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Page 4 - Smooth Stays Smooth

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Smooth Stays Smooth
Sounds simple, but how can it be guaranteed that the surface quality achieved will not be partially or possibly totally ruined when a wrench is used for the first time? This was the next challenge. The basic idea was to prevent the contact of metal on metal. Moreover, this applied to the contact of base metal with noble metal in particular so that contact rust does not develop on account of particles on the stainless steel screws. A non-metallic material had to be found, which can achieve A4-70 quality class tightness for screws and nuts and at the same time be used with commercially available tools. The material has to be able to be reused repeatedly and not burst the normal budget during production.
The result of the series of tests was protective sockets made of high-tensile plastic, which can be used in combination with commercially available sockets. The shape of the plastic inserts ensures that even under the most unfavourable operating conditions the insert bit in the socket has a secure hold and is virtually undetachable. The plastic inserts are designed as interchangeable parts, are food safe and easy to recycle.
The series of tests with the sockets have shown that with the plastic inserts the tightening torques permissible for the A4-70 quality class are easy to generate. It was even possible to exceed the permissible values by more than 50% across more than 200 cycles without hesitation during the course of proper application.
The surfaces of the screws and nuts are left absolutely undamaged. As a result, the EHEDG requirements of RA 0.8 μm are met even after repeatedly tightening and untightening the screw connection. Ease of cleaning the screw heads after assembly is also assured. These protective sockets are patent-protected as well.
EHEDG Test and Results
The European Hygienic Engineering and Design Group (EHEDG) came up with a way in which deposits of microorganisms build up at hygienically problematic spots in the component, i.e. in potential cavities. Then using a cleanability test it is possible to detect critical spots that the cleaning agent cannot adequately penetrate (1). This method was also used to test the cleanability of the Hygienic Usit® as a screw/cap nut combination. This was tested on the M6 size as exemplary of the present type. In the Cleanability Method one compares the cleanability of a reference pipe having a known inner surface roughness that is easy to clean (RA = 0.7 μm) with the Hygienic Usit® screw/nut combination.
Before the test could be started it was first necessary to test the elastomers for germ-killing properties so as to rule out the possibility that the test result is affected by them. The test of the EPDM material did not indicate any bactericidal influence, with the result that nothing else stood in the way of an EHEDG cleanability test.
To test the cleanability the component is contaminated on purpose with a suspension that contains spores of a thermophilic strain. The spore strain not only remains stable at higher cleaning temperatures, but also exhibits a resistance to the cleaning agents. Following the targeted contamination cleaning was carried out for ten minutes using the CIP process involving a 1% alkaline concentration and a temperature of 63° C and rinsing with water ensued. After that the test area is coated with an agar culture medium and left to breed for 18 hours at 58° C. Then an analysis is conducted on the basis of the changes in the colour of the MSHA agar culture medium; change from purple to yellow occurs in consequence of the growth of the spores (1, 2). To ensure the reproducibility of the results the cleanability test is conducted many times. Every test following the incubation of the agar coating which was removed from the Hygienic Usit® screw and cap nut indicated zero yellow colouration. The yellow colouration in the reference pipe, averaging 13% of the inner face of the pipe, is within the tolerance range of 5 to 30% as described in the EHEDG Guideline (1). This is consistent with contamination permitted following a standard cleaning cycle. Thus the Hygienic Usit® as a screw/cap nut combination demonstrates better cleanability than the reference pipe.
[1] EHEDG Guideline No. 2, A method for assessing the in-place cleanability of food processing equipment. 3rd edition, July 2004, updated June 2007
[2] Report EHEDG 01 Cleanability test, Hygienic Usit with screws, Research Center
Weihenstephan for Brewing and Food Quality, TU of Munich, of 05.12.2011
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