Summary of 16 items: problems and solutions for sheets and blister products

Summary of 16 items: problems and solutions for sheets and blister products

1. The sheet is blistering
(1) Heating is too fast. The following methods can be used to exclude:
①Appropriately reduce the heater temperature.
②Slow down the heating speed appropriately.
③ Properly increase the distance between the sheet and the heater to make the heater farther away from the sheet.
(2) Uneven heating. The following methods can be used to exclude:
①Adjust the distribution of hot air with baffles, air hoods or screens, so that all parts of the sheet are evenly heated.
②Check whether the heater and the shielding net are damaged, and repair the damaged parts.
(3) The sheet is wet. The following methods can be used to exclude:
① Carry out pre-drying treatment. For example, a polycarbonate sheet with a thickness of 0.5mm should be dried for 1-2h at a temperature of 125-130, a sheet with a thickness of 3mm should be dried for 6-7h; a sheet with a thickness of 3mm should be dried for 1-2h at a temperature of 80-90 , And it should be thermoformed immediately after drying.
② Carry out pre-heat treatment.
③Change the heating method to double-sided heating. Especially when the thickness of the sheet is more than 2mm, double-sided heating must be adopted.
④Do not open the moisture-proof packaging of the sheet prematurely. It should be unpacked and molded immediately before thermoforming.
(4) There are bubbles in the sheet. The production process conditions of the sheet should be adjusted to eliminate air bubbles.
(5) Improper sheet type or formula. Appropriate sheets should be selected and the formula should be adjusted reasonably.

2. the sheet is torn
(1) The mold design is poor, and the arc radius at the corner is too small. The radius of the transition arc should be increased.
(2) The heating temperature of the sheet is too high or too low. When the temperature is too high, you should appropriately reduce the heating time, lower the heating temperature, and heat evenly and slowly, using compressed air to cool the sheet; when the temperature is too low, you should appropriately extend the heating time, increase the heating temperature, and preheat the sheet , Heat evenly.

3. the sheet is burnt
(1) The heating temperature is too high. The heating time should be appropriately shortened, the temperature of the heater should be lowered, the distance between the heater and the sheet should be increased or a cover should be used to isolate the sheet, so that the sheet is slowly heated.
(2) Improper heating method. When forming a thicker sheet, if single-sided heating is used, the temperature difference between the two surfaces is relatively large. When the back surface reaches the molding temperature, the front surface has been overheated and scorched. Therefore, for sheets with a thickness greater than 2mm, heating on both sides must be adopted.

4. the sheet melts down
(1) The sheet is too hot. The following methods can be used to exclude:
①Appropriately shorten the heating time.
②Appropriately reduce the heating temperature.
(2) The melt flow rate of the raw material is too high. When making tablets, try to use a lower melt flow rate
Or appropriately increase the stretch ratio of the sheet.
(3) The thermoforming area is too large. Screens and other shields should be used to make the heating uniform, and it can also be used for the sheet
District heating, so that the middle area does not produce overheating and collapse.
(4) Uneven heating or inconsistent raw materials used lead to different melting and collapse of each sheet. The following methods can be used to exclude:
① Install air distribution plates at each part of the heater to make the hot air evenly distributed.
②The amount and quality of recycled materials in the sheet should be controlled.
③The mixing of different raw materials should be avoided

The heating temperature of the sheet is too high. The heating temperature should be appropriately lowered and the heating time should be shortened. The heater can also be kept away from the sheet.
Heat slowly. If the sheet is partially overheated, a shielding net can be used to cover the overheated part.

5. surface water ripples
(1) The temperature of the pressure-assisting plunger is too low. Should be increased appropriately. It can also be wrapped with wooden pressure-assisting plunger or cotton flannel and blanket
The plunger plays a role of heat preservation.
(2) The mold temperature is too low. It should be increased appropriately, but it should not exceed the curing temperature of the sheet material.
(3) Uneven mold cooling. Add cooling water pipes or water tanks, and check whether the water pipes are blocked.
(4) The heating temperature of the sheet is too high. It should be lowered appropriately, and air can be used to cool the surface of the sheet slightly before forming.
(5) Improper selection of molding process. Other molding processes should be used instead.

6. Surface scars and stains
(1) The surface finish of the mold cavity is too high, and air is trapped on the smooth mold surface, causing acne spots on the surface of the product. Responsive
The cavity surface is sandblasted, and additional vacuum holes can be added.
(2) Poor evacuation. Air extraction holes should be added. If the acne spots only occur in a certain area, check whether the air suction holes in that area are blocked
Or add a suction hole in this area.
(3) When a plasticizer-containing sheet is used, the plasticizer accumulates on the surface of the mold to form scars. The following methods can be used to exclude:
① Use a temperature-controllable mold and adjust the mold temperature appropriately.
②When heating the sheet, keep the mold away from the sheet as much as possible.
③Appropriately shorten the heating time.
④ Clean the mold in time.
(4) The mold temperature is too high or too low. Should be adjusted appropriately. If the mold temperature is too high, the cooling should be strengthened and the mold temperature should be lowered; if the mold temperature is too low, the mold temperature should be increased and the mold should be insulated.
(5) Improper selection of mold material. When processing transparent sheets, do not use phenolic resin to make molds, but use aluminum molds.
(6) The mold surface is too rough. The surface of the cavity should be polished to improve the surface finish.
(7) The surface of the sheet or mold cavity is not clean, so the dirt on the surface of the sheet or mold cavity should be completely removed.
(8) There are scratch marks on the surface of the sheet. The surface of the sheet should be polished, and the sheet should be stored with paper.
(9) The dust content of the air in the production environment is too high. The production environment should be purified.
(10) The mold draft is too small. Should be increased appropriately

7. yellowing or discoloration of the surface
(1) The heating temperature of the sheet is too low. The heating time should be appropriately extended and the heating temperature should be increased.
(2) The heating temperature of the sheet is too high. The heating time should be appropriately shortened and the heating temperature should be lowered. If the sheet is locally overheated, it should be checked
Check whether the related heater is out of control.
(3) The mold temperature is too low. It should be preheated and kept warm, and the mold temperature should be appropriately increased.
(4) The temperature of the pressure-assisting plunger is too low. It should be heated appropriately.
(5) The sheet is excessively stretched. A thicker sheet should be used or a sheet with better ductility and higher tensile strength should be used.
Overcome this failure by modifying the mold.
(6) The sheet is cooled prematurely before being completely formed. The mannequin speed and evacuation speed of the sheet should be appropriately increased, and the mold should be suitable
When keeping warm, the plunger should be heated appropriately.
(7) Improper mold structure design. The following methods can be used to exclude:
① Reasonably design the draft angle. Generally, it is not necessary to design the demolding slope when the female mold is formed, but designing some slopes is conducive to the uniform wall thickness of the product. When forming a male mold, for styrene and rigid polyvinyl chloride sheets, the demolding angle is preferably about 1:20; for polyacrylate and polyolefin sheets, the demolding angle is preferably greater than 1 : 20.
② Increase the fillet radius appropriately. When the edges and corners of the product need to be rigid, the bevel can be used instead of the arc, and then the bevel can be connected with a small arc.
③Appropriately reduce the drawing depth. Generally, the drawing depth of the product should be considered in conjunction with its width. When the vacuum method is directly used for molding, the drawing depth is preferably less than or equal to half of the width. When deep drawing is required, a pressure-assisted plunger or pneumatic sliding molding method should be used. Even with these forming methods, the drawing depth should still be limited to a range less than or equal to the width.
(8) The amount of recycled materials is too much. Its dosage and quality should be controlled.
(9) The raw material formula does not meet the requirements of thermoforming. The formula design should be adjusted appropriately when making the sheet

8. Sheet arching and wrinkles
(1) The sheet is too hot. The heating time should be appropriately shortened and the heating temperature should be lowered.
(2) The melt strength of the sheet is too low. The resin with a lower melt flow rate should be used as far as possible;
Stretching ratio: When thermoforming, use a lower forming temperature as much as possible.
(3) Improper control of stretch ratio during film production. Should be adjusted appropriately.
(4) The extrusion direction of the sheet is parallel to the die pitch. The sheet should be rotated 90 degrees. Otherwise, when the sheet is stretched along the extrusion direction, it will cause molecular orientation, which cannot be completely removed even if the molding is heated, resulting in wrinkles and deformation of the sheet.
(5) The part of the material that the plunger hits first is over-extended or the mold design is improper. The following methods can be used to exclude:
①It is formed by a female mold.
②Add a plunger and other pressure-assisting devices to flatten the wrinkles.
③ Increase the demolding taper and fillet radius of the product as much as possible.
④ Speed up the movement speed of the pressure-assisting plunger or the mold appropriately.
⑤ Reasonably design the frame and pressure-assisting plunger

9. warpage deformation
(1) Uneven cooling. The cooling water pipe of the mold should be increased, and check whether the cooling water pipe is blocked.
(2) Uneven wall thickness distribution. The pre-tensioning and pressure-assisting devices should be improved, and pressure-assisting plungers should be used. The sheet used for forming should be thick and thin
Consistent, even heating. Where possible, the structural design of the product should be appropriately modified, and reinforcing ribs should be set on the large plane.
(3) The mold temperature is too low. The mold temperature should be appropriately increased to slightly lower than the curing temperature of the sheet, but the mold temperature should not be too high, otherwise
The shrinkage rate is too large.
(4) Demoulding is too early. The cooling time should be appropriately increased. Air cooling can be used to speed up the cooling of the product. The product must be cooled to
The sheet can be demolded below the curing temperature.
(5) The sheet temperature is too low. The heating time should be appropriately extended, the heating temperature should be increased, and the evacuation speed should be accelerated.
(6) Poor mold design. The design should be modified. For example, during vacuum forming, the number of vacuum holes should be appropriately increased, and the mold should be increased
Trim the grooves on the line.

10. Uneven sheet pre-stretching
(1) The thickness of the sheet is uneven. The production process conditions should be adjusted to control the thickness uniformity of the sheet. When thermoforming, it should be slow
heating.
(2) The sheet is heated unevenly. Check the heater and shielding screen for damage.
(3) There is a large airflow in the production site. The operating place should be shielded.
(4) Uneven distribution of compressed air. An air distributor should be installed at the air inlet of the pre-stretching box to make the air blow evenly.

11. The wall at the corner is too thin
(1) Improper selection of molding process. Inflatable plug pressure-assisted technology can be used instead.
(2) The sheet is too thin. A thicker sheet should be used instead.
(3) Uneven heating of the sheet. The heating system should be checked, and the temperature of the part that will form the corner of the product should be lower. Before pressing, some cross lines can be drawn on the sheet material to observe the flow of the material during forming, so as to adjust the heating temperature.
(4) Uneven mold temperature. Should be properly adjusted to uniformity.
(5) Improper selection of raw materials for film production. Raw materials should be replaced

12. Uneven thickness at the edge
(1) Improper mold temperature control. Should be adjusted appropriately.
(2) Improper temperature control of sheet heating. Should be adjusted appropriately. Generally, when the temperature is high, uneven thickness is likely to occur.
(3) Improper control of molding speed. Should be adjusted appropriately. In actual molding, the initially stretched and thinned part is rapidly cooled
However, the elongation decreases, thereby reducing the thickness difference. Therefore, the wall thickness deviation can be adjusted to a certain extent by adjusting the molding speed.

13. Uneven wall thickness
(1) The sheet material melts badly. The following methods can be used to exclude:
① Use resin with lower melt flow rate when making tablets, and appropriately increase the stretch ratio.
②Using vacuum rapid pull-back process or inflatable vacuum pull-back process.
③Using a shielding net to control the temperature in the middle of the sheet.
(2) The thickness of the sheet is uneven. The sheet-making process should be adjusted to control the thickness uniformity of the sheet.
(3) The sheet is heated unevenly. The heating process should be improved to make the heat distribution uniform, and if necessary, air distribution panels and other facilities can be used; each heating element should be checked whether it is working properly.
(4) There is a large airflow around the equipment. The operating site should be shielded to block the flow of gas.
(5) The mold temperature is too low. The mold should be evenly heated to the appropriate temperature, and check whether the mold cooling system is blocked.
(6) The sheet slides away from the clamping frame. The following methods can be used to exclude:
①Adjust the pressure of each part of the clamping frame to make the clamping force even.
②Check whether the thickness of the sheet is uniform, and use a sheet of uniform thickness.
③Heat the clamping frame to an appropriate temperature before clamping the material, and the temperature around the clamping frame must be uniform.

14. Cracking at the corner
(1) Stress concentration at the corners. The following methods can be used to exclude:
① Increase the radius of the arc at the corner appropriately.
② Increase the heating temperature of the sheet appropriately.
③ Increase the mold temperature appropriately.
④Slow cooling can be started after the product is completely formed.
⑤Use a resin sheet with high stress crack resistance.
⑥Add stiffeners at the corners of the products.
(2) Poor mold design. The mold should be modified in accordance with the principle of reducing stress concentration.

15. Adhesion plunger
(1) The temperature of the metal pressure-assisted plunger is too high. Should be reduced appropriately.
(2) The surface of the wooden plunger is not coated with a release agent. Should be coated with a layer of grease or spray a layer of PTFE paint.
(3) The surface of the plunger is not wrapped with wool or cotton cloth. Plunger should be wrapped with cotton flannel or blanket

16. sticky mold
(1) The product temperature is too high during demolding. The mold temperature should be reduced slightly or the cooling time should be extended.
(2) The mold draft is insufficient. The following methods can be used to exclude:
①Increase the demolding angle of the mold.
②Use a female mold instead.
③ Demould as soon as possible. If the product has not been cooled to below the solidification temperature when the product is demolded, the cooling mold can be used to further
cool down.
(3) There are grooves on the mold, causing mold sticking. The following methods can be used to exclude:
①The demoulding frame is used to assist demoulding.
②Increase the air pressure of pneumatic demoulding.
③ Try to demould as soon as possible.
(4) The product adheres to the wooden mold. A layer of release agent or a layer of PTFE can be sprayed on the surface of the wooden mold
coating.
(5) The surface of the mold cavity is too rough. Should be polished