Present methods of commercial steel production often call for taking the liquid metal of an initial steel melt and pouring it into large molds so as to cast giant ingots. These ingots may then be shipped and/or stored as desired. Later these giant ingots are remelted and the steel therefrom utilized in specific manufacturing operations. For obvious reasons, it is generally preferred that these ingots be formed substantially free of large voids.
It is well known in the industry that large voids will tend to appear in the ingots if premature solidification is allowed to take place about the upper edges of the mold while the metal in the center of the mold is still molten. As a result, steps are usually taken to stop this premature solidification. The most common method of preventing or reducing such premature solidification is to apply a liner of suitable insulation, generally available in the industry under such names as Hot-Top, Riser, etc., to the upper inside portion of the mold. This insulation then acts to prevent heat loss through the mold at its upper end, thereby assuring that the melt will not prematurely freeze on the mold.
One current method of attaching the insulation to the mold involves first suspending the insulation adjacent to the upper interior rim of the mold and then securing the insulation to the mold using nail-like fastening pins. The insulation may be suspended by hand in position prior to fastening or, as is more preferable due to the high mold temperatures involved and the great size of the molds, mechanical suspension systems may be employed. Such suspension systems are well known in the art and are exemplified in U.S. Pat. Nos. 3,797,801, 3,966,167, 3,506,236 and 4,083,528. While these mechanical suspension systems are generally satisfactory for suspending the insulation adjacent the interior rim of the mold, they have difficulty holding the insulation sufficiently tightly against the walls of the mold to insure that no molten steel can get in between the insulation and the mold and "float" the insulation away from the mold. Hence, the nail-like fastening pins are used to secure the insulation tightly to the mold walls.
One consequence of using fastening pins (and their attendant high-powered driving tools) to secure the insulation to the mold is that a washer must typically be deployed with each pin. More specifically, it has been found that in order to prevent the fastener from excessively penetrating the insulation, washers must be positioned between the head of the fastener and the insulation. This is necessary due to the relatively soft nature of the insulation material, the small bearing surface provided by the head of the fastener, and the relatively high driving power needed to set the fastener into the mold wall.
This need to deploy a washer with each fastener has lead to a number of difficulties. For example, where the fastening pins are being set by a driving tool which is not adapted to hold the washer prior to fastening, e.g., a tool such as the one disclosed in U.S. Pat. No. 4,040,554, an operator must manually position each washer between the driving tool and the workpieces. This manual washer positioning is usually quite slow and tiring, and can be inconvenient given the large size of the molds. In those tools adapted to receive and support a washer hand-loaded onto the tool prior to each fastening, e.g., a tool such as the one disclosed in U.S. patent application Ser. No. 964,955, now U.S. Pat. No. 4,227,637 issued Oct. 14, 1980, there still remains the problems of slow operation and added operator labor and fatigue. Finally, even in those tools which have a washer magazine and means for automatically deploying washers and fasteners together in response to the stimulating of a single trigger, e.g. a tool of the type disclosed in U.S. patent application Ser. No. 129,713, there still remains the problem of having to periodically reload the magazine with fresh washers. This reloading can involve considerable amounts of time given the design of some washer magazines.
Another problem associated with all hot top mounting systems which employ washers is that the cost of producing the washers can become significant when large numbers of washers are involved. In addition, the washers constitute another supply and inventory problem.