Rubber products defects and solutions

- Oct 03, 2019-

Defects in rubber products


cause


solution


First, rubber-metal bonding is poor


1. improper selection of glue


Refer to the rubber design manual to select the appropriate adhesive;


2. The metal surface treatment fails, so that when the primer coating is vulcanized, it can not be physically adsorbed with the metal surface.


1. Roughen the metal surface to ensure that the primer is smoothly adhered to the metal surface when it is vulcanized. The commonly used treatment method is: metal insert blasting and shot blasting in the product;


2, the metal surface can not be rusted, can not be stuck with oil, dust, water droplets and other impurities;


3. The process of the glue coating process is poor, the glue is too thin, the leakage coating, the less coating, the residual solvent, etc.


1. Pay attention to the surface coating operation to prevent the glue from leaking and coating. The importance and influence of the surface coating (the surface film formation of the coating is related to the surface tension of the coating, gravity, construction mechanical force, the interaction between the materials and the chemical reaction force) Therefore, the quality of the topcoat is affected by these forces. It is extremely important to use different techniques, superb skills and skilled craftsmanship.)


2. The metal parts coated with the glue should be fully dried to allow the solvent to fully evaporate to prevent the residual solvent from volatilizing during vulcanization, resulting in failure of bonding;


3, to ensure a certain thickness of the coating on the metal surface. In this way, on the one hand, it can ensure that sufficient glue on the metal surface and the rubber entering the cavity mutually diffuse and co-crosslinking fully, so that the metal surface is fully bonded with the vulcanized rubber; on the other hand, the metal surface to the surface of the product A certain modulus gradient layer can also be achieved to provide a soft to hard progression between the rubber surface of the article and the metal insert. (stiffness gradients) The beneficial gradient of the elastic and rigid ratio of the rubber section;


4. The formula is unreasonable, the vulcanization rate of the rubber compound is inconsistent with the vulcanization rate


(Recipe refers to the compound formula and glue formula)


1. Improve the formula to ensure sufficient scorch time;


2. Improve the mold and formula of the product to ensure that the rubber material reaches the bonding part of the metal insert at the fastest speed;


3. Try to use ordinary and semi-effective vulcanization systems (the fatigue resistance of different vulcanization systems and the heat-resistant oxygen aging properties are obviously different. In general vulcanization systems, the ratio of accelerator to sulfur varies from small to large, and the vulcanization system consists of The ordinary vulcanization system transitions to the semi-effective vulcanization system to the effective vulcanization system. The vulcanized rubber network structure is transformed from polysulfide crosslinks to polysulfide bonds, disulfide bonds and monosulfide bonds. It is a brittle structure mainly composed of monosulfide bonds and disulfide bonds. The physical and chemical properties of general rubber products can be better adapted to production in the first two vulcanization systems.), increasing the amount of sulfur (relatively speaking, not the more More is better) to achieve polysulfide crosslinks;


4. Improve vulcanization conditions (temperature, time and pressure);


5. Reduce the use of easy-to-spray and plasticizers to prevent migration to the rubber surface during vulcanization, thereby affecting the bonding;


6, the rubber material parking time is too long, contact with the air to produce a certain physical and chemical reaction, resulting in rubber vulcanization failure. Need to use fresh rubber.


5. Under pressure


1. Increase the clamping pressure during vulcanization


2. Pay attention to the position and size design of the overflow port and the vacuuming groove to prevent the pressure in the cavity from being released through the pressure, resulting in insufficient pressure during vulcanization of the product;


3, to ensure that the mold is closely matched to prevent excessive pressure loss;


6. The active ingredient of the glue is volatilized or cured.


1. Metal parts that need to be pre-baked before vulcanization should pay attention to the time and temperature control of pre-baking. Excessive pre-baking will lead to volatilization of reactive substances and scorch (or curing) of the glue; (baking: heating and drying)


2. Pay attention to prevent the metal parts from staying in the mold for too long during operation;


7. Vulcanized rubber, rubber and other foreign matter are mixed into the rubber compound and vulcanized with the rubber compound, causing a small area of debonding of the metal insert and the rubber compound during vulcanization, thereby causing large-area peeling of the product.


Strengthen material management


Second, the big bubble


1. The product is not sufficiently vulcanized, resulting in large bubbles on the surface of the rubber product, and the inside is cut into a honeycomb sponge.


1. Extend the vulcanization time, increase the vulcanization temperature, and ensure sufficient pressure during vulcanization;


2. Adjust the formula to increase the vulcanization speed;


2. Rubber-metal bonding failure causes a large amount of gas to remain in the bonded portion, and the gas contracts when pressurized. Once the pressure is removed, the gas diffuses, and a thin layer of rubber and a large area of air bubbles appear between the rubber and the metal.


Solved by the method described in the above rubber-metal bonding failure;


3. There is gas trapped in the rubber, the gas is not easy to remove, and vulcanizes with the rubber, so that bubbles appear on the surface of the product.


1. Increase the number of deflation after mold clamping;


2. Vacuuming the mold;


3. Increase the temperature of the rubber compound;


4. Rubber with higher Mooney viscosity; (Mooney viscosity is measured by Mooney viscometer, Mooney viscometer is a standard rotor, with constant speed (generally 2 rpm), sample in sealed chamber The rotation of the rotor is related to the change of the viscosity of the rotor during the vulcanization process. It can be displayed on the dial in Mooney by the force measuring device, and the value can be read at the same time interval. Mooney vulcanization curve, when the Mooney number first rises and then rises, the time when the unit rises by 5 units from the lowest point is called the Mooney scorch time, and the time from the Mooney burnt point rises again by 30 units is called the Mooney vulcanization time. .


 


The Mooney viscosity reaction rubber has good processing properties and a high molecular weight and a wide distribution range. Mooney viscosity high rubber is not easy to mix and extrude, and its molecular weight is high and the distribution range is wide. Mooney viscosity low-size adhesive roll, which has low molecular weight and narrow distribution range. When the Mooney viscosity is too low, the tensile strength of the product after vulcanization is low. The Mooney viscosity-time curve also shows the performance of the compound vulcanization process. )


5. Pick up the bubbles on the rubber compound before feeding; (more original)


6, improve the mixing process of the open mill, try to avoid gas mixed into the rubber;


7, improve the pressure injection conditions, so that the rubber can enter the mold cavity slowly; (generally not desirable, easy to produce lack of glue phenomenon)


8. Improve the exhaust groove and overflow groove of the mold;


4. Volatile matter in the compound formula


1, pay attention to adjust the appropriate vulcanization conditions, the temperature should not be too high;


2, should pay attention to the moisture-proof work of all kinds of rubber before use, if necessary, can be dried; (vulcanizing machine with a large role of the oven)


3. Reduce or eliminate the use of raw materials for gas small molecular substances during vulcanization;


4. Reduce the use of low boiling plasticizers, filling oils and softeners;


 Third, thin skin bubbles


1. Vulcanization conditions, improper vulcanization agent


1, pay attention to the vulcanization conditions of the rubber, the temperature should not be too high


2, the appropriate adjustment of the proportion of accelerators, should not be too high


2. Volatile matter in the compound formula


Strengthen material management;


3. The plastic bag containing some rubber raw and auxiliary materials in the mixing process is not completely melted and is not evenly dispersed in the rubber compound.


Increase the mixing temperature; (considering taking out the plastic bag)


Fourth, the rubber surface is sticky


1. The mold cavity partially retains gas, which affects heat transfer and heat vulcanization of the rubber compound.


1. Vacuum the mold to ensure that the rubber enters the cavity in a vacuum state. Ensure that the vacuum pressure is applied and the gas in the mold is fully extracted;


2. Increase the number of deflation after mold clamping;


3. venting groove or overflow tank on the mold;


2. The mold cavity is asymmetrical, with dead angles, uneven heat transfer leads to uneven vulcanization.


1. Adjust the compound formula and use the compound with a long flattening curve;


2. Adjust the vulcanization conditions, extend the vulcanization time or increase the vulcanization temperature;


3. The rubber is extruded or calendered into the gas.


Improve the extrusion, calendering conditions and process of the rubber compound;


Five, lack of glue


1. Use too little glue


1. Increase the amount of glue used; 2. Adjust the injection hole to ensure sufficient injection; (Injection hole refers to the mold into the rubber port)


2. The overflow port is too large, so that the rubber cannot fill the cavity, overflowing from the overflow port or the position of the overflow port is incorrect.


1. Change the size of the small overflow port or reduce the number of overflow ports;


2. Reasonably choose the location of the overflow port;


3. The amount of release agent is too much, so that the rubber can not be closed at the junction of the cavity.


1. Reduce the amount of release agent;


2, pay attention to the rubber can not be stained before use;


4. The vulcanization speed of the rubber material is too fast, and the rubber compound is vulcanized when it is not filled with the cavity, so that the fluidity of the rubber material is deteriorated, and the rubber compound cannot fill the cavity.


1. Adjust the rubber compound formula to extend the scorch time;


2. Increase the size of the inlet or increase the number of inlets;


5. The design of the mold inlet is unreasonable, and the rubber cannot fill the cavity.


Improve the mold;


6. The rubber is too hard or the fluidity is not good, and it has been vulcanized without filling the cavity.


Improve the compound formulation or increase the pre-plastic temperature and increase the fluidity;


6. Deep edges and thick edges


1. The rubber scorch time is insufficient, and it is easy to form vulcanized rubber particles and rubber chips.


1. Extend the scorch time of the rubber; 2. Adjust the vulcanization time (lower the temperature and prolong the vulcanization time);


3. Avoid using rubber materials that have been parked for too long;


2. The process is unreasonable, too much rubber can not overflow, vulcanization is preceded by vulcanization on the surface of the product to sandwich it between the parting surface and other parts.


1. Try to adopt mold transfer and transfer molding; (flat vulcanizing machine products do not belong to this type). The compound transfer molding process is to close the mold before feeding, and the raw materials are heated in a separate feeding chamber, which is in a molten state, and then Under the action of pressure, the casting system of the mold is pressed into the cavity at a high speed, and continues to be heated and pressed in the cavity to be solidified. It is the same as the stamping machine of the flat vulcanizing machine, and has a feeding chamber and a cavity, which are all pressed on the hydraulic machine. The main differences are:

(1) The rubber material transfer molding is first molded and then cast, and the compression molding is firstly added and then closed, and heated and pressed in the cavity.

(2) The transfer mold has a gating system, and the compression mold has no gating system.


2. The rubber compound should accurately weigh the feeding material;


3. Mold contamination, rubber is not clean


Clean molds and compounds;


4. The mold parting surface is not tightly matched, the design is unreasonable, and the overflow port is too large.


Improve the mold, the parting surface should avoid the sensitive position such as the bonding part of the product;


5. The heat transfer rate of the rubber compound is slow. The temperature of the inner and outer layers of the rubber compound is inconsistent during vulcanization, the outer rubber compound has been vulcanized, and the inner rubber compound is thermally expanded. The forced overflow causes the shrinkage cavity interlayer.


1. Improve the compound formula;


2. Improve the vulcanization process conditions, such as low temperature vulcanization for a long time. (especially thick products);


 Seven, spray cream


1. Excessive amount of raw materials such as vulcanizing agent, accelerator, active agent, etc., the solubility in the rubber is saturated, and it slowly migrates to the rubber surface.


Through testing, reasonable control of the amount of various raw materials;


2. The product is not vulcanized enough, and the sulfur is not enough (one of the three items of pressure, temperature and time is not satisfied or many are not satisfied)


Fully vulcanized; (improved pressure, temperature, time)


Eight, layering


1. Rubber surface contamination, especially oil stains


Clean the surface of the compound or replace it with a clean compound;


2. Spraying


Solved according to the method described in the seventh item above;


3. Poor compatibility of different rubber blends unevenly


Select a good compatibility rubber in the formulation design;


Nine, tearing, pulling hair


1. The mold release method is unreasonable, and the mold release is hard, which causes the product to be torn or pulled.


1. Improve the demoulding mode and improve the mold structure; 2. Spray release agent;


2. The product is excessively vulcanized, causing the physical properties such as rubber strength to drop and being torn.


Adjust the vulcanization conditions to positive vulcanization;


3. The vulcanization temperature is too high


Adjust the compound formula to reduce the vulcanization temperature;