NPT thread standard pipe thread types of injection molding thread
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Pipe Thread Types and Designations
Overview: Different types of screw threads have evolved for
fastening, and hydraulic systems. Of special concern are
plastic-to-metal, taper/parallel threaded joints in hydraulic
circuits. A discussion and recommendations are provided to create
an awareness of different types eads and how they are used.
Over time many different types of screw threads have been
developed. Applications include fastening components, and hydraulic
and pneumatic circuits. In the nineteenth century, manufacturers
needing fasteners would devise their own systems. This resulted in
compatibility problems. The English mechanical engineer and
inventor, Sir Joseph Whitworth devised a uniform threading system
in 1841 to deal with these difficulties. The Whitworth thread form
is based on a 55 degree thread angle with rounded roots and crests.
In America, William Sellers set the standard for nuts, bolts, and
screws which became the National Pipe Tapered Thread (NPT) in 1864.
His 60 degree thread angle, in common use by early American
clockmakers, enabled the American Industrial Revolution. These
thread forms later became the American National Standard.
The Whitworth thread form was selected as a connecting thread for
pipes, which was made self sealing by cutting at least one of the
threads on a taper. This became known as the British Standard Pipe
thread (BSP Taper or BSP Parallel thread). The Whitworth thread is
now used internationally as a standard thread for jointing low
carbon steel pipes.
The best known and most widely used connection where the pipe
thread provides both the mechanical joint and the hydraulic seal is
the American National Pipe Tapered Thread, or NPT. NPT has a
tapered male and female thread which seals with Teflon tape or
Pipe threads used in hydraulic cir cuits can be divided into two
a)Jointing threads -are pipe threads for joints made pressure tight
by sealing on the threads and are taper external and parallel or
taper internal threads. The sealing effect is improved by using a
b) Fastening threads ?are pipe threads where pressure tight joints
are not made on the threads. Both threads are parallel and sealing
is affected by compression of a soft material onto the external
thread, or a flat gasket.
Forwa-Mould , locating in Dongguan, China, is a professional
plastic injection mould manufacturer with years experience in this
field. We can provide high precision complex hardened moulds,
prototype and soft moulds.
We equipped high speed CNCs, Wire cuts in house. We use software
(i.e. UG, Pro-E, IGS, Master Cam, AutoCAD, and Solidwork ) for
mould design and MoldFlow analysis for our customers before mould
manufacturing. Standard components we use to build the mould are
purchased from DME, HASCO etc. Also, COC for all steel we purchase
will be provided.
Component parts that are critical in the manufacturing of products
for a wide arrage of industries and applications including:
- Point-of Purchase
Male threads are less complicated to produce than female threads.
Male threads are cast as an open and shut injection mold except in some instances where the rest of the part design
dictates where the parting line will be located. If male threads
need to be cast in the vertical position, the use of cam action or
hydraulic action slides is required because of the undercut that is
produced from the thread.
On the contrary, casting female threads always present an undercut
situation. These type of threads need to be unscrewed in order to
have the part removed from the injection mold. There are different
ways to achieve this. The most common way used is by hydraulic or
electrical motors that automatically unscrew the threaded core from
the molded part. The hydraulic motor is the least expensive option.
Threaded cores have wurm gears attached which mate with the main
drive gear. There is a chain that connects the mold drive gear to
the gear on the drive motor shaft. There are a few different
options of unscrewing the cores which are sometimes dictated by the
part design. The most common application is after the injection mold opens, the cores are unscrewed by the actuation of the unscrewing
motor. The time can be set so the motor stops once the part is
unscrewed off the core. In this application the part needs to be
held in place so the part does not turn during the unscrewing
cycle. This can be achieved by a variety of designs. Again, this is
always dictated by the part design. In some instances the threads
need to be unscrewed before the mold opens. This is achieved by
timers and/or the machine control. Usually, this option of molding
female threads is incorporated for high production parts because of
the expense involved.
In the case of low volume and prototype injection molded parts, the female threads are cast with hand-loaded cores. In this
process threads are commonly ground on three hand-loaded cores. One
core needs to be loaded into the mold by the means of locating pins
to position the core into the mold open position. The mold then
goes through the injection molding cycle. After the mold opens, the part is ejected with a
hand-loaded core attached. Another hand-loaded core is inserted
into the mold. During the next molding cycle the hand-loaded core
that was ejected with the part after the previous cycle is manually
unscrewed from the injection molded part. This process usually
doubles the cycle time of the injection molded part which in effect
raises the part price but is very cost effective in producing
Another option to cast female threads is by the use of collapsible
cores, but this is a very expensive option. By the use of these
collapsible cores essentially the injection mold is considered an open and shut mold.
These are some of the most common options of producing threads on
injection molded parts. These threads are able to be cast to a +/-