Molded products: are small and medium-sized rubber products that are molded and vulcanized on a flat vulcanizer.

The same type of problems that occur in rubber molding are reflected in different products, such as: lack of rubber, bulging and so on. Due to the different types, batches and origins of rubber materials, machines and operators, it can only be analyzed on a case-by-case basis.

1. Lack of glue

Performance of the surface (all or local) loose, pockmarked or hollow, the causes and prevention methods.

(1) Insufficient amount of material added To ensure that there is no shortage of glue in each cavity, the amount of material used should be accurately determined, added to the full amount of material and reflected in the process documentation.

(2) Insufficient pressure, the amount of glue can not fill the mold cavity, the pressure should be increased appropriately.

(3) The liquidity of the adhesive is too poor. If the performance of the product allows, adjust the rubber formula to increase plasticity. Increase the pressure or apply a layer of lubricant such as zinc stearate or silicone oil on the surface of the mold.

(4) The mold temperature is too high, and the rubber is partially scorched and the fluidity is reduced. Should be appropriate to reduce the temperature of the mold when loading, but should not be too much, otherwise the mold temperature in the specified time can not rise to the vulcanization temperature and make the whole mold rubber scrap. Silicone rubber can be loaded at a lower temperature.

(5) The scorching time of the rubber is too short. The formula should be improved to enhance the scorching resistance of the rubber.

(6) The speed of loading and closing the mold is too slow, causing scorching and burning, and the operation technique should be improved.

(7) Improper placement of the blank makes the rubber not easy to fill the cavity.

(8) The mold structure is unreasonable, also will make the rubber is not easy to fill the mold cavity such as: for narrow products, should facilitate the product length direction and the direction of pressure perpendicular.

(9) Pressurization is too fast, the rubber is extruded out of the mold before filling the cavity, so that the flying edge thickens and the product lacks material, the pressurization speed should be slowed down, and the rubber slowly flows into the cavity under pressure.

2. Cracking of the buttress line

The performance of the mold after the start-up in the mold at the product cracking, sometimes flying edge shrinkage phenomenon (commonly known as edge extraction), the causes and prevention methods.

(1) Insufficient pressure or pressure fluctuation Make the internal pressure of the rubber cavity during the vulcanization process is greater than the vulcanization pressure. And make the mold slightly up, causing the product cracking, should check the pressure or check the pressure fluctuation reason.

(2) The vulcanization pressure is too large. The rubber is seriously compressed, when the mold is opened, the pressure drops sharply, the volume of vulcanized rubber increases, the other part of the product is restricted by the mold can not expand, and the mold is free to expand at the mold line, the internal stress caused by uneven expansion will lead to cracking of the line, the vulcanization pressure should be adjusted to a suitable state, to prevent too large and too small. If the flying edge is thickened after the pressure is lowered, the amount of material added can be reduced or the flow groove can be increased as appropriate. (Cool down under pressure and get out of the mold).

(3) High vulcanization temperature and short time cause the main reason of thick products, after the external vulcanization of the products, due to the slow heat transfer of the rubber, the internal is still in the unvulcanized state, if the pressure is lowered to start the mold, the internal vulcanization reaction in the play of the material will quickly overflow, and at the same time, due to the temperature drop, the rubber shrinkage is serious (compared with the complete vulcanization of the rubber shrinkage rate is larger). These two factors make the cracked edge at the mold line, should be adjusted to the vulcanization conditions, using low temperature and long time vulcanization method or phased warming vulcanization method.

(4) The local looseness at the mold line and the small bonding strength between the adhesive materials are the common reasons for the local cracking at the mold line. There are many reasons for local looseness, such as poor mold closing, too much glue flowing from the gap, improper material release method. It is not obvious that there is a lack of glue in a certain part of the line; the mold structure is unreasonable (the direction of the line is parallel to the pressure direction is a typical unreasonable structure, should be avoided), the glue is too hard, etc. Specific problems should be analyzed and improved.

(5) Slow pressure too late. If the surface of the rubber has been vulcanized and then slow pressure, often make the pair of lines cracked.

3. Puffy, porous or spongy

Causes and prevention methods

(1) The vulcanization is not sufficient. The temperature is too low or time is too short, so that the volatiles generated by the vulcanization are not eliminated cleanly, the cause should be identified and corresponding measures should be taken.

(2) Insufficient vulcanization pressure, the gas and vulcanization volatiles retained in the mold cavity cannot be discharged in time, and the pressure should be increased appropriately.

(3) pressurize too fast, close the mold quickly, the gas can not be discharged, should be slowly pressurized, so that the mold slowly closed.

(4) Improper or no venting of the slow pressure (commonly known as venting). For most products need to exhaust. Timing, too early or too late have been inappropriate exhaust, but also bring other bad.

(5) unreasonable mold structure For complex structure products, should be used more block mold, using other from the mold seam escape; easy to appear air holes can be added to open the air running slot, the upper template wall cavity should not be too deep.

(6) Improper loading method, the air in the cavity is not easily discharged. For the mold with complex structure and dead ends, the material should be evenly distributed in each position of the cavity when it is put in the mold.

(7) Air and moisture are trapped in the rubber. This is usually caused by improper heat refining or storage. You should improve the quality of hot refining and keep the mixed rubber well. Seal or dry it.

(8) high vulcanization temperature, premature vulcanization of the rubber surface, preventing the free precipitation of air, water vapor and volatile components in the rubber, especially thick products rubber. Measures with 2.(3)

(9) Inadequate loading In addition to causing a lack of glue on the surface of the product, it can also make the interior not dense and have air holes.

(10) The vulcanization speed of the rubber is too fast and the internal volatiles cannot be precipitated to harden. The formula should be adjusted to improve the induction period of the rubber.

4. Delamination and cracking

Production causes and prevention methods

(1) return to the rubber (after mixing the rubber material is not used up and mixed with the new rubber material, this rubber material is called return to the rubber) and the new rubber material mixing when the refining is not uniform, resulting in inconsistent vulcanization degree of layering. Increase the number of thin pass, mixing evenly.

(2) The rubber or mold is contaminated by grease and other impurities. Layer the contaminated area, protect the rubber and clean the mold cavity.

(3) spraying too much mold release agent, so that part of the immersion in the rubber, resulting in products delamination, cracking, as little as possible to spray or not spray.

(4) Uneven mixing or spraying frost Spraying frost is a physical phenomenon of rubber compounding agent (such as vulcanizing agent, antioxidant, plasticizer, etc.) precipitating from the rubber. Unvulcanized rubber and vulcanized rubber can occur, rubber in the mold before the immersion if you can not well eliminate the spray frost phenomenon, the parts of the product can not be well integrated, and in the spray frost parts cracking or layering. Preventing method, fully mixing before use, can not be parked for too long.

(5) The plasticity of the rubber is too poor. The heat refining is sufficient and the vulcanization is as high as possible.

5. Demoulding cracks

This defect refers to the tearing of the product in the process of demolding, the tearing area varies due to different reasons for tearing, the causes and prevention methods are as follows.

(1) over sulfur because over sulfur products are not flexible enough, easy to cause mechanical strains when out of the mold, in general, appropriate to reduce the vulcanization temperature to shorten the vulcanization time, can solve such problems

(2) The mold temperature is too high when demoulding The rubber molecules are still in violent movement, and when they encounter cold air, they will be cooled locally first and form internal pressure with the post-cooling flying part, which will easily cause demoulding cracks. Silicone rubber has more such defects.

(3) Not using the release agent or the amount of release agent is not enough

(4) The method of mold exit is improper and should be improved.

(5) The mold structure is not reasonable.

(6) The mold cavity is poorly processed or used for a long time, which increases the difficulty of mold exit.

(7) The choice of material is unreasonable, should use good tear strength, elongation of rubber materials, such as NR.

6. Spray frost

Vulcanized products spray frost, production causes and prevention methods.

(1) Insufficient vulcanization, more vulcanizing agent for complete reaction and precipitation of the product surface.

(2) The amount of a certain compound is too much, exceeding the solubility of vulcanized rubber, the formula should be adjusted.

(3) Uneven mixing of the compound.

(4) The storage temperature of the product is too low, and the solubility of the compound in the rubber is reduced.

7. Distortion and deformation

Causes and prevention methods

(1) the vulcanization department is not sufficient, the material plasticity, out of the mold due to mechanical force to make it distortion deformation, vulcanization is not sufficient products, after the vulcanization phenomenon is also more serious, in the post-vulcanization process can also occur deformation.

(2) uneven vulcanization First, the product is too thick, uneven vulcanization inside and outside, the internal continue to vulcanize, the product deformation, the same measures as 2 (3). Second, the temperature of the upper and lower plate is not consistent, resulting in differences in the degree of vulcanization of various parts of the vulcanized products, causing deformation.

(3) out of the mold temperature is too high rubber still has a large plasticity, easy to deformation under the action of mechanical forces, with 5 (2)

(4) For products with metal parts, the size of the metal parts is not qualified. Although the rubber can be placed in the mold cavity with its elasticity, it returns to its original state immediately after leaving the mold, resulting in deformation of the whole product.

(5) Products with clamped fabric Because the shrinkage rate of fabric and adhesive are different. Deformation due to uneven shrinkage after cooling out of the mold.

(6) wall thickness difference, cooling shrinkage speed is not the same, easy to make the thin wall part of the deflection deformation. Metal products pure rubber thin part out of the mold is also easy to cause deformation. Fixed cooling.

(7) Improper protection and preservation.