Rust-free connections

Stainless steel the material of choice


From the cable to the gland to the connector, from plastic to metal. Here, the answer seems clear: stainless steel is the material of choice when connector housings or cable and hose glands need to withstand chemicals or cleaning agents. In the foodstuffs industry, stainless steel is often essential. It does not rust and there is no coating that could eventually flake off. But the situation is not as easy as it appears, as there are different types of stainless steel. Conventional V2A stainless steel is relatively low-cost but is not as robust when it comes to chemical resistance. Stains can appear on the metal when it is immersed in substances containing chlorides. The foodstuffs industry often uses hypochlorous acid that disintegrates into hydrochloric acid and kills organic substances. V2A stainless steel is not suitable here. V4A stainless steel offers a tougher alloy and is also used on expensive Swiss watches. It is extremely hard and withstands impacts and cleaning with coarse brushes.



20180116 Skintop nach Korrosionsversuch 01

As ever in life, however, for every advantage there is a disadvantage. Stainless steel is harder than brass or standard steel, and is therefore more difficult to process. This is especially true of V4A due to the alloy elements chromium, nickel and molybdenum. If its surface is left untreated, V4A is rougher, leading to higher abrasion. Screws that have to withstand high forces across their thread would therefore be stuck. This is why Lapp gives its products made from V4A stainless steel (such as the EHEDG-certified SKINTOP® HYGIENIC cable gland) a special surface treatment that reduces abrasion and makes it easy to tighten and release the cable gland.





20180116 Skintop nach Korrosionsversuch 06

Stainless steel cannot be used everywhere. One example of this is in rectangular connectors. Stainless steel is unsuitable here because the metal is too hard to be processed. The connector would have to be milled from a complete block, which would be far too expensive for customers. Lapp therefore found a different solution for its EPIC® ULTRA. The housing on this rectangular connector is made from nickel-plated cast zinc. This material resists corrosion, such as from salt spray on oil platforms or in the foodstuffs industry. For bolts and brackets, however, Lapp recommends using stainless steel. This is because any coating would be quickly worn off by the frequent opening and closing when separating the modules, such as during cleaning. Cast-on bolts are not suitable here, as the clamping forces and therefore the tightness reduces over time due to the low stability of the material, whether plastic or cast aluminium.