阅读说明：本技术 一种铝溶胶凝胶粘度检测装置及检测方法 (Aluminum sol-gel viscosity detection device and detection method ) 是由 葛传金 井良霄 于 2021-07-22 设计创作，主要内容包括：一种铝溶胶凝胶粘度检测装置及检测方法,涉及检测技术领域,包括底座,底座两侧各安装有一升降柱组件,两个所述升降柱组件顶部通过顶杆相连,所述顶杆底部固定连接有密封盖,所述升降柱组件驱动密封盖竖直升降,所述底座中部安装有检测台,检测台上安装有检测筒。本发明解决了检测过程中铝溶胶凝胶的剪切变稀现象,确保了检测结果的准确性；操作简单实用,检测稳定性高；可实现全自动检测运行。(The utility model provides an aluminium sol gel viscosity detection device and detection method, relates to and detects technical field, including the base, a lift post subassembly is respectively installed to the base both sides, two lift post subassembly top links to each other through the ejector pin, ejector pin bottom fixedly connected with sealed lid, the sealed vertical lift of lid of lift post subassembly drive, the base mid-mounting has the detection platform, installs the detection section of thick bamboo on the detection platform. The invention solves the problem of shear thinning of the alumina sol gel in the detection process and ensures the accuracy of the detection result; the operation is simple and practical, and the detection stability is high; and the full-automatic detection operation can be realized.)

1. The utility model provides an aluminium sol gel viscosity detection device, its characterized in that, includes the base, and a lift post subassembly, two are respectively installed to the base both sides the lift post subassembly top links to each other through the ejector pin, the sealed lid of ejector pin bottom fixedly connected with, the sealed vertical lift of lid of lift post subassembly drive, the base mid-mounting has the detection platform, detects and installs on the platform and detect a section of thick bamboo.

2. The aluminum sol gel viscosity detecting device of claim 1, wherein a level gauge and a controller are mounted on the base; the rear part of the left side of the base is provided with a constant temperature water machine, and the rear part of the right side of the base is provided with a vacuum pump.

3. The aluminum sol-gel viscosity detection device of claim 1 or 2, wherein the lifting column assembly comprises an outer tube and an inner rod, wherein the outer tube is fixedly connected to the base, the inner rod is in sliding fit in the outer tube, and the top of the inner rod is connected with a push rod.

4. The device for detecting the viscosity of the aluminum sol-gel as claimed in claim 1, wherein the detecting cylinder comprises a straight cylinder, a funnel and a connecting sleeve, the funnel is connected with the straight cylinder through the connecting sleeve, the right side of the funnel is provided with a first electrode through an internal thread, the connecting sleeve is provided with an electric valve through an external thread, and the lower part of the straight cylinder is provided with a second electrode through an external thread.

5. The device for detecting the viscosity of aluminum sol-gel according to claim 1 or 4, wherein the detection table comprises an upper support plate, a lower plate and support rods, the upper support plate is connected with the lower plate through a plurality of support rods, the upper support plate is provided with insertion holes, straight cylinders are inserted into the insertion holes, the lower plate is provided with a vacuum tube, the vacuum tube is connected with a vacuum pump through a hose, the upper part of the vacuum tube is provided with a vacuum degree sensor, and the lower plate is provided with a sealing ring.

6. The device for detecting the viscosity of the aluminum sol-gel as claimed in claim 5, wherein the sealing cover comprises a sealing cover body, the sealing cover body is of a double-layer structure, constant-temperature water is filled in an interlayer of the sealing cover body, a constant-temperature water inlet pipe and a constant-temperature water outlet pipe are arranged on the sealing cover body, the constant-temperature water inlet pipe and the constant-temperature water outlet pipe are connected with a constant-temperature water machine through hoses, and a temperature sensor is arranged on the constant-temperature water outlet pipe.

7. The apparatus for detecting viscosity of aluminum sol-gel as claimed in claim 6, wherein the sealing cap is mounted with a pressure gauge on the front surface thereof.

8. The aluminum sol-gel viscosity detecting device as claimed in claim 6, wherein the sealing cover body is provided with a connecting flange at an upper side thereof, and the connecting flange is connected with a push rod.

9. A method for detecting the viscosity of an aluminum sol-gel is characterized by comprising the following steps:

s1 an aluminum sol-gel sample was prepared,

s11 filling the funnel on the top of the detection cylinder with the sample to be detected, using the lowest liquid level of the sample to align with the scale, using the scraper to scrape the protruding part of the sample, placing the detection cylinder and the sample in a sealed constant temperature box at 25 deg.C to be detected, configuring a plurality of detection cylinders for continuously detecting a plurality of samples,

s12, mounting the detection cylinder with the sample on the upper supporting plate, adjusting the base support leg to the middle position of the level meter, connecting the first electrode, the second electrode, the electric valve and the vacuum degree sensor to the quick socket by the lead,

s2, the start button is pressed, the controller automatically executes the detection process,

s21, the lifting column assembly is operated to descend, the sealing cover descends along with the descending lifting column assembly until the sealing ring on the detection platform is pressed tightly,

s22, starting the constant temperature water machine, starting the vacuum pump at the same time, waiting for the temperature and the vacuum degree to reach the set values, automatically keeping stable,

s23 opens the electric valve, the controller starts timing at the same time, the timing unit is millisecond (ms), the sample flows downwards along the detection cylinder under the action of gravity, when the sample falls to the bottom of the detection cylinder, a path signal is formed between the first electrode and the second electrode, the controller is triggered to stop timing, and the stored data are displayed on the controller and the display screen.

Technical Field

The invention relates to the technical field of detection, in particular to a device and a method for detecting viscosity of aluminum sol-gel.

Background

The aluminum sol is a water-soluble high molecular polymer and is a main raw material for producing alumina fibers, and the aluminum sol conforms to the characteristics of non-Newtonian fluid in a gel state. The viscosity of the aluminum sol gel directly influences the quality index of the subsequent fiber forming process, the viscosity is too low, the fiber forming performance is poor, the viscosity is too high, and the fiber index is reduced, so the accuracy of viscosity detection is very important.

The current methods for detecting the viscosity of the liquid include: capillary, rotary, falling ball, vibratory, etc. Due to the high thixotropy of the aluminum sol-gel, the viscosity is reduced sharply (shear thinning) under the action of shear force, so that the viscosity cannot be measured accurately. The verification proves that the rotation method and the vibration method cannot be well suitable for the viscosity detection of the aluminum sol gel; the falling ball method has measurement errors, particularly large repeated measurement errors, on the aluminum sol-gel sample with lower viscosity, and the operation is complex; the universal capillary viscosity measuring instrument needs to apply larger pressure to a sample, has the phenomenon of shear thinning, and is not suitable for the detection of aluminum sol gel.

Disclosure of Invention

The invention aims to solve the problems, provides a device and a method for detecting the viscosity of the aluminum sol-gel, solves the problem that the existing viscosity detection technology cannot be suitable for shear thinning of the aluminum sol-gel, and realizes simple, quick and accurate detection of the viscosity of the aluminum sol-gel.

The technical scheme adopted by the invention for solving the technical problems is as follows:

the utility model provides an aluminium sol gel viscosity detection device, includes the base, and a lift post subassembly, two are respectively installed to the base both sides lift post subassembly top links to each other through the ejector pin, the sealed lid of ejector pin bottom fixedly connected with, the sealed vertical lift of lid of lift post subassembly drive, the base mid-mounting has the detection platform, detects and installs on the platform and detect a section of thick bamboo.

Furthermore, a level gauge and a controller are installed on the base; the rear part of the left side of the base is provided with a constant temperature water machine, and the rear part of the right side of the base is provided with a vacuum pump.

Further, the lifting column assembly comprises an outer tube and an inner rod, wherein the outer tube is fixedly connected to the base, the inner rod is in sliding fit in the outer tube, and the top of the inner rod is connected with a push rod.

The scheme is refined, the lifting column assembly further comprises a driving motor, and the driving motor drives the inner rod to move along the outer pipe.

Further, it includes straight section of thick bamboo, funnel and adapter sleeve to detect a section of thick bamboo, the funnel is connected through the adapter sleeve with straight section of thick bamboo, the funnel right side is installed first electrode through the internal thread, the motorised valve is installed through the external screw thread to the adapter sleeve, and the second electrode is installed through the external screw thread in straight section of thick bamboo lower part.

The scheme is refined, and a snap ring is arranged on the straight cylinder.

The scheme is refined, and the whole detection cylinder is made of 316L materials;

the scheme is refined, and a coating for reducing the friction coefficient is sprayed on the inner wall of the detection cylinder; the coating is made of polytetrafluoroethylene.

The scheme is refined, and the electric insulation is kept between the first electrode and the second electrode; the whole detection cylinder can be detached, and the detection cylinder can be configured with a plurality of specifications according to the range of viscosity measurement;

the scheme is refined, and the inner wall of the funnel is provided with a scale value with the specification of 50 ml-200 ml;

furthermore, examine test table and include backup pad, lower plate and bracing piece, go up and be connected through a plurality of bracing pieces between backup pad and the lower plate, be equipped with the jack in the backup pad, it has straight section of thick bamboo to peg graft in the jack, install the evacuation pipe on the lower plate, evacuation pipe passes through the hose and is connected with the vacuum pump, and vacuum sensor is installed on evacuation pipe upper portion, be equipped with the sealing washer on the lower plate.

The scheme is refined, a quick socket is arranged on the lower bottom plate, the quick socket is connected with the first electrode, the second electrode, the electric valve and the vacuum degree sensor through leads,

the scheme is refined, and the vacuum pump can be one or a combination of a centrifugal vacuum pump, a screw type vacuum pump and a roots pump.

Further, sealed lid is including sealed lid body, sealed lid body is bilayer structure, lead to constant temperature water in the sealed lid body intermediate layer, be equipped with constant temperature inlet tube and constant temperature outlet pipe on the sealed lid body, constant temperature inlet tube, constant temperature outlet pipe pass through the hose and are connected with the constant temperature water machine, install temperature sensor on the constant temperature outlet pipe, can keep invariable with the temperature in the sealed lid.

Further, a pressure gauge is arranged on the front face of the sealing cover.

The scheme refines, sealed lid body upside is equipped with flange, flange is connected with the ejector pin.

The scheme is refined, and the controller is connected with the quick socket, the lifting column assembly, the constant temperature water machine and the vacuum pump through a control lead.

The scheme is refined, the controller is provided with a digital-to-analog conversion chip, a timing chip, a temperature measuring chip, a vacuum measuring chip and a liquid crystal display screen, the viscosity value, the temperature value and the resistivity detection result of the sample are measured and displayed, and the detection data are stored for more than 1 year.

A method of detecting the viscosity of an aluminum sol gel comprising the steps of:

s1 preparation of an aluminum Sol gel sample

S11 filling the funnel on the top of the detection cylinder with the sample to be detected, using the lowest liquid level of the sample to align with the scale, using the scraper to scrape the protruding part of the sample, placing the detection cylinder and the sample in a sealed constant temperature box at 25 deg.C to be detected, configuring a plurality of detection cylinders for continuously detecting a plurality of samples,

s12 mounting the detection cylinder with sample on the upper support plate, adjusting the base support to the level meter at the middle position, connecting the first electrode, the second electrode, the electric valve and the vacuum degree sensor to the quick socket by the lead, S2 pressing the start button, the controller automatically executing the detection process

S21, the lifting column assembly is operated to descend, the sealing cover descends along with the descending lifting column assembly until the sealing ring on the detection platform is pressed tightly,

s22, starting the constant temperature water machine, starting the vacuum pump at the same time, waiting for the temperature and the vacuum degree to reach the set values, automatically keeping stable,

s23, opening the electric valve, starting timing by the controller in milliseconds (ms), allowing the sample to flow downwards along the detection cylinder under the action of gravity, forming a channel signal between the first electrode and the second electrode when the sample falls to the bottom of the detection cylinder, triggering the controller to stop timing, storing data in the controller and displaying on the display screen,

further, the viscosity of the sample is characterized in milliseconds (ms) based on the time count of the recorded sample.

Furthermore, the vacuum degree is-98 to-100 KPa, and the temperature is 30 +/-5 ℃.

Further, the aluminum sol gel is water-soluble and has conductivity.

Furthermore, according to the viscosity measurement range, the detection cylinder is provided with a plurality of specification grades from 50ml to 200 ml.

The invention has the beneficial effects that: the invention solves the problem of shear thinning of the alumina sol gel in the detection process and ensures the accuracy of the detection result; the method is simple and practical to operate and high in detection stability; the invention can realize full-automatic detection operation; the main detection part of the invention is convenient to disassemble and easy to clean.

Drawings

FIG. 1 is an overall schematic view of the present invention;

FIG. 2 is a front view of the present invention;

FIG. 3 is a schematic three-dimensional structure of a detection cartridge;

FIG. 4 is a schematic three-dimensional structure of the inspection station;

in the figure: 1 a base, 11 a level gauge, 12 a controller,

2 lifting column component, 21 outer tube, 22 inner rod, 23 top rod,

3 sealing covers, 31 connecting flanges, 32 sealing cover bodies, 33 pressure gauges, 34 constant-temperature water outlet pipes, 35 constant-temperature water inlet pipes,

4 detection table, 41 upper support plate, 42 lower bottom plate, 43 support rod, 44 jack, 45 vacuum tube, 46 vacuum sensor, 47 quick socket, 48 sealing ring,

5 a detection cylinder, 51 a straight cylinder, 52 a funnel, 53 a connecting sleeve, 54 a clamping ring, 55 an electric valve, 56 a first electrode, 57 a second electrode, 6 a constant temperature water machine and 7 a vacuum pump.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

As shown in fig. 1 to 4, an aluminum sol-gel viscosity detection device comprises a base 1, wherein a lifting column assembly 2 is respectively installed on two sides of the base 1, the top of the lifting column assembly is connected through a top rod 23, a sealing cover 3 is fixedly connected to the bottom of the top rod, the sealing cover is driven by the lifting column assembly to vertically lift, a detection table 4 is installed in the middle of the base, and a detection barrel 5 is installed on the detection table 4.

In at least one embodiment, the base is provided with a level 11 and a controller 12; the constant temperature water machine 6 is arranged at the rear part of the left side of the base, and the vacuum pump 7 is arranged at the rear part of the right side of the base.

In at least one embodiment, the lifting column assembly comprises an outer tube 21 and an inner rod 22, wherein the outer tube is fixedly connected to the base, the inner rod is in sliding fit in the outer tube, and the top of the inner rod is connected with a push rod.

The scheme is refined, the lifting column assembly further comprises a driving motor, and the driving motor drives the inner rod to move along the outer pipe.

The lifting mode of the inner rod relative to the outer tube can be one or a combination of a spiral lifting mechanism, a hydraulic lifting mechanism, a chain transmission mechanism or a gear transmission mechanism. For example the outer tube bottom is equipped with driving motor, driving motor is connected with the gear, and sliding fit has the rack on the outer tube is inside, the bar connection has interior pole, the gear cooperatees with the rack, and driving motor drives the gear and rotates, and the gear drives the rack and reciprocates along the outer tube to interior pole reciprocates along the outer tube inner wall, perhaps the outer tube bottom is equipped with a miniature electronic jar, the telescopic link of miniature electronic jar is connected with interior pole, the miniature electronic jar can drive interior pole and remove along the outer tube.

In at least one embodiment, as shown in fig. 3, the detecting cylinder includes a straight cylinder 51, a funnel 52 and a connecting sleeve 53, the funnel is connected with the straight cylinder through the connecting sleeve, the right side of the funnel is internally provided with a first electrode 56 through an internal thread, the connecting sleeve is externally provided with an electric valve 55 through an external thread, and the lower part of the straight cylinder is externally provided with a second electrode 57 through an external thread.

The scheme is refined, and the straight cylinder is provided with a snap ring 54.

The scheme is refined, and the whole detection cylinder is made of 316L materials; the inner wall of the detection cylinder is sprayed with a coating for reducing the friction coefficient; the first electrode and the second electrode keep electrical insulation; the whole detection cylinder can be detached, and the detection cylinder can be configured with a plurality of specifications according to the range of viscosity measurement; the inner wall of the funnel is provided with a scale value with the specification of 50 ml-200 ml; the coating is made of polytetrafluoroethylene.

In at least one embodiment, the inspection table 4 comprises an upper support plate 41, a lower base plate 42 and support rods 43, the upper support plate and the lower base plate are connected through a plurality of support rods, the upper support plate is provided with insertion holes 44, and straight cylinders 51 can be inserted into the insertion holes, wherein the straight cylinders can be clamped in the insertion holes by means of clamping rings.

The vacuum detection platform is characterized in that an evacuation pipe 45 is installed on the lower bottom plate and connected with a vacuum pump through a hose, a vacuum sensor 46 is installed on the upper portion of the evacuation pipe, a sealing ring 48 is arranged on the lower bottom plate, and when the sealing cover vertically falls onto the lower bottom plate, the edge of the sealing cover is inserted into the sealing ring to seal the detection platform. The lower bottom plate is provided with a quick socket 47, the quick socket is connected with the first electrode, the second electrode, the electric valve and the vacuum degree sensor through leads, and the sealing cover can keep vacuum sealing after being tightly pressed with the detection platform. The detection platform is made of 316L materials. The vacuum pump can be one or a combination of a centrifugal vacuum pump, a screw vacuum pump and a roots pump.

As shown in fig. 2, the sealing cover comprises a sealing cover body 32, the sealing cover body is of a double-layer structure and made of 316L materials, constant temperature water is filled in the interlayer, the lower portion of the left side of the sealing cover is a constant temperature water inlet pipe 35, the upper portion of the left side of the sealing cover is a constant temperature water outlet pipe 34, the sealing cover is connected with a constant temperature water machine through a hose, and a temperature sensor is mounted on the constant temperature water outlet pipe and can maintain the temperature in the sealing cover to be constant. The front surface of the sealing cover is provided with a pressure gauge 33 for detecting constant temperature water circulation pressure. The constant temperature water machine has the functions of refrigeration, heating, constant temperature and circulating water.

The upper side of the sealing cover body is provided with a connecting flange 31, and the connecting flange is connected with an ejector rod 23.

The controller 12 is connected with the quick socket, the lifting column assembly, the constant temperature water machine and the vacuum pump through control wires, is provided with a digital-to-analog conversion chip, a timing chip, a temperature measurement chip, a vacuum measurement chip and a liquid crystal display screen, measures and displays a sample viscosity value, a temperature value and a resistivity detection result, and stores detection data for more than 1 year.

The invention also provides a method for detecting the viscosity of the aluminum sol-gel, and the detection principle of the method for detecting the viscosity of the aluminum sol-gel is as follows: the sample in the detection cylinder is detected, on the premise of determining the density, the friction coefficient and the temperature of the liquid, the time of the liquid falling from the detection cylinder is in direct proportion to the viscosity of the liquid, namely the longer the time is, the higher the viscosity is, the time from the beginning of detection to the stop signal is calculated, and the measurement unit is in milliseconds, so that the viscosity of the sample can be accurately represented.

First embodiment

The method for detecting the viscosity of the aluminum sol-gel comprises the following steps:

1) preparing an aluminum sol-gel sample:

the method comprises the steps of measuring 400ml of a sample with the viscosity of 500cps by using a HAAKE Mars rheometer, filling a funnel on the upper part of a detection cylinder with the sample to be measured, wherein the funnel has the specification of 50ml, leveling a protruding part sample by using a scraper with the reference of the lowest liquid level alignment scale of the sample, repeating the operation, filling 5 detection cylinders, and placing the detection cylinders in a sealed incubator at 25 ℃ for measurement.

2) And mounting the detection cylinder with the sample on an upper support plate, and connecting the electrode I, the electrode II, the electric valve and the vacuum degree sensor to the quick socket by using a lead.

3) And pressing a starting button, and automatically executing the detection process by the controller. The process is as follows:

A. an inner rod in the lifting column assembly is operated to descend, and meanwhile, the sealing cover descends until a sealing ring on the detection table is pressed tightly.

B. Starting the constant temperature water machine, starting the vacuum pump at the same time, waiting for the temperature to reach 25 ℃ and the vacuum degree to reach-100 KPa, and keeping the temperature stable.

C. And opening the electric valve, starting timing by the controller, wherein the timing unit is millisecond ms, enabling the sample to flow downwards along the detection cylinder under the action of gravity, forming a passage signal between the first electrode and the second electrode when the sample falls to the bottom of the detection cylinder, triggering the controller to stop timing, and storing data to the controller and displaying the data on the liquid crystal display screen.

D. The time value of the sample is recorded, the above tests are repeated, and the measured values are: 1545ms, 1535ms, 1540ms, 1539ms and 1542ms, and the deviation is between 0 and 10ms, which shows that the viscosity of the sample can be objectively, stably and accurately detected according to the above conditions.

Second embodiment

A method for detecting the viscosity of aluminum sol gel comprises the following steps:

1) preparing an aluminum sol-gel sample:

the method comprises the steps of measuring 400ml of a sample with the viscosity of 500cps by using a HAAKE Mars rheometer, filling a funnel on the upper part of a detection cylinder with the sample to be measured, wherein the funnel has the specification of 50ml, leveling a protruding part sample by using a scraper with the reference of the lowest liquid level alignment scale of the sample, repeating the operation, filling 5 detection cylinders, and placing the detection cylinders in a sealed 35 ℃ incubator to be measured.

2) And mounting the detection cylinder with the sample on an upper support plate, and connecting the electrode I, the electrode II, the electric valve and the vacuum degree sensor to the quick socket by using a lead.

3) And pressing a starting button, and automatically executing the detection process by the controller. The process is as follows:

A. an inner rod in the lifting column assembly is operated to descend, and meanwhile, the sealing cover descends until a sealing ring on the detection table is pressed tightly.

B. Starting the constant temperature water machine, starting the vacuum pump at the same time, waiting for the temperature to reach 35 ℃ and the vacuum degree to reach-100 KPa, and keeping the temperature stable.

C. And opening the electric valve, starting timing by the controller, wherein the timing unit is millisecond ms, enabling the sample to flow downwards along the detection cylinder under the action of gravity, forming a passage signal between the first electrode and the second electrode when the sample falls to the bottom of the detection cylinder, triggering the controller to stop timing, and storing data to the controller and displaying the data on the liquid crystal display screen.

D. The time value of the sample is recorded, the above tests are repeated, and the measured values are: 1473ms, 1481ms, 1475ms, 1470ms and 1476ms, and the deviation is between 0 and 11ms, which shows that the viscosity of the sample can be objectively, stably and accurately detected according to the above conditions.

Third embodiment

A method for detecting the viscosity of aluminum sol gel comprises the following steps:

1) preparing an aluminum sol-gel sample:

using HAAKE Mars rheometer to measure 1200ml of a sample with the viscosity of 1000cps, filling a funnel on the upper part of a detection cylinder with the sample to be measured, wherein the funnel has the specification of 200ml, taking the lowest liquid level of the sample to be aligned with a scale as a standard, strickling the sample on the protruding part by a scraping ruler, repeating the operation, filling 5 detection cylinders, and placing the detection cylinders in a sealed 30 ℃ incubator to be measured.

2) And mounting the detection cylinder with the sample on an upper support plate, and connecting the electrode I, the electrode II, the electric valve and the vacuum degree sensor to the quick socket by using a lead.

3) And pressing a starting button, and automatically executing the detection process by the controller. The process is as follows:

A. an inner rod in the lifting column assembly is operated to descend, and meanwhile, the sealing cover descends until a sealing ring on the detection table is pressed tightly.

B. Starting the constant temperature water machine, starting the vacuum pump at the same time, waiting for the temperature to reach 30 ℃ and the vacuum degree to reach-100 KPa, and keeping the temperature stable.

C. And opening the electric valve, starting timing by the controller, wherein the timing unit is millisecond ms, enabling the sample to flow downwards along the detection cylinder under the action of gravity, forming a passage signal between the first electrode and the second electrode when the sample falls to the bottom of the detection cylinder, triggering the controller to stop timing, and storing data to the controller and displaying the data on the liquid crystal display screen.

D. The time value of the sample is recorded, the above tests are repeated, and the measured values are: 3247ms, 3251ms, 3255ms, 3261ms and 3269ms, and the deviation is between 0 and 22ms, which shows that the viscosity of the sample can be objectively, stably and accurately detected according to the above conditions, compared with the examples 2 and 3, the detection result is integrally increased, the viscosity is visually reflected to be increased, the flow time is prolonged, and the detection value shows a regular increase and a composite theoretical rule.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.