HRP960145A2 - A method of manufacturing a cylinder liner for a piston engine , and a cylinder liner - Google Patents

Description

This invention relates to a method of making a cylinder liner for a piston engine, such as a large two-stroke piston engine, in which the working surface for the piston rings on the inner surface of the liner is made by first carving corrugations with a difference between the peak and trough levels of the waves of at least 0.005 mm on inner surface with at least one cutting tool having a curved cutting edge and then removing the crests of the waves, at least on the working surface closest to the end center position of the piston tip, so that the longitudinal portion of the inner surface of the finished liner has a partially corrugated surface where the crests of the waves are separated by a generally flat surfaces.

German patent no. 683262 describes a cylinder liner made by a method of this type, where the crests of the waves are removed by grinding the inner surface of the liner. This method requires moving away from the device for machine engraving the corrugation on the inner surface, and placing it in a new position on the grinder. In addition, grinding itself is expensive and time-consuming machining, where a head with several rotating grinding stones passes along the liner, while it rotates so that the grinding stones scrape the material off the crests of the waves. Especially in the case of large cylinder liners, grinding equipment is an expensive investment.

Swiss patent no. 342409 describes a cylinder liner in which the working surface for the piston rings is made by cutting corrugations into the inner surface of the liner. Such a liner is called a wavy cut, and the shape is usually spiral, the cutting tool is pushed in the longitudinal direction of the liner at a certain speed while the liner rotates. An improvement mentioned in the Swiss patent is that lubrication oil collects in the grooves so that pockets of oil are formed which promote lubrication between the piston rings and the inner surface of the liner.

Cutting the corrugation in the inner surface of the liner, which coincides with the longitudinal direction of the liner, provides the manufacturing advantage of avoiding grinding the inner surface, due to machines for cutting the corrugation of the liner to the desired inner diameter measurement. When the liner is put into operation, the piston rings remove the crests of the waves, so that flat surfaces are formed between the troughs of the waves, but the piston rings wear out at the same time.

The development of large two-stroke piston engines leads to an ever-increasing cylinder power, and thus also to an increase in the effective average pressure. Most modern engines can be built with cylinder power up to 5,700 kW with an effective average pressure of 18.2 bar. This places very high demands on piston rings and cylinder liners, because the pressure drop across the piston rings, and thus also the force of their contact with the inner surface of the liner, becomes large. Therefore, it is possible to foresee problems when running in the pistons and the liner if a clean corrugation is etched into the inner surface of the liner, the remaining, sharp crests of the waves can cause corrosion of the piston rings.

Danish patent no. 139111 describes a cylinder liner having a spirally cut groove in its inner surface in which the rise of the spiral shape is so large that the bottoms of the waves are separated by flat surfaces of length L of, for example, 4 mm in the longitudinal direction of the cylinder. Before the groove is cut, the liner must be ground, which makes the manufacture of the liner expensive, because in the first stage it has to be machined to its approximate innermost dimension, then it has to be ground and ground, and then returned to its original position for grooving. Cylinder liners for large engines are heavy parts that take a long time to move on machining equipment.

JP-A 5-65849 describes a cylinder block for a reciprocating engine, in which the cylinder, after drilling, is subjected to a grinding process to create grinding marks or grooves in the form of grooves. These grinding marks include small sharp protrusions that can cause damage to the piston rings. To prevent this, the inside of the cylinder is polished with several rolling tools. This process of removing small protrusions by grinding on a cylindrical surface is a well-known process. The cylinder block described in that Japanese document also needs to be placed in several positions on different stands.

The object of the invention is to provide a method of manufacturing cylinder liners with improved undulation interruption in such a way that expensive grinding equipment can be avoided and that the handling of the liner is facilitated, and that the time required for its manufacture is less.

From this point of view, the method according to the invention is indicated by the fact that the cylinder liner has an inner diameter in the range from 25 cm to 100 cm and a length in the range from 100 cm to 400 cm, that the crests of the waves are removed without applying grinding, by plastic compression of at least 0.004 mm from their heights into said mostly flat surface, and that the bottoms of the waves, after compression, are at a level at least 0.001 mm lower than that surface.

Plastic compression can be carried out by a technically uncomplicated process with relatively simple and inexpensive equipment. And very large liners can be held in one and the same fixed position while corrugation is cut into the inner surface of the liner and the crests of the waves are compressed into a mostly flat surface. In addition, investments in grinding equipment were saved, said equipment is very expensive for those large liners. Furthermore, in the approximately flat surface between the bottoms of the waves, the inner surface of the liner takes on a property that is highly desirable for running in the liner and piston rings. There are no sharp bumps on the rolled surface, but on the other hand, it is not completely polished or shiny like a mirror, which could cause lubrication difficulties between the liner and the piston rings.

Plastic compression of the corrugations can be carried out, for example, by rolling with a small rolling tool, which is preferred because the equipment for this is very simple. Alternatively, rolling can be carried out using a single roller that extends along the entire length of the liner. The aforementioned limitations of the height of the surface corrugation are especially useful for the corrugation which, before rolling, has a level difference between the bottom and the top of the waves of 0.01 - 0.02 mm. With the plastic deformation of the crests of the waves within the upper range of limits, the inner surface of the liner acquires a surface that ensures easy running-in of the piston rings. If the depth of the bottom of the waves becomes less than 0.001 mm, the obtained lubrication conditions will not be satisfactory.

The corrugation is preferably incised in the inner surface of the liner by said at least one cutting tool which is moved in the longitudinal direction of the liner by means of a drill rod at a feed rate, while the liner is rotated to form the corrugation as at least one spiral notch, and the plastic compression is carried out by rolling internal surfaces with the rolling tool moved forward by the same drill rod as the cutting tool. This saves the time needed to move the cylinder liner from one machine and to adjust it to another machine. When the spiral notch is cut into the inner surface of the liner, the drill rod can be withdrawn from the liner and the rolling tool mounted, after which the drill rod is reinserted into the liner and rolling is carried out. Cutting and rolling tools can also be mounted in specific cross-slides or in specific holders, so that proper tool change can be accomplished by pulling the tool back or forward relative to the liner surface as needed. The drill rod with cutting tool is adapted to adjust the cutting depth of the cutting tool by radially moving the tool, i. so the rolling pressure can be conveniently adjusted by moving the rolling tool in the radial direction of the liner so as to take advantage of the existing possibilities of adjusting the drilling rod.

Rolling can also be carried out with a rolling tool, which has several rollers mounted in the tool head, which is known for rolling the inner surface of the pipe, but such a tool is most suitable for relatively small diameter pipes, where the diameter of the pipe is constant. Plastic compression is primarily carried out by rolling with a rolling tool having only one roller, the radial position of which can be adjusted relative to the inner surface of the liner, and which can be moved forward in the longitudinal direction of the liner as the liner rotates. This allows the same tool to be used for rolling liners of different diameters. The use of a single roller also allows the rolling pressure to be adjusted very precisely by radially moving the roller, thus avoiding excessive corrugation alignment. If several rollers are used, the simultaneous control of the rollers must be carried out within narrow limits, which can be difficult, especially since changes in the forces on one roller can be transmitted to the other roller(s).

Preferably, the rolling tool is connected to a current rolling pressure indicator so that the rolling pressure can be observed and final adjustments can be made while rolling the inner surface. Cylinder liners are often produced in series for a single engine or for different engines of the same type, and in such series production the indicator can also be used to re-apply experience as to the appropriate rolling pressure for a specific cylinder liner size and to set up the rolling tool at the start of liner rolling.

To facilitate liner fabrication, corrugation notching can be performed with a liner inner diameter notch spacing tolerance of, for example, ±0.1 - 0.2 mm when the liner diameter is in the range of 25 and 100 cm. Despite this tolerance, the waviness height is cut with a much smaller tolerance, for example ±0.003 mm or less, because the arcuate shape of the cutting edge of the cutting tool has a very large radius of, for example, 100 mm to 800 mm, depending on the inside diameter of the liner and the desired corrugation height, and since diameter changes occur so slowly that adjacent corrugations are cut with mostly equal diameters. Thanks to the liner diameter tolerance, the rolling tool can conveniently maintain the desired rolling pressure by moving the tool in the longitudinal direction of the liner, even though the inner diameter of the liner changes along the length of the liner.

Since diameter changes are small, rolling pressure can be maintained with a very simple tool design using a rolling tool supported by a lever that is bent inwards within its elastic limits in the radial direction of the liner when rolling pressure is applied, whereby the lever compensates for diameter changes by springing back into radial direction. Alternatively, the rolling tool can be mounted on a cross slide which can be continuously adjusted in the radial direction by means of an adjusting device based on the signal from the top indicator for the current rolling pressure.

When a reciprocating engine is in operation, the pressure in the chamber above the piston decreases with subsequent movement from the upper end center position, and the reduction in pressure leads to lower forces between the piston rings and the liner.

In certain cases it may be possible to manufacture the liner in such a way that only rolling is carried out in the upper section of the liner which includes the surface on which the uppermost piston ring slides as the piston moves from its upper end center, and part of the way of the piston towards the lower end center position. The rolling of the inner surface takes place so quickly that limiting the rolling to only the upper section of the liner does not save significant time, but saves rolling equipment, especially in the case of very large liners up to 400 cm long, because the drill rod does not have to be so large.

The tops of the waves can be deformed by rolling so that the area of mostly flat surfaces between the bottoms of the waves forms from 25% to 75% of the total surface of the liner in the rolled area. If the flat areas make up less than 25%, the contact surface of the piston rings becomes too small, which can cause damage to the material of the rings due to excessive heating, because the heat is not dissipated enough from the liner. Insufficient contact surface can also destroy the pressure sealing effect of the piston rings. If the flat areas make up more than 75%, the lubrication conditions (tribological conditions) deteriorate because the oil pockets become too small. The crests of the waves are primarily deformed by the wave so that the area of mostly flat surfaces between the bottoms of the waves forms 40% to 60% of the total surface in the rolled area. It is a compromise between the conflicting considerations of lubrication conditions and thermal loads and pressure sealing, while providing adequate clearance to the proud initial constraints, so that certain manufacturing inaccuracies will not be of vital importance to the operating conditions of the liner.

The ability of the piston rings to seal against very high pressures in the combustion chamber can be ensured by deforming the tops of the waves by rolling so that the generally flat surface between consecutive bottoms of the wave extends in the longitudinal direction of the liner, within an interval of ±1 mm, corresponding to a quarter of the height of the piston ring at least Heights. When the piston in the cylinder liner thus made is moved longitudinally in the undulation region, each of the piston rings is surrounded by at least two consecutive flat surfaces, which prevent the compressed gas from blowing above the piston through the spiral grooves or all the way down under the piston ring. Most conveniently, the crests of the waves can be deformed so that the generally flat surface is compressed at least 0.006 mm and at most 0.018 mm, preferably at most 0.015 mm from the height of the crests of the waves, and the bottoms of the waves at the same level are at least 0.002 mm below those surfaces. If these uneven boundaries are exceeded in places, it is still possible for the inner surface of the liner to be acceptable.

The preferred waviness cutting method according to the invention is reshaped so that the average radial level difference between the obtained, generally flat surfaces and the bottom of the waves represents between 7% and 66% of the average level difference between the wave crests and the wave bottoms of the shape before compression, and preferably between 16% and 36% of that.

The invention also relates to a cylinder liner for a reciprocating engine, such as a large two-stroke reciprocating engine, having a working surface for the piston rings on the inner surface of the liner, which working surface at least in the region closest to the highest end center position of the piston has a partially wavy shape in which wave bottoms separated by mostly flat surfaces. These cylinder liners according to the invention are characterized by the fact that they have an inner diameter ranging from 25 cm to 100 cm and a length ranging from 100 cm to 400 cm, that they are mostly flat rolled surfaces without sharp protrusions, that the bottoms of the waves are level for at least 0.001 mm below those surfaces, and that a generally flat surface between consecutive wave bottoms extends in the longitudinal direction of the liner corresponding within ±1 mm to a quarter of the height of the smallest piston ring. The cylinder liner has the improved working surface properties mentioned above.

Examples of the invention will now be explained below in further detail with reference to the fully schematic drawings, of which

figure 1 shows a partial side view, especially the longitudinal average of the cylinder liner,

Fig. 2 shows a perspective view of a cylinder liner placed in a machining apparatus, partially shown,

Figure 3 is a perspective view of the rolling tool,

Figure 4 shows a side view of another rolling tool,

figure 5 shows a greatly enlarged longitudinal section of the inner surface of the cylinder liner, rolled according to the invention,

figure 6 shows a five-fold enlarged photograph of the inner surface of the corrugated notch and a partially ground cylinder liner,

Figure 7 is a similar photograph of a liner cylinder that has been corrugated and rolled in accordance with the invention,

Figure 8 is a snapshot of the roughness measurement made on the inner surface of the liner shown in Figure 6, i

Figure 9 is a snapshot of the roughness measurement made on the inner surface of the liner shown in Figure 7.

Figure 1 shows cylinder liner 1 for a large two-stroke piston engine. Depending on the size of the engine, the cylinder liner can be made in various sizes with internal diameters typically ranging from 25 cm to 100 cm, and corresponding typical lengths ranging from 100 cm to 400 cm. The liner is normally made of cast iron, and can be cast integral or separate, in two parts joined together, end to end. In Figure 1, half of the liner is shown in longitudinal section. The liner can be mounted in a well-known manner in the engine, not shown, by placing the annular, downward facing surface 3 on the upper plate of the engine housing frame or cylinder block, after which the piston 4 with piston rings 5 is mounted in the cylinder, and the cylinder cover is placed is on top of the liner on its annular, upwardly facing surface 6 and is clamped to the top plate.

The piston rings 5 slide along the inner surface of the liner 7, and therefore it is important that the inner surface has a structure that ensures good lubrication between the rings and the inner surface, -so as to avoid scraping or etching between the sides of the rings and the inner surface of the liner. During the operation of the piston and liner in a new engine, the surface structure is particularly important.

As mentioned above, it is therefore desirable to make a cylinder liner with corrugations on its inner surface, where the crests of the corrugations are removed. It is possible to make a liner of the respective shape along the entire length of its inner surface. The corrugation can also be machined only in the upper part of the liner, so that the piston rings 5 engage a section from the first 40% of the piston's travel down. The reverberation can also be of different relative magnitudes, such as 20%, 25%, 30%, or 35%, or some intermediate value.

The machining of the inner surface 7 of the liner is finished before the air gap 8 is compressed by machining in the lower part of the liner. This is done on a very large drill constructed as a type of large lathe, shown only partially in Figure 2. Hereinafter the machine is referred to as a lathe. Using a crane, a liner with horizontal longitudinal edges is lifted and centered in relation to the axis of rotation of the lathe, after which one end of the liner is tightened onto the drive spindle of the lathe by means of four tensioners 9, while the other end of the liner is supported in the central position with a holder 10, which has several supporting rollers 11 that travel on the outer surface of the liner. The holder 10 can be moved on the support 12 of the lathe.

At the opposite end of the spindle, the lathe has a saddle, not shown, which supports a very heavy and rigid boring bar 13, which is moved by moving the saddle on the lathe carriage into or out of the cylinder liner coaxially with its longitudinal axis. At the end nearest the spindle, the bar for drilling has a tool holder 14 in the form of a cross slide capable of adjusting the tool 15 in the radial direction of the liner.

When the liner is installed, the spindle with the liner rotates, and the inner surface 7 rotates in a direction with an accuracy of, for example, 5 mm according to the diameter. Fine turning is then performed with a tool blade that has a curved cutting edge so that the desired shape of the bottom of the waves in the corrugated inner surface of the liner is obtained by fine turning and scoring. The distance S (Figure 5) between two consecutive crests of the wave is adjusted as desired by moving the drill rod forward longitudinally, the distance is the same speed as the feed speed. In a cylinder liner with an inner diameter of 98 cm, a feed rate of 8 mm per cylinder liner revolution may be suitable, while a feed rate of 4 mm was chosen for a cylinder liner with an inner diameter of 50 cm or less. The gap can be chosen to match half the height of the smallest piston ring.

The radial difference in levels h (Figure 5) between the crests and bottoms of the waves is determined by the curvature of the edge of the tool blade, so that a stronger curvature ensures a greater difference in levels. The difference in levels can be a maximum of 0.06 mm, but normally 0.01 to 0.02 mm is recommended.

After cutting the corrugations, the drill rod is pulled out of the liner, and the rolling tool is placed radially in relation to the inner surface 7, after which the inner surface is rolled so that the material in the crests of the waves is plastically deformed, i.e. is pressed radially outward, so that the finished inner surface takes the shape shown in Figure 5 with a spiral groove or wave through 17. The longitudinal section in the inner surface of the liner, shown in Figure 5, is destroyed due to clearance, so that the dimensions in the radial direction are extended Multiple times. In the longitudinal direction, the bottoms of the waves are separated by flat areas 18, forming together 25-75%, and typically 40-60% of the distance of the liner from the corrugated form.

In the simple construction shown in Figure 3, the rolling tool may include a roll 19, which is rotatably mounted in a forked head 20 at the end of a cross arm 21 fixed in a recess in the tool holder 22, which is supported with a drill rod 13. Holder of the tool or the tool itself may have a certain limited flexibility in the radial direction of the liner, so that with the elastic bending of the holder, changes of several tens of millimeters in the diameter of the liner are absorbed. The cross handle can be adjusted in its longitudinal direction, i.e. in the radial direction of the liner. Another example of the construction of the rolling tool can be seen in Figure 4, where the roller 23 is immersed in the head 24 on one side, and on its back side the roller touches the supporting roller 25.

The head is mounted on an arbitrarily expanding rigid part divided into two parts, 26a and 26b, which are mutually spring-loaded but maintain the set rolling pressure. Indicator 27 shows the magnitude of the current rolling pressure. Instead of a visual indicator, the tool can be equipped with an inductive system for measuring the rolling pressure and for generating an electrical signal that can be used for setting purposes or for dislocation reading. Via the intermediate part 28, the rigid part is mounted in the tool holder 14 of the drill rod, so that the rolling pressure can be adjusted by radially moving the tool holder. A tool of this type is commercially produced by the German company W. Hegenscheidt GmbH, Gelle, under the type designation EG 14.

A rolling pressure indicator can be incorporated into the cross slide of the drill rod, the cross slide acts with substantially the same radial pressure as the rolling tool. The latter can also have a display with, for example, a digital display of the displacement of the cross slider in the radial or axial direction. Such a display can be reset when the rolling tool is placed in contact with the inner surface of the liner with less force, after which the outward movement of the cross slide will represent the rolling pressure. The longitudinal axis of the roller can form a free angle α with the inner surface of the liner, where the top of the angle is turned in the direction of indentation shown by arrow A.

Now follows a description of examples carried out with a cylinder liner that had an inner diameter of 35 cm.

Example 1

The liner was made from a liner material common to large engines, cast iron, and after rough turning, the inner surface of the liner was finally turned to its full length with a spiral, wavy kerf shape with a gap of S = 4 mm between wave crests and a wave height of approx. h = 0.015 mm. Then, the drill rod cutting tool was replaced with the rolling tool shown in Figure 3. The rolling pressure was adjusted by first bringing the roller into contact with the inner surface of the liner with less force, after which the cross slide of the drill rod was adjusted to move toward out by F = 0.03 mm measured on the diameter, i.e. at a radial displacement of 0.015 mm. It should be mentioned that adjusting the cross slide does not entail the corresponding radial displacement of the rolling tool, as an essential part of the displacement for the compressive load of the cross slide, i.e. to create the rolling pressure, the tool holder and the tool are taken. This is a significant difference from the setting of a cutting tool normally used in a lathe. The liner was rotated at 90 min-1, giving a relative velocity between the rolling tool and the inner surface of the liner of V = 100 m/min, and the drill rod was moved in the liner at a feed rate of s = 0.5 mm/ they spin.

Visual inspection showed that a higher rolling pressure would be desirable and that the feed speed could be significantly higher.

Example 2

Regardless of the rolling parameters, the cylinder liner was made in the same way as in example 1. Rolling was performed with the parameters V = 100 m/min, F = 0.10 mm on the diameter and s = 4.0 mm/rev.

Visual inspection and roughness measurement showed that the feed rate was adequate, and that the areas between the bottoms of the waves had a well-defined width and were generally flat.

Example 3

Regardless of the rolling parameters, the cylinder liner was made in the same way as in example 1. The rolling was performed with the parameters V = 100 m/min, F = 0.15 mm on the diameter and s - 4.0 mm/revolution.

Visual inspection and roughness measurement showed that the feed rate was adequate, and that the areas between the bottoms of the waves were wider and formed approximately 30% of the inner surface of the liner.

Example 4

Regardless of the rolling parameters, the cylinder liner was made in the same way as in example 1. Rolling was performed with the parameters V = 100 m/min, F = 0.20 mm on the diameter and s = 4.0 mm/rev.

Visual inspection and roughness measurement showed that the feed rate was adequate, and that the areas between the bottoms of the corrugations were wider and formed approximately 40% of the inner surface of the liner.

Comparative tests were carried out in which the cylinder liner was made in the same way as in Example 1, but the rolling was replaced by partial grinding to remove the crests of the waves.

The surfaces of the liners produced in example 4 by partial grinding were photographed at a magnification of five times, see figures 6 and 7, and the surface roughness was measured with a Perthen roughness measuring device, see figures 8 and 9, where they were set to a very large magnified a in the radial direction. Records on the tapes, 10 mm in the direction of the y axis show a distance of 0.025 mm, while 10 mm in the direction of the x axis prove a distance of l mm.

Figure 6 shows the circular scraping marks or grinding grooves, and the roughness test in Figure 8 shows a large number of small points in an approximately flat area where the crests of the waves have been removed.

The rolled surface shown in Figure 7 has a significantly better appearance, and the roughness test in Figure 9 shows flat areas between the bottoms of the waves with far less sharp raised points, but the surface still has numerous small rounded level differences in the flat surfaces, which contribute to achieving good oil adhesion on the surface.

In the dimensional views above, under cut waviness and waviness, the model should understand that the mentioned values are average values. As the printouts on the roughness test strips show, the surface has large indentations in places that are not included in the dimensions, as these are typical graphite deposits in the surface or similar variations determined by the alloy. Indentations are also present mainly in flat areas which can also be called plateau areas.

Claims (11)

1. A method of making a cylinder liner (1) for a piston engine, such as a large two-stroke piston engine, in which the working surface for the piston rings on the inner surface (7) of the liner is made by first notching a corrugation, which has a level difference (h) between peaks and bottoms of waves of at least 0.005 mm, in the inner surface with at least one cutting tool, which has a curved cutting edge, and then removing the peaks of the waves at least in the working surface closest to the extreme central position of the piston tip, so that in the longitudinal part of the inner surface (7) the finished liner (1) has a partially corrugated surface, in which the bottoms of the waves (17) are separated by mostly flat areas (18), characterized in that the cylinder liner has an inner diameter in the range of 25 cm to 100 cm and a length in the range of 100 cm up to 400 cm, that the crests of the waves were removed without applying sanding, but by plastic compression for at least 0.004 mm of their height in said mostly flat areas (18), and that the bottom of the wave (17) after compr ession at a level at least 0.001 mm lower than that surface. 2. The method according to claim 1, characterized in that the corrugation is incised in the inner surface of the liner by said at least one cutting tool, which is protruded in the longitudinal direction of the liner by means of a drill rod with a feed speed (s) while the liner is rotated so that the corrugation is formed as at least one helical notch, and that the plastic compression is carried out by rolling the inner surface with the rolling tool, which is moved forward by the same boring bar as the cutting tool. 3. The method according to claims 1 or 2, characterized in that the plastic compression is performed with a rolling tool having one roller (19; 23), the radial position of which can be adjusted. adjust in relation to the inner surface of the liner, and can move forward in the longitudinal direction of the liner while the liner (1) rotates. 4. The method according to claim 3, characterized in that the rolling tool is associated with an indicator (27) of the current rolling pressure. 5. Method according to claims 3 or 4, characterized in that the rolling tool maintains the desired rolling pressure when moving the tool in the longitudinal direction of the liner, although the inner diameter of the liner (1) changes along the length of the liner. 6. A method according to any one of claims 2 to 5, characterized in that the rolling is carried out only in the upper part of the liner including the area over which the end piston ring slides when the piston (4) is removed from its upper end center position and part of the stroke of the piston travel down towards the lower end central position. 7. The method according to any one of claims 2 to 6, characterized in that the crests of the waves are deformed by rolling so that the area of the mostly flat surface (18) between the bottoms of the waves (17) represents 25% to 75%, preferably from 40% to 60% of the total surface of the liner (1) in the rolled area. 8. Method according to claim 7, indicated by the fact that the tops of the waves are deformed by rolling so that the surface of the mostly flat areas (18) between the consecutive bottoms of the waves (17) extends in the longitudinal direction of the liner, which, within a range of ±1 mm, corresponds to a quarter of the height of the piston ring of the smallest height. 9. The method according to any of the preceding claims, characterized in that the crests of the waves are deformed so that at least 0.006 mm and at most 0.018 mm, preferably at most 0.015 mm of the height of the wave is compressed into generally flat areas (18), and that the waves (17) ) at a level of at least 0.002 mm below these surfaces. 10. The method according to any of the preceding claims, characterized in that the incised corrugation is deformed so that the average radial difference in levels between the obtained substantially flat surfaces (18) and the bottom of the waves (17) represents between 7% and 66% of the average difference in levels (h) between wave crests and wave troughs in undulation before compression, preferably between 16% and 36% thereof. 11. A cylinder liner (1) for a piston engine, such as a large two-stroke piston engine, having a working surface for piston rings on the inner surface (7) of the liner, which working surface, at least in the region closest to the top of the piston in the end center position, has a partially corrugated shape, in which the bottoms of the waves (17) are separated from the generally flat surfaces (18), characterized in that the cylinder liner has an inner diameter in the range of 25 cm to 100 cm and a length in the range of 100 cm to 400 cm, that are generally flat areas (18) rolling surface without sharp bulges, that the bottoms of the waves (17) are at a level at least 0.001 mm lower than these surfaces and that the generally flat area (18) between consecutive bottoms of the waves (17), which extends in the longitudinal in the direction of the liner in the range of ±1 mm, corresponds to a quarter of the height of the smallest piston ring.