GB2034572A

GB2034572A - Preventing formation of a wedge of coating material on a conveyor belt during coating of wafer sheets

Info

Publication number: GB2034572A
Application number: GB7936262A
Authority: GB
Original assignee: HAAS ING JOHANN; HAAS SEN F HAAS F
Current assignee: HAAS ING JOHANN; HAAS SEN F HAAS F
Priority date: 1978-10-27
Filing date: 1979-10-18
Publication date: 1980-06-11
Also published as: AT360459B; DE2941318C2; BR7906691A; ATA772478A; DE2941318A1; GB2034572B

Abstract

Wafer sheets (W) are fed on to a conveyor belt (3) beneath a spreader roller (2) to coat the sheets, e.g. with cream. The gap between the spreader roller (2) and the belt (3) is controlled to be greater than the thickness of sheets (W) during the approach of each wafer to the roller (2). When the leading edge of the wafer has passed beneath the lowest point of the roller (2) the wafer is applied to the roller to receive the cream therefrom. Build up of cream on the leading edge of the wafer (W) is thus avoided. <IMAGE>

Description

SPECIFICATION A method and apparatus for preventing the formation of a wedge of coating material on a conveyor belt during a contact coating process The present invention relates to a method of avoiding the formation of a wedge of coating material on a conveyor belt feeding spaced wafer sheets to a contact coating apparatus, and to a device for carrying out the method.

When wafers are spread with cream by the contact method, a coating of cream is formed on a revolving roller. This coating of cream is picked up from the roller in that a wafer sheet is moved past the roller tangentially and against its direction of rotation. The gap between the creamless roller and the conveyor belt carrying the wafer sheets corresponds to the thickness of the wafer sheets. When the leading edge of the wafer sheet is introduced between the spreader roller and the conveyor belt, the coating of cream present on the spreader roller builds up on the leading edge of the wafer sheet until the distance between the leading edge and the axis of rotation of the spreader roller is greater than the radius of the spreader roller increased by the thickness of the cream coating.The cream which builds up on the leading edge forms a wedge of cream which remains on the conveyor belt after the wafer has been removed and which has to be removed from the conveyor belt by a scraper as the belt revolves. If the cream is not removed from the belt a following wafer may come to rest on the wedge of cream and be broken as it passes under the spreader roller. If the scraper is not functioning efficiently there is the constant risk that the conveyor belt will become dirty. In addition, the wedges of cream increase the cream consumption. The cream waste caused by the wedges of cream can be reprocessed but this occasions additional cost.

There is a further problem associated with contact spreading, namely, that if the spreader roller is switched off while the cream container is full, cream runs out through the gap between the spreader roller and the cream container and makes the conveyor belt dirty, as well as creating additional wastage of cream.

It is an object of the present invention to avoid the formation of a wedge of cream.

According to the present invention there is provided a method of avoiding the formation of a wedge of coating material on a conveyor belt feeding wafers successively past a spreader roller during a contact coating process, in which coating process the wafers are fed tangentially with respect to the constantly revolving spreader roller against the direction of rotation thereof, the wafers being passed beneath the spreader roller, wherein during the approach of the wafers to the spreader roller, the gap between the spreader roller (which is provided with a layer of coating material) and the conveyor belt is greater than the thickness of the wafers, and wherein only after the leading edge of a wafer, in the direction of movement of the conveyor belt, so projects beyond the lowest point of the spreader roller that upon radial application of the wafer against the spreader roller, which is provided with a layer of coating material, the leading edge of the wafer come to rest outside the coating of cream present on the spreader roller, does the wafer bear radially against the spreader roller and then passes tangentially under the spreader roller.

Preferably, the amount by which the wafer projects beyond the lowest point of the spreader roller is equal to or slightly greater than the product of the thickness of the layer of coating material on the spreader roller and the diameter of the spreader roller increased by the thickness of this layer.

In one embodiment of the invention, the gap between the spreader roller and the conveyor belt only corresponds to the thickness of the wafer to be coated while cream is being applied to the wafer.

In an alternative embodiment, the gap between the spreader roller and the conveyor belt is greater than the thickness of the wafer only while the leading edge of the wafer is passing under the spreader roller.

Apparatus for carrying out the method according to the invention may comprise means for briefly lowering the conveyor belt in relation to the spreader roller or means for briefly raising the spreader roller in relation to the conveyor belt or a presser roller located beneath the spreader roller for briefly raising a part of the conveyor belt.

According to the invention, cream is prevented from running out of the cream container of a contact spreading machine through the gap between the stationary spreader or scraper roller and the wall of the container by way of an elastic apron fixed to the wall of the container, the free end of the apron bearing tangentially on the relevant roller and projecting beyond the point of contact.

When the rollers are stationary, these aprons are pressed against the rollers by the cream in the container and thus the gap between the roller and the wall of the container, which is necessary for returning to the container cream present on the spreader roller while the spreading machine is idling, i.e. when no wafers are being passed under the spreader roller, is sealed. On the other hand, when the spreading machine is running, the apron lies only loosely against the roller so that any cream which may happen to be scraped off by the apron will be drawn under the apron by the suction action of the spreader roller and returned to the container.

Embodiments ofthe present invention will hereinafter be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows schematically a coating apparatus illustrating two alternative embodiments of the present invention; Figure 2 shows a third embodiment of coating apparatus, and Figure 3 shows a further embodiment of coating apparatus provided with aprons to prevent the coating material running out whilst the rollers thereof are stationary.

Figure 1 shows schematically coating apparatus comprising a spreader device 1 which is constructed in known manner and which is provided with spreader rollers 2, and a conveyor belt 3. The conveyor belt which runs below the spreader device 1, is stretched over drums 4 and 5, the drum 5 being capable of being driven as required.

The drums 4 and 5 are supported by a frame 6. A support roller 8, which is rigidly connected to the frame 6, is located below the belt 3 in the region of the spreader roller 2.

In a first embodiment of the invention, the frame 6 is pivotable about the rear bearing 7. The upper end position of the frame 6 is established by one or more stops (not shown). By means of this upper end position, the thickness of the coating applied to wafer sheets W carried by the conveyor belt 3 under the spreader roller 2 is determined. At its front end, the frame 6 is connected to a lifting magnet or equivalent drive means which, when energised, causes the frame 6 to be lowered against the action of a spring and out of the position shown in the drawing, to a sufficient extent that a wafer sheet placed at the front end of the conveyor belt can move freely under the spreader device 1 without being coated, as is necessary for the wafer cover sheets which are used when building up wafer blocks.

In a second alternative embodiment it is not the frame carrying the conveyor belt 3 which is lowered in relation to the spreader device 1: instead, the frame 6 is rigid and the spreader device 1 is pivoted for example about a pivoting axis 10 and is moved out of the position shown by solid lines in Figure 1 into the position indicated by broken lines so that a wafer sheet placed at the front end of the conveyor belt can pass freely below the spreader device 1 without being coated. The pivoting movement of the spreader device 1 can be replaced by a lifting movement of the spreader device.

In a third embodiment of the invention shown in Figure 2, both the frame 6 carrying the conveyor belt 3 and the spreader device 1 are rigidly disposed.

Only the conveyor belt 3 itself is moved upwards and downwards in the region of the spreader roller 2 by means of a presser roller 11 which can be raised and lowered. In the position of the presser roller 11 shown in Figure 2, the gap between the conveyor belt 3 and the spreader roller 2 is determined in dependence upon the thickness of the coating to be applied to the wafer sheets W carried by the conveyor belt under the spreader roller 2. If a wafer placed at the front end of the conveyor belt is to move freely beneath the spreader device 1 without being coated, the presser roller 11 is lowered so that the conveyor belt 3 assumes the position indicated by broken lines in Figure 2.

The raising and lowering of the frame or of the spreader device or of the pressor roller 11 for increasing the depth of the gap between the conveyor belt and the spreader device in order to pass through a wafer cover sheet without coating may, for example, be controlled by means of a light barrier which is coupled to a counting mechanism.

The counting mechanism is adjustable in accordance with the number of layers in the wafer blocks which are to be produced.

The apparatus described above operates in the following manner: wafer sheets are placed one after another onto the front end of the conveyor belt 3 so that they are passed in sequence underneath the spreader device 1 and are coated with filling, for example, cream, to the desired thickness. After a predetermined number of wafers, corresponding to the number of layers required in the wafer blocks which are being produced, have been coated, the conveyor belt or the presser roller 11 is briefly lowered or the spreader device is briefly raised so that a wafer can pass beneath the spreader device without being coated. The uncoated wafer forms the top, cover wafer of the block.Where this is necessitated by the stacking process for the wafer cover sheet, the uncoated wafer sheet may be passed through the coating apparatus as the first of the predetermined number of wafer sheets required to make up a wafer block.

During the coating process, the gap between the spreader roller and the conveyor belt is continuously adjusted by control means such that the leading edge of each wafer moves under the spreader roller to project beyond the lowest point thereof before the spreader roller comes into contact with and coats the wafer. In Figure 3, r ... designates the radius of the actual spreader roller 2.

s ... designates the thickness of the coating, for example, of cream present on the spreader roller 2, and X ... denotes the amount by which the wafer sheet to be coated must be transported beyond the lowest point of the spreader roller 2, in the direction of feed of the conveyor belt 3, to ensure that the leading edge of the wafer does not come in contact with the coating.

The amount X can be calculated by the formula x = s.(2 r + s).

The spreader device 1 illustrated in Figure 3 is provided with means for preventing coating material running out of the coating material container 12 through the gap between each of the spreader and scraper rollers of the spreader device and the corresponding part of the container wall when the rollers are stationary. Said prevention means consists of two elastic aprons 13, one end of each apron being attached to the inside wall of the container whilst the other end of each apron rests tangentially on the respective roller and projects beyond the point of contact between the apron and the roller.

Claims

1. A method of avoiding the formation of a wedge of coating material on a conveyor belt feeding wafers successively pasta spreader roller during a contact coating process, in which coating process the wafers are fed tangentially with respect to the constantly revolving spreader roller against the direction of rotation thereof, the wafers being passed beneath the spreader roller, wherein during the approach of the wafers to the spreader roller, the gap between the spreader roller (which is provided with a layer of coating material) and the conveyor belt is greater than the thickness of the wafers,and wherein only after the leading edge of a wafer, in the direction of movement of the conveyor belt, so projects beyond the lowest point of the spreader rollerthan upon radial application ofthewafer against the spreader roller, which is provided with a layer of coating material, the leading edge of the wafer come to rest outside the coating of cream present on the spreader roller, does the wafer bear radially against the spreader roller and then passes tangentially under the spreader roller.

2. A method as claimed in claim 1, wherein the amount by which the wafer projects beyond the lowest point of the spreader roller is equal to or slightly greater than the product of the thickness of the layer of coating material present on the spreader roller and the diameter of the spreader roller increased by the thickness of this layer.

3. A method as claimed in claim 1 or 2, wherein only during application of coating material to the wafer does the distance between the spreader roller and the conveyor belt correspond to the thickness of the wafer which is to be coated.

4. A method as claimed in claim 1 or 2, wherein only while the leading edge is running underthe spreader roller is the distance between the spreader roller and the conveyor belt greater than the thickness of the wafer.

5. Apparatus for carrying out the method claimed in any preceding claim, wherein the conveyor belt can be briefly lowered in relation to the spreader roller.

6. Apparatus for carrying outthe method claimed in any of claims 1 to 4, wherein the spreader roller can be briefly raised in relation to the conveyor belt.

7. Apparatus for carrying outthe method claimed in any of claims 1 to 4, wherein a part of the conveyor belt can be briefly raised by a presser roller located beneath the spreader roller.

8. A device for preventing material running out of the coating material container of a contact spreader device through the gap between the or each stationary roller and the container wall, wherein an elastic apron is fixed on the container wall, the free end of the apron resting tangentially on the relevant roller and projecting beyond the point of contact.

9. A method of avoiding the formation of a wedge of coating material on a conveyor belt feeding wafers successively past a spreader roller during a contact coating process substantially as hereinbefore described with reference to the accompanying drawings.

10. Apparatus for carrying out the method claimed in claim 1, and substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.