US3844621A

US3844621A - Device for spreading oriented stockings

Info

Publication number: US3844621A
Application number: US00277254A
Authority: US
Inventors: G Tiranov; G Kuligin; K Dzhermakian
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-08-04
Filing date: 1972-08-02
Publication date: 1974-10-29
Anticipated expiration: 1991-10-29
Also published as: DE2238533A1; IT970693B; CS159485B1; DD97616A1; DE2238533B2; FR2148248B1; FR2148248A1; GB1370031A

Abstract

A device comprising a chamber having a dumping bottom, an inlet duct for feeding stockings and an outlet duct to draw off air from the chamber. An arrangement installed inside the chamber near the inlet duct is for catching the end of a stocking, said arrangement representing a strip which is disposed along the walls of the chamber and dividing the air flow into two streams. One of the streams presses the stocking delivered by the flow of the air being drawn off against a retaining baffle which is disposed across the chamber within the space confined by one of the chamber walls and the strip, while the other stream turns the stocking within the space confined by said strip and the other wall of the chamber. This device can be operated in cooperation with an automatic stocking producing machine or with a machine for sewing up the tip of a stocking.

Description

United States Patent Tiranov et al.

DEVICE FOR SPREADING ORIENTED STOCKINGS Inventors: Gennady Petrovich Tiranov, proezd Shokalskogo, 31, korpus 2, kv. 78; Georgy Alexandrovich Kuligin, ulitsa Bolshaya Pochtovaya, 18/20, korpus 10, kv. 41; Karen Jurievich Dzhermakian, ulitsa Taldomskaya, l5, kv. 27, all of Moscow, USSR.

Filed: Aug. 2, 1972 Appl. No.: 277,254

Foreign Application Priority Data Aug. 4, 1971 U.S.S.R 1689976 Feb. 21, 1972 U.S.S.R 1745101 US. Cl. 302/2 R, 214/1 Q Int. Cl. B65g 47/24 Field of Search 198/33 R, 33 AA, 33 AC,

198/33 AD; 214/1 Q, 1 BE, 1 R; 302/2, 2 A

References Cited UNITED STATES PATENTS 2/1969 Sparso et a1. 302/2 Primary Examiner-Frank E. Werner Attorney, Agent, or Firm-Holman & Stern [57] ABSTRACT A device comprising a chamber having a dumping bottom, an inlet duct for feeding stockings-and an outlet duct to draw off air from the chamber. An arrangcment installed inside the chamber near the inlet duct is for catching the end of a stocking, said arrangement representing a strip which is disposed along the walls of the chamber and dividing the air flow into two streams. One of the streams presses the stocking delivered by the flow of the air being drawn off against a retaining baffle which is disposed across the chamber within the space confined by one of the chamber walls and the strip, while the other stream turns the stocking within the space confined by said strip and the other wall of the chamber.

This device can be operated in cooperation with an automatic stocking producing machine or with a machine for sewing up the tip of a stocking.

11 Claims, 13 Drawing Figures DEVICE FOR SPREADING ORIENTED STOCKINGS The present invention relates generally to the production of stockings, and more particularly to devices for spreading oriented stockings.

The stocking industry at present is noted for the ever growing popularity of the containerized stocking production system which requires the incorporation of devices for spreading directed stockings or the like products.

Devices for spreading oriented stockings are known in the art. Incorporated within these devices is a cham ber comprising an inlet and an outlet duct. Installed outside the chamber or at the inlet duct is a photocell sending a signal to the actuating mechanism which cuts off the air flow and opens the bottom of the chamber.

The employment of photocells calls for a special electrical portion of the device, requiring skilled servicing personnel. Due to the fact that the photocellcontrolled light beam is crossed not by a solid body but by a stocking made of for example, capron with its loop structures allowing for the passage of the light beam there through and insignificantly varying its intensity (brightness), this entails the following:

a. a photocell possessing a higher sensitivity;

b. an electrical-signal amplifier having a high amplification factor;

c. most important is that the glass pipe through which a stocking is flying be kept clean because even an insignificant variation in the transparency will cause irregular functioning of the device as a whole. All the above explains the difficulties occurring when photocells are employed either in devices for spreading stockings, or in those for controlling the length of stockings.

Another deficiency of the photocell-employing devices for spreading stockings is associated with the fact that after shutting-off the air flow, the stocking is being moved in the directing chamber only because of the force of inertia and its motion is no longer controlled. To avoid the extensive dispersion of the articles, provision must be made for an air flow having constantvelocity which is achieved by using a separate exhaust blower. This circumstance makes it impossible to connect such devices to a single common air system which for the purpose of reducing microwave noises in the production shop which has its blowers located beyond the limits of the production room. Dispersion of the articles is also observed in handling products which are different in weight (stockings of different size, different length, different yarn, tights), and makes it indispensable to readjust the devices when changing from handling one type of product to another.

Also at the present time devices are known in the art for spreading oriented stockings comprising a chamber with a dumping bottom to discharge straightened articles, an inlet duct to feed the article and an outlet duct to draw-off the air. Installed inside the chamber close to the inlet duct is a mechanical arrangement for gripping the end of the article, which arrangement is mounted on a retaining swivel flap positioned across the chamber and adapted to pass through the air being drawn-off. A safety flap is located at the outlet from the chamber to prevent ejection of an article into the outlet duct.

This device is simpler in design than the device employing the photocell, reveals no extensive dispersion in spreading the directed articles, and requires no spe cial skill from the attending personnel. However, the mechanical arrangement for gripping the end of a stocking is rather sophisticated and calls for programmed control.

This arrangement is made in the form of a mechanical clamp installed at the inlet of the guiding chamber on the retaining swivel flap connected to the programming mechanism. The mechanical clamp includes a fixed jaw and a lever cooperating with two fixed stops fitted with a spring and adapted to occupy either of two fixed positions. The end of a stocking is clamped when the lever is tumbled by the spring from one fixed position to the other and in so doing the lever strikes against the fixed jaw of the clamp. The support surface of the level being small, the mechanical impact on the yarn (especially on that of high count) can damage the latter thus reducing wear resistance of the stocking. The retaining flap swivels to provide room for turning the stocking concurrent with the running air flow which can draw the stocking into the slot formed between the chamber wall and the retaining flap thus causing damage to the stocking or the like.

Stockings possess varying crumpling properties depending on the yarn they are made of, and with various types of automatic stocking machinery they can be delivered to the guiding chamber either with their edge or tip forward, therefore provision is made in the device for a deflecting lever to guide the stocking to the gripping zone thus adding an extra adjustment point in the device. The adjustment is indispensable as the deflecting lever can otherwise impede the normal approach of the stocking toward the clamp, or will not deflect the end of the stocking toward the clamp. In order to put the mechanical clamp into action, it is necessary to start moving it away from the stocking to be gripped which, being forced by the air flow, can be brought to the slot formed when the retaining flap swivels and it is ejected into the chamber, or it can be gripped not by the end but by its middle portion adversely affecting the operation of the device. Besides, the. operating cycle period of the device with the mechanical clamp -is larger as compared to that of the photocellemploying devices because of the following operating stages: gripping of the stocking by the clamp; swivelling of the flap; release of the stocking'from the clamp.

It is therefore an object of the present invention to eliminate the above disadvantages.

The principal object of the present invention is to provide a device for spreading oriented stockings, wherein the arrangement for catching the end of a stocking is simple, reliable in operation and requires no programmed control for turning the stocking.

Another object of the invention is to provide a device for spreading oriented stockings wherein the catching arrangement utilizes the air flow not only for turning the entire stocking but also for catching the end thereof.

Still another object of the invention is to provide a device for spreading oriented stockings wherein the arrangement for gripping the end of a stocking permits an increasing of the capacity of the device atthe expense of a reduction of the operating time cycle per single stocking handled, without affecting the quality thereof.

With these and other objects in view, in a device for spreading oriented stockings, which comprises a chamber with a dumping bottom to discharge spread stockings, an inlet duct for feeding stockings, and an outlet duct for drawing air thereof the chamber, an arrangement located inside the chamber close to the inlet duct to catch the end of a stocking with a retaining baffle installed across the chamber and adapted to pass air being drawn off through said baffle, and a safety baffle installed at the outlet of the chamber to prevent ejection of the stocking into the outlet duct, the catching arrangement, according to the invention, is made in the form of a strip installed along the walls of the chamber and dividing the flow of the air being drawn off into two streams, one of said two streams pressing the end of the stocking against the retaining baffle which is positioned between one wall of the chamber and said strip, and the other air stream for turning the stocking within the space restricted by said strip and the other wall of the chamber, whereas the outlet opening of the inlet duct is so arranged in relation to the retaining baffle that the air flow being drawn off is directed along the chamber wall toward which the retaining baffle is adjacent.

The embodiment of the baffle arrangement in the form of a strip dividing the air flow into two streams re veals a very simple design, and positioning of the retaining baffle being between one of the chamber walls and said strip permits while feeding the stocking being drawn off by the air flow to partially cover the surface of the retaining baffle thus varying the ratio of the air streams passing around the strip at both sides thereof. A partial vacuum is thus created behind the retaining baffle, which forcibly attracts the end of the stocking toward the retaining baffle, i.e. the end of a stocking is gripped without any possible damage to the stocking being handled.

Due to the fact that the strip is installed along the wall of the chamber and the retaining baffle seperating only a portion of the chamber, the other stream of the air flow passing between the strip and the other wall of the chamber turns the stocking within this space and spreads it along the length of the chamber, thus making it unnecessary to rotate the entire arrangement for turning the stocking.

The flow of air being drawn off and directed along the chamber wall to which the retaining baffle is adjacent allows the stocking to be constantly guided towards the retaining baffle irrespective of the weight of the stocking for more reliable batch processing thereof.

Also, the complete elimination of mechanical gripping, turning and releasing of a stocking makes it possible to minimize the period of spreading the stocking in the device which results in a substantial increase in the production capacity of the device.

In accordance with one embodiment of the invention, the inlet duct of the device is installed at an angle with respect to the longitudinal axis of the chamber, while the outlet duct is located near the chamber wall opposite of that to which the retaining baffle is adjacent. With this positioning of the inlet duct, the stocking, under its own momentum upon turning in the air flow, is directed toward the retaining flap.

The invention is further characterized in that the strip is so installed that the chamber is sectionally divided into two unequal portions, the lesser portion accomodating the retaining baffle. This creates most favourable conditions for turning the entire stocking after its end is caught and allows the turning air stream to be made more powerful in relation to the catching air stream.

in accordance with one variant of positioning the strip, said strip is disposed along the entire length of the chamber, thus dividing the chamber into two spaces.

With this positioning of the strip constant air rarefaction is maintained in the space which accomodates the retaining baffle, and the moment when a stocking covers the retaining flap said arrangement makes the catching of the end of the stocking more dependable.

In accordance with another variant of the positioning of the strip, the latter is disposed in the intake portion of the chamber and is made almost twice as long as the retaining baffle.

This arrangement of the strip provides most favourable conditions for utilizing the entire flow of the air being drawn through for attaching the end of a stocking for subsequent turning and spreading the latter along the chamber length without impairing the conditions of the stocking end being caught.

To prevent swirling of the air flow behind the retaining baffle, the latter is, according to the invention, connected to the strip so that the ends of the strip are equally distant from the retaining baffle.

For a more reliable retention of a stocking onto the retaining baffle while turning the stocking by the air steam, the end surface of the strip facing the air stream is, according to the invention, is fitted with an insert made of a frictional material.

Another feature of the present invention is that the retaining baffle is offset in relation to the axis of the inlet duct in the direction of the air flow, thus ensuring a more reliable contact for the stocking upon the retaining baffle.

Another feature of the present invention is that the device is provided with an ejector made in the form of a shaped rod encompassing the strip on the insert side and installed on the dumping bottom for a more efficient discharge of a stocking after it has been spread along the chamber.

Yet another feature of the invention is that the end wall of the chamber near the inlet duct is inclined in relation to the axis of the latter in the direction of the air flow, thus preventing the air flow from swirling along the end wall of the chamber and providing the best possible conditions for directing a stocking toward the retaining baffle.

Still another feature of the invention is that the crosssectional area of the chamber in the zone of the retaining baffle is larger than the crosssectional area of the chamber at the end portion thereof, which enhances the reliability of the turning of a stocking.

Thus, the proposed device for spreading directed stockings is simple in design, reliable in operation and is in high production capacity.

A fuller understanding of the invention may be had from the following description of a presently preferred embodiments thereof with due reference to the accompanying drawings, wherein:

FIG. 1 is a general view, partly broken, of a device for spreading directed stockings according to the present invention;

FIG. 2 is a layout of for the kinematic and the pneumatic connections of the proposed device to the control mechanism of an automatic stocking machine and its stocking delivery pipe;

FIG. 3 is a general view of another embodiment of the device according to the disclosure;

FIG. 4 shows the embodiment of the arrangement for catching the end of the stocking;

FIG. 5 shows one of the usages of the proposed device in cooperation with a stocking tip sewing machine;

FIG. 6 a,b,c,d is the process diagram of the device, according to the invention, shown in FIG. 3',

FIG. 7 a,b,c,d is the process diagram of the device according to the invention, shown in FIG. 1.

The device for spreading directed stockings comprises a box-sectioned chamber 1 (FIG. I) having a dumping bottom 2, an inlet duct 3 for feeding stockings to the chamber and an outlet duct 4 for drawing off air from the chamber 1, said duct being connected to the suction side of a blower 5 (FIG. 2) via a pipe 6.

Positioned inside the chamber 1 close to the inlet duct 3 is an arrangement 7 (FIG. 1) for catching the end of the stocking, which incorporates a retaining baffle 8. Located at the outlet of the chamber 1 is a safety baffle 9 to prevent ejection of the stocking into the outlet duct.

The

baffles

8 and 9 can be made perforated, as shown in FIG. I, or of a bent wire 10, as shown in FIGS.'3 and 4, or of a pipe, which is necessary to pass the air being drawn off therethrough.

The outlet duct 4 (FIG. 1) accomodates a cut-off valve 11 which is used to stop the flow of the air being drawn off from the chamber 1 upon discharging the stocking therefrom.

The dumping bottom 2 is connected to the chamber 1 by means of brackets 12 installed on the chamber 1, with an axle 13 inserted in a hole (not shown) made in these brackets, and hinges 14 secured on the axle 13 and rigidly fixed to the bottom 2. The dumping bottom 2 is provided with a counterweight 15 for retaining the bottom in the initial position, i.e., closing the chamber.

When using the device for spreading stockings in cooperation with an automatic stocking machine, the valve 11 and the bottom 2 are turned by means of a cover 16 of a control drum 17 of the automatic stocking machine through the means of corresponding pull rods 18 and I9,

cables

20 and 21 and levers 22 and 23.

In order to return it to the initial position, the cut-off valve 11 and the dumping bottom 2 are loaded respectively by tension springs 24 and 25. When the device is used in cooperation with an automatic stocking machine, the inlet duct 3 of the chamber 1 is connected to a stocking delivery pipe 26 of the machine.

In case the proposed device is installed on a table 27 (FIG. 5) of a stocking tip sewing machine, the cut-off valve 12 is actuated by a turn pipe 29 mounted on an axle 28 through a pull rod 30, while the dumping bottom is actuated by means of a pneumatic cylinder 31. The turn pipe 29 is adapted for periodic coupling with the inlet duct 3 of the chamber 1 and conveying therethrough a stocking from the sewing machine and can be also utilized as a means for single or double turning out the stocking.

The arrangement 7 (FIG. I) for catching the end of a stocking represents a strip 32 installed vertically along walls 33 and 34 of the chamber 1 so that the chamber is sectionally divided into two unequal portions 35 and 36 (FIG. 6). The smaller portion 35 is formed by the wall 33 of the chamber and the strip 32 and accomodated the retaining baffle 8.

When air is being drawn off from the chamber, the strip 32 divides the air flow into two streams A and B, the stream A passing via the portion 35, while the other stream B passes via the chamber portion 36 confined by the strip 32 and the wall 34 of the chamber 1.

When a stocking is brought into the chamber at the moment of drawing off the air from said chamber, one end of the stocking is carried by the stream A into the portion 35 wherein it is retained by the baffle 8, while the other air stream B turns the stocking within the space of the chamber portion 36 and spreads it lengthwise along the chamber 1.

In order to carry a stocking via the air stream A onto the retaining baffle 8, the inlet duct 3 is positioned at an angle close to in relation to the longitudinal axis 0-0 the chamber, whereas an outlet opening 37 of the duct 3 is disposed opposite to the chamber wall 33 to which the retaining baffle 8 is adjoined, thus the flow of the air being drawn off is directed along said latter wall to ensure reliable conveyance of the stocking to the baffle 8.

The strip 32 can be disposed along the entire length of the chamber to divide the latter into two equal spaces 38 and 39 (FIG. 7), the smaller portion 38 accomodating the retaining baffle 8 and when the latter is covered by a stocking, partial vacuum is maintained in said space due to which the stocking is held on the retaining baffle 8, while, within the space 39, the entire stocking is carried and turned by the air stream B passing through said space, the latter accomodating the safety baffle 9 and a valve 40 (FIG. 1) which is used to regulate the air flow through the space 39.

The strip 32 (FIG. 6) can be installed in the front portion of the chamber 1 as well and in this respect we have found that the strip should be almost twice as long as the retaining baffle 8, and if this condition is ob served, almost all of the air flow drawn from the chamber 1, upon covering the retaining baffle 8 by a stocking, will pass through the portion 36 of the chamber, resulting in the quick turning of the stocking therein and spreading of the latter lengthwise along the chamber.

The retaining baffle 8 is secured to the strip 32 in such a way that the ends of the strip are equidistant from the retaining baffle 8, Le. the retaining baffle 8 and the strip 32 form a T in design, however the strip and the baffle can be connected otherwise to form an L in design, but the experiments have revealed that the most favourable conditions for catching the end of a stocking and for turning the stocking in the space are provided by a T-shaped arrangement of the baffle 8 and the strip 32.

For a more reliable conveyance of a stocking to the retaining baffle 8, the latter is offset in relation to the axis O,--0 of the inlet duct in the direction of the air flow, while an end wall 41 of the chamber 1 is inclined in relation to the axis 0 0, of the inlet duct 3 and also in the direction of the air flow being drawn therethrough.

For a more reliable holding of a stocking on the baffle 8 while the stocking is turning and running about the strip 32, the end portion of the latter on the side facing the air flow 4 is fitted with an insert 42 (FIG. 4) made of a friction bearing material such as rubber.

For a more reliable discharge of a stocking from the chamber upon having been spread, the device is provided with a stocking ejector made in the form of a shaped rod 43 (FIG. 1) which is bent round the strip 32 on the side of the position the insert 42 and is rigidly fixed to the dumping bottom 2.

The chamber 1 is narrower toward its end (FIGS. 3 and 6), and therefore the cross-sectional area of the chamber in the zone of the position of the retaining baffle 8 is larger than the crosssectional area of the chamber at its end, thus ensuring a more reliable turning of a stocking within the space of the portion 36 of the chamber 1.

The device for spreading oriented stockings operates as follows.

A stocking 44 (FIG. 2) coming off the automatic stocking machine is taken by the air being drawn off by the blower 5 into the delivery pipe 26 and the inlet duct 3 and at a high velocity is brought into the chamber 1. The inlet duct 3 is disposed at an angle close to 90 in relation to the axis 0---() of the chamber, while the outlet opening 37 (FIG. 6) of the duct is disposed opposite to the wall 33 to which the retaining baffle 8 is adjoined, therefore the induced air flow deflected by the end wall 41 of the chamber is directed along the chamber, whereas the stocking overcomes the deviating effort of the air flow under its own momentum and runs with its tip or edge onto the retaining baffle 8, but as the automatic stocking machine produce stockings starting either from the tip, or the edge, the stockings are delivered into the chamber in one position, i.e., the stockings are already directed.

As the front part of the chamber 1 incorporates the strip 32, the latter divides the air flow into two streams A and B and the stream B passes through the space 36 of the chamber, while the stream A passes through the retaining baffle 8 disposed in the space 35 of the chamber and presses the end of the stocking to said baffle, thus partly covering the surface thereof. This latter action changes the ratio of the air streams A and B which results in the intensification of the stream B which, as is shown in FIG. 6a, starts turning the stocking 44 until it is completely spread out and positioned along the chamber 1 (FIG. 60). During this period, partial vacuum is maintained behind the retaining baffle 8 and due to the effect thereof the end of the stocking is held fast on the baffle 8. The insert 42 also aids in holding of the stocking reliably the baffle 8.

After the stocking 44 has been completely spread out, the cover 16 (FIG. 2) of the control drum l7 first cooperates with the pull rod 18 and then with the pull rod 19 and through the medium of the

cables

20 and 21 and the

levers

22 and 23 and firstly turns the cut-off valve 21 to close the outlet duct 4 and discontinues the drawing off of the air from the chamber 1 and the inlet duct 3, then it opens the bottom 2.

The spread out stocking 44 drops into a container 45 (FIG. 6d) placed under the chamber 1 and the shaped rod 13 (FIG. 1) being displaced at the same time as the bottom 2 is opened and contributes to a quick release of the end of the stocking from the retaining baffle 8 and accordingly assists in uniformly laying the stocking in the container 45.

Catching, turning, spreading and dropping the stocking from the chamber are effected in a similar way when the chamber 1 is divided into two

spaces

38 and 39, as shown in FIG. 7a,b,c,d, and in this case turning and spreading the stocking take place in the space 39.

Upon completion of the above, the dumping bottom 2 (FIG. 2) and the cut-off valve 11 are returned to the initial position by the

springs

24 and 25 respectively. Another stocking then comes off the automatic stocking machine and is delivered to the described device for spreading.

When the proposed device is operated in cooperation with a sewing machine used for sewing up the tip. the inlet duct 3 is periodically connected to the bent pipe 29 through which the stocking 44 with the sewn tip is conveyed to the chamber wherein catching, turning and spreading of the stocking are effected similarly to the procedures as described above and as illustrated in FIGS. 6 a,b,c,d and 7 a,b,c,d.

What is claimed is:

1. A device for spreading oriented stockings comprising a chamber having an end and side walls; a dumping bottom provided in said chamber to discharge the spreaded stockings therefrom; an inlet duct provided for this chamber to deliver stockings thereinto through the outlet openings of said duct; an outlet duct provided for the chamber for drawing off air from said chamber and the inlet duct; an arrangement for catching the end of a stocking positioned close to said inlet duct and made in the form of a strip disposed along said walls of the chamber of said strip to divide the air flow being drawn off into two streams; a retaining baffle installed across said chamber near the inlet duct between said strip and one of the walls of said chamber and which is adapted to pass air therethrough and through which is passing one of said streams of the air being drawn off, said stream pressing one end of the stocking against said baffle; another stream turning the stocking inside the space confined by said strip and the other side wall of said chamber; a safety baffle installed at the outlet of said chamber to prevent ejection of the stocking into said outlet duct; said outlet opening of the inlet duct is so disposed in relation to said retaining baffle that the flow of the air being drawn through is directed along the wall to which the retaining baffle is adjoined; and a means for drawing off air from said ducts and chamber.

2. A device as claimed in claim 1 wherein the inlet duct is positioned at an angle with respect to the longitudinal axis of the chamber, while the inlet opening of said duct is located opposite to the chamber wall with respect to which the retaining baffle is adjoined.

3. A device as claimed in claim 2 wherein the retaining baffle is offset in relation to the axis of the inlet duct and in the direction of the air flow.

4. A device as claimed in claim 2 wherein the end wall of the chamber at the inlet duct is inclined in relation to the axis of said duct and of the direction of the air flow being drawn off.

5. A device as claimed in claim 1 wherein the strip is installed in such a way that the chamber is sectionally divided into two unequal portions, the smaller portion incorporating the retaining baffle.

6. A device as claimed in claim 5 wherein the strip is disposed along the entire length of the chamber and divides the latter into two spaces.

7. A device as claimed in claim wherein the strip is installed in the front portion of the chamber and is made almost twice as long as the retaining baffle.

8. A device as claimed in claim 7 wherein the retaining baffle and the strip are so connected that the ends of the latter are equidistant from the retaining baffle 9. A device as claimed in claim 1 wherein the end portion of the strip facing the air flow is provided with an insert made of a friction material zone of the safety baffle.

Claims

7. A device as claimed in claim 5 wherein the strip is installed in the front portion of the chamber and is made almost twice as long as the retaining baffle.

8. A device as claimed in claim 7 wherein the retaining baffle and the strip are so connected that the ends of the latter are equidistant from the retaining baffle.

9. A device as claimed in claim 1 wherein the end portion of the strip facing the air flow is provided with an insert made of a friction material.

10. A device as claimed in claim 9 wherein provision is made for a stocking ejector which is made in the form of a shaped rod encompassing the strip on the side of positioning the insert and is mounted on the dumping bottom.

11. A device as claimed in claim 1 wherein the cross-sectional area of the chamber in the zone of the retaining baffle is larger than the cross-sectional area in the zone of the safety baffle.