GB2204255A

GB2204255A - Short-dwell coater

Info

Publication number: GB2204255A
Application number: GB08808818A
Authority: GB
Inventors: Erkki Kirveskari; Markku Grasten
Original assignee: Valmet Paper Machinery Inc
Current assignee: Valmet Paper Machinery Inc
Priority date: 1987-05-07
Filing date: 1988-04-14
Publication date: 1988-11-09
Anticipated expiration: 2008-04-14
Also published as: SE8801604D0; SE8801604L; DE3815764A1; FR2614807B1; FI82107B; FI82107C; GB8808818D0; GB2204255B; FI872028A; FR2614807A1; FI872028A0

Description

SHORT-DWELL COATER 2204255 The present invention relates to a short-dwell

coater for applying a coating mix to the surface of a travelling web, and is particularly concerned with the end seals of the coater.

In known coater constructions the coating material application chamber is confined at the edges of the web by rubber or plastic seals which prevent the coating mix from escaping by flowing. out from the coating compartment.

A disadvantage of the conventional constructions is that mounting conventional end seals sufficiently close to the backing roll is difficult. The large clearance of the seal results in an inferior tightness making the edge of the coated area of the web to vary widely in the cross-direction. Further, a rubber or plastic seal wears down and abrades the backing roll, especially if the coating mix contains agglomerates. A coating mix also has a tendency to accumulate on the seal surface, causing disturbance. The procedure for mounting the seal is inconvenient and time-consuming; furthermore, changes in either the web speed or the constitution of the coating mix generate need for additional control operations.

2 The aim of this invention is to overcome the disadvan tages associated with the known constructions referred to above and provide a short-dwell coater having new and improved end seals.

The invention is based on providing the end seals of a short-dwell coater with cavities through which a liquid can be introduced between the upper surface of the seal and the web in order to improve seal tightness and reduce seal wear.

According to the invention, therefore, there is provided a short-dwell coater comprising a backing roll whose circumferential surface is arranged to carry a web which is to be coated, a doctor blade extending over the entire width of the web and suitable for applying a coating mix over a surface of the web while backed by the backing roll, a trim blade aligned at least approximately parallel to the doctor blade so that a coating mix application zone is formed in the space confined between the trim blade, the doctor blade, and the web carried by the backing roll, and two end seals mounted over the margins of the web and extending essentially over the cross-section of the application zone, characterized in that each of the end seals is provided with at least one channel through which a 3 liquid, such as water, can be introduced between the upper surface of the end seal and the web in order to improve the seal tightness and reduce the wear of the end seal and the doctor blade.

With the construction in accordance with the invention, the life of the seal is increased and the wear of the doctor blade is decreased about the blade's dry area.

The tendency of the coating mix to accumulate on the doctor blade is reduced by virtue of the cooling effect of the water or other liquid, and water losses from the mix are diminished. Also, the time required for seal replacement is shortened and the replacement operation is made easier. The seal may also be fabricated from a softer material, making it possible to allow the seal to attain its proper shape through natural wear after installation. These alternatives permit the seal to be mounted closer to the edge of the web so that the border of coated area of web is even and located as desired. A water -lubricated seal is suitable for different coating mixes and web speeds without specific adjustments.

Further, the wetting of the uncoated, dry margin improves the runnability of the web.

Embodiments of the invention will now be described, by way of example, with reference to the attached drawings, 4 in which: - Figure 1 is a cross-sectional side view showing part of a short-dwell coater to which end seals can be mounted in accordance with the invention; Figure 2 is a side view of the short-dwell coater shown in Figure 1 and showing one embodiment of an end seal in accordance with the invention; Figure 3 is a front view of the end seal shown in Figure 2 removed from the short-dwell coater; and, Figure 4 is a partially cut-away projectional view of part of a short-dwell coater having another embodiment of an end seal in accordance with the invention.

With reference to Figure 1, a short-dwell coater is arranged by means of conventional technology over a part of a web 2, which is backed by a backing roll 1. The coater has a width in the cross-direction of the web approximating that of the web 2.

In the art, web speeds for this kind of a coater are in the range of 500 to 1500 m/min and the coating weights 2 in the order of 5 to 16 g/m The coating mix is fed via an inlet chamber 16 via, e.g., pumps (not shown) through inlet feed channels 17 to an application zone 18, in which a proportion of the mix tacks to the web 2. The excess mix flows over a trim blade 4 back into the mix circulation for reuse. A doctor blade 3 doctors off the excess mix. The angle and pressure of the blade 3 is controlled by means of a compressed air hose 5.

The distance from the trim blade 4 to the doctor blade 3 over the circpmferential surface of the backing roll 1 is referred to as application distance A.

According to Figure 2, end seals 6 in accordance with the invention are adapted to both ends of a short-dwell coater placed under the web 2 and aligned approximately to the marginal areas of the web 2. The seal 6 is attached to a body piece 7. The seal is advan tageously fabricated of cellular rubber. The body piece 7, fabricated of a resilient material, e.g. rubber, is further adapted at a support point 8 to transfer means (not shown), which provide for a movement of the body piece in a plane perpendicular to the plane of the figure, that is, parallel to the axis of the backing roll 1. The body piece 7 is provided with a water feed joint 9, which widens into a cavity, or a channel 11 towards the seal 6 and opens into a nozzle 10 at that end (front end) of the seal which primarily meets the 6 web 2. In the situation illustrated in the figure, a small slot remains between the blade 3 and the rear end of the seal 6, as well as between the blade and the rear end of the body piece 7. The figure illustrates the situation of mounting the seal. During run conditions, the slot is reduced as the blade 3 is pressed with help of the rubber hose 5 towards the seal 6.

According to Figure 3, the seal 6 is attached to the body piece 7 by a dovetail fastening so that, when mounted, the seal 6 is in alignment with the machine direction of the web 2. Further, the seal 6 becomes wider from the upper level of the body piece 7 towards the surface of the web. The nozzle 10 is located at the middle of the front edge of the seal 6.

In the embodiment illustrated in Figure 4, the upper part of the seal 6 is provided with an oblong groove 15, whose longitudinal axis is parallel with the machine direction of the web 2. Water is fed to a nozzle located at the leading end of the groove 15 via a pipe 14 adapted between the doctor blade 3 and the trim blade 4. The excess coating mix is carried off mainly via a flow C over the trim blade 4. A proportion of the mix flows of f via a f low D over the seal 6, under the surface of the web 2, as well as between the blade 3 and 7 the seal 6, then continues through a hole formed in the trim blade 4 as a flow B up to a return trough 12, from where it is conveyed to reuse circulation. The seal 6 together with its body piece is sideways movable by means of a control screw 13 and a control bar 19.

Conceivably, other liquids than water can be applied between the web 2 and the seal 6.

8

Claims

A short-dwell coater comprising a backing roll whose circumferential surface is arranged to carry a web which is to be coated, a doctor blade extending over the entire width of the web and suitable for applying a coating mix over a surface of the web while backed by the backing roll, a trim blade aligned at least approximately parallel to the doctor blade so that a coating mix application zone is formed in the space confined between the trim blade, the doctor blade, and the web carried by the backing roll, and two end seals mounted over the margins of the web and extending essentially over the cross-section of the application zone, characterized in that each of the end seals is provided with at least one channel through which a liquid, such as water, can be introduced between the upper surface of the end seal and the web in order to improve the seal tightness and reduce the wear of the end seal and the doctor blade.
2.

A coater in accordance with claim 1, in which the liquid f eed channel of each end seal is arranged to pass through the end seal to a position adjacent the middle of its front edge.

I. I - 9 -
3. A coater in accordance with claim 1, in which the upper end of the liquid feed channel of each end seal is adapted to open substantially at the leading edge of the end seal into an oblong groove or other similar space in order to guide the liquid flow over the surface of the end seal substantially parallel to the direction of travel of the web.
4. A coater in accordance with any one of the preceding claims, in which each end seal comprises a body piece and a sealing member which is attached to the body piece by a dovetail joint substantially aligned with the direction of travel of the web.
5. A coater according to claim 1, substantially as described with reference to Figures 1 to 3, or Figure 4 of the accompanying drawings.

(0122H) Published 1988 at The Patent Office, State House, 66171 High Holborn, London WCIR 4TP. Further copies may be obtained from The Patent Office, Sa-les Branch, St Mary Cray. Orpington. Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1/87.