Wyman-Gordon worked in conjunction with Mech-Chem to establish a design for the new Acid Etch and Chem Mill Operation with the following features:

1. Increase the volume in the acid etch and chem mill tanks from 250 gallons to 375 gallons to extend the life of the chemical baths.
2. Increase the basket size to provide a 50% increase in the number of small parts that can be processed per batch and a 100% increase in the number of large parts that can be processed per batch.
3. Provide an additional acid tank in the new Acid Etch and Chem Mill Operation which allows two baskets to be in production at the same time.
4. Add an alkaline cleaner tank and rinse tank to allow all components to be pre-cleaned before entering the acid tanks. Processing only clean parts extends the life of the acid baths.
5. The new acid tanks have an eductor system to provide agitation of the solution. This eliminates air agitation from the design, reducing the evaporative losses of hydrofluoric acid and nitric acid.

The facility also features a PLC control system built to NEMA 4X specifications, with a color display and a Windows environment for controlling the Chem Mill line.

The following describes the components of the facility:

Acid Etch and Chem Mill System

The new Acid Etch and Chem Mill System consists of the following components:

• The Acid Etch and Chem Mill System have a total of nine tanks: one alkaline tank, four acid tanks, three cold water rinse tanks, and one hot water rinse tank.
• The system uses new, larger chem mill rotating baskets, which are handled and transferred by an overhead crane structure.
• Teflon coated electric heaters are installed in the tanks which contain solutions that require heating.
• Teflon heat exchangers are installed in the tanks which contain solutions that require cooling.
• A pump with eductor recirculating system was installed in all the tanks for agitating the solutions in the tanks instead of using an air agitation system.
• The rinse tanks have countercurrent water flow.
• All the tanks have level instruments with alarms for high/low level.

Ventilation System with Fume Scrubber

• All the tanks in the acid etch and chem mill system, including the rinse water tanks, are equipped with push/pull ventilation.
• The push/pull ventilation system is designed to meet the OSHA regulations for air flow and fume venting requirement for the chem mill and acid etch tanks.
• The blowers for the push/pull ventilation system are mounted on the roof of the building to keep the noise level in the building below the OSHA regulations.
• The fume scrubber is designed to meet the State of New Hampshire’s DEQE current regulations for air emissions for HF and NO3.

Wastewater Recovery System

• The Acid Etch and Chem Mill Operation uses deionized water in the hot and cold water rinse tanks for rinsing the parts and makeup of the acid baths.
• The operation is designed to process the wastewater discharged from the rinse tanks through an ion exchange resin system which recovers the contaminated wastewater and provides deionized water for recycling back to the tanks.This allows approximately 80% of the wastewater generated by the operation to be recycled.
• The ion exchange resin system is an automated dual bed (2-anion and 2-cation cylinders) unit which allows it to remain in operation continuously. The system is also equipped with prefilters before the resin beds.
• The ion exchange resin system has a wastewater hold tank to feed the ion exchange resin system and DI water hold tank with a recirculating piping loop to the acid etch and chem mill system.
• The backwash from the ion exchange resin system and the aqueous discharge from the fume scrubber are processed through a wastewater pretreatment system before being discharging to the local POTW. This system removes the metal ions, fluorides, and insoluble particulates from the wastewater.
• The system has a final pH monitoring and adjustment tank with pH recorder and flow measurement which is required by Federal EPA regulations. Federal EPA regulations require final pH control and monitoring and continuous flow measurement for process wastewater entering a POTW.

Acid Storage and Piping Systems

The new Acid Etch and Chem Mill Operation requires storage and handling for hydrofluoric acid Hydrofluroic Acid Delivery System(HF), nitric acid (HNO3) and sodium hydroxide (NaOH) solution.

• Hydrofluoric acid is small volume usage and is purchased, stored, and handled in 55 gallon drums. The drums are placed in a small containment unit and pumped through a double contained pipe to the acid tanks.
• The nitric acid has a fairly significant volume of usage and is stored in a 5,000 gallon bulk storage tank. The nitric acid is pumped through a welded stainless steel pipe to the acid tanks.

Waste Acid Storage and Piping Systems

• The concentrated waste acid solutions discharged by the treatment operation is pumped through a double containment pipe to a double contained waste acid storage tank.
• The concentrated waste acid collected in the storage tank is then shipped off site for disposal. The storage tank and piping systems are designed to meet the EPA’s current Risk Management and Certification requirements.

Secondary Containment for Tanks, Equipment, and Tank Trucks

There are several sections of the new Acid Etch and Chem Mill Operation which required secondary containment, including:

• Secondary containment for the process tanks and wash down area.
• Secondary containment for the ion exchange resin system and wastewater treatment system.
• Secondary containment for hydrofluoric acid, nitric acid, and waste acid storage.
• Secondary containment for bulk tank trucks for delivery of nitric acid and pick up of waste acid solution.