Improving the “Safety Lock” to Improve the Operation Safety of Injection Molding Machine

In the field pipe production, the injection molding machine is inputted by human workers to complete the action of premolding, seat entering, mold closing, injection molding, mold opening, and manual auxiliary operation is smooth.

The sequence is: manual injection – adjust the position – open the safety lock.

Injection molding machine safety mechanical lock is located in the middle of the fuselage, the role is in the entire production process, to ensure that the mold, mold and other processes will not be intended outside the mold wounding, so that the operator from being injured, safety lock see Figure 1.

Problem analysis

The original safety lock has the problems of inoperative structural rotation, large friction, and insufficient reset force, so it often can not be automatically reset, and there is a large security risk. If a production safety accident occurs because of this, it may lead to physical injuries. 2020 Working Group on Safety Lock Failures

Lock plate

handle

The field simulation experiment is carried out, and the analysis shows that the average rate of non-reset has reached 7.82%, which directly threatens the safety of production and has a great hidden danger.

At the same time, it is also found that the original safety lock cannot realize two-hand operation protection, resulting in the operation of the safety lock. The idle hand can be free to move, and the safe lock manual unlocking device is close to the mold opening and closing work area, and the operator can still touch the mold with one hand during the operation of the safe lock. If the operator forgets to remove the free hand in the process of unlocking and injection molding, it will cause the accident that the mold will pinch the free hand.

Through the above analysis, the safety management personnel agreed that to ensure the high reliability of the safety lock of the injection molding machine, the safety lock must meet the following requirements: First, the safety lock can achieve reliable reset; The second is to achieve double-hand operation protection to prevent injury of idle hands.

Solutions

Improvement Scheme of Mechanical Transmission Part

At present, the injection molding machine adopts “handle transmission,” which has the following defects: there are 3 rotating joints on the mechanical lock structure, and the rotational resistance is large; The height of the handle seat is large, especially when the safety lock is opened, the handle is in a horizontal state and the transverse width is huge, which interferes with the hose and the mold body, and there is a safety hazard. Without the positioning pin, as shown in Figure 2, it is possible to open the safety lock in a nearly vertical state of the lock plate, resulting in a significant reduction in the return torque. New design “tie rod” transmission scheme: As shown in Figure 3,

Cancel the rotation of the handle to reduce the transverse width, thicken the lock plate to prevent deformation, and add a positioning pin to prevent the lock plate from not returning. The scheme has the advantages of simple structure, small number of joints, small rotational resistance, using limit pin to prevent non-return position, small transverse width and no extrusion deformation by injection molding machine.

Output blocking design

In view of the requirement of realizing two-hand operation, the technician proposed that the principle of two-hand protector for punch operation can be used for reference. Press the two buttons of the two-hand protector at the same time to trigger the action, that is, one hand to operate the mechanical part of the safety lock, and the other hand to press the electronic control button, you can achieve two-hand protection.

At the same time, in order to achieve two-hand operation protection and prevent injury of idle hands, a blocking switch is set up. The blocking switch directly controls the power supply part easily to produce high induced voltage in the on-off process, which causes the proximity sensor to be damaged. Therefore, in the proximity switch power supply circuit, adding the manual switch as the blocking device to realize the two-hand operation mode closing method is not feasible. In contrast, in the proximity switch output circuit, the manual switch is added as a blocker to achieve two-hand operation mode closing, the structure is simple, the improvement is not difficult, and the switch is instantaneous no large induced voltage. Therefore, an output blocking scheme is adopted, as shown in Figure 4.

Processing and experiment

After the completion of the design drawings, the technical personnel reviewed the drawings and found that the drawings were reasonable and could meet the requirements of use. After the drawings are approved, the design team will submit the design drawings to the Production Safety Section and the Technology Research and Development Center for joint review. Production safety section, technology research and development center after the audit that the design of the production process has not changed, does not affect the implementation of the current production process, at the same time, the production section also on the installation safety review, that the device design reasonable can effectively reduce safety risks, can be put into use.

The technical staff invited the Technology R & D Center and the Production Safety Section to the site for technical performance and safety performance acceptance. The non-reset test was carried out on the DN100 and DN250 sealing injection molding machine which installed the mechanical part of the safety lock of the injection molding machine with high reliability. The experimental results proved that the safety lock did not reset during the experiment. After on-site acceptance, the device meets the technical and safety requirements.

In order to verify that the new safety lock must be operated by two hands to close the mold, the field test was carried out. The technical personnel mainly carried out one-hand operation misoperation test on DN100 and DN250 sealing plastic injection machines installed with safety locks, and the experimental results showed that the number of one-hand misoperation was 0.

On-site promotion

The processing cost of the safety lock is only 747 yuan, after the full installation, the technical personnel monitored the application effect, and from April 1, 2020 to the present, the safety lock does not reset problem has not occurred. At the same time, the new safety lock uses the principle of two-hand operation, which eliminates the one-hand operation and greatly improves the safety.

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