09-22-2012, 07:10 PM
Hello Folks,
The issues surrounding wipers and what is the best material from which to make them is a potentially confusing subject, As with many topics in engineering there is no right or wrong answer;
1, No wipers at all, even without wipers the clearances between the two sliding surfaces are so small that very small particles are the only materials that can get between the two sliding surfaces, and providing that the oil film is thicker than the largest particles there is no harm done, the greatest harm is done when a large piece of swarf exceeding the oil film thickness in which case cold welding to one sliding surface and subsequent relative movement causes gouging, gouging that is relatively common on sliding surfaces without any form of wipers.
2, Felt wipers, successful at keeping large swarf pieces from getting between sliding faces while allowing some oil to pass through them, while they do hold onto fine swarf the swarf works it's way deep into the felt where it does little damage, and the fine hairs from which the felt is made tends to roll up around the swarf protecting the sliding surfaces from the sharp edges of the swarf pieces, the way lube oil should be introduced into oil grooves in between the sliding surfaces, with the flow of oil being from the centre of the sliding faces out which effectively washes out much of the contamination. the lubrication also builds up in the felt itself which can help to lubricate any contact points between any entrapped swarf and the slide ways.
3, Rubber lipped wipers, act primarily like squeegies scraping off any dirt, oil, coolant etc that threatens to get in between the sliding faces, on the down side, any dirt that gets behind the lips is retained there increasing the risk of it getting between the sliding faces, the easiest way for dirt to get behind the lips is for it to be pushed there by compressed air, or in some cases a stiff bristled brush can lift a lightweight lip, if there is a lack of coolant or oil on the slideway a lip can flip inside out and this actually acts to catch swarf and dirt, so while the lip type wipers are very efficient they do require quite a lot of care to ensure that they are working properly, if they cease to function properly then they can be more of a liability than an asset. Removing and replacing is often difficult as they are often made of a moulded rubber compound that swells or remoulds around the mounting screws, which means that after refitting they rarely function properly.
4, solid rubber or semi rigid plastic block style wipers, these work as "Block wipers" rather than lipped wipers, with quite a large surface are in contact with the way, the lip style has only a fine edge in contact with the ways. the block style wipers unless fitted correctly are rarely effective, if adjusted too low then the sliding faces are actually held apart by the wipers allowing easy access for fine swarf into the sliding surfaces, if adjusted too high they trap swarf at the edge of the sliding surfaces waiting for any lift in the sliding surfaces at which point the swarf wedges between the ways and sliding surfaces, also as the leading edge of the block wiper comes into contact with the greater quantity of swarf it wears more over time this leads to a wedge shaped cavity forming that will force dirt under the wiper block.
5, double lipped wipers, made of a ground steel or extruded aluminium strip with a leading edge wiper made of nitrile, which is angled out away from the strip, which acts as a first line of defense against swarf and dirt, with a second vertical wiper often made from urethane or nitrile which is a second line of defence these are not breeched easily by compressed air, they are not prone to deformation by mounting screws, they can build up dirt between the lips and do need maintenance but as they are easy to adjust and to remove and replace this is not too difficult.
This is just my observations after many years working on and around older machine tools, I have found that making felt wipers is by far and away the easiest solution, cheapest as well and regular replacement of the felt parts is pretty easy too.
I have had double lipped wipers on some machines and I am a big fan of them, they are difficult to fit in an after market form as each straight edge has to be cut from straight stock, which is fine on flat or square ways but on prismatic ways is difficult
Regards
Rick
The issues surrounding wipers and what is the best material from which to make them is a potentially confusing subject, As with many topics in engineering there is no right or wrong answer;
1, No wipers at all, even without wipers the clearances between the two sliding surfaces are so small that very small particles are the only materials that can get between the two sliding surfaces, and providing that the oil film is thicker than the largest particles there is no harm done, the greatest harm is done when a large piece of swarf exceeding the oil film thickness in which case cold welding to one sliding surface and subsequent relative movement causes gouging, gouging that is relatively common on sliding surfaces without any form of wipers.
2, Felt wipers, successful at keeping large swarf pieces from getting between sliding faces while allowing some oil to pass through them, while they do hold onto fine swarf the swarf works it's way deep into the felt where it does little damage, and the fine hairs from which the felt is made tends to roll up around the swarf protecting the sliding surfaces from the sharp edges of the swarf pieces, the way lube oil should be introduced into oil grooves in between the sliding surfaces, with the flow of oil being from the centre of the sliding faces out which effectively washes out much of the contamination. the lubrication also builds up in the felt itself which can help to lubricate any contact points between any entrapped swarf and the slide ways.
3, Rubber lipped wipers, act primarily like squeegies scraping off any dirt, oil, coolant etc that threatens to get in between the sliding faces, on the down side, any dirt that gets behind the lips is retained there increasing the risk of it getting between the sliding faces, the easiest way for dirt to get behind the lips is for it to be pushed there by compressed air, or in some cases a stiff bristled brush can lift a lightweight lip, if there is a lack of coolant or oil on the slideway a lip can flip inside out and this actually acts to catch swarf and dirt, so while the lip type wipers are very efficient they do require quite a lot of care to ensure that they are working properly, if they cease to function properly then they can be more of a liability than an asset. Removing and replacing is often difficult as they are often made of a moulded rubber compound that swells or remoulds around the mounting screws, which means that after refitting they rarely function properly.
4, solid rubber or semi rigid plastic block style wipers, these work as "Block wipers" rather than lipped wipers, with quite a large surface are in contact with the way, the lip style has only a fine edge in contact with the ways. the block style wipers unless fitted correctly are rarely effective, if adjusted too low then the sliding faces are actually held apart by the wipers allowing easy access for fine swarf into the sliding surfaces, if adjusted too high they trap swarf at the edge of the sliding surfaces waiting for any lift in the sliding surfaces at which point the swarf wedges between the ways and sliding surfaces, also as the leading edge of the block wiper comes into contact with the greater quantity of swarf it wears more over time this leads to a wedge shaped cavity forming that will force dirt under the wiper block.
5, double lipped wipers, made of a ground steel or extruded aluminium strip with a leading edge wiper made of nitrile, which is angled out away from the strip, which acts as a first line of defense against swarf and dirt, with a second vertical wiper often made from urethane or nitrile which is a second line of defence these are not breeched easily by compressed air, they are not prone to deformation by mounting screws, they can build up dirt between the lips and do need maintenance but as they are easy to adjust and to remove and replace this is not too difficult.
This is just my observations after many years working on and around older machine tools, I have found that making felt wipers is by far and away the easiest solution, cheapest as well and regular replacement of the felt parts is pretty easy too.
I have had double lipped wipers on some machines and I am a big fan of them, they are difficult to fit in an after market form as each straight edge has to be cut from straight stock, which is fine on flat or square ways but on prismatic ways is difficult
Regards
Rick
Whatever it is, do it today, Tomorrow may not be an option and regret outlasts fatigue.