Plastic thermoforming technology production of plastic cup began about in the late 1980 s on domestic, after more than ten years development, is now at the peak stage. No matter from equipment （sheet extruding production line、thermoforming machine—cup making machine、mould、cup printing machine） or technology is ripe.
main material commonly used in the production of plastic cup ： PS、PP、PVC、PET、ABS、BOPS and so on。According to the different packing requirement for different customer，can be divided into single layer(HIPS、CPS、PP、PVC、PET、ABS、BOPS) of different color, and composed of one or more material multi-layer composite structure. For example, the plastic cup which has a high separation performance, need at least two materials and five layer co-extrusion composite structure.
From raw materials to products generally divided into three stages:
- Extruding plastic sheet
This step is making the plastic raw material into plastic sheet by the plastic sheet production line. The equipment composition: Material mixing machine-Crystallization of drying system -Single or more extruder-net changing-melt pump-T-die –Three rollers press polish device-Cutting edge device-draft gear device-Festoon device-Curly winding device. Finished plastic sheet thickness is 0.25mm-2.5mm.width is 300mm-1400mm.
Thermoforming is a productive process that make the plastic sheet into plastic cup. Thermoforming is a special process in plastics processing. Its characteristic is: Sheet is heating to high elastic state, and then by compressed air pressure and mould pre-stretching device makes sheet laminating mould surface, cooling, forming, shearing, get the products.
Because mould need air pressure is positive pressure （0.4-0.8MP） when forming, this cup process called positive pressure thermoforming, The mould using in plastic thermoforming productive process is called “positive pressure plastic thermoforming mould”.
Decorate is used print or stick mark method to beautify the plastic cup appearance.
Because of the positive pressure thermoforming mould plays an important role in the production, so is very important to maintenance and repair of it.I combined with the experience and the related files, put forward some opinion, hoping to be useful to you. Just for your reference, welcome to discuss and correct.
Positive plastic thermoforming mould, which product disposable plastic cup, Adopts forming and cutting structure in the integrated now
It mainly has the following characteristics:
1.Upper cutting plate、lower cutter have the effect of blanking, some lower cutter also have the effect to make the cup edge forming.
2.Upper and lower is not move up generally, but can replace the cavities flexibly, so one set of mould can product many size of plastic cup. Both reduced the mould manufacturing costs, but also accelerated the speed of the mould, and raised the production efficiency.
- Use pressure assist force plug stretched and compressed air pressure forming.
4.Upper cutting plate、lower cutter can be use 1000000-5000000 times. After grinding, the dull Upper cutting plate and lower cutter can be use multiple times.
Therefore, in “disposable plastic cup” production, the good and bad of mould maintenance and repair directly affects the production efficiency and product quality. So the effective maintenance of the mould is particularly critical.
thermoforming mould is best to install in a positive pressure thermoforming machine which is match the mould. Because replaced the mould frequently, not only reduce the production efficiency but also the mould in the process of disassembly, storage, installation, debugging, intangible increases the chance of damage, and cooperate precision will gradually reduce, which affect the product quality and production efficiency.
No matter what imported or domestic positive pressure thermoforming machine (include domestic CAM type, domestic hydraulic type positive pressure thermoforming machine), die installation, adjustment, remove and so on have the same basic principle.
The following discussion of installation and debugging method in the CAM type positive pressure thermoforming machine for reference.
- Mould installation and commission step
Used the clean cloth to clean the base of upper mould stock and mould, and spraying the right amount of anti-rust oil, Daub transparent color food grade lubrication oil on the assist pressure plug rod.
Install the upper mould body base on the upper mould stock, do not tighten bolts, it is convenient to collate cutter when closing mould.
- Hold up the assist pressure plug, and indent it into upper cutter
- Used the clean cloth to clean the base of lower mould stock and mould, and spraying the right amount of anti-rust oil,Daub lubrication grease on the mould pushing rod.
•Install lower mould body on the lower mould stock, do nottighten bolts.
•Operate the jigger let the lower mould body reach the forming position (means radius blends cambered surface), by adjusting the machine mould stock fixed nut.
Screw and nut of the lower mould stock (when coarse), or inclined plate (when fine-tuning), make the distance between the upper cutting plate and lower cutter is 1/3 -1/5 of the sheet thickness. (Some can be set in, associated with the structure of parts and mould.)
- Manual turning to shear position, to make the lower cutter into the upper cutting plate.
•Locking the bolt of upper and lower mould: first the upper mould, and then the lower, from inside to outside, before and after the diagonal. In order to ensure that all the mould influence by the force equilibrium, it is recommended to use torque wrench, can be selected the proper torque according t0 the screw.
- Install cooling water pipe and air pipe correctly
- For domestic CAM device, before open the machine, should through adjusting plug、forming gas、blower、feeding induction switch start and stop position, to determine the action program.
- For hydraulic equipment, should determine the start position of the induction switch, and then set the time length of the action program.
•For the import thermoforming machine with angle control program, should through setting the starting and stopping angle of plug、forming gas、 blower、 feeding to determine the action and length of time.
- Application of rough adjustment can be according to normal process control diagram, it is to simulate a lot of practical production and processing program summary, has a certainly universality. Only fine-tuning, make the necessary adjustment to individual mould.
•Adjust assist pressure plug fall depth, forming air pressure, feeding width, ingress width, egress width, heating temperature, cooling water speed, or set up the cooling water temperature when use die temperature controller.
- normal assist pressure plug fall height (H) computing method
assist plug fall height（H）=finished product height（H1）—2–10mm（normal 3—5 mm）
•All the air hole on the mould cutter, cavities and bottom pushing plate should keep passing rate.
- Under the condition of the equipment without materials, low speed or using the method of inching operation to check these settings is correct.
•Feeding material and try to lathe, debugging accurately machine and mould, make the process parameters reached the standard of normal production.
- cooling and protection of mould in production
In order to obtain the biggest potential productivity, the mould temperature should be kept low. Of course, this associated with the material and the thickness of the plastic sheet.
•When processing the most commonly material, such as PS, PVC, PP, ABS, 16—18℃ is a typical temperature.
- But mould temperature can not be lower than 10℃,
Because there will be condensed water produced, affect the product quality, cause mould rust.
•High temperature will reduce the production efficiency. Such as ILLIG positive pressure thermoforming machine, General provisions should not exceed 30℃.
- A large amount of cooling flowing through the mould, it is decided whether to obtain a constant temperature in the whole operation. Require average flow rate about 80L/min.
- It’s important to keep same temperature of upper and lower mould table. Otherwise, under the different thermal expansion will lead to blade of upper cutting plate and lower cutter split, make the upper cutting plate、lower cutter and guide pillar wear and tear, reduce their use life.
•Generally upper cutting plate and lower cutter temperature difference not more than 5℃
- If size allowed, cooling water should be through in mould pushing plate. If the size is small, it will provide additional cooling methods in the mould pushing plate.
•Domestic thermoforming mould bottom has almost not set the cooling waterway. But after practice has proved that through the natural cooling, can satisfy the general production requirement. The main reason is :
（1） Compressed air of blowing cup acts as part of the cooling
（2） At prevent, a lot of products smaller, thinner, easy to cooling .
（3） Production speed is slow
（4）”The disposable products” demand is low“
Generally the upper cutting mould stock and lower cutter mould stock, which near the heating cabinet, need to paste the layer 3-8mm thick felt cloth. Mainly in order to prevent transmission of the heating cabinet to the mould, cause mould temperature is not consistent(not only make the mould easy deformation, and affect the quality and cooling effect of product ).
- Before starting, check whether the heating tile (especially above) is fixed and reliable, clean up the sundry and tools around the machine, to prevent shock and fall into the mould in production, damage the upper cutting plate and lower cutter.
• When stop the machine ,to prevent foreign bodies fall into the mould, upper and lower mould table should place in the closed mould at the forming stage.
3．Maintenance and lubrication
in order to let the mould in the state that can product good quality products, must perform regular routine maintenance.
- All the place need to lubricate in the mould, like oil filler or other similar, should be maintain every 8 hours.
•check whether there were any scratch marks on the straight bear and guide pillar, guide bushing, if have, ensure the reason of scratch.
•add lubricating grease into straight bear and guide bushing twice a week.
- Daub food grade lubrication oil on the assist pressure plug rod every 8 hours.
• Daub lubrication grease on the mould pushing rod every 8 hours.
•check whether the lock nut on the mould pushing rod and the assist pressure plug rod flexible every 16 hours.
•Clean up the upper and lower mould table with air gun every 8 hours, and put the mould in the lowest position
A. Clean up the sediment which hiding in the pushing plate.
B. Fall down the assist pressure plug, clean up the crushed plastic which caught in blank holder
- Daily checking (visual) cooling system pressure and flow. When use more polluted water for cooling, cooling system should be cleaned every three months at a time. Once found stain accumulation, should add appropriate solute in liquid detergent, or replacement of cooling water on a regular basis.
•Check the wear condition of the assist pressure plug every week. Due to wear and tear, their shape will be change and affect product forming. Therefore, we should reserve a certain amount of spare assist pressure plug.
• check whether the assist pressure plug flexible (Such as lock nut)、 high and low are consistent (Use level bar)every 8 hours.
4.Strorage of mould
•Mould should be stored in a dry room which has air-conditional. If the room air humidity is bigger, should be apply Vaseline and rust inhibitor on the all light surface to protect the mould.
•If local permitting, independence placed the two half mould. You must pay attention to putting the assist pressure plug rod and pushing rod vertical upward. Deposit in this way, can prevent the steering mechanism of the mould transmuting, therefore, the blade of the mould cutter can be protected and not damage.
•If two pieces of half mould can not be placed separately, can be upright on the special mould frame, and placed a piece of wood plate in the middle of the upper cutting plate and lower cutter, to prevent the upper and lower blade fit for each other too deep to wear.
•Cleaning the cooling water inside of the mould cooling water way and pore. Especially pay special attention in winter, when the mould store in the house which do not prevent frost, any canal water retention in the mould cooling water way may cause damage to the mould.
•Blade of the upper cutting plate, lower cutter and other sportive part are easy to wear and tear.
•To prolong the service life of cutter, the blade of the upper cutting plate and lower cutter will process a bit longer, so that can be grinded a few times more. Cutting depth of the machine (commonly known as CAM high) lower, as far as possible, in order to not make the blade into the cutter too much, decrease the wear.
•When using fill metal (like welding) to repair the broken cutter, the blade will deformation or fracture. In order to repair easily and guarantee the quality of product, the hardness of upper cutter is smaller than lower cutter when processing. Upper cutter usually hardness is 55-58HRC, lower cutter usually hardness is 60-65HRC.
•According to the degree of material ground, in the front of the upper mould table blank holder possible need to rework (grind thin). No matter what, must ensure that there is enough space to make the blank holder rim to the upper cutting plate. The distance at least equal to cutting depth of the machine(common 2.0-2.5mm, with slightly different machines).
•In most of the mould, the lower cutter also plays the part of forming. So keep in mind that, unless the size and shape of the plastic cup changing or other mould parts processing again at the same time, the lower cutter can be in the range of high-precision tolerance to grind.
•The grind which effect the height may lead to the cavities and pushing plate process again, to ensure that the size and shape has not be changed.
•If the cutter blade needs to grind again, should check the wear condition of other mould parts at the same time. If necessary, need to replace the wear parts. These parts includes sealing rings, pushing rods, assist pressure plug rods, guide bushing, assist pressure plug and cavities.
Note: When installing a new upper cutting plate, general advice to reinstall orientation and positioning parts.
——Upper mould install the new positioning pin、guide bushing or guide pillars.
——Lower mould install the new positioning pin、guide bushing or guide pillars.
•these operation must be operate in the room with good equipment by the good master who has experience.
If do not have conditions for maintenance person and tools, it is best to send back the mould to original factory, prevent mould damage.
- Domestic thermoforming machine and mould need to continuously improve.
No matter what imported or domestic “plastic positive pressure mould ”,there is no good idea to solve lubrication and sealing problem. Bad lubrication inside the mould will cause pollution. Therefore, think in terms of cleaning and maintenance, should adopts free of lubrication material, for example, free of lubrication bear and guide bushing.
Domestic mould is faced with selecting correct material and improving machining accuracy. Due to the cost competition, cutter、cutting plate、 assist pressure plug rod and cavities choose the material which is low performance or not have heat treatment or heat treatment not enough, the cavities do not have hard anodic oxidation and sand blast treatment(such as aluminum cavities) , some machining accuracy(concentricity、verticality、roundness) was not enough. To a certain extent, reduce the service life of the mould, increase the difficulty of repair and maintenance in the process of production.
In addition, most of domestic thermoforming machine without automatic tuning device. Less experienced parallel manual mode is difficult to guarantee upper and lower mould body. Accelerate cutting plate and cutter wear and tear, reduce the life and precision of the mould , also reduces the production efficiency