Smooth fastenings

Thread-rolling screws – secure, high-quality and metric. If you are looking to reduce assembly costs whilst at the same time improving the safety and quality of screwed connections, these 2-in-1 screws are the right choice. Intelligent corrosion protection is also possible and urgently required here.

Thread-rolling screws are both tools and fasteners at the same time, examples of their use include in gearboxes and steering boxes, engines and safety fastenings. Their characteristic feature is their ability to alter the material in their counterpart to create a matching thread. The screw is fastened to a cast, drilled, punched or lasered hole. The advantage of this procedure is that components can be utilised directly without an existing nut thread, meaning that not only the costs of tools for thread cutting are saved, but also significant process costs. Work stages such as thread cutting or forming as well as cleaning after shaving removal are not required.

A further advantage is increased process safety. The material solidification within the thread results in higher strength of the fastening as a whole. The firm contact between bolt and nut thread enhance loosening security, which often makes it possible to dispense with the need for screw locks. In addition, the cut, metric thread enables the problem-free usage of a metric screw in the case of repair. Thread-rolling screws are produced in a range of different geometries, materials and surface finishes. For optimal fastening the component, fastening element and assembly must harmonise with one another. There is a danger involved here: as thread-rolling screws are often threaded in other materials, there is a risk of contact corrosion.

Double up for a better hold

To prevent the screw from corroding, a thin zinc flake coating from Dörken MKS with lubricant can be applied. The zinc-containing basecoat determines the corrosion properties and is responsible for the cathodic corrosion protection. Subsequently, the DELTA- LUBE® 50 from the DELTA-LUBE®- series of the Dörken MKS portfolio can be used for screws. This is a colourless lubricant which brings the properties of the typically used topcoat with it: it enhances corrosion protection and influences coefficients of friction as well as the thread forming torque. DELTA-LUBE® 50 is applied in either a dip-spin process or by spraying. If the screw needs to be coated in color, it is necessary to apply a topcoat before the lubricant.

DELTA-LUBE® 50 complements the zinc flake system that securely protects the thread-rolling screws, is available worldwide and fulfils high quality standards. Extensive tests with thread-rolling screws coated with DELTA-LUBE® 50 have shown that not only can the specified thread forming torque be met, but also the highest corrosion protection requirements in salt spray testing. The screws were coated with a zinc flake basecoat and the lubricant. They were then screwed into an aluminium block or into steel in accordance with DIN 267-30 respectively ISO 7500-1 and tested in the salt spray test (as per DIN EN ISO 9227). The results speak for themselves (see figure).

The DELTA-LUBE® 50 lubricant therefore helps to ensure that a constantly low thread forming torque is maintained, enabling thread-rolling screws to be utilised safely and process savings achieved. In combination with the zinc flake coating, it protects the screw against corrosion.


A construction screw without Dörken MKS lubricant heats up to 120°C due to the high clamping pressure and high thread forming torque.

 


A construction screw with Dörken MKS lubricant heats up to only 80°C due to the low clamping pressure and low thread forming torque.