Patent CA-1057577-A (CA)
Inventor: SPRAGGS RICHARD W
IPC: F42B3/10
Filed: 1975-07-25
Granted: 1979-07-03
Abstract: ABSTRACT OF THE DISCLOSURE A non-electric double delay borehole downline unit is provided for delaying transmission of an explo-sive signal down a borehole and also delaying initiation of the charge within the borehole after the signal has been received therein.  The double delay unit comprises a length of flexible impulse propagating tubing having first and second ends and an impulse propagating hollow channel extending along the length thereof, a non-electric high strength blasting cap containing a first delay element connected to the first end for initiating a borehole explosive charge, an impulse amplifying and transmitting cap containing a second delay element con-nected to the second end and a protective block having a plurality of elongated apertures with one of said aper-tures fully and snugly receiving the amplifying cap therein.      The present invention relates generally to explosive signal transmission assemblies for borehole blasting operations.  More particularly it is concerned with a new and improved non-electric delay blasting unit for use in boreholes to provide a delay in both the ini-tiation of the borehole charge and the transmission of the signal to succeeding boreholes.          In borehole blasting operations certain advan-tages have been achieved by providing dual delays for explosive signal transmission to each borehole charge.  A first delay is provided at the detonator cap positioned within the borehole while a second delay controls signal travel into the borehole.  Heretofore, in order to accomplish this, it has been necessary to splice a delay connector into the surface trunkline of the system and to use a blasting cap having a different delay interval within the borehole.  Conventionally, the delay provided within the cap is of substantially longer duration than the delay provided by the surface connector.  This assures that the signal is transmitted along the trunkline to a sufficient number of borehole downlines prior to the initiation of the explosive charge within the first bore-hole.  Such sequential or rotational firing minimizes the possibility of cut-offs at the trunkline due to ground movement while at the same time reduces vibration and improves fragmentation in the blasting operation.  As will be appreciated, dual delay blasting systems used heretofore have required warehousing of a number of different types of delay devices having different time delay intervals.  From a practical standpoint, such blasting operations also have been limited to about 7 to 8 delays within the system in order to maintain the requisite control over the time delay period.  Additional-ly, not only have two separate delay products been required but these products have also been extremely noisy in operation, and their use has been limited to those areas where their inherent noise character would not pre-sent a problem, thus limiting their use.          The present invention provides for a substantially more simplified delay hook-up for borehole blasting oper-ations by the utilization of a single non-electric double delay borehole downline unit that will provide the re-quisite delay in sending the signal down the borehole as well as the appropriate delay in initiating the charge with-in the borehole after the signal has been received therein.    Another feature of the present invention is to provide a new and improved non-electric double delay bore-hole downline unit that effects millisecond delay blasting coupled with the efficiency of purchasing and warehousing only a single product while at the same time achieving these advantages at a substantially reduced noise level.          Still another object of the present invention is to provide a new and improved double delay unit of the type described wherein the explosive content of the assembly is significantly lower than presently available non-electric delay systems yet provides improved reli-ability and safety coupled with ease of hook-up and use of the same unit to initiate a larger number of sequen-tially fired holes.          A further object of the present invention is to provide a double delay unit of the type described that is capable of functioning as a replacement for a portion of the trunkline at substantially reduced noise levels and permits rapid, easy interconnection within the blasting system while exhibiting advantages of manufacture, distribution and use.          Other objects will be in part obvious and in part pointed out more in detail hereinafter.          These and related objects are accomplished in accordance with the present invention by providing a new and improved non-electric double delay borehole downline unit for both delaying transmission of an explosive signal down a borehole and also delaying initiation of the charge within the borehole after the signal has been received therein.  This single double delay unit is com-prised of a length of flexible explosive impulse pro-pagating fuse or tubing having first and second ends and an impulse propagating channel extending along the length thereof.  A non-electric high strength detonator or blasting cap containing a first delay element is connected to the first end of the signal propagating tubing for initiating the borehole explosive charge.  Connected to the second end of the tubing is an impulse or signal amplifying and transmitting cap containing a second delay element.  A protective connecting block having a plurality of elongated apertures protectively houses the amplifying and transmitting cap within one of the apertures and fully and snugly retains the cap while facilitating interconnection with adjacent signal transmitting lines.          A better understanding of the invention will be obtained from the following detailed description and the accompanying drawing of an illustrative application of the invention.