Case Study, Minnesota Technical Assistance Program, University of Minnesota
Company: Dayton Rogers Manufacturing Company, Minneapolis, MN.
Industry: Short-run metal stamping. Short run jobs vary from 10 to 100,000 parts, specializing in quick order turn around.
Waste Stream: 1,1 1-trichlorethane (TCA)
Process: Cleaning stamped and drawn metal parts in a vapor degreaser to remove oil-based lubricants.
Change: Replaced a vapor degreaser with an upgraded abrasive deburring system that uses a vibratory tumbler and a wet sander, along with water-based cleaning solutions.
Cost: $9,000 for a wet-sanding machine and a sheet metal drier.
Savings: Saved over $26,000 in operating costs by 1991 by:
Background
Dayton Rogers of Minneapolis, Minnesota was founded in 1929, and is the oldest short-run metal stamping company in the United States. Dayton Rogers processes all common sheet metal alloys and sizes, and provides fast turnaround on short-run orders by maintaining an inventory of common sheet metals in thicknesses up to 3/8".
Before the process change, a vapor degreaser was used to clean parts prior to deburring. Approximately 70% of all parts were deburred in a dry sander, and the remainder were deburred in vibratory tumbling machines. The vapor degreaser removed a forming lubricant off of parts which, if not removed, would gum up the belts in the dry sander.
The degreaser had an open-top, three-sump design equipped with condenser coils that used a single-pass cooling system. The condenser consumed 10 gallons of water per minute, which cost the company approximately $8,500 in annual water-usage fees. 1,1,1-trichloroethane (TCA) was the solvent used in the vapor degreaser, and approximately 1,100 gallons were purchased annually at a cost of $10,500. Of this total, 970 gallons of TCA evaporated into the atmosphere in 1989. Approximately 2-3 drums of waste TCA were generated annually, which were sent off-site for recycling at a cost of $75 per 55-gallon drum. Total annual costs of operating the vapor degreaser, including solvent, labor, condenser water and electricity, was approximately $30,000.
Reasons for Change
Dayton Rogers decided to discontinue using the vapor degreaser because of increased operating and maintenance costs, and new regulations phasing out the production and use of TCA. In addition, the recycling facility that recycled Dayton Rogers' waste TCA was discontinuing their service. Dayton Rogers employees also discovered that some cleaning operations using the vapor degreaser were unnecessary. For example, parts sent to platers were being degreased twiceCDayton Rogers would degrease parts before sending them to the platers, and then the platers would degrease the parts again to ensure cleanliness prior to plating.
Another reason why Dayton Rogers decided to stop using the vapor degreaser was that their previous efforts to limit its use had failed. Dayton Rogers attempted to control the use of the vapor degreaser by limiting the type and amount of parts cleaned in it. However, they found that as long as the vapor degreaser was still in the plant, employees continued to use it to clean all parts rather than just selected parts.
Waste Reduction Technique
The first step in reducing TCA waste was to reschedule parts processing so that the abrasive deburring process was the final step for the vast majority of all parts produced. The second step was to eliminate the vapor degreaser and upgrade the existing deburring operation to accomodate parts cleaning. This was done by adding a wet sander and modifying the vibratory tumbling machines. To make the removal of the forming lubricants easier in the water-based system, the oil-based lubricant was replaced with a water-based lubricant.
Dayton Rogers believed that the vibratory tumbler and the wet sander were capable of cleaning and deburring parts simultaneously, so they incorporated these existing machines into their new system. Currently, 75% of all parts manufactured are cleaned and deburred in the vibratory tumbler. The remaining 25% of the parts are made of flat metal that are cleaned and deburred in the wet sander and dried in a sheet metal drier placed in-line with the sander. To facilitate air drying after vibratory tumbling, most parts with formed designs are bent and shaped prior to deburring. All parts are air dried without being rinsed to avoid removing the rust inhibitor.
Implementation Problems
Dayton Rogers experienced or expected the following problems when implementing the new cleaning system:
Limited capacity in the deburring area was solved by switching from a powder soap to a liquid cleaner. This allowed setting up automatic metering of the liquid cleaner into a flow-through water stream using flow-control orifices. The metered flow-through system freed operators from manually filling the tumbling machines with water and detergent for each batch of parts. Quality control has improved with the new metered system which feeds the liquid cleaner into the tumbling machines at a constant 180:1 dilution ratio (0.5%). Because of its neutral pH, the liquid cleaner has eliminated concern about high pH wastewater, which was an intermittent problem with the alkaline powder soap.
Rust problems on steel parts caused by using water-based solutions have been prevented by adding sodium nitrite (0.2% by weight) to the detergent solution when processing steel parts. Flat parts that may adhere to one another when wet are dipped in a solvent-based rust proofing chemical after deburring. This process is avoided whenever possible by completing the bending/shaping of flat parts prior to deburring.
A small percentage of parts (1%), which must meet specific cleaning requirements that cannot be achieved using the new cleaning system or are too fragile for tumbling, are sent off-site and cleaned in a vapor degreaser.
Tool-wear was a potential problem in the stamping operations with the switch to a water-soluble oil lubricant. However, no additional tool wear has been observed.
A high oil content in the wastewater was a potential problem with the new system. However, oil concentrations have been within discharge limits to date. This is probably due to the use of water-soluble stamping oils which are much more dilute.
Costs and Benefits
By eliminating the use of TCA in the vapor degreasing operation in 1990, Dayton Rogers saved over $26,000 in 1991. Capital investment in new equipment to replace the vapor degreaser totalled $9,000 in 1990. A comparison between the costs of the two systems is detailed below:
Capital Investment for
Cleaning/Deburring System:
- Wet sanding machine with sheet metal drier
(purchased used) $ 8,000
- Metered detergent set-up $ 800
TOTAL $ 8,800
Increased Costs for Deburring
Operations1 and New Costs for Operating Costs for
Contracted Degreasing Vapor Degreasing System
- Water-based cleaner negligible2
- Coolant/lubricant for stamping negligible2
- Electricity $ 125
- Water $ 500
- Labor $ - 0 -
- Off-site vapor degreasing $ 3,000
TOTAL $ 3,625
- Annual TCA purchase $ 10,500
- Annual TCA recycling $ 200
- Electricity $ 1,000
- Water $ 8,500
- Labor $ 10,000
TOTAL $ 30,200
Total annual savings from new cleaning/deburring system = $ 26,575
Dayton Rogers required approximately four months to select, design, construct and implement the new cleaning system. Payback period on capital investment was approximately three months.
The new flow-through cleaning system also flushes parts constantly and keeps the media clean. The wastewater from this system has the following characteristics: a) it contains very dilute amounts of the water-based cleaner, rust inhibitor and lubricant oils; b) it has a neutral pH; and c) it can be directly sewered.
Dayton Rogers employees believe that the parts cleaned in the new system have a better appearance (burnished look) than parts cleaned in the vapor degreaser. No customers complaints have been received about the quality of the parts' appearance, even though there has been a general trend toward customers demanding higher appearance quality.
1The deburring operation was used along with the vapor degreaser in the old system. Therefore, this cost analysis looks only at the change in operating costs and not the total operating costs for deburring.
2Cleaner and lubricant costs were not fully analyzed, but Dayton Rogers personnel believe that because the new chemicals are diluted when used, the costs are very similar to the costs of the old system.
Application to Other Companies
Using a vibratory tumbler with a water-based cleaner to both clean and deburr parts simultaneously should work in other stamping and machining operations where deburring is done, but precision cleaning is not necessary. In some cases, it may be cost effective to purchase deburring equipment for the sole purpose of cleaning. Modifications to Dayton Rogers' system may be required in some situations. Suggested modifications include the following:
When cleaning parts with heavier oil films, try using higher detergent concentrations and heating the cleaning solution.
When cleaning parts with holes that are inaccessible to abrasive media, try using higher detergent concentrations. The tumbling action will also help knock out metal chips and allow the holes to drain.
Dayton Rogers made changes in their parts cleaning operations to reduce the cost of operating and maintaining a vapor degreaser. Other companies considering changes to their degreasing operations should keep in mind that the Federal government plans to ban the production of TCA by the end of 1995. Companies that delay implementing TCA alternatives may find that changes made at the last minute may be less than optimal. For more information about TCA alternatives, contact Karl DeWahl at MnTAP at 612/624-1300, or 800/247-0015 in greater Minnesota.
This publication was created with the assistance of Dayton Rogers employees, Dennis Wulff and Robert Reed.
(5/92-87)