Norbar Case Study
EziTite Hydraulic Nut for Vibratory Screen Motor Bolts
Maintaining bolt tension in vibrating equipment.
Vibratory ScreensA mining client from Kalgoorlie, WA processes crushed rock through a vibratory screen, a piece of equipment commonly used in mining to classify crushed material into different grades. This process allows crushers to achieve maximum performance by efficiently removing the finishing product from the rock/ore-processing circuit as it is produced.
The Effects of Vibration On BoltsVibratory screens comprise a screening box, single, double, or triple layers of screen mesh, a vibrator, damping springs and hold-down mount bolts. There are many types and configurations of vibratory screens, but they all operate on the same principal and are therefore subject to the same risk of bolt-tension loss through constant vibration. Although the damping springs provide some shock absorption, the equipment is nonetheless subjected to repeated shock, including the hold-down mount bolts. These constant changes in load cause momentary losses of friction in the joint. Eventually, these small repeated movements result in the loosening of the mount bolts. This inevitable self-loosening can only be avoided by using a thread locking device.
The Previous Method
For the hold-down mount bolts, the client was using the standard hex nuts that were supplied with the equipment, tightening them with a flogging spanner. By performing the task manually, the client was experiencing the following issues:
- No control of bolt load
- Inaccurate torque application resulting in bolts vibrating loose frequently
- Manual task required 2 to 3 personnel and took approximately 6 hours to complete
- The task was physically demanding, increasing risk of injury
A Proven Solution
Each EziTite® Hydraulic Nut is screwed by hand onto the existing studs (replacing the original nuts) until the base is tight against the working face. Hydraulic hoses are connected to each of nipple fittings, then hydraulic pressure is applied simultaneously through the nipple fittings on top of each nut body. This forces the piston and the nut body apart, thus stretching and tensioning the bolt through the joint.
The threaded lock ring mounted on the nut body is then screwed against the abutting face to retain the induced load in the bolt. The pressure is then simply released and the hydraulic coupling removed from the nipple fitting to complete the operation.
The outcome was the successful tensioning of bolts with the added benefits:
Safe, hands-free tensioning — The use of hydraulic pressure replaced the strenuous physical effort previously required, and eliminated the use of an unsafe flogging spanner. Now, the pre-tensioned nuts only need to be locked by hand with zero risk to the technician.
Reduction in service time — The task can be completed in just 2 hours, by only 2 personnel, for a massive time saving of 4 hours.
Accurate and simultaneous tensioning — By linking the nuts to a hydraulic pump in series and then tensioning them simultaneously from a single pressure source, every nut is tensioned equally and evenly. This protects the joint from bolt tension loss when exposed to vibration.