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• 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% H2SO4

4 - 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 System : Salzle Plant

Current Polishing System : “Salzle”

• Three double and two single plants• Series of polishing and rinse tanks• Open system• Composition 65% – H2SO4

3% - HF1 – 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

Drum Polishing Plant

Drum Polishing Plant

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

Acid Related Problems “Filling/Emptying”

SystemSystem ProblemProblem SolutionSolution

Salzle Fuming • Adjustment of the dippingstroke• Use of risers• Weights on the basket

Drum “Blue” Fume • Change loading method

Adjustment of the Dipping Stroke

Adjustment of the Dipping Stroke

Practical Solutions to Aid the Reduction of “Fumes”

Acid Related Problems - “The Dipping Motion”

SystemSystem ProblemProblem SolutionSolution

Salzle Basket Marks • Adjustment of the stroke• Change loading techniques i.e. use of tubes

Drum White Scratching

• Speed control • Changing the loading techniques

Tubes to Assist in the Reduction in Basket Marks

Acid Related Problems - “The Effect of Pressure within the Polishing Tank”

SystemSystem ProblemProblem SolutionSolution

Salzle “Tails/Flicks” • Crossbar in the insert

Drum “Runs” • Change loading method

Inserts with Crossbars

Inserts with Crossbars

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.

Ends