Master of rubber products, what are the causes of bubbles in rubber production?

Compared with compression molding process, injection molding process has obvious advantages: simple process, convenient operation, mechanization, high degree of automation, low labor intensity, short vulcanization time, less flash, stable performance and high qualified rate. However, the biggest problem in the trial production of injection molding products is the easy generation of bubbles. Bubble is a common quality defect of rubber products, which not only affects the appearance quality of products, but also affects the internal quality of products. Through on-site observation and analysis of the causes of bubbles during vulcanization, measures to solve the problems are formulated to minimize bubbles and improve the appearance quality of products. There are many factors that cause bubbles in rubber products, and the key reasons are raw materials, rubber compound mixing and processing, process operation, vulcanization equipment and mold.

First, raw material factors.

cause analysis

(1) The moisture and volatiles of natural rubber exceeded the standard.

(2) The storage and batching of chemical raw materials and additives are affected by moisture, and the moisture increases.

(3) The steel rope is affected with damp and the steel wire mortar is wet.

(4) The moisture regain of fiber cord is high, which is higher than 2% in the original cord and higher than 1% before calendering.

Solution measures

(1) After cutting natural rubber, rubber drying measures should be taken, and water and volatiles should be controlled according to standards. It is forbidden to exceed the standard to reduce the moisture content in the raw rubber.

(2) When chemical raw materials and additives are stored, moisture-proof measures should be taken, especially in rainy season, rainy season and foggy weather, so as to facilitate transportation, storage, processing and other links and avoid raw materials from getting wet. Fill the prepared raw materials with plastic.

(3) The steel cord should be unpacked 1 hour before use, and the indoor humidity should not exceed the standard, so as to avoid the steel cord from being damp and being dried after gluing.

(4) The fiber cord is heated and dried before calendering, and the moisture regain of the cord before calendering is lower than 65438 0%.

Second, the factors of semi-finished parts

cause analysis

The additives in (1) rubber compound are unevenly dispersed during mixing.

(2) The stirring temperature is low, and the water is not completely volatilized. When the temperature is high, when sulfur is added to the open mill, it is easy to melt or scorch.

(3) Rubber mixture is produced and used under the condition of insufficient parking time or no parking.

(4) The rubber compound is not evenly heated, and the surface is not smooth during molding.

(5) When the rubber mixture is hot-melted on the open mill, the surface is wrapped by air, and the molded rubber mixture contains air.

Solution measures

(1) Optimize the production formula, select easily dispersible additives to replace existing additives, increase the application of processing additives such as dispersants and homogenizers, and improve the dispersibility of various additives.

(2) Production of rubber compound by two-stage internal mixer. In the first stage of mixing, the temperature is raised to make the moisture and volatiles in the raw materials fully volatilize. After the rubber compound is parked, it is mixed in the second stage, and the temperature is controlled within the temperature range of adding sulfur and accelerator to avoid short scorch time or scorch.

(3) Strictly control the parking time of semi-finished products during plastication, primary mixing, secondary mixing and molding. Let all kinds of additives fully diffuse, improve the uniformity of rubber mixture, and at the same time be conducive to the recovery of stress and strain under mechanical action.

(4) The rubber compound should be heated evenly, and the rubber compound should be mixed evenly by cutting knife, falling plate and tamping. The operation mode of separating glue supply and molding during hot smelting is adopted to improve the smoothness of the surface of molding compound.

(5) The rubber mixture is extruded by an extrusion process, so that there is no air entrapment phenomenon on the surface of the molded rubber mixture.

Third, the reasons for production and operation

cause analysis

(1) The roll profile temperature, hot melt glue supply temperature and extrusion glue temperature of the open mill are not strictly controlled, and there are bubbles on the surface of semi-finished products.

(2) There is a lot of air in cord rubber and cord rubber, which is difficult to be discharged during molding and vulcanization.

(3) The thickness and width tolerance of semi-finished parts are too large, and the weight tolerance is too large, which affects the flow of rubber compound in the mold.

(4) In the pre-forming process, when the rubber mixture is laminated, it is easy to harbor air, resulting in foaming in the rubber.

(5) The steel cord is only hung on the surface when dipped in glue, and the air content in the steel wire is high, and the gap between the steel wires is large, so it is easy to harbor air when sticking the film.

(6) When curing, the pressure is low, the density of the rubber compound is poor, and bubbles are easily generated.

(7) The temperature and time during vulcanization can't meet the technological requirements, which will also cause sulfur-deficient bubbles.

Solution measures

(1) Control the temperature and capacity of the roll profile of the open mill to prevent bubbles generated by overheating of the rubber compound from being wrapped in rubber and being difficult to remove.

(2) After calendering, a plurality of groups of cotton threads are arranged on the rubber curtains along the warp to increase the exhaust effect between the rubber curtains. Before winding, a bubble-pricking device is added to the calendered rubber cord to increase the exhaust effect between rubber cords.

(3) Modify the design of extrusion die plate to make the shape of rubber compound beneficial to the die, strictly control the structural size and tolerance of semi-finished rubber compound to prevent the product from entraining air.

(4) When multiple layers of rubber need to be stacked during preforming, the exhaust valve is pressed out of the rubber to reduce the phenomenon that air is easily trapped between rubber layers or bubbles on the rubber surface are punctured by bubbles.

(5) The steel cord is improved from dipping and pasting to extrusion coating, which reduces the air content in the steel wire in the glue and reduces the phenomenon that air is easily trapped when pasting.

(6) Set the mold cavity pressure reasonably, ensure the pressure that vulcanization should reach, and make the rubber flow and fill the mold cavity.

(7) Control the production operation in strict accordance with the specified curing temperature and time, and change manual operation into microcomputer group control production operation.

Four, equipment and mold reasons

cause analysis

(1) The temperature control system of the flat vulcanizer has a large deviation. When the temperature control is high, the mold temperature is high, which reduces the die flow time of the rubber compound.

(2) The surface of the mold is damaged and uneven, which affects the fluidity of the rubber compound.

(3) Dirt is easy to form on the surface of the mold, which affects the fluidity of the rubber compound and easily produces obvious scars.

(4) Unreasonable distribution of exhaust lines and holes in the die, thin exhaust lines and small diameter of exhaust holes affect the exhaust effect.

(5) The design of the iron tooth slot and the guide angle on the back of the die is unreasonable, which leads to the delamination of the rubber compound when it enters and cannot be discharged after air mixing. When the mold is closed and exhausted, the rubber compound is prone to vortex, turbulence and overlap here.

Solution measures

(1) The temperature measuring point and temperature sensing system of the flat vulcanizing agent are improved, so that the temperature in the mold cavity is consistent with the temperature displayed by the instrument.

(2) Repair the damaged part of the mold surface in time, and the manufacturer shall take measures to protect and prevent the mold surface from being damaged.

(3) Regularly and quantitatively clean and polish the mold surface to ensure the smoothness of the mold surface.

(4) Improve the layout of the exhaust line and vent hole of the die, so that they can run through vertically and horizontally, and the distribution tends to be reasonable. Properly thicken the exhaust pipe line and increase the diameter of the exhaust hole to enhance the exhaust effect.

(5) Optimize the design of groove and guide angle on the die side to reduce the product vortex and overlap of rubber compound here.

Through the analysis of the causes of air bubbles in rubber track vulcanization, the rectification scheme to solve the problems was formulated, the use and management of raw materials were strengthened, the processing of rubber compound was standardized, the process operation was improved and the mold design was optimized. The quality defects such as bubbles and bright scars on the surface of rubber track, between rubber layers, patterns and steel cords are obviously reduced, and the appearance quality of products is improved.

Five, analysis of the causes of bubbles in molded products

The main reasons are:

1, material problem, the rubber material has moisture during mixing, storage and use, and the moisture is not eliminated, resulting in bubbles, or the weather is wet. Most of the reasons may be that there are problems with raw materials. We have had a similar situation before, just change a batch of materials.

2. If the vent holes of the mold are improperly set or blocked, bubbles will also be generated, and the vent holes will be improperly arranged. When raw materials are mixed with rubber, air is wrapped inside the material, which leads to the material and air entering the mold together during the processing. If the mold is not equipped with an exhaust slot or exhaust process during processing, air can easily stay in the mold, resulting in bubbles or pores in the product.

3. In the production of rubber products, there are bubbles after vulcanization, which may be a problem with the rubber formula. You can find a technician to adjust the formula.

Six, rubber products have bubbles during vulcanization.

1, uneven rubber mixing and irregular operators.

2. Rubber membrane parking is not standardized and the environment is unsanitary. Management is not standardized.

3, the material has moisture (add some calcium oxide when stirring)

4, insufficient vulcanization, unfamiliar looks like bubbles.

5. Insufficient curing pressure.

6, vulcanizing agent impurities are more, small molecular impurities are decomposed in advance, and bubbles remain in the product.

7. The exhaust design of the mold itself is unreasonable, and the air cannot be exhausted in time when washing the rubber!

8. The product is too thick, the rubber is too little, and the heat transfer of rubber is slow. After surface vulcanization, the fluidity of rubber decreases, resulting in material shortage, so bubbles may appear.

9. Improper exhaust emission during vulcanization.

10, formulation problem, vulcanization system needs to be improved.

Solution:

1, prolong the curing time or increase the curing speed.

2, thin times several times before vulcanization.

3. The number of times of exhaust during vulcanization is a little more.

Seven, analysis of the causes of bubbles on the surface of rubber products.

1. moisture (add some calcium oxide when stirring);

2. Incomplete vulcanization, which looks like bubbles when it is not ripe;

3. There are many impurities in the vulcanizing agent, and small molecular impurities are decomposed in advance, leaving bubbles in the product;

4. The exhaust design of the mold itself is unreasonable, and the air cannot be exhausted in time when washing the rubber;

5. Poor dispersion;

6. The rubber compound takes a long time to plasticate, and there are bubbles when the product is vulcanized.

8. What are the causes of bubbles in silica gel molding?

1. Insufficient exhaust. After the silicone material is put into the molding die, a large amount of air will be brought in at the moment of closing the mold, and it is impossible for the air to blend with the silicone material. If the air is not exhausted, bubbles will be generated on the surface of the molded silicone button.

2. Vulcanization temperature is too low. Vulcanization temperature is an important parameter in silicone rubber molding. Usually silicone rubber products are set at 160~200 degrees Celsius. However, sometimes the mold is not heated in the vulcanizer for a long time due to the long time of mold discharging operation or other reasons, which leads to the low temperature of the silicone rubber molding mold and the low vulcanization temperature of silicone rubber, which will cause bubbles in the molded products. In this regard, we only need to increase the molding temperature, or open the empty mold into the machine to heat for a period of time to solve the problem.

3. The curing temperature is too high. Just now, I said that too low curing temperature will cause bubbles in silica gel molding. In fact, many times, too high molding temperature will also cause bubbles when silica gel is molded. Why? Personally, when the molding temperature is too high, the silica gel raw material on the surface has begun to take shape in the process of clamping and pressurizing, and the air at this time has been trapped inside, so it is difficult to discharge, so it will cause molding bubbles. Therefore, it is only necessary to appropriately reduce the molding temperature.

4. Vulcanization time is too short. Like vulcanization temperature, vulcanization time is also one of the important parameters of silicone molding, and the length of vulcanization time determines whether silicone can be completely vulcanized. If the vulcanization time is too short, it will not only lead to the softening of silica gel after molding, but also more likely to cause surface bubbles. Such defects can appropriately prolong the vulcanization time of silica gel.

5. Unreasonable mold structure and unreasonable design of silicone molding mold will also cause bubbles in silicone molding. For example, the arrangement of products in the mold, the way of division, the way of parting and the design of mold size will all cause bad bubbles, but the cost of opening a set of molds is very high and it is not easy to modify. If the bubbles in silica gel molding are caused by the mold structure, they are usually solved from the above points.