Product Material Data Steerman Product Range.
All Steerman systems (with the exception of the SX5 front frame which is fabricated) are produced from Spheroidal Graphite Cast Iron also know as Ductile Iron. The material is produced in accordance with the British Standard BS 2789: 1985 (now known as BS EN 1563: 1997) the material designation is 420-12. (420Nmm tensile strength-12% elongation)
Tensile strength: 27.2 Tons/in2
Proof Stress (0.2%): 17.5 tons
Elongation: 12%
The castings are produced in resin bonded rigid sand moulds for repeated accuracy. The SG iron is melted using electric induction furnaces for complete material control.
The finished castings are shot blasted to remove any residue from the casting process and dressed to remove flashing and bars.
This ductile material is very resilient in service, providing a higher carrying capacity to weight ratio then conventionally fabricated steel frames, which are usually much bigger and heavier. Like for like on capacity SG Iron is some 10% lighter than steel.
All SX series frame designs were subject to finite element analysis during the design stage. Destructive testing was completed during development with some very satisfactory results. The wheel bearings are the limiting factor on all skate models.
SX10 rated capacity: 5 ton tested capacity before failure 33 ton
SX20 rated capacity: 10 ton tested capacity before failure 26 ton
In all test cases the castings did not fracture, they simply deformed at the designed point of yield.
There are 2 types of cast nylon material used for the production of the wheel assembly, simply identified by their colours BLACK or BLUE. The black wheels having approximately 25% greater load carrying capacity in comparison to the blue,
Both types of material have similar mechanical properties with a much-improved performance compared with natural cast nylons. The wheels are machined from bar stock and the bearings are pressed into place to complete the assembly.
Compared with natural cast nylons BLACK Moly and HS BLUE gives:
Both materials provide high resistance to shattering and deformity when striking debris in use where normal natural cast nylons would fail.
The cast nylon turntable absorbs a large percentage of any dynamic load placed on the turntable assembly, this can occur through natural means such as the movement of the skates under load or the extreme case where a load is lowered by a crane onto the turntable (this practice is not recommended).
To provide a quality finish all painted components are finally prepared and polyester powder coat finished to meet the current European “Qualicoat” Standards giving an average surface finish of between 70-80 microns.
The coated components are baked to achieve a metal temperature of 180ºC to ensure a properly stoved finish which gives a much more durable coating then wet paint systems.
All finish machined axle shafts, handle pivot pins and wheel box pivot pins are bright zinc plated and completed with a clear passivated finish to prevent corrosion. With an average depth of covering of between 15 to 20 microns this process ensures that the unit remains easily serviceable in extreme environmental conditions.
On all SX models 5 thru to 30 the wheels are fitted with single row deep groove ball bearings, shielded both sides to prevent ingress of debris and fitted with an extended outer race. The extended outer race gives low resistance when the wheels contra-rotate and provides a predetermined working clearance between each wheel. Due to the low ground speeds achieved with this type of equipment the radial loadings of the bearings increase accordingly. The bearing has sealed for life lubricant and is therefore unserviceable.
All models are fitted with single direction thrust ball bearings designed to accept high axial loadings, the three part bearing consists of 2 outer races with a central bearing race, the roller ball bearings are housed in a cage and the bearing can be cleaned and serviced as and when required.
The cast nylon turntable absorbs a large percentage of any dynamic load placed on the turntable assembly, this can occur through natural means such as the movement of the skates under load or the extreme case where a load is lowered by a crane onto the turntable (this practice is not recommended).
United Kingdom - EN
