MOVING WEB STRIPS

Field of Invention:

The present invention relates to manufacturing of thermo-plastic products like monofilament, plastic web strips, narrow film strip, multi-filament, in particular to a hot air circulating chamber with air-flow control system.

Background of invention:

Various thermoplastic objects having a very high length to width ratio, during manufacturing undergo thermal treatment using known apparatuses like hot plate or hot air oven. These thermoplastic objects could be in form of monofilaments, narrow web strips, multi-filaments and other webs of plastics.

A typical apparatus for thermal treatment of moving web strips is a conventional hot air oven (see Figure 1) which consists of an upper chamber and a lower chamber which are interconnected by hinges along one edge of the chambers. Each chamber has an insulated body in which the fan with desired volute is installed. The airflow guiding casing (not shown) forms the suction inlet and outlet for each fan. On closure of both chambers, a hot-air channel is formed (at the interface of the chambers). The hot-air channel receives hot air from the chambers through inlet port(s) provided in the chambers at one end (the inlet end) of the channel. The air from the hot-air channel is leaves the channel and re-enters the chambers through the outlet port(s) provided in the chambers at the other end (the outlet end) of the channel. On the suction inlet casing path (not shown), set of heater are installed enabling the suction of hot air of desired temperature by the fan. The hot air which is been blown by the fan is guided through flow guide channel and an air-flow control lever. The amount of hot air inflow at hot air oven inlet section is controlled by this individual flapper position.

As it can be seen from the schematic given for the conventional system, it is not really possible to control of temperature and the air-flow in the hot air channel/chamber to achieve uniformity across the channel. Further, it should be noted that the air-flow in the hot air channel gets disturbed with the introduction of rapidly moving endless web strips, from inlet end to outlet end of chamber. It is also noted that in the conventional ovens, there is no provision of controlling airflow at multiple location nor there is provision for monitoring of the temperature at various points of the hot air channel. Therefore, the airflow and temperature regime throughout the hot air channel may not be uniform and may adversely affect the quality of the stretched strips.

The hot air channel is provided to aid the stretching of tapes/strips made from thermoplastic material from which a woven fabric is made. During the stretching process, the group of web strips is passed through the hot air channel in order to achieve the required mechanical properties of the stretched strips. With the advancement in application areas of end product, there are ever more stringent requirements on the product uniformity both across the width of hot air channel and along the length the end product. This normally translates into a need for a better control over the process parameters during the manufacturing process. Further, with the increase in the production speed and stringent requirements of end product, there is requirement for improvement in air-flow uniformity and temperature precision in the hot air oven.

Objects of Invention:

The main object of this invention is to provide and apparatus and a method for thermal treatment of moving web strips such that the thermal treatment is uniform throughout the hot-air channel which forms a part of the apparatus.

Another object of the invention is to ensure that air flow is uniform across the width and length of hot air channel. Yet another object is to provide uniform temperature in the hot air channel with precision control.

A further object is to provide ability to control air flow in the hot air in the chamber ducts independently.

A further object is to provide ability to control the air flow in different parts of the hot air channel separately. Summary Of Invention:

The present invention relates a hot air circulating chamber with air-flow control system used in manufacture of thermo-plastic products such as monofilament, plastic web strips, narrow film strip, multi-filament. Conventional systems do not allow controlling temperature and air-flow in hot air channel/chamber to achieve uniformity. With the increased production speed and stringent product requirements, improved air-flow uniformity and temperature precision in the hot air oven is necessary. Invention discloses an apparatus (1) provided with air-flow path having provision of number of fans (7), optimisation of heater (6) location and increased number of air-flow regulators (8) having control levers (9).

Moving web strips (5) enter apparatus into a hot air channel (4) formed between upper chamber (2) and lower chamber (3). Entry point of moving strips into the hot air channel (4) is the web-strip inlet (5 A). After getting heat treated, the moving web strips (5) leave the apparatus through the web strip outlet (5B).

Brief Description Of Figures:

Figures 1 and 1 A show a conventional apparatus for thermal treatment of moving web strips

Figure 2 shows the apparatus of the invention in its longitudinal view

Figure 2A shows the apparatus of the invention in its cross sectional view

Figure 3 shows a cross sectional view of an embodiment of the apparatus of the invention having a plurality of ducts in upper and lower chambers List of Parts:

1 - Hot air oven 10 6 - Heater

2 - Upper chamber 7 - Fan

3 - Lower chamber 8 - Air flow regulator

4 - Hot-air channel 9 - Lever (or control lever)

5 - Web strip 10 - Air Inlet

5 A - Web strip inlet 15 11 - Air Outlet

5B - Web strip outlet 12 - Hinge

Description of Invention:

As discussed previously, the conventional hot air oven, as shown in figure 1, has an upper chamber and a lower chamber. Further, each chamber has an insulated body in which the fan with desired volute is installed. The airflow guiding casing (not shown) forms the suction inlet and outlet for each fan. On the suction inlet casing path (not shown), set of heater are installed enabling the suction of hot air of desired temperature by the fan. The hot air which is been blown by the fan is guided through flow guide channel and an air-flow control lever. The amount of hot air inflow at hot air oven inlet section is controlled by this individual flapper position.

As discussed earlier, the conventional ovens (see Figures 1 and 1A) do not allow uniform control over the temperature and airflow in general in the hot air channel. As we have also noted, the air-flow in the hot air channel gets disturbed with the introduction of rapidly moving endless web strips, from inlet end to outlet end of chamber. It is noted that in the conventional ovens, there is no provision of controlling airflow at multiple location nor there is provision for monitoring of the temperature at various points of the hot air channel. Therefore, the airflow and temperature regime throughout the hot air channel may not be uniform and may adversely affect the quality of the stretched strips.

To resolve the above referred issues in conventional hot air oven, the invention discloses an apparatus (1) (or hot air oven) of thermal treatment of moving web strips (5). As shown in Figure 2, the apparatus (1) is provided with an air-flow path which has a provision of a number of fans (7), optimisation of heater (6) location and increased number of air-flow regulators (8) or control points provided with levers (9). An air flow regulator has a mechanism such as flaps or fins whose angle may be adjusted using the level (9) to adjust the airflow passing through the regulator (8).

In one aspect of the invention, a single lever may control more than one regulator (8)·

The moving web strips (5) enter the apparatus into a hot air channel (4) that is formed between an upper chamber and a lower chamber. The entry point of the moving chambers into the hot air channel (4) is the web strip inlet (5A). After getting heat treated, the moving web strips (5) leave the apparatus through the web strip outlet (5B).

As shown in Figure 3, as a preferred embodiment, thermal apparatus of the invention, the upper chamber (2) and the lower chamber (3) was further compartmentalised into multiple ducts (2a and 3a) depending on overall working width of hot air oven (1). The upper and lower chambers may be divided into multiple ducts. At least one fan (7) and heater (6) set are provided in each of the ducts (2a and 3a). However, the construction of upper chamber (1) and lower chamber (2) is similar and preferably but not necessarily has same number of ducts (2a and 3a). Each duct has an air blowing fan (7), a heater (6) set and a single air-flow regulator (8) that opens into the hot-air channel.

According to the invention, each duct (2a and 3a) has specifically designed airflow path with individual fan/blower (7) having heater (6) set arranged adjacent to blower impeller, minimising the heat loss. Further, the hot-air from the upper and lower chambers (2, 3) is let out into the channel (4) through more than one air outlets (10) arranged sequentially along the length near the web strip inlet zone of the apparatus. Also, an air inlet (11) is provided at the web strip outlet (5 B) end of each of the compartments (2, 3) to introduce the circulated hot air from the channel back into the ducts (2a, 3a). Further, each air outlet (10) provided to send hot air from the chamber s/ducts into the hot-air channel (4) has individual flow regulator(s) (8) provided with levers (9), giving more controlled air-flow as per the design requirement of apparatus.

The upper chamber and bottom chamber (2, 3) are connected on any one longitudinal side by a hinged system, preferably operated by pneumatic mechanism, for ease of opening of the hot air oven, for the threading of group or individual web strips (5), through the hot air channel (4). During the working of hot air oven, the upper chamber (2) comes down over bottom chamber (3) and a hot air channel (4) is formed. The hot air channel (4) is thus closed or sealed on its sides (in the direction of the moving strips (5)). The hot air channel (4) extends between the air-outlet (10) and air-inlet (11) arranged at respective opposite ends of the hot-air channel (4).

As the hot air introduced into the channel (4) travels through the length of the channel from the web strip inlet (5 A) towards web strip outlet (5B), it loses heat and cools down. Once the cooled air is reintroduced from the channel (4) back into the chambers (2, 3), it is heated up by the heater/fan blower set. The heated air travels down the length of the chambers (2, 3) towards the web strip inlet end (5 A) where it is once again introduced into the channel (4) through the air inlet(s) (11). The heating and cooling cycle of the air thus continues.

The air-outlet (10) end has provision of more than one air flow regulator (8) for each duct (2a, 3a) or chamber (2, 3), with the help of which the air flow through the individual outlet (10) ports (provided at the air-inlet end of the hot-air channel(4)) into the hot-air channel (4) is regulated. The airflow levers (9) are adjustable with at least one operational positions whereby the amount of air passing through air flow regulators (8) is adjustable. Through the adjustable positioning of airflow levers (9) provided in the air-flow regulators (8), the required amount/velocity of air flow into the hot-air channel (4) is controlled. Individual air flow regulator (8) has a number of positional settings that are adjustable using the levers (9) which enables repeatability of process. Further, as the heater(s) (6) in the ducts/chambers (2, 3) are arranged in close proximity of the corresponding fans (7), more precise controlling of temperature is achieved. The multiple air duct and multiple air flow regulators ensures a pressure equalization and more uniform air flow in the hot-air channel. The overall insulation of each chamber further ensures effective energy utilisation.

In a preferred embodiment of the invention, sensors (not shown) for monitoring of the temperature at various points of the hot air channel (4) are provided. The temperature and the speed of the airflow into the channel (4) through the outlet ports (10) depend on the denier and speed of tapes, and final product requirement. Since this may vary greatly depending on the end user requirements, provision of multiple outlet ports (10) is an important feature of the present invention.

In another preferred embodiment, airflow sensors (not shown) are provided to sense and measure airflow speed in the hot air channel. The position of airflow regulators (8) is adjusted to control the air flow passing through the regulators (8) depending on the data obtained from the temperature and airflow sensors.

The invention also provides a method for thermal treatment of moving web-strips using the apparatus disclosed herein. The method comprises the step of adjusting the temperature and the speed of the air in the ducts (2a, 3a) of the chambers (2, 3) depending on the known parameters such as the denier of the tapes and the speed of their travel through the channel (4) so that air of required temperature and speed is released from the chambers through the outlet ports (10) into the hot air channel (4).

It is evident from the foregoing discussion that the invention has a number of embodiments. The preferred embodiment discloses an apparatus for thermal treatment of moving web strips, said apparatus comprising an upper chamber (2) and a lower chamber (3), with a channel (4) situated between said two chambers to carry hot air from the web strip inlet (5 A) to the web strip outlet (5B) during which travel said hot air cools down, and through which channel (4) said moving web strips (5) travel in longitudinal direction, characterised in that each of said chambers (2, 3) have at least one separate air outlet (10) and a separate air inlet (11), said at least one air outlet to bring said hot air from said chambers (2, 3) into said channel (4), and said air inlet (11) to take air which cools down upon its travel through said channel (4) back into said chambers (2, 3), and wherein each of said inlets (10) is provided with at least one individual air-flow regulator (8) having operational levers (9), further wherein each of said chambers (2, 3) have at least one heater (6) and a fan (7) near the web strip outlet (5B) to heat up the cooled air for further circulation.

In one aspect of the invention, a single lever (9) may control more than one air flow regulator (8). In another aspect of the invention, the chambers (2, 3) are divided into individual ducts (2a, 3a).

In a further aspect of the invention, each of said ducts (2a, 3a) are provided with each of at least one heater (6), at least one fan (7) and at least one flow regulator (8) having an operational lever (9).

In a still further aspect of the invention, the number of ducts (2a) in the upper chamber (2) and the number of ducts (3a) in the lower chamber (3) are same. In another aspect of the invention, the fan (7) and heater (6) are mounted adjacent to each other. In yet another aspect of the invention, there may be more than one air outlet (10) for each of the chambers (2, 3) or ducts (2a, 3a).

In still another aspect of the invention, the upper chamber (2), and the lower chamber (3) are connected by at least one hinge (12) on any one longitudinal side of said apparatus.

In a further aspect of the invention, the operational leavers (9) are adjustable with at least one operational position whereby the velocity (or speed) of air passing through air flow regulators (8) is adjustable.

In a still further aspect of the invention, the fan (7) and heater (6) are located near the air inlet (11) end of said chambers (2, 3). In another aspect of the invention, the channel (4) is provided with temperature measurement and monitoring sensors. The channel (4) is also provided with airflow speed measurement and monitoring sensors.

In a further aspect of the invention, temperature and speed of the air released into channel (4) is controlled on the basis of denier and speed of the moving strips (5) and the final product requirement. In another aspect of the invention, a method of treatment of moving web strips (5) is disclosed comprising the steps of:

providing the apparatus as claimed in any of claims 1 to 12, and heating air to the required temperature inside chambers (2, 3) - releasing airflow at required speed from said chambers (2, 3) into said channel (4) through said air flow regulators (8), using control levers

(9).

The following example illustrates the manner in which the invention is used. Tapes or a film of 1000 denier was passed through the oven made according to the invention. The upper compartment of the oven comprised two ducts and the lower compartment comprised two ducts. The set temperature of the oven was 160 °C. The tapes travelled at a speed of 8 m/s. The airflow velocity was set at 10 to 11 m/s using five individual airflow regulators in each of the ducts. Temperature of the tapes was measured at various locations across the width of the oven at randomly chosen location along its length. It was found that the variation of the temperature of the tapes from the set temperature was between -0.25% and 1.88%. This is much lower than the variation of 0.44% to 3.6% which was experienced using a conventional oven. This represents nearly 100% reduction in variation of temperature as compared with the tapes treated using conventional ovens.

While the above description contains much specificity, these should not be construed as limitation in the scope of the invention, but rather as an exemplification of the preferred embodiments thereof. It must be realized that modifications and variations are possible based on the disclosure given above without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.