阅读说明：本技术 一种冷轧支承辊的修复方法 (Repairing method of cold-rolled supporting roller ) 是由 程四华 穆相林 吕迺冰 孙齐松 晁月林 徐士新 周洁 王晓晨 佟倩 于 2020-12-08 设计创作，主要内容包括：本发明涉及一种冷轧支承辊的修复方法,所述方法包括,获取支承辊的缺陷深度；根据所述支承辊的缺陷深度,确定所述支承辊缺陷修复所用激光同轴送粉工艺；对所述支承辊采用所述确定的激光同轴送粉工艺进行修复。采用本发明提供的同轴送粉工艺修复冷轧辊,修复后的支承辊洛氏硬度为54-58HRC,在线服役周期为45-51天,大幅度的提高冷轧支承辊的服役周期。(The invention relates to a repairing method of a cold-rolled supporting roller, which comprises the steps of obtaining the defect depth of the supporting roller; determining a laser coaxial powder feeding process for repairing the defects of the supporting roller according to the defect depth of the supporting roller; and repairing the supporting roller by adopting the determined laser coaxial powder feeding process. The Rockwell hardness of the repaired support roll is 54-58HRC, the online service period is 45-51 days, and the service period of the cold-rolled support roll is greatly improved.)

1. A method for repairing a cold-rolled backup roll, comprising,

acquiring the defect depth of the supporting roller;

determining a laser coaxial powder feeding process for repairing the defects of the supporting roller according to the defect depth of the supporting roller;

and repairing the supporting roller by adopting the determined laser coaxial powder feeding process.

2. The method for repairing a cold-rolled supporting roller as claimed in claim 1, wherein the laser coaxial powder feeding process for repairing the defects of the supporting roller is determined according to the defect depth of the supporting roller, and specifically comprises,

when the defect depth of the supporting roller is 1-5mm, a first laser coaxial powder feeding process is adopted to repair the supporting roller, and in the first laser coaxial powder feeding process, the laser power is 2000-2500w, and the scanning speed is 25-30 mm/s.

3. The method for repairing a cold-rolled supporting roller according to claim 2, wherein in the first laser coaxial powder feeding process, the spot diameter is 4-5mm, and the overlapping amount is 2.5-3.0 mm.

4. The method for repairing a cold-rolled supporting roller as claimed in claim 2, wherein in the first laser coaxial powder feeding process, the vertical distance from a powder feeding head to the cold-rolled supporting roller is 8-12mm, and the layer thickness is 1.0-1.2 mm.

5. The method for repairing a cold-rolled supporting roller as claimed in claim 2, wherein the first laser coaxial powder feeding process is performed at a powder feeding rate of 1.0-1.2r/min under the protection of argon gas with a flow rate of 5.0-5.7m³/s。

6. A method for repairing a cold-rolled supporting roller according to claim 1, wherein said determining a laser coaxial powder feeding process for repairing the defect of the supporting roller according to the defect depth of the supporting roller further comprises,

and when the defect depth of the supporting roller is 6-10mm, repairing the supporting roller by adopting a second laser coaxial powder feeding process, wherein in the second laser coaxial powder feeding process, the laser power is 1800-2000w, and the scanning speed is 15-20 mm/s.

7. A method for repairing a cold-rolled supporting roller according to claim 6, wherein in the second laser coaxial powder feeding process, the diameter of a light spot is 3-4mm, and the overlapping amount is 1.5-2.0 mm.

8. The method for repairing a cold-rolled supporting roller as claimed in claim 6, wherein in the second laser coaxial powder feeding process, the vertical distance from a powder feeding head to the cold-rolled supporting roller is 8-10mm, and the layer thickness is 0.8-1.0 mm.

9. The method for repairing a cold-rolled supporting roller as claimed in claim 6, wherein the first laser coaxial powder feeding process is performed at a powder feeding rate of 1.0-1.2r/min under the protection of argon gas with a flow rate of 4.5-5.0m³And s. The powder feeding rate is 0.8-1.0 r/min.

10. The method for repairing a cold-rolled supporting roller is characterized in that the grain sizes of the metal powder used in the first laser coaxial powder feeding process and the second laser coaxial powder feeding process are both 50-150 μm, the grain sizes of the metal powder obey normal distribution N (0, 1), and the metal powder comprises the following chemical components in percentage by mass: c: 0.4-0.5%, Si: 0.3-0.5%, Mn: 0.4-0.5%, P is less than or equal to 0.02%, S is less than or equal to 0.015%, Cr: 4.5-5.5%, Ni: 0.15-0.82%, Mo: 0.2-0.4%, V: 0.1 to 0.2 percent of the total weight of the alloy, less than or equal to 0.03 percent of O, less than or equal to 0.03 percent of N, and the balance of Fe and inevitable impurities.

Technical Field

The invention belongs to the technical field of cold-rolled supporting roller repair, and particularly relates to a method for repairing a cold-rolled supporting roller.

Background

The cold rolling supporting roll is a part of a cold rolling production line, can prevent a working roll of the cold rolling production line from deflecting and deforming during strip steel rolling, has complex and severe service conditions, needs to bear additional stress caused by irregular abrasion, roll bending force, rolling impact and the like, and has the roll surface working pressure of about 1000t and local parts even reaching more than 2000 t. On the domestic conventional cold rolling production line, the service cycle of the cold rolling supporting roll is generally 15-20 days, and the time from the use of a new roll to the scrapping is about 2 years and a half. There are two main failure modes of cold rolls: firstly, fatigue wear is caused, and the size of a workpiece reaches the limit size of a rolling mill; secondly, due to overlarge stress, cracks or roll surface peeling and sinking are generated in the rolling process, the defects of the roll surface directly cause the surface defects of the product, and the failed supporting roll needs to be replaced or repaired in time.

After the cold roll produces surface defect, domestic manufacturing enterprise mostly adopts to change brand-new backing roll and guarantees product surface quality, but the cost is too high, therefore constantly improves to cold roll surface repair demand. The supporting roller main body is almost made of alloy forged steel, a Cr5 alloy forged steel roller is commonly used at present, a quenching layer is arranged on the surface of the roller, a laser quenching process is generally adopted, and the thickness of the layer reaches 100 mm. When the cold roll fails, the surface depression depth is generally 5-15mm, but the welding defects such as cracks, air holes, slag inclusion and the like are easily generated due to the overlarge heat affected zone of the conventional CMT electric arc additive manufacturing method, a surfacing layer is easy to peel off, the roller surface repairing quality and the bonding degree of a repairing material and a matrix cannot be ensured after repairing, and the backup roll does not have the condition of re-service under the process condition; moreover, the CMT process has low fineness, and the repair of the distinguishing process cannot be realized according to different cold roll recess depths.

Therefore, a new method for repairing a cold-rolled backup roll is needed.

Disclosure of Invention

In order to solve the technical problems, the invention provides a method for repairing a cold-rolled supporting roller, which ensures that the repaired supporting roller has strong anti-stripping capability and can realize pit depth differential repair.

The invention provides a method for repairing a cold-rolled supporting roller, which comprises the following steps,

acquiring the defect depth of the supporting roller;

determining a laser coaxial powder feeding process for repairing the defects of the supporting roller according to the defect depth of the supporting roller;

and repairing the supporting roller by adopting the determined laser coaxial powder feeding process.

Further, the laser coaxial powder feeding process for repairing the defects of the supporting roller is determined according to the defect depth of the supporting roller, and specifically comprises the following steps,

when the defect depth of the supporting roller is 1-5mm, a first laser coaxial powder feeding process is adopted to repair the supporting roller, and in the first laser coaxial powder feeding process, the laser power is 2000-2500w, and the scanning speed is 25-30 mm/s.

Further, in the first laser coaxial powder feeding process, the diameter of a light spot is 4-5mm, and the lap joint amount is 2.5-3.0 mm.

Further, in the first laser coaxial powder feeding process, the vertical distance from the powder feeding head to the cold rolling supporting roller is 8-12mm, and the layer thickness is 1.0-1.2 mm.

Further, in the first laser coaxial powder feeding process, the powder feeding speed is 1.0-1.2r/min, and the repair is carried out by adopting argon protection, wherein the flow of argon is 5.0-5.7m³/s。

Further, the laser coaxial powder feeding process for repairing the defects of the supporting roller is determined according to the defect depth of the supporting roller, and the method also comprises the following steps,

and when the defect depth of the supporting roller is 6-10mm, repairing the supporting roller by adopting a second laser coaxial powder feeding process, wherein in the second laser coaxial powder feeding process, the laser power is 1800-2000w, and the scanning speed is 15-20 mm/s.

Further, in the second laser coaxial powder feeding process, the diameter of a light spot is 3-4mm, and the lap joint amount is 1.5-2.0 mm.

Further, in the second laser coaxial powder feeding process, the vertical distance from the powder feeding head to the cold rolling supporting roller is 8-10mm, and the layer thickness is 0.8-1.0 mm.

Further, in the first laser coaxial powder feeding process, the powder feeding speed is 1.0-1.2r/min, and the repair is carried out by adopting argon protection, wherein the flow of argon is 4.5-5.0m³And s. The powder feeding rate is 0.8-1.0 r/min.

Further, the particle size of the metal powder used in the first laser coaxial powder feeding process and the particle size of the metal powder used in the second laser coaxial powder feeding process are both 50-150 μm, the particle size of the metal powder obeys normal distribution N (0, 1), and the metal powder consists of the following chemical components in percentage by mass: c: 0.4-0.5%, Si: 0.3-0.5%, Mn: 0.4-0.5%, P is less than or equal to 0.02%, S is less than or equal to 0.015%, Cr: 4.5-5.5%, Ni: 0.15-0.82%, Mo: 0.2-0.4%, V: 0.1 to 0.2 percent of the total weight of the alloy, less than or equal to 0.03 percent of O, less than or equal to 0.03 percent of N, and the balance of Fe and inevitable impurities.

One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

the invention provides a method for repairing a cold-rolled supporting roller, which comprises the steps of firstly obtaining the defect depth of the supporting roller, then determining a laser coaxial powder feeding process for repairing the defect of the supporting roller according to the defect depth of the supporting roller, finally repairing the supporting roller by adopting the determined laser coaxial powder feeding process, repairing by adopting the laser coaxial powder feeding process to locally melt the supporting roller, then realizing metallurgical bonding with molten metal powder, and bonding tightly and difficultly stripping after cooling. The Rockwell hardness of the repaired support roll is 54-58HRC, the online service period is 45-51 days, and the service period of the cold-rolled support roll is greatly improved.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.

FIG. 1 is a macro topography of a cold-rolled backup roll before repair in example 1 of the present invention;

FIG. 2 is a microstructure of a repaired layer after the cold-rolled backup roll is repaired in example 1 of the present invention.

Detailed Description

The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the invention.

Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. If there is a conflict, the present specification will control.

Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.

In order to solve the technical problems, the embodiment of the invention provides the following general ideas:

the invention provides a method for repairing a cold-rolled supporting roller, which comprises the following steps,

s1, acquiring the defect depth of the supporting roller;

s2, determining a laser coaxial powder feeding process for repairing the defects of the supporting roller according to the defect depth of the supporting roller;

and S3, repairing the supporting roller by adopting the determined laser coaxial powder feeding process.

The laser coaxial powder feeding is adopted for repairing, so that the supporting roller is locally melted, then metallurgical bonding is realized with the melted metal powder, and the bonding is tight and difficult to peel off after cooling. The coaxial powder feeding process provided by the invention is adopted to repair the cold roll, so that the service cycle of the cold roll can be greatly improved.

As an implementation mode of the embodiment of the invention, the laser coaxial powder feeding process for repairing the defects of the supporting roller is determined according to the defect depth of the supporting roller, and specifically comprises the following steps,

when the defect depth of the supporting roller is 1-5mm, a first laser coaxial powder feeding process is adopted to repair the supporting roller, and in the first laser coaxial powder feeding process, the laser power is 2000-2500w, and the scanning speed is 25-30 mm/s.

When the depth of the defect is shallow, higher laser power and higher scanning speed can be used, the repair efficiency is improved, the number of repair layers is small, and the crack defect is difficult to cause by the accumulation of thermal stress. The metal powder is easy to over-burn due to the fact that the laser power is too high and the scanning speed is too low, the crack sensitivity of a cladding layer is increased, and incomplete melting of the metal powder is caused due to the fact that the laser power is too low and the scanning speed is too high, so that the metallurgical bonding strength is affected.

As an implementation manner of the embodiment of the invention, in the first laser coaxial powder feeding process, the diameter of a light spot is 4-5mm, and the lap joint amount is 2.5-3.0 mm. The method has the advantages that the larger spot diameter and the larger lap joint quantity are controlled, the repair efficiency is improved, if the spot diameter is too large, the specific energy of laser in unit time is not enough to melt the cladding material of a repaired area, and the specific energy of too small laser is too large to easily generate cladding cracks. If the overlapping quantity is too large, the cladding structure is disordered and uneven, and the surface quality is affected due to the fact that the small cladding layer is uneven.

As an implementation mode of the embodiment of the invention, in the first laser coaxial powder feeding process, the vertical distance from a powder feeding head to the cold rolling supporting roller is 8-12mm, and the layer thickness is 1.0-1.2 mm. The vertical distance between the powder feeding head and the cold rolling supporting roller is mainly controlled by the thickness of the cladding layer. The thickness of the cladding layer is too large, the thickness of the cladding layer is too small, the thickness of the cladding layer is too large, and the repair quality, especially the toughness of the repair layer is seriously influenced, so that the repair failure is caused.

As an implementation manner of the embodiment of the invention, in the first laser coaxial powder feeding process, the powder feeding rate is 1.0-1.2r/min, and the repair is performed by adopting argon protection, wherein the flow rate of argon is 5.0-5.7m³And s. The powder feeding speed affects the uniformity of the cladding layer, and the metal powder is easily accumulated when the powder feeding speed is too high and is discontinuous when the powder feeding speed is too low. The powder feeding speed is controlled by argon flow, and the uniformity of a repair layer is seriously influenced by overlarge cladding amount and insufficient powder feeding amount due to undersize.

As an implementation mode of the embodiment of the invention, the laser coaxial powder feeding process for repairing the defects of the supporting roller is determined according to the defect depth of the supporting roller, and the method further comprises the following steps,

and when the defect depth of the supporting roller is 6-10mm, repairing the supporting roller by adopting a second laser coaxial powder feeding process, wherein in the second laser coaxial powder feeding process, the laser power is 1800-2000w, and the scanning speed is 15-20 mm/s.

When the depth of the defect is deeper, the scanning speed needs to be reduced, and the laser power is reduced, so that the main purpose is to match the proper specific energy of the laser and reduce the crack defect caused by the accumulation of thermal stress, and at the moment, the laser power is too high, and the scanning speed is too fast, cladding cracks are easily generated, and waste products are caused.

As an implementation manner of the embodiment of the invention, in the second laser coaxial powder feeding process, the diameter of a light spot is 3-4mm, and the lap joint amount is 1.5-2.0 mm. The smaller spot diameter and the lapping quantity are controlled, so that the proper laser specific energy is controlled, and the repair quality of each layer of powder is ensured. At the moment, the diameter of the light spot is too large, the powder is easily insufficiently melted due to too large overlapping amount, and the defect of holes is easily generated.

As an implementation mode of the embodiment of the invention, in the second laser coaxial powder feeding process, the vertical distance from the powder feeding head to the cold rolling supporting roller is 8-10mm, and the layer thickness is 0.8-1.0 mm. The vertical distance between the powder feeding head and the cold-rolled supporting roll is also controlled to control the thickness of a cladding layer, the powder feeding head and the cold-rolled supporting roll are properly adjusted along with the difference of defect depth, and the improper distance control can influence the toughness of a repairing layer.

As an implementation manner of the embodiment of the invention, in the first laser coaxial powder feeding process, the powder feeding rate is 1.0-1.2r/min, and the repair is performed by adopting argon protection, wherein the flow rate of argon is 4.5-5.0m³And s. The powder feeding rate is 0.8-1.0 r/min. Similarly, the powder feeding rate influences the uniformity of the cladding layer, and along with the change of other process parameters, the powder feeding rate is not matched with the argon flow, so that the repairing layer is not uniform easily, the repairing quality is influenced, and the wear resistance of the cold roll is influenced.

As one implementation mode of the embodiment of the invention, the particle diameters of the metal powders used in the first laser coaxial powder feeding process and the second laser coaxial powder feeding process are both 50-150 μm, the particle diameters of the metal powders obey normal distribution N (0, 1), and the metal powders are composed of the following chemical components in percentage by mass: c: 0.4% -0.5%, Si: 0.3-0.5%, Mn: 0.4-0.5%, P is less than or equal to 0.02%, S is less than or equal to 0.015%, Cr: 4.5% -5.5%, Ni: 0.15% -0.82%, Mo: 0.2% -0.4%, V: 0.1% -0.2%, O: less than or equal to 0.03%, N: less than or equal to 0.03 percent, and the balance of Fe and inevitable impurities.

The grain diameter of the metal powder is subject to normal distribution, so that the metal powder is tightly arranged, the gap is smaller, and the metal powder is prevented from contacting with air to generate secondary oxidation in the melting process, thereby reducing the content of inclusions and gas at the repaired part, and ensuring that the repaired supporting roller has good fatigue strength and wear resistance.

The metal powder matched with the chemical components of the supporting roll is designed, wherein the contents of Cr, Ni and Mo elements are matched with those of Cr, Ni and Mo elements in the cold roll, so that the continuity with a matrix after repair can be realized; the content of elements such as Mn, Si and the like is higher than that of components of the supporting roll, the element burning loss in the laser coaxial powder feeding process can be compensated, the components of the repair part are matched with the components of the supporting roll, the content of O and N in the powder is reduced, the cleanliness of the repair powder can be improved, the oxidation in the repair process is avoided, the generation of impurities and abnormal hard phases is avoided, and the fatigue resistance of the repair layer is improved. The powder is matched with the composition of the supporting roller, so that the two properties are the same, and therefore, the two are combined more tightly and are difficult to peel, thereby improving the anti-stripping performance.

The supporting roll is made of Cr5, and the chemical components of the supporting roll are C: 0.4-0.5%, Si: 0.2-0.3%, Mn: 0.2-0.4%, P is less than or equal to 0.02%, S is less than or equal to 0.015%, Cr: 4.5-5.5%, Ni: 0.15-0.82%, Mo: 0.2-0.4%, V: 0.1-0.2%, the balance being Fe and unavoidable impurities.

The method for repairing a cold-rolled backup roll according to the present invention will be described in detail with reference to examples, comparative examples and experimental data.

Example 1

Embodiment 1 provides a method for repairing a cold-rolled backup roll, including the steps of:

the defect depth of the supporting roller made of Cr5 is detected to be 2mm, and the following coaxial powder feeding process is adopted according to the defect depth: laser power 2400w, scanning speed 30mm/s, spot diameter4.5mm, the overlap amount is 2.8mm, send whitewashed speed 1.1r/min, send whitewashed head to work piece vertical distance 10mm, the layer thickness is 0.9mm, argon protection gas flow: 5.5m³/s。

The repair metal powder for coaxial powder feeding comprises the following chemical components in percentage by mass: c: 0.4%, Si: 0.35%, Mn: 0.43%, P: 0.02%, S: 0.015%, Cr: 4.5% -5.5%, Ni: 0.18%, Mo: 0.4%, V: 0.15%, O: 0.03%, N: 0.03 percent, the balance being Fe and inevitable impurities, and the particle size of the powder is 60-150 mu m.

Example 2

Embodiment 2 provides a method for repairing a cold-rolled backup roll, including the steps of:

the defect depth of the supporting roller made of Cr5 is 5mm, and the following coaxial powder feeding process is adopted according to the defect depth: laser power 2200w, scanning speed 25mm/s, facula phi 4mm, lap joint amount 2.5mm, powder feeding speed 1.0r/min, vertical distance 9mm from powder feeding head to workpiece, layer thickness 0.8mm, argon protective gas flow: 5.2m³/s。

The repair metal powder for coaxial powder feeding comprises the following chemical components in percentage by mass: c: 0.45%, Si: 0.37%, Mn: 0.45%, P: 0.015%, S: 0.013%, Cr: 4.9%, Ni: 0.48%, Mo: 0.3%, V: 0.18%, O: 0.03%, N: 0.03 percent, the balance being Fe and inevitable impurities, and the particle size of the powder is 50-140 mu m.

Example 3

Embodiment 3 provides a method for repairing a cold-rolled backup roll, including the steps of:

the defect depth of the supporting roller made of Cr5 is 10mm, and the following coaxial powder feeding process is adopted according to the defect depth: laser power 2000w, scanning speed 18mm/s, facula phi 4mm, lap joint amount 1.6mm, powder feeding speed 0.9r/min, vertical distance 9mm from powder feeding head to workpiece, layer thickness 0.8mm, argon protective gas flow: 4.8m³/s；

The repair metal powder for coaxial powder feeding comprises the following chemical components in percentage by mass: c: 0.48%, Si: 0.40%, Mn: 0.47%, P: 0.011%, S: 0.01: 4%, Cr: 5.0%, Ni: 0.43%, Mo: 0.4%, V: 0.2%, O: 0.02%, N: 0.025%, and the balance of Fe and inevitable impurities, and the particle size of the powder is 50-120 μm.

Comparative example 1

Comparative example 1 with reference to example 1, the difference from example 1 is that: 1) the adopted material is in the shape of a welding wire, the diameter of the welding wire is 1.2mm, and the chemical components are as follows: c: 0.38%, Si: 0.91%, Mn: 0.47%, P: 0.013%, S: 0.01: 2%, Cr: 4.8%, Mo: 1.3%, V: 0.25%, the balance being Fe and unavoidable impurities; 2) the supporting roller is repaired by adopting an arc surfacing method, the heat affected zone is large, cracks are easy to generate, the radial structure of the supporting roller is affected, and the fatigue performance is caused. The adopted surfacing process comprises the following steps: welding speed: 0.2m/min, wire feed speed: 5m/min, 5.74mm of track spacing, protective gas flow: 15L/min, current 144A and voltage 20V.

In examples 1 to 3 and comparative example 1, two cold rolls were repaired by the laser coaxial powder feeding process, and the repaired cold rolls were subjected to rockwell hardness testing and applied to count the service life of the repaired backup rolls, as shown in table 1.

TABLE 1

The method for repairing the cold-rolled supporting roller provided by the embodiment 1 to 3 enables the Rockwell hardness of the repaired supporting roller to be 54 to 58HRC, the online service period to be 45 to 51 days, and the service life of the supporting roller is prolonged. The repairing method of the cold-rolled supporting roller provided by the comparative example 1 enables the Rockwell hardness of the repaired supporting roller to be 41-45HRC, the online service period to be 19-22 days, and the repairing method is obviously lower than that of the embodiment of the invention.

The invention provides a method for repairing a cold-rolled supporting roller, which comprises the steps of firstly obtaining the defect depth of the supporting roller, then determining a laser coaxial powder feeding process for repairing the defect of the supporting roller according to the defect depth of the supporting roller, finally repairing the supporting roller by adopting the determined laser coaxial powder feeding process, repairing by adopting the laser coaxial powder feeding process to locally melt the supporting roller, then realizing metallurgical bonding with molten metal powder, and bonding tightly and difficultly stripping after cooling. The Rockwell hardness of the repaired support roll is 54-58HRC, the online service period is 45-51 days, and the service period of the cold-rolled support roll is greatly improved.

Finally, it should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.