1、 Sheet foaming
(1) Heating too fast. The following methods can be used to eliminate:
① Reduce the heater temperature appropriately.
② Slow down the heating speed appropriately.
③ Appropriately increase the distance between the sheet and the heater to keep the heater away from the sheet.
(2) Uneven heating. The following methods can be used to eliminate:
① Adjust the distribution of hot air with baffle, air distribution hood or screen to make all parts of the sheet heated evenly.
② Check whether the heater and shielding net are damaged, and repair the damaged parts.
(3) The sheet is wet. The following methods can be used to eliminate:
① Carry out pre drying treatment. For example, 0.5mm thick polycarbonate sheet shall be dried at 125-130 temperature for 1-2h, and 3mm thick sheet shall be dried for 6-7h; The sheet with thickness of 3mm shall be dried at 80-90 temperature for 1-2h, and hot forming shall be carried out immediately after drying.
③ Change the heating mode to two-sided heating. Especially when the thickness of the sheet is more than 2mm, it must be heated on both sides.
④ Do not open the moisture-proof packaging of the sheet too early. It shall be unpacked and formed immediately before hot forming.
(4) There are bubbles in the sheet. The production process conditions of sheet shall be adjusted to eliminate bubbles.
(5) Improper sheet type or formulation. Appropriate sheet materials should be selected and the formula should be adjusted reasonably.
2、 Sheet tear
(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 sheet heating temperature is too high or too low. When the temperature is too high, the heating time shall be appropriately reduced, the heating temperature shall be reduced, the heating shall be uniform and slow, and the compressed air slightly cooled sheet shall be used; When the temperature is too low, the heating time shall be appropriately extended, the heating temperature shall be increased, the sheet shall be preheated and heated evenly.
3、 Sheet charring
(1) The heating temperature is too high. The heating time shall be appropriately shortened, the temperature of the heater shall be reduced, the distance between the heater and the sheet shall be increased, or a shelter shall be used for isolation to make the sheet heat slowly.
(2) Improper heating method. When forming thick sheets, if one side heating is adopted, the temperature difference between the two sides is large. When the back reaches the forming temperature, the front has been overheated and charred. Therefore, for sheets with a thickness greater than 2mm, the method of heating on both sides must be adopted.
4、 Sheet collapse
(1) The sheet is too hot. The following methods can be used to eliminate:
① Shorten the heating time properly.
② Reduce the heating temperature appropriately.
(2) The melt flow rate of the raw material is too high. Low melt flow rate should be used as far as possible during production
Or appropriately improve the drawing ratio of the sheet.
(3) The thermoforming area is too large. Screens and other shields shall be used to heat evenly, and the sheet can also be heated
Zone differential heating to prevent overheating and collapse in the middle area.
(4) Uneven heating or inconsistent raw materials lead to different melting collapse of each sheet. The following methods can be used to eliminate:
① Air distribution plates are set at all parts of the heater to make the hot air evenly distributed.
② The amount and quality of recycled materials in the sheet shall be controlled.
③ Mixing of different raw materials should be avoided
The sheet heating temperature is too high. The heating temperature and heating time shall be properly reduced, and the heater can also be kept away from the sheet,
Heat slowly. If the sheet is overheated locally, the overheated part can be covered with shielding net.
5、 Surface water ripple
(1) The temperature of the booster plunger is too low. It should be properly improved. It can also be wrapped with wooden pressure aid plunger or cotton wool cloth and blanket
Plunger to keep warm.
(2) Mold temperature is too low. The curing temperature of the sheet shall be increased appropriately, but shall not exceed the curing temperature of the sheet.
(3) Uneven die cooling. Cooling water pipe or sink shall be added, and check whether the water pipe is blocked.
(4) The sheet heating temperature is too high. It shall be properly reduced, and the sheet surface can be slightly cooled by air before forming.
(5) Improper selection of forming process. Other forming processes shall be used.
6、 Surface stains and stains
(1) The surface finish of the mold cavity is too high, and the air is trapped on the smooth mold surface, resulting in spots on the product surface. Coping type
The surface of the cavity is sand blasted, and additional vacuum extraction holes can be added.
(2) Poor evacuation. Air extraction holes shall be added. If the acne spots only occur in a certain part, check whether the suction hole is blocked
Or add air extraction holes in this area.
(3) When a sheet containing plasticizer is used, the plasticizer accumulates on the die surface to form spots. The following methods can be used to eliminate:
① Use the mold with controllable temperature and adjust the mold temperature appropriately.
② When heating the sheet, the mold shall be as far away from the sheet as possible.
③ Shorten the heating time properly.
④ Clean the mold in time.
(4) Mold temperature too high or too low. It shall be adjusted appropriately. If the mold temperature is too high, strengthen cooling and reduce the mold temperature; If the mold temperature is too low, the mold temperature shall be increased and the mold shall be insulated.
(5) Improper selection of die material. When processing transparent sheets, do not use phenolic resin to make molds, but aluminum molds.
(6) The die surface is too rough. The cavity surface shall be polished to improve the surface finish.
(7) If the surface of the sheet or mold cavity is not clean, the dirt on the surface of the sheet or mold cavity shall be completely removed.
(8) There are scratches on the surface of the sheet. The surface of the sheet shall be polished and the sheet shall be stored with paper.
(9) The dust content in the air of the production environment is too high. The production environment should be purified.
(10) Mold demoulding slope is too small. It should be increased appropriately
7、 Surface yellowing or discoloration
(1) The sheet heating temperature is too low. The heating time shall be properly extended and the heating temperature shall be increased.
(2) The sheet heating temperature is too high. The heating time and temperature shall be appropriately shortened. If the sheet is overheated locally, it shall be checked
Check whether the relevant heater is out of control.
(3) Mold temperature is too low. Preheating and thermal insulation shall be carried out to properly increase the mold temperature.
(4) The temperature of the booster plunger is too low. It shall be heated properly.
(5) The sheet is stretched excessively. The thicker sheet shall be used or the sheet with better ductility and higher tensile strength shall be replaced, which can also pass through
Modify the die to overcome this failure.
(6) The sheet cools prematurely before it is fully formed. The human mold speed and evacuation speed of the sheet shall be appropriately increased, and the mold shall be suitable
When heat preservation, the plunger shall be properly heated.
(7) Improper die structure design. The following methods can be used to eliminate:
① Reasonably design the demoulding slope. Generally, it is not necessary to design the demoulding slope during female mold forming, but designing some slopes is conducive to the uniform wall thickness of the product. When the male mold is formed, for styrene and rigid PVC sheets, the best demoulding slope is about 1:20; For polyacrylate and polyolefin sheets, the demoulding slope is preferably greater than 1:20.
② Appropriately increase the fillet radius. When the edges and corners of the product need to be rigid, the inclined plane can replace the circular arc, and then the inclined plane can be connected with a small circular arc.
③ Reduce the stretching depth appropriately. Generally, the tensile depth of the product should be considered in combination with its width. When the vacuum method is directly used for molding, the tensile depth should be less than or equal to half of the width. When deep drawing is required, the pressure assisted plunger or pneumatic sliding forming method shall be adopted. Even with these forming methods, the tensile depth shall be limited to less than or equal to the width.
(8) Too much recycled material is used. Its dosage and quality shall be controlled.
(9) The raw material formula does not meet the thermoforming requirements. The formulation design shall be properly adjusted when making sheets
8、 Sheet arching and wrinkling
(1) The sheet is too hot. The heating time shall be properly shortened and the heating temperature shall be reduced.
(2) The melt strength of the sheet is too low. Resin with low melt flow rate shall be used as far as possible; Properly improve the quality of the sheet during production
Tensile ratio; During hot forming, lower forming temperature shall be adopted as far as possible.
(3) Improper control of drawing ratio during production. It shall be adjusted appropriately.
(4) The extrusion direction of the sheet is parallel to the die spacing. The sheet shall be rotated 90 degrees. Otherwise, when the sheet is stretched along the extrusion direction, it will cause molecular orientation, which can not be completely removed even by molding heating, resulting in sheet wrinkles and deformation.
(5) The local position extension of the sheet pushed by the plunger first is excessive or the die design is improper. The following methods can be used to eliminate:
① It is formed by female mold.
② Add pressure aids such as plunger to flatten the wrinkles.
③ Increase the demoulding taper and fillet radius of the product as much as possible.
④ Appropriately speed up the movement speed of the pressure aid plunger or die.
⑤ Reasonable design of frame and pressure aid plunger
9、 Warpage deformation
(1) Uneven cooling. The cooling water pipe of the mold shall be added, and check whether the cooling water pipe is blocked.
(2) Uneven wall thickness distribution. The pre stretching and pressure aid device should be improved and the pressure aid plunger should be used. The sheet used for forming shall be thick and thin
Uniform heating. If possible, the structural design of the product shall be appropriately modified, and stiffeners shall be set at the large plane.
(3) Mold temperature is too low. The mold temperature shall be appropriately increased to slightly lower than the curing temperature of the sheet, but the mold temperature shall not be too high, otherwise
Shrinkage is too large.
(4) Demoulding too early. The cooling time shall be appropriately increased. Air cooling can be used to speed up the cooling of products, and the products must be cooled to
Only when the curing temperature of the sheet is below, can it be demoulded.
(5) The sheet temperature is too low. The heating time shall be appropriately extended, the heating temperature shall be increased and the evacuation speed shall be accelerated.
(6) Poor mold design. The design shall be modified. For example, during vacuum forming, the number of vacuum holes should be appropriately increased, and the number of mold holes should be increased
Trim the groove on the line.
10、 Sheet pre stretching unevenness
(1) The thickness of the sheet is uneven. The production process conditions shall be adjusted to control the thickness uniformity of the sheet. When hot forming, it shall be carried out slowly
(2) The sheet is heated unevenly. Check the heater and shielding screen for damage.
(3) The production site has large air flow. The operation site shall be shielded.
(4) The compressed air is unevenly distributed. The air distributor shall be set at the air inlet of the pre stretching box to make the air blowing uniform.
11、 The wall at the corner is too thin
(1) Improper selection of forming process. The air expansion plug pressure aid process can be used.
(2) The sheet is too thin. Thicker sheets shall be used.
(3) The sheet is unevenly heated. The heating system shall be checked and the temperature of the part to form the corner of the product shall be lower. Before pressing, draw some cross lines on the sheet to observe the material flow during forming, so as to adjust the heating temperature.
(4) Uneven die temperature. It shall be properly adjusted to be uniform.
(5) Improper selection of raw materials for production. Raw materials shall be replaced
12、 Uneven thickness of edge
(1) Improper mold temperature control. It shall be adjusted appropriately.
(2) Improper control of sheet heating temperature. It shall be adjusted appropriately. Generally, uneven thickness is easy to occur at high temperature.
(3) Improper molding speed control. It shall be adjusted appropriately. In actual forming, the part that is initially stretched and thinned 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 forming speed.
13、 Uneven wall thickness
(1) The sheet melts and collapses seriously. The following methods can be used to eliminate:
① The resin with low melt flow rate is used for film making, and the drawing ratio is appropriately increased.
② Vacuum rapid pullback process or air expansion vacuum pullback process are adopted.
③ A shielding net is used to control the temperature in the middle of the sheet.
(2) Uneven sheet thickness. The production process shall be adjusted to control the thickness uniformity of the sheet.
(3) The sheet is heated unevenly. The heating process shall be improved to make the heat evenly distributed. If necessary, air distributor and other facilities can be used; Check whether each heating element works normally.
(4) There is a large air flow around the equipment. The operation site shall be shielded to block the flow of gas.
(5) Mold temperature is too low. The mold shall be heated evenly to the appropriate temperature and the mold cooling system shall be checked for blockage.
(6) Slide the sheet away from the clamping frame. The following methods can be used to eliminate:
① Adjust the pressure of each part of the clamping frame to make the clamping force uniform.
② Check whether the thickness of the sheet is uniform, and the sheet with uniform thickness shall be used.
③ Before clamping, heat the clamping frame to an appropriate temperature, and the temperature around the clamping frame must be uniform.
14、 Corner cracking
(1) Stress concentration at corner. The following methods can be used to eliminate:
① Appropriately increase the arc radius at the corner.
② Appropriately increase the heating temperature of the sheet.
③ Properly increase the mold temperature.
④ Slow cooling can be started only after the product is fully formed.
⑤ The resin film with high stress cracking resistance is used.
⑥ Add stiffeners at the corners of the products.
(2) Poor mold design. The die shall be modified in accordance with the principle of reducing stress concentration.
15、 Adhesion plunger
(1) The temperature of metal pressure aid plunger is too high. It shall be reduced appropriately.
(2) The surface of wooden plunger is not coated with release agent. One coat of grease or one coat of Teflon coating shall be applied.
(3) The plunger surface is not wrapped with wool or cotton cloth. The plunger shall be wrapped with cotton wool cloth or blanket
16、 Sticking die
(1) The product temperature is too high during demoulding. The mold temperature should be reduced slightly or the cooling time should be extended.
(2) Insufficient mold demoulding slope. The following methods can be used to eliminate:
① Increase the mold release slope.
② Use female mold to form.
③ Demould as soon as possible. If the product is not cooled below the curing temperature at the time of demoulding, the cooling mould can be used for further steps after demoulding
(3) There are grooves on the die, causing die sticking. The following methods can be used to eliminate:
① Demoulding frame is used to assist demoulding.
② Increase the air pressure of pneumatic demoulding.
③ Try to demould as soon as possible.
(4) The product adheres to the wooden mold. The surface of the wooden mold can be coated with a layer of release agent or sprayed with a layer of polytetrafluoroethylene
(5) The surface of the mold cavity is too rough. It shall be polished
Post time: Oct-28-2021