Hygienic Design and Installation of Switch Boxes
Control boxes should be preferably made of smooth, corrosion-resistant stainless steel plate with low surface roughness, and should be constructed with >6 mm radiused edges and without pits and crevices. Seams should be minimized and bolted connections should be avoided. With an IP67 to IP69K rating, they are protected against the penetration of water or damp during high-pressure hose-down cleaning operations. The switchbox should be mounted to equipment at least 6 cm from the equipment framework (Fig. 6.74), with suspending members constructed of solid steel round tubing.
Hygienic Design and Installation of Control Panels With Control and Indicator Devices
In noncomputer-based control panels, control and indicator devices are the machine components used as interfaces between man and machine. Adequate space should be provided between control and indicator devices for easy cleaning and disinfection (Fig. 6.75). Very often, control panels are provided with more holes than necessary for the installation of control and indicator devices. Unused holes in a control panel can be closed by means of blanking plugs. Installation of control and indicator devices in control panel bore holes that are larger than required can occur by means of adapter rings.
Push buttons, knobs, valve handles, switches and locks must be designed so as to ensure that food product, water or product liquid do not penetrate into the interface or accumulate onto the enclosure. Therefore push buttons,
FIGURE 6.74 Control boxes either can stand apart (courtesy of MENNEKES Electronics, Inc.) or can be mounted remotely from the equipment framework/wall at a distance of about 6 cm. Suspending members are constructed of solid steel round tubing (courtesy of Electrix International Ltd).
FIGURE 6.75 Control panel with hygienic control and indicator devices. An IP67 or IP67K ingress protection rating for control panel enclosures is highly recommended. Courtesy of K.A. Schmersal GmbH & Co. KG.
when touched, should not penetrate deeply in the front panel far beyond a protruding frame edge surrounding the button (Fig. 6.76).
Control and indicator devices must be constructed of durable and mechanically stable (unbreakable, resistant to steam, moisture, cleaning agents and disinfectants, abrasion and corrosion resistant) material, such as stainless steel or plastic (polyamide, polycarbonate, polyoxymethylene, silicone, and acrylonitrile butadiene styrene). Antimicrobial push buttons are commercially available. Knurling on hand grips should not be used, and device heads must have crevice-free and easily cleanable surfaces with smooth finish. Actuators of devices with grip or mushroom shape must have curvature radiuses $ 3.2 mm at all corners and edges. The device seals of the control devices shown in Fig. 6.77 make contact with the actuator and bezel (gray), hence preventing hygiene-critical gaps. The outer surfaces of the device seals all make a smooth, flush (in the case of push buttons and indicator lights) or continuous (in the case of other device versions) transition from the free outer surface of the actuator to the bezel. Front plate seals inside the control device help to avoid the penetration of pressurized water. Front plate and outer surface of the bezel are at an angle of approximately
FIGURE 6.76 The push button, when touched, penetrates deeply in the front panel far beyond the protruding frame edge surrounding the button. Every time the button is pushed, food debris built up at the inside cylindrical frame moves deeper to the inside. As the inside of the actuator forms a niche in which microorganisms may grow, the inside of the protruding frame edge becomes heavily contaminated with microorganisms every time the button moves back. Thus, the actuator becomes a serious source of cross-contamination from operator to operator. The sharp corners and gaps, as indicated by the arrows in orange, are areas where, respectively, accumulation or ingress of product residues and cleaning solutions may occur. Frank Moerman, ©2016.
FIGURE 6.77 Control devices such as (A) push buttons, (B) position/selector switches, (C) mushroom buttons finally become integrated in a control panel. They must be shaped in such a manner that no accumulation of dirt and bacteria occurs and cleaning is facilitated. Also device head to front panel transitions must be smooth and without corners and edges. Perfect, hermetic device and front seals prevent the ingress of moisture, dust, and dirt within the control panel. Devices with damaged or destroyed seals should be replaced immediately. Courtesy of K.A. Schmersal GmbH & Co. KG.
135 degrees, thereby creating a surface without “sharp” transitions (Elan Schmersal, 2010; Moerman, 2011).
Control panels should be positioned away from the product zone, so that the operator does not have to lean over product to operate. The preferred installation positions for control and indicator devices are declining and
FIGURE 6.78 Touchscreen display installed inclined. Courtesy of OctoFrost Group; Frank Moerman, ©2016.
vertical surfaces, such that fluids (splashed food and cleaning solutions) are able to flow from the control panel, at least in the cleaning position.