Black M16 M20 Carbon steel Flat head Hexagon tapping screws Class8.
8 CSK screws
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.
Choice of Class 4.8 bolt and Class 8.8 bolt
In practical applications, appropriate grades of bolts should be
selected according to specific engineering requirements and design
requirements. If the engineering structure does not have high
strength requirements for bolts and the budget is limited, you can
choose 4.8 class bolts. For connections that need to withstand
strong or heavy loads, class 8.8 bolts should be selected to ensure
the safety and reliability of the connection.
Therefore, when selecting bolts, various factors should be
comprehensively considered according to the specific use scenario
and engineering requirements, and the appropriate grade of bolts
should be selected to ensure the quality and safety of the project.
At the same time, in the process of use, it is also necessary to
install and use in strict accordance with relevant standards and
specifications to ensure the effect and safety of bolt connection.
Through the understanding and selection of 4.8 bolts and 8.8 bolts,
the bolted connection technology can be better applied in various
engineering structures, so as to improve the quality and safety of
the project. Different grades of bolts play different roles in the
project. Reasonable selection of bolt grades will have a positive
impact on the implementation and use of the project.
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.
| No. | C% | Cr% | Ni % | Mo % |
| 304 | 0.07 | 17.5-19.5 | 8.0-10.5 | / |
| 316 | 0.08 | 16.0-18.0 | 10.0-14.0 | 2.00-3.00 |
| 301 | 0.15 | 16.0-18.1 | 6-8 | / |
| 310 | 0.08 | 24-26 | 19-22 | / |
| 304L | 0.03 | 18-20 | 8-12 | / |
| 316L | 0.03 | 16-18 | 10-14 | 2-3 |
| 321 | 0.08 | 17-19 | 9-12 | / |
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