Отсутствие зажигания стенки из жесткого пенополиуретана от искры дуговой электросварки

Abstract

Ствие случаев зажигания пенополиуретана, которое объясняется малым временем контакта искры с поверхностью пенополиуретана t. Приводятся экспериментальные оценки фактического значения t и минимально необходимого для зажигания пенополиуретана времени контакта с искрой t. It is known that sparks of electric arc welding, representing drops of molten metal (hereinafter - iron sparks), have a high incendiary ability. However, due to a number of reasons, there is possible a situation when electric welding does not lead to the ignition of nearby combustible materials. The identification of such causes can have an important impact on the development of a standard method for investigating the ignition power of sparks. The work investigated the possibility of spark ignition of a vertical layer of rigid polyurethane foam installed on a laboratory table (hereinafter referred to as walls). The wall was exposed to sparks from electric arc welding with a power of up to 6 kW. The distance from the source of sparking to the wall was (15 ± 3) 10 m. A separate experiment lasted several minutes until the electrode burned out, the diameter of which varied from 2 mm to 4 mm. Research results and their discussion. In none of the experiments was it possible to ignite the wall with sparks. Sparks bounced off the surface of the polyurethane foam and fell down onto the horizontal surface of the laboratory table. To explain the results, an experimental estimate was made of the time t of the interaction of the drop with polyurethane foam and the minimum time t of such interaction, leading to the ignition of the wall. The estimate t < 30 · 10 s is based on frames of video recording with a frequency of 30 s of a luminous trail of a spark, curved by a collision with a wall. The estimate t > 1 s is based on simulated droplet exposure with small scale Bunsen burner flames of varying duration. Therefore, t << t. The reason for the lack of ignition of polyurethane foam was the short contact time of the electric arc welding spark with the surface of the polyurethane foam.