M12 M20 Carbon steel Round head Philip crosses tapping screws grade8.8 Black coating

M12 M20 Carbon steel Round head Philip crosses tapping screws grade8.8 Black coating

 
Product Description:
1,Ordinary self-tapping screws
The thread is ‘self-tapping thread’, also known as ‘wide thread’. The surface is mostly plated.
2,Self-cutting tapping screws
China's standard called ‘self-tapping screws shaved end’, the thread for the self-tapping thread or machine thread, cross groove is also ‘H’ type. Self-cutting tapping screws have the following types: cross recessed pan head self-cutting tapping screws, cross recessed countersunk head self-cutting tapping screws. Cross recessed raised countersunk head self-cutting tapping screws, hexagonal head self-cutting tapping screws.
3, self-extruding tapping screws (self-tapping lock screws)
Self-extruding tapping screws thread is generally machine thread, rarely use self-tapping thread. In the wrenching method, in order to ensure the use of high-speed automatic assembly wrenches, generally do not recommend the use of slotted. Self-extruding self-tapping screws have a three-pronged screw cross-section. So also known as triangular thread screws.
4, self-drilling tapping screws (self-drilling screws)
Self-drilling tapping screws thread, China, Germany and international standards for self-tapping thread. U.S. ASME and SAE standards in the BSD type self-drilling tapping screws for self-tapping thread, CSD type self-drilling tapping screws for machine thread. Self-drilling tapping screws do not recommend the use of ‘slotted’ and ‘ordinary hexagon head’.
5, metal drive screws (metal tapping screws)
Metal drive screws thread for the multi-head, and with a certain helix angle of the special thread. Only the U.S. standard metal drive screws, our country and the German standard is not.
6, wallboard tapping screws (drywall nails)
Wallboard white tapping screws for the trumpet head, cross groove (H-type), 60 ° tooth angle of the special thread, the surface of more phosphate treatment (phosphating).
7,Fibreboard nails
Cross slot for Z-type, the surface treatment is mostly plating. Fibreboard nails have the following types of several types: countersunk head, double countersunk head fibreboard nails, pan head, pan head flange (with pad) fibreboard nails, half countersunk head, half countersunk head flange (with pad) fibreboard nails.
8,Combination of self-tapping screws
Ordinary self-tapping screws, self-cutting self-tapping screws, self drilling self-tapping screws and flat washers, elastic washers (including spring washers, elastic lock washers shaped t into a combination of self-tapping screws.
9. Other self-tapping screws type
High and low teeth double lead self-tapping screws, coarse and fine teeth (different pitch) thread self-tapping screws, thread coated with sealing material (drop-resistant) self-tapping screws, a variety of composite groove self-tapping screws, other special equipment juice self-tapping screws.
Applications
Although there are many types of self-tapping screws, they all have the following common points:
(1) They are generally manufactured from carburised steel (99% of total production). They can also be manufactured from stainless steel or non-ferrous metals.
(2) The product must be heat-treated. Carbon steel self-tapping screws must be carburised, and stainless steel self-tapping screws must be solution-hardened. In order to make the self-tapping screws to achieve the mechanical properties and the use of performance required by the standard.
(3) high surface hardness, good core toughness. That is, ‘soft outside’. This is a major feature of the performance requirements of self-tapping screws. If the surface hardness is low, it is not screwed into the matrix; if the core toughness is poor, a screw on the break, can not be used. So ‘soft outside steel’ is a self-tapping screws to meet the performance, very important requirements.
(4) The surface of the product requires surface protection treatment, generally plating treatment. Some of the product surface shall be treated with phosphate (phosphating), such as wallboard tapping screws are mostly phosphated.
(5) Cold heading process is adopted. Recommended high-speed cold heading machine and high-speed thread rolling machine or high-speed planetary thread rolling machine production. High speed is emphasised here to ensure product quality. Only high-speed machine production of self-tapping screw head forming good, high thread quality.
 
Class 8.8 bolt
Class 8.8 bolts have higher strength than class 4.8 bolts. The number 8.8 represents its material strength grade, which provides greater tensile strength and torque tolerance than Class 4.8 bolts.
Class 8.8 bolts are usually used for some occasions that require large loads or important connections, such as the assembly of Bridges and large mechanical equipment. Class 8.8 bolts have high reliability and durability, which can ensure the fastness and safety of the connection.
 
What is blackening treatment
Blackening treatment has the following advantages.
Improved rust prevention
The protective film of iron tetraoxide (black rust) on the surface of parts is in a strong and stable state. The presence of this film inhibits the formation of red rust (rust that corrodes steel into a ragged state) on the surface of steel to a certain extent. In addition, the protective film of iron tetraoxide is porous and is characterised by the presence of a large number of fine pores and unevenness. As a post-treatment, soaking these holes with anti-rust oil prevents moisture from entering and further improves rust prevention. Although this treatment process does not achieve rust protection as strong as galvanising or nickel plating, blackening is recommended if some rust protection is desired while imparting aesthetic appeal.
In addition, post-treatment using rust preventive oils allows the oils to remain on the surface of the skin and therefore also improves the sliding properties of tools and machine parts.
Less likely to flake off
Plating and painting are surface treatment processes that attach layers of other materials to the surface of parts. As a result, the plating or coating to which they are attached may flake off. In contrast, blackening is a surface treatment process that merely changes the surface of the part into a different substance (a protective film of iron tetraoxide) by triggering a chemical reaction, which is difficult to peel off. It can be said that this is a surface treatment process that has a longer lasting effect.
 

 
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