ACTUATORS FOR WASHDOWN
30 October 2012
At this year’s Drives & Controls show, David Schuh, director of sales at US-based linear actuator specialist, Tolomatic, delivered a presentation on actuators in washdown environments for the food & beverage industries
Pneumatic, hydraulic and electric actuators are critical moving components in equipment used for processing and packaging in the food and beverage industry. In addition to being highly efficient, machines used to process food should not harbour or introduce bacteria, lubricating fluids or other contaminants that could harm consumers.
Machinery used in food and beverage processing uses several types of actuators, two of the most common being rod-style and rodless.
Rodless actuators, which carry loads back and forth, cannot be sealed adequately to prevent the ingress of liquids into the internal components, so are not considered to be the best choice for washdown applications. A low Ingress Protection (usually IP54 or less), combined with the fact that many are made from anodized aluminium with its inherent corrosion risk, means that if they are used in the food and beverage industries they need to be well shielded from any washdown process. They should also be mounted with the carrier/band facing downwards so that any liquids that it does come into contact with will roll off.
EASY TO SEAL
For applications that require the actuator to come in direct contact with washdown solutions, the rodstyle actuator, which push/pulls loads back and forth, is a far better choice since it is easy to seal against the ingress of fluids.
Stainless tubing is readily available and provides a cost-effective solution. In terms of application, it is best if rod actuators are mounted rod down and washdown occurs when the equipment is stationary.
Pneumatic rod-style actuators are still widely used in the food and beverage industry due to their low cost, but electric rod-style actuators are becoming more popular for a variety of reasons including: flexibility of control (multiple positions and motion profiles); efficiency (elimination of compressed air); and higher performance (precision, accuracy, repeatability).
Even though the working parts of a rod actuator may never come into direct contact with the product or packaging, inevitably there will be the occasional spill, drip or splatter. In food and beverage applications it is vital that this residue is removed from the equipment on a regular basis to prevent it from harbouring dust, bacteria and fungi – all of which pose a contamination risk to the product or packaging.
Whatever the design of actuator used, in a washdown environment they should be either made of corrosion-resistant materials and properly sealed, or carefully shielded to prevent water, product and chemicals from reaching the actuator mechanism. While shielding of lower priced actuators not designed for washdown is widely practiced, shields can complicate equipment design and interfere with maintenance.
Ideally, actuators should be constructed from stainless steel types: 316 which offers superior durability; 304 with excellent corrosion resistance; or 303 with good corrosion resistance. Plastic or rubber parts, such as seals and gaskets, also need to be carefully selected – some of the most popular products are Viton Orings and seals and Ultra High Molecular Weight (UHMW) polyethylene for mechanical parts.
As well as being approved for use with food and drinks, these are resistant to the heat and chemicals of washdown and offer good compression set resistance. Surface coatings used to reduce corrosion on components that have product contact can include white epoxy, chromium, fluoropolymer and electroless nickel plating. All materials should be free of pitts, cracks, corrosion and roughed surfaces.
While proper seals between the actuator body and the rod will keep lubricant exposure to a minimum, food-grade oil and greases should always be used.
The design of electric rod-style actuators for food and beverage applications needs to be free of crevices that may harbor bacteria, be sealed for washdown and have rounded surfaces with a smooth finish that sheds moisture. Motor housings, actuator bodies, corners and edges should be rounded to promote moisture runoff. Where possible, a hex head bolt is preferable to a socket head bolt.
Ideally, permanent joints, such as where the motor housing joins the screw barrel should be welded in a form that is fully cleanable.
For instance, when joints are gasketed it is important to make sure the adjacent surfaces and the gasket are flush. If the gasket protrudes or is recessed, it can form crevices that collect moisture, food debris and bacteria. In cases where the actuator is assembled with Orings instead of gaskets, the Oring must completely fill the gap between the two mating parts.
For further information contact Motion Control Products, the sole distributor in UK and Ireland for Tolomatic.
- Rodless and rod-style actuators are two of the most commonly used in food and beverage applications
- Rod-style actuators are easier to seal against the ingress of fluids
- Units should be made from corrosion resistant material or carefully shielded
- Food-grade oil and greases should always be used