CN111037828A

CN111037828A - Mould for hot-press forming of wood-plastic composite board and cavity cleaning method thereof

Info

Publication number: CN111037828A
Application number: CN201911354902.4A
Authority: CN
Inventors: 杨帆
Original assignee: Chuiou Educational Equipment Shanghai Co ltd
Current assignee: Chuiou Educational Equipment Shanghai Co ltd
Priority date: 2019-12-25
Filing date: 2019-12-25
Publication date: 2020-04-21

Abstract

The invention provides a mould for hot-press forming of a wood-plastic composite board, which comprises an upper mould and a lower mould which are approximately rectangular; the upper die is provided with first alignment parts facing downwards at four corners respectively, and third alignment parts facing downwards are arranged at the centers of the four sides respectively; the lower die is provided with second alignment pieces which face upwards and correspond to the first alignment pieces at four corners respectively, and fourth alignment pieces which face upwards and correspond to the third alignment pieces are arranged at the centers of the four sides respectively; the lower die is provided with an air nozzle on three of the four sides respectively, and the air nozzles are used for blowing air to clean the die cavity. According to the invention, the alignment degree between the upper die and the lower die is better through the two groups of alignment parts, and the surface flatness of the product is higher; the interior of the cavity is cleaned in a blowing mode, so that the surface damage of the mold is effectively avoided, the service life of the mold is prolonged, and the surface quality of a product is improved; and the surface performance of the product is further improved through a special air blowing mode and gas components, and the defective rate of the product is obviously reduced.

Description

Mould for hot-press forming of wood-plastic composite board and cavity cleaning method thereof

Technical Field

The invention belongs to the field of synthetic plates, and particularly relates to a die for hot press molding of a wood-plastic composite plate and a cavity cleaning method thereof.

Background

The wood-plastic composite board is a novel synthetic board which is briskly developed in recent years, and is prepared by mixing wood powder and plastic according to a certain proportion and then putting the mixture into a mould and performing hot-press molding, and the strength and the processing performance of the wood-plastic composite board are superior to those of the traditional wood board and other synthetic boards. Wherein, the wood powder is generally prepared by mixing waste plant fibers such as wood powder with high wood fiber content (such as pine wood powder, poplar wood powder, fir wood powder, bamboo wood powder and the like), rice hull, straw and the like. The plastic is usually thermosetting plastic such as amino resin, epoxy resin, etc., or thermoplastic such as High Density Polyethylene (HDPE), polypropylene (PP), polyvinyl chloride (PVC), etc. For example, the applicant provided in the patent application CN110126052A of the invention of the chinese state thereof a high-strength and high-stability wood-plastic composite board, comprising a substrate and a decorative film covering the surface of the substrate, wherein the decorative film is made of solid paper impregnated with melamine formaldehyde resin.

However, the inventor finds in practice that the phenomenon that the decorative film of the wood-plastic composite board produced by the hot press molding die is wrinkled or even cracked after being used for a long time often occurs, so that the defective rate is obviously improved, especially under the condition that the temperature rise rate and the temperature drop rate are high in the hot press molding process. The inventors believe that this may be due to damage to the die coating. In order to facilitate demolding in the hot press molding process, the mold surface is generally subjected to nitriding and electroplating treatment to ensure the hardness and smoothness of the mold surface. However, in the prior art, when the inside of a mold cavity is cleaned in the production process, a bronze scraper knife is generally adopted, which may cause some slight damage invisible to naked eyes, thereby affecting the demolding effect, the surface quality and the qualification rate of the wood-plastic composite board product. In addition, due to the differences in the composition and physical and chemical properties of the substrate and the decorative film, too fast temperature rise and temperature fall may cause the substrate and the decorative film to be subjected to different thermal stresses and deformation amounts, thereby causing wrinkles and even cracks.

Disclosure of Invention

In view of the above defects in the prior art, the present invention aims to provide a mold for hot press forming of a wood-plastic composite board, which has better alignment between an upper mold and a lower mold and higher surface flatness of a product through two sets of alignment members; the air blowing mode replaces a scraper knife in the prior art to clean the interior of the cavity, so that the surface damage of the mold is effectively avoided, the service life of the mold is prolonged, and the surface quality of a product is improved; the performance of the decorative film on the surface of the product is further improved through a special air blowing mode and gas components, and the defective rate of the product is remarkably reduced.

In order to achieve the above object, in one aspect, the present invention provides a mold for hot press forming of a wood-plastic composite board, comprising an upper mold and a lower mold which are substantially rectangular; wherein the content of the first and second substances,

the upper die is provided with first alignment parts facing downwards at four corners respectively, and third alignment parts facing downwards are arranged at the centers of the four sides respectively;

the lower die is provided with second alignment pieces which face upwards and correspond to the first alignment pieces at four corners respectively, and fourth alignment pieces which face upwards and correspond to the third alignment pieces are arranged at the centers of the four sides respectively; in addition to this, the present invention is,

the lower die is provided with an air nozzle on three of the four sides of the lower die respectively, namely three air nozzles in total, and the air nozzles are used for blowing air to clean the die cavity.

Further, the internal diameter of air cock is 5 ~ 20 mm.

Furthermore, the first alignment piece is a cylinder, and the second alignment piece is a round hole matched with the cylinder; the third alignment piece is a square protrusion, and the fourth alignment piece is a square clamping groove matched with the square protrusion. The invention utilizes two groups of alignment parts for guiding, ensures better alignment between the upper die and the lower die, and thus the surface flatness of the product is higher.

Furthermore, the height of the air nozzle outlet is approximately positioned at the joint of the lower die and the upper die, the three air nozzles are connected with an air source through electromagnetic valves, and automatic control can be performed on whether the cavity is blown or not through the on-off of the electromagnetic valves. Preferably, the solenoid valve is disposed on one of four sides of the lower mold.

Further, the air blown out by the air nozzle is compressed air, and the air source is an air compressor.

Further, a certain amount of glycerol or diethylene glycol, preferably glycerol, can be added into the compressed air, which is beneficial to improving the physical and chemical properties of the melamine formaldehyde resin impregnated decorative film and avoiding wrinkles or cracks.

Further, the pressure of the compressed air is 0.3-2.0 MPa, and the glycerol or the diglycol is injected through an automatic injector.

Furthermore, the lower die is further provided with a distance sensor on one of the four edges of the lower die, the distance sensor is used for detecting the distance between the upper die and the lower die and is linked with the electromagnetic valve, so that when the upper die and the lower die are opened to a set distance, the electromagnetic valve acts, and the three air nozzles blow air to the die cavity.

In another aspect, the present invention provides a method for cleaning a cavity of a mold in a mold opening process after hot press molding, including the following steps:

(1) in the die opening process after the hot-press forming, a distance sensor detects the distance between an upper die and a lower die in real time;

(2) when the distance between the upper die and the lower die reaches a set value, starting the electromagnetic valve to enable the three air nozzles to blow air to the cavity for a period of time;

(3) and closing the electromagnetic valve to enable the three air nozzles to stop blowing air to the cavity.

Further, the set value of the distance between the upper die and the lower die in the step (2) is 5-20 mm.

Further, the air blowing process in the step (2) is divided into two stages: blowing compressed air containing glycerol or diethylene glycol for a first period of time; the second stage is a second blowing period in which compressed air containing no glycerin or diethylene glycol is blown in for a period of time.

Further, the pressure of the compressed air is 0.3-2.0 MPa, wherein the content of glycerol or diethylene glycol is 0.5-3.0 vol%. The first air blowing time is 2-5 s; the second air blowing time is 6-15 s.

The beneficial technical effects of the invention are at least shown in the following aspects:

(1) according to the die, the alignment degree between the upper die and the lower die is better through the two groups of alignment parts, the surface smoothness of a product is higher, and the quality is better;

(2) according to the invention, the air blowing mode is adopted to replace a scraper knife in the prior art to clean the interior of the mold cavity, so that the surface damage of the mold is effectively avoided, the service life of the mold is prolonged, and the mold can still ensure that the product has good surface quality after being used for a long time;

(3) according to the invention, the glycerin or the diglycol is added into the compressed air, and a special blowing procedure is adopted, so that the physical and chemical properties of the decorative film on the surface of the product are improved, and the defective rate of the product is obviously reduced.

Drawings

Fig. 1 is a schematic structural diagram of a mold for hot press forming of a wood-plastic composite board according to a preferred embodiment of the invention.

Detailed Description

The following examples are given to illustrate the present invention in detail, and the following examples are given to illustrate the detailed embodiments and specific procedures of the present invention, but the scope of the present invention is not limited to the following examples.

Example 1

As shown in fig. 1, in a preferred embodiment, the mold for hot press forming of wood-plastic composite board of the present invention comprises an upper mold 1 and a lower mold 2, which are substantially rectangular; wherein, the upper die 1 is provided with downward cylinders as the first aligning member 31 at four corners, and is provided with downward square bulges as the third aligning member 41 at the centers of the four sides; the lower die 2 is provided with round holes facing upward and corresponding to the first aligning members 31 at four corners as second aligning members 32, and square slots facing upward and corresponding to the third aligning members 41 at the centers of the four sides as fourth aligning members 42.

In addition, the lower die 2 is provided with an air nozzle 5 on three of the four sides of the lower die respectively for blowing air to clean the die cavity, the inner diameter of the air nozzle 5 is 5mm, the height of the outlet of the air nozzle 5 is approximately positioned at the joint of the lower die 2 and the upper die 1, the three air nozzles 5 are connected with an air source (not shown in the figure) through an electromagnetic valve 7, and whether the air blowing of the die cavity is carried out or not can be automatically controlled through the on-off of the electromagnetic valve 7. The electromagnetic valve 7 is arranged on one of the four sides of the lower die 2.

The air blown out from the air nozzle 5 is compressed air, the pressure of the compressed air is 1.0MPa, and the air source is an air compressor.

According to the automatic control program, glycerol can be added into the compressed air, which is beneficial to improving the physical and chemical properties of the melamine formaldehyde resin impregnated decorative film and avoiding the appearance of wrinkles or cracks. The glycerol can be added in various modes, and the automatic injector can automatically control the opening and closing and adjust the flow rate. The outlet of the automatic injector is arranged outside the outlet of the air tap 5, and the glycerol liquid drops ejected from the automatic injector can be quickly atomized and dispersed into the compressed air due to the impact of the compressed air, and then are blown into the die cavity. In this embodiment, the content of glycerin in the compressed air is measured by sampling the four sides of the lower mold 2 without the air nozzles 5 for a plurality of times, and measuring the content of glycerin by gas chromatography, and the content of glycerin has a certain fluctuation, which is approximately between 0.5 to 3.0 vol%.

The lower die 2 is further provided with a distance sensor 6 on one of the four sides of the lower die for detecting the distance between the upper die 1 and the lower die 2, and the distance sensor is linked with the electromagnetic valve 7, so that when the upper die and the lower die are opened to a set distance, the electromagnetic valve 7 acts, and the three air nozzles 5 blow air to the die cavity.

In this embodiment, the wood-plastic composite board is produced by using the mold, and the cavity of the mold is cleaned in the mold opening process after the hot press molding, which includes the following steps:

(1) in the process of opening the die after the hot press forming, the distance sensor 6 detects the distance between the upper die 1 and the lower die 2 in real time;

(2) when the distance between the upper die 1 and the lower die 2 reaches 5mm, starting the electromagnetic valve 7 and the automatic injector to ensure that the three air nozzles 5 blow compressed air containing glycerol into the cavity for 2 s; keeping the electromagnetic valve 7 started but closing the automatic injector, so that three air nozzles 5 blow compressed air 6s without glycerol into the cavity;

(3) the solenoid valve 7 is closed so that the three air nozzles 5 stop blowing air into the cavity.

Example 2

Example 2 the mold and cavity cleaning method used was substantially the same as example 1 except that the compressed air was injected with diethylene glycol instead of glycerin.

Example 3

The mold and cavity cleaning method used in example 3 is substantially the same as in example 1, except that in step (2) of the cavity cleaning method, three air nozzles 5 blow compressed air 3s containing glycerin into the cavity; then, compressed air containing no glycerin was blown for 9 s.

Example 4

Example 4 the mold and cavity cleaning method used was substantially the same as example 3 except that the compressed air was injected with diethylene glycol instead of glycerin.

Example 5

The mold and cavity cleaning method used in example 5 is substantially the same as in example 1, except that in step (2) of the cavity cleaning method, three air nozzles 5 blow compressed air 4s containing glycerin into the cavity; then, compressed air containing no glycerin was blown for 12 s.

Example 6

Example 6 used a mold and cavity cleaning method substantially the same as example 5 except that the compressed air was injected with diethylene glycol instead of glycerin.

Example 7

The mold and cavity cleaning method used in example 7 is substantially the same as in example 1, except that in step (2) of the cavity cleaning method, three air nozzles 5 blow compressed air 5s containing glycerin into the cavity; then, compressed air containing no glycerin was blown for 15 seconds.

Example 8

Example 8 used substantially the same mold and cavity cleaning method as example 7, except that the compressed air was injected with diethylene glycol instead of glycerin.

Example 9

The mold and cavity cleaning method used in example 9 was substantially the same as in example 1 except that in step (2) of the cavity cleaning method, compressed air was blown into the cavity through three air nozzles 5 for 10 seconds, and the compressed air contained no glycerin or diethylene glycol.

Comparative example 1

Comparative example 1 is prior art, the mold used is the same as in example 1 except that it does not contain the air nozzle 5, the distance sensor 6 and the solenoid valve 7, and the cavity cleaning is performed by using a conventional bronze blade.

In 18 months, the molds and the cavity cleaning methods of the examples 1 to 9 and the comparative example 1 are used for producing the wood-plastic composite board, the molds are customized to a uniform specification and are all brand new when being used, the surface qualification rates of the wood-plastic composite boards produced by the molds in 1 st, 6 th, 12 th and 18 th months are counted and recorded, and the results are shown in the following table.

Compared with the prior art, the method has the advantages that the mold cavity is cleaned in a blowing mode, so that the surface damage of the mold is effectively avoided, and the product can still keep higher surface quality and qualified rate after the mold is used for 18 months. In addition, the addition of glycerol or diethylene glycol to the compressed air is beneficial to further improving the surface quality and the yield of the product, especially glycerol. For example, after the mold of example 5 is used for 18 months, the surface yield of the product is still kept above 99%, and the glycerol is non-toxic and cheap, so the scheme of example 5 can significantly improve the service life of the mold and reduce the rejection rate of the product under the condition of increasing a small amount of cost, thereby having high economic benefit.

The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.

Claims

1. A mould for hot-press forming of a wood-plastic composite board is characterized by comprising an upper mould and a lower mould which are approximately rectangular; wherein the content of the first and second substances,

the lower die is provided with second alignment pieces which face upwards and correspond to the first alignment pieces at four corners respectively, and fourth alignment pieces which face upwards and correspond to the third alignment pieces are arranged at the centers of the four sides respectively;

and the lower die is provided with an air nozzle on three of the four sides of the lower die respectively, and the air nozzles are used for blowing air to clean the die cavity.

2. The mold for hot press forming of a wood-plastic composite board according to claim 1, wherein the air tap has an inner diameter of 5 to 20 mm.

3. The mold for hot press forming of a wood-plastic composite board according to claim 1, wherein the first aligning member is a cylinder, and the second aligning member is a circular hole matched with the cylinder; the third aligning piece is a square protrusion, and the fourth aligning piece is a square clamping groove matched with the square protrusion.

4. The mold for hot press forming of wood-plastic composite boards according to claim 1, wherein the height of the air tap outlet is approximately at the joint of the lower mold and the upper mold, and the air tap is connected with an air source through a solenoid valve.

5. The mold for hot press forming of wood-plastic composite boards according to claim 4, wherein the gas blown out from the gas nozzles is compressed air, and the gas source is an air compressor.

6. The mold for hot press molding of a wood-plastic composite board according to claim 5, wherein the pressure of the compressed air is 0.3 to 2.0MPa, a certain amount of glycerol or diethylene glycol can be added to the compressed air, and the glycerol or diethylene glycol is injected through an automatic injector.

7. The mold for hot press forming of a wood-plastic composite board according to claim 6, wherein the lower mold is further provided with a distance sensor on one of four sides thereof for detecting a distance between the upper mold and the lower mold.

8. A method of cleaning the cavity of the mold according to claim 7 in the process of opening the mold after hot press molding, comprising the steps of:

(1) in the die opening process after the hot-press forming, the distance sensor detects the distance between the upper die and the lower die in real time;

(2) when the distance between the upper die and the lower die reaches a set value, starting the electromagnetic valve to enable the air nozzle to blow air to the cavity for a period of time;

(3) and closing the electromagnetic valve to enable the air nozzle to stop blowing air to the cavity.

9. The method as set forth in claim 8, wherein the distance between the upper mold and the lower mold in the step (2) is set to 5 to 20 mm.

10. The method of claim 8, wherein the blowing process in step (2) is divided into two stages: blowing compressed air containing glycerol or diethylene glycol for a first period of time; blowing compressed air without glycerol or diglycol in the second stage for a second blowing time; wherein the content of the first and second substances,

the content of glycerol or diethylene glycol in the first-stage compressed air is 0.5-3.0 vol%, and the first air blowing time is 2-5 s; the second air blowing time is 6-15 s.