Equipment for Mechanical Processing of Milk: Separators, Homogenizers, and Filters

Mechanical processing of milk is carried out using separators: separator-clarifiers, cream separators, separators for high-fat cream, and homogenizers. These machines either split whole milk into cream and skimmed milk, clean it of contaminants, or refine the fat structure of the product.

Mechanical processing means the separation of whole milk into cream and skimmed milk with simultaneous removal of contaminants — or separation alone, or cleaning alone — together with homogenization. To remove mechanical impurities, sediment, or individual constituent components from milk and dairy products, filters and filter presses are used. In the production lines for cheese and other protein products (caseinates), centrifuges are employed.

What is a homogenizer used for?

A homogenizer is designed for the mechanical processing of milk and liquid dairy products in order to break fat globules down into smaller ones. Structurally, the homogenizer is a horizontally arranged high-pressure pump fitted with a homogenizing head.

All parts of the homogenizer are mounted on a cast-iron frame. The machine is driven by an electric motor through a V-belt transmission, whose driving pulley is fitted onto the crankshaft. The crankshaft, acting through a crank-and-connecting-rod mechanism, drives the plungers in a reciprocating motion.

How is the homogenizer built?

The homogenizer (Fig. 1) consists of a frame (1), a crank-and-connecting-rod mechanism (2), and a plunger block (7) with a homogenizing and manometric head (6). The frame houses two seats for the crankshaft bearings, three guide openings for the sliders, a mounting platform for the cylinder block, and an oil bath cast as part of the frame itself. Figure 1 — Homogenizer K5 – OGA – 1.2: 1 – frame; 2 – crank-and-connecting-rod mechanism; 3 – pin; 4 – slider; 5 – plunger; 6 – manometric head; 7 – plunger block; 8 – crankshaft; 9 – electric motor.

What does the plunger block do?

The plunger block (Fig. 2) is intended to draw the product in from the supply line and force it under high pressure into the homogenizing head. Figure 2 — Homogenizer cylinder block: 1 – block body; 2 – suction valve; 3 – discharge valve; 4 – plunger; 5 – sealing cuff; 6 – manometric head; 7 – valve body; 8 – valve seat; 9 – homogenizing valve; 10 – wedging ring; 11 – needle; 12 – pressure screw.

The homogenizing head is designed for single- or two-stage homogenization of the product, while the manometric head provides control over the homogenization pressure. The manometric head (6) consists of a housing and a pressure gauge with a hermetically sealed tube filled with transformer oil.

To cool the plungers and wash residual product from their surfaces, a drain device with a water inlet and outlet is provided. Milk enters through the inlet branch pipe, flowing in by gravity or fed by a pump into the suction cavity of the cylinder block. From there the plungers force it under pressure toward the homogenizing head.

The flow of milk out of the homogenizing head is blocked by the homogenizing valve, which is pressed firmly against its seat by a spring tightened with the screw (12). Overcoming the spring pressure, the milk pumped by the plunger pushes the valve open and passes at high velocity in a thin layer through the narrow annular gap formed between the valve and its seat.

It is at this point that dispersion — the breaking up — of the fat phase of the milk takes place. The homogenized milk leaves through the branch pipe of the homogenizing head and is directed along the pipeline for further processing or storage.

How is the homogenizer adjusted?

Adjusting the homogenizer is done as follows: the force pressing the homogenizing valve against its seat is regulated by the pressure screw (12) of the spring (Fig. 4.2), setting the required homogenization pressure, while the minimal fluctuation of the pressure-gauge needle during operation is regulated by the needle (11).

Because the homogenized product tends to form clusters of the broken-down fat globules, two-stage and even three-stage homogenization is used to prevent them from sticking together at the apparatus outlet. In two-stage homogenization, the product passes sequentially first through the slit formed by the valve and valve seat of the first stage, and then through the second. The homogenization pressure at the second stage amounts to 0.3–0.5% of the pressure in the first.

Self-check questions

1. What is pasteurization used for?
2. Pasteurization modes.
3. What is sterilization used for?
4. What equipment is used for pasteurizing milk, fermented milk products, and cream?
5. Plate-type pasteurization-and-cooling units: purpose and sections.
6. Purpose, construction, and operating principle of a pasteurization-and-cooling unit for drinking milk.
7. Purpose, construction, and operating principle of a pasteurization-and-cooling unit for fermented milk products.
8. Purpose, construction, and operating principle of a pasteurization-and-cooling unit for drinking cream.
9. Purpose, construction, and operating principle of tubular pasteurization units.
10. Classification of processing equipment for the mechanical treatment of raw materials.
11. Purpose, construction, and operating principle of the homogenizer.
12. How is the homogenizer adjusted?
13. Purpose of separators.
14. Classification of separators.
15. Main assembly units of separators.
16. Purpose, construction, and operating principle of a cream separator.
17. Purpose, construction, and operating principle of a high-fat cream separator.
18. Purpose, design features, and operating principle of a separator-clarifier.
19. Purpose, design features, and operating principle of a curd-separating separator.
20. Purpose and classification of centrifuges.
21. Construction and operating principle of a centrifuge.
22. Construction and operating principle of a continuous-action centrifuge.
23. Purpose and classification of filters and filter presses.
24. Construction and operating principle of a disc filter.
25. Construction and operating principle of a cylindrical filter.
26. Design features and operating principle of a filter press.