Precision in silicone - Stainless-steel/silicone composite component reliably seals weight sensor
R.E.T. REIFF Elastomertechnik GmbH has produced far more than one million seals for a weight sensor manufactured by the automotive supplier Bosch. An LSR (Liquid Silicone Rubber) ring, which is injection-moulded into the stainless-steel punched part, performs the sealing function.
The stainless-steel/silicone composite component seals the cavity between the bolt and the sleeve of the sensor and protects the sensing element against all liquid, solid and dusty media. A total of four weight sensors measure the forces acting on the seat frame of the passenger seat. Based on these data, the occupant protection electronics calculates a tailored airbag deployment for the passenger.
R.E.T. selected a combination of stainless-steel disc and silicone sealing ring as this material combination meets Bosch’s high requirements on the component best. Radial forces effect a deflection at the sealing spot of up to 0.02 in. On the one hand, the sealing element has to fully compensate this movement and, on the other hand, must not transfer force to the sensor, as this might distort the measuring result.
The required force neutrality and the preload in combination with the required chemical resistance is best achieved with a silicone sealing made of standard LSR (Liquid Silicone Rubber). It has a weight of only 0.02 ounces, a height of 0,08 in. and a foot width of 0.03 in. The material offers uniform mechanical characteristics exceeding the required temperature range from -40 to +80 degrees Celsius by far. As sealing seat R.E.T. selected a precision punched part made of stainless steel.
The actual know-how of this solution is embodied in the injection-moulding process. R.E.T. is one of the pioneers in Germany who inject the LSR material directly on metal. The company has developed a special surface treatment for the stainless steel, which ensures that the LSR paste is injected in a chemically optimum way and permanently connected to the metal surface. Adhesives, primers or bonding agents are not required.
As R.E.T. handles the difficult injection-moulding process with utmost perfection, the finished component does not require any rework. The three basic components of LSR are precisely mixed and accurately dispensed by means of a positioned-controlled screw. Engineers have optimally matched all procedural parameters such as injection speed, temperature and parameter profiles within the scope of an intensive fine tuning process.
R.E.T. has established a fully automated production line with two injection-moulding machines, which together achieve an annual output of up to seven million units. Cameras monitor the insertion of the stainless-steel discs and the removal of the finished seals from the tool. Then, every single seal is subjected to a quality check by means of further cameras. The seals are not released and automatically packed until seven criteria, for example uniform rubber application, optimum bonding, no trapped air in the rubber, are complied with.
The iBoltTM weight sensor by Robert Bosch GmbH
U.S. legislation requires that the passenger airbag is only deployed if the seat is occupied. If the seat is empty or children are put on it (in an infant car seat), the airbag must not be deployed. For adult passengers, however, the airbag must reliably be activated. To accomplish this differentiation, the weight resting on the seat can be used. This is measured with the four iBoltTM sensors. Instead of the customary bolts, these sensors connect the seat structure with the seat rails.
R.E.T. REIFF Elastomertechnik GmbH
At the Reutlingen site, R.E.T. develops and produces intelligent sealing and damping systems made of special and high-performance elastomers primarily for the automotive supplier industry. In close cooperation with the customers, approximately 150 employees search for solutions which are almost exclusively used in complex and safety-relevant automotive electronics components.
R.E.T. is a company of the internationally operating REIFF group. With approximately 1,500 employees at 80 European sites, the family-owned company with a history of almost one hundred years records annual turnovers of more than 300 million euros. The three divisions “Tyres and Automotive”, “Technical Products” and “Elastomer Technology” offer a wide range of services and technical solutions for automobiles.