GB1593162A

GB1593162A - Continuous flow screen changer

Info

Publication number: GB1593162A
Application number: GB21856/77A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-05-26
Filing date: 1978-05-26
Publication date: 1981-07-15

Description

(54) CONTINUOUS FLOW SCREEN CHANGER (71) We, C. E. POYNTER LIMITED, a British Company, of Equipoise House, Grove Place, Bedford (formerly of Hardwick Hill Works, Ampthill Road, Kempston Hardwick, Bedford), do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state menu: This invention is concerned with continuous flow screen changers and has for an object to provide for the changing of screens without interrupting the flow of material or allowing the introduction of air or impurities into the system.

It is particularly advantageous in the plastics industry for incorporation in the lines supplying plastics material for film blowing, sheet lines, stranding and filament production and the like and will for convenience be described hereinafter in relation to its use in connection with plastics. It will be understood however that the invention is not restricted to such use but is applicable to any process in which it is necessary to maintain a continuous flow of material through screens whilst the screens are being changed without risk of introducing impurities such as air into the system.

Screen changers are known in which there are alternative passages for the flow of material and breaker plates supporting a screen or filter are slideable across the passages so as to bring the screen into alignment with the passage or to withdraw the screen for cleaning or replacement whilst closing the passage against the flow of material.

According to the present invention there is provided a continuous flow screen changer comprising a body having an inlet and an outlet a sealing plate mounted in said body providing two passages connecting the inlet and the outlet two breaker plates mounted between the sealing plate and the outlet, one breaker plate being associated with each passage, said breaker plates each having a screen supporting portion and an imperforate portion and each being arranged to be independently movable transverse to its passage between two positions, one position where flow can take place through the respective passage and screen and another position where flow is prevented by the imperforate portion.

The sealing plate preferably is secured in the body by an adjustable screwed ring and presses the breaker plates against an abutment on the outlet side or preferably against a thrust block formed with passages similar to those in the sealing plate.

The area of the inlet to the sealing plate preferably is greater than the total area of the openings of the two passages so that in use there is a hydrostatic pressure within the system which effectively seals the changer against egress of plastics. When one of these passages is closed, this pressure increases so that sealing is maintained during screen changing.

Other parts of the invention are embodied in the preferred form which will now be described in some detail with reference to the drawings accompanying in the Provisional Specification in which: Fig. 1 is a diagrammatic section of a continuous flow screen chamber; Fig. 2 is a section on the line IIII of Fig.

1; Fig. 3 is a section on the line Ill-Ill of Fig. 2.

As shown diagrammatically in Fig. 1, a continuous flow screen changer comprises a body 1 having an inlet 2 and outlet 3 between which are mounted two breaker plates 4.

Each breaker plate 4 is slidable transversely across the path between the inlet 2 and outlet 3 and each has a flow passage 5 therethrough housing a screen 6.

The breaker plates 4 are sandwiched between a sealing plate 7 on the inlet side and a thrust block 8 on the outlet side. Close abutting relationship between the sealing plate, the breaker plates and the thrust block is obtained initially by means of a threaded ring 9 pressing the plate 7 so that the thrust block 8 is urged against an abutment 10 in the housing.

The construction of the sealing plate 7 which is shown in Figs. 2 and 3 is particularly important. The sealing plate is formed with an inlet 11 which is aligned with the inlet 2 of the screen changer. Two passages 12 diverge from the inlet 11 to open on the face 13 abutting the breaker plates 4 at locations in diagonally opposite quadrants of that face.

The opening 14 of each passage 12 is entirely within the quadrant in which it is located. In other words, the openings 14 of the passages 12 lie entirely on opposite sides of the line AA dividing the two breaker plates and also entirely on opposite sides of a line BB at right angles to the direction of movement of the breaker plates. It should be noted here that in Fig. 1, the passages are not shown in their correct positions to avoid complication of this diagrammatic view.

Passages 15 similar to the passages 12 are provided in the thrust block 8 leading from the downstream side of the breaker plates to the outlet from the screen chamber. The openings of these passages 15 are aligned with the openings 14 so that when the breaker plates are positioned with the screen aligned with the openings alternate passages are provided for the flow of material.

During normal operations, both breaker plates are in position to allow fluid flow through them. The area A3 adjacent the inlet 11 of the sealing plate 7 is arranged to be greater than the total area A, + A2 of the two openings 14 so that at all times when material is flowing, a hydrostatic pressure is set up which, since the plastics pressure is higher than atmosphere, prevents any egress of the plastics between the abutting faces of the sealing plate and the breaker plates.

When it is desired to change or clean a screen, the breaker plate containing that screen is slid lenghthwise so that an imperforate portion thereof seals the relevant passage 12 so that the screen comes outside the changer and is available for treatment.

Flow of material continues through the other screen. After treatment, the breaker plate with the clean screen is returned to its original position. As soon as the screen begins to overlap the opening 14 material will begin to flow into the breaker plate expelling air and filling the breaker plate with the material. When the breaker plate is filled with material, as will be evidenced by a slight seepage of the material from grooves 17, the breaker plate can be returned finally to the full flow position.

The passages 12 may be of any crosssection corresponding to the shape of the screens. As shown, the passages 12 are circular in section. This would mean that the opening at the face adjacent the breaker plates would be elliptical and, to secure a circular opening, a conical boring is provided. This cone is of base diameter equal to the major axis of the ellipse, its axis is at right angles to the face of the sealing plate 7. The inlet to the passages is also conical, so that a smooth flow of material through either or both passages is provided.

The sealing plate is provided with passages 16 to receive means such as cartridge heaters for heating the material and maintaining it molten whilst a screen is being changed and whilst in operation. Each passage 16 extends across a quadrant of the sealing plate in which there is no opening to the breaker plates so that material in the closed passage is heated. Plate heaters may be provided at the top and bottom of the body. The breaker plates may be moved manually by means of a handwheel or by hydraulic cylinders, air motors or the like.

WHAT WE CLAIM IS: I. A continuous flow screen changer comprising a body having an inlet and an outlet, a sealing plate mounted in said body providing two passages connecting the inlet and the outlet two breaker plates mounted between the sealing plate and the outlet, one breaker plate being associated with each passage said breaker plates each having a screen supporting portion and an imperforate portion and each being arranged to be independently movable transverse to its passage between two positions, one position where flow can take place through the respective passage and screen and another position where flow is prevented by the imperforate portion.

2. A continuous flow screen changer according to Claim 1, in which said breaker plates are arranged to move in opposite directions to one another when moving between their respective two positions.

3. A continuous flow screen changer as claimed in Claim 1 or 2, in which the sealing plate is secured in the body by an adjustable screwed ring and presses the breaker plates against an abutment on the outlet side of the body.

4. A continuous flow screen changer as claimed in Claims 1 to 3, in which the breaker plates abut against a thrust block formed with passages similar to those in the sealing plate.

5. A continuous flow screen changer as claimed in any of the preceding Claims, in which the area of the inlet to the sealing plate is greater than the total area of the openings of two passages therethrough, whereby in use there is a hydrostatic pressure within the system which effectively seals the changer against egress of plastics.

6. A continuous flow screen changer as claimed in any of the preceding claims, in which the outlets from the passages in the sealing plate are of circular section to complement the shape of circular screen supporting portions in the breaker plates.

7. A continuous flow screen changer as

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Claims

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which is shown in Figs. 2 and 3 is particularly important. The sealing plate is formed with an inlet 11 which is aligned with the inlet 2 of the screen changer. Two passages 12 diverge from the inlet 11 to open on the face 13 abutting the breaker plates 4 at locations in diagonally opposite quadrants of that face.

The opening 14 of each passage 12 is entirely within the quadrant in which it is located. In other words, the openings 14 of the passages 12 lie entirely on opposite sides of the line AA dividing the two breaker plates and also entirely on opposite sides of a line BB at right angles to the direction of movement of the breaker plates. It should be noted here that in Fig. 1, the passages are not shown in their correct positions to avoid complication of this diagrammatic view.

Passages 15 similar to the passages 12 are provided in the thrust block 8 leading from the downstream side of the breaker plates to the outlet from the screen chamber. The openings of these passages 15 are aligned with the openings 14 so that when the breaker plates are positioned with the screen aligned with the openings alternate passages are provided for the flow of material.

During normal operations, both breaker plates are in position to allow fluid flow through them. The area A3 adjacent the inlet 11 of the sealing plate 7 is arranged to be greater than the total area A, + A2 of the two openings 14 so that at all times when material is flowing, a hydrostatic pressure is set up which, since the plastics pressure is higher than atmosphere, prevents any egress of the plastics between the abutting faces of the sealing plate and the breaker plates.

When it is desired to change or clean a screen, the breaker plate containing that screen is slid lenghthwise so that an imperforate portion thereof seals the relevant passage 12 so that the screen comes outside the changer and is available for treatment.

Flow of material continues through the other screen. After treatment, the breaker plate with the clean screen is returned to its original position. As soon as the screen begins to overlap the opening 14 material will begin to flow into the breaker plate expelling air and filling the breaker plate with the material. When the breaker plate is filled with material, as will be evidenced by a slight seepage of the material from grooves 17, the breaker plate can be returned finally to the full flow position.

The passages 12 may be of any crosssection corresponding to the shape of the screens. As shown, the passages 12 are circular in section. This would mean that the opening at the face adjacent the breaker plates would be elliptical and, to secure a circular opening, a conical boring is provided. This cone is of base diameter equal to the major axis of the ellipse, its axis is at right angles to the face of the sealing plate 7. The inlet to the passages is also conical, so that a smooth flow of material through either or both passages is provided.

The sealing plate is provided with passages 16 to receive means such as cartridge heaters for heating the material and maintaining it molten whilst a screen is being changed and whilst in operation. Each passage 16 extends across a quadrant of the sealing plate in which there is no opening to the breaker plates so that material in the closed passage is heated. Plate heaters may be provided at the top and bottom of the body. The breaker plates may be moved manually by means of a handwheel or by hydraulic cylinders, air motors or the like.

WHAT WE CLAIM IS: I. A continuous flow screen changer comprising a body having an inlet and an outlet, a sealing plate mounted in said body providing two passages connecting the inlet and the outlet two breaker plates mounted between the sealing plate and the outlet, one breaker plate being associated with each passage said breaker plates each having a screen supporting portion and an imperforate portion and each being arranged to be independently movable transverse to its passage between two positions, one position where flow can take place through the respective passage and screen and another position where flow is prevented by the imperforate portion.
2. A continuous flow screen changer according to Claim 1, in which said breaker plates are arranged to move in opposite directions to one another when moving between their respective two positions.
3. A continuous flow screen changer as claimed in Claim 1 or 2, in which the sealing plate is secured in the body by an adjustable screwed ring and presses the breaker plates against an abutment on the outlet side of the body.
4. A continuous flow screen changer as claimed in Claims 1 to 3, in which the breaker plates abut against a thrust block formed with passages similar to those in the sealing plate.
5. A continuous flow screen changer as claimed in any of the preceding Claims, in which the area of the inlet to the sealing plate is greater than the total area of the openings of two passages therethrough, whereby in use there is a hydrostatic pressure within the system which effectively seals the changer against egress of plastics.
6. A continuous flow screen changer as claimed in any of the preceding claims, in which the outlets from the passages in the sealing plate are of circular section to complement the shape of circular screen supporting portions in the breaker plates.
7. A continuous flow screen changer as

claimed in any of the preceding Claims, in which the sealing plate has passages therein to receive means for heating the material and maintaining it molten whilst a screen is being changed and/or whilst in operation.
8. A continuous flow screen changer as claimed in any of the preceding Claims, including plate heaters at top and/or bottom of the body.
9. A continuous flow screen changer as claimed in any of the preceding Claims, including actuator means for moving said breaker plates.
10. A continuous flow screen changer substantially as described with reference to the drawings accompanying the Provisional Specification.