EP0712673A1 - Calibration of Assel rolls - Google Patents

Abstract

To calibrate iso-pod rollers, for rolling thin-walled tubes from perforated hollow bodies, on a diverging roller, the transport angle of each iso-pod roller (1) is set at 7-17 degrees , according to the dia. and smoothed roller section length, where the transport angle is smaller with an increasing tube diameter. The spread angle (alpha) is set at 7-30 degrees . The opening angle (beta) of the round cone (5) is 4-15 degrees , formed between the extended mantle line of the smooth section (4) and the opposing mantle line of the short round cone.

Description

The invention relates to the calibration of the rolls of a wood mill for rolling thin-walled tubes made of pre-perforated hollow bodies over a mandrel with at least three staggered by 120 ° to each other, inclined by the spreading angle α with respect to the rolling axis and arranged pivoted by the transport angle γ to the rolling axis, each with an inlet cone , a working part (shoulder) and a smoothing part, which is followed by a round cone.

The Assel rolling process developed by Walter Assel around 60 years ago for the production of rolling bearing and thick-walled turned part tubes with a diameter / wall thickness ratio of approximately 16: 1 has been further developed into a powerful stretching process through permanent improvements. It is used in the production of pipes with medium and thick wall thicknesses and in particular those which should have flawless surfaces and close tolerances, as is the case, for example, for the manufacture of bearing steel pipes. The Assel rolling mill works on the principle of cross-rolling over mandrel bars, whereby three conical rolls are in engagement, which are mounted at an angle of 120 ° to the rolling stock axis. In addition, the rolls are adjustable perpendicular to the roll axis, so that a large number of pipe diameters can be produced on an Assel mill

The rolls of the Assel mill consist essentially of an inlet part, a working part (shoulder), a smoothing part and an outlet and rounding part. The main forming work takes place in the working section on the shoulders. Compared to the Diescher process, in which two so-called barrel rollers are known to be used, the Assel process has advantages, such as better rolling stock management due to the use of at least three rollers and the lack of necessity, To have to use guide washers. A particular advantage is that Assel rolling mills require a much smaller roll diameter, which means that these plants can generally be built smaller than corresponding Diescher rolling mills.

As is known in the case of other cross-rolling processes, helix-shaped wall thickness inequalities can also occur on the hollow block or tube in the Assel rolling process, the so-called coils. In the cross section of the hollow body, these act as eccentricity, i.e. Deviation of the center points of the inner and outer circle from each other and in longitudinal section as a periodically running and alternating thickening and thinning of the wall. The main reason for the helix formation in the Assel process is inadequate calibration of the rollers. For this reason, narrow wall thickness tolerances of ± 4% to ± 7% can be achieved with conventional woodloom methods, i.e. with relatively thick walls, but the tolerances with thin walls still leave something to be desired.

Another disadvantage of the Assel rolling process compared to other cross rolling processes is the relatively low possible rolling speed, which limits the capacity of the plant. The limits for the rolling speed are the max. possible speed of the rolling stock itself and the max. possible transport angles. Too high a speed of the rolling stock can lead to damage on the rolled pipe, a too large transport angle leads to a large helix formation in conventional roll calibrations, ie to poorer pipe tolerances. Since the rolling stock speed could no longer be increased noticeably and the transport angle γ was limited to around 7 ° for tolerance reasons, there seemed to be no further possibilities for increasing the rolling stock speed. It was not taken into account at all that the pitch of the bead running helically around the tube depends not only on the transport angle of the rolls, but also on the tube diameter. The larger the pipe diameter with the same transport angle, the greater the pitch of the helix and the greater the difference between the thinnest and thickest wall. In principle, however, this also means that small pipe diameters can be rolled with a larger transport angle than previously customary if, for example, the pitch height is assumed to be a constant value.

The woodlouse procedure could also only be used for a limited application, namely for a max. D / s ratio, i.e. Diameter-wall thickness ratio, from 12 ... 16: 1, i.e. for thick-walled roller bearing and turned part pipes and the like. If larger D / s ratios were selected, the triangulation of the rear pipe end caused the plugs to exit when leaving the rolls, which could only be prevented by timely lifting of the rolls at the end of the roll.

If it were also possible to roll thin-walled pipes with the Assel rolling process with tolerances and good surface qualities, the field of application of this process could be expanded, for example to oilfield pipes, boiler pipes and line pipes. After all, the advantages of the Assel process could be exploited, for example compared to the Diescher rolling process, which are there, good rolling stock through at least three rolls, good wall thickness tolerances for the pipes, low investment costs overall and - because of the lower stress on the pipes in the roll gap - better pipe quality than diescher rolling.

Based on the above-described problems and disadvantages in the prior art, it is an object of the present invention to increase the capacity of woodloom mills for rolling thin-walled tubes without deteriorating the tube quality by providing an appropriate calibration of woodlead rollers.

• a) bei divergenter Walzenstellung beträgt der Transportwinkel (γ) jeder Asselwalze in Abhängigkeit vom jeweiligen Rohrdurchmesser und der Glätteillänge der Asselwalze zwischen 7°und 17°, wobei der Transportwinkel (γ) mit steigendem Rohrdurchmesser kleiner wird
• b) der Spreizwinkel (α) wird zwischen 7°und 30° eingestellt,
• c) der Öffnungswinkel (β) des Rundekonus, gebildet zwischen der verlängerten Mantellinie des Glätteils und der gegenüberliegenden Mantellinie des kurzen Rundekonuses, beträgt zwischen 4° und 15°.

The following measures are proposed in combination to solve the task:

• a) with a divergent roll position, the transport angle (γ) of each woodlayer is between 7 ° and 17 °, depending on the respective pipe diameter and the smooth length of the woodlice, the transport angle (γ) becoming smaller with increasing pipe diameter
• b) the spreading angle (α) is set between 7 ° and 30 °,
• c) the opening angle (β) of the round cone, formed between the extended surface line of the smoothing part and the opposite surface line of the short round cone, is between 4 ° and 15 °.

The solution to the problem according to the invention includes several considerations which, in combination, lead to the desired success. Experience has shown that a large feed angle γ favors the widening of the tube in the roll gap. This effect is deliberately used to create larger pipe diameters with the same wall thickness, i.e. a large D / s ratio. The claimed transport angle γ from 7 ° to 17 ° is also the setting range of the system.

Dabei bedeuten:

Z =

Anzahl der Walzen

f =

Faktor für die Glätteillänge = 1,15 bis 1,50 = Überdeckungsfaktor.

η =

Vorschubwirkungsgrad.

10,7 =

Konstante

Aus dieser Formel läßt sich am Beispiel der Faktoren f = 1,15 und η = 0,9 folgende Glätteillänge bei drei Walzen errechnet: $$\text{L = 3 x 10,7 x 1,15 x 0,9 = 33,22 mm.}$$

Für den Rohrdurchmesser D = 100mm ergibt sich als Beispiel $$\text{tan γ =}\frac{\mathit{\text{Z}}\text{·}\mathit{\text{L}}}{\mathit{\text{D}}\text{·π·η·}\mathit{\text{f}}}\text{=}\frac{\text{99,66}}{\text{324,99}}\text{= 0,3067}$$

entsprechend einem Transportwinkel von γ = 17°
und für den Rohrdurchmesser D = 250mm $$\text{tan γ =}\frac{\mathit{\text{Z}}\text{·}\mathit{\text{L}}}{\mathit{\text{D}}\text{·π·η·}\mathit{\text{f}}}\text{=}\frac{\text{99,66}}{\text{250·π·0,9·1,15}}\text{= 0,1222}$$

entsprechend einem Transportwinkel von γ = 7°.The possible transport angle γ depends on the pipe diameter and the smoothing length of the woodlice. With a tube diameter of 250 mm, a transport angle γ = 15 ° and three rollers, the pitch on the tube is about 70 mm in relation to one roller (with a feed efficiency of η = 1.0). However, this would mean that the smoothing part of the roller is too long. This long smoothing part is unfavorable because it hinders the elongation of the tube in the longitudinal direction. A rule is therefore established that the transport angle γ becomes smaller as the pipe diameter increases. One can say: The length of the smoothing part of the roller is three rollers $$\text{L = Z x 10.7 xfx η}$$

Here mean:

Z =

Number of rolls

f =

Smoothness length factor = 1.15 to 1.50 = coverage factor.

η =

Feed efficiency.

10.7 =

constant

Using the example of factors f = 1.15 and η = 0.9, this formula can be used to calculate the following smooth length for three rolls: $$\text{L = 3 x 10.7 x 1.15 x 0.9 = 33.22 mm.}$$

For the pipe diameter D = 100mm, this is an example $$\text{tan γ =}\frac{\mathit{\text{Z.}}\text{·}\mathit{\text{L}}}{\mathit{\text{D}}\text{· Π · η ·}\mathit{\text{f}}}\text{=}\frac{\text{99.66}}{\text{324.99}}\text{= 0.3067}$$

corresponding to a transport angle of γ = 17 °
and for the tube diameter D = 250mm $$\text{tan γ =}\frac{\mathit{\text{Z.}}\text{·}\mathit{\text{L}}}{\mathit{\text{D}}\text{· Π · η ·}\mathit{\text{f}}}\text{=}\frac{\text{99.66}}{\text{250 · π · 0.9 · 1.15}}\text{= 0.1222}$$

corresponding to a transport angle of γ = 7 °.

Therein means: D = pipe diameter in the smoothing part.

If the number of rollers changes in e.g. four, as before, the transport angle γ = 7 ° forms the lower and γ = 17 ° the upper setting limit for the rolling mill.

To adjust the angular velocity of the respective point of the round cone of the roller and the part of the tube opposite this point, a divergent roller position with a large spreading angle α is provided, which is between 7 ° and 30 °. At the same time, a short, rapidly opening round cone of the roller is provided. An opening angle of approximately β = 2 to 3 ° in relation to a roller according to FIG. 1 is known. The opening angle is formed between the surface line of the round cone and the opposite, extended surface line of the smoothing part; it increases with increasing transport angle γ. It has been shown that an opening angle β of at least 4 ° improves the rounding of the tube emerging from the smoothing part and prevents the risk of the tube forming a sack between the rollers and thus the triangulation of the rear tube end. The angle range found for the opening angle is between 4 ° and 15 °.

With a calibration of the proposed type, surprisingly well thin-walled tubes can be produced at relatively high rolling speeds, so that not only is the capacity increased when rolling thin-walled tubes according to the Assel rolling method, but also the tolerance values correspond to the required values.

Figur 1

eine der drei Asselwalzen in der Längsmittelebene des Rohres und

Figur 2

eine Draufsicht auf die um den Transportwinkel γ verschwenkte Walze.

To explain the individual roller angles, two drawing figures are attached and described below. It shows:

Figure 1

one of the three woodlice in the longitudinal median plane of the pipe and

Figure 2

a plan view of the roller pivoted about the transport angle γ.

According to FIG. 1, the roller 1 consists of the inlet cone 2, the working part (shoulder) 3, the smoothing part 4 and the round cone 5. In the inlet cone 2, the hollow block 6 is gripped, set in rotation and drawn into the roller 1. The outer and inner diameters of the hollow block 6 are reduced to such an extent that the hollow block touches the mandrel rod 8 with its inner surface lying under the roller. The wall thickness reduction takes place essentially only under the shoulder 3, the smoothing part 4 serves to even out the wall thickness of the tube 7 rolled from the hollow block 6. When rolling under the shoulder 3 and in the smoothing part 4, the tube is expanded and takes on a triangular cross section with three rollers because the wall bulges into the spaces between the rollers. In the subsequent round cone 5, the polygonal tube 7 is rounded.

In the drawing figure 1 it can be seen that the roller 1 is pivoted by the spreading angle α to the longitudinal axis Y-Y, the roller axis Z-Z meeting the longitudinal axis Y-Y at point A. The opening angle β is formed between the extended surface line of the smoothing part and the opposite surface line of the short round cone 5 and is also shown in FIG. 1.

In the plan view of the roller in Figure 2 it is clear that the transport angle γ is created by pivoting the roller 1 to the longitudinal axis Y-Y. The transport angle γ serves to move the rolling stock in a spiral and directly influences the roll speed. The advantages of the present invention can only be achieved by coordinating the individual angles with one another and a combination, namely the economical rolling of thin-walled pipes of good quality using the Assel rolling method.

Claims (1)

Calibration of the rolls of an Assel rolling mill for rolling thin-walled tubes from pre-perforated hollow bodies over a mandrel with at least three staggered by 120 ° to each other, inclined by the spreading angle α relative to the rolling axis and the transport angle γ pivoted to the rolling axis, each with an inlet cone, a working part (shoulder ) and a smoothing part, which is followed by a round cone, characterized by the combination of the following measures: a) with a divergent roll position, the transport angle (γ) of each woodlayer is between 7 ° and 17 °, depending on the respective pipe diameter and the smooth length of the woodlice, the transport angle (γ) becoming smaller with increasing pipe diameter b) the spreading angle (α) is set between 7 ° and 30 °, c) the opening angle (β) of the round cone, formed between the extended surface line of the smoothing part and the opposite surface line of the short round cone, is between 4 ° and 15 °.

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