Common Faults of Sachet Packing Machine

Long-time, continuous and overload running will all cause some electrical and mechanical faults of a sachet packing machine, such as infirm sealing, fusing once production starts, squeak during production, uncontrollable temperature, intermittent production, bubbles or irregular mark at seal, and so on.

With practical experience of operating sachet packing machine, we can find out some causes of these failures and come up with solutions to them. Besides, some suggestions for machine maintenance are given in the end. Hope these solutions and suggestions be helpful to the sachet packing machine users.

1. Infirm sealing for sachet packing machine

Infirm seal is one of the commonest faults occurring on sachet packing machine. This item has three meanings: 1) sachets cannot be sealed; 2) although sachets are sealed, the seal are torn open easily; 3) a part of sachet seal is firm while the other part can be peeled apart easily. The sachets of the third case are also not qualified, since their contents will go out when being pressed during product storage and transport. This problem often happens when the inner layer of composite film is OPP or PE.

1) Causes for the first case

A. Low heat sealing temperature: Normally speaking, the composite film with OPP as the inner layer should be heat sealed at the temperature of 170°C to180°C when the total sachet is 80μm to 90μm thick. And the composite film with PE as the inner layer should be heat sealed at the temperature of 180°C to 200°C when the total sachet is 85μm to 100μm thick. As sachet thickness increases, heat sealing temperature have to be increased too.

B. High heat sealing speed: Sealing effect is also related to sealing speed. Sachets are not sealed firmly under high speed but be quickly conveyed to the cold pressing station at which they are cold pressed.

C. Improper pressure of cold pressing wheel: The pressure between two cold pressing wheels should be moderate. It can be adjusted by controlling tension of the spring.

D. Bad quality of heat sealing film: Infirm sealing can also be caused by bad quality of the composite film. For example, sachets cannot be sealed when the inner layer of composite film is not uniformly treated with corona and corona exactly appear at the seal. Products will be all scrapped once this rare case happens. In this case, analyze causes and solve the problems as soon as possible. Besides, water and dirt at seal will also cause infirm sealing. All in all, to solve the problem of infirm sealing of the first case, increase heat sealing temperature, reduce heat sealing speed and increase cold pressing pressure.

2) Causes for the second case

A. Low heat sealing temperature: Increase heat sealing speed moderately.

B. Uneven heat sealing boards: Two heat sealing boards are inset with thermocouple to sense temperature transfer. There are three screws on the heat sealing boards. The middle screw can support and reinforce the boards while the other two screws are equipped with pressure springs and shims for pressure control. The main cause for uneven board surface might be the sloping middle screw or non-uniform pressure of the pressure spring of the upper heat sealing board. The solution is to calibrate the middle screw and level it, or to adjust the pressure spring to parallel the upper and lower heat sealing boards. Pull the spring and the heat sealing board falls while push the spring of the lower board and the heat sealing board rises.

C. Non-uniform cold pressing wheel pressure: Non-uniform pressure will also cause seal infirmity. Its solution is the same with that to the third cause of case 1.

3) Causes for the third case

A. Non-uniform heat sealing pressure or cold pressing pressure: Heat sealing boards and cold pressing wheels are adjusted in the same methods.

B. Uneven heat sealing boards: Refer to the solution to the second cause of case 2.

2. Fusing once production starts

The motor of a sachet packing machine mainly acts to drive gear box and gears of all stations. The equipment sometimes squeaks and cannot run normally as it is started and the fuse on the live wire even goes. To solve this problem, please firstly check whether power supply is normal. Then cut off the power and test the power supply with the resistance gear of a multimeter. Besides, check the circuit and motor to determine whether they are damaged. The fuse always goes as the equipment is started when motor circuit is short, winding is burnt or broken. The other cause of this fault is low specification of the fuse. Increase its specification and the fault can be cleared.

3. Squeak during production

The equipment often squeaks suddenly and then its sealing speed reduces. The sealing effect is not good and product’s appearance is influenced.

The main causes for squeak are heavy equipment damage or wear and poor lubrication. In this case, find out the faulty part following the noise. Remove the protection board on the back and it’s the gear box that squeaks. Then remove all screws and it’s found that grease in the box dries and hardens. It represents that lack of lubrication is the fault cause. Add the mixture of engine oil and grease into the gear box and fasten the screws. Start running once again and squeak disappears and sealing turns normal.

In addition, loose connection, heavy wear, dirty surface or asynchronous motion with traction wheel of high-temperature belt will also cause the equipment to squeak. The solution is to change a high-temperature belt of the same specification. There are some skills of high-temperature belt change. At first, compress the pressure wheel spring with hands. Place one end of the high-temperature belt on one rubber wheel and make the other end close to the other rubber roller with hand. Then start running at low speed. The belt will be installed automatically due to the motion inertia. Sometimes DC shunt motor also squeaks, perhaps due to lack of lubrication of motor bearings. In this case, remove the bearings and lubricate them.

4. Uncontrollable temperature

This fault mainly appears as displaying malfunction of thermometer, uncontrollable temperature, unsteady heat sealing temperature, and burnt, infirm or deformed seal. One cause for this fault is that the thermometer is damaged and needs repair. In addition, the thermocouple might also be damaged and cannot induce temperature. Change the thermocouple with one of the same model and specification. Some mechanical causes will also lead to this fault, such as non-uniform heat sealing pressure. Uniforming the pressure can solve the problem in this case. Besides, do keep the contact surface of the heat sealing boards clean and tidy. At last, poor heat sealing quality of the composite film can also have an influence as the heat sealing coefficient varies and the temperature induced is not steady.

5. Intermittent production

This fault once occurred on our equipment. After we removed the board on the back, we found that the joint of motor shaft rod and gear box was loose. We fastened screws and gripped them and the problem was solved easily. Besides, the main motor running relies on contact with carbon brush. If the carton brush is heavily worn and doesn’t contact well with sliding ring, the equipment will also run intermittently. A new carbon brush of the same model can be a solution.

6. Bubbles or irregular mark at seal

This fault is somewhat common and can have an influence on package appearance and commodity image, although no contents leaks. Two causes for this fault include: 1) After long-time use of the equipment, high-temperature belt is stained with dust, plastic chips and other dirt. These stains make the belt not smooth or flat, causing non-uniform heat sealing temperature. After cold pressing, the sachet seal bubbles. The fault can be cleared by cleaning or changing the high-temperature belt. A high-temperature belt is normally 1.5cm wide and 22μm thick. If the stains are stubborn, the belt can only be scrapped. 2) Concave or convex traces on the cold pressing rubber wheels are not regular and will be embossed on the package. It’s better to change the cold pressing wheel for more beautiful sachet appearance.

7. Suggestions

1) A sachet packing machine should be placed in airy and dry room where the room temperature is kept at about 25°C.

2) Lubricate gears, bearings and other moving parts in the gear box with 6# engine oil every 48 running hours.

3) Dust the equipment regularly and keep it clean. Do cut off the power supply and cover the equipment with cover cloth when the equipment is not in use.

4) Turn on the cooling fan to cool the equipment after long-time continuous running and then turn off the equipment. High-temperature belt can be easily damaged due to no cooling.

5) High-temperature belt should be cleaned regularly to maintain its sealing effect.

6) Heavily worn parts should be replaced in time to extend service life of the equipment.