Emerald Group Publishing Limited
Copyright © 2004, Emerald Group Publishing Limited
Rocket motor bodies processed on automatic grit blasting machine
Rocket motor bodies processed on automatic grit blasting machine
Keywords: Roxel Ltd, Blasting, Rockets, Missiles
Roxel (UK Rocket Motors) Ltd, based at Summerfield, near Kidderminster, UK, has recently installed a “Vector 150P” automatic grit blasting machine from Vacu-Blast International (part of the International Surface Preparation Corporation), for the processing of the internal surfaces of rocket motor bodies used in a range of tactical missiles. The machine is employed to provide an effective surface key for the subsequent processing of rocket motor bodies (Plate 1).
The Vector machine features a “Vacutrol III” PLC based control system operating with Windows software, and replaces a much older, purpose-designed Vacu-Blast machine, which has more than stood the test of time, having been installed at the site in the 1960s and used with only minimal modification ever since. Although this machine is still operational, its replacement was necessitated by latest health and safety and noise limitation requirements.
Plate 1 The new Vacu-Blast “Vector” automatic grit blasting machine at Roxel (UK Rocket Motors) Ltd, which is used to provide the optimum surface etch on the internal bores of rocket motor bodies
Handling and loading operations have also been streamlined, with the motor body sections being loaded vertically into the Vector machine by overhead hoist directly from adjacent production machinery.
The new machine utilises a special twin-nozzle grit blasting lance that traverses down through the internal bore of the rocket motor body, which is located on a powered turntable. The traversing speed of the lance, turntable rotating speed, blast pressure and blast duration are programmable according to the type of motor body being processed, to ensure a consistent, even and reproducible surface. The machine has the capability of using three different media grades, depending upon the nature of the motor body being processed.
The process is contained within a 1,500 × 1,500 ×3,000 mm high, fully sealed and acoustically insulated blast enclosure, which ensures that there is no dust escape and which keeps the noise level under 80 dB(A). The enclosure features a Vacu-Blast “Waffle Floor”, a system that uses a series of “mini-hoppers” to collect spent blast media, dust and debris, which are then conveyed pneumatically via a common duct to a power-pack/reclaimer unit. The latter separates out degraded material and returns reusable media to the media hopper for reuse. A “blast elapsed timer” is incorporated into the machine's software to ensure that recycled media quality and input can be closely controlled.
Commenting on the new installation, a Roxel representative stated: “The critical nature of our surface treatment operations obviously dictates that we have to use efficient, quality engineered equipment that does the job effectively and reliably. The existing Vacu-Blast grit blasting machine more than demonstrates this, and we also have a number of other Vacu-Blast machines at this site, so we had no hesitation in looking to the company again when it came to updating this particular operation.”
The recent installion of the latest “Ventus 92PR” pressure-fed dry abrasive blasting cabinet machine from Vacu-Blast International, by a leading specialists in advanced physical vapour deposition (PVD) coating and ion implantation technology, Tecvac Ltd, Swavesey, Cambridge (a Wallwork Group company) demonstrates the scope of VacuBlast's equipment (Plate 2).
The machine was introduced specifically for the dedicated surface preparation of titanium alloy and nickel alloy based aeroengine components. These are PVD coated to enhance their resistance to wear: titanium alloy components, mainly turbine compressor blades, are titanium-nitride (TiN) coated, and nickel alloy parts are chromium nitride (CrN)coated.
Plate 2 A “Ventus 92PR” cabinet machine is used to ensure optimum surface preparation of critical components, such as the aeroengine compressor blades pictured, prior to the application by Tecvac of a wear-resistant PVD coating
The Ventus machine is used to remove the “dead surface layer”, which results from heat treatment, and simultaneously create the optimum surface key for the PVD coating to adhere successfully. Following trials at the ISPC sample processing and demonstration facility in Birmingham, the powerful pressure-fed Ventus blasting system was selected in order to facilitate the fastest possible processing of the surface.
This minimises any potential adverse modification of the existing substrate, particularly when parts have been shot peened after heat treatment. The parts are retained in tailored polyurethane fixtures, with pink alumina media being used for the blasting operation, which is carried out manually.
To ensure a consistent surface result, Ventus “PR” models feature a high integrity, in-cycle blast media recovery and separation system, housed in a separate free-standing “power-pack”, allowing the machine to be used for the most demanding, precision surface treatment applications, with most types of media. The power-pack can be situated on either side of the machine to facilitate installation in virtually any location. The machine's processing enclosure measures 900 × 800 × 800 mm high. To minimise any risk when working with titanium parts, the machine at Tecvac includes special over-pressure relief panels.
The machine's large 640 × 740mm access door has been designed to eliminate dust spillage and is safety-interlocked, and the blast enclosure features a raised workplate which avoids potential damage to the door seal when loading and unloading the machine.
The media recovery and separation system automatically separates out and recycles reusable blast media back to the blast nozzle. A COSHH- compliant reverse-jet dust collector with quick- release filter cartridges is used to collect degraded media, dust and debris.
The dust collector provides pulsing of the cartridges whilst the machine is operating, to ensure that they are cleaned as efficiently as possible. A special isolating system is also included to enable optional downtime pulsing of the cartridges following heavy dust removal applications.
In addition to providing advanced-technology coating services, Tecvac manufactures PVD coating systems for the production of hard coatings on tooling, moulds and a wide variety of precision engineered components. These machines are functional and robust, and incorporate the latest process automation and control systems. The company also produces industrial-scale ion implanters for specialised surface modification applications. With an increasing demand for its contract coating services, driven largely by the need for less environmentally damaging engineering coating processes and the growing use of wear-resistant surface treatments, the company is currently adding additional production capacity at its Swavesey site.