Every year, Alpi, a company based in Ried im Innkreis (Austria) converts 200 million kilograms of skimmed milk and whey into milk and whey powder. Approximately half of the milk powder produced in this way is transported in silo trucks using compressed air. The manufacturer uses the food grade Airduc Pur 356 MHF-AS reinforced hose, which is permanently antistatic and capable of electrostatic discharge, for this purpose. The hose is clamped using the Connect Safety Clamp System 230, which was specially developed for loading and unloading silo vehicles.
Milk powder is an essential ingredient of chocolate, convenience products and baby foods. It is also employed in the production of tablets. Alpi, a subsidiary of Berglandmilch Cooperative, the largest dairy enterprise in Austria, makes milk powder, milk powder blends, whey powder, lactose, and much more besides. Around 250 tons of milk powder are produced here every week. The transport hose system resorted to at Alpi not only has to be capable of handling huge quantities of product; it also has to meet a wide range of requirements such as a high hygienic standard and compliance with regulatory approvals for food applications. Safety aspects and optimised process costs are equally vital. Leopold Lobmaier, Production Manager at Alpi, is only too aware of the tough challenges confronting the transport hoses: “Contamination is a topic of immense importance to us. We are extremely conscious of our huge responsibility when it comes to food hygiene in the milk powder production process. Production samples are taken every two hours and analysed in-house in our own laboratory“. Although the food hose used in the past complied with the regulatory requirements for food applications, it nevertheless had one serious downside. When milk powder is transported using compressed air, it is important to fit the hoses with wall materials that are conductive or capable of electrostatic discharge because the powder (particle size: 148 to 2830 µm) is a combustible bulk material. More explicitly, friction occurs both in the milk powder itself and on the hose wall, resulting in the build-up of static charge that could not be safely dissipated with the old system owing to the insulating wall material. Earthing the spiral was not sufficient, because this had no influence on the static charge in the hose.
Burn holes in the hose
The charge that builds up owing to the friction of the milk powder was released when corona discharges occurred inside the hose; it then pierced the hose wall, creating burn holes from the interior to the wire. It is clear that these holes also had a detrimental effect on the hose’s service life as well as on its hygienic characteristics. In unfavourable conditions, the pumped medium may additionally ignite inside the hose. Alpi fills the powder into the silo trucks off the premises and therefore outside the hazardous area. In the past, however, it has only rarely been possible to employ conductive materials, or materials capable of electrostatic discharge, to dissipate the static charge safely. The legal and regulatory approvals and conformities necessary for food applications are generally lacking for the blacks used to obtain the stipulated conductivity. The fact that hoses whose conductivity is achieved by adding carbon blacks are – not surprisingly – also coloured black is a further drawback. This obscures the user’s view of the product being pumped and the conveyed material may be contaminated due to wear. The electrostatic discharge-capable hoses previously available in the market likewise failed to provide a satisfactory solution, because their antistatic properties were normally assured using an antistatic additive. The biggest problem with these hoses is that the effect of the antistatic material is exclusively attributable to its migration to the hose surface, leading to an accumulation of moisture from the ambient air. However, when solids are conveyed, the antistatic material that migrates to the inner surface is continuously abraded, with the result that the antistatic is leached out and the discharge effect of the hose wall is gradually weakened. Moreover, the antistatic material can also be absorbed by the product being conveyed – in this case, milk powder.
No exclusion criteria
The terms food grade and antistatic have always appeared to be mutually exclusive. However, Lobmaier’s frustration with the situation caused him to embark on a search for a solution that would fulfil both requirements. He found what he was looking for in Norres Schlauchtechnik and the Airduc Pur 356 MHF-AS reinforced, the hose specialist’s abrasion-proof suction and transport hose. This hose type is food grade, capable of electrostatic discharge and permanently antistatic. All hoses in the Pur-AS series are made from a special wall material. Hoses manufactured in this way set themselves apart from conventional designs with a permanent electrostatic discharge capability < 109 V as well as a milky transparent surface through which the delivered material is clearly visible. Since the wall material is non-migrating, there is no contamination of the conveyed material and no deterioration in the electrostatic discharge effect. All Airduc Pur MHF-AS hoses, the Airduc Pur 356 MHF-AS included, have obtained legal and regulatory approvals from an independent testing laboratory for the complete hose in food applications; they meet the requirements of EU Directive 2002/72/EC, including the amending Directive 2007/19/EC, and bear the EU’s glass / fork symbol. Since changing over to the antistatic food hose, Alpi has recorded roughly three times better durability as well as lower costs for maintenance. The Airduc Pur 356 MHF-AS is clamped in the compatible Connect Safety Clamp System 230. This system for thick-walled polyurethane spiral hoses used to load and unload silo vehicles was developed and successfully launched by Norres back in early 2008. The Connect Safety Clamp System 230 – which is designed for tank truck, Kamlok and Storz couplings – particularly impresses with its reusable clamp, and is quick and easy to fit. The hose adapter with male thread is available in light metal, steel or stainless steel. The previous solution, which involved connecting the food hose to the adapter with an ordinary hose clamp, had several disadvantages: Under high pressure, this inevitably entails a risk that the adapter could become displaced or the system gradually loses its tightness. This can no longer happen in future because the hose is fixed to the metal adapter. At the same time, the new system has brought about an improvement in hygiene compared to the old clamp connection.