Injection molding machine tie rod fracture reason analysis
Fatigue damage
The working process of injection molding machine is the process of alternating stress, so any factors that lead to stress concentration can cause fatigue damage. Such as:
(1) Shaft diameter changes in the step.
(2) The lack of rounded corners, back to the groove at the transition.
(3) Surface scars or machining threads inadvertently damaging the surface of the bare shaft.
(4) The surface roughness of the thread is too large.
(5) Threads are pressurized for a long time and the surface is damaged by extrusion due to insufficient surface strength (at the adjusting nut).
(6) Improper heat treatment of the thread surface causes stress concentration.
7) Material defects.
Overload failure
Since the elbow type receives its clamping force from the deformation of the four tie rods, if the length of the four tie rods is different, the deformation will be different. If one of the four tie rods is shorter, the shorter tie rod may be subjected to more than 1/4 of the clamping force it should be subjected to, resulting in tensile fracture.
Tensile fracture due to thermal expansion
If the plastic injection molding machine has four anchor bars of different lengths, e.g. one is longer and three are shorter, then due to thermal stresses caused by a sudden rise or fall in temperature, the ferrocement will be restrained by the other three anchor bars and will be in a super static state, resulting in anchor breakage.
Breakage caused by composite strain
If the die is not flat and the combination error of parts such as connecting rod length (joint side), bearing seat height and tie rod length is too large, when the connecting rod is straightened, the force on both sides is not uniform. So:.
1) It makes the rear template swing and the tie rod bend and the tie rod is easy to break under bending and tensile stress.
2) Due to product flash, usually inexperienced operators will further increase the clamping force, causing the tie rod to break under overload and the mould to deform under overload.
Damage caused by transient impact stress
Since the clamp force of the elbow type can only be released before the mould is opened, the following can occur
1) Transient shock during mould opening can cause the machine to vibrate and damage the crossbars and other parts.
2) Premature fatigue failure of parts may occur due to prolonged stress on the entire clamping part (including the mould).
Solution
In the design to avoid drastic changes in the diameter of the shaft, in the step or unloading groove, as far as possible to use a large rounded transition, choose a better overall performance of the material, special treatment to solve the problem of hardness of the surface of the threads (wear-resistant), and try to reduce the concentration of stress on the surface, to improve the surface finish, and minimise stress damage.
Ensure the moulding machine accuracy, especially the length of the connecting rod, the height of the bearing seat, the accuracy of the crosshead, the positioning accuracy of the bearing seat in the template.
During assembly or after disassembly of the adjusting nut, pay special attention to adjusting the length of the four tie rods and the distance between the adjusting nut and the rear template.
If the product produces flashes, the cause must be analysed and the clamping force must not be increased unilaterally. If the mould is found to be uneven, it should be sanded flat. For example, the length of the connecting rod should not be corrected, including the pad copper, paper, etc., or the mould adjustment nuts should be corrected.
