Analysis and introduction of common threads of the

2022-09-23
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Analysis and introduction of common threads of injection molding machine and the problem of mold adjusting screw nut strain

first, introduce the types of common threads of injection molding machine: (1) fastening connection threads mainly include metric common threads (m), British Whitworth threads (B.S.W., b.s.f., whit.s. and whir.): (2) Transmission connection thread mainly includes metric trapezoidal thread (30) (TR), American trapezoidal (ACME) thread (29.) (ACME); (3) Pipe threads mainly include inch pipe threads (55.) That is, general sealing pipe thread (R) and non sealing pipe thread (g)

in the tooth pattern matching the coring column and the die adjusting screw nut, the company uses metric ordinary thread (m), metric time 1 long trapezoidal thread (30) (TR) two. First of all, the shortcomings of tooth profile and some details that should be paid attention to in processing and manufacturing are analyzed and introduced (and the factors causing strain of material and overall structure are not analyzed)

metric common thread (m) is classified as fastening connection thread, not transmission connection thread, and the axial accuracy control during machining is not as good as metric trapezoidal thread (30), Therefore, when reaching or approaching the international advanced level, accounting for more than 20% of the teeth as the coring column, it is only suitable for small computers. The external thread profile is shown in Figure 1

it can be seen from Figure 1 that there is an arc at the bottom of the external thread. What is it used for? We can take another look at the metric Aerospace screw thread (MJ), which specially adopts the tooth base arc with a larger radius in order to improve its fatigue resistance (see the national standard gjb3.1a-2003 for details) Therefore, we should pay attention to the machining of this arc when machining. Generally, we should use the formed blade for finishing machining, and do not use the hand sharpening knife for finishing machining. According to the national standard gb/t for metric common thread (m), the radius r of the tooth bottom arc of external thread for threads with mechanical property grade higher than or equal to grade 8.8 shall not be less than 0.125p. For threaded parts with mechanical property grade lower than grade 8.8, the shape of the tooth bottom shall be consistent with that of threaded parts with mechanical property grade higher than or equal to grade 8.8 as far as possible. It should also be emphasized here that in order to ensure the positional relationship between the thread profile and the thread axis, it is generally necessary to use special auxiliary tools for tool setting during machining, such as tool setting for the blade, so as to ensure that the tooth profile blade is perpendicular to the thread axis (i.e. 90 in Figure 1). The radial clearance between the mold adjusting screw nut and the coring column we commonly use is actually to ensure that the four coring columns are balanced, that is, to ensure that the axial clearance values of the four coring columns and the mold adjusting screw nut are consistent, and the smaller the error, the better. From the geometric relationship of tooth shape, it is not difficult to pile up: metric ordinary thread (60) Axial clearance = radial clearance × tg30。、 Metric trapezoidal thread (30.) Axial clearance = radial clearance × tg15。 The radial clearance is controlled during machining, so when the radial clearance error value is equal, the metric ordinary thread (60.) The axial error value of is metric trapezoidal thread (30) It is obvious that trapezoidal thread is more suitable for our mold adjusting structure

metric trapezoidal thread (30.) (TR) is mainly used in transmission and position adjustment devices, and can also be used in connection and fastening occasions. During processing, it is also required to use formed blades and special auxiliary tools to set the knives, so as to ensure that the tooth blade is perpendicular to the thread axis. As we all know, it is common for the die adjusting screw to get stuck with the coring column, which is a difficult problem to solve. In 1942, in order to meet the large demand for in World War II, the U.S. government requested the urgent formulation of a special war standard for Ike female thread. This standard was completed in 1945 and issued as asab1.5. Since then, it has been continuously improved through five revisions. At present, there are three kinds of American AGC female threads, including general-purpose AGC female threads, centering AGC female threads, and low tooth AGC female threads. If the internal and external threads are often stuck, the centering AGC female thread shall be selected. The main feature of the centering AGC female thread is that the radial clearance of the crown is larger than that of the general AGC female thread, and it is particularly emphasized that the crown of the external thread must be chamfered (45), The minimum depth is p/20) Foreign countries also use round Cao Ike female thread to prevent jamming. The tooth shape of round groove Ike female thread is as shown in figure 2:

from the composition of various threads on various materials, we can see how important the apical clearance and tooth chamfer and fillet of trapezoidal thread are. Metric trapezoidal thread (30.) (TR) tooth shape standard gb/t5796 This is also specified in. The top and bottom of the external thread should be rounded in the middle corner of the international architecture exhibition held in Las Vegas, and the bottom of the internal thread should also be rounded. Therefore, when designing coring column and adjusting nut, we must draw a tooth chart and carefully process according to the tooth chart during processing. Only in this way can the failure of our machine be reduced to the greatest limit to meet the needs of customers. (end)

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