Hygienic Design for Washdown Computers and Monitors

Hygienic design is the practice of building equipment so that it cannot harbour soil or bacteria and can be cleaned quickly and completely. For a washdown computer or monitor, that means a smooth, sealed stainless steel housing with no crevices, a flush glass front, sealed connectors and an ingress rating, usually IP69K, that survives high-pressure, high-temperature cleaning every shift.

Hygienic design, called sanitary design in North America, is a set of engineering principles for equipment used where food, drink or medicines are made. The aim is simple: every surface a hygiene team can reach should come clean in one pass, and no surface they cannot reach should be able to collect product, water or microbes.

In Europe the principles are set out in the guidelines of EHEDG, the European Hygienic Engineering and Design Group; in North America, 3-A Sanitary Standards and NSF cover similar ground. They share the same core rules: cleanable materials, smooth surfaces, no crevices or dead spaces, self-draining shapes, and seals and fasteners that do not trap soil.

Most of this guidance was written for product-contact equipment such as fillers, pipework and conveyors. A washdown computer or monitor usually sits in the splash zone instead: close enough to be sprayed, foamed and wiped with everything around it, but not touching the product. The same principles still apply, because anything that holds water or residue in the splash zone can drip back onto the line.

Washdown is the open-plant cleaning that happens at the end of a shift or a production run. A typical sequence, following the steps the NSF summarises for food plants, looks like this:

1. Dry clean. Remove debris by hand, brush or scraper.
2. Pre-rinse. Warm water, typically below 50 °C so proteins do not bake onto surfaces.
3. Foam. Alkaline foam to lift fats and proteins, with an acid descaler where water is hard.
4. Rinse. Hotter water to remove every trace of detergent.
5. Inspect. Check corners, seams and fixings where soil hides.
6. Sanitise. Chlorine-based, peracetic acid or quaternary ammonium sanitisers.
7. Dry. Usually air drying, helped by the heat left from the rinse.

Every one of those steps lands on the HMI. The housing sees hot water, repeated thermal shock, caustic and acidic chemistry and, often, a pressure washer held a few centimetres from the seals. Enclosed process equipment is cleaned differently, by clean in place (CIP), where cleaning solutions are pumped through pipework and tanks without opening them. The HMI that runs a CIP cycle is still washed down on the outside.

An ingress protection rating tells you what an enclosure has been tested against. For washdown, three ratings matter:

• IP66: dust tight and protected against powerful water jets from any direction, 100 litres per minute from a 12.5 mm nozzle at about 3 metres.
• IP67: protected against temporary immersion to 1 metre for 30 minutes. Useful, but immersion is not what a hygiene team does.
• IP69K: protected against close-range, high-pressure, high-temperature jets: water at 80 °C, 80 to 100 bar and 14 to 16 litres per minute, from 10 to 15 cm, for 30 seconds at each of four angles while the unit turns.

IP69K is the only one of the three that matches a pressure washer in the hands of a cleaning crew, which is why it has become the default for HMIs on open food lines. Many washdown units carry IP66 and IP69K together, because the two tests cover different things. A front-only rating such as front IP65 protects a panel-mount display from the operator side only, so the rear must sit inside a sealed cabinet.

Our guide to IP ratings from IP65 to IP69K covers every level, and the IP69K FAQ summarises the test.

Stainless steel is the standard housing for washdown equipment because it resists corrosion, takes a smooth finish and tolerates the chemicals used in food plants. Two grades cover almost every washdown HMI. Grade 304 contains around 18% chromium and 8% nickel and suits most food, bakery and packaging areas. Grade 316 adds 2 to 3% molybdenum, which improves resistance to pitting from chlorides: the chlorine in sanitisers, brines and salt.

As a rule of thumb, choose 316 where chlorinated sanitisers are used every shift, in meat, poultry, fish and dairy processing, near brines and marinades, and anywhere salt air reaches the line. The extra cost is small against a housing that pits and harbours bacteria. Whichever grade you choose, keep the finish smooth: abrasive pads scratch the passive layer that protects the steel.

Our comparison of 304 and 316 stainless steel in industrial computing goes further into the differences.

The screen is the part of a washdown HMI that operators touch most and cleaners spray hardest. Projected capacitive (PCAP) touch sits behind a single sheet of flush glass, so there is no film or bezel edge to lift or trap residue, and controllers tuned for water rejection ignore droplets left after a rinse. Resistive touch still has a place where operators wear thick work gloves, and our guide to touch technology compares the two.

Hot rinses followed by cold production air can fog the inside of a display. Optically bonded screens fill the gap between the glass and the LCD, removing the air layer where condensation forms and improving readability under bright factory lighting. It also helps to give operators a cleaning lock on the screen, so a wipe-down does not register as a string of touches while the line software is running.

Having supplied panel PCs and displays into washdown areas for many years, we see the same weak points again and again. Cable entries and standard connectors let water in long before a sealed housing does, which is why sealed M12 connectors matter as much as the rating on the front. Buttons, antenna housings and speaker grilles add seams; a flat antenna cover and a touch screen in place of buttons remove them.

Seals are the other wear item. Repeated thermal shock and strong chemicals harden gaskets over time, so check them at planned maintenance, follow the chemical concentrations your supplier recommends and avoid holding a pressure lance on a seal from point-blank range for longer than the clean needs.

Environment. Start with the cleaning regime: how often, how hot, what pressure and which chemicals. That sets the ingress rating, usually IP69K, and the steel grade.

Performance. Match the processor and screen to the software: a line HMI, a SCADA client, a recipe station or a vision system each need different compute and display sizes.

Expansion. List the devices the unit must connect to, from barcode scanners and scales to PLCs, and make sure every port is sealed, whether through M12 connectors, PoE or wireless behind a sealed antenna.

Lifecycle. Food lines run for years. Choose a platform with long availability and replaceable seals so a failed unit can be swapped like for like.

Browse our stainless steel panel PCs and stainless steel monitors, or see how we support food and beverage manufacturers. For particle-controlled production rather than wet cleaning, read our guide to clean room computers.