MXPA00010775A - Plasticizing screw - Google Patents

Abstract

The present invention relates to a screw (27) for use in, for example, an injection molding machine or an extruder. The screw (27) includes a screw shaft (39) having a thread (41) spirally positioned about the screw shaft (39) so as to form a plurality of flights (43, 45, 47). The screw (27) has three zones (29, 31, 33), a feeding zone (29), a compression zone (31) and a metering zone (33), and the depth and pitch of the flights (43, 45, 47) of the screw (27) are designed based upon the material to be used in the screw (27) so that the difference in the ratio of the actual flow to the theoretical drag flow of material in the feeding zone (29) and the ratio of the actual flow to the theoretical drag flow of material in the metering zone (33) is less than 0.2, preferably less than 0.1, and more preferably less than 0.05. This design results in a screw (27) which has a balanced mass flow, and thus a constant pressure gain along the screw without pressure peaks.

Description

PLASTICIZING SCREW BACKGROUND 1. FIELD OF THE INVENTION This invention relates to the field of screws that is used, for example, to melt or soften polymer, such as in a polymer injection molding machine or a machine for extruding polymer. 2. DESCRIPTION OF THE RELATED TECHNIQUE The use of screws for injection molding or polymer extrusion is well known. Returning to Figure 1, a conventional or standard screw 11 for use in injection molding is shown which includes three zones: a feeding zone 13, a compression or transition zone 15 and a dosing zone 17. The screw 11 is housed in a hollow cylindrical barrel 19 having a constant inside diameter and preferably a uniform interior surface. The polymer resin, which may be in any form such as grit, granules, flakes or powder, is fed through an opening 21 in the barrel 19 into the feed zone 13 where the screw 11 Ref: 124242 rotates to pack and then push the granules into compression zone 15. The granules are melted in the compression zone and then pushed to the dosing zone 17 where the molten polypeptide is homogenized. Subsequently, the homogenized melt is molded by injection or further processed. The screw 11 has a screw body 23 having a thread 25 spirally placed around the body 23 to form the legs 25. The legs 25 are characterized by their depth, which is the height of the section 25 above the body 23 and by its pitch, which is the length P of the distance between two adjacent sections 25 plus the width of a stretch. The outer diameter OD of a screw 11 includes the depth of a section 25 above and below the body 23, while the diameter of the foot RD of the screw 11 is the diameter only of the body 23, without including the depth of the sections Conventionally, the sections 25 in a screw 11 have the same pitch in each feeding zone 13, compression zone 15 and dosing zone 17, but have a depth that changes from one zone to another. Specifically, the sections 25 have a constant depth x in the feeding zone 13, a depth and constant in the dosing zone 17 where y < x, and a gradual decrease in the depth of x a and in the compression zone 15.

Screws are often characterized by their compression ratio, which is a ratio used to quantify the amount that the screw compresses or tightens the resin. The concept behind the compression ratio is to divide the volume of a section in the feed section between the volume of a section in the dosing section, but the current standard that is used is a simplified method based on the following equation: depth of stretch in the area Compression ratio = feed depth of section in the dosing zone - This compression ratio is referred to as the depth compression ratio. Screws with high compression, which are commonly used for crystalline or semicrystalline materials, such as polymers, have compression ratios greater than about 2.5. Standard compression screws, which are commonly used for amorphous materials, have compression ratios from about 1.8 to about 2.5, most commonly 2.2. Various problems with high compression screws include: overheating caused by compression so that it is too high or not controlled, "counted", which occurs when the molten polymer rotates with the screw and is not pushed forward; and deposits in the screw which accumulate in the compression and dosing zones. These problems limit the maximum rotation speed of the screw and consequently the amount of molten material produced. In an attempt to solve these problems, some users switch to standard screws, but the depth of the section in the dosing zone of a standard screw is too high to provide good homogeneity fused under certain conditions, especially with crystalline materials. Many attempts have been made to improve the performance of the screws. U.S. Patent No. 4,129,386 discloses an extrusion device which includes a screw having a helix angle or pitch D in the feed zone that is constantly increased through the transition zone at a helix angle F in the dosing zone. The feed zone has a height G of constant section, the metering zone has a constant section I, and the transition zone B has a section height that decreases steadily from the height G of the section of the feed zone to the height I of the dosing zone section. This screw design suffers from overfeeding problems of the material to be extruded, and requires a slotted barrel in order to avoid the accumulation of excessive pressure gradients along the screw. What is needed, therefore, is a screw which produces a homogeneous melting without the problem associated with screws having a high compression ratio.

BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a screw for use, for example, in an injection molding machine or an extruder. The screw includes a thread placed spirally around the body of the screw so that it forms a plurality of sections which are divided into three zones: a feeding zone, a compression zone and a dosing zone. The depth, width and pitch of the sections of the screw are designed based on the material to be used in the screw so that the difference in the actual flow ratio * with respect to the theoretical material flow of material in the area of feed and the actual flow ratio relative to the theoretical carryover flow of material in the dosing zone is less than 0.2, preferably less than 0.1, and more preferably less than 0.05. In a preferred embodiment, the ratio of the actual flux to the theoretical flux of material in the feed zone and / or the ratio of the actual flux to the theoretical flux of material in the dosing zone is from about 0.8 to 1.0. This design results in a screw which has a balanced mass flow and therefore a constant pressure gain along the screw without pressure peaks. An example of a screw that has the desired difference in the ratio of the actual flow to the theoretical flow of material in the feed zone and the actual flow to the theoretical flow rate of material in the dosing zone is a screw wherein the passage of at least a portion of the sections in the dosing zone is greater than the passage of at least a portion of the sections in the feeding zone; the passage of at least a portion of the sections in the feeding zone is less than the external diameter of the screw; the passage of at least a portion of the sections in the dosing zone is greater than the external diameter of the screws; the passage of at least a portion of the sections increases through the compression zone; and the depth of at least a portion of the sections decreases through the compression zone moving from closer to the feed zone closer to the dosing zone.

The screw of the invention allows a greater speed of rotation of the screw, has a greater capacity of treatment and decreases the cycle time of injection molding compared with conventional screws.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side elevational view of a standard screw; and Figure 2 is a side elevation view of a screw made in accordance with this invention.

DETAILED DESCRIPTION The present invention relates to a screw for use, for example, in an injection molding machine or an extruder. The screw includes a screw body having a thread spirally positioned around the body of the screw so as to form a plurality of sections. The screw has three zones: a feeding zone, a compression zone and a dosing zone, and when used, it is mounted in a hollow cylindrical barrel having a preferably uniform inner cylindrical wall which allows the screw to rotate inside the barrel hole.

As used herein, the term "feed zone" refers to that area of the screw where the material has not been compressed. In the case of polymeric granules, for example, the granules are present in their non-molten volume form. The term "dosing zone" refers to that area of the screw where the material has been fully compressed. In the case of resin shots, for example, the shots are present in a completely molten form. The term "compression zone" refers to that area of the screw where the material is compressed. In the case of polymer granules, for example, the shots are present in a mixed state between their shape in volume and their molten form. A section is characterized by its depth, which is defined as the height of the section above the body of the screw, by its width, and by its passage, which is defined as the length of the section (the distance between two adjacent turns of the section in the body of the screw) plus the width of a section. If the section has a pitch of 25 mm, it means that when the screw has rotated once, the polymer in the section has moved 12.5 mm axially in the screw. The present invention is based on the discovery that if the design of the sections is based on the volume of material that is present in the sections, a screw is obtained that has a higher screw speed, a greater treatment capacity and a decrease In the injection molding cycle time compared to conventional screws. Accordingly, in the present invention the depth, width and pitch of the sections of the screw are designed based on the material to be used in the screw so that the absolute difference in the ratio of the actual flow to the flow of drag Theoretical material in the feed zone and the ratio of the actual flow to the theoretical feed flow of material in the dosing zone is less than 0.2, preferably less than 0.1, and more preferably less than 0.05. This design results in a screw which has a balanced mass flow, and therefore a constant pressure gain along the screw without pressure peaks. In a preferred embodiment, the ratio of the actual flux to the theoretical flux of material in the feed zone and the ratio of the actual flux to the theoretical flux of material in the dosing zone is from about 0.8 to 1.0. The above relationships can be calculated on a mass basis by time or volume by time.

The actual flow of material and the theoretical carryover flow of material into the feed zone and the metering zone is determined as follows. The actual flow of material in the dosing zone is determined by weighing the amount of screw material produced during a given period of time. This mass flow rate can be converted to a volumetric flow rate by dividing the mass flow rate by the mass density of the material used in the screw. By "melt density" it means the density of the material, such as the polymer, used in the screw when the material has melted. The mass flow rate of the material in the screw is assumed to be constant, and the actual volumetric flow of material in the feed zone is determined by considering the mass flow rate of the material from the dosing zone and dividing this flow rate of mass between the apparent density of the material used in the screw. By "bulk density" is meant the mass of the material, such as polymer particles or granules used in the screw divided by the total volume of the solid particles or granules and the gaps or open spaces between them. By "drag flow" is meant the theoretical volumetric flow of material which results from the relative movement between the screw and the inner surface of the screw barrel, that is, the forward flow of material due to helical screw rotation on the which forces the material forward and through the barrel. The drag flow is proportional to the product of the average relative velocity of the material and the cross-sectional area of the cylindrical barrel channel. In other words, the drag flow is the volumetric pumping capacity of the material, and is usually calculated on a volume basis per time. The flow of drag is based on numerous factors related to the • screw that include the pitch, depth, width and angle of the sections and the speed of the screw. The flow of drag, which is directed towards the outlet end of the screw, can be increased by increasing the speed of the screw and / or by increasing the depth of the screw sections. The theoretical carry-over flow is calculated using conventional recognized formulas such as shown in Gerhard Schenkel, "Kunststoff-Extrudertechnik", published by Cari Hanser Verlag, Munich (1993), p. 123-125. The theoretical drag flow calculated for the feed zone must be adjusted by a correction factor to the geometry of the sections in that zone and the material used in the screw. This correction factor is necessary due to the nature in volume of the material in the feeding zone and the influence of the flanks in the sections, and it is usually in the range of 0.7 to 0.95, more typically in the range of 0.8 to 0.95. The correction factor can be obtained using known methods such as those shown on page 123 of Schenkel where it is presented as a graph of the ratio of the section height to the section length with respect to the correction factor. The correction factor is determined by taking the ratio of the section height to the section length and reading an appropriate correction factor from the diagram. Although theoretically the theoretical drag flow calculation in the dosing zone also needs to be adjusted by a correction factor, in fact the correction factor is very close to 1.0, because in the dosing zone the material melts, and therefore this factor of correction approaches 1.0. A screw having the relationships described above has a relatively constant pressure gain per pitch along the screw. If the pressure peaks occur in a screw, tension will be applied to the material in the screw which will result in deposits in the screw and a decrease in the mechanical properties of the material. There are no limitations regarding the type of material that can be used in screw, although screws have been found that are especially useful in injection molding and polymer extrusion. An example of a screw having the desired difference in the ratio of the actual flow to the theoretical flow of material in the feed zone and the actual flow to the theoretical flow rate of material in the dosing zone is a. screw in which: a step of at least a portion of the sections in the dosing zone is greater than the passage of at least a portion of the sections in the feeding zone; the passage of at least a portion of the sections in the feeding zone is less than the external diameter of the screw; the passage of at least a portion of the sections in the dosing zone is greater than the external diameter of the screw; the passage of at least a portion of the sections increases through the compression zone; and the depth of at least a portion of the sections decreases through the compression zone that moves closer to the feed zone closer to the dosing zone. In a preferred embodiment, the geometry of the sections is such that the passage of the sections in the dosing zone is greater than the passage of the sections in the feeding zone, the passage of the sections in the feeding zone is less than the external diameter of the screw, the passage of the sections in the dosing area is greater than the external diameter of the screw, the passage of the sections is increased through the compression zone and the depth of the sections decreases through the area of compression moving from closer to the feed area closer to the dosing zone. As used herein, the term "outer diameter of the screw" means the diameter measured to include the body of the screw and the depth of the section above and below the body of the screw. The compression ratio of a screw quantifies the relative amount that a screw compresses a resin, and is based on the concept of dividing the volume of a section in the supply zone between the volume of a section in the dosing zone. An approximation that is normally used as the compression ratio and the depth ratio of the sections in the feeding area with respect to the depth of the sections in the dosing zone. Therefore, the usual method for changing the compression ratio of a screw has been to change the depth of the sections in the feeding and dosing zones. Since the depth of the sections in the conventional screws is constant in the feeding zone and constant in the dosing zone, the compression ratio of the screw will increase as the depth of the sections in the feeding area increases, or when the depth of the sections in the dosing area, or when doing both. However, if the compression ratio of the screw is too high, it leads to the problems discussed above, specifically bridging and the accumulation of undesirable heat accumulations and deposits in the screw. The present invention is based on the discovery that one can obtain the benefits of a high compression screw having a relatively high depth of section in a feeding zone and a relatively small depth of sections in the dosing zone without the disadvantages associated with a high compression screw, by providing a screw that has an absolute difference in the ratio of the actual flow to the theoretical drag flow of the material in the feed zone and the ratio of the actual flow to the theoretical drag flow of material in the Dosing zone is less than 0.2, preferably less than 0.1, and more preferably less than 0.05. In effect, by changing the pitch and depth of the screw of the invention, as described above, the compression ratio of the screw decreases substantially, and therefore eliminates the disadvantages associated with a high compression ratio screw. At the same time, the screw of the invention provides all the benefits associated with relatively high feed zone section depths and relatively low dosing zone section depths associated with a screw with a high compression ratio. The volume of compression ratio, calculated by considering the ratio of the volume of the feeding zone to the volume of the compression zone, it is not simple to measure when the pitch and the depth of the screw sections change. One reason is that the change in the pitch causes a variation in the angle of the sections along the body of the screw. It has been found that the volume of compression ratio for a screw having changing step steps and changing step depths can be approximated by taking the ratio of the melt density to the volume density for many polymeric materials, which is approximately equal to 1.3, and this value of 1.3 is a minimum for the compression ratio of the screw. Below a ratio of 1.3, the polymer granules are not compressed enough to push trapped air out of the polymer during the injection molding process.

With the present invention, improved results have been obtained with a screw having a very low compression ratio, ie, equivalent to the lower limit of 1.3 or higher, but lower than the compression ratio of a screw with high compression. The discovery that a screw can be made and can be used successfully designed under a small difference in the ratio of the actual flow to the theoretical carryover flow of material in the feed zone and the actual flow to flow ratio Theoretical material in the dosing zone, and with different steps in the feeding and dosing areas, and when changing the step in the compression zone, is unexpected in view of the conventional teaching that the screw designed based on the volume of material and the sections would have the same step in each of the areas of feeding, compression and dosing. The features of the screw of the present invention allows the screw to have a higher screw rotation speed, a higher processing capacity and a decrease in injection molding cycle time compared to conventional screws. The invention is illustrated in Figure 2 is where a screw 27 having a feeding zone 29, a compression zone 31 and a dosing zone 33 is shown. The screw 27 is housed in a hollow cylindrical barrel 35 having a substantially constant inside diameter. The polymeric resin, which may be in any convenient form, such as grit, granules, flakes or powder, is fed through the opening 37 in the barrel 35 into the feed zone 29 where the screw 27 rotates to pack and then pushing the granules in the compression zone 31 as with a conventional screw. The screw 27 has a screw body 39 and a thread 41 spirally placed around the body 39 to form sections 43 of the feed zone, sections 45 of the compression zone and sections 47 of the metering zone. The passage of the sections 43 of the feeding zone is smaller than the external diameter of the screw 27 and, in a preferred embodiment, the passage of each of the sections 43 of the feeding zone is approximately equal. The passage of the sections 47 of the dosing zone is greater than the external diameter of the screw 27 and, in a preferred embodiment, the passage of each of the sections 47 of the dosing zone is approximately equal. In addition, the passage of the sections 43 of the feeding zone is smaller than the passage of the sections 47 of the dosing zone. As shown in Figure 2, the depth of the sections 25 of the compression zone gradually decreases as it moves from near the feed zone 29 to the dosing zone 33, and the passage of the sections 45 of the compression zone is gradually increases by moving from nearer the feed zone 29 to the dosing zone 33. The change in the depth of the sections 45 of the compression zone is obtained because in the compression zone 31 the body 39 of the screw has the shape of a tapered cone. Although the depth of the sections 45 of the compression zone decreases as they move closer from the supply zone 29 to the dosing zone 33, it is not necessary that the depth of each section 45 of the successive compression zone be smaller than the depth of the compression zone. previous. Similarly, although the passage of the sections 45 of the compression zone increases from near the supply zone 29 to the dosing zone 33, it is not necessary that the passage of each of the sections 45 of the successive compression zone be more great than the previous one. The screw of the invention can be used in an injection molding machine, or an extruder, or it can be used as a casting section for a larger screw. Although the invention has been illustrated with a section, it is known to those skilled in the art that the scope of the present invention includes a screw having more than one section.

EXAMPLES EXAMPLE 1 AND COMPARATIVE EXAMPLE 2 In the example 1 a screw according to the invention is manufactured and in the comparative example 2 a conventional screw is manufactured. The physical dimensions of the screws are set forth in Table 1 below. It is injection molded using both Delrin ™ 500 P screws, a polyacetal resin available from E.I. DuPont de Nemours and Company (DuPont). The resin has a melt density / bulk density ratio of 1.16 / 0.87 = 1.33. The results are summarized in table 1 below.

TABLE 1 The screw of example 1 has a small difference in relation to the actual flow of the theoretical feed flow of the material in the feed zone and the ratio of the actual flow to the theoretical feed flow of material in the metering zone compared to the screw of comparative example 2. Therefore, the screw of example 1 produces a homogeneous melt, a more consistent screw retraction time and allows a higher number of revolutions per minute (RPM), that is, a greater amount of resin produced compared to the screw of the comparative example 2, without generating deposits in the screw, flared, bridged or other defects.

EXAMPLE 3 AND COMPARATIVE EXAMPLE 4 - Zytel ™ 135 F is also injection molded, a nylon resin available from DuPont as in the previous examples. In example 3, the resin is injection molded using a screw according to the invention and in example 4 the resin is injection molded using a screw according to the prior art. The results are summarized in table 2 below.

TABLE 2 The screw of Example 3 has a difference in the ratio of the actual flow to the theoretical flow of the material in the feed zone and the ratio of the actual flow to the theoretical flow of material in the dosing zone compared to the difference 0.31 of the screw of comparative example 4. Therefore, the screw of example 3 produces a homogeneous melt, a more consistent screw retraction time and allows a greater number of RPM, that is, a greater amount of resin produced in comparison with the screw of comparative example 4 without generating a deposit in the "screw, flares, bridging or other defects.

EXAMPLE 5 AND COMPARATIVE EXAMPLE 6 Delrin ™ 500 P is also injection molded, as in the previous examples using a screw having a diameter of 65 mm. In example 3, the resin is injection molded using a screw according to the invention and in example 4 the resin is injection molded using a screw according to the prior art. The results are summarized in table 3 below.

TABLE 3 The screw of Example 5 has a small difference in the ratio of the actual flow to the theoretical flow of material in the feed zone and the ratio of the actual flow to the theoretical flow of material in the dosing zone compared to the flow rate. 0.33 difference from the screw of comparative example 6. Therefore, the screw of example 5 produces a homogeneous melt, a more consistent screw shrink time and allows a greater number of RPM, that is, a greater amount of resin produced in comparison with the screw of comparative example 6, without generating a deposit in the screw, flared, bridged or other defects. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention

Claims (16)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property: "

1. A screw comprising a screw body having a thread spirally positioned around the body of the screw so as to form a plurality of sections, the screw having a feeding zone, a compression zone and a metering zone, characterized by the depth, width and pitch of the sections in the feeding area are designed based on the apparent density of the material to be used in the screw and the depth, width and pitch of the sections in the dosing zone is designed based on the density of the material to be used in the screw so that a real volumetric flow of material and a theoretical volumetric flow of material in the feeding zone and a real volumetric flow of material and a flow of drag are provided. volumetric theoretical of the material in the dosing zone, so that the difference in the ratio of the actual volumetric flow of material to the flux or of theoretical volumetric drag of material in the feeding zone and the ratio of the actual volumetric flow of material to the theoretical volumetric drag of the material in the dosing zone is less than 0.2.

2. The screw according to claim 1, characterized in that the difference in the ratio of the actual volumetric flow to the theoretical volumetric flow rate of material in the supply zone and the ratio of the actual volumetric flow to the theoretical volumetric flow rate of the material in the dosing zone it is less than 0.1.

3. The screw according to claim 1, characterized in that the difference in the ratio of the actual volumetric flow to the theoretical volumetric flow rate of material in the supply zone and the ratio of the actual volumetric flow to the theoretical volumetric flow rate of the material in a dosing zone it is less than 0.05.

4. The screw according to claim 1, characterized in that the ratio of the actual volumetric flow of material to the theoretical volumetric flow of material in the feed zone is between 0.8 and 1.0.

5. The screw according to claim 1, characterized in that the ratio of the actual volumetric flow of material to the theoretical volumetric flow of material in the dosing zone is between 0.8 and 1.0.

6. The screw according to claim 1, characterized in that the passage of at least a portion of the sections in the dosing zone is greater than the passage of at least a portion of the sections in the feeding zone, the passage of at least a portion of the sections in the feeding zone is smaller than the external diameter of the screw, the passage of at least a portion of the sections in the dosing zone is greater than the external diameter of the screw, the passage of less a portion of the sections is increased through the compression zone, and the depth of at least a portion of the sections decreases through the compression zone that moves from nearer the feed zone to closer of the dosing zone.

7. The screw according to claim 6, characterized in that the passage of the sections in the dosing area is greater than the passage of the sections in the feeding zone.

8. The screw according to claim 6, characterized in that the passage of the sections in the dosing zone is approximately equal.

9. The screw according to claim 6, characterized in that the passage of the sections in the feeding zone is smaller than the external diameter of the screw.

10. The screw according to claim 6, characterized in that the passage of the sections in the feeding area is approximately equal.

11. The screw according to claim 6, characterized in that the passage of the sections in the dosing zone is greater than the external diameter of the screw.

12. The screw in accordance with the claim 6, characterized in that the depth of the sections in the dosing zone is approximately equal.

13. The screw according to claim 6, characterized in that the depth of the sections decreases through the compression zone moving from closer to the feeding zone closer to the dosing zone.

14. The screw according to claim 6, characterized in that the depth of the sections in the feeding zone is approximately equal.

15. An improved screw comprising a screw body having a thread spirally placed around the body of the screw so as to form a plurality of sections, the screw has a feeding zone, a compression zone and a dosing zone where the passage of at least a portion of the sections in the dosing zone is larger than the passage of at least a portion of the sections in the feeding zone, the passage of at least a portion of the sections in the feeding zone is less that the external diameter of the screw, the passage of at least a portion of the sections in the dosing zone is greater than the external diameter of the screw, the passage of at least a portion of the sections is increased through the area of compression and the depth of at least a portion of the sections decreases through the compression zone that moves from closest to the feeding zone closer to the dosing zone Now, the improvement is characterized because the depth, width and passage of the sections in the feeding area is based on the apparent density of the material to be used in the screw and the depth, width and passage of the sections in the area The dosing machine is based on the melt density of the material to be used in the screw, so that a real volumetric flow of material and a theoretical volumetric flow of material in the feeding zone and a real volumetric flow are provided. of material and a theoretical volumetric flow of material in the dosing zone so that the difference in the ratio of the actual volume flow of material to the theoretical volumetric flow of material in the feed zone and the actual volumetric flow rate of material with respect to the volumetric theoretical flow of material in the dosing zone is less than 0.2.

16. A method for designing a screw, for use in injection molding or extrusion, which screw comprises a screw body that has a thread spirally placed around the screw body so as to form a plurality of sections, the screw has an area of feeding, a compression zone and a dosing zone, characterized in that it comprises the steps of: selecting the material to be used in the screw, selecting a material mass flow rate, calculating a volumetric flow rate of material in the feeding area, calculate a volumetric flow rate of material in the dosing zone, select the depth, width and pitch of the sections in the feeding zone and the depth, width and pitch of the sections in the dosing zone so that provide a real volumetric flow of material and a theoretical volumetric flow of material in the feeding zone, and a real volumetric flux of material and a theoretical volumetric flow of material in the dosing zone, so that the difference in the ratio of the actual volumetric flow of material to the theoretical volumetric flow of material in the feed zone and the ratio of the actual volumetric flow of material to the theoretical volumetric flow of material in the dosing zone is less than 0.2.