Food grade lubrication
EHEDG has drawn up a guideline for establishing procedures relating to the manufacture of food grade lubricants and for the use of those lubricants in the food industry, specifically in relation to incidental food contact.
|2 Air release|
|3 Resistance to foaming|
|6 Corrosion Resistance|
|7 Oxidation Resistance|
|9 NGLI Class for greases|
|10 Food grade classification|
Machinery producing food or feed must be designed and constructed in a way that no ancillary substances, like lubricants, can come into contact with the food.
However, lubricants, grease and oil are necessary to ensure the efficient operation of corrosion protection of machinery, the lubrication of machine parts such as bearings and other equipment and instruments.
Incidental contact between lubricants and food can not always be fully excluded and may possibly result in contamination of the food product.
Lubricants are designed to perform a variety of functions in different applications.
For example stress in a gear is concentrated in a very small region so the lubricant must
- firstly reduce friction by preventing metal to metal contact;
- secondly it must be able to dissipate frictional heat to keep the contact areas cool.
ISO viscosities grades range from the thinnest at ISO 2 to ISO 1500, being the thickest.
The kinematic viscosity is measured by measuring the time required to empty a reservoir filled with the lubricant. The equipment is temperature controlled. The kinematic viscosity is expressed in centistokes.
In general high speed rotations of equipment require lower viscosity lubricants, while slower moving parts generally require more viscous lubricants.
The viscosity varies with the temperature. In order to determine the pour point the temperature is lowered until the moment the lubricant becomes solid. This temperature is called pour point and is an indication of the minimum operating temperature of the lubricant, which in general is 5 to 10 degrees Celsius above the pour point.
air bubbles causes overheating and reduces the pressure the pump can generate. In tests the abilities of the fluid to release the entrained air bubbles is determined. A specimen of lubricant is weighed and a fixed amount of air is injected. After a set period the density is measured again.
ceramic air divider is placed in the lubricant and connected to a constant air supply and the amount of foam is measured.
Foaming can cause equipment damage with resultant plant downtime, as well as potential food and environment safety issues. It is therefore important to use a lubricant with good air release properties.
water especially in plants where a high pressure cleaning system is used. Water has an adverse influence on the performance of the lubricant in the system. In a hydraulic system small quantities of water can enter through seals or as a result of condensate formed by incoming air when there is a change in the oil level in the reservoir.
When a lubricant is mixed with water an emulsion can be formed which can affect lubrication efficiency. Water can also cause rust. In general good water separation or demulsibility is an essential property. vacuum filter. No residue found on the filter indicates good filterability.
A lubricant with an inhibitor prevents corrosion. Additives that have an adverse reaction with water form an acidic environment, which can attack yellow metals.
oxygen is bubbled for thousands of hours through a lubricant containing metal coils that are used to catalyze oxidation. Water is also added. When oils degrade, the viscosity increases and deposits form. These deposits can block valves and filters and cause equipment breakdown.
A thickener is added to keep the oil in the grease and hence in the bearing. An important property and test of grease is how much oil separates from the grease at different temperatures and how much load it can carry. The anti-wear and extreme pressure performance can be checked by the four ball test. Here a number of steel balls are rotated under a defined pressure. Measured will be under what (extreme high) pressure the balls weld together.
- NLGI 00 is a very soft grease for central lubrication with very small hoses.
- NLGI 0 and NLGI 1 require bigger hoses.
- NLGI 2 grease is commonly used in bearings