Restoring the geometry of the body and eliminating through corrosion are tasks that the owner of a used car sooner or later faces. The lower part of the sidewalls, known as rapids, takes the brunt of moisture, reagents and mechanical damage flying from under the wheels. That is why the question of how to properly digest the thresholds is one of the most relevant for those who plan to prolong the life of their iron horse.
The process of replacing body elements requires not only high-quality equipment, but also a deep understanding of metallurgy and welding technology. An unprofessional approach can lead to a weakening of the power structure of the car or the reappearance of rust in the shortest possible time. In this article, we will discuss in detail all stages of work, from dismantling to finishing.
The first thing to decide before starting work is the choice of material for replacement. In the modern market of auto parts you can find various options for execution, each of which has its own features of installation and operation.
Material choice: ready-made thresholds or sheet metal
The most popular and simple solution for garage repairs is stamped-threshold. They are already formed parts that repeat the geometry of the factory elements. Their advantage is the minimum fit: the master can only cut out the rotten area and boil a new one. However, it is worth considering that the quality of metal from different manufacturers can differ significantly.
The alternative is reinforced-thresholdinside which a strengthening profile has already been established. This solution is ideal for cars where the threshold is part of the body structure. The use of such parts allows you to maintain the rigidity of the body to twist, which is critical for safety.
- 🚗 Ready-made stampings are quick, but the metal can be thinner than factory.
- 🛡️ Reinforced options - provide additional strength and durability.
- 📏 Sheet metal – requires flexible skills, but allows you to recreate any complex shape.
Sometimes, when working with rare or old models of cars, it is impossible to find ready-made parts. In such cases, masters use sheet metal with a thickness of 0.8-1.2 mm. This method requires high qualification, as it is necessary to manually recreate complex curves and ribs of stiffness. It is critically important to use zinc-coated steel or to conduct high-quality galvanizing immediately after molding.
Do not save on the material, as it depends on its quality how long the result of your work will last. Cheap metal can burn out in a couple of winters, negating all efforts.
Necessary tool and workplace preparation
Qualitative digestion of thresholds is impossible without appropriate technical equipment. The basic tool here is the welding machine. For bodywork the most optimal semi-automatic (MIG/MAG)operating in a protective gas environment. It provides a smooth seam with minimal thermal impact on the surrounding metal, which reduces the risk of warping.
In addition to welding, you will need a corner grinding machine (Bulgar) with a set of disks for cutting and cleaning. Can not do without a drill or screwdriver for drilling technological holes under electrodes during spot welding. Strubs, clamps and magnetic horns are also needed to fix the parts in the correct position.
☑️ Tools for boiling thresholds
Particular attention should be paid to safety. Working with metal and electricity requires the use of protective glasses, gloves and workwear. In the process of welding, harmful gases are emitted, so the room should be well ventilated. If the work is carried out in the garage, make sure that the hood is functioning properly.
⚠️ Warning: Never do welding work near flammable liquids, including gasoline in the tank or oil. Sparks can cause fuel vapor to ignite.
Preparation also involves dismantling anything that could interfere with access to the threshold: plastic linings, moldings, door seals and, in some cases, seats to access internal amplifiers.
Technology of dismantling and cleaning of rotten areas
The first step is to remove the damaged part of the body. There are two main approaches: complete replacement of the threshold on the racks or partial welding of the repair insert. A complete replacement is preferable as it removes all hidden corrosion, but requires more time and skill.
In partial repairs, it is necessary to cut the rotten metal with a margin of 2-3 cm in the direction of the whole metal. The edges of the cut should be even to ensure a tight fit of the new part. All hidden cavities accessible through the cut opening must be thoroughly cleaned of rust and treated with a transducer.
It is important not to damage internal amplifiers if they are preserved. It often happens that the outer part of the threshold has rotted, and the internal force structure is still intact. In this case, the reinforcement is repaired separately, superimposing a new external part on top of it. If the rotten and the internal sparser, its recovery is a priority for safety.
Nuances of working with hidden cavities
When cutting the thresholds, it is often found that the inside of the bottom has also been corroded. In this case, it is necessary to clean all the layers of rust to live metal, using brushes on the drill and sandblaster, if possible. After that, the cavities are necessarily spilled anticory.
After mechanical cleaning, the surfaces are degreased. This is a critical stage, as any residues of oil, dirt or anticork will worsen the adhesion of the weld and paint coating. Use special degreasing agents that do not leave films.
Welding process: methods and sequence of actions
The most important thing is to fix the new part. The threshold should stand perfectly in place, repeating all the lines of the body. To check geometry, doorways are often used: the door should close tightly, without distortions. If the new part is longer, the extra is cut, if shorter - increases.
Welding starts with the tents. The detail is fixed at several points so that it does not shift from the thermal expansion. Then, moving from the center to the edges or using the method of "chess" order, the main seams are applied. It is important not to overheat the metal, making pauses to cool down to avoid deformation of the thin body iron.
There are several basic ways of connecting:
- 🔥 Continuous seam - provides maximum tightness, but heats the metal more.
- 🔩 Spot welding – imitates factory technology, minimizes warping, but requires access from both sides.
- ⚡ The seam through the drilled holes (plug weld) is a compromise option when access is only on one side.
After welding work is completed, the seams must be cleaned. With the help of a Bulgarian with a petal circle or file, all irregularities are removed. The surface should become smooth, the transition from the old metal to the new – smooth. This is necessary so that when painting, the boundaries of repair are not visible.
Use the copper plate as a lining when welding together on the through holes. Copper does not stick to the welded metal and helps to form a smooth seam on the back side, preventing burnouts.
Anti-corrosion treatment and protection of hidden cavities
Many craftsmen make the fatal mistake of ignoring the protection of the inside of the threshold immediately after welding. The metal in the seam zone is devoid of the factory zinc layer and protection, so it rusts in the first place. The treatment should be carried out before the stage of priming the outside.
To protect hidden cavities, special wax or oil-based compounds are used, which come with long flexible spray tubes. The tube is inserted inside the threshold through the technological holes, and under pressure the cavity is filled with a protective composition. It is important that the composition covers all internal surfaces, including hard-to-reach corners.
| Type of composition | Basis | Advantages | Deficiencies |
|---|---|---|---|
| Bituminous mastics | Oil | Cheap, making a thick layer | They dry for a long time, can crack in the cold. |
| Wax compositions | Wax/Resins | Elasticity, self-tightening scratches | Requires careful surface preparation |
| Oil inhibitors | Oils. | They penetrate into microcracks, displace water. | Require regular updates (every 1-2 years) |
The outer part of the threshold after cleaning the seams is covered with epoxy soil. The epoxy base creates an impermeable barrier to oxygen and moisture, preventing the development of corrosion under the paint. Only after the complete drying of the soil can you go to spatula and painting.
⚠️ Warning: Do not apply anticor on the outside of the threshold under the paint! Most hidden cavity formulations are not designed to come into contact with the paint coating and can cause it to swell or detach.
Common mistakes and advice from professionals
Even knowing the theory, beginners often make mistakes that reduce the quality of work to zero. One of the most common problems is the “burning” of metal. With too much current or slow movement of the burner, the metal thins and burns out, forming holes instead of a reliable connection.
Another mistake is poor preparation of the edges. If there is rust or paint on the edges, the welded seam will be porous and leaky. Moisture will quickly penetrate inside, and after a year you will see the swollen varnish again. Always clean the metal to shine at a minimum of 2 cm from the seam.
It is also important to note the importance of geometry control. If you cook the threshold "by eye", without checking the door gaps, you risk getting a skewed body. The door may start to touch the threshold when opening or, conversely, will not fit tightly, creating drafts and noise.
The main secret of durability is not so much the quality of welding, as careful anticorrosion preparation and protection of the ends and internal cavities from moisture.
Don't forget the drainage holes. At the bottom of the sills, condensate drain holes are often provided. When installing new thresholds or applying anticores, they can not be clogged tightly, otherwise water will accumulate inside.
Frequently Asked Questions (FAQ)
How long does it take to replace the thresholds on a single car?
The working time depends on the condition of the body, the model of the car and the qualifications of the master. On average, replacing one threshold in a garage takes 4 to 8 hours of clean time, not including drying time for soils and anticor. If the recovery of the power elements is required, the time can be increased to 12 hours or more.
Can I cook the thresholds with an inverter (electrode)?
Technically possible, but not recommended for thin body metal (0.6-0.8 mm). Electrode welding gives too much heat, burns through metal and creates rough, corrosion-prone seams. For bodywork, use only carbon dioxide or argon semi-automatic.
Do I need to remove the doors when changing the door?
Remove the doors is not necessary, but it is highly desirable. This will provide better access to the racks and will allow you to freely check the gaps during fitting and welding. In addition, removed doors reduce the risk of damage by sparks or tools.
What if the bars rot with the rapids?
If the racks (central or rear) are damaged, repair becomes more difficult and requires the restoration of the power structure. In this case, it is often necessary to cut out a part of the rack and boil a new one, observing the technology on the fly. Such work is better to trust professionals, as safety in an accident depends on it.