Gaskets come as a set suitable for waterproofing one aluminium enclosure. A set comprises two white silicon foam gaskets and a number of polythene washers. The washers are optionally fitted under the heads of the screws and raise the rating of the gasket set from IP65 to IP66.
The E-Case aluminium enclosure range was not originally designed to be waterproof. Even with a gasket seal around the edge of the profile water could enter under the heads of the screws and enter the enclosure through the open screwport. The original waterproof aluminium enclosure range was the Linc-Ace range which had drilled ‘blind’ holes for the screws. Even if these holes filled with water, it did not enter the main part of the enclosure. Linc-Ace was a heavy extrusion, costly to manufacture and is now obsolete.
Use of a flat gasket will render the aluminium enclosure “waterproof” to IP65 and addition of a washer under each screw will give an increased rating of IP66. Use of these gaskets will not reliably give a rating of IP67. If you type (say) “IP66” into Google Search Engine you will be able to find a definition of IP66 which most engineers will have trouble relating to their practical application. In practice, it has been found that the following applies:
A diecast aluminium enclosure with a rating of IP67 was put under 1 metre of water for 24 hours with no water ingress.
An E-Case aluminium enclosure with a rating of IP66 was put under 1 metre of water for 24 hours and it contained a few drops of water (say 0.1ml).
An E-Case aluminium enclosure with a rating of IP65 when put under water took a few minutes to fill up.
These results, which have been found in practice, probably exceed the strict requirements of the IP rating, but this gives a margin of confidence. The diecast enclosure is better than an E-Case enclosure because one half of the sealing surface (metal to rubber) is a smooth (die-cast) metal ridge whereas on an extrusion it is a cut face. It has small saw cut marks on the sealing surface which will not be completely filled by the gasket thus forming small channels from the outside to the inside of the box. Normally, surface tension will prevent water flowing down these channels, but under pressure water might flow. In order to get round this one might consider a liquid gasket compound painted on to the end of the extrusion. This will also help align the gasket on the extrusion prior to fitting the end plate.
GEA1 – E-Case A Gasket Set supplied as a pair
GEB1 – E-Case B Gasket Set supplied as a pair
GEC1 – E-Case C Gasket Set supplied as a pair
GED1 – E-Case D Gasket Set supplied as a pair
Another feature of the flat gasket is that it needs to be fitted with some care – it has offset holes and needs orienting like the end plate. Also, failure to completely screw down one screw will reduce the IP rating and this will not be obvious when inspected. On-the other hand a diecast enclosure is fool proof. However, it is very ugly, and all the holes for the connectors have to be individually machined, whereas end plates can be mass-produced, complete with connector holes, by using a cnc punch.
It should be noted that if a bezel is to be used then the four washers can be omitted from under the screw heads. The plastic of the bezel gets squeezed under the screw heads and makes a seal. The benefit of the bezel is that it conceals the gasket in applications where appearance is important.
Practical Advice on Waterproofing.
There are occasions when an enclosure can be too waterproof. Water somehow gets into the enclosure and cannot get out. A common cause of failure in these situations is that a copper track on a circuit board dissolves under water.
Example 1: A hand made racing motorcycle ignition system made with a die-cast box where the lid has been sealed with epoxy. Unit has failed and was found to be full of water – circuit board track had dissolved.
Example 2: Linc-Ace system (now obsolete) with flat gasket used for another motorcycle ignition system on an American bike. Driving rain would cause the unit to fail (and what a time to fail).
Example 3: On site external wireless security system powered by 12v derived from a small plug-in mains transformer. The housing was a plastic IP67 enclosure. The unit was found to fail after 12 months and when opened the sachet of silica gel inside was found to have turned to liquid. If you put silica gel in your electronics, then you know you have a problem. Even if the enclosure was IP67, once the hole has been made for the antenna, it may not be IP67 any more. The solution was to drill a 12mm hole in the bottom and glue some mesh across to discourage spiders, and to put a gold coloured metal-clad resistor in the unit. The resistor was placed low down and to one side to encourage air circulation and the value was selected so that it dissipated a watt or so – quite enough to keep the atmosphere inside from condensing. No units have failed for seven years.
Product and data subject to change without notice. User knows application and must determine fitness for purpose and appropriateness of advice verbal or written. See terms and conditions of sale.
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