Bernie Forster, Director, Primary Metals Group, Lechler, Inc., St. Charles IL, USA

Foreword:
The following illustrated paper was presented at the 1999 AISE Annual Convention held in conjunction with the Iron and Steel Exposition at the Cleveland Convention Center, Cleveland Ohio, on September 27th - 30th.  It describes a special type of clog less spray header that cold mills incorporate into their process to minimize downtime and maintenance costs.

Introduction:
Galvanized sheet, used in the construction industry, has been one of the fastest growing steel markets in the past ten years because it offers significant advantages over traditional wood products. These advantages include higher strength to weight ratios, less "creep" and distortion with temperature changes, far greater fire resistance, and increasingly faster and lower construction costs. The advantages are important; not only in wall and roof coverings but also in new applications such as wall studs made from galvanized sheet steel.

To meet the demand of these new applications and the increased use of galvanized sheet by automotive, canning and other traditional markets, the United States Steel Group, USX Corporation significantly increased its capability and capacity. This was accomplished by both improving existing operations, such as the East Galvanizing and Electro Galvanizing lines at its Gary Works, the lines at Mon Valley, Fairless and Fairfield Works, and adding capacity through joint ventures like Pro-Tec Coating Co.

In addition to increased demand, rising customer expectations, especially in the automotive sector, required that the additional capacity meet ever-tightening quality standards with little or no increase in price. Hence, yield of premium quality material became critical, both for optimum profit margins and to meet customer demand.

One of the most significant changes made in galvanizing lines to improve operations, was the introduction of self-cleaning shower headers in the early nineties. The initial units were installed on the East Galvanizing line at USS, Gary Works in 1993. This paper will focus on the application of this technology to the Electro Galvanizing line and the two galvanizing lines at Pro-Tec Coating Co., the gains in productivity achievable with them and the basic operation of the self-cleaning shower header.

Background:
Prior to the installation of self-cleaning headers, the Electro Galvanizing line experienced significant losses due to 'insufficient rinse" and "zinc pick-up" problems. Plugged nozzles were the major source of these problems. Unscheduled line stoppages to correct "insufficient rinse" created the most severe problems because product was diverted. The minimum loss was approximately six tons of product if the line could be stopped at the end of a coil. Often, the entire coil still had to be diverted because losing the six tons of sheet resulted in an underweight coil that customers would not accept. If it could not be stopped at the end of the coil, the entire coil was diverted. The product could not be sold as prime material because it became discolored in the eighteen plating cells when the line stopped for more than two minutes. Plugged nozzle stoppages lasted an hour and most often longer because the tank covers had to be pulled and the entire header replaced. The average number of unscheduled line stoppages was two per month. Plugged nozzles were also replaced each week during a scheduled downturn. Also, the headers required complete cleaning four times annually. During this cleaning, the headers were removed from the tanks, scraped and pickled in an acid bath. Also, all nozzles were replaced in them. Cleaning the twenty-six (26) headers required forty (40) man-hours. The stoppages, spare header maintenance, weekly nozzle cleaning and lost production totaled more than $150,000 annually.

Perhaps more significant than the money involved was the risk of losing business. By contract, the mill was responsible for maintaining a three-week supply of material in an offsite warehouse. However, the issues of "insufficient rinse" and "zinc pick-up" were causing severe delivery problems. The mill was nearly always behind in supplying prime product to its warehouse.

While not as grave as the problems at the Gary Works Electro Galvanizing line, the situation at Pro-Tec was similar. Pro-Tec had a new galvanizing line with the latest technology in terms of pumps, rolls, tanks, filters, etc. In spite of this, they noticed that the flow through their rinse headers began to decrease between outages. This indicated that the nozzles were plugging. Consequently, they removed the nozzles during each outage and thoroughly cleaned them.

However, this was not ideal because this situation caused pump damage due to back-pressure build-up, shorter brush life on the scrub brush rolls, and a steady deterioration in the cleanliness of the product over the three weeks between planned maintenance outages. Furthermore, the increased contaminants on the strip were carried into the zinc baths causing more frequent dross removal.

The cleaning of the nozzles themselves created several problems. They had to be removed and reinstalled. To accomplish this two people had to go into each tank and an additional person, a "standby person", had to watch those in the tank at all times to ensure their safety. This required a permit, arranged prior to each outage, for entering a confined spare, "Tyvek" suits, gloves, face shields, and close adherence to lockout procedures. To clean the headers all nozzles were removed and cleaned with strong acid in Pro-Tec's lab area. Then they were reinstalled. In addition the entire header was removed and thoroughly cleaned annually.

In short, poor rinsing of sheet steel prior to galvanizing created significant costs and customer satisfaction problems for the Electro Galvanizing line at USS, Gary Works. Furthermore, it caused significant cost and safety issues at Pro Tec Coating Co. Control of the problem was a long, labor intensive process, which required close attention to all safety procedures due to both the area involved and the chemicals used.

Solution:
To correct the problems noted above both USS, Gary Works and Pro-Tec investigated self-cleaning shower headers. This product offered the ability to maintain clean nozzles while running the lines rather than cleaning them during planned and unplanned shutdown periods.

Self-cleaning shower headers are used primarily where the nature of the process causes standard headers and nozzles to clog easily and frequently. They are especially useful in processes where the failure of one nozzle in the header can create a severe problem situation, or in processes requiring very high quality of the output product.

The concept behind the header design is quite simple. The header uses an internal brush to loosen contaminants, which are clinging to the sidewall of the header and lodging in the nozzle orifices. As the brush is rotated within the header, it scrapes the sidewall and the orifices clean. A valve is incorporated in the design to allow the loosened particles to be carried out of the header via a large exhaust rather than leave them loose in the header to clog the nozzles again or force them out through the nozzles themselves.

Pro-Tec used an approach similar to that originally used in by the East Galvanizing line at the Gary Works. Specifically, they purchased headers over approximately one year beginning in 1997. In this manner they were able to retrofit headers gradually rather than having to install them in one outage. It also enabled them to test the performance of the initial headers at a relatively low investment. A third advantage for Pro-Tec was that they were able to test the features that they wanted in the headers. For example, they wanted headers that could be flanged specifically for their tanks. By purchasing only a few headers initially, they were able to ensure that modifications could be made in future purchases to refine the design. When the headers proved to be precisely the design they wanted and advantageous operationally, the remaining headers were purchased.

Figure 5

1. It is not accurate to state that self-cleaning headers eliminated every problem faced by the Electro Galvanizing line. Other improvements made include modifying the conductor rolls by changing to a better covering material and installing new pickle and cleaner rinse pumps to provide constant and consistent pressure for these rinsing operations. However, it is safe to say that the headers were a significant part of improving the operation. After installing these headers the following was documented:
2. Line stoppages for cleaning nozzles have been eliminated. The annual savings from this benefit alone amounts to approximately $150,000.
3. Cleaning of headers has been eliminated. This is an additional savings in labor of at least $4,000 annually.
4. Most importantly, the Electro Galvanizing line is back on schedule and maintaining the offsite warehouse inventory levels per the contracts with its customers.
5. Eliminating the problems associated with plugged nozzles has helped uncover other problem sources. For example, although improved, zinc pick-up remains the major cause of diverted product. The mill is now able to evaluate other modifications to reduce or eliminate this problem.
6. The need for spare headers has been reduced to only those needed in case of a catastrophic cobble in the line that would destroy the headers.

At Pro-Tec the benefits were also significant. Specifically,

1. Some headers have been operating for more than two years without the need to clean or maintain them during outages. However, it should be pointed out that the brush rods might require changing shortly.
2. Up to 30 man-hours have been freed from cleaning headers and replacing nozzles during planned outages every three weeks. This represents a savings of $16,000annually.
3. The potential safety hazard of having personnel inside the confined space of a rinse tank has been eliminated. If the headers must be removed, it is now done from outside the tank.
4. The hidden costs of scheduling the header cleaning, obtaining permits, proper clothing, etc., and ensuring that proper lockout procedures and other safety procedures are followed have all been eliminated.
5. Scrub brush life has improved. However, it should be noted that Pro Tec has also "foot printed" the loads on brushes to avoid over-pressuring them. Also, they have changed brush roll manufacturers. The improvement from these actions has increased brush life from two to six months. This saves Pro-Tec $42,000 annually.
6. Strip cleanliness no longer deteriorates between outages. Hence, dross removal at the Zinc baths has decreased.
7. Since there is no longer a back pressure build-up over the three weeks between outages, the mechanical seals on the pumps last longer. Pro-Tec estimates that the seals last nearly twice as long, resulting in savings of nearly $14,000 per year. These savings are for the seals only and do not include the labor to install them.

Conclusions:
Obviously, both mills have benefited from the installation of self-cleaning shower headers. Impressive as the benefits just listed are, probably the two most compelling arguments for using self-cleaning headers in galvanizing operations are:

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