The formation of flash on the parting surface of rubber products not only causes material waste and process cost increase, but also affects product performance and environmental pollution. This work takes the rubber seal as an example to discuss the cause of forming the flash edge of the rubber product and the solution.
Formation reason
According to the nature, the size of rubber products is divided into functional size (sealing performance size and mechanical performance size) and structural size; According to the forming characteristics, it is divided into fixed size and sealing size. The flash directly affects the functional size (sealing performance size) and sealing mold size of rubber products.
The reasons for the flash are as follows.
· Mold design and manufacturing: unreasonable mold structure and improper processing technology with low processing accuracy.
· Mold use: template deformation and parting surface is not clean and damaged.
Vulcanization equipment: vulcanization machine clamping force is small and pressure drop during work.
· Others: the skeleton sealing mold size is larger than the mold sealing mold size and the amount of sealant is too large.
2. Solution
2.1 Product structure design
When designing the structure of rubber products or imitation rubber products, it is necessary to rationally frame or strictly distinguish the functional size and structural size of the product, and carry out the classification treatment of its geometric model, for designing less flash author Introduction: Wu Shengxu (1944). Male, born in Xi 'an, Shaanxi Province, senior engineer of Yuhuan Hetian Automobile Rubber & Plastics Co., LTD., mainly engaged in rubber molding mold design and manufacturing research and technical management.
Or no flash product mold to lay the foundation.
2.2 Skeleton design and manufacture
It is very important to design the mold size and positioning size of the frame reasonably and make the frame strictly according to the design size and precision requirements for the manufacture of molded products with little or no flash edges. The size of the frame sealing mold is too large, which will cause the product to become thick or crush the mold or the frame; The skeleton sealing mold size is too small, which will cause the product to lack of glue. The radial positioning size is too large or too small, which will cause the product to be eccentric or difficult to release.
2.3 Mold design, production and use
2.3.1 Design
(1) Design as far as possible the mold structure without flash 0 sealing ring mold structure example, as shown in Figure 1, both sides of the mold cavity are provided with flash cutting edge (narrow partition between the mold brain and the residual groove), the cutting edge directly eliminate (cut) the flash when the product is formed. The width of the cutting edge of the mold is generally 0.05~ 0.15mm. When the HRC hardness of the template is 42-48 degrees, the width of the cutting edge is controlled at about 0.05mm.
The remaining groove width (4) of the mold is
A=2B
B=(2% ~ 3%) d
Type B a residual groove depth,mm;
d Cavity section diameter,mm.
The layout of the mold cavity is basically the same as that of the ordinary 0-shaped sealing ring, and the cavity spacing (I, the distance between the center of the two cavities) is calculated according to the following formula:
L = d1+ 2d + 2A + W1-W2
In formula d1 -- cavity diameter,mm
FIG. 1 Schematic diagram of die structure without flash 0-shape sealing diagram
A- Residual groove width,mm;
W1- Sum of the width of the edge cutting edge between adjacent cavities, generally 0.10-0.30mm;
w2- The overlap width of the adjacent residual groove is generally 0.5~1.0 mm.
The accuracy of the mold with more complex structure usually decreases with the increase of the number of cavities. In general, with each additional cavity, the mold accuracy decreases by about 4%. Therefore, the number of mold cavities depends on the shape, structure and accuracy requirements of the product, that is, the layout of the mold cavity should be reasonable, and the multi-cavity can not be unilaterally pursued.
(2) The sealing size of the mold containing the skeleton rubber products and the sealing size of the skeleton (as shown in Figure 2, where H and H are the sealing size of the outer skeleton and the inner skeleton, respectively) should be matched. Generally speaking, the skeleton material is aluminum alloy or copper, and the sealing size of the mold is 0.10 mm smaller than that of the skeleton; The skeleton material is steel, and the sealing size of the mold is 0.05mm smaller than that of the skeleton
(3) The permanent pressure area of the main parting surface of the mold is less than its projected area. Except for small molds, the pressure area of the mold is generally 75% to 80% of the projected area. The example of the mold structure with small pressure area is shown in Figure 3
(4) The remaining rubber groove and the exhaust system should be smooth. The example of the rubber groove and the exhaust groove in the molding mold of rubber products without flash is shown in Figure 4.
2.3.2 Production
Exhaust system structure schematic
Mold production should meet the requirements of mold dimensional accuracy, positioning tolerance (especially the parallelism of the upper and lower planes of the mold) and cavity surface roughness to ensure that the dimensional accuracy and surface quality of the molded products meet the requirements.
2.3.3 Usage
Mold operation specification for rubber products with or without flash edges
As follows
Vulcanization equipment matched with the mold is used, that is, the size and clamping force of the vulcanization machine are equivalent to the size and clamping force of the mold respectively. It is strictly forbidden to use steel prying tools to open the mold, usually with brass screwdriver or steel hammer. Timely clean and prevent damage to parting surface and cavity. · Gently handle disassembled mold parts, and pad the operating table with wood, plastic or rubber plates. Strictly control the amount of glue filling.
2.4 Vulcanization equipment
If the upper and lower plates of the vulcanization machine are deformed or the upper and lower plates are not parallel, it must be repaired in time, otherwise it will lead to the deformation of the mold template and make the product flash thicker.
3. Conclusion
The key to reduce or eliminate the flash of molded rubber products is mold design and manufacturing. Reasonable mold structure and high manufacturing precision, mold loading and mold opening operation specifications are the prerequisite for the production of less or no flash rubber products.