For the construction of prefabricated frame structures based on metal profiles, various fastening methods are used. Among them, the most rational in terms of speed, reliability and cost is the so-called. crab mount or bracket.
The crab system is a double clamp that follows the shape of the connected rectangular profiles. It covers the profile pipe on both sides, fitting tightly to it. The two halves of the clamp are connected using standard fasteners - bolts and nuts of the appropriate size.
Crab systems: area of use
Fastenings like a crab system are the best choice if you need to equip a small metal structure. Such elements can be used both in situations with pipes of rectangular cross-section and if the cross-section is square.
Crab-type products are used to make:
- various types of awnings, awnings;
- showers and changing rooms on the beach;
- various types of fences, terraced areas;
- aviaries for poultry and livestock;
- greenhouse buildings;
- warehouse equipment;
- advertising signs.
This technology for installing structures has an important advantage - such buildings can be easily dismantled and moved to a new location.
Scope of application
The fastening is universal and is applicable for the construction of frames of rectangular buildings and structures, in which a rectangular metal profile serves as the base for the frame.
Below is a small selection of applications for the crab system:
- pavilions, awnings, warehouses, canopies, summer gazebos in cafes;
- stalls and small architectural forms for trade;
- country buildings - animal enclosures, showers, frames for rain shelters, greenhouse greenhouses, etc.;
- frame shelves, cabinets and racks;
- billboards and banners.
The only tools needed to assemble the structure are a wrench of the appropriate size. The structure is assembled according to the attached diagram, and you do not need to be a qualified specialist to assemble it.
Although the assembled structure itself weighs little, it has significant mechanical strength. The frame is able to withstand the weight of corrugated sheets, polycarbonate, MDF, OSB, and many other materials.
Advantages
The crab system for profile pipes has the following advantages:
- Wide range of use.
- High strength, rigidity and reliability.
- Relatively light weight.
- Low cost.
- Aesthetic appearance.
- No need for welding.
- Easy to use.
- There is no need to have special equipment and experience for installation.
- High quality of the final result.
- Reusable.
- Versatility.
- The load is distributed as optimally as possible across all elements of the metal structure.
From numerous reviews of crab systems it follows that they represent the ideal combination of quality and speed of installation.
Method of fixing profile pipes
One profile pipe is attached to another by pressing and then fixing with bolts. To make the structure more reliable, the connecting fasteners must be installed from the inside. This way you can avoid external influences that can lead to the formation of rust. And this, in turn, can lead to destruction of the installation.
The profile pipe can be secured using clamps and fittings, as well as other elements of a connecting nature. Clamps are used to fasten rectangular profiles consisting of two parts or elements, one of which is attached to the wall, then a 40x40 profile pipe is inserted into it, and the other element fixes it all with bolts.
A fitting is a fastener offered by the manufacturer that allows for the installation of elements with a rectangular cross-section.
Minuses
The crab type fastening also has disadvantages:
- it can only be used for installing small pipes;
- it can only be mounted at an angle of 90 degrees;
- the likelihood of structural failure increases;
- requires systematic and regular care;
- the risk that the geometry of the metal structure will be disrupted increases;
- low resistance to corrosive destruction.
Method of fastening to the profile
Installation of single-level crabs:
- Take the fastener so that its petals are directed downwards.
- Place it on the metal profile. A characteristic click will indicate the correct landing and complete securing of the crab.
- Bend the connector tabs and secure them with “bugs” to the main profile.
- Insert the frame jumpers into the crab until they click, then secure them with self-tapping screws.
- Install the remaining elements.
You must be careful when lowering the “antennae” - in order to prevent the metal from breaking at the bend and damage to the product, you should not make great physical efforts.
Installation of two-level connectors:
- When creating a multi-level metal sheathing, the supporting profile must be secured to the main one.
- Give the product a U-shape and insert it over the main profile until it clicks. Secure with self-tapping screws.
- Position the guide bar perpendicular to the main one and place the “butterfly” on the crab so that the hooks fit into the grooves of the profile.
Types of crab systems
By design, as can be seen in the photo of the crab system, such fasteners look like special clamps. They are:
- In the shape of the letter "T". Serve to connect three small diameter pipes. They are distinguished by the simplicity of the installation process.
- In the shape of the letter "G". Allows you to fix two pipes at the corners of the structure.
- In the shape of the letter "X". Designed to fix four pipes at once, located in the center of the metal structure.
To produce the crab system for water supply, a steel sheet 1.5 mm thick with zinc or other special coating is used.
The design of such parts is quite simple. They consist of a pair of elements connected by bolts. Standard sizes are 9.5*6.5 cm and 9.5*9.5 cm. A wrench is required for installation.
Rules for making connections
To fasten the clamps you will need two wrenches of the appropriate size. Bolts and nuts are most often used M8. Before installing the structure, it is necessary to cut the profile pipes in accordance with the drawing and remove burrs from the ends.
The pipes are inserted into the clamp, slightly twisted with bolts, angles are checked, and the bolts are tightened. You need to ensure that the pipes are inserted into the clamp all the way. If you are installing a large structure, it is advisable to “bait” the entire structure, measure the verticality and squareness of the corners and then tighten all the bolts, starting from the bottom. This work is best done with an assistant.
You can assemble part of the structure on a flat horizontal platform, and then lift it and install it. Having installed the two walls of the greenhouse, install and attach all the transverse pipes, measure them, and finally tighten the bolts.
Specifics of the crab system
Crab systems are classified as overhead type fasteners. Typically, elements of this kind are used for profile pipes of the following sizes:
- 20*20 mm;
- 20*30 mm;
- 40*40 mm;
- 20*40 mm.
The weight of fasteners can range from 30 to 70 g. As for the color range, they are most often produced in metallic shades, but you can also find examples in red, black, blue, and gray tones. The price of a crab system depends on many factors, including the brand of the manufacturer.
Fastening occurs through clamping force. Bolts are tightened on the system, not on the structure. This explains the fact that the fastener has low tensile strength. Once the pipe is installed, it can be easily removed from the mounting structure.
If you used a crab system to erect a structure that is constantly located outdoors, you should not forget to regularly check the reliability of the fastening to prevent distortions.
Anti-corrosion treatment is of utmost importance. Moisture will constantly accumulate in the fasteners, and this can lead to rust. Therefore, the condition of the crab system must be monitored in order to prevent the appearance of corrosion traces in time.
In conclusion, if you need to connect pipes, then the crab system will be the best solution. Its simple design allows you to assemble the mount yourself. And, if you take proper care of it and regularly, it will serve you for many years.
The main purpose
The main advantage is that structures connected with their help can be assembled and disassembled easily. Such structures are used in greenhouses, summer showers and other mobile objects. Among other things, the crab fastening system is very durable, as well as the welding system, however, the welding structure cannot be disassembled.
Corner mount
The crab system is much cheaper in cost, since the installation and disassembly of the structure does not require the use of welding, and since this saves electricity and gas, there is no need to hire a professional welder. The procedure for connecting the frame with crab fasteners is very simple; you do not need to have special skills for this, since you just need to insert the pipes into the fasteners and secure with bolts.
However, when attaching small-sized profile pipes, slight difficulties may arise, because they should only be joined at right angles.
Photo crab systems
Manufacturers and cost
Components for the installation of frame systems are presented on the building materials market by various manufacturers in a wide range. When choosing connectors, you need to focus on the type of drywall and the conditions of the room in which it will be used to level the walls or ceiling. In places with high humidity or frequent temperature changes, materials will be subject to significant exposure to negative factors, which can lead to deformation and damage to the entire surface of the coating.
The best ratio of price and quality of fastenings is typical for the German brand Knauf. The components of this production are designed taking into account their use in adverse conditions. The average price for them ranges from 13-17 rubles per unit.
Selecting elements
The main criterion when choosing crab connectors for drywall is the quality of the material, so you should pay attention to the following points:
- Presence of burrs. This defect is typical for low quality products. There is a risk of injury when using these connectors. In addition, the burrs indicate the use of low-grade material for the manufacture of the element, calling into question the strength characteristics of the connector.
- Rust on the surface. A defect of this nature occurs when the manufacturing process is violated or as a result of improper storage in warehouses.
In addition, the fixation of the curly petals on the profile should be clear, and the petals for additional fixation should bend without difficulty.
