Largest ever rotors manufactured in UK

Precision Components, Milnrow, Rochdale, part of the Precision Technologies Group (PTG), has produced the largest sets of screw rotors ever manufactured, for a gas compression project in the Far East. The screw rotors, which are 816 mm in diameter by 33,500 mm long, and weigh in at 6 tonnes each, are manufactured in stainless steel to resist corrosion from highly contaminated gases and gas mixtures. The rotors are produced on an uprated Holroyd 8A milling machine - the largest helical profile-machining centre in the Precision Components workshop, able to produce rotors up to 816 mm in diameter. Due to the amount of material that had to be removed, the 8A required approximately two-weeks to rough-cut each rotor form. The rotors were then heat treated to relieve metal stress and finish milled at Precision Components facility. Unlike smaller screw rotors that are produced in higher numbers in a semi-automated process, each large set had to be manufactured as a matched pair. The finished dimensional tolerances of the corresponding male and female forms were maintained to just a few tens of microns throughout the complete intermeshing profile surfaces. The bespoke tooling and checking procedures required to achieve this were all designed and produced in-house to ensure total control and consistency throughout the manufacturing process. The female rotor required less tooling, so was produced first. The male rotor was initially milled 100 microns oversize, and then the sets were meshed together in a test cell where the profile clearances were measured and mapped. The male rotor was then progressively machined down close to finished size providing the opportunity to modify or ‘fine tune’ the form where necessary. Once this process was completed, a finish cut was made to remove the last 25 microns, resulting in two intermeshing profiles. The Precision Group’s engineering advantage is that it both manufacturers the 8A machine and is also a sub-contract supplier of the precision helical components, hence the company is able to direct the development of new machines to match market requirements for larger rotors. The result has been a comprehensively re-designed new 8EX machine from Holroyd Precision which is the first machine of the new generation of machines, and the only machine capable of accurately cutting deep helical profiles with a diameter of over 850mm. Commenting upon the order, Precision Components’ managing director, Colin Carr, said: “We are proud to have won this contract based upon our abilities as a provider of truly world-class engineering solutions. Doubly so, since it comes hard on the heels of a £2.4 million order for Holroyd Precision from a Far Eastern customer for what is the world’s largest rotor milling machine. These orders are confirmation of our advanced skill levels, and of our investment in new product development to remain at the forefront of helical profile-machining technology.”