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What is More Important in Acid Polishing Chemistry or Motion ?. Chris Sandby-Thomas B. Eng. ICF Conference, Waterford 2002. People’s Perceptions of Acid Polishing. Still consider polishing a “black” art Viewed as a “potentially” hazardous place to work
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What is More Important in Acid PolishingChemistry or Motion ? Chris Sandby-Thomas B. Eng. ICF Conference, Waterford 2002
People’s Perceptions of Acid Polishing • Still consider polishing a “black” art • Viewed as a “potentially” hazardous place to work • Working with toxic/corrosive chemicals that have possible health/environmental implications • Chemistry is complex • Unpredictable
What benefits have the current polishing systems brought to Waterford ? • Consistency of polished product • Better understanding of the chemical process • Better control of the process through monitoring and measuring • Increased awareness of relevant health, safety and environmental issues • Improved “working” environment • Increased productivity • Lower unit cost.
History of Polishing Systems Within Waterford Crystal Auto acid – now replaced. • Based on the carousel type system • Composition 37 – 42% HF 15 – 20% H2SO44 - 5% H2SiF6 • 2 minute cycle time • Visual monitoring “grey edge” • High acid repair and scrap levels • High acid usage (HF) • Inconsistent performance in relation to quality
History of Polishing Systems Within Waterford Crystal Robotic acid – now replaced. • Same composition and cycle times as auto acid • Constant breakdowns • High losses • High levels of acid related repair • High productivity, poor yield • Now operate two processes: • Salzle plant • Drum polishing system
Current Polishing System : “Salzle” • Three double and two single plants • Series of polishing and rinse tanks • Open system • Composition 65% – H2SO4 3% - HF 1 – 3% H2SiF6 • Cycle time 40 minutes (26 minutes acid time) • Dipping arm works in vertical motion, moves between acid/rinse tanks • Patented chemical system
Benefits of the Salzle Plants to Waterford Crystal • Clarity of the blank glass • Definition of the polished cuts • Consistency of polish • Low levels of acid related repair • Operator friendly • Suitable for stemware and hollowware products • Acid parameters easily controlled • Significant reduction in acid consumption • Lower scrubber emissions • Lower unit cost per glass
Current Polishing System : “Drum” Plant • Currently 1 system, with 3 drums • Closed system • Rotating drum in horizontal mode • Acid / rinse acids pumped from working tanks to reaction tanks as required • Cycle time 60 minutes (19 minutes acid time) • Works at higher temperature than Salzle (60 degrees versus 52)
Benefits of the Drum Process to Waterford Crystal • Suitable for polishing heavy solid giftware items and narrow necked products • High volume throughout • Flexibility in relation to the loading of product • Low repair figures
Basic Chemical Reactions ApplicableTo Both Systems: • Formation of silica tetra-fluorideSi02 + 4HF SiF4 + 2H20 • Formation of lead sulphatePb0 + H2S04 PbS04 + H20 • Formation of soluble salts e.g. (KF)K20 + 2HF 2KF + H20 • Formation of hydrofluorosilicic acidSiF4 + 2HF H2SiF6
What are the main reasons behind “Acid Related Problems” Each system has its own distinctive “acid related” problems – why do they occur ? • Is it simply because the acid conditions vary and can be out of balance ? • Or can each problem be resolved logically without adjusting the acid parameters ? • i.e. is it a chemical problem or a physical problem or both ?
What Causes Acid Related Problems ? We can determine by assessing the mechanisms that surround the polishing process : • How the glassware fills and empties • The effect the dipping motion has on the polishing process • The effect of pressure within the polishing bath It may be shown that acid related problems are dictated more by external forces than the chemistry of the system
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Acid Related Problems - “The Effect of Pressure within the Polishing Tank”
Conclusion • By applying logical principles to both polishing systems under constant chemical conditions, it has been shown that acid related problems can be more systematic of “Motion” rather than “Chemistry” • As new designs emerge, motion has become even more critical, especially to counteract the effect of • Heavy hollowware (the W Collection) • Thin, tall contemporary stemware.
Chemistry or Motion ? • As a chemical engineer, I am not stating that motion is more important than chemistry. • It is important to understand the possible chemical reactions that occur within a polishing tank, especially in respect to new glass compositions or even if new acid formulations are used. • However, Waterford’s experience suggests that “Motion” has an equally important part to play in the modern polishing system, to allow us to continue to operating at consistently high quality and low cost.
