Screws and bolts knowledge

Screws and bolts knowledge
1 screw - screw thread marked as high precision, in addition to mark thread code, we must also mark thread tolerance tolerance and threaded together with a code length. Thread mark Marks are: Code Thread - thread tolerance code (in diameter, top diameter) - Screwing Length l) tolerance band code by the number of additional letters (female in capital letters, lowercase letters with external thread) such as 7H, 6g, etc., should be noted that, 7H, 6g and other representatives of thread tolerance, and H7, g6 tolerance code on behalf of the cylinder. 2) The provisions of short-rotation combined length (indicated with S), medium (indicated with N), length (indicated with L) types. In general, do not mark the length of threaded together, the thread tolerance by the middle Screwing Length (N) determined. Necessary, can be combined length of the code notation spin S or L, such as "M20-5g6g-L". Special needs, they can specify the length of rotary joint values, such as "M20-5g6g-30". Common thread of ordinary coarse thread: Feature code M + nominal diameter + rotation + thread tolerance code (in diameter, top diameter) - Screwing Length ordinary fine thread: Feature code M + nominal diameter * pitch + rotation + thread tolerance with code (in diameter, top diameter) - combined length of the right hand rotary screw omitted Note, L with "LH" said. M 16-5g6g said coarse screw thread, nominal diameter 16, right hand, thread tolerance in diameter 5g, large diameter 6g, Screwing Length considered at moderate length. M16 × 1 LH-6G fine tooth that common thread, nominal diameter 16, pitch 1, L, thread tolerance in diameter, large diameter are 6G, Screwing Length considered at moderate length. Pipe Thread annotation format: Feature code (cylindrical pipe threads with G said tapered pipe threads with NPT that) + size code + Tolerance class code + rotation G1A - LH said the British non-threaded sealing pipe thread, size code 1in, dextral, tolerance levels for the A-level. Rcl / 2 inch screws that seal tapered pipe thread, size code 1/2in, dextral.

2 screws corrosion treatment

Paint
Paint is an organic coating, mainly used to protect metal parts, equipment and structure to the corrosion resistance of air is used as a protected barrier between metal objects and the environment. Paint to prevent corrosion of metals has a long history, is also a most widely used and most common anti-corrosion technology, construction convenient, low cost.

Effective life of paint coatings, determined by the durability of the paint itself and the coating for the adhesion of metal to be protected, and the appropriate application of paint adhesion and to obtain a permanent protective effect, the main method. According to the test showed that the most important influence paint a life factor is the metal surface should be appropriate for Chu Li, Bei processing metal surface must be free of dust, oil, grease, rust, oxides and Renhe initial corrosion Wu Zhi Deng. This factor than the quality of the paint itself is also important, the low quality paint used in surface treatment of good quality and better paint than metal used in metal surface treatment bad even better. Metal surface all dirt, grease and oil can be used to remove solvent or alkaline solution and then washed, rust and oxide removal is available pickling or sand blasting.

Clean metal surface, the first Road to the drying paint should be immediately coated surface to achieve good absorption, good idea to first coated with phosphate Reapply paint. Normally coated paint, count the number and types of coating, rust to reach the appropriate role of the important factors. In the painting process, the primer of the brush is extremely important use for the supply of basic adhesion of metal, generally to coated anti-rust primer and one two finish. Some researchers think that the fog in the corrosion of steel violence, at least to the four paint and the thickness of not less than 0.l3mm, Taiwan Power Company nuclear power plant for the 3 primer, two finish of the Formosa Plastics plant was 3 Mailiao Road primer, a topcoat. Promising anti-rust primer were used for the red lead paint and the zinc-rich coatings are two kinds of red lead paint is the red lead (lead oxide) with a variety of paint tone from the system, zinc-rich coating is by a large number of zinc powder and a small amount of The film-forming material (binder) blend film after drying, which accounts for most of the zinc powder (about 90%). Red lead paint in the oxidation of lead ions on metal corrosion inhibited, it can rust. The zinc-rich coating is zinc dependent effect on the cathodic protection of metals, so there are good anti-rust properties.

Commonly used to prevent corrosion of metal finish with epoxy paint, silicone resin paint, vinyl chloride resin paint, melamine resin paint, alkyd paint, epoxy paint of which are coal tar pitch epoxy paint is present the most widely used high-performance anti-corrosion coating, its adhesion, ruggedness, water resistance, chemical resistance than other coatings are all excellent.

Ceramic protective film

Ceramic protective film is applied on the metal surface ceramic material to increase its high temperature oxidation resistance and heat resistance, other than for the alkali and hydrofluoric acid corrosion are all good for the corrosion, and a wear-resistant, easy to Clean, pleasant appearance and sound of the advantages of insulation. Ceramic is the metal oxides, carbides, borides, silicides and nitrides of the general, with high melting point, high hardness, brittleness and other performance characteristics, the present application is more oxides and carbides, but also a small amount of application of boron and silicide.

Proper use of spraying methods to molten particles of ceramic materials, spray attached to the metal surface to form a cover coating, protective film that is ceramic. Thickness of 0.4 mm or less are generally referred to as pond or porcelain enamel, 0.4 mm or more commonly known as glass lining. Sprayed ceramic for high temperature use, sprayed ceramic layer to prevent the metals and alloys can be intergranular corrosion, as a corrosive gas separation barrier, reducing the chance of hot spots, for the important parts can be replaced by low-alloy metal, and can pollutant resistance erosion. The use of dip coating method, you need to dry and then dried in a furnace to form a good adhesion of the protective layer.

Taiwan galvanized the company introduced earlier this year called RUSPERT the composite ceramic membrane production techniques, special screws and fasteners used in the anti-rust treatment. The composite ceramic membrane by the metal zinc layer (first layer), phosphate film (second layer) and sintered ceramic surface layer (third layer) is composed of film thickness of about 10, is said to have in the harsh environment of excellence rust corrosion and heat resistance properties, are Tian ceramics from the island of Taiwan, Inc. (San command) to promote the industry.

Oxidation

Immersed in the steel parts of the alkaline solution containing antioxidants, such as potassium nitrate or sodium nitrate solution of sodium hydroxide, and to maintain its boiling point is about 140 ℃, or sodium nitrate and potassium nitrate steel pieces immersed in the molten salt , remove and quenched in water availability in the surface layer of oxide that is pleasing to the eye of the black iron oxide film, the composition of ferrous oxide and iron oxide mixture, is to improve the ability of ferrous metal corrosion of a simple and economic Methods. Steel thin chemical oxide film thickness, usually 0.5 ~ 1.6μm, corrosion resistance is limited, the thickness of 2μm on the film, the appearance of luster, black or dark gray, the film has good absorption, such as the Baptist with anti-rust oil or paint, its resistance to salt spray corrosion properties increased several times to several times.

In the oxidation of iron and steel parts required before degreasing and pickling, surface fat and no less part of corrosion products can be directly into the concentrated alkaline solution for chemical oxidation. An oxidation process is completed in a bath, two oxidation in the solution of two different components to complete bath, with an oxidation treatment, the resulting thin film, corrosion resistance is poor. When using two oxidation treatment, the resulting thick film, the corrosion resistance is also good. After oxidation of parts, must be fully cleaned, then boiled in soapy water, following drying and oiled.

 The meaning of grade 3 bolt performance
 
 Steel connecting bolt performance levels more than 10 minutes 3.6,4.6,4.8,5.6,6.8,8.8,9.8,10.9,12.9 grades, including 8.8 and above or bolts made of low carbon alloy steel and heat treated carbon steel (quenching and tempering), commonly known as high strength bolts, the other known as ordinary bolts. Bolt performance rating label has two figures, namely that the nominal tensile strength of bolt material value and yield strength ratio. For example, the performance level of 4.6 of the bolt, which means:
1, bolt material tensile strength up to 400MPa nominal level;
2, bolt material yield strength ratio of 0.6;
3, bolt nominal material yield strength up to 400 × 0.6 = 240MPa-class performance grade 10.9 high strength bolts, the material after heat treatment to achieve:
1, the nominal tensile strength of bolt material up to 1000MPa level;
2, bolt material yield strength ratio of 0.9;
3, bolt nominal material yield strength up to 1000 × 0.9 = 900MPa class
Bolt performance levels of meaning is an international standard, the same level of performance bolt, regardless of the difference between material and origin, its performance is the same design level of performance can only choose.
The so-called strength grade 8.8 and 10.9
Is the shear stress level bolts to 8.8GPa and 10.9Gpa
8.8 Nominal Nominal yield strength tensile strength 800N/MM2 640N/MM2
General bolt is "X.Y" said the strength,
X * 100 = the bolt tensile strength,
X * 100 * (Y/10) = yield strength of this bolt
(As identified by the provisions of: the yield strength / tensile strength = Y/10)

4 screw thread
One thread is a solid outer surface or inner surface of the cross section, there is even the shape of spiral protrusions. According to their structural characteristics and uses can be divided into three categories:
  (A), common thread: for the triangular-shaped teeth, for connecting or fastening parts. Common thread by pitch divided into coarse and fine thread two, fine thread of connection strength is higher.
  (B), drive screw: a trapezoidal tooth shape, rectangular, saw-shaped and triangular, etc..
(C), sealing thread: for sealing connections, mainly useful thread, taper thread and taper pipe thread.
Second, with the level of thread:
Together with a rotating screw thread between the size of loose or tight, with the role of the hierarchy is the thread of bias and tolerance within and outside the provisions of combinations.
  (A), the Unified Inch Screw Threads, male thread, there are three grades: 1A, 2A and 3A levels, internal thread, there are three levels:
        1B, 2B and 3B-class, all clearance fit. The higher the rating number, with the more compact. In the British thread, the deviation of the provisions of 1A and 2A level only, 3A-class bias is zero, and the 1A and 2A grade level deviations are equal.
        The smaller the number the greater the tolerance level.
  1) 1A and 1B class, a very loose tolerance level, it applies with internal and external thread tolerance.
   2) 2A and 2B grades Inch Series mechanical fasteners provides the most common thread tolerance class.