The case for steel pilots in larger couplings
Isoflex’s larger coupling range uses steel pilots, also called spigots or registers. In the early days, it was found that competitive couplings had significant run-out issues leading to vibration. So instead of minimizing vibration, it was creating it. Isoflex set to work looking at the range of polymer couplings on the market. All materials have some coefficient of thermal expansion, however, it was found that polymers have quite a significant thermal coefficient, approximately 5 times that of steel.
Whilst we machine our polymer spigots to a 0.05mm tolerance, it was found that changes in ambient temperature made the male spigot possibly loose in cold climates, i.e. 0-3 degrees C, and tight in say 30 degree C installations (the females being the opposite). This was found to contribute to run-out and consequent vibration on larger couplings where the factor resulted in up to 0.4mm variation in diameter. Isoflex found that by fitting and precision-machining steel pilots, this thermal coefficient was negated and the run-out removed. And, this did not affect the coupling’ performance or purpose.
A further source of run-out was removed by precision machining the coupling faces, removing any polymer standing proud of the steel bolt inserts.
Further improvements to all Isoflex couplings include machining the couplings torqued to a jig, ensuring absolute true running upon installation, and a variation to internal bolt insert fittings to prevent them from spinning on installation and removal.
These precision-machined steel male and female pilots are molded into the polymer disc in Isoflex’s 8-bolt and larger couplings.