DE10236757A1 - Process for producing a hollow block of metallic material - Google Patents

Abstract

Production of a hollow block (1) made from metallic material, especially roller bearing steel comprises deforming a cylindrically deformed starting material (2) in a cross rolling mill (3, 4) using an axially fixed mandrel (5) to form a tubular hollow block. The starting material is made from a pre-deformed material produced by direct continuous casting, in which the starting material is not pre-rolled before being introduced into the cross rolling mill.

Description

The invention relates to a method for producing a hollow block of metallic material, in particular of bearing steel, in which cylindrically shaped starting material is formed in a cross-rolling mill using an axially fixed piercing pin to form a tubular hollow block. A method of this kind is for example from the EP 0 940 193 A2 known.

For example, for the production of rolling bearing rings be seamless tubes made of bearing steel needed by the generic method can be produced. Cylindrical shaped starting material becomes a cross rolling mill supplied which is equipped with an axially fixed piercer. to Forming the cylindrically shaped stock into a seamless one Pipe becomes the starting material over rolled the piercer.

In addition to the punching of the starting material by oblique rolling and the press holes is also known, as for example in the DE 195 20 833 A1 is described.

The advantages of the cross rolling process are mainly the low eccentricity of the hollow blocks and a high operating weight of the blocks, d. H. it can relatively long pipes are made. The disadvantage is in the known Sawing method that Tensile stresses occur in the core zone, thereby reducing the risk the internal defect formation by tearing exists; continues Here a relatively high input material quality is necessary, which is why usually For materials with reduced forming capacity only pre-rolled material can be processed.

The advantages of the press hole are especially the occurrence of compressive stresses in the material core zone, whereby there is no danger of internal defects, even with steel types with restricted Formability. The disadvantage here is the relatively high eccentricity of the hollow blocks and their lower weight.

Due to the mentioned disadvantages of this Schrägwalzverfahren sees the EP 0 940 193 A2 suggest that before punching the starting material, a massive reduction of the material is made. Reduction and perforation can be done in a single step (s. 1 of the EP 0 940 193 A2 ); Alternatively, two steps can be provided for the reduction and the perforation (s. 2 and 3 of the EP 0 940 193 A2 ).

When using the slanting method for Perforation of cylindrical starting material has been found that it is special in the processing of bearing steel and here in particular with steel of type 100 Cr 6 with the known method problems gives. This according to the state mass reduction of the starting material used the manufacturing process is not insignificant.

The invention is therefore the task based on creating a method with which hollow blocks made Bearing steel economically by the cross rolling method let produce. In particular, the starting material for the production of tubes as the starting product for the production of bearing rings become cheaper.

This object is achieved according to the invention solved, that the starting material consists of non-pre-formed material, which is produced by direct extrusion, and that the starting material before the feeder in the slanting mill none Pre-rolling is subjected. The starting material is preferred in the cross rolling mill then when punching only one rolling process with defined diminished, d. H. subjected to low degree of deformation; the forming parameters are then so limited, so that only a small transformation takes place.

According to the gist of the invention ie directly extruded starting material for the production of seamless Tubes used without passage a rough rolling process the cross rolling mill supplied becomes. When punching the starting material in the cross rolling mill, the material is only a rolling process with defined reduced, i. low degree of deformation compared with the possibilities known Schrägwalzverfahren. It takes place during the oblique rolling therefore, no mass reduction before or during punching, like this common in previously known methods is. In this way, the manufacturing process can be seamless Pipes, especially from bearing steel, essential simplified and thus more economical be designed.

The cross rolling mill is preferred as a three-roll cross rolling mill educated; preferably tapered tapered rollers are used for use.

It has proven to be particularly beneficial proven, if the following conditions are met:

The reduction in the cross section of the starting material while the punching process in the cross rolling mill should with reducing punching with convergent roll position a maximum of 71% and in the expanding holes with divergent roller position maximum 60%. Under cross-section decrease is the difference between exit cross-sectional area and reshaped cross-sectional area understood based on the initial cross-sectional area.

The constriction in the punching process should be at least 75%, preferably at least 87%, from the initial diameter. By constriction here is meant the diameter reduction at the narrowest point, the high point; it thus results as a quotient of the diameter at the high point relative to the initial diameter. The high point is the narrowest point between the rolls, ie where the material diameter is smallest.

Advantageously, the maximum extension of the Starting material in convergent punching 3.5, preferably 3.0, and at divergent punching 2.5, preferably 2.0. The stretching arises as a ratio the pipe length after transformation to the original one Block or pipe length or as a ratio the cross-sectional area before forming to the reshaped cross-sectional area.

The diameter decrease of the starting material in the cross rolling mill should - if a massive Vorreduzieren is made, so in the case of a Vorumformung - maximum 42%, preferably at most 15%. It is defined as difference between the diameter before forming and the diameter after the deformation based on the starting diameter, i. before forming.

The method is particularly advantageous Apply if the starting material before punching to a temperature between 1,050 ° C and 1,140 ° C, preferably at a temperature between 1060 ° C and 1080 ° C, is heated.

The punching process is preferred performed with divergent aligned rollers. When divergent rolling the roll axes move away from each other in the rolling direction while in convergent rolling, the roll axes increasingly increase in the rolling direction approach.

The proposed procedure comes particularly preferred in the processing of bearing steel of the type 100 Cr 6 to use.

The method according to the invention is characterized through various advantages: through the measures mentioned will it be possible Bearing steel, which was manufactured in direct casting without processing prereduction and to reshape the hollow block. Lie in the core area of the material while advantageous compressive stresses.

By applying the proposed method a hollow block with low eccentricity is generated. Furthermore, it is possible relative produce long tubes, since the operating weight of the blocks in the Cross rolling process be great can. Due to the existing compressive stresses in the core material zone the danger of the emergence of internal defects is small, too especially positive for steel grades with limited forming capacity makes noticeable.

Since a pre-rolling of the starting material before Punching can be dispensed with by the proposed method the hollow block produced in a substantially cheaper manner compared to the cross rolling method according to the state of the technique.

With the proposed approach is also achieved in an advantageous manner that the quality of the hollow block remains at a high level: with the proposed rolling parameters Triangulation (triangulation) at the rear hollow block end becomes large avoided, and there is also no major "trumpeting" (diameter expansion at the front end of the hollow block).

The inventive method therefore combines the advantages of the cross rolling process in terms of good concentricity, high application weight and low material losses with the advantages of the press hole in terms of predominant Compressive stresses in the core area of the material while avoiding the Disadvantages of both process principles. Thus arise next to economic Advantages also quality improvements of the hollow block.

Overall, there is a saving of energy, material and production costs for the supply of input material, especially for the production of rolling bearing rings, at a high quality level the manufactured pipes.

In the drawing, an embodiment of the Invention shown. The single figure shows schematically the metallic Starting material, which is formed by rolling to the hollow block.

In the figure, 1 designates the hollow block to be produced, which is then formed into a seamless tube. This consists in the embodiment of bearing steel of the type 100 Cr 6. The hollow block 1 is made from raw material 2 manufactured with circular cylindrical cross section. The transformation of the starting material 2 to the hollow block 1 takes place in a three-roll cross rolling mill; shown are two rolls 3 and 4 of the cross rolling mill. The rollers 3 . 4 have a tapered section. The axes 6 and 7 the rollers 3 and 4 remove in the rolling direction R from each other, ie there is a divergent punching.

For punching the starting material 2 to the hollow block 1 is an axially fixed piercer 5 provided over which the starting material 2 through the rollers 3 and 4 is rolled.

As an essential feature of the present invention, it is provided that the starting material 2 made of non-preformed material produced by direct casting. Before the feed of the starting material 2 in the cross rolling mill 3 . 4 the material is not subjected to a pre-rolling process. In the cross rolling mill 3 . 4 itself, when punching the starting material 2 , is rolled with a defined only reduced, ie low degree of deformation.

This is to be understood in particular that the reduction in the cross-section of Ausgangsmateri when 2 during the punching process in the cross rolling mill 3 . 4 at most 60% for divergent punching and at most 71% for convergent punching. In the prior art three-roll cross rolling method, the reduction in the cross-section is up to 80%.

Furthermore, the constriction of the starting material 2 during the punching process at least 75%, particularly preferably at least 87%.

The punching process is carried out according to the embodiment with divergently employed rollers. Here, the maximum stretch of the starting material 2 . 5 ,

Of importance is also that the reduction in the cross section of the starting material 2 when preforming - if it is carried out for reasons of assortment expansion - a maximum of 66%, which corresponds to a stretch of 1 to 3. This value is much larger in the prior art; it is 67 to 75% and higher, which corresponds to an elongation of greater than or equal to 3 to 4.

The method is preferably applicable to the processing of low alloy steels of non-pre-formed continuous casting material and high alloy steels while avoiding significant internal defects and end losses at low eccentricity. The feedstock may be specially melted, pan-treated and potted, such that it has a fine-grained, homogeneous microstructure with finely dispersed primary carbide and high purity distribution, with particularly limited O ₂ and S contents.

In summary, one can say that in the proposed method no pre-reduction, pre-forming or Massive reduction needs to take place, resulting in a cost savings results. However, it can also be a prereduction, for example take place on a three-roll cross rolling mill, from a parent block output blocks of different diameters manufacture; This allows the range of dimensions of the resulting to be rolled hollow blocks be extended.

As an example of this is a Mother block with a diameter of 120 mm, out the hollow blocks rolled with a diameter of 127 to 144 mm. Will the Mother block before, d. H. before carrying out the method according to the invention, by skew rolling on z. B. 100 mm or 80 mm prereduced, can from the resulting blocks hollow blocks rolled with a diameter of 106 to 120 mm or 85 to 96 mm become. That way you can So from the mentioned mother block hollow blocks in the diameter range of 85 mm to 144 mm rolled. In that regard comes a Vorreduzieren of the mother block into consideration before carrying out the method according to the invention.

In the prior art, however, a pre-forming by longitudinal rolling or forging is necessary, wherein the stretch 3 to 4 or the cross-sectional decrease must be at least 67% to 75%.

The punching of the block, so the starting material, to the hollow block takes place with a defined moderate degree of deformation (extension maximum 2.0 to 3.5) under complex simultaneous combination of several Forming parameters specified in the claims and the an optimum for represent the production of the present hollow blocks.

The degree of deformation or the extension can with a cone slanting mill with 2 rolls up to 6.0. In a barrel rolling mill with 2 Rolls can be up to 4.0. In the three-roll cross rolling mill is when using barrel rollers depending on the diameter change a maximum value of 2.8 to 3.5 is possible, a value of 2.3 is usual. A maximum value of 2.5 to 3.5 is suggested, depending on the roller position. The stretching area for Rotary piercing mills is between 1.2 and 6.0.

In the pre-forming by massive reduction 66% reduction in cross-section, corresponding to 42% decrease in diameter, not exceeded become. During the subsequent punching, the stretch is, for example at values of 3.5, 3.0 or 2.5, which is a cross-sectional decrease of 71%, 67% and 60% respectively.

1

hollow block

2

starting material

3

roller of the cross rolling mill

4

roller of the cross rolling mill

5

piercer

6

axis the roller 3

7

axis the roller 4

R

rolling direction

Claims (10)

Method for producing a hollow block ( 1 ) of metallic material, in particular of bearing steel, in which cylindrically shaped starting material ( 2 ) in a cross rolling mill ( 3 . 4 ) using an axially fixed piercer ( 5 ) to a tubular hollow block ( 1 ), characterized in that the starting material ( 2 ) consists of non-pre-formed material produced by direct continuous casting and that the starting material ( 2 ) before being fed into the cross rolling mill ( 3 . 4 ) is not subjected to a rough rolling process. Process according to claim 1, characterized in that the starting material ( 2 ) in the cross rolling mill ( 3 . 4 ) is only subjected to a rolling process with defined reduced degree of deformation when punching. A method according to claim 1 or 2, characterized in that the starting material in a three-roll cross-rolling mill ( 3 . 4 ) is transformed. Method according to one of claims 1 to 3, characterized in that the cross-section decrease of the starting material ( 2 ) during the punching process in the cross rolling mill ( 3 . 4 ) is a maximum of 71% for convergent punching and a maximum of 60% for divergent punching. Method according to one of claims 1 to 4, characterized in that the constriction of the starting material ( 2 ) is at least 75%, preferably at least 87%, of the initial diameter during the punching process. Method according to one of claims 1 to 5, characterized in that the maximum elongation of the starting material ( 2 ) with convergent punching 3 . 5 , preferably 3.0, and with divergent punching 2.5, preferably 2.0. Method according to one of claims 1 to 6, characterized in that the diameter decrease of the starting material ( 2 ) during massive pre-reduction in the three-roll cross-rolling mill ( 3 . 4 ) is a maximum of 42%. Method according to one of claims 1 to 7, characterized in that the starting material ( 2 ) is heated before being punched to a temperature between 1050 ° C and 1140 ° C, preferably to a temperature between 1060 ° C and 1080 ° C. Method according to one of claims 1 to 8, characterized in that the punching process with divergently oriented rollers ( 3 . 4 ) he follows. Method according to one of claims 1 to 9, characterized that as a metallic material, a bearing steel of the type 100 Cr 6 is transformed.