Standard Operating Methods for Mixing Units

Improper operation of hot and cold mixing units in plastic processing may affect product quality, equipment service life, and even cause safety hazards. The following key points should be noted during use:

I. Preparation and Inspection Before Startup

1. Equipment Status Check

• Check whether there are foreign objects (such as tools, impurities) in the pots and stirring paddles of the hot mixer and cold mixer, and whether the inner walls are clean, to avoid residual materials affecting the mixing quality of new batches.

• Ensure that all connecting parts (such as stirring shaft seals, discharge valves) are tight to prevent material leakage or splashing.

• Inspect the smoothness of the heating system (heating jacket and heating coil of the hot mixer) and cooling system (cooling jacket and circulating water pipeline of the cold mixer), and check whether the heating medium (such as heat-conducting oil) or cooling water is sufficient, so as to avoid failure of heating/cooling due to energy shortage.

• Test whether the transmission system (motor, reducer, belt) is normal, whether there is abnormal noise or jamming, and whether the lubricating oil/grease is sufficient, to ensure the stable rotation of the stirring paddles.

2. Parameter Setting and Material Preparation

• Preset the hot mixing temperature, time, stirring speed, and cooling temperature of the cold mixer according to the material characteristics (such as resin type, additive ratio), to avoid material overheating decomposition or insufficient cooling agglomeration caused by incorrect parameters.

• Materials need to be screened in advance to remove metal impurities, large particles, etc., to prevent damage to the stirring paddles or impact on mixing uniformity.

II. Operational Specifications During Operation

1. Key Points for Hot Mixer Operation

• When feeding, follow the order of "adding main materials first, then auxiliary materials" (e.g., adding resin first, then plasticizers, stabilizers, etc.) to prevent additives from       decomposing in advance due to local high temperatures.

• Overloading is prohibited. The material height should not exceed 2/3 of the pot to prevent material overflow during stirring or motor burnout due to excessive load.

• Monitor the hot mixing temperature in real-time. If the temperature rises abnormally (e.g., exceeding the material decomposition temperature), immediately stop heating and open the pot cover to cool down, and check for faults in the heating system (such as thermostat failure).

• If abnormal noise or violent vibration occurs during stirring, stop the machine immediately for inspection. Possible causes include loose stirring paddles, material jamming, or bearing wear. Operation with faults is strictly prohibited.

2. Key Points for Cold Mixer Operation

• Before discharging the hot-mixed materials into the cold mixer, ensure that the cold mixer has been started in advance to avoid difficulty in stirring caused by material accumulation at the bottom.

• Maintain stable flow and temperature of the cooling circulating water (usually the water temperature is controlled at 20-30℃). If the cooling effect decreases (e.g., slow material cooling), check whether the water pipes are blocked or the jacket is scaled, and clean them in time.

• Do not open the pot cover during cold mixing to prevent cold air from entering, which will affect the cooling efficiency, and avoid material splashing and hurting people.

3. Material Transfer and Connection

• Before discharging the hot-mixed materials into the cold mixer, confirm that the cold mixer is ready to avoid overheating of materials due to long-term retention in the hot mixing pot.

• Observe the material state during transfer. If abnormalities such as agglomeration or discoloration are found, stop the transfer and check the causes (such as uneven hot mixing, mixing of impurities).

III. Maintenance and Cleaning After Shutdown

1. Equipment Cleaning

• After each use, timely clean the inner walls and stirring paddles of the hot mixing pot and cold mixing pot. If residual materials are caked due to long-term high temperature or cooling, they will affect the next mixing effect and may corrode the pots (especially when corrosive additives are contained).

• Power off during cleaning, and use special tools (such as plastic scrapers). Avoid scratching the stainless steel inner wall with hard metal tools, which may cause material residue or pot rust.

2. System Shutdown and Maintenance

• After shutdown, turn off the stirring motor, heating/cooling system in sequence. Cut off the main power supply after the equipment stops completely to avoid current impact during the next startup.

• Regularly (e.g., weekly) check the sensitivity  of temperature control components such as heating coils and thermocouples to prevent temperature out of control; if cooling water is used in the cold mixer jacket, regularly clean the scale (descaling agents can be added) to ensure cooling efficiency.

IV. Safety and Personnel Specifications

1. Safety Protection

• Wear protective equipment (such as high-temperature resistant gloves, goggles) during operation to avoid contact with the high-temperature surface of the hot mixing pot or splashing materials.

• Do not open the pot cover or put hands into the pot when the equipment is running. During maintenance, power off and hang the "No Switching On" sign.

• If the hot mixer is heated by gas, check the tightness of the gas pipeline to avoid leakage and fire; fire extinguishers and other fire-fighting equipment should be equipped in the workshop.

2. Personnel Training

• Operators should be familiar with the equipment operating procedures and understand the characteristics of different materials (e.g., the decomposition temperature of PVC resin is about 160℃, so the hot mixing temperature must be strictly controlled) to avoid material scrapping or equipment damage caused by misoperation.

V. Long-Term Maintenance

• Regularly (e.g., monthly) check the wear of the stirring paddles. If the paddles are deformed or severely worn on the surface, replace them in time; otherwise, the mixing uniformity will be affected.

• Change the lubricating oil of transmission components such as reducers and motors regularly according to the instructions to prevent component wear due to insufficient lubrication.

• Clean idle equipment thoroughly, apply anti-rust oil on the inner and outer surfaces of the pots, and cover with dust covers to avoid moisture or impurities entering.

By following the above standard operations and maintenance, the service life of the hot and cold mixing unit can be effectively extended, the stability of product quality can be ensured, and safety risks can be reduced.