CR 242 & EPDM 414 tape on electrical cabinets
Metal Cabinets are manufactured for electrical switch gear, electrical terminals and telecommunications.
The basic design generally has internal channel for sealing on the main cabinet with a flat sealing flange and return on the door.
Sealing rubber can be applied to either the cabinet or the door, but very rarely both surfaces.
The waterproof sealing requirements are known as IP standard. In simple terms this means that when closed, water must not penetrate the cabinet. The IP test is basically blasting the seal areas with a multi number of pressure jet heads for about 20 minutes.
Achieving a waterproof seal starts with the sheet metal manufacturer, even when CNC bending and folding is used, all sheet metal and its processing demonstrates a high degree of dimensional "float " margins otherwise referred as tolerances These are referred to as “ +/-“ variations of the dimensions within the production run . Misalignment of the door hinge pins will also create a "float " at all corners of the door, for example one corner may be a hard fit whilst the opposite side may have a large gap.
Before attempting to make an IP rating the manufacturer must know his tolerances over the production run and how to shim the door hinge to compensate for the dimensional variations
This can easily be found by using engineering modelling clay on the seal area and measuring the impression at a number of points.
When this is known the thickness of seal can be decided upon including an allowance for compression to ensure a firm fit.
The largest number of seal failure is because too thick a material is used resulting in over compression of the sponge rubber which causes cell crushing and long term compression set. The correct calculation of thickness is essential to a good seal and most material’s compression should never exceed 10% of the high end of the tolerance figure and not exceed 25% of the low end.
The correct sealing solution should also take into account the type of coating that is on the cabinet. Most cabinets are powder coated which is an exothermic process (a reaction of 2 substances to form a single thermosetting compound) that results in some wax residue being left on the surface. Surface wax has a low surface tension therefore difficult very difficult to adhere to.
The proposed adhesive surface of a powder coated cabinet must have its surface energy increased & this can be done by abrading it with a fine sandpaper and then once done clean the surface with methylated spirits & wiped dry.
Application of the sponge tape should be ideally around 20 - 25o C surface temperature. The colder the temperature, the more pressure & time the adhesive will need to “wet out” and form a strong bond.
In applying pressure sensitive adhesives(PSA) the PSA and substrate material (CR 242 or EPDM 414 sponge) must not be stretched as this will result in self delamination from the surface due to the fact the sponge rubber will always try to return to its original size. CR242 & EPDM 414 sponge tapes include a stretch inhibitor to avoid this, but it still is possible to stretch, particularly around a radius so care should be taken. Even pressure should be applied to the sponge rubber during application to help the bonding process
The type of epdm sponge rubber used for the seal depends greatly on the service application & the degree of “float" or tolerance variation. Doors that open and shut frequently need a different seal to one that is closed and only opened for annual service or irregularly. CR 242 is best for a regular opening application, EPDM 414 super soft best for irregular opening.