Үзіліссіз өндіріс әдісі

Production method without interruption

Continuous production is a flow production method used to manufacture, produce, or process materials without interruption. Continuous production is called a continuous process or a continuous flow process because the materials, either dry bulk or fluids that are being processed are continuously in motion, undergoing chemical reactions or subject to mechanical or heat treatment. Continuous processing is contrasted with batch production. Continuous usually means operating 24 hours per day, seven days per week with infrequent maintenance shutdowns, such as semi annual or annual. Some chemical plants can operate for more than one to two years without a shutdown. Blast furnaces can run from four to ten years without stopping.

Many processes such as assembly lines and light manufacturing that can be easily shut down and restarted are today considered semi continuous. These can be operated for one or two shifts if necessary.

The oldest continuous flow processes is the blast furnace for producing pig iron. The blast furnace is intermittently charged with ore, fuel and flux and intermittently tapped for molten pig iron and slag; however, the chemical reaction of reducing the iron and silicon and later oxidizing the silicon is continuous. Semi continuous processes, such as machine manufacturing of cigarettes, were called "continuous" when they appeared. Many truly continuous processes of today were originally batch operations. The Cromford mill of 1771, designed by Richard Arkwright, was the first factory to use a continuous process from raw material to finished product in a series of operations. The Fourdrinier paper machine, patented in 1799, was one of the earliest of the Industrial Revolution era continuous manufacturing processes. It produced a continuous web of paper that was formed, pressed, dried and reeled up in a roll. Previously paper had been made in individual sheets. The paper machine influenced other continuous processes such as the continuous rolling of iron and later steel. Another early continuous processes was Oliver Evans'es flour mill (ca. 1785), which was fully automated. Early chemical production and oil refining was done in batches until process control was sufficiently developed to allow remote control and automation for continuous processing. Processes began to operate continuously during the 19th century. By the early 20th century continuous processes were common.

In addition to performing maintenance, shut downs are also when process modifications are performed. These include installing new equipment in the main process flow or tying in or making provisions to tie in sub processes or equipment that can be installed while the process is operating. Shut downs of complicated processes may take weeks or months of planning. Typically a series of meetings takes place for co ordination and planning. These typically involve the various departments such as maintenance, power, engineering, safety and operating units. All work is done according to a carefully sequenced schedule that incorporates the various trades involved, such as pipe fitters, millwrights, electricians, mechanics, laborers, etc., and the necessary equipment (cranes, mobile equipment, air compressors, welding machines, scaffolding, etc.) and all supplies (spare parts, steel, pipe, wiring, nuts and bolts) and provisions for power in case power will also be off as part of the outage. Often one or more outside contractors perform some of the work, especially if new equipment is installed.

Safety meetings are typically held before and during shutdowns. Other safety measures include providing adequate ventilation to hot areas or areas where oxygen may become depleted or toxic gases may be present and checking vessels and other enclosed areas for adequate levels of oxygen and ensure absence of toxic or explosive gases. Any machines that are going to be worked on must be electrically disconnected, usually through the motor starter, so that it cannot operate. It is common practice to put a padlock on the motor starter, which can only be unlocked by the person or persons who is or are endangered by performing the work. Other disconnect means include removing couplings between the motor and the equipment or by using mechanical means to keep the equipment from moving. Valves on pipes connected to vessels that workers will enter are chained and locked closed, unless some other means is taken to insure that nothing will come through the pipes.