Wear Analysis of Die and Rail Guide of Rotary Tablet Press
Dai Guoming
(Liaocheng Wanhe Industrial Manufacturing Co., Ltd., Liaocheng, Shandong 251022)
Abstract: According to the force analysis of the die during the tableting process, the wear of the die and the rail guide are briefly described.
Key words: die; rail guide; force analysis; wear
The rotary tablet press is a multi-die tablet press. The die is evenly arranged on the edge of the turntable. When the plate is rotated, the upper and lower punches are moved up and down along the fixed rail guide, and the filling, pressing and discharging are continuously performed. .
one, Â Â Â Â Â Â Â Â Stress Analysis of Upper Punch in Motion and Orbital Guide
During the operation, the upper punch is in contact with the pressure of the pressure wheel and the reaction force of the particles when the pressure roller is in contact with the pressure roller. The other steps are in contact with the rail guide, and the bearing force and sliding friction force of the rail guide are analyzed as follows. Figure:
In the vertical plane, the force G is applied , the bearing force F of the rail guide rod and the pressure N of the dial hole punch .
Balance condition according to force   N=F ×sinα=Fx
G=F ×cosα=Fy
Where α is the size of direct impact plunger guide rail in contact with the plane and the angle between the radial plunger, and the angle of the guide rail wear ram.
When the angle α is 45°,
Fx=Fy=Fsin45 °=√2/2F,
At this time, the upward force of the ram and the force outward in the radial direction are equal, and the upper punch cannot move upward when the output is up, so the angle must be less than 45°, and the upper punch can be normally operated, generally 30°. It is easy to 40°. Due to processing error, when the contact gap between the upper punch and the upper rail is large, the transitional fillet of the upper punch and the transition of the rail guide are often as shown in the figure.
Although the slope of the tail of the punch and the slope of the rail guide are both less than 45°, the actual contact point is not at the slope and at the point A of the transition arc, the angle between the tangent to the point A and the radial direction is obviously greater than 45°. The radial force is greater than the axial force, ie Fx>Fy. The ram is difficult to move upward under the action of the couples Fx and N. In the forced upward movement, a large frictional force occurs at the contact between the slant slope and the rail guide. Generally, the friction surface is similar in shape and size. The rough peak is composed. When the sliding friction is large, the surface friction peaks are embedded in each other, and the surface is in a plastic deformation state. Since the deformation heat and the friction heat are concentrated in a small area, the contact point generates an instantaneous high temperature. At present, the material used for the punch or rail guide is generally bearing steel. The hardness of the material is higher at normal temperature after quenching, but the hardness is drastically lowered at high temperature, unlike the high-speed steel, which has "red hardness", so the contact temperature rises. When the material reaches the yield limit б s , the material begins to plastically flow, and the contact will be scratched by the shear fracture, causing the ram or rail guide to be scrapped or even damaged.
In order to avoid the shortcomings of the upper rail to improve the ram, the upper rail of many presses has been changed into a two-way lifting mode, so that the bilateral axial forces cancel each other, reducing the wear and increasing the use of the ram and the rail guide. life.
two, Â Â Â Â Â Â Â Â Contact wear of the lower punch and the lower rail
The lower rail device is located on the main body below the turntable, the main body is a solid body, and the left and right slots are provided with a lower pressing wheel, and the circular sides of the plane are provided with two symmetrical lower heat-treated lower guide rails, the lower guide rail has a groove, and the screws are closely pointed A certain slope is formed on the plane of the main body. When the lower punch is in motion, its tail is embedded in the guide groove, and the movement of the groove is performed as the slope of the groove moves up and down. The material of the lower rail is generally bearing steel GCr15, and the quenching hardness is generally controlled below HRC60. The main wear is the friction between the end of the punch and the inclined surface of the output rail when the ejector piece is ejector.
When the film is released, the punch is forced as shown in the figure.
Subject to: Power F
The sum of the weight of the punch and the pressure of the tablet
Out of the track support N
Friction force f with the output rail
The ram is in a uniform circular motion under the action of these four forces, regardless of the centrifugal force and the force couple factor, according to the common point force balance condition
∑Fx=F-Nsinα-fcosα=0
∑Fy=F-Ncosα-fsinα=0
In the formula, the α position is the angle between the slope of the undershoot and the horizontal plane, and f is the frictional force related to the contact between the bottom surface of the punch and the inclined surface of the rail.
It can be seen from the above formula that when the power F is constant, the smaller the α is, the smaller the friction is, and the smoother the film is during the operation. This requires that the spiral angle of the track be minimized during the design process, considering the installation. Space, the angle of elevation is generally set at about 10 °, in order to reduce the friction, the end of the punch, the slope of the track to reduce the roughness, improve the finish, generally controlled at Ra0.2---0.4, and polished, so that Reduce the friction to a low zui.
To reduce the wear of the die and rail guide, in addition to the reasonable design structure, the lubricant film should be added on the friction surface, and the upper oil film should not be too much to avoid contaminating the tablet. The contact surface of the undershoot and the guide rail should always have an oil film to lubricate, to reduce friction, improve wear resistance, extend the use time of the punch and the rail guide, reduce the cost, reduce the production cost, and improve the economic efficiency.
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