New method revolutionizes furnace refractory installation.

A system has evolved to automate the unpleasant task of refractory relines. Foundries have also realized other production benefits.

Since the dawn of metal, some type of refractory container has been needed to hold the metal long enough to allow it to be melted and transferred to its final destination.

These refectory linings last only for a limited period before they are damaged by melting's harsh environment, and need to be replaced with fresh refractory. Otherwise, a runout will occur.

The process of relining coreless induction furnaces, however, has long been recognized as an unenviable foundry chore, and one fraught with potential hazards.

Silica, a low-cost material, is the refractory of choice for coreless induction furnaces because it withstands repeated cycles of physical shock, temperature differences and chemical attack. The crystalline silica used in refractory products, however, is significantly more toxic than amorphous silica.

Excessive inhalation of crystalline silica can result in silicosis, and the substance is also suspected to be a human carcinogen. For these reasons, it is regulated. The primary means to preventing crystalline silica-related disease is reducing the amount of silica dust inhaled. Local exhaust ventilation and the proper use of National Institute of Occupations Safety & Health- (NIOSH) approved respirators are the most common control methods.

In addition to the health considerations, the constant lifting, twisting and bending involved in handling refractory bags can result in injury. Meanwhile, repetitive-strain injuries (which can be caused by rodding and deaerating in reline processes) represent more than 60% of all newly reported occupational illnesses. According to the Bureau of Labor Statistics, such injuries cost businesses more than $20 billion per year in direct workers' compensation claims.

Safety and health issues and a glimpse of potentially tough regulatory responses [the U.S. Occupational Safety and Health Administration (OSHA) drafted an ergonomic standard that failed last year] are forcing foundry managers to consider alternative methods to manual relines of coreless induction furnaces. Effectively balancing workplace environmental and safety control with longer furnace lining campaigns is a task that until just recently, hadn't been achieved.

Conventional Relines

Currently, relining coreless furnaces involves two main steps:

Installing the Furnace Bottom and Setting the Form--The two most common methods used to compact the furnace bottom are through hand ramming and the hand-held vibrator. With each method, workers enter the confined space of the furnace to ram or vibrate the loose silica material until the surface is solidly knitted.

This practice exposes the worker to airborne silica. Once the bottom is completed, the steel form is set into place and centered. The form supports the silica until the lining attains enough strength during the sintering process to be self-supporting. Afterward, the form is melted away and becomes part of the first melt of iron.

Installing the Furnace Side. walls--When filling the sidewalls of the furnace, many foundries screen silica into a hopper, and then fill buckets with refractory. The buckets are passed along worker by worker, and the material is eventually poured down the sidewall.

Some foundries use a hand-held funnel that extends down the sidewall. Be. cause even material distribution is needed, the funnel is manually rotated around the circumference of the wall as the refractory is dumped into the sidewalls.

As the material is deposited, one or more workers are assigned to deaerate (or fork) the material by forcing a rod fork into the loose silica. This is done to avoid entrapped airpockets, which compromise the integrity of the lining. As each bag is opened, and each bucket of material is dumped, loose silica is emitted to the workplace atmosphere, generating a cloud of hazardous material.

The problems associated with the conventional reline methods are common and continue to be experienced in most foundries today (Fig. 1). At General Motors-St. Catharines, Ontario, where the new system was developed, the following difficulties were identified using conventional methods.

[Figure 1 ILLUSTRATION OMITTED]

Silica Hazard--Despite availability of NIOSH-approved respirators and engineering controls such as local exhaust systems, pressure to reduce silica exposure continued from workers, union officials, and health and safety organizations.

Workers' Compensation Claims--Back injuries were common due to constant lifting of refractory bags. Fatigue and injury to wrists and shoulders due to repetitive rodding or deaerating during filling also contributed to musculoskeletal disorders.

Working Conditions--Because of unattractive working conditions, supervisors experienced difficulty finding workers willing to perform relines, resulting in a high rate of refusal for voluntary overtime.

Material Distribution--Manual filling of the sidewalls resulted in nonuniform refractory densities due to inconsistent distribution of material. When the atmosphere became thick with free-floating silica dust, the urgency to complete the job as quickly as possible outweighed the principles of achieving consistent distribution and adequate deaerating.

Automatic Reline System

The birth of the refractory installation and vibration system (RVIS) to automatically install and vibrate dry refractory began in the late 1980s. Like most other foundries, GM-St. Catharines' furnace relines were being performed manually with crystalline silica refractory.

Following an ergonomic and environmental study of refractory relines on its 60-ton coreless furnaces, the foundry committed to finding a way to improve the work conditions. A machine was designed in-house and fabricated locally, and project trials began in 1987.

The automatic relining of coreless induction furnaces using the RVIS is a series of processes that begins with adding the material to the furnace bottom. Bulk bags containing 3000 lb of silica were lowered by hoist onto the furnace floor. Little dust is emitted from the bulk bag using this method.

Once the material is in place and evenly distributed, the bottom is ready for vibrating. The entire bottom of the furnace is compacted in one operation using a 2000-lb vibrator plate.

After the furnace form is placed and centered, the RVIS is positioned on top of the form using an overhead crane or hoist, where it performs two functions. The rotary material feeder automatically dispenses dry refractory into the annular space between the furnace wall and form. At the same time, the air extractor automatically deaerates the material, eliminating manual deaerating or forking tasks.

Instead of 100 lb silica bags, 3000 lb "supersacks" (size depends on furnace capacity) are used. The sack is positioned by crane above the hopper of the rotary material feeder. After it is lowered inside, the material is released (Fig. 2). The hopper is refilled until the material reaches the top of the form.

[Figure 2 ILLUSTRATION OMITTED]

In use, the rotary material feeder was set to rotate 360 every 2 min and distributed 250 lb of material per revolution. Meanwhile, the auto air extractor was set to deaerate at 260 strokes per revolution. The system requires two operators, one used as a safety backup. During operation, airborne silica was virtually eliminated (Fig. 2). Once the sidewalls are filled, the machine is simply removed, cleaned and stored until the next reline.

Sidewalls are vibrated using a four-legged machine equipped with four air vibrators. The unit is lowered by hoist land positioned on the furnace bottom. It is slowly raised, vibrating the entire form simultaneously (Fig. 3).

[Figure 3 ILLUSTRATION OMITTED]

Test Results

GM officials, in running tests on the RVIS, came to the following conclusions on the new installation method.

Silica Dust Control--Free-floating silica was virtually eliminated from the work environment. Workers were no longer required to wear the NIOSH face masks for exposure rates exceeding 10.0 mg/[m.sup.3].

Workers'Compensation Claims--Over seven years, no claims associated with the reline process were reported.

Worker Response--There was no opposition from the union to the introduction of the automated process. Working conditions dramatically improved.

Increased Furnace Lining Life--An additional 600 lb of material was used in the furnace reline. While consistent material distribution and uninterrupted deaerating resulted in greater material use, the foundry realized the system provided substantially denser linings. The linings lasted 30% longer, decreasing rebuilds from 33 per year to 28.

Increased Tonnage per Lining--Tonnage per campaign increased 35% using the system.

Human Resources Utilization--The conventional rebuild required 6 workers for 2 full shifts. Following the implementation of the system, only two workers were needed, reducing manpower by 67%. The annual net savings in labor alone was $96,000.

Reduction in Rebuild Time--The time taken to replace the furnace lining was reduced by 35%. Vibration time for the 60 ton furnace was reduced from 2 hr to 16 min.

Return on Investment (ROI)--The ROI was less than one year. In addition, 15 more production days were realized.

Initially, safer working and environmental concerns for workers were the overriding motivation for the development of the equipment. While this goal was achieved, the foundry also realized significant labor cost savings and improved material utilization.

This technology provides an opportunity to address a difficult and hazardous problem that metalcasters have come to accept as an inherent part of foundry work life.

RELATED ARTICLE: Recent Case History at Ford-Windsor Casting

Ford Motor Co., Windsor Casting Plant, Windsor, Ontario, Canada, began using a single RVIS to reline its 20-ton and 35-ton capacity furnaces in the spring of 1995.

Protecting health and safety of employees is an overriding policy at Ford, and reducing airborne silica-based refractory in the workplace has been a long-standing concern of both management and workers.

This factor, and other safety concerns, prompted Ford to adopt the technology. The Ontario Ministry of Labour-Occupational Health and Safety Branch's issue of entering the confined space of a furnace during a reline can't be resolved using conventional reline procedures. Potential workers' compensation injuries created by repetitive, manual processes were difficult to resolve.

Economic motivators to convert to an automated process included the desire to reduce labor costs per reline, increase melt capacity utilization and coil life, and improve productivity on the mold line.

Once the system was operational, Ford realized an immediate and sustained savings in material and labor costs. With the new system, manpower was reduced from 8 to 2 workers (75%), resulting in an annual labor and material costs savings of more than $70,000.

The dramatic reduction of airbone silica permitted workers to exchange their cumbersome airpacks for disposable dustmasks. The workplace safety/health improvement has resulted in improved morale. Workers assigned to reline a furnace no longer view the job to be one of the worst assignments in the foundry.

Annual rebuilds have been reduced from 30 using the conventional process to an expected 24 by the end of the first year of operation. Tonnage per campaign per furnace has increased from 3500 to 4800. Linings now average 14 more operating shifts than before, an increase in duration from 5-6 weeks to 6-8 weeks.

Sidewall vibration time has been reduced from 2 hr to 16 min and the overall rebuild time for each furnace has been reduced by 5 hr, allowing the sintering process to begin sooner to bring furnaces back on-line more quickly.