As we all know, the tie-bar (column) of the general toggle type injection molding machine is easier to break than the fully hydraulic tie rod. What is the reason?
In the design of the toggle lever type, the rigidity of the system must be considered. Because the toggle lever type generates the clamping force by rigidity, the diameter of the tie rod is generally larger. But what is strange is that the tie rods are easy to break, especially in some industries, such as the production of video cassettes, plastic fast food box, cutlery and other industries. Due to the thin wall of the product, the material flowability is good, the forming area is large, and the production speed is required. Therefore, the break of the tie-bar is very common, and it may even cause the mold platen to break.
However, daya brand high speed injection molding machine has made much improvement on the toggle system , tie-bar and mold platen. and has win good repution from many local and foreign customers on the past years.
Analysis of the causes of tie-bar break
1. Fatigue damage
The working process of the injection molding machine is a process of alternating stress, so any factors that cause stress concentration may cause fatigue damage.
1) Steps where the shaft diameter changes greatly.
2) The transition part lacks rounded corners, undercuts, etc.
3) Surface scratches or machined threads accidentally damage the surface of the optical axis.
4) The surface roughness of the thread is too large.
5) The thread is compressed for a long time, and the surface is damaged due to insufficient surface strength (at the die adjusting nut).
6) Improper heat treatment of the thread surface causes stress concentration.
7) Material defects.
2. Overload break
Since the toggle lever type relies on the deformation of the four tie bars to obtain the clamping force, if the length of the four tie bars is different, the deformation will be different. 1/4 of the clamping force it bears, causing it to break.
3. Temperature strain causes breakage
If the four tie bars are different in length, for example, one is long and three are short, then the thermal stress caused by the rapid temperature increase or decrease of the longer tie bar will be constrained by the other three bars and be in a static state, which will cause the tie bar fracture.
4. Breaking caused by compound strain
If the mold platen is not flat, the combined error of the length of the connecting rod (hinge), the height of the bearing seat and the length of the tie bar is too large. When the connecting rod is straightened, the force on both sides is uneven. Then
1) The rear mold platen swings and the tie rod is bent. The tie rod is easily broken under the action of bending stress and tensile stress.
2) If the product flashes, operators who are generally inexperienced will further increase the clamping force, which will cause the pull rod to break and the mold to deform due to overload.
5. Destruction caused by instantaneous impact stress
Since the toggle lever type can only release the clamping force before the mold is opened,
1) The instantaneous impact when opening the mold causes the machine to vibrate and damage the tie rods and other parts.
2) Since the entire clamping part (including the mold) is kept under stress for a long time, it will lead to premature fatigue failure of the part.