Grease - Lubrication
Due to the high viscosity, progressive central lubrication is selected for the lubricant "grease" in most cases. Exceptions are provided, for example, by relubrication distributors, which will not be discussed in detail here. Grease central lubrication systems are always operated with piston pumps.
Features of a progressive system
Universally applicable with regard to operating mode and lubricant
Central function monitoring of all distribution points possible with little effort
Robust construction of the distributors
Low susceptibility to failure due to fitted pistons
Exact distribution of the lubricant even with back pressure at the lubrication points
Possible pressures for oil circulation systems 30 - 100 bar, for grease systems up to 200 bar
The principle.
The lubricant is supplied by the pump via main and sub-distributors in precisely metered quantities progressively (i.e. progressively) in a fixed sequence to the lubrication points. A lubrication point is assigned to each outlet of a distributor, but several outlets can be combined into one even if a larger quantity of lubricant is required (crossporting connection). A characteristic feature of the progressive distributor is that the lubricant can only leave the respective metering chamber when the chamber in front of it has discharged its contents. This principle allows - with little additional effort - a central function monitoring of the entire system.
Design
A progressive system consists of a feed pump and one or more progressive distributors. Each lubrication point outlet may only be connected to one lubrication point. Up to 20 lubrication points can be supplied from one progressive distributor, depending on the design. If more lubricating points have to be connected, one or more sub-distributors must be arranged behind the main distributor to reach the required number of outlets. In case of a very large number of lubrication points or unfavourable position of lubrication points on moving machine parts, it may be necessary to connect another sub-distributor to the sub-distributor. This is possible if correctly designed for oil systems, but is not recommended for systems for grease. A parallel connection of several progressive distributors leads to uncontrollable lubricant splitting and is therefore not permissible.
Sub-distributors are also used if the lubricant requirements of the individual friction points are so different that these ratios cannot be achieved by the dosing possibilities of a progressive distributor.
An adjustment of the lubricant requirement to the mode of operation of the machine can be achieved by using an electronic control unit with which the lubrication interval can be shortened or extended.
The piston detector can be used to control the lubrication cycle time and monitor the function of the system
The maximum number of lubrication points for a progressive system, consisting of a main distributor and sub-distributor, is about 100.
For larger machines and plants, e.g. transfer lines, transfer presses, beverage filling machines, it is advisable to divide the plant into several separate (controllable) lubrication sections (lubrication circuits). Leakage-free seat valves are used for this purpose in oil and grease systems. Individual sections can be switched on or off by the control system. The lubricant requirement can be adapted to the actual operating time of the individual sections or machine group.
Circulation lubrication with progressive distributors
Planning a circulation lubrication system with progressive distributors is similar to a consumption lubrication system. In addition to the quantity per cycle, the number of cycles per minute, i.e. the quantity per minute, is now included in the calculation of the quantities.
A progressive system is a volumetrically dosing circulating lubrication system. When designing and selecting the components, the technical limit values, e.g. number of cycles and maximum pressure of the distributors, operating pressure of the pump and level of pressure losses must be taken into account.
From a progressive system, the lubricant quantity is fed to a lubrication point in cyclical quantity pulses, whereby the pulse sequence depends on the number of cycles and the quantity per pulse depends on the disc size of the distributor.
The distributor has the following structure:
The quantities delivered from outlets 1 to 6 are calculated as follows:
Determination of the distributor volume VV
VV = ∑ V (1 .. n) [cm³]
VV = 2 x 0.2 + 2 x 0.3 + 2 x 0.5 = 2 cm³
Calculating the number of cycles Z (min-1)
Z = Qg : VV = 300 cm³/min : 2 cm³ = 150 cycles/min [min-1].
This means that from each distributor outlet the quantity of the dosing disc size is conveyed 150 times per minute, e.g. outlet 1 - 150 [min-1] x 0.2 [cm³] = 30 cm³/min.
Example outlet 6 - 150 [min-1] x 0.5 [cm³] = 75 cm³/min.
Due to the compressibility of the oil and breathing of the volume in the lines behind the outlets, the lubricant pulses are more or less smoothed out depending on the length of the lines.
For sensitive lubrication points, the volume pulses (and pressure pulses) can have a disturbing effect, e.g. in sliding guides in fine machining. In most cases, however, the quantity pulses have no effect on the lubrication.
Progressive systems are widely used in mechanical and plant engineering. The main areas of application are machine tools (presses, transfer lines, press lines), printing and paper machines.
Design of a plant
The illustration shows a circulation lubrication system with progressive distributors.
In the drawing, values for flow rates and number of cycles are entered, which refer to the chapter "Planning and Calculation Example" on this page.
A gear pump unit (14a) delivers through a non-return valve (14c) and a filter (15) into the main line (21). The main distributor HV (16) is connected to the main line, from which the 4 sub-distributors UV1, UV2, UV3 and UV4 (17-20) are supplied.