Plug for sealing preservative in wood

#The invention relates to a plug for sealing substances in holes drilled in wooden structures, particularly for sealing wood preservative in holes drilled in standing wood utility poles.

#Exceedingly large numbers of standing wooden poles are used by power and communications utilities. To prolong the life of these poles, wood preservative is injected into holes drilled in the pole, which tends to reduce the spread of rot within the pole. Usually, the first internal rot treatment is applied after the pole has been in service for a number of years, and additional treatments are applied at regular intervals. The holes drilled into the wood structures are usually sealed with wooden dowels or plugs which are hammered into the holes after the treatment. When additional treatment is required the wood plugs are removed from the hole, and this can present some difficulty. The dowel can be damaged when being removed from an opening, and commonly it cannot be reused, and thus another dowel is required. Also, old wooden dowels split, and can fall from the opening with the risk of contaminating the immediate area with wood preservative, which can be highly toxic. After many years, the utility pole may have been treated several times, and each time a separate hole might be required, each hole having a separate plug. Installation and maintenance of many plugs is time consuming, and also increases the risk of inadvertent loss of a plug from an opening.

#It is known to provide specially adapted threaded plugs to plug openings in treated poles or trees. Typical examples are found in U.S. Pat. Nos. 3,968,594 issued to Kawakami and 4,724,793 issued to Sletten. Both of these patents disclose tapered plugs having threads on the outer periphery thereof, with a central opening extending through the plug. An orifice is provided adjacent the thread or tip of each plug, the orifice communicating with the central opening of the plug to distribute chemicals into the wood. It would appear that both these plugs are fabricated from a rigid material, and require screwing in and screwing out, which can be a time consuming process.

#FIG. 1 is a side elevation of a first embodiment of the invention, some internal detail being shown in broken outline, the invention being shown installed in an opening in a wooden structure, a portion of a driver being shown fragmented,

#FIG. 2 is an end view of the first embodiment of FIG. 1,

#FIG. 3 is a fragmented section taken on line 3--3 of FIG. 2 showing a portion of a thread portion and a portion of a recess adjacent an outer end thereof,

#Referring to FIG. 1, a first embodiment 10 of a sealing plug according to the invention has a body portion 12 having a central longitudinal axis 14. The body has a periphery 16 which is a portion of a shallow angled cone having a half angle 18 of approximately 1.3 degrees. However, the angles 18 can vary between 0.6 degrees and 3.6 degrees.

#The body has inner and outer end portions 20 and 22 respectively, the inner end portion having a smaller diameter than the outer end portion to facilitate entry into an opening 24 in a wood structure 26, for example, a utility pole. The opening 24 is drilled with a parallel sided drill and thus is generally cylindrical, and the inner end portion 20 of the plug has short parallel-sided unobstructed section with a diameter equal or slightly less than diameter of the opening 24 to facilitate entry into the opening. The plug 10 has an opening 27 adjacent the inner end which serves no other function apart from reducing volume of material required to produce the plug.

#The plug 10 include a thread portion 28 which is helically wound around the periphery 16 extending from a position adjacent the inner end portion and extending outwardly to the outer end portion. Adjacent turns of the thread portion are spaced apart at a thread pitch or lead 30, which is equal along the length of the plug. For a single start thread as shown, the pitch 30 or lead represents the distance the plug moves axially during one revolution of the plug within the opening 24. Preferably, the pitch 30 is 6.35 millimetres (0.25 inches), but can be between 4.23 millimetres (0.17 inches) and 8.46 millimetres 0.33 inches). Thus, for a plug having a thread length of 34.92 millimetres (1.375 inches), between 5 and 6 turns are required to unscrew the plug from the opening as would be described. The thread portion has a leading face 32 facing towards the inner end portion 20, and a trailing face 34 facing towards the outer end portion 22. Further details of the thread form are described with reference to FIG. 3. Clearly, a multi-start thread can be substituted if desired.