Getting to know with kinds of threads and the way of its determination
Thread, fittings and their type determination are the goals that have been pursued in this article,
the first of which is a series of papers familiar with the types of threads.
This article describes the general specifications of threads and fittings and a method for identifying them.
It is worth noting that recognizing the thread type is one of the first steps in determining the fittings.
Traditional problem that has engaged engineers and
operators to itself is recognition of fittings and not being familiar with their scientific name.
Hekmat Industrial Complex is trying to prepare some articles by using of the knowledge and
experience of this collection in supply and produce various types of hydraulic and
pneumatic fittings in Iran to, so that the young engineers of this land
can find their full knowledge of hydraulic and pneumatic connections.
It should be noted that the Hekmat industrial complex in the standards sector also
introduces a variety of standards related to piping and
the dear reader by referring to that section will be able to download
and use this standard in addition to the familiarity and the way of using of the standards.
This section will add in the future.
1-1 Use of the standards to determine the threads
Threads have a lot of use in the industry, therefore, there are a lot of standards in this area.
Some of these standards are limited to thread, and others have investigated fittings.
Among the standards that address only the threads can be mentioned as, ASME B1.1, EN 10226-1, ISO 261.
In the articles section on the standard, it will be dealt with extensively.
Some other standards, including DIN 3852, JIS R, or JIS RC,
as well as some industrial standards such as SAE J512, are included in the type of fittings,
end sections, sealing, geometry, and their diameter size.
In these standards, threading standards are commonly used in the attachment section.
2-1 Introduction to Threads and Fittings Parameters
Threads in fittings have the following specifications
Thread crown: the crown of the threads is different according to the type of design.
The crown of the thread is the same as the outer surface of the tooth. On the next articles will talk more about this.
The roots of the thread: just like the crown, the root of the thread is different.
Thread support: The thread is said to be in the shape of a tooth lateral surf
Screw: The screw is usually considered as the number of gears per inch and for the metric threads as thread spacing.
Threads supports angle: These angles vary in different connections.
Cone shaped angle: In some fittings, a mechanism for creating cone angles during threading is used to create sealing.
Male outer diameter OD
Female inner diameter ID
This specification is indicated by the number given in the figure below.
Figure 1-1 Specification of male thread and female thread
In addition to the thread, three other effective parameters in the fittings are shown in the figure below.
1.Body dimensions
2.Fitting support
3.Its end surface
Figure 1-2 Parameters determining fittings
3-1 Procedures for detecting stage-to-stage threads and connections
The following step-by-step procedure can be used to diagnose threads and fittings.
It is worth mentioning that this work is sometimes difficult for professionals and needs to be experienced and practice.
Determine whether the thread is conical or not
Measuring the diameter of the thread
Determine the thread screw
Determine the ruler standard
Determine the type of connection using the head and bottom specifications
In the following, each of these steps will be explained and described.
1-3-1 The first step: Determine whether the thread is conical or not
At this stage, which is the first step in detecting the type of connection,
it is determined whether the thread is conical or direct. (Tapered or straight).
Consequently, we show cone connections with T and straight connections with S, the first Latin word for it.
You can use a coulis to do this.
As shown in the figure below, by measuring the diameter on the crown in thread 1, thread 4 and the end thread,
the cone connection can be determined.
The figure below shows how to use the coulis to measure the outer diameter of the thread.
If the size of the outer diameter of the crown of the thread increases in these three parts
of the stirrup fitting or decreases for the bearer, the type of fitting is cone (T).
If the size of the outer diameter of the crown of the thread is fixed in these three parts of
the stirrup or bearer fitting, the type of fitting is straight(S).
Figure 3.1 Measurement of OD Threads in the first, fourth, and last thread using a coulis to detect it conically.
In the following figure has shown the form of a conic (T) and direct (S) gear.
Figure. 4-1. Shape of the conical gear (T) and straight gear (S)
2-3-1 step two: Measuring the diameter of the thread
The diameter of the thread crown (outer diameter) can be measured using the appropriate tool.
For this purpose, the nominal diameter is used in cone threads.
In cone fittings, the outer diameter of the fourth or fifth thread is used as the diameter of the nominal
In direct connections, since the diameter is constant, each one can be measured.
Note: The measurements taken at this stage may not accurately match the tables.
The main reason for this difference is constructive tolerance.
3-3-1 Step 3: Determine the thread screw
In the industry, to determine the screw thread, a gauge is used to determine the screw.
Below is a sample of these gauges.
As can be seen, in gauge, the angles of threaded supports are 55 and 60 degrees
1-5 Gauge for determining Thread Screw
It is possible by testing these items, determine the gear screw.
Also, by identifying the cone or the straight of the fitting and having the diameter of the nominal,
refer to the relevant tables in the future articles,
it is possible to guess the screw and directly use of desired gauge for confirmation.
Also, when gauges are not available, you can use this information and tables to guess the thread screw.
For using of the gauge in order to determining the screw,
It is necessary for operator to be careful and being sure of matching the thread and stencil.
In below figure this subject has been showed.
4-3-1 Step Four: Specify the thread standard
If you specify the following until this step, you will be able to determine the thread standard.
1.Male or Female
2.Conic or straight
3.Male or female nominal diameter
4.Thread screw
By this specification, you will have all of required information for determining the thread.
In future articles, tables and references will be used and the practical examples will be used to illustrate the subject.
5-3-1 Step Five: Determine the characteristics of the beginning and end of the fittings
For conic and straight threaded fittings, future articles in this section will feature types, samples and tables.
By referring to these sections, you can specify the type of fitting.
Also, the ends of some fittings have angles for sealing
These angles are 45, 37 and 30 degrees, which are specified using the conveyor or the corresponding tabs.
The following figure shows a fitting and its angle determination method.
Figure 1-6 Determine the angle of the fittings seat
As mentioned, in future articles, the tables for assigning fittings will be presented by using the relevant standards.