The coolest SLA models ever?

From: Murphy, Matt (
Date: Mon Jan 26 1998 - 17:00:00 EET


I was surprised at how well some SLA prototype nozzles for cryogenic
blasting withstood a demanding test programme at very low temperatures. It
is a nice general case study illustrating cost / time benefits of additive
fab., but may be relevant to any of you with sub-zero

Blast cleaning is conventionally associated with the use of a solid
recoverable blast medium which can cause damage to components in the
vicinity of the item being cleaned, and any residual blast medium will
create a potential contamination risk. By using food quality dry ice (solid
CO2) as the blast medium there is neither the possibility of damaging the
environment around the item being cleaned, nor risk of contamination with
the residual blast media, because the dry ice simply sublimes from solid to
gas as soon as the cleaning process is complete.

Clean Surface is a UK designer and manufacturer of dry ice blasting
equipment, and the company is currently leading a CEC funded research
project to develop dry ice blasting for application in the food industry.
 Pera Technology have been contracted to perform most of the research and
development work on this project at their site in Melton Mowbray, UK.

The first stage of the programme was to improve the performance of the
existing blast nozzle to give faster cleaning rates and improved levels of
cleanliness. Clean Surface provided seven potential Venturi nozzle designs
to be tested in order to identify the most effective. In production these
nozzles are assembled from a number of component parts, each machined from

The performance testing procedures dictated that the prototype nozzles did
not need to be produced from steel, but did have to operate effectively at
temperatures approaching -50 C, whilst carrying compressed air at 5.5 bar
(travelling at 300 m/s through a Venturi) and delivering 30 kg of dry ice
per hour to the work piece.

The seven prototype nozzles were built on Pera Technology's 3D Systems Inc
SLA-350 StereoLithography system in SL 5190 resin with a layer thickness of
0.1 mm. Each nozzle was 250mm high and all seven were built together in 65
hours. The use of additive fabrication uniquely allowed the Venturi
nozzles to be manufactured as a single piece, and the transparency of SL
5190 allowed the complex internal cavities to be clearly seen. This use of
StereoLithography yielded a cost saving of 60% and a time saving of 90% (2D
drawing to 3D CAD to finished SLAs in 7 days) over conventional prototype
manufacturing methods using steel.

Following a successful three month test programme (during which full
functionality was assessed) the SLA nozzles were sectioned to reveal an
insignificant amount of wear. The new nozzle design is already in
production and has been enthusiastically received in a number of industry
sectors for applications including de-coking racing engines, cleaning
printed circuit boards and cleaning various types of dies and moulds.

For further information please contact

Dr Matt Murphy
Practice Leader - Rapid Manufacturing
Pera Group, Technology Division
Melton Mowbray, Leicestershire, LE13 0PB
Tel: + 44 (0) 1664 501 501
Fax: + 44 (0) 1664 501 589

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