Wall plug

A dowel (also screw anchor ) is a used in connection technology component that is used in materials, in which a screw directly, such as leaves in a wood screw wood screw. It is used in a cylindrical hole in predominantly brick, concrete or laminated plates walls, ceilings or floors as an intermediate part. The wood or chipboard screw spreads the anchors when screwing, with a force fit and sometimes creates a form fit against pulling him between anchor and surrounding material to a lesser extent. To create the hole in the hard material a drill is used with carbide cutting edges (concrete drill bit).

It was originally meant by a dowel of today still used in the carpentry and joinery trade wooden dowels. The current standard plug is made of plastic and is used in conjunction with standard wood or chipboard screws.

For special applications, it is available in various versions, which include pre-made combinations with special and included screw. For the introduction of heavy loads in concrete mainly only metal components are used, which are often referred to as anchors, but are better described by the term steel anchor. Such an anchor is provided on the outside with a metal thread for receiving a fastening nut. It can be combined with metal parts, which are spread in the well, or be glued into the hole as a so-called composite anchor.

Dowels in all variants are available in various diameters and lengths. Criteria in the choice of the anchor are:

• Building material of the substrate (eg concrete, masonry and board materials (eg gypsum) )
• Homogeneity of the subsurface (eg, exposed brick basement ceiling ) or multiple layers (eg, finishing plaster, flush, limestone )
• Underground voids (eg plasterboard wall with insulation behind it) ( there are special toggle bolts )
• Forces which hold the dowel or transferred by screw or hook to the substrate must be
• Thickness of the substrate ( eg, a non - load-bearing partition wall made of limestone usually is 12.5 cm thick - the elected dowels should not be so long that it protrudes from the wall in the next room )

• 5.1 Metal expansion
• 5.2 Chemical Anchor
• 5.3 undercut anchor
• 5.4 Screwed (concrete screw)
• 5.5 dowels

• 6.1 Technical Approval
• 6.2 Specifications
• 6.3 Miscellaneous

History

The term anchor was of wood dowel (also: Dolle ) taken over, although the functions are different. The screw anchor makes it possible to connect by means of a screw, while the wooden dowels - like a nail - connects itself.

Before using concrete screws holes were abandoned or beaten with the chisel, in a piece of wood was put in plaster or mortared. In this wood the screw could be screwed. Another method was to pursue a breakaway wooden piece with the hammer in a wellbore and spread with the screwed-in screw, and thus to compress further.

The first was the expansion anchor industrially produced in 1910 by John Joseph Rawlings, invented in 1911 and the Patent Office in London declared type ( grant of the patent 22680/11 on January 14, 1913). The anchor consisted of hemp twine and a glue made ​​from animal blood.

The first expansion anchor industrially manufactured in Germany was delivered in 1926 by Upat from Hamburg. It consisted in a metal sleeve pressed hemp string.

In 1928, at the Reich Patent Office under DRP was 555 384 patent for the " Sleeve- " in the name of engineer Fritz ax handle - founder and co-owner of the company NIEDAX (est. 1920) - issued and subjected to an official resilience of the State Material Testing Office Berlin. The NIEDAX dowel was first made ​​of metal and after the war made ​​of plastic.

The first plastic - purpose fixings are made of nylon rods. They are inserted into a drilled hole ( Inventor: Oswald Thorsman, 1957 / Artur Fischer, 1958).

Modern plugs are made ​​of plastic or metal or both, and are available in many different designs for many different types of walls, ceilings and floors.

Action principle

The screw is formed in the inner part of the anchor a mating thread, where she anchors the material deforms plastically and additionally displaced radially outwards, she spreads the dowel. Free rooms at uneven or pored hole wall to be filled by the dowel material, with a form-fit to pull-out occurs. Mainly this connection, however, is non-positive or frictionally. The resulting material in the dowel radial forces lead mainly to its elastic radial deformation. The elastic forces acting on the relentless hole wall as normal force perpendicular to a proportional static friction force result. The elastic hollow cylinder between the screw and, for example, masonry is thick enough that the radial forces are evenly distributed on a possibly uneven hole. At the outer edge of the hole, the radial forces increase steadily, so that even with brittle masonry there is no flaking may occur.

For materials with porous structure and / or low pressure resistance, such as gypsum boards, dowels are used with very long expansion. This must be longer than those piercing plate is thick. This expansion shields go until the cavity apart behind the plate and thereby give support.

Dowel general application

Plastic anchors

The most commonly used dowel is generally made ​​of polyamide. It is used in conjunction with standard, usually wood screws. Its inner diameter is smaller than the diameter of the screw. A result, the screwed- in plug screw the plug radially deformed. To facilitate the deformation, the anchor is partially longitudinally slotted.

A recent development are so-called nail anchors ( also: knock-in anchor ) in which a specially designed, supplied screw is driven into the plastic sleeve. The so-called nail is matched in length to the thickness of the fixture. The anchor is with the nail inserted through the device into the hole in the wall (through-hole assembly), and then the nail is completely smashed. Therefore, the installation is much faster, but Nail anchors are not as viable as the normal plugs ( so-called screw anchors ). The thread on the nail is cut sawtooth. It is relatively easy to follow, but not easily pull out. His head has a connection form for a screwdriver to allow the disassembly.

Plasterboard fixing

Plasterboard has low compressive strength, and most of the plates are a little thick, so no expansion anchor can be used. Special plasterboard anchors are Einschraubhülsen. They cut themselves with their relatively low external thread form a circuit in the plasterboard can be introduced via the smaller loads. They are screwed to a mounting means which simultaneously creates the required hole directly into standard plasterboard. They charge a small cavity for the commercially supplied tool and for too long introduced into it fixing screws behind the plate. For highly loaded compounds called hollow wall anchors are used where sufficient space is required behind the plate to anchor component radial " extend " and to establish with them axial form-fit over a larger contact area.

Insulation fixings

Insulation materials are still less firm than gypsum. Insulation panels, however, are usually thicker than plasterboard, so that the lower strength can be compensated with greater thread engagement. Insulation fixings are longer than drywall anchors to which they are otherwise very similar. They sometimes have a dish-shaped outer degree, but may therefore not be confused with the so-called plate anchors with which an insulating panel itself is mounted on a solid base. These nail-like plugs have a long stalk, which is driven into a hole in the solid surface and there holds through terminals and so fastened the insulating plate.

Hollow wall anchors

A in the cavity behind the plate like a rivet to a deforming cavity anchor is made ​​of metal ( see picture ). In a large number of relevant fastening elements is one (or more ) part / s behind the plate to the projecting portion (armature, hook ) is rotated against the back. They are called toggle or toggle bolts.

Heavy-duty dowel

Metal expansion

These anchors consist entirely of metal. Because elastic material is missing, their function is based mainly on form-fitting. When screwing is over -boosting cone surfaces generates large forces on the rear part of the wall hole and deforms plastically. Because of the higher material strength and the usual use of larger diameter metal dowels are in solid materials ( concrete) sustainable and safer than plastic anchors. For fastenings on concrete ceilings only expansion anchor made ​​of metal are approved in Germany at the moment, since the risk of plastic, flowing ' is (slow plastic deformation due to pull-out forces ). Metal anchors are also prescribed because of their better thermal stability for certain applications.

Chemical anchor

The composite anchor is introduced along with two-component reaction resin into the hole, where it is not spread but combines cohesively with the wall material. The serving for fastening metallic threaded rod ( anchor bar or rod ) is usually together with the resins, which are located in a glass ampoule or a coaxial foil pouch mounted. The anchor often carries a cutter at the top, so that the vial is securely destroyed and can escape the resins. The armature is then rotated, whereby the components of the resin mixed and dispersed. In addition to the cartridge system, there are an injection system in which the resin mixture is injected with a dispenser to the borehole. The resin mixture fills the cavity between the bore hole and anchor rod, partially penetrates into the pores of the surrounding masonry or concrete and hardens. The main advantage unlike expansion anchors is that no radial forces occur in the concrete and thus high stresses are avoided. Shear connector can be used near the end of the wall.

Certain composite anchor with a so-called Spreizreserve can also be used in the cracked tensile zone of the concrete member. Such anchors consist of many consecutively set cones which have in borehole wall direction at cracks caused by (eg earthquakes) force components and press the resin mixture against the wall. In practice, this dowel slips at a crack slightly and then stabilizes again.

The use of composite anchors is governed by the building.

Undercut anchors

In addition to the anchor bolts, there are also several officially approved undercut anchors for concrete. Here, a positive engagement is achieved in that the hole is widened at its base by means of a special drill. Through a wedge construction Ä o. ensures that the undercut anchor this flared hole completely fills. Undercut anchors are commonly used for the installation of heavy equipment. They carry much higher loads than expansion anchor, which is partly related to the mentioned form-fitting, but also so that they initiate further defined from the surface of the loads. There are also undercut anchor, which may be used in the cracked tensile zone of the concrete member.

Screwed (concrete screw)

Screwed (better known as concrete screws) are a relatively new fastening system. The anchor is screwed into a predrilled cylindrical hole. The special thread of the anchor cuts an internal thread on the base material. The anchorage is characterized by the form in the special thread. Whether the object may be secured with concrete screws, therefore depends mainly on the base material. Concrete screws are allowed ( in this case only in stainless steel A4) depending on admission to the heavy-duty fastening in cracked or non-cracked concrete indoor or outdoor use and are partly processed in the system with mortar. Typical applications include railings and noise fixtures on roads and bridges and the anchoring of high shelves in the interior.

Dowel

Dowels are as wooden dowels, dowel type fasteners, but standardized and metal according to EN 14592. They are used to manufacture carrying connections between wood and steel and between wood and wood.

Dowels are arranged perpendicular to the shear plane and mainly subjected to bending. You are chamfered usually at the ends, cylindrical, with smooth surface and low thickness tolerance. Its diameter is limited 6 to 30 mm.

Preferably dowel made ​​of steel S235JR, S275JR or S355J2 are manufactured according to EN 10025. In wood, the wells are drilled 0.2-0.5 mm smaller than the diameter of the anchor, whereas the hole in the steel is up to 1 mm larger.

Safety aspects

Official Approval

Especially when the failure of a component connection can result in a risk to life or health of humans or severe economic consequences, dowels should be sized and mounted after approval in principle.

Many of the commercially available plastic anchors are not permitted by the building and thus may not be used for safety-related fasteners. Each pack officially approved dowel is either a leaflet with the installation instructions in, or the instructions on the package. The official approval is to be obtained from the manufacturer and get a PDF file usually on the manufacturer's website. The approval must be obeyed. It regulates everything from the calculation of the anchorage, about the creation of the hole, until the correct installation of the anchor. This document is legally relevant and must be taken by the client to the construction documents.

Specifications

For anchors or anchors are the specs usually the building approval to take in not officially approved products to the manufacturer's instructions. Typical data are the effective anchorage depth, the minimum axis of the dowel from each other, the minimum edge distance of the anchor, the minimum thickness of concrete, the allowable load.

Others

In safety-related anchorages in concrete, where is to be expected with cracks in the anchorage area, which affect the viability of anchors should be used in principle fixings suitable for cracks. Otherwise, a proof should be furnished that the concrete in the installation area during the useful life remains uncracked.

With attachments for cleaning the thickness of the plaster counts with the thickness of the fixture.

Corrosion ( due to stress cracks and component connections) must be avoided. To avoid contact corrosion can not be fixed with galvanized screws for example stainless steels. While ordinary steel anchors may be used with a galvanic zinc coating only in dry rooms, come for fixings in the outer region (wet rooms, industrial atmosphere ) usually anchor made of stainless steel (A4 ) are used. Particularly aggressive environments ( chloride atmosphere, road tunnels or direct sea water contact) plugs should be used with special alloys.

A cleaning of the borehole after drilling, eg by blowing or vacuuming is recommended, since the debris may affect the liability of the anchor in the borehole negative. Dry holes, however, are filled with mortar as a rule.