TW201816126A - Manufacturing method for a calender stack roller, method for providing a calender stack, calender stack roller and calender stack - Google Patents

Abstract

The invention refers to a manufacturing method for a calender stack roller, characterized in particular in that it has been quenched and tempered; to a method for providing a calender stack; to a calender stack roller and to a calender stack. The calender stack rollers from the state of the art are surface-layer-hardened, tempered at a low temperature, and they tend to form recesses in particular during the first months of usage. Subsequently, they need to be re-grinded and the surface needs to be refined again, if necessary. The invention provides an improvement or an alternative to the state of the art.

Description

Manufacturing method for calender stack roll, method for providing calender stack, calender stack roll and calender stack

The present invention relates to a manufacturing method for a calender stack roll, a method for providing a calender stack, a calender stack roll, and a calender stacking device. In particular, the invention relates to a manufacturing method for a calender stack roll intended to be used in a calender stack, the calender stack being adapted for use in making a plastic sheet from a thermoplastic, wherein the calender stack roll is subjected to A heat treatment in which the calendering stack roll is quenched and tempered; the present invention relates to a method for providing a calendering stack for manufacturing a plastic sheet from a thermoplastic plastic, the calendering stack using a calendering roll; a A calendering roll intended for use in a calendering stack, the calendering stack being adapted for making a plastic sheet from a thermoplastic; and the invention relates to a corresponding calendering stack.

A plastic film (foil) or plastic plate is understood as an object having a substantially two-dimensional extension and a thickness between 30 μm and 12 mm. In a case with a thickness of up to 2.0 mm, the object is called a "plastic film"; if the thickness exceeds 2.0 mm, the object is called a "plastic plate". In particular, a plastic film and a plastic plate are such objects corresponding to DIN ISO 11963 or ISO 15988. When producing films or plates made of thermoplastics, depending on the intended use, frequent occurrences of the desire or necessity to provide a structured or matte surface or one or both sides of a smooth and glossy surface Sex. There are different ways to achieve this. For example, calender stacks are used to produce plastic films and plastic plates, in which a melt produced in an extrusion process is output from a wide slot nozzle and then guided between rolls through a calendering slit, the calendering The slits are usually adjustable in width. During this process, the melt is cooled and formed to produce a thin film sheet with a uniform thickness and homogeneous appearance across its entire surface. Then, if desired, the plastic sheet can be guided around one or more additional calender stacking rollers and then guided to another target. That is, a calender stack generally includes at least two rollers arranged in a support, one of the at least two rollers is stationary and at least one of the at least two rollers is usually embodied as an adjustable roller. This adjustable roller can be replaced by means of an adjustment system so that different settings of the calender slit can be achieved between the stationary roller and the replaceable roller. In this way, plastic sheets of different thicknesses can be produced. For example, these calendered stacked films or calendered stacks can be produced from polystyrene, polypropylene, polymethyl methacrylate, polyester and also from other types of plastic or composite materials (so-called blends), And it has a wide range of applications in conveying and protecting the food and automotive industries, among others.

The invention is based on the task of providing an improvement or an alternative to the current state of the art. In a first aspect of the invention, this task is solved by a manufacturing method for a calendering roll intended to be used in a calendering stack, the calendering stack being adapted for producing a thermoplastic from a thermoplastic Plastic sheet, wherein the calender stack roll is subjected to a heat treatment and is thus quenched and tempered. In the following, some terms will be explained: First, it is clearly stated that in the framework of this patent application, indefinite articles and numerals such as "one", "two", etc. are generally understood to indicate a minimum value, that is, "at least one ... "," At least two ... ", etc., unless clearly clear from the context or obvious to those skilled in the art, or from a technical point of view must mean" exactly one ... "," exactly two " …"Wait. A "plastic sheet" is a sheet made of a thermoplastic plastic. The "plastic sheet" has a substantially constant thickness and a substantially constant width. A "calender stack" is a plastic sheet formed from a thermoplastic. The melt produced during an extrusion process is discharged from a wide groove nozzle and then guided through a calendering slit between the rolls, which calendering slit is usually adjustable in width. During this process, the melt is cooled and formed to produce a thin film sheet with a uniform thickness and homogeneous appearance across its entire surface. Then, if desired, the plastic sheet may be guided around one or more additional calender stacking rollers and then directed towards another target. That is, a calender stack generally includes at least two calender stack rolls arranged in a stand, one of the at least two rolls is stationary and generally at least one of the at least two rolls is tied in its position. The alternative makes it possible to produce plastic sheets of different thicknesses in the same calender stack. A "calendering slit" is a gap between a first general stationary calendering roll and a second calendering roll. The second calendering roll is generally replaceable in its position and is also referred to as "may Adjustment roller ". If one of the calender rolls is not stationary but replaceable, the width of the calender slit in the calender stack can be adjusted. A "calender stack roll" is a roll of a calender stack. The "calender stack roll" can have a highly polished or rough surface or an engraving. In addition, the "calender stack roll" may be provided with an internal cooling system. The calender stack roll may have multiple walls or a peripheral hole. A calender stack roll can be cylindrical or shaft-shaped. A "heat treatment method" is a method or a combination of several methods for processing a metal workpiece, which heats and cools the metal workpiece in a specific order in order to change the material properties. For example, surrounding matter can alter carbon or nitrogen content, crystal lattice, or crystal structure. Examples of heat treatment methods are hardening and quenching and tempering. "Quenching and tempering" is a combination heat treatment of one metal, which is composed of quenching and subsequent tempering. The purpose of this treatment is to provide materials with high roughness and high tensile strength or hardness, respectively. If hardening occurs across the entire metastable martensitic structure, the highest tensile yield strength ratio and maximum roughness are achieved. If the material is to be quenched and tempered, a short-term tempering after hardening is preferred in order to avoid cracks caused by internal tension. The prerequisites for quenching and tempering are the hardenability of a material, that is, the ability to form a stable martensitic structure under specific conditions. For classical quenching and tempering, a carbon content of at least 0.2% to 0.3% of steel is necessary. Due to their excellent suitability, certain engineering steels are also called tempered steels (which usually contain 0.35% to 0.6% carbon). The process of rapid cooling from the austenite phase is called "hardening". Importantly, the material has been almost completely austenitized before, that is, the ferrite must have been completely dissolved and the carbides have been almost completely dissolved. After austenitizing, the material is quenched. During this process, a martensitic structure is usually produced; in some materials, an intermediate stage or a mixture of martensite and intermediate stages is also possible. These structures have a highest possible hardness. "Quenching" is the rapid cooling of a heated workpiece by the use of a quenching member, such as preferably water, oil, or air. The choice of quenched components affects the rate of quenching to be achieved and the resulting structure. The essential differences between hardening on the one hand and quenching and tempering on the other can be found in the tempering process steps. Tempering reheats the hardened steel. Tempering immediately after quenching at about 150 ° C is advantageous. During this process, the brittle cubic martensite produced during hardening is converted into a cubic martensite structure with fine carbide deposits. This structure has a smaller volume, which reduces tension in the crystal lattice and therefore eliminates the "glass hardness" of the material. This process continues at higher temperatures (200 ° C to 350 ° C) during the additional tempering phase. In addition, any remaining austenite is further decomposed and converted into martensite by a diffusion process. Therefore, a further increased hardness can be observed. The various stages of tempering can be in a time-delay step. To avoid or minimize the risk of stress cracking, tempering should occur as soon as possible after quenching. The goal of tempering is to alleviate the material stress caused by hardening and finally set the required technical properties, such as tensile strength, significant yield point, expansion and lateral shrinkage. Several processes occur during tempering. During tempering, no crystal changes occurred. As the martensite decomposition begins, the hardness decreases, with the finest ε carbides (over about 100 ° C) being formed and the fine carbides "Fe3C" (copper iron, over about 250 ° C) being deposited. The degree of carbide deposition and the size of these particles increase with the tempering temperature; at the same time, the hardness decreases to the same extent. After the tempering is completed, the structure is composed of a ferrite matrix with intercalated carbides. At about 200 ° C, cubic martensite is transformed into cubic martensite. The purpose of "stress relief" or "stress relief annealing" is to reduce the tension in the material. There were no structural changes during this process. Depending on the temperature and holding time, there will be small formation effects in the structure, and the strength can be slightly reduced. "Austenite" is a metallurgical term for the face-centered cubic modification (phase) of pure iron and its mixed crystals. If the material contains carbon, austenite is present in the form of an interstitial solid solution. "Martensite" is a metastable structure in a metal, which is generated athermally from the original structure by a cooperative shear movement without diffusion. During this process, the material must be cooled (specifically, quenched) from a high temperature (austenite) below one of the equilibrium temperatures to a low temperature (ferrite). Cooling below the equilibrium temperature must be sufficiently strong to produce an athermal phase change, but it must also occur fast enough to prevent diffusion. "Ferrite" is a metallurgical term for the face-centered cubic modification (phase) of pure iron and its mixed crystals. "Surface layer hardening" is also called surface hardening. By the process of surface hardening, it is understood that one of the surfaces is hardened without introducing other elements such as carbon or nitrogen. This is achieved by limited heating of one of the workpieces, where only the surface is brought to the hardening temperature and the core is not affected during quenching. With this heat treatment method, the surface of the workpiece is heated to austenitizing temperature by a gas flame or by current induction (induction hardening). After quenching, the component is relieved of stress. The surface hardness depends on the carbon content, and the effective hardening depth depends on the degree of alloying of the material. The targets of the treatment are a hard and wear-resistant surface and a hard core. To date, the state of the art has provided calender stack rolls to be subjected to a heat treatment which simultaneously ensures a hard and wear-resistant surface and a hard core. The roughness of the surface of the calender roll has been ignored so far. The most suitable method for this purpose is surface hardening. The induction hardened surface layer of the calender stack roll has a high hardness and a correspondingly low roughness. The material difference between the hard surface and the hard core is so high that considerable internal stresses occur in the material and the calender stack rolls become less stressful. It is well known that under the condition of already having a tempering temperature in the range of 150 ° C to 200 ° C and a holding time of 1 h to 2 h, martensite subjected to extreme stress is converted into harder tempered martensite. This results in a slight reduction in hardness. Abrasion resistance does not decrease. A higher tempering temperature results in reduced hardness, which is undesirable. Therefore, the calender stack rolls relieve stress at lower temperatures after hardening, which may not necessarily relieve all internal stress groups. However, when using calendering rolls in a calendering stack, the calendering rolls contact a plasticized plastic material that is at a temperature between 220 ° C (generally even 290 ° C) and 320 ° C. . In the case of longer processing times, this surface temperature completely heats the calender stack roll. In the hardened surface area, a temperature exceeding the tempering temperature in the heat treatment process for calendering the stacked rolls occurs. This results in an unplanned continuous tempering process at a higher temperature and results in the deposition of fine carbides (colloidal iron) at temperatures in excess of 250 ° C. This in turn results in a change in one of the density of the material structure. This change in density results in additional internal stresses in the material structure. After a longer period of use, concave depressions or convex protrusions with a depth generally up to about 30 µm appear on the surface of the roller, respectively. In the state of the art, the recesses are trimmed by disassembling the calender rolls and by grinding or by plating with new chrome before grinding. This process must be repeated several times until the calender stack rolls are completely tempered at the "use temperature" and no density change occurs within the structure of the material. However, the recesses so far have not been attributed to a change in the density of the material but to insufficient solidity on the surface of the calender stack roll. In order to overcome this problem, it is proposed here not to reduce the stress of the calendering stack rolls, but to temper the calendering stack rolls at a higher temperature. It has been shown that with higher tempering temperatures, no change in material structure occurs and no recesses appear on the surface of the calender stack roll during use. Therefore, subsequent processing of the recesses in the surface of the calender stack roll is no longer necessary. It has been further shown that the tempered calender stack roll does have a surface hardness that is lower than the surface layer processed calender roll according to the current state of the art, but the surface hardness achieved is still sufficiently high for use in applications. Advantageously, it can be achieved in this way that the calender stack roll no longer has any recesses after longer use and therefore no longer needs to be reground or equipped with a new chrome plate and then reground. This increases the availability of the calender stack and can avoid high preventive maintenance and repair work. Preferably, the calender stack roll is hardened before tempering, in particular completely austenitized and then quenched. Advantageously, in this way, it is possible to achieve an almost completely homogeneous material structure of one of the calender stack rolls. Optionally, the calender stack rolls are surface hardened before tempering, in particular partially austenitizing and then quenched. A term will be explained below: "Partial austenitization" is intended to mean not austenitizing the entire material structure of the calender stack roll but only a part of the volume (preferably positioned on one of the "surface layers" Structure ") austenitizing. During this process, the "core structure" (not the surface layer structure) of the calender stack is not fully austenitized. "Partial austenitization" does not refer to the degree of austenitization of a particular volume element. Instead, a distinction is made between completely austenitized peripheral regions and incompletely austenitized core regions with a "core structure". Advantageously, the advantages of continued use of surface hardening, in particular induction hardening, can be achieved in this way. These advantages are in particular: the possibility of partially heat-treating large workpiece sizes and extremely difficult shapes; homogeneous heating resulting in a homogenous effective hardening depth in each location; the heating time is short, so there is low scale buildup, so only Minimal need for reprocessing due to low scale accumulation; no toxic or explosive substances for cleaning operations; low oxidation of the workpiece and minimal distortion of the workpiece. Preferably, the tempering is performed at a temperature window between 220 ° C and 320 ° C and / or over 300 ° C, specifically over 250 ° C, and specifically over one of the specified nominal use temperatures of the thermoplastic. . A term is explained below: "Nominal use temperature" is the temperature to which a portion of the material structure that has been austenitized during the heat treatment is subjected during the long life of the calender roll in a calender stack. That is, the nominal use temperature is the temperature that has been used to generate the roll. This temperature information will be found in the roll's order document or in the corresponding use instruction, or the temperature information can be determined based on the data of the plastic to be processed, where the melting temperature of this plastic is used as the nominal use temperature. Advantageously, in this way it can be ensured that the calender stack roll no longer exhibits any tempering effect (in particular no recesses are formed) and that the calender stack roll maintains a high surface hardness due to the relatively low tempering temperature. It is clearly pointed out that without departing from the aspects of the present invention, the temperature values mentioned above should not be understood as strictly limited but may be higher or lower for a project scale. In other words, these values will be used as reference values for the temperature ranges presented here. Optionally, a tempering process occurs shortly after hardening, specifically within seven days after hardening, and / or before the calender stack is first used to make a plastic sheet. In the following, a term will be explained: "Soon after hardening" is intended to mean tempering the calender stack rolls immediately after hardening. In particular, "not shortly after hardening" is intended to mean that the calender stack roll is tempered only after first contact with one of the plasticized plastics, and specifically not after one first normal use in a calender stack or period. As an alternative or addition to "soon after hardening", hardening can occur at the same site of generation. Advantageously, the risk of forming stress cracks can be minimized in this way. In a second aspect of the invention, the task is solved by a method for providing a calender stack roll for manufacturing a plastic sheet from a thermoplastic, which calender stack uses the first aspect according to the invention One kind of calendering stack roll is produced. It should be understood that, as explained above, the advantages of a manufacturing method for a calendering roll intended to be used in a calendering stack (where the calendering stack is adapted for making a plastic sheet from a thermoplastic, wherein according to the invention In a first aspect, the calendering stack roll is subjected to a heat treatment) (directly extended to provide a calendering stack for manufacturing a plastic sheet from a thermoplastic, wherein the calendering stack uses a calendering stacker, which has been in accordance with the present invention The first aspect is produced. In a third aspect of the present invention, the task is solved by a calendering roll intended for use in a calendering stack, the calendering stack being adapted for use in manufacturing a thermoplastic Plastic sheet, the calender stack roll has been produced according to one of the manufacturing methods of the first aspect of the present invention. It should be understood that, as explained above, it is used for a manufacturing method of a calender stack roll intended to be used in a calender stack. Advantages (where the calender stack is adapted for making a plastic sheet from a thermoplastic, and according to a first aspect of the invention, the calender stack roll Subject to a heat treatment) directly extended to be used in a calender stack in a calender stack, the calender stack being adapted for use in making a plastic sheet from a thermoplastic, the calender stack has been in accordance with a first aspect of the invention The production method of one kind is produced. It is clearly pointed out that the object of the third aspect can be advantageously combined with the object of the above aspect of the present invention (whether individually or additionally in any combination). In one of the present invention In a fourth aspect, the task is solved by a calender stack for manufacturing a plastic sheet from a thermoplastic, the calender stack being provided with a calender stack roll according to one of the third aspects of the present invention. It should be understood that as described above Describe the advantages of using a calender stack roll in a calender stack (the calender stack is adapted for making a plastic sheet from a thermoplastic, wherein according to a first aspect of the invention, the calender stack roll is subjected to a heat treatment Method) is directly extended to a calender stack for manufacturing a plastic sheet from a thermoplastic, the calender stack is provided with a third aspect of the present invention. Calender roll stack. It is clearly stated that the subject matter of the fourth aspect can be advantageously combined with the subject matter of the above aspect of the present invention (whether individually or additionally in any combination).

The calender stack 1 in FIG. 1 is substantially composed of a wide groove nozzle 2 and a calender stack roll (ie, a first calender stack roll 3, a second calender stack roll 4 and a third calender stack roll 5). During operation, the calender stack 1 is used to make a plastic sheet 6. For this purpose, once the plasticized thermoplastic 7 leaves the wide-groove nozzle 2 and encounters a calendering slit 8, the calendering slit is rotated first clockwise stacking roll 3 and second clockwise stacking roll rotated counterclockwise. There is a rolling slit width 9 between 4. Due to the rotation of the first calender stack roll 3 and the second calender stack roll 4 next to the calender slit, the thermoplastic plastic forms an alignment film sheet 6 in the calender slit 8. The film sheet 6 follows the path of the second calender stack roll 4 and then encounters a third calender stack roll 5 having an extra calender slot 10.1 with a calender slit width 10.2 and a clockwise rotation. Leaving from the second calendering slit 10.1, the plastic sheet 6 follows the path of the third calendering stack roll 5 and then unwinds from the third calendering stack roll 5. After this, the plastic sheet 6 is output from the calendering stack 1 and is subjected to further processing that is not explained in detail here. The second calender stack roll 4 is stationary. The first calender stack roll 3 can be moved toward the second calender stack roll 4 by an adjustment system (not shown), so as to adjust the calendering slit 8 of the calender slit 8 between the first calender stack roll 3 and the second calender stack roll 4 Ew width 9. The third calender stack roll 5 can also be moved toward the second calender stack roll 4 by an adjustment system, so as to adjust the calender slit width 10.2 of the calender slit 10.1 between the third calender stack roll 5 and the second calender stack roll 4. . By adjusting the width of the calendering slit, the calendering roll substantially determines the final thickness of the film sheet. The temperature-time diagram of the heat treatment method in FIG. 2 shows one or more curves 20, 21 of the temperature 12 of the heat treatment method in time 13. In time 13, the heat treatment method enters the process stages of austenitizing 14, quenching 15, and tempering 16. The timely transition between austenitizing 14 and quenching 15 during the process phase changes almost directly at the process boundary 17. Fast and almost immediate quenching is important so that the carbon remains dissolved in the grid structure of the material and does not diffuse out of the structure. The time process phase between quenching 15 and tempering 16 may occur with a time delay. That is, the boundary 18 between the process stage of quenching 15 and the process stage of tempering 16 is not necessarily continuous. Instead, it is common to pass an extra time between quenching 15 and tempering 16 (not shown in the schematic diagram in FIG. 2). The temperature-time curve 11 depends on the material, the selected heat treatment method and the size of the material. These dependencies are ignored in this diagram. However, the process stage of austenitizing 14 and the process stage of quenching 15 are independent of the process stage of tempering 16. A substantial difference in the temperature-time curve 11 was found during tempering 16. Observe the curves of the heat treatment method of hardening 20 and the heat treatment method of quenching and tempering 21. The temperature 12 reached during quenching and tempering 21 is much higher than the temperature during hardening 20. Here again, there are dependencies on materials, methods, and dimensions of components. However, in all possible combinations, the temperature 12 during quenching and tempering 21 is much higher than during hardening 20. Different heat treatment methods lead to different material behaviors and, in particular, different stress-strain curves 31. The stress-strain curve 31 in FIG. 3 is composed of a stress 32, a strain 33, and curves 34, 35, 36 of one material (in this case, C45) treated by different heat treatment methods. Once the hardened material is extremely strong and reaches a curve 34 under load before breaking due to overload, the internal stress 32 is extremely high, but the strain 33 is very small. The hardened material is particularly resistant to high loads, but is not suitable for absorbing plastic deformation. The hardened material is quite brittle. A hardened and tempered material is not as strong as hardened steel, but harder. Under load, the quenched and tempered material reaches a curve 35 before breaking due to overload, that is, the internal stress 32 is high and the strain 33 is also at a high level. Compared with hardened materials, quenched and tempered materials are less rigid, but can absorb more plastic deformation before breaking. In contrast, the curve 36 of a regular annealed material exhibits the minimum amount of internal stress 32 and the highest degree of plastic deformation 33 before breaking due to overload.

1‧‧‧calender stack

2‧‧‧ wide slot nozzle

3‧‧‧The first calender stacking roller

4‧‧‧Second Calender Stacking Roller

5‧‧‧The third calender stacking roller

6‧‧‧Straighten film sheet / film sheet / plastic sheet

7‧‧‧ plasticized thermoplastic

8‧‧‧ calender slit

9‧‧‧ Calender slit width

10.1‧‧‧Extra calender slit / second calender slit / calender slit

10.2‧‧‧ Calender slit width

11‧‧‧Temperature-Time Curve

12‧‧‧ temperature

13‧‧‧time

14‧‧‧Austenitizing

15‧‧‧hardened

16‧‧‧Tempering

17‧‧‧ process boundary

18‧‧‧ boundary / process boundary

20‧‧‧ curve

21‧‧‧hardened

31‧‧‧stress-strain curve

32‧‧‧stress / internal stress

33‧‧‧strain / plastic deformation

34‧‧‧curve / hardened material

35‧‧‧curve / hardened and tempered material

36‧‧‧curve / normalized material

In the following, the invention will be explained in detail by means of an example with reference to the drawings in which FIG. 1 schematically shows a calender stack, and FIG. 2 schematically shows "hardening" and "quenching and tempering" The temperature-time diagram of the heat treatment method, and FIG. 3 schematically shows the stress-strain diagram of a hardened, a quenched and tempered, and a normalized nealed material.

Claims (8)

A manufacturing method for a calendering roll intended to be used in a calendering stack, the calendering stack being adapted for manufacturing a plastic sheet from a thermoplastic, the calendering roll being subjected to a heat treatment method, characterized in that Calendering and stacking rolls are quenched and tempered. The manufacturing method as claimed in claim 1, wherein the calendering stack roll is hardened before the tempering procedure, wherein in particular the calendering stack roll is fully austenitized and then quenched. The manufacturing method as claimed in any one of claims 1 or 2, wherein the calender stack roll is subjected to surface hardening before the tempering procedure, wherein the calender stack roll is partially austenitized and then quenched. The manufacturing method according to claim 1 or 2, wherein the temperature window is between 220 ° C and 320 ° C and / or the temperature exceeds 300 ° C, specifically a temperature exceeding 250 ° C, and specifically exceeds one of the thermoplastic plastics The tempering procedure is performed at a temperature that is one of the operating temperatures. The manufacturing method of claim 1 or 2, wherein the tempering process is performed shortly after hardening, specifically within seven days after hardening, and / or before the calender stack is first used to manufacture a plastic sheet. A method for providing a calender stack for manufacturing a plastic sheet from a thermoplastic, wherein the calender stack uses a calender stack roll, characterized in that the calender stack roll is according to any one of claims 1 to 5 Manufacturing method. A calender stack roll intended for use in a calender stack, wherein the calender stack is adapted to make a plastic sheet from a thermoplastic, characterized in that the calender stack roll is manufactured according to any one of claims 1 to 5 Method. A calender stack for manufacturing a plastic sheet from a thermoplastic, wherein the calender stack has a calender stack roll as claimed in item 7.