The present invention relates to safes, vaults, strong boxes and the like, and more particularly to a method and structure of reinforced slabs, as well as to a modular construction of safes using the novel slabs. As a general rule, safes are constructed of large, heavy, hardened steel plates, welded together into the complete structure.
This traditional method of construction dictated strict standardization both in manufacturing techniques and dimensions. Customers had to adapt themselves to the commercially-available safe sizes, or make special orders for safes tailored to their particular space requirements and handling conditions.
One, obvious solution to this problem would be to devise safes based on the modular concept, whereby safes would be assembled, like LEGO(.TM.) pieces, into a variety of sizes, based on a stock of walls and door plates or slabs of various dimensions, and appropriate assembly fixtures. The reason that such a method has not been put into practice is that it would have seriously impaired the security level of the complete structure. An assembled structure is inherently liable to the disassemble thereof in the same way, unless welding, riveting or other non-reversible assembly techniques that can be performed only within the factory are applied, which, of course, brings us back to the practice of supplying completed, unitary safes. From another aspect, such modular safes which are to be supplied to the customer in a knocked-down or kit form, i.e. as a set of plates to be assembled at the customer's premises, would only be feasible and economically justified if the slabs were made by casting technique. However, although there are several known methods of casting slabs or plates that meet the high demands of torch-and-drill protection, yet they all still suffer various drawbacks, rendering them unsuitable for the purpose of mass production of modular safes.
Thus, for example, it has been proposed according to U.S. Pat. No. 4,505,208 to produce safe walls cast of high heat conductivity nonferrous metal such as aluminum or copper alloys, into which there is embedded a grille of special cast steel alloy. Although this method is satisfactory as far as security is concerned, it necessarily requires special casting dies and techniques to achieve the casting of a grille in suspension within a surrounding body of molten metal.
The traditional less sophisticated, so called "aluminum oxide nugget" method (an aggregate of aluminum clods dispersed within a body of cast aluminum or other nonferrous metal) is also unsuitable because the outer surfaces of the product are received so irregular and uneven that sheet metal covers had to be used, adding to production costs and to the dead weight of the safe.
The invention aims to remedy the above-listed disadvantages in both respects, of devising a simple and inexpensive method of production of safe wall plates, as well as proposing a method of quick and easy-to-perform construction of modular safes assembled of such plates.
It is a further object of the invention to provide a method of manufacture of high-security safe plates made of cast nonferrous metal, reinforced by drill-proof members, of higher resistance than cast steel grilles.
It is a still further object of the invention to perform the reinforcement of the cast slabs by hard elongated steel members, not during the casting stage--whereby the cooling-together of the composite structure may cause the annealing of the steel and the formation of cracks, due to differences in the thermal shrinkage coefficient to the two metals--but in a "cold" process, after the casting has become solidified.