APPARATUS FOR COATING A SUBSTRATE

Abstract

The present inventions is concerned with an apparatus and a method of improving the accuracy of coating a ceramic or metallic honeycomb body, which can usually be used as a catalyst in automotive exhaust mitigation. The invention achieves to directly test whether the coating slurry in the coating chamber is ready to be submitted to the monolith or needs to be replaced before coating the monolith.

Claims

1. An apparatus is presented for coating substrates (121) for the production of exhaust gas purification catalysts, particularly for motor vehicles, which are cylindrical support bodies and each have two end faces, a circumferential surface and an axial length L and are traversed from the first end face to the second end face by a multiplicity of channels, with a liquid coating slurry (113); said apparatus comprising: a coating chamber (100) designed to receive said substrate (121) from the top and to attach said substrate in a liquid tight manner to the coating chamber (100) and further being able to receive said coating slurry (113) from below; said coating chamber (100) further comprising a device to check the height of said coating slurry within said coating chamber (100) by measuring a variable; said device having one sensor in a lower position (124) in the coating chamber relative to at least a first (123) and a second sensor (125) being installed on equal height in the coating chamber (100); said device being able to: measure said variable via the lower sensor, and said at least first and second sensors separately; and compare the measured variables with each other.

2. Apparatus according to claim 1, wherein said at least first and second sensors (123, 125) are positioned with maximum distance to each other around the coating chamber (100).

3. Apparatus according to claim 1, wherein said variable is an electric variable and can be selected from the group consisting of current, capacity, and frequency.

4. Apparatus according to claim 1, wherein said device gives notice if the delay between the electric variables is below a predefined value.

5. Apparatus according to claim 1, wherein said substrate (121) is a wall-flow filter or a flow-through monolith.

6. A method for coating substrates for the production of exhaust gas purification catalysts, particularly for motor vehicles, the method comprising the steps of: subjecting a cylindrical support body (121) having two end faces, a circumferential surface and an axial length L, said support being traversed from the first end face to the second end face by a multiplicity of channels, to the apparatus of claim 1 from the top; attaching said support body (121) to said apparatus in a liquid tight manner; pumping coating slurry (113) into the coating chamber (100) from below while measuring a variable via the sensors (123, 124, 125); signaling if conditions for further processing the coating operation are or are not met.

7. Apparatus according to claim 2, wherein said device gives notice if the delay between the electric variables is below a predefined value.

8. Apparatus according to claim 3, wherein said device gives notice if the delay between the electric variables is below a predefined value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG. 1/FIG. 2:

[0036] 100 coating chamber [0037] 110 channelsin the substrate 121 [0038] 113 coating slurry [0039] 116 line section [0040] 117 filling flow direction [0041] 118 return flow direction to remove coating medium 113 [0042] 121 substrate [0043] 122 coating apparatus [0044] 123 first sensor for detecting the level 130 [0045] 124 lower sensor for detecting the level 130 [0046] 125 second sensor for detecting the level 130 [0047] 130 first levelof 113 in the coating device 122 [0048] 132 second levelof 113 in the substrate 121 [0049] 140 control unit

DETAILED DESCRIPTION OF THE DRAWINGS

[0050] FIG. 1 shows an arrangement of the invention for coating channels (110) in a substrate (121). The liquid coating medium (113) is filled through line sections (116) into the coating apparatus (122), wherein the coating apparatus (122) is provided with the substrate (121) and with sensors (123, 124 125) for determining the first level (130) and its accuracy. The values determined by the sensors (via 123 and 124 and via 123 and 125) are transmitted to a control unit (140) which, for its part, controls at least the further pumping or suction of the coating slurry based on the above-mentioned analysis.

[0051] After the filling of the coating apparatus (122) with coating medium (113) up to the first level (130) in the filling flow direction (117) has been performed, and after the second level (132) in the substrate (121) is reached, the coating slurry can be sucked out in the return flow direction (118), leading to a storage tank for excess coating medium (113) and for holding it ready for further use. All the control commands required for this purpose are preferably likewise output by the central control unit (140).

[0052] The finished substrates, which are suitable for the production of exhaust gas filters for motor vehicles, have a particularly uniform coating height, which is characterized in that the coated lengths of the different channels differ from one another by no more than 5 mm, in particular 3 mm, this applying to at least 95% of all the channels of a substrate, advantageously at least 99% of all the channels of a substrate, in particular 100% of all the channels. Defects of the substrate itself may mean that the flow and pressure conditions in some channels differ greatly from the other channels, the effect being that the liquid coating medium penetrates with considerably more or considerably less difficulty and is deposited either over a shorter or longer length of the individual channels under the coating conditions. In these cases, the desired uniform coating length may be achieved only in the case of some of the channels, but this is generally more than 95% of all the channels.

[0053] The present invention achieves this result in a very easy but nevertheless surprisingly effective manner. In that more sensors are located in the coating chamber in an intelligent way it is possible not only to measure the level of the coating slurry directly in the coating chamber but one may also determine whether the coating slurry is in a proper shape for further processing or not. This greatly helps to shorten the cycle time (time needed to coat one body) but on the other hand also serves to have less coated monoliths falling out of specification. Hence, this invention allows to greatly improve the economy of a process for coating exhaust catalysts. This was not made obvious from the prior art teaching at the date of this invention.

[0054] FIG. 2 is a zoomed view in FIG. 1 showing an uneven distribution of the washcoat surface (130) in the coating chamber (100).