EXPERTISE & TECHNOLOGIES
- High resistance to vibration due to positive locking of the serrations.
- Concentrical force transmission and uniform axial load eliminate bending torques and deformation of the bolt stem.
- The design of the serrations prevents friction and damage to components when tightening.
- Extremely high safety against loss of pretension force and loosening.
- Wide variety for materials and different finishes.
- The closed ring form results in high degree of pretensioning, while avoiding burst-open effect.
- Development and design of the washers take place on the basis of the screw geometrics, tightening torque as well as the constructive circumstances.
- Also applicable for clearance holes (safety washer is necessary on both sides).
- Applicable for elongated holes (using type VS).
- Equivalent locking effect like wedge-locking washers.
- DIN EN 16984 – Calculation
CORRECT USAGE OF SAFETY WASHERS
The Original SCHNORR® Safety Washer is only able to obtain its full effectiveness as a bolt locking device if it is used correctly.
To obtain the maximum locking effect of the Original SCHNORR® Safety Washers when fastening at bulkheads, the screw head as well as the bolt nut must be fastened in conjunction with a safety washer.
INCORRECT USAGE OF SAFETY WASHERS
To obtain the maximum locking effect of the Original SCHNORR® Safety Washers, we recommend not to use them in combination with a flat washer.
To obtain the maximum locking effect of the Original SCHNORR® Safety Washers, we recommend not to use them up-side down.
To obtain the maximum locking effect of the Original SCHNORR® Safety Washers, we recommend not to use them stacked.
TIGHTENING TORQUES FOR ORIGINAL SCHNORR® SAFETY WASHERS
The Junker test is a well-known test to determine the point at which a bolt joint loses preload. It compares the locking attributes of dynamically strained bolted joints under vibration. A bolted joint is mounted into a testing bench and is subjected to a transversely simulated vibration with a defined frequency and amplitude. Preload (FV) force reduction is measured by a force sensor.
Results of vibration test according to DIN 65151:
- Connections secured using a Original SCHNORR® Safety Washers maintain the pretension force also after 2.000 cycles.
- The test clearly shows a superior locking performance of the Original SCHNORR® Safety Washer in terms of number of cycles lasted and in terms of residual clamping force after 2,000 cycles in comparison to split lock washers, detent-edged washers, ribbed washers and spring washers (acc. to DIN 137 B)
- Furthermore, the test shows an equivalent locking effect of the Original SCHNORR® Safety Washer compared with a wedge-locking washer.
ADDITIONALLY AVAILABLE SURFACES
- Zinc Flake Coatings
- Nickel-Plated Surfaces
ADDITIONALLY AVAILABLE MATERIAL GRADES
- CUSN8 (2.1030)
- Inconel (2.4668)
- X39 CrMo 17-1 (1.4122)
- X22 CrMoV 12-1 (1.4923)
- X2CrNiMo17-12-2 (1.4404)
- X5CrNiMo17-12-2 (1.4401)
What are the effects of different initial forces?
Tests, where bolts had been tightened only to 75% instead of 100% of the initial force corresponding to the minimum required bolt tension, produced poorer results. A certain percentage of the joints came loose. This effect was even more evident with only 50% initial force. Hence it can be concluded that fastening up to 100% of the force corresponding to the minimum required bolt tension acc. DIN ISO 898 T1 is essential for a good connection.
What effects do SCHNORR® Safety Washers have for the initial torque?
To reach the same initial force when using a SCHNORR® Safety Washer type “S”, the initial torque has to be about 10% larger than for a bolt without a securing device. The same applies to SCHNORR® Safety Washers type “VS”. For the use of zinc plated safety washers, the initial torque does not have to be raised, because the additional friction induced by the serrated surface of the safety washers, is compensated by a certain lubrication effect from the zinc coating. The variation in initial torque is not greater with use of SCHNORR® Safety Washers than in bolted connections without securing device.
What is the effect of the hardness of the different parts?
With increasing hardness of the base surface in the joint, the “biting” effect of the serration of the safety washers, which results in partially elastic and partially plastic deformation, decreases. The securing performance is directly correlated with this effect. Since the hardness of SCHNORR® Safety Washers is 39–45 HRC (380–450 HV30), this applies only for higher hardness of the contact surface. We recommend to use the high duty type “VS” in combination with hardened surfaces and to tighten the bolt up to 100% of the force corresponding to the minimum required bolt tension.
What is the effect of a surface treatment on the securing effect?
The best securing effect is reached with a safety washer with a black surface. But zinc coated safety washers can also secure bolt joints perfectly if the bolt is tightened with the appropriate initial force. In this case it is necessary to apply no less than 100% of the minimum required bolt tension force.
What happens on a slot?
When tightened up to 100% of the minimum required bolt tension force, bolts without securing device do not loosen, but the bolt head is being damaged considerably, and a relatively high initial torque is required. In combination with a SCHNORR® Safety Washer type “VS”, the required initial torque is about 25% lower, and the damages on the bolt head are minor. The securing effect is high.
Can SCHNORR® Safety Washers be used several times?
When a bolt joint secured with SCHNORR® Safety Washers is being unscrewed and tightened again, the securing effect does not diminish. The initial torque decreases only slightly, i.e. the originally applied momentum produces a slightly higher initial force. Ergo SCHNORR® serrated safety washers can be used two or more times without any restrictions.