drum mixer is one in which a plurality of substances are charged into a drum and the drum is rotated to mix the plurality of substances.

  1 and 2 show a schematic structure of a general drum mixer. Here, FIG. 1 is a side view, and FIG. 2 is a cross-sectional view taken along line AA of FIG.

  As shown in FIGS. 1 and 2, this type of drum mixer 10 is provided with a girth gear 4 on the outer surface of the drum 1, and the drum 1 is driven by a drive motor 5 via a speed reducer 6, a pinion 7, and a girth gear 4. Is designed to rotate.

  A plurality (two in this case) of tires 2 are installed on the outer surface of the drum 1 at a predetermined interval in the longitudinal direction, and each tire 2 is provided corresponding to the position of the tire 2. Is supported by a pair of support rollers 3.

  Accordingly, during operation of the drum mixer 10, the tire 2 installation portion of the drum 1 rotates while receiving the reaction force from the support roller 3 via the tire 2, and the drum tire 2 installation portion includes a support roller. Periodic stress (repetitive stress) due to the reaction force from 3 is generated.

  Therefore, as the drum 1 is continuously used, due to aging deterioration, as shown in an enlarged vertical sectional view in the vicinity of the tire 2 installation portion 1A (hereinafter referred to as drum 1A) of the drum 1 as shown in FIG. Fatigue cracks 11 (a crack 11o on the outer surface 1Ao side and a crack 11i on the inner surface 1Ai side) occurred from the outer surface 1Ao side and the inner surface 1Ai side. In particular, there were many occurrences in the vicinity of the fillet weld 8 of the drum 1 and the tire 2.

  The crack 11 generated from the outer surface 1Ao side or the inner surface 1Ai side of the drum 1A does not hinder the operation of the drum mixer 10 in the initial stage (initial fatigue crack stage), but the crack 11 develops and the critical crack depth (normally) When the thickness td) of the drum 1A is reached, that is, when the crack 11 penetrates the thickness td of the drum 1A, the operation of the drum mixer 10 cannot be continued. In some cases, it can lead to a major accident.

  Therefore, conventionally, when the drum mixer 10 is periodically repaired, the crack occurrence state of the drum 1A is observed by ultrasonic flaw detection. If the crack depth of the drum 1A exceeds a predetermined amount, the crack 11 is generated. The portion is removed and repaired by overlay welding (welding repair), or the drum mixer 10 itself is updated in some cases. This prevents the crack 11 from penetrating the thickness of the drum 1 </ b> A during periodic repairs of the drum mixer 10 so that it is not possible to continue operation of the drum mixer 10.

  In general, since the repair of the drum mixer 10 takes about one week, the regular repair timing of the drum mixer 10 is generally once a year.

  On the other hand, in Patent Document 1, the surface hardness of the tire 2 and the support roller 3 of the drum mixer 10 is measured, and the measured surface hardness is compared with the limit hardness at which cracks are generated on the surface of the tire 2 and the support roller 3. And the technique of evaluating that deterioration of the tire 2 or the support roller 3 is progressing, so that the measured surface hardness is near limit hardness is disclosed. Moreover, the technique of recovering deterioration and prolonging a lifetime by heating the surface of the tire 2 or the support roller 3 for a predetermined time and softening is also shown. In other words, the progress of deterioration of the tire 2 and the support roller 3 of the drum mixer 10 is evaluated before cracks are generated, and the deterioration is recovered to extend the life.

Japanese Patent Laid-Open No. 6-101973

  As described above, when a drum mixer is regularly repaired, the crack occurrence state of the drum is observed by ultrasonic flaw detection, and if the crack depth of the drum exceeds a predetermined amount, the crack occurrence location By repairing the welds and, in some cases, renewing the drum mixer itself, cracks can penetrate through the drum thickness and continue to operate the drum mixer during regular repairs of the drum mixer. Is not impossible.

  However, in this case, if it is not possible to accurately estimate the time when cracks propagate and penetrate the drum thickness (the remaining life of the drum, that is, the remaining life of the drum mixer), the welding repair was sufficient, but the drum mixer It will be necessary to renew and add extra costs, or conversely, it would be necessary to renew the drum mixer, but it would be impossible to continue operation because it was repaired by welding. Become.

  The technique described in Patent Document 1 is for evaluating deterioration of a tire or the like before a crack is generated, and as described above, cannot be applied when evaluating the progress of a crack after the crack is generated. .

  The present invention has been made in view of the circumstances as described above, and in a drum mixer, a drum deterioration evaluation method for a drum mixer capable of accurately calculating the remaining life due to crack growth of the drum, and drum deterioration recovery based thereon. It is intended to provide a method.

  In order to solve the above problems, the present invention has the following features.

  [1] A method for evaluating the deterioration state of a drum mixer due to crack growth in a drum mixer, in which the drum crack becomes a critical crack depth in consideration of drum thickness increase over time and drum stress increase based on vibration increase. A drum deterioration evaluation method for a drum mixer, characterized by calculating a remaining life until the end.

  [2] A drum deterioration recovery method based on the drum deterioration evaluation method for a drum mixer described in [1], wherein the remaining life of the drum is calculated at each periodic repair timing, and the calculated remaining life of the drum is calculated. A method for recovering drum deterioration of a drum mixer, comprising determining whether to repair a crack in the drum or to update the drum mixer itself.

  ADVANTAGE OF THE INVENTION According to this invention, the deterioration state (remaining life by crack progress) in a drum mixer can be evaluated accurately. Then, it is possible to select an appropriate drum deterioration recovery method (repair, update) based on the deterioration state of the drum (remaining life due to crack propagation).

It is a side view which shows a drum mixer. It is AA sectional drawing of FIG. It is an enlarged vertical sectional view of the vicinity of the connecting portion between the tire and the drum. It is a figure which shows the example of the stress increase rate by thinning and a vibration. It is a figure which shows the example which calculates the remaining life of a drum.

  An embodiment of the present invention will be described with reference to the drawings.

  As described above, in the general drum mixer 10 as shown in FIGS. 1 to 3, when the drum mixer 10 is regularly repaired, the crack occurrence state of the drum 1 </ b> A is detected by ultrasonic flaw detection. Observe that if the crack length of the drum 1A exceeds a predetermined amount, welding repair is performed by removing the crack 11 and welding, or in some cases, the drum mixer 10 itself is updated. It was. This prevents the crack 11 from penetrating the thickness of the drum 1 </ b> A during periodic repairs of the drum mixer 10, thereby making it impossible to continue the operation of the drum mixer 10.

  Therefore, the present inventors first investigated the state of welding repair so far. As a result, it was noticed that the crack growth rate after welding repair increased as the operational life of the drum mixer increased, that is, as the number of welding repairs increased.

  This means that even if the welding of the drum is always performed during regular repairs every year, the crack growth rate of the drum will eventually win, and the cracks in the drum will reach the critical crack depth before the periodic repairs. Means to reach.

  In other words, assuming that the number of years until the crack reaches the critical crack depth after performing the welding repair of the drum and not performing the subsequent welding repair is assumed to be the temporary remaining life of the drum, Assuming that the drum is always welded and repaired, the number of years until the provisional remaining life of the drum becomes less than one year is the true remaining life of the drum.

  As described above, as the operation period of the drum mixer increases, the crack growth rate after welding repair increases, because the stress generated in the drum increases due to the decrease in drum thickness and vibration due to deterioration over time. It was estimated that there was.

  Increase rate of stress generated in drum due to drum thickness reduction (thinning) and vibration increase (vibration acceleration increase) as described above (stress increase rate: stress increase rate due to thinning, stress increase rate due to vibration) An example) is shown in FIG. In the figure, Y means year, and G means acceleration unit gal.

In this example, on the drum outer surface side, the stress increase rate due to thinning is 0.07 kgf / mm ² / Y, and the stress increase rate due to vibration is 0.48 kgf / mm ² / Y. The increase rate is 0.55 kgf / mm ² / Y, which is the sum of both. On the other hand, on the drum inner surface side, the stress increase rate due to thinning is 0.07 kgf / mm ² / Y, the stress increase rate due to vibration is 0.30 kgf / mm ² / Y, and the stress increase rate on the drum inner surface side is The sum of both is 0.37 kgf / mm ² / Y.

  From the above, in order to accurately evaluate the deterioration state of the drum in the drum mixer, the increase in drum stress due to the decrease in drum thickness and vibration over time as described above is taken into account. It is important to calculate the remaining life of the drum (ie, the remaining life of the drum mixer).

  The procedure for calculating the remaining drum life will be specifically described below.

  First, the provisional remaining life due to crack propagation after welding repair can be calculated by the following equations (1) to (3).

here,
Nc: Cumulative drum rotation speed after welding repair a: Crack depth a _c : Limit crack depth (usually drum thickness)
a ₀ : initial crack depth (depth of initial fatigue crack, depth of crack remaining)
σ: drum generation stress ΔK ₁ : fluctuation range of stress intensity factor K ₁ (function of drum generation stress σ)
C, m: constant determined by the material of the drum Ny: annual number of rotations of the drum Yc: provisional remaining life of the drum (years)

Based on the above formulas (1) to (3) on the assumption that welding repair is always performed in regular repairs every year, the drum generated stress that makes the provisional remaining life of the drum one year, that is, welding The drum generation stress that causes the crack to become the critical crack depth one year after repair is calculated as the limit generation stress (outside outer surface limit generation stress σ _c , inside surface inner limit generation stress σ _c ), and is calculated separately for the current drum generation Stress (outside outer surface generated stress σ _{1 outside} , inner surface current generated stress σ _{1 inside} ) is a critical generated stress (outside outer surface generated stress σ _c , inner inner surface generated stress σ _c ) due to drum generated stress increase based on thickness reduction and vibration increase. The number of years until reaching ( _inner ) is _defined as the true remaining life Ys of the drum.

  In addition, when performing said calculation, a FEM analysis program etc. can be used.

FIG. 5 shows an example in which the true remaining life Ys of the drum mixer is calculated by such a method. The drum thickness td was 35 mm, and the crack limit depth _ac was the drum thickness td (= 35 mm). The drum generation stress increase rate based on the drum thickness reduction and vibration increase is shown in FIG. In addition, the initial crack depth a ₀ was set to 0.1 mm on the outer surface side for fatigue cracks (initial fatigue cracks) and 2 mm on the inner surface side for remaining cracks (cracks remaining after welding repair).

  In FIG. 5, since the crack propagation on the drum inner surface side determines the remaining life of the drum, attention is paid to the crack propagation on the drum inner surface side.

First, the current generated stress on the drum inner surface side ( _{within the} inner surface generated stress σ ₁ ) is 9 kgf / mm ² , and the provisional remaining life Yc at the present time is 2 based on the equations (1) and (2). 7 years. On the other hand, the drum inner surface generated stress with a temporary remaining life of one year, that is, the drum inner surface generated stress at which the crack becomes the critical crack depth one year after welding repair ( _within inner surface limit generated stress σ _c ) Is 11 kgf / mm ² based on the equations (1) and (2). Therefore, since the stress increase rate of the drum inner surface is 0.37kgf / ^mm 2 / Y, from 9 kgf / mm ² of the inner surface current generated stress sigma ₁ to 11 kgf / mm ² _{in the} inner surface limits the generated stress sigma _c The number of years until is 6 years. That is, the true remaining life Ys is calculated as 6 years. The current generated stress on the outer surface side of the drum (outside generated current stress σ _{1 outside} ) is 15 kgf / mm ² , and the generated stress on the outer surface side of the drum 6 years after the inner surface side of the drum becomes the limit generated stress (outer surface limit generated stress). σ _{c out} ) is 18 kgf / mm ² .

  If the remaining life due to the crack growth of the drum is calculated as described above, an appropriate drum deterioration recovery method (crack welding repair, drum mixer update) can be selected based on the calculated remaining life.

  That is, in this embodiment, since the limit of the repair of the drum mixer can be estimated, an appropriate deterioration recovery method can be selected flexibly, and a serious trouble that may lead to a major accident or the like can be avoided. . In addition, it is not necessary to carry out unnecessary repairs, and it is possible to formulate an appropriate aging and renewal plan, so that the production plan, production efficiency, and investment efficiency can be optimized.

DESCRIPTION OF SYMBOLS 1 Drum 1A Drum tire installation part 1Ao Drum outer surface of tire installation part 1Ai Drum inner surface of tire installation part 2 Tire 3 Support roller 4 Garth gear 5 Drive motor 6 Reducer 7 Pinion 8 Tire and drum fillet weld 10 Drum mixer 11 Crack 11o Crack from drum outer surface 11i Crack from drum inner surface

Claims (2)

This is a method to evaluate the deterioration state due to crack growth of the drum in the drum mixer , and is the number of years until the crack reaches the limit crack depth after the welding repair of the drum is performed and the subsequent welding repair is not performed. Then, the drum generated stress at which the provisional remaining life of the drum becomes 1 year is calculated as the limit generated stress, and the current drum generated stress is reached until the limit generated stress is reached by the drum generated stress increase based on the thickness reduction and vibration increase. A drum deterioration evaluation method for a drum mixer, wherein the number of years is calculated as the true remaining life of the drum. A drum deterioration recovery method based on the drum deterioration evaluation method for a drum mixer according to claim 1, wherein a true remaining life of the drum is calculated at each periodic repair timing, and the calculated true remaining life of the drum is obtained. A method for recovering drum deterioration of a drum mixer, comprising determining whether to repair a crack in the drum or to update the drum mixer itself.

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