‘Feeder expendables’ is the name given to refractory parts used in the gob forming process. They are ‘expendable’ because they are changed frequently during the life of the furnace depending upon the requirements of the forming operation. As the final link between the melting and the forming processes however their properties have immense influence on the success or failure of the entire forming operation. They must be able to resist the corrosion from molten glass at the same time as being able to withstand the thermal shock of immersion in molten glass. Here at PSR we understand the importance of this final link in the glass forming operation and we exercise rigorous control over our manufacturing and inspection procedures to ensure that all our refractory parts meet these critical criteria.
The gob forming process is dominated by the technology of and as their sole worldwide refractory licensee we are able to ensure that all our feeder expendable refractory parts comply with the original Emhart manufacturing drawings and tolerances.
Our refractory compositions are slip cast not chemically bonded or pressed, ensuring a homogeneous ceramic body with a densely packed surface texture.
Slip cast into plaster moulds, dried in humidity controlled drying chambers and sintered at high temperatures, PSR feeder expendable refractories are renowned for their consistency, reliability and longevity.
PSR-333 – 11.25% ZrO2
PSR-333 is the international standard for feeder expendable refractory material. A direct bonded zircon-mullite composition, the constituent oxides react at high temperature to form a strong ceramic bond, combining excellent resistance to alkali corrosion with resistance to thermal shock.
PSR-315 – 18% ZrO2
PSR-315 combines higher zirconia content with higher firing temperatures to achieve enhanced corrosion resistance without compromising thermal shock properties. PSR-315 can be specified for most feeder expendable parts but is particularly beneficial for spouts, tubes and high tonnage applications.
PSR-333 FG is a derivative of PSR-333 with similar characteristics to PSR-333 but is reformulated for the casting of small complex shapes such as orifice rings.
PSR-311 91% Al2O3
PSR-311 is a high alumina refractory that is used mainly in tableware production where the presence of zirconia causes excessive seeding after refractory replacement.
PSR-993 99.7% Al2O3
PSR-993 is the bonded alternative to fused-cast α-β alumina. Developed for use as the glass contact material for distributors and forehearths PSR-993 exhibits equivalent corrosion resistance to fused-cast alpha-beta alumina and is commonly used for long life spout bowl applications. Its lower thermal shock resistance make it generally unsuitable for other feeder expendable applications.
PSR-SM62 62% Al2O3
PSR-SM62 is an andalusite based composition sintered at high temperature to facilitate the development of mullite and was specially developed for forehearth superstructure applications. In the feeder its excellent thermal shock properties also make it the ideal refractory material for spout cover blocks and spout burner blocks.
METERING SPOUT SYSTEM
At the forefront of modern gob feeder technology is the Metering Spout System, a special design of feeder expendable refractory parts developed by that brings new levels of sophistication to the gob forming operation. As a licensee of Emhart PSR have complete access to all the metering spout refractory designs, including the high tonnage 585 feeder.
The metering spout system has the following unique features:
- A special metering tube with a taper on the bottom that leads into a matching taper on the spout throat to form a metering valve. The diverging tapers reduce sensitivity to tube height changes, improving gob weight control.
- A special shaped orifice ring that allows more space around the outer cavities, improving the glass flow patterns within the orifice ring.
- A special metering spout bowl with an elliptical outlet and tapered throat to match the special shaped orifice ring and tapered tube. Additional insulation in the lower part of the spout bowl reduces heat losses and enhances thermal homogeneity.
- A heat baffle located inside the tube. This enables heat entering through the tube vents to be deflected down towards the glass. Heat losses from the surface of the glass are further reduced by removal of the ‘chimney’ effect within the tube.
PSR PREFORMS & GASKETS
PSR PREFORMS are pressed ceramic fibre shapes moulded to fit the exterior contours of the orifice ring and the interior contours of the orifice ring holder. Made from bio-soluble grade fibres they provide a clean and highly efficient form of orifice ring insulation, reducing heat losses from the holder and improving the thermal homogeneity of the gob forming operation. Formed to fit the precise shape of the orifice ring they also provide support over its entire exterior surface, reducing the risk of orifice ring cracking through mechanical failure.
Gaskets are also available as a sealing ring between the orifice ring and the spout. Manufactured from bio-soluble grade fibres PSR gaskets are available in a range of diameters and thicknesses and are a clean and efficient alternative to the use of the traditional orifice luting cement.
Spouts manufactured in PSR-315 offer excellent service life under most operating conditions. For extended service life, or where operating conditions are more aggressive, we recommend the use of our dense bonded alumina material PSR-993.
An alternative method of extending spout life is the use of inserted spouts where the tube seating area is replaced by a special ceramic insert. PSR offer the insert manufactured from a void-free fused-cast AZS material containing 32% ZrO2. For ease of installation the insert and spout are supplied as a pre-assembled unit held together by a specially designed clamp which can be removed following installation.