Is it possible to thread the fittings
How to cut threads by hand
Threaded connections are widely used in the device of various mechanisms and machines. Bolts, studs, screws, nuts are versatile, interchangeable fasteners. However, there are times when you need to cut threads by hand. A specialized tool will help to perform this work qualitatively.
In mechanical engineering, there are three main systems of fastening threads: metric, inch and pipe.
Metric thread is the most widespread. It has a 60˚ triangular profile. Its main parameters, diameter and pitch, are expressed in millimeters. Example of designation: M16. This means that the thread is metric, has a diameter of 16 mm with a coarse pitch of 2.0 mm. If the step is small, then its value is indicated, for example, M161.5.
Inch and pipe thread diameters are expressed in inches. The pitch is characterized by the number of threads per inch. The specified parameters are standardized, so there is always an opportunity to choose the necessary tool.
Tapping internal threads
The following tools and materials are required to form an internal thread:
- hammer, center punch, drill, drill;
- a set of taps, a knob, a bench vise;
- machine oil.
External threading with a die
To cut external threads, the following tools and materials are required: die or pipe die, die holder, file, vice, vernier caliper, machine oil.
The most widespread are round dies (lerki). They come in one piece or split. The diameters of solid round dies are standardized. This allows you to choose a suitable option from a wide range of sizes, for example, M10, M12, M14, M16.
A feature of split dies is the ability to adjust the diameter of the cut thread within 0.1. 0.25 mm. However, they have a reduced rigidity, which affects the accuracy of the resulting profile.
The die is placed in a die holder of a suitable size. After that, it is fixed with screws. In the case of external pipe threads, ratchet ram holders are often used. They provide convenience for working in hard-to-reach places, such as against a wall.
The thickness of the rod is chosen 0.1. 0.25 mm less than the diameter of the external thread. For example, for M6 with a large pitch it is 5.80. 5.90 mm; M8. 7.80. 7.90 mm; M10. 9.75. 9.85 mm. Measurements are performed using a caliper. The diameters of rods for cutting metric threads of average accuracy class 6g are presented in the table.
To ensure a better plunge into the die, a chamfer is cut at the end of the rod. Its width should be 1. 1.5 mm for M6. M18. The workpiece is lubricated with machine oil, which facilitates subsequent work and allows you to get a better surface.
The die is placed on the end of the rod so that its plane is perpendicular to the axis of the bolt being cut. Then, with a slight pressure, rotate the die holder clockwise (if the thread is left, then counterclockwise). When the die hits the rod one or two threads, it should be turned half a turn back for better chip removal. After that, 1-2 turns are made again along the thread and 0.5 turns in the opposite direction. Acting according to this scheme, the bolt is cut to the required length.
The diameter of the external thread is checked with a conventional nut or ring gauge. If necessary, the step is controlled by a thread gauge.
The first step is to mark the workpiece and center the center of the future hole. A drill is selected that corresponds to the required thread diameter. This can be done using look-up tables or approximately by the formula d = D. P. Here D is the thread diameter, P is its pitch, d is the drill diameter. For example, for М10 d = 10. 1.5 = 8.5 mm.
A hole is drilled in the part to the required depth, which must exceed the length of the cut part. Using a drill with a diameter greater than d, a chamfer is made at the edge of the hole. It serves for centering and better entry of the tap.
According to the main parameters of the thread. diameter and pitch. the cutting tool is selected. Typically, a set of two taps is used. One of them is rough, the other is final. By the size of the square of the tail part of the taps, choose a knob.
The part is securely fixed in a vice. The rough tap and hole are lubricated with machine oil. After that, the tap is installed strictly perpendicular to the surface of the part and, pressing along its axis, rotate the knob by the handles.
Having cut one or two threads of thread, make a quarter of a turn in the opposite direction. This facilitates crushing and removal of chips, and prevents jamming of the tool. The work is continued, carrying out alternating rotation: ½ turn forward, назад. back. In this case, it is necessary to ensure that there is no misalignment of the tap. You should also not put excessive effort on it. To prevent jamming, the cutting tool is periodically removed, and the hole is cleaned of chips.
After cutting the internal thread to the required depth, a finishing tap is installed in the hole. When he goes in a given direction, they put a knob on him and continue to work. Add lubricant periodically.
The threads are checked using a plug gauge or bolt. It should screw in effortlessly and not wiggle. If necessary, make an additional cut with a finishing tap.
On the territory of the CIS countries there is a metric thread standard. Its angle is sixty degrees in cross section. In Western countries, an inch thread (an angle of 55 degrees) is used. This circumstance should be remembered when buying any spare parts for a car or other equipment.
Depending on the geometric shape of the thread teeth in the section, rectangular, triangular, trapezoidal and other options are distinguished.
A special type of thread is a ball screw. She found application only in machine tool construction. With intensive use, the helical surface wears out. However, the design of the ball screws allows you to adjust and eliminate the backlash.
There are right-handed threads (the most common) and left-handed threads (they have limited and highly specialized use). You can hardly find a die or tap for left-hand threading. Cutting on a lathe is perhaps the only possible way. It is recommended to use it in the absence of other versions.
Surface preparation for external cutting
How to thread a bar? It should be noted that the diameter of the rolled bar must be at least a millimeter larger than the diameter of the thread, so that there is an allowance for removing blackness on a lathe. Cutting on a black untreated surface is highly undesirable: there is a high probability that the die will find a non-metallic inclusion and break.
After grooving the outer diameter on a lathe, it is necessary to groove a chamfer. This element is necessary, firstly, in order to ensure the plunging of the die, and secondly, to remove a sharp burr obtained when cutting the end on a lathe.
Pipe surface thread
When carrying out plumbing work, it is often necessary to cut threads on the pipe. How it’s done? There are no fundamental differences. The only difference is that the pipe is hollow inside. That’s all. For these purposes, a conventional die and a crank or a screw-cutting lathe can be used.
Also, to carry out the process on the pipe surface, so-called shanks are used. In this case, you can use both sliding and solid dies.
The cutting procedure is preceded by reliable fastening of the pipe section (in a vice or in special prisms), after which the surface is cleaned of dirt and oxides, and the burr from the band saw is removed. It is recommended to lubricate the surface with oil. Only after these preparatory operations can one proceed directly to cutting.
Selection of the diameter of the workpiece when cutting external threads
The correct choice of the outer diametrical size of the original workpiece is a guarantee of the quality of the resulting thread. Cutting threads (both external and internal) on the surface (in the hole) is possible only if certain requirements are met. So that the die does not break and does not jam, the cylinder diameter should be several tenths of a millimeter less than the nominal thread. In the process of cutting, the metal will be squeezed out to some extent and filled in the shape of the die, so that the gap will be minimal.
Thread. a kind of helical groove on the outer surface of the cylinder (outer) or on the surface of the hole (inner).
A die is used for cutting an external thread, a tap for an internal thread.
But this method and tool are suitable only at home or in repair production, because they require a lot of time for cutting. In the mass production of hardware (bolts), the thread is not cut, but rolled on special equipment for metal processing by pressure. At the same time, it is important that the workpiece be heated to a temperature of over 750 degrees (then dynamic recrystallization and texture elimination will occur). This performance is imprecise. And therefore, for critical connections, the threads are cut.
The threaded surface can be obtained by machining on a screw-cutting lathe. For this, both a die with a tap and special turning tools can be used.
In addition, the rapid development of electronics made it possible to process threaded surfaces on turning and even CNC milling machines.
How to cut a thread: methods and tools
Modern technology is simply unthinkable without threaded connections. The thread has a number of advantages over other types of detachable and one-piece fasteners: the clamping force can be adjusted using a dynamometer, which excludes possible destruction of body parts. Such a connection withstands dynamic loads well, it is easy to disassemble and reassemble.
However, the use of threaded connections is not limited to the industry. At home, in everyday life, it is very often necessary to cut a thread. How and in what sequence is it correct to do it? What tool is needed for this? The article contains useful information that will help people who have no similar experience in this.
External thread: how to cut into a die
The easiest and most affordable way to cut a thread on the outer cylindrical surface is to use a die. Depending on the design, the device can be round, prismatic, sliding.
The round die is somewhat reminiscent of a nut. Only the outer contour is not a hexagon, but an ordinary circle with small indentations for attaching to the knob. It differs from the nut in the presence of three grooves for the exit of chips when threading.
Round dies form threads in just one tool pass. Therefore, during their operation, it is necessary to supply lubricant to the cutting zone. The maximum thread diameter obtained in this way is 52 millimeters.
The sliding plate consists of two identical parts. They are installed in the die with a certain gap. In the process of work, the parts come closer.
To cut internal threads, taps are used. tools like a screw with cutting grooves. Typically, two taps are required for the black cut and the finish cut. The difference is in the grooving depth. There are also three-pass taps and other cutting options. To work with them, special wrenches are required, which may be different in design, but must necessarily be suitable in size for the working tool.
It is very important to prepare a hole of the correct diameter before threading. Otherwise, you will either break the tap (if the hole diameter is less than required), or you will get a poor-quality thread. So, if an internal thread M10 is required, i.e. 10 mm in the groove diameter, then the hole diameter should be 8.5 mm. This is determined based on the thread pitch. For M10, it is 1.5 mm and, accordingly, the required hole diameter will be 10-1.5 = 8.5 mm. The steps of the threads can be found using special formulas, although the simpler option will not be to calculate the diameter, but to find out its value from the table.
After preparing the hole, we proceed directly to considering the issue of how to properly cut the thread. We attach the tap to the holder and start slowly screwing it into the hole, paying special attention to the accuracy of the direction. Slicing is performed clockwise with the application of certain efforts.
For successful cutting, the tap must be sharp and of good quality. The duration of its operation and the likelihood of breakdown depend on the use of the lubricant. A few drops of oil will not only make cutting easier, but also improve the quality of the threads. This is especially important for cutting blind holes. Naturally, it doesn’t hurt to have certain skills that come with practice. However, this operation is relatively simple and skills are acquired after 3-4 threads.
How to cut threads correctly
You can talk for a very long time about how to cut the thread correctly. Whole books and monographs are devoted to this. But, the overwhelming majority of the threads used do not require special skills when cutting, and we will stop our attention on the main methods.
How to properly thread a bolt or stud
Bolts, studs and other similar fasteners have external threads and, accordingly, you will need a die (lerka) or klupp. The first ones are used for metric threads, and die plates are used for pipe threads. Cutting with a die is a little easier. they have special pipe runs (put it on and start cutting) and ratchet holders. To work with a die, it is very important to make the first turns exactly, therefore it is strongly recommended to first make a small chamfer with a file.
Unlike internal threads, there are no difficulties with diameters. So, for the M10 thread, you need a workpiece with a diameter of 10 mm. The basic rules for cutting are not much different from working with a tap. The dies must be sharp and of good quality, and lubricant must be used when cutting. Sometimes it is more difficult to start the carving and if a skew is noticeable, then it is necessary to cut off the defective section and start again. For any type of thread, the workpiece must be firmly clamped in a vice.
In conclusion, I want to warn you that there is another formula for determining the diameter of the hole for an internal thread. tap diameter x 0.8. But it is only relevant for manual three-pass taps. For all other cases, it is better to use the appropriate tables.
BSPP Fittings / Threads – Identification & Installation – Heads Up for Hosers
⏺ Saving of reinforcement up to 20% in comparison with overlapping joints;
⏺ Saving energy and time for assembling the structure in comparison with welding;
⏺ Docking of two rods takes no more than 5-10 minutes;
⏺ Effective procedure for control of joints (it is enough to make a test-rupture of two joints from each batch);
⏺ The use of coupling joints allows to significantly increase the distance between the reinforcing bars, which is important when erecting a sliding or walking formwork;
⏺ Compact overall dimensions (outer radius of the coupling. 1.3 reinforcement diameters, coupling length. 3.5 reinforcement diameters). This indicator is especially important in structures with high reinforcement saturation and when joining column reinforcement;
⏺ The use of a tapered thread ensures the maximum concentration of material at the section of the coupling subject to the greatest stress;
⏺ Allows you to combine reinforced concrete structures with metal structures (use in steel-reinforced concrete construction);
⏺ The production of this type of connection does not require highly skilled workers.
To connect the rods using tapered couplings, it is necessary to cut tapered threads on the reinforcement using a special cutting device SPN14-88.
Tapered thread couplings. this is the only method of connecting reinforcing bars approved for use on the territory of the Republic of Belarus, according to STB 2152-2010 (Couplings with tapered thread for mechanical connection of reinforcement for reinforced concrete structures).
Special device for cutting tapered threads on steel reinforcement SPN14-88
A special device for threading on SPN14-88 reinforcement is used for cutting tapered threads on steel bar reinforcement of periodic profile GOST 5781-82 (diameter 22.40 mm).
|Working height (mm)||Minimum. 900
|Overall length (mm.)||1200|
|Possible thread diameter (mm)||22-40|
|Voltage (V)||three-phase, 380V. frequency 50Hz|
|Power consumption (kW):||El engine is the main one. 2.6 / 3.2 Electric motor for coolant pump. 0.12|
|Estimated productivity, pcs / hour||15|
|The device is intended for the manufacture of threaded reinforcement rods used for mechanical connection of reinforcement in concrete structures using couplings manufactured according to STB 2152-2010.|
Torque wrench for tightening the thread
Torque wrench. a spanner with a built-in torque gauge. This tool for tightening union bolts to the exact specified torque.
The state enterprise “Institute NIISM” has mastered the production of couplings with tapered threads for connecting reinforcement in monolithic housing construction of the following standard sizes, presented in the table below.
Is it possible to thread the fittings
The thread is a helical groove formed on the rotating parts. It is widely used for connecting parts to each other (fastening) and for transmitting motion (as, for example, in the lead screw of a lathe or vice).
Bolts, studs and screws are used in threaded connections. Bolt. a cylindrical rod with a head at one end and threaded at the other (see the figure on the right a). Hairpin. cylindrical rod with threads at both ends. One end of the stud is screwed into one of the parts to be connected, and the other end is fitted with the part to be fastened and the nut (b) is screwed on. Screw. a cylindrical rod with a thread for screwing into one of the parts to be joined and a head of various shapes (c).
The main elements of the thread: the angle of rise of the helix a,
thread pitch p, profile angle y, outer and inner diameters (Figure on the left). Different types of threads are used depending on the purpose of the threaded connection.
In the direction of the turns, the thread is right and left (fig. On the right). Most often right-handed thread is cut.
To cut the external fastening thread, use a special tool. dies. They are round (fig. On the left a), thread rolling (b) and sliding (c).
The round die (fig. On the right) is made in the form of a hardened steel nut. The thread of the die is crossed by the through longitudinal holes. The formed cutting edges in the form of a wedge and groove ensure the cutting of the workpiece and the simultaneous exit of chips. In order for the end of the rod (workpiece) to better enter the die from the end sides, its thread has a lower profile height. This is the so-called intake part. Round dies in accordance with the standard are provided for cutting metric threads with a diameter of 1 to 76 mm. They are laid in the sockets of the die holder and fixed there with studs (or bolts) with a slot for a screwdriver.
Die 4 (Fig. On the left) with special cutouts 6 is fixed in the ram holder 5 or in the knob with three or four screws, depending on its size and operating conditions. One or two screws 7 are used for fastening, screws 1 and 3. for fastening and compressing the die when adjusting its size after cutting the bridge. The die is unclenched with the screw 2.
In the body of the thread rolling die (Fig. B above), adjustable knurled rollers with thread are installed. The metal of the workpiece is not cut, but squeezed out. Due to this, the surface of the thread is cleaner, and the thread itself is of higher quality and more accurate.
Sliding prismatic dies (Fig. C above) consist of two sliding and sliding half-dies.
Of particular interest is a knob for installing and attaching dies (Fig. On the right) with an additional guide ring 16, which helps to maintain the direction on cylindrical blanks 12 (rods, pushers of molds and screws, die removers). Additional device can be used in conventional wrenches.
In the inner part of the cage 1 of the crank there is a machined square window with inserted prismatic dies. A screw 15 is installed on the side of the cage, which presses the dies 9 during operation, and from the sides of the cage, two handles 13 are screwed into the housing 11 for gripping by hands. In the lower part of the cage there is a washer 14, fixed with screws 8, and two guide pins 10, along which the ring 16 moves.
In order to cut a thread with a die on a rod, you must first find out the outer diameter of the thread d and its pitch p (see the figure on the left). These data are indicated on the plate. Then, using the table (see table below), determine the diameter of the rod for this thread and select the workpiece.
|Thread diameter||Step (P)||Bar diameter|
It should be borne in mind that when the thread is cut, the metal, especially copper, mild steel, “stretches”. As a result, the diameter of the rod increases slightly and the pressure on the threaded surface of the die increases. It heats up, the chips stick to the cutting edges, and the threads become “ragged”. All this reduces its quality. Therefore, the diameter of the shank must be less than the outer diameter of the thread by 0.1. 0.3 mm depending on thread size. If the diameter of the bar is smaller by 0.4. 0.5 mm of the outer diameter of the thread, the thread profile is incomplete.
The selected workpiece must be straightened, marked, cut off according to the markings and, fixing it in a vice, remove the chamfer with a file (Figure on the right a) in order for the intake part of the die to more easily grip the metal. Check the quality of the die by visual inspection and screwing it onto a bolt or stud with intact threads. It is also necessary to carefully check the quality of the fixing of the die in the ram holder in order to exclude its possible distortion and slippage in the socket.
Before cutting the thread, mark its length on the rod, the rod is fixed in a vice so that the end protruding above the upper plane of the jaws is 20.25 mm larger than the cut part. The rod is placed in a square at an angle of 90 ° to the upper planes of the jaws (Fig. B). The die, fixed in the die holder, is placed on the upper end of the rod and, with slight pressure, not allowing the die to be skewed, rotate it (Fig. C). After cutting 1-2 threads of thread, once again check the coincidence of the axes of rotation of the die and the rod.
After that, the threaded part of the rod is lubricated with oil, the cutting of the die and the die is rotated, evenly pressing on both handles of the die holder (Fig. D). The rotation should be reciprocal: one or two turns to the right and half a turn to the left. In this case, the chips break and exit through the longitudinal hole. This makes threading easier and improves thread quality.
The quality of the cut threads under production conditions is checked with threaded micrometers, threaded ring gauges and threaded plugs (see the figure on the left). In school conditions, it is allowed to check the thread with nuts.
After the end of the work, the die is removed from the die holder, thoroughly cleaned with a brush from shavings, wiped with a rag and lubricated with oil.
Die-cutting can also be performed on a lathe.
When threading, the die should be securely fastened in the die holder.
When working, be careful not to get your hand between the ram holder handle and the support.
Use a brush or oil can to lubricate.
Do not blow chips off the die, but use a broom brush.
Do not allow oil to come into contact with clothes, hands.
In factories, hardened screws are used, which are screwed through punched holes in two or more sheet metal parts to be joined. Screws, threading in the holes, connect these parts. This method of screwing is economical and speeds up the assembly process. Many factories now use hardened self-extruding screws for steel and cast iron parts, the hardness of which is less than the hardness of the screws.
Threads on bolts and small diameter studs are made on automatic lathes simultaneously with the manufacture of the bolts themselves. Screws and bolts are also stamped on presses.
In mass production, external thread rolling is widespread. After the passage between the rollers, a thread forms on the rod. Some threading devices use carbide inserts instead of rollers.
Below are the basic terms and concepts that are necessary to assimilate the material.
The main elements of the thread:
Outside diameter of the thread. is the diameter of an imaginary cylinder whose surface coincides with the tops of the external thread and the troughs of the internal thread.
Internal thread diameter. diameter of a cylinder whose surface coincides with the tops of the internal thread and the troughs of the external thread.
Average thread diameter. diameter of an imaginary thread-coaxial cylinder whose generatrix intersects the thread profile at the point where the groove width is half the thread pitch.
Profile corner. the angle between the sides of the profile, measured in the axial section.
Top of the profile. section of the profile connecting the sides of the protrusion.
Profile depression. section of the profile connecting the groove sides.
Thread pitch. distance between adjacent side sides of the same name in a direction parallel to the thread axis.
Lead angle of the thread. angle formed by a helix tangent to a point on the mean diameter of the thread and by a plane perpendicular to the thread axis.
Profile corner. angle between the flanks of a thread, measured in a plane passing through the axis of the thread.
The following threads are used in industry:
Metric thread. has a triangular profile and serves mainly to connect parts to each other.
Metric threads are divided into two groups: metric coarse threads and metric fine threads for diameters 0.25-600 mm.
Tapered pipe thread. has the same purpose as cylindrical. The required tightness of the connection is achieved by deformation of the turns of the tapered pipe thread.
Tapered inch thread with a profile angle of 60 degrees. Tapered inch thread is used to obtain tight connections.
Inch thread. used for fastening machine parts with bolts, screws and studs.
Trapezoidal threads. mainly used for lead screws of machine tools and other power transmissions.
Trapezoidal threads are classified into coarse, normal and fine.
Thrust threads. large, normal and small. They are mainly used for lead and load (with a large load) screws with a unilaterally acting load. In rare cases, they are used as fastening.
Rectangular thread. used for cargo and lead screws. The thread is difficult to manufacture and has drawbacks that limit its use.
The pipe thread is cylindrical. cylindrical pipe thread is used in the joints of hollow thin-walled parts when the connection must be especially tight.
Modular thread. applies to worms.
Scheme of helical lines: a. helix sweep; b. cylindrical triangular thread; c. cylindrical square thread; g. cylindrical rectangular thread; d. cylindrical
trapezoidal thread; e. cylindrical round thread; g. single-start thread; h. double-start thread; and. three-start thread.
In order to find out the thread pitch, use special gauges (see the figure on the right).
Threaded connections of the valve with the pipeline, depending on the placement of the thread on the connecting ends of the valve, are of two types. COUPLING or FITTING-END.
The German origin of the term “fitting” from the verb stutzen (cut, cut) gives out even its sound. So, due to the presence of a rifled barrel, muskets used to arm armies up to the 19th century were called. In modern technology, this noun is used to define a short piece of pipe (in other words, a sleeve) with a thread at both ends, used to connect pipes and pipeline fittings to units, installations and tanks.
In the threaded connection, the connecting end of the valve with an external thread is pulled to the pipeline by means of the union nut. It is used for fittings of small and ultra-small (with a nominal diameter of up to 5.0 mm) diameters.
As a rule, these are laboratory or other special fittings. For example, reducers installed on compressed gas cylinders. With the help of a choke connection, various control and measuring devices (instrumentation) are “implanted” into pipeline networks, evaporators, thermostats, many types of equipment that are part of the technological lines of chemical production are mounted.
The most widely used is the COUPLING CONNECTION. In this case, an internal thread is cut in the connecting ends of the valve body, with the help of which the valve is screwed onto the corresponding external thread on the pipeline. Sealing of the connection is carried out directly along the thread with sealing materials in the form of flax, hemp, fum, etc. This connection is usually used in cast fittings, since such a technology for manufacturing the body makes it possible to obtain the external configuration of the connecting end in the form of a socket with a hexagon at minimal cost or special lugs on a turnkey basis.
Fittings with female thread connection ends are called COUPLING VALVES. It is made, as a rule, from alloys of non-ferrous metals (brass, bronze), cast irons (gray and malleable) and is used at low and medium pressures. However, there are also steel couplings for pressures up to 16 MPa.
To connect to the pipeline, a cylindrical pipe thread according to GOST 6375-81 or a tapered pipe thread according to GOST 6211-81 is used. The dimensions of the coupling ends with a cylindrical pipe thread for each DN from 6 to 80 for fittings made of brass, bronze and cast iron are set by GOST 6521-68. For tapered threads, as well as for other body materials, the dimensions are according to the technical documentation of the factories. manufacturers of such fittings.
The second type of threaded connection of the valve to the pipeline is by means of an external metric thread at the connecting end of the valve body. A union nut is screwed onto this thread, pressing the flared end of the pipeline or nipple welded or soldered to the pipeline to the valve.
Sealing is carried out with a gasket or flared end of the connected pipe. For this purpose, the structural elements necessary for sealing the connection are made at the connecting end of the body. Such a connection is called FITTING-END.
Fittings with an external thread at the connecting ends are called COLLAR VALVES. It is made of brass, bronze, aluminum and titanium alloys, carbon and corrosion-resistant steel.
It should be noted that for straight-through and corner fittings, both connecting ends are made coupling or pinned, nipple. Exceptions to this rule are some standard sizes of fittings, in which one end is made with an internal thread, and the other with an external thread (for example, brass fire valves, valves made of acid-resistant steel at PN 1.6 MPa). For more information, see the following videos. :
A method of obtaining a thread on a grooved rod
The invention relates to the processing of metals by pressure, in particular to the process of obtaining a thread on a grooved rod. According to the method for producing a thread on a grooved rod, the thread is made at one of its ends. In this case, before upsetting in the hot state of the threaded end of the rod so that the cross-sectional area of the formed thread was at least equal to the cross-sectional area of the rest of the rod, the ribs and grooves of the rod are removed. The end of the rod is subjected to controlled heating, starting from the beginning of the corrugated free portion and raising the temperature towards the other end of the corrugated free portion. The corrugated rod, clamped motionlessly, is pressed into a movable cylindrical mold. The thread is made on the upset part by rolling. 1 wp f-ly, 3 mud.
The invention relates to a process for producing a thread on a grooved rod.
The corrugated bar used as a blank in the method of the present invention is made from a round profile using a special molding method, which results in corrugated bar ribs and at the same time increases the strength of the steel during the production process. This method of production increases the strength of the grooved bar while increasing the hardness of the ribs, which are made of a much harder material.
Conventional threads for knurled shank nuts are made using known techniques including either rolling or tapping. In these cases, the cross-section of the shank is reduced in the threaded portion, and the tensile strength of the shank is entirely determined by the cross-sectional area of the thread. The reduction in tensile strength of the rod is in the order of 20-30%. Thus, the tensile strength of a threaded rod is determined solely by the cross-sectional area of the thread, leaving the strength of the rest of the rod unused, which means uneconomical use of steel. An economic task is to obtain a thread, the cross-section of which in the tension zone is greater than or equal to the nominal cross-section of the corrugated bar.
Several methods have been patented to produce threads that have the full rupture strength of a grooved bar. All of them are based on the application of the method of cold flattening of the end of the grooved rod, at room temperature. So, for example, the patent application UK 2227802 provides for the use of a connection of rods as reinforcement for reinforced concrete, in which the cross-section of the ends of the rods to be connected is increased by cold flattening, after which a tapered thread is made at the ends. Finnish patent application 890509 proposes a method for mechanically connecting round reinforcing bars using threaded sleeves installed at the joints. According to this application, one of the two ends of the rods to be joined is cold flattened prior to threading. Flattening is performed along the length of the threaded section in such a way that the diameter of the base of the threaded section is at least equal to or greater than the normal diameter of the rods to be connected.
Cold flattening does not entail any changes in the material or strength properties of the grooved bars. After cold flattening, the thread on the flattened section is applied by cutting. This method allows you to keep the strength properties of steel rods unchanged, but at the same time removes material from the surface of the rod. With the cold flattening method, the end of the grooved bar can only be extended over a short length, since the steel structure does not resist cold flattening well enough to thread the grooved bar longer than is required for the nut. Cold flattening is not acceptable for connections requiring long threads.
The aim of the invention is to eliminate the disadvantages of the known technical solutions and to propose such a method for making a thread on a corrugated rod, which retains the increased strength of steel obtained during the production of a corrugated bar, as well as the hardness of the steel surface and its internal toughness even in the process of threading, making it possible to obtain grooved rod thread with full tensile strength.
In the method of the present invention, the end of the corrugated rod is turned by removing the ribs and side grooves of the rod, then the end of the rod is heated and hot-flattened, thereby increasing its cross-sectional area. After hot flattening, this end of the grooved rod is cooled. The thread at the end of the rod is made by rolling. The features of the method which is the subject of the present invention are presented in the claims.
This method makes it possible to obtain threads with a tensile cross-section equal to or larger than the net cross-section of a solid grooved bar, which is decisive in terms of bolt rating. In addition, regardless of the diameter of the grooved rod, the threaded section can be of the desired length, depending on the purpose for which it is intended. This means that the full tensile strength of the grooved bar can be utilized, including the threaded portion, and the method allows a thread of any desired length. Thus, a grooved threaded rod can be used in applications that require a thread longer than the height of the nut, or in other words, the thread can be long enough to make the necessary adjustments. Such applications include, for example, anchoring bolted connections in columns.
FIG. 1, a shows a corrugated rod; in fig. 1b is the same, with a machined end; in fig. 2 hot flattening process; in fig. 3, a. the end of the rod after hot flattening; in fig. 3b corrugated threaded rod.
According to the method for obtaining a full-size thread, the end of the grooved rod is first turned on a lathe to remove the ribs 1 and side grooves 2 (Fig. 1, a) on the section of the rod 3, which is to be threaded (Fig. 1, b). This removes the hardest part of the grooved bar. During the production of a corrugated bar, the material of the ribs undergoes the greatest changes. In the method of the present invention, the areas of greatest hardness of the material are removed from the corrugated shaft, which interfere with the hot flattening used in the threading process.
The processed end 3 of the corrugated rod (Fig. 1, b) is heated in a controlled manner in order to achieve a smooth transition of temperatures in the processed area 3 between the end of the rod 4 and the beginning 5 of the corrugated part, and a high temperature is observed at the end 4 of the corrugated rod, gradually decreasing in the direction of the other end 5 of the treated area. The temperature of the untreated part 6 of the corrugated rod is not increased, excluding the heat transfer from the heated part 5.
The heated corrugated rod 7 (Fig. 2) is clamped by a hydraulic press 8 so that it cannot move. Another hydraulic press 9 presses the end 11 of the rod against the closed cylindrical mold so that the end 11 of the corrugated rod is hot flattened, its cross-sectional area increases and becomes equal to the inner diameter of the cylindrical mold 10 of the press.
The end 7 of the grooved rod is widened to such an extent that the cross-sectional area of the thread 15 formed thereon is at least equal to the cross-sectional area of the rest of the rod 7, so that the tensile strength of the rod is completely retained even in the threaded portion.
The pressing force is applied to the end 11 of the rod in the direction of the nip 8 and is large enough to melt the rod and increase its cross-sectional area to the size of the mold. The purpose of changing the temperature distribution in the turned part of the rod is to ensure that the hot flattening effect begins to appear at the end 11 of the rod and, as the pressing increases, this effect propagates towards the other end 12 of the machined part. With a smooth change in temperature, it is possible to ensure constant control over the spread of the rod flattening zone, while eliminating the possibility of the initial manifestation of the flattening effect in the middle of the treated area. In addition, the rise in temperature towards the end 11 of the core ensures that the flattened portion does not bend before the flattening effect occurs at the hottest point 11. The molding process is stopped only after the machined portion 13 has expanded and fills the mold. ten.
The flattened end 14 of the rod (Fig. 3, a), after hot flattening, is subjected to controlled cooling so that during the cooling process the original strength characteristics of the corrugated rod can be preserved.
To obtain a full-size thread, a thread rolling method known in the art is used, in which the cylindrical part 14 formed on the rod by hot flattening is processed with rollers to form a thread at the flattened end of the rod without removing any material from it.
In the process of rolling, a thread is formed on the surface of the rod, and the rolling also has a hardening effect on the material, since steel 17 during rolling undergoes shape change in the cold state, which leads to an increase in its strength and hardness. The hardening effect during cold working does not reach the inside of the bar 18, so that the material inside the bar remains tough and the toughness of the entire threaded portion remains.
Thread rolling begins only after the end of the grooved bar has cooled to room temperature. Threads are made over the entire flattened portion 14 of the corrugated bar. After that, the bar is not turned.
Using the rolling method allows you to restore the original hardness of the material in the threaded section, which was lost during the heating process. In addition, rolling also causes the rod material to tilt in the threaded portion, helping to restore the original surface hardness of the grooved rod in this portion. The hardening effect during cold working does not reach the inner part of the rod and therefore satisfactory toughness values can be maintained even in the threaded portion.
Hydraulics – Part 1 – Bending, Fitting, Threading, and TIG Welding
It should be obvious to a person skilled in the art that various embodiments of the present invention are not limited to the example described above, and may be varied within the scope of this invention as defined by the following claims.
A method for producing a thread on a grooved bar used in concrete reinforcement joints, such as anchor bolt joints, in which, before hot upsetting of the threaded end of the grooved bar, so that the cross-sectional area of the thread formed is at least equal to the cross-sectional area of the rest of the bar. remove the ribs and grooves of the rod, characterized in that the end of the grooved rod is subjected to controlled heating, starting from the beginning of the part free of corrugations and raising the temperature towards the other end of the part of the rod free from corrugations, the grooved rod, clamped imperceptibly, is pressed into a movable cylindrical press.form, and the temperature difference between different parts of the rod causes upsetting at the hottest end of the rod and its propagation to the region of decreasing temperature.
The method according to claim 1, characterized in that the thread is performed on the flattened part by rolling.
What is a die and how to thread it.
Very often it is required to cut an external thread, for such work you will need a special tool. a die, also called a die. With the help of a die, you can easily cut a thread on an armature, any other cylindrical object, correct it on a loose bolt. Let’s try to figure out the types of thread.
Metric threads are the most common and are used in screws, bolts and other fasteners. Such levers are designated by the letter M. The next number means the diameter and pitch of the thread. That is, the same thread is cut with an M16 die. The standard pitch of such a thread is 2. A detailed table of diameters and pitch of threads can be found in this article. If you need to cut a simple thread, then measure the diameter of the pin on which you plan to cut, it is best to use the standard thread pitch for the selected diameter, as this will facilitate the purchase of nuts in the future.
Pipe threads differ significantly from metric threads, first of all, this is the number of turns, it is noticeably larger and is measured not in centimeters, but in inches. The most common sizes of dies are 1/2 ″, 3/4 ″, 1 ″, more rarely 1 1/4 ″ and 1 1/2 ″ and very rare large dies of 2 or more inches. There are 2 types of tube dies: standard (J) and conical (K). often, the farm uses a standard cylindrical thread, conical more rarely. The conical die has a deeper entry, it is easier to cut, it is noticeably thicker. Photo of a standard 1/2 ” pipe die.
Article. pipe threading tool. After reading this article, you can find out the best way to cut threads on a pipe, with a die or a die.
At the moment, most of the dies are sold in China, they are not to say that they are bad, but they differ markedly from the Soviet ones, which have survived since the days of the Soviets. They are the best, they cut metal perfectly, they do not dull, they serve for a very long time. And if you see the Soviet quality mark, then do not hesitate to buy it, it is the best. Still, they knew how to make tools before, Soviet drills (best of all cobalt drills) and other metal-cutting tools are valued by craftsmen higher than imported ones, even the most expensive ones.
In order to cut an external thread using a die, you will need the die itself and a special knob in which the stick is fixed. It is worth noting that the die holder is a universal tool, several types of dies can be fixed into it at once. For example, holders m3-m10 are in good demand (you can fix sticks from m3 to m10), small sizes are most often cut at home. If a larger diameter is required, then the next size is m10-m20 (for large diameters).
How to fix the die in the holder. On the side of the die you will see special recesses for the bolts, into them then insert the bolts of the wrench and firmly clamp.
When cutting threads, follow simple rules. use household oil (machine oil can be used), it lightens the load on the die, it is much easier to cut with oil than without it. Turn the knob slowly, trying not to twist. I remember once the M10 thread was cut (it was necessary to make an impromptu bolt half a meter long), the most difficult thing was to start the thread, for the first time it was warped with us, it’s good that we noticed it in time. So when entering, align the plate strictly horizontally. and when we cut the thread, our Chinese die simply broke, it could not withstand the load. We took the Soviet one and it did an excellent job, when we played it without oil, the creak was terrible, but everything worked out. Here you see the difference between imported and Soviet.