Installation Recommendations - Welch Plugs
HOLE PREPARATION RECOMMENDATIONS – HUBBARD SPRING
“d” Hole = Plug upper limit +.002”, more clearance may be needed for plugs over 2.5”.
Depth = 1-1/2 to 2 material thicknesses (1 material thickness minimum).
Shoulder = 1 material thickness
- The counter bore should be of a diameter that will take the plug without forcing, no larger. Typically this means .002” larger than the maximum plug diameter, although more clearance than .002” should be given to larger diameter plugs. If the plug is forced or press fit in the hole prior to expansion, the edge of the plug and the edge of the hole are apt to become marred, and leakage will occur.
- The counter bore should be round and free of tool chatter marks. 100 micro inches or smoother is a good finish guideline.
- The counter bore should be finished without any fillet. A fillet can prevent the proper seating of the plug. The counter boring tool should dwell long enough at the bottom of the counter bore to leave the bottom clean and smooth. The sharper the corner, the better the seal.
- The counter bore should be at least the depth of the material thickness of the plug to be installed.
- For the best condition, the width of the bottom of the counter bore should be approximately equal to the thickness of the plug to be used.
- For best results, the angle between the cylindrical sides and the bottom of the counter bore should be 95 to 97 degrees. This allows the plug to turn inside out slightly, and then spring back to an almost flat position – providing maximum sealing quality.
NOTE: The above hole configurations are for optimal sealing. Flat bottomed counter bores with varying shoulder widths are used for general sealing – applications with no liquid retention or pressure requirements.
INSTALLATION RECOMMENDATIONS – HUBBARD SPRING
Optimal installations require a consistently perpendicular installation tool and possible calibration of installation forces. The goal should be an installed plug that is visually flat.
We have traditionally advised “If only a few plugs are to be installed, the best tool for setting them is a short piece of cold drawn shafting 8 or 10 inches long and of a diameter slightly less than the diameter of the plug to be set. By placing it perpendicularly over the plug, and striking the shafting one or two blows with a fairly heavy hammer, the plug can be set down sufficiently to not quite a flat position”.
Sealant is used in more severe applications, but this can be eliminated with the use of Hubbard Ground Plugs.
The edges of an installed plug can be staked to improve general retention.
INSTALLATION RECOMMENDATIONS – DIN 470
Barrel plating of larger expansion plugs will nick the edges and impair their sealing quality.
Applications in which Hubbard (Welch Type) Expansion Plugs are used vary widely. It is the responsibility of the end user to develop the combinations of hole, plug, and installation that are appropriate to their specific application.
Installation Recommendations - Cupped Plugs
- The hole diameter should be larger than the minor outside diameter but smaller than the major outside diameter - .003” larger than the minor diameter is a good guideline.
- 100 micro inches or smoother is a good finish guideline for the hole.
- The hole should be round within .002” T.I.R.
- Plugs should be driven from the inside bottom of the plug, not from the rim of the cup.
- If a sealant is not used, lubricating the plug and hole with oil or grease before insertion minimizes scoring / galling and resulting leaks.
- Plugs should be driven squarely into the hole.
- A bottoming shoulder on the installation tool controls the depth of insertion and plug alignment.
- After installation, the top of the cup should be at least .035” past the end of the lead in radius of the hole to be sealed.
- The radius on the end of the installation tool should not interfere with the radius on the inside bottom of the cup – it should be large enough to provide adequate clearance. A clearance chamfer works as well.
- Cupped Plugs should not be driven against a counter bore – this can damage the plug and cause leaks.
- Barrel plating of larger expansion plugs will nick the edges and impair their sealing quality.
- Applications in which Cupped Plugs are used vary widely. It is the responsibility of the end user to develop the combinations of hole, plug, and installation that are appropriate to their specific application.