Rubber sheathed cables produced using traditional techniques are generally not compatible with high-end household appliances. The main reason is that the appearance of the cable is poor, and the copper wire is severely oxidized, making it unsuitable for use with household appliances. Plastic flexible cables are generally used as a substitute. With China's accession to the WTO, all product standards in China are also consistent with international IEC standards. Many household appliances require the use of rubber sheathed cables for power supply lines, such as indoor and outdoor connection lines for air conditioners, which require the use of 245IEC57 (YZW) rubber sheathed flexible cables. Therefore, improving the appearance quality of rubber sheathed flexible cables is an urgent practical problem that needs to be solved.

1. Introduction
The processing method of rubber sheathed cables. This article discusses some process parameters in the production process of rubber sheathed cables and deduces a complete set of sulfur vulcanization process parameters to continuously improve the product quality of rubber sheathed cables, providing reference for colleagues in the cable industry.

2. Determination of specifications
Generally, the technical specifications for continuous vulcanization units specify the size range of the mold, that is, the minimum aperture of the mold core and mold sleeve, which is one of the basis for determining the specifications. In addition, the range of screw speed is also specified. When extruding rubber, if the screw speed is lower than the specified speed, the rubber plasticity will be uneven, the flowability will be poor, the extrusion amount will not be stable enough, the cable processing will be difficult, and the pressure inside the machine head will be high, which can easily damage the machine head.

If it exceeds the range and the rubber extrusion amount is insufficient, the output speed can only be reduced to make up for it, which affects production efficiency.

3. Determination of screw speed and traction speed

The screw speed and traction speed determine the production efficiency and the outer diameter and appearance of the product. The basic principle for determining the screw speed and traction speed is the principle of material balance, which means that the amount of rubber extruded by the screw is equal to the amount of rubber required to wrap the product being pulled out.

Generally speaking, when determining the screw and traction speed, the traction speed, that is, the vulcanization time, is first determined. It is the main factor that determines the mechanical and physical properties of the product. This article will provide a detailed introduction.

The continuous vulcanization extruder screw adopts a plasticizing screw with a length to diameter ratio of 12:1 or more. The return amount between the screw and the cylinder is small, and the screw speed is basically proportional to the extrusion amount, that is, there is a linear relationship.

For example, the technical specifications of a certain rubber extrusion unit stipulate that the screw speed is 10-50rpm/min and the maximum extrusion rate is 120kg/h.

Based on these data, a relationship chart between screw speed and extrusion volume can be created.

For example, for a certain product with extruded sheath, the theoretical calculation of sheath material consumption is 78.7 kg/km, and the output speed is 20m/min. The material consumption per minute can be calculated as follows:

Material usage=20 × 78.7 ÷ 1000=1.574 kg/min

According to the principle of material balance, the rubber extrusion rate also requires 1.574 kg/min. According to Figure 1, the screw speed is around 39 revolutions per minute, which is within the speed range specified in the equipment specifications and meets the technical specifications of the equipment. According to this method, the screw speed and traction speed for producing various specifications of the equipment can be determined.

The temperature in the feeding section of the fuselage is generally controlled to be lower, about 30-40 degrees. If the temperature is too high, there may be a phenomenon of material return, and the rubber is prone to burning.

The temperature of the machine head should be determined according to the type of rubber and the residence time of the rubber material in the body, generally between 60-70 degrees. The temperature of the middle section is determined by gradually decreasing the temperature of the machine head, usually between 40-50 degrees. Continuous sulfurization feeding generally adopts cold feeding, and the rubber sheet thickness is controlled between 0.5-1.0mm. If hot feeding is used and cut into strips, it is also very good

5. The steam pressure and outlet speed are indeed

Steam pressure and outlet speed are important parameters for sulfur continuous operation, which are related to the mechanical and physical properties, appearance quality, production efficiency, etc. of the product.

Chemical reaction kinetics states that when the reaction concentration remains constant, the reaction rate increases by approximately 2-3 times for every 10K increase in temperature. Alennius summarized a large number of experimental facts and pointed out the relationship between reaction rate constant and temperature:

k=A·e-E/RT

In the formula: k - reaction rate constant;

E - Reaction activation energy;

R - gas constant;

T - Absolute temperature, K;

E - the base of the natural logarithm (e=2.718).

This formula has difficulties in practical use. The relationship between practical rubber reaction rate and temperature can be calculated using the following formula:

V2=V1 2 0.1(t2-t1

Reaction speed at V1 and t1;

Reaction speed at V2-t2;

T1, t2- Temperature (℃);

2-- Temperature coefficient

These theories all propose that for every 10 ℃ increase in rubber vulcanization temperature, the vulcanization rate doubles, that is, the vulcanization time is shortened by twice.

We usually have the production and technical parameters for can vulcanization, and we should have a good understanding of the various vulcanization parameters of a mature rubber formula. Calculate the saturated vapor pressure during continuous vulcanization based on the temperature under the saturated vapor pressure of the tank type vulcanization, and then determine the vulcanization time and outlet velocity.

For example, a continuous vulcanization unit with a continuous vulcanization pipeline length of 50 meters produces cable outer sheaths. According to mature rubber formula vulcanization process parameters, the vulcanization time is 15 minutes at 4kg/cm2 (151 ℃). If produced on a continuous vulcanization unit with a sheath outlet speed of 25 meters, what is the steam pressure for continuous vulcanization.

First, calculate the time required for continuous vulcanization as 50/25=2 minutes. According to the relationship that for every 10 degrees increase in temperature, the vulcanization time is reduced by half. Calculate that the time multiplier is three times. The temperature needs to be increased by 30 degrees. That is to say, the temperature for continuous vulcanization is 181 degrees.

The higher the steam pressure of continuous vulcanization, the faster the vulcanization rate, and the production efficiency will also be greatly improved. Practice has proven that it is not the infinite increase in steam pressure that can improve the speed of continuous vulcanization.

How to determine the maximum value of sulfur vapor pressure (i.e. sulfurization temperature). After analysis, the product undergoes high steam pressure and high vulcanization temperature on the outside of the sulfur pipe during vulcanization. The small amount of low boiling point volatile matter in the air inside the product and the gas generated during vulcanization will expand. In the vulcanization pipe, the internal and external pressures cancel each other out and generally do not expand.

When the terminal seal enters normal pressure, the interior of the product cannot cool quickly and is still in a high-temperature expansion state. The gas inside will rapidly expand. If the radial stress of the product cannot withstand the internal pressure, it will bubble and, in severe cases, crack. If the rubber mixing is uneven, this phenomenon is even more pronounced.

If the product is treated as a pressure vessel at the moment of terminal sealing, this article summarizes a set of formulas for the highest sulfur vapor pressure:

δ=P · D within/(2 [σ] t-P

In the formula: δ - the thinnest point thickness controlled by the product, mm ;

P - maximum sulfurization steam pressure, MPa ;

D - the outer diameter of the product before extrusion, mm ;

[σ] T ---- Radial stress of the product at vulcanization temperature, N/ mm 2 。

Among them, the radial stress [σ] t of rubber at the vulcanization temperature is lower than the axial original expansion strength of the product. The stress during foaming can be used to calculate the sulfurization vapor pressure during foaming, the stress during cracking, the sulfurization vapor pressure during foaming, the stress during cracking, and the sulfurization vapor pressure during cracking. The determination of [σ] t can be based on a combination of factors such as the tensile strength of the product, the thermal deformation of rubber at high temperatures, and the relatively low radial tensile strength. Based on the sulfurization steam pressure, i.e. sulfurization temperature, the sulfurization time, i.e. the line velocity, can be calculated. At the same time, the tightness of filling the gaps in the cable core should also be considered.

For example, a certain heavy-duty rubber sheathed cable has an outer diameter of 38.5mm, an average thickness of 5.0mm for the sheath, and a thinnest point thickness of 4.15mm. The sheath material is a natural/styrene butadiene rubber SE3 rubber mixture, with a tensile strength of 8.4N/mm2. The radial tensile strength is generally 60% of the axial tensile strength, that is, the radial tensile strength is 5.04 N/mm2. By substituting the above formula, the maximum continuous vulcanization steam pressure can be calculated as:

4.15=P× 38.5÷(2×5.04- P)

P=0.98 N/mm

The steam pressure of the heavy-duty rubber sheathed cable is 10kg/cm2

Given the maximum steam pressure, the maximum outlet velocity of the product can be calculated using the vulcanization rate formula.

The wire speed of thicker products also needs to consider the heat transfer speed of rubber. The heat conduction formula of rubber is:

Q = λ A [ ( t1 - t2 )/ δ ]

In the formula: Q - Thermal conduction heat flow rate, W;

λ - Thermal conductivity of rubber, W/(m ·℃);

A - Unit heat transfer area, mm 2 ;

T1, t2- external temperature, internal temperature, ℃;

δ - thickness, m 。

In the above equation, the thermal conductivity λ of rubber remains unchanged, the unit heat transfer area A remains basically unchanged, and the thermometers t1 and t2 required for internal and external vulcanization of rubber products remain unchanged. It can be seen that the thermal conductivity Q is inversely proportional to the thickness over δ. To achieve the same sulfurization effect, the wire speed needs to be doubled when the thickness is doubled. Of course, this is a theoretical statement that still needs to be verified through practice.