2) Water can be the cause of many plating difficulties. disposal problem

Transcription

1 REASONS WHY WATER IS VITAL TO A PLATER 1) Suitable water is becoming more costly 2) Water can be the cause of many plating difficulties 3) Water once used represents a disposal problem

2 WATER TERMINOLOGY 2 Water Sources: The source of raw water for a plating shop is either a surface water or a ground water. Water Quantitv: Measured in gallons. One gallon of pure water weighs 8.33 pounds and has a volume of A34 cubic feet. Water Flow: Measured in gallons per minute (gpm) or gallons per hour (CJPh). Water Qualitv: Described in the broad categories of: Hard --hard to wash in, because of dissolved mineral salts that form insoluble substances after contact with soap;

3 WATER TERMINOLOGY 3 Soft --low in mineral salts Distilled -all mineral and organic matter removed by converting water to vapor and then condensing the vapor in aclean vessel Deionized-mineral salts totally or partially removed, or replaced with another salt.

4 4 Raw water may contain any or all of the following: Dissolved mineral salts Dissolved organic salts Dissolved gases Undissolved matter (turbidity and sediment) Microorganisms (living matter) THE ONLY WATER SUITABLE FOR USE IN THE PLATING ROOM IS PURE WATER. Doing rinsing process modifications makes pure water affordable.

5 5 WHAT HAPPENS IN RINSING? Three mass transport phenomena: Diffusion =-adding water to a cup with molasses --part at the bottom of a still rinse Natural (free) convection --drops of blue food coloring --rack hanging in a still rinse Forced convection --bubbler in the fish tank --moving the rack (or ice cube tray) vigorously up and down

6 6 WHAT IS GOOD RINSING? 1. Turbulent relative motion between the work and the water. 2. An adequate period of contact between the work and the water. 3. The presence of sufficient water during the contact period to properly reduce the concentration of the salts that are washed off the surface.

7 Examples of Turbulent -Relative Motion 7 The direct flow of water Manual motion of the work Mechanical motion of the work Blowing of air through the water Pumping of water Propeller agitation Vibratory agitation (ultrasonics)

8 8 SUMMARY OF GOOD RINSING PRINCIPLES d Use agitation in the rinse tanks 4 Allow sufficient time for good mixing d Use properly designed rinse tanks d Use more than one rinse tank wherever possible d Use rinse tanks of the smallest size compatible with easy handling of the work d Have rinse tanks of equal size d Use a wetting agent in the rinses d Use warm or hot water where possible

9 WASTE REDUCTION PRINCIPLES for PLATERS 9 4 Keep plating solutions in the tanks where they belong -d Return to the tanks as much escaping liquid as possible 4 Use the least amount of rinse water required for good rinsing

10 10 CALCULATIONS The Concentration Effect =-the result or reducing dragout or high evaporation rates Cp = Cw (1 + E/d) Cp = concentration in the process solution of the substance (contaminant) Cw = concentration of the substance (contaminant) in the water (or dragin) E = evaporation rate of the process solution in gallons per unit time d = dragout rate in gallons per unit time

11 11 CALCULATIONS Example: In a bright nickel solution the evaporation rate is 1 gph and the dragout rate is 0.01 gph. Copper is present in the input water at 3 mg/l. To what value will the copper be increased in the plating tank? Answer: Cp = 3(1 + 1/0.01) = 303 mg/l Is this a problem?

12 12 CALCULATIONS Averaue Steady State Concentration --knowing how much of the substance (contaminant) is in the rinse Cs = dcp/(w + d) Cs = average steady state concentration of the substance (contaminant) in the rinse Cp = concentration of the substance in the process tank immediately preceding the rinse d = dragout volume W = total amount of water used in the rinse per rack, over the time interval between racks

13 13 CALCULATIONS Example: The concentration of chrome salts being rinsed directly into a single rinse tank is 50 ozlgal. The water flow is 3 gpm, and there are 5 minutes between loads. The rinse tank holds 100 gallons of water and the dragout rate is 0.1 gallon. What will the steady state concentration of chrome in this rinse tank be, given this rinse cycle? Answer: W =5~3=15 d = 0.10 CS = 0.1 x 50(15 = 0.1) = oz/gai Is this a problem?

14 14 CALCULATIONS Final Rinse Concentration ==knowing what is in the last (most critical) rinse Cn = (d/w)ncp Cn = concentration of the substance (contaminant) in the final rinse d = dragout W = water used between loads of work n = number of rinse tanks Cp = concentration of substance (contaminant) in the process tank before the rinse line

15 15 CALCULATIONS Example: For chrome plating, the concentration of chrome in the final rinse should not exceed 0.01 ozlgal. If two rinse tanks are installed with parallel feed on the revi0us line (the concentration of chrome salts I? eing rinsed directly into a single rinse tank is 50 oz/gal; the water flow is 3 gpm, and there are 5 minutes between loads; the rinse tank holds 100 gallons of water and the dragout rate is 0.1 gallon) what will the water flow have to be to maintain that final rinse concentration? Answer: C2 = (.10/15)2 x 50 = 2.2 gpm