|Frequency||10 to 200 Hz|
|Stroke||20 µm to 2.0 mm|
|Load||0 to 1.0 kg with supplied weights|
|Maximum friction force||Dependent on amplitude maximum 10.0 N|
|Temperature||Ambient to 150°C (400°C with high power heater box)|
|Standard upper specimen||6.0mm diameter ball|
|Standard Lower specimen||10.0mm diameter x 3.0mm thick disc|
|Power||Mains power 100 - 240VAC, 50/60 Hz, 400W|
|Heaters||Two 24VAC, 15W cartridge heaters|
|Fuses||Mains power 3.15A|
HFRR Mechanical and Control Unit Dimensions
Dimensions & Weight
|Control Unit||300mm / 12in||400mm / 16in||150mm / 6in||8KG (18lb)|
|Mechanical Unit||150mm / 6in||340mm / 13in||225mm / 9in||24KG (53lb)|
HFRR Mechanical Unit
An electromagnetic vibrator. This drives the upper specimen holder back and forth via a pushrod. The vibrator is pivoted to allow the upper specimen holder to be removed more easily.
Attached to the front of the vibrator is the LVDT and flexure housing, which carries the fretting flexure lock which protrudes from the front of the casing. The fretting flexure lock has a knurled section at the front and is engaged by screwing it fully in to the front of the LVDT housing and disengaged by screwing it fully out. The LVDT (linear variable differential transformer) is an electrical displacement measuring device which allows the electronics unit to monitor the motion of the pushrod and adjust the frequency and amplitude of the vibrator as necessary.
Upper specimen holder
This is made from 316 stainless steel and holds the upper specimen, which is normally a 6.0 mm diameter ball. The upper specimen is held in place by a small grub screw. The upper specimen holder also has a loading pin to which the dead weight loading is applied. The upper specimen holder is attached to the pushrod by a single M3 socket head cap screw. Two pins protrude from the pushrod end to ensure the specimen holder is correctly aligned. The upper specimen holder is electrically insulated from the rest of the machine. This is important for the contact resistance measurements.
Lower specimen holder
This is in the form of a shallow bath, again made from 316 stainless steel. The lower specimen, normally a 3 mm thick by 10 mm diameter disc, is held in a recess in the specimen holder. The lower specimen is retained by two M3 button headed socket screws. The specimen holder is clamped to the heater block by two M3 socket head cap screws. An angled hole in the left side of the specimen holder provides location for the 1.6 mm diameter main RTD used to measure the lower specimen temperature.
HFRR Lower Specimen Holder
Platinum RTDs (resistance temperature devices) are used in preference to thermocouples as they offer greater precision of temperature measurement and an easily diagnosable response in the event of a sensor failure. NOTE: The main RTD contains a ceramic sensor in the tip of the probe. This will be permanently damaged if the probe is bent even by a small amount. Take care not to bend the probe when fitting and removing it from the lower specimen holder.
An aluminium heater block, containing two 24V electric heaters. These can be switched by the control system to give either full or quarter power. The upper surface of the heater block and the underside of the lower specimen holder are ground flat and care should be taken not to damage these surfaces as this would impair the heat transfer to the lower specimen holder.
The heater block is supported on two flexible supports which are designed to be vertically and laterally stiff but relatively flexible in the direction of relative motion between the specimens.
The heater block is longitudinally restrained by a piezoelectric force transducer which measures the friction force generated between the two specimens as they slide relative to each other. This force transducer is relatively much stiffer than the flexible supports and this ensures that the majority of the friction force appears at the transducer rather than at the supports.