Comparison of sealing systems

for safe sealing of drill holes

The following list describes the various possibilities available today for permanently sealing a cross hole or auxiliary hole. Depending on the pressure range, accessibility, force application, materials, degree of automation and economy, the strengths and weaknesses of the individual systems for the respective areas of application result.

Ball

The ball is a very cost-effective element in order to close a hole. The bore to be closed is drilled as 0.2 mm in diameter smaller than the ball diameter used. A stepped bore can define the position of the ball. The ball is mounted with a hammer, an air hammer or an installation system plugs and can safe side, be caulked. The element ball is preferably at low pressures e.g. used in pneumatics in diameters 1.5, 2.0, 2.5 and 3.0 mm. The safe pressure range should be determined by tests.

Cylinder pin

The cylinder pin is a cost-effective element to close a hole. There should be a press fit can be chosen. A stepped bore can define the position of the cylinder pin. The cylinder pin is like for closing transverse holes for supplying lubricating oil in light alloy or supply bores as used for hydraulic tappets. The safe pressure range should be determined by tests.

Cap for pressing DIN 443

The cap according to DIN 443 are very often found in gearboxes and motors. The cap form A conical and B are cylindrical available in diameters from 8 to 63 mm. They are pressed into bores with the tolerance H9 (N8). If necessary, the hole can be provided with sealant prior to insertion. The cap is available as a deep-drawn part in the materials DC03, 1.4301, 1.4016, 1.4571, DX51, DX53, aluminum and brass.

Screw plugs

The screw plugs are available in many dimensions with and without collar with different threads. They are mounted with or without sealant and with or without additional sealing washer. They should be tightened to a defined tightening torque. Hexagon socket, external hexagon and hexagon socket (Torx) are available for the drive. The bore must be provided with the matching thread to the screw plug.

The screw plug without head with hexagon socket, tapered fine thread (DIN 906), is available from M8 to M42 and R1/8 to R2.

The screw plug with head and hexagon socket (DIN 908) is available from M8x1 to M48x2 and G1/8 to G11/2. Form A is without seal, Form AC is with copper seal and Form AA is with aluminium seal.

The screw plug with head and hexagon socket (DIN 910), is available from M10x1 to M52x1.5 and G1/8 to G2.

Welded bore

In order to be able to close a bore by welding, the workpiece and the material must be suitable for the welding process and the introduction of high temperatures. Reworking is often carried out to avoid the bad appearance. The tightness depends largely on the quality of the welding.

One-piece conical sealing plug

The conical sealing plugs are a one-piece element with a conical sleeve that is inserted into a hole with a corresponding angle. The tapered bore is produced by mechanical processing. The bore with the appropriate angle makes the system less sensitive to bore tolerances. The backlash-free fit means that the sleeve only has to be driven in to a small extent.

The conical sealing plugs made of free-cutting steel are available from ø4 to ø12 mm and are used for low pressures up to 60 bar.

Two-piece conical sealing plug (LEE BETAPLUG)

The conical sealing plugs are a two-part pre-assembled element with an expanding pin and a conical sleeve which is inserted into a hole with a corresponding angle. The tapered bore is either produced by machining or corresponds to the demoulding angle of the core supports in moulds, e.g. of a gearbox housing. The bore with the corresponding angle makes the system less sensitive to bore tolerances. Due to the backlash-free fit, the sleeve only has to be pushed apart slightly by driving in the expanding pin.

The conical sealing plugs are available in a short version from ø7 to ø16 mm and are used for low pressures up to 35 bar in oil and cooling channels and core support holes in engines and transmissions.

The conical sealing plugs in a long version from ø4 to ø6 mm are suitable for high pressures up to 483 bar and from ø7 and ø8 mm for pressures up to 276 bar in industrial and mobile hydraulics.

In the left process curve, the expanding pin was already slightly depressed before assembly (incorrectly assembled)

The middle curve shows an IO process. In the right curve, the conical sealing plug was pressed into the air. This curve would be similar in an oval or dirty bore.

Ball plug

The ball plug consists of a sleeve with a bottom, which is cylindrical on the outside and accommodates a ball on the inside. When the ball is pressed into the sleeve, it expands and closes the bore with ø3 to ø22 mm for pressures up to max. 450 bar.

The ball sealing plug is mounted with a hammer, air hammer or a press-in device. Only with a press-in device the process can be controlled by monitoring force and travel. The materials of the sleeve are stainless steel, steel and aluminium. The ball is usually made of stainless steel or steel.

IIn the curve with the slightly delayed increase in force, the tool was not mounted without axial gap after the change. A path-controlled processing would probably have produced an error. If the bore is too large or the ball plug is placed in the air, the force increase will occur very late.

Rivet plug

The rivet plug consists of a sleeve which is cylindrical on the outside and conical on the inside and a pin with a conical head. During processing, a clamping mechanism on the pin pulls the conical head deeper into the sleeve, causing the sleeve to be pressed apart and close the bore. At the end of the process, the pin leaves at a predetermined breaking point, as known from blind rivets.

The rivet plugs are available in ø4 to ø16 mm for low pressures up to 60 bar. For high pressures up to 350 or 500 bar there is a design from ø4 to ø10 mm.

Extended pins are available for difficult to access places and if the rivet plug is to be mounted deep in a hole. During processing, only forces are introduced into the workpiece via the hole soffit. The materials of the sleeve are stainless steel, steel and aluminium. The pin is usually made of steel.

Process monitoring can be used to check the correct bore tolerance. If the bore is too large, the increase in force occurs much later. The pretension of the sleeve is then no longer sufficient to close the bore securely. A too large bore is often caused by a blunt drill.

At the apex of the curve, the pin is torn off and thus a check is made whether the breaking force of the pin is within the specified range.

Threaded plugs

The threaded plug consists of a sleeve which is cylindrical on the outside and conical on the inside and an expanding pin with a conical outer contour and an internal thread in the blind hole. During processing, the expanding pin is threaded onto a threaded adapter and the sleeve is pulled against a mouthpiece, which presses it apart and closes the bore. At the end of the process, the threaded adapter is unscrewed from the expanding pin, as known from blind rivet nuts. The threaded sealing plugs are available for ø7 to ø22 mm.

For hard to reach places and if the threaded plug is to be mounted deep in a bore, extended nosepieces and threaded mandrels are a cost-effective solution. During processing, only forces are introduced into the workpiece via the hole soffit. The materials of the sleeve and the expanding pin are steel.

Another version of the threaded plug is manufactured in one piece and only becomes a two-piece during the setting process (b&m-KL Plug®).

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