Purposes and methods of painting self-tapping screws, common problems and their solutions
The appearance and service life of technological structures, roofing depends on the quality of fastening materials, in particular, hardware. Painting fasteners, including self-tapping screws, is an effective way to protect against corrosion and preserve the decorative qualities of the connected elements. Special dyes and equipment are used for painting.
General information about painting self-tapping screws
Self-tapping screw - a type of screw, consisting of a pointed shank with a thread and a head / cap. Fasteners are used when performing work:
- with wooden / metal structures;
- plasterboard panels;
- metal profile.
For use in manufacturing:
- brass;
- stainless;
- carbon steel (galvanized / ungalvanized).
The head of a carbon steel self-tapping screw is subjected to painting, for which powder paints and special technology are used.
Goals and Objectives of Coloring
The coloring layer protects steel screw heads from moisture, extending their service life, which is especially important for roofing structures.In addition, painting the hardware store caps makes the fasteners on the surface of the products invisible, if they match in color.
Dyeing methods
Hardware with a painted cap can be purchased from the building shelves of supermarkets or, if not available in the range, painted by yourself.
Industrial painting method
Before painting, the fastening material undergoes preliminary processing, which includes:
- mechanical cleaning in sandblasting machines;
- degreasing with technical ethanol / white spirit;
- rinsing with running water;
- drying in a drying chamber.
Self-tapping screws made of galvanized steel do not undergo pre-treatment. The dies are used to paint the material. Externally, the matrix is a sheet of metal measuring 50x50 or 60x120 centimeters with holes for fixing self-tapping screws of a certain diameter. Every 2-3 painting cycles, traces of powder paint are removed from the matrix using abrasive materials.
Self-tapping screws are attached to the die and placed in the paint booth. The metal plate, together with the hardware, is grounded with a negative potential. A powdered metallic pigment with a positive charge is blown into the chamber. The particles are electrified using a high voltage electrode or by friction against the walls of the gun.
Under the influence of an electromagnetic field, the electrified pigment is deposited on the heads of the screws. Loose paint particles are blown out of the chamber by a fan and collected in an additional chamber (cyclone). The prepared dies are transferred to the firing chambers, heated to a temperature of 200 degrees. The capacity of a chamber is 50 to 70 dies.
The chamber is heated from a heating element located in the lower part. The agitation of the air flow and the equalization of the temperature are carried out by means of a fan in the upper part of the chamber. The preheating time depends on the power of the oven and varies from 30 minutes to 2 hours .
The dies are held at a temperature of 200 degrees for 5 minutes. Then they move to the cooling chamber, where they cool to 70-30 degrees in 30 minutes. Dies are removed from the chamber, freed from self-tapping screws. The material is cooled to 18-20 degrees and sent for packaging.
The duration of the coloring process is influenced by the number of matrices, the total area of coverage with the coloring composition. In the oven, you can simultaneously bake matrices with material of different colors, except for contrasting ones, for example, white and black. During heating, the pigment can peel off and move to dies with self-tapping screws of a different shade. As a result of sintering, the coating will be intercalated.
Self-painting method
Self-tapping screw caps can be painted on their own if hardware in the desired shade is not readily available.
This will require:
- a small piece of expanded polystyrene or foam;
- degreaser;
- spray paint.
The polystyrene/expanded foam will work as a matrix for two reasons: ease of wrapping fasteners to any depth; solvent resistance. Work should be done in a well-ventilated area or outdoors in calm weather.
The required number of material is glued into a homemade matrix at a minimum distance from each other. The hats are treated with white spirit.The aerosol is sprayed from a distance of 50-70 centimeters. Closer spraying may cause dripping and melting of the top layer of Styrofoam / Styrofoam.
Coloring is done in 2 steps. The second layer is applied after the complete drying of the first. Fasteners are released from a self-made matrix after 12 hours. In appearance and performance, they differ little from industrial designs. Fasteners can be coated with alkyd or acrylic paint after installation depending on the color of the finish.
Common problems with industrial painting of fasteners
The smaller the product, the more economically profitable it is to paint. For painting on material per unit area, a more coloring composition is required. Part of the paint protrudes from the room, increasing its specific consumption per unit of output.
Solve the small target problem
Regardless of the method used to place the caps, some of the paint will go beyond the detail. The more the screws are colored at the same time, the lower the specific consumption will be. The use of a metallized pigment in an artificial electromagnetic field is more effective than liquid dyes.
In this case, the installation density of fasteners has a limit value due to the need to paint on the side surfaces. The use of uniform matrices for each diameter makes it possible to obtain an optimal consumption of coloring agents.
Batch processing
Simultaneous processing of several matrices during pigment application, subsequent polymerization, cooling gives saving in energy and labor costs per part, increase equipment utilization efficiency.
For batch processing, the dyeing, cooling and heating chambers are equipped with special equipment:
- picture frames;
- hooks;
- shelves.
To protect the tools from paint, the parts in contact with the die are made of refractory dielectric. Metal parts are protected by caps, tapes, plugs.
Conveyor
The highest efficiency is achieved in large enterprises, where all stages of production are automated. Technological operations are carried out on conveyor lines without direct human intervention.